diff --git a/src/Composer/Autoload/AutoloadGenerator.php b/src/Composer/Autoload/AutoloadGenerator.php
index 73ec3d5e7..cbabb867b 100644
--- a/src/Composer/Autoload/AutoloadGenerator.php
+++ b/src/Composer/Autoload/AutoloadGenerator.php
@@ -441,7 +441,7 @@ EOF;
      * @param array<string, true> $scannedFiles
      * @return array<class-string, string>
      */
-    private function addClassMapCode(Filesystem $filesystem, $basePath, $vendorPath, $dir, $excluded, $namespaceFilter, $autoloadType, array $classMap, array &$ambiguousClasses, array &$scannedFiles)
+    private function addClassMapCode(Filesystem $filesystem, $basePath, $vendorPath, $dir, $excluded, $namespaceFilter, $autoloadType, array $classMap, array &$ambiguousClasses, array &$scannedFiles): array
     {
         foreach ($this->generateClassMap($dir, $excluded, $namespaceFilter, $autoloadType, true, $scannedFiles) as $class => $path) {
             $pathCode = $this->getPathCode($filesystem, $basePath, $vendorPath, $path).",\n";
@@ -464,7 +464,7 @@ EOF;
      * @param array<string, true> $scannedFiles
      * @return array<class-string, string>
      */
-    private function generateClassMap($dir, $excluded, $namespaceFilter, $autoloadType, $showAmbiguousWarning, array &$scannedFiles)
+    private function generateClassMap($dir, $excluded, $namespaceFilter, $autoloadType, $showAmbiguousWarning, array &$scannedFiles): array
     {
         if ($excluded) {
             // filter excluded patterns here to only use those matching $dir
diff --git a/src/Composer/Autoload/ClassMapGenerator.php b/src/Composer/Autoload/ClassMapGenerator.php
index 9d0c73f1f..babb3d892 100644
--- a/src/Composer/Autoload/ClassMapGenerator.php
+++ b/src/Composer/Autoload/ClassMapGenerator.php
@@ -157,7 +157,7 @@ class ClassMapGenerator
      * @param  ?IOInterface             $io            IO object
      * @return array<int, class-string> valid classes
      */
-    private static function filterByNamespace($classes, $filePath, $baseNamespace, $namespaceType, $basePath, $io)
+    private static function filterByNamespace($classes, $filePath, $baseNamespace, $namespaceType, $basePath, $io): array
     {
         $validClasses = array();
         $rejectedClasses = array();
@@ -215,7 +215,7 @@ class ClassMapGenerator
      * @throws \RuntimeException
      * @return array<int, class-string> The found classes
      */
-    private static function findClasses($path)
+    private static function findClasses($path): array
     {
         $extraTypes = self::getExtraTypes();
 
@@ -296,7 +296,7 @@ class ClassMapGenerator
     /**
      * @return string
      */
-    private static function getExtraTypes()
+    private static function getExtraTypes(): string
     {
         static $extraTypes = null;
 
diff --git a/src/Composer/Autoload/PhpFileCleaner.php b/src/Composer/Autoload/PhpFileCleaner.php
index 17341a935..8fc077418 100644
--- a/src/Composer/Autoload/PhpFileCleaner.php
+++ b/src/Composer/Autoload/PhpFileCleaner.php
@@ -78,7 +78,7 @@ class PhpFileCleaner
     /**
      * @return string
      */
-    public function clean()
+    public function clean(): string
     {
         $clean = '';
 
@@ -260,7 +260,7 @@ class PhpFileCleaner
      * @param string $char
      * @return bool
      */
-    private function peek($char)
+    private function peek($char): bool
     {
         return $this->index + 1 < $this->len && $this->contents[$this->index + 1] === $char;
     }
@@ -270,7 +270,7 @@ class PhpFileCleaner
      * @param ?array<int, string> $match
      * @return bool
      */
-    private function match($regex, array &$match = null)
+    private function match($regex, array &$match = null): bool
     {
         return Preg::isMatch($regex, $this->contents, $match, 0, $this->index);
     }
diff --git a/src/Composer/Command/DiagnoseCommand.php b/src/Composer/Command/DiagnoseCommand.php
index a39ffd541..9d231e247 100644
--- a/src/Composer/Command/DiagnoseCommand.php
+++ b/src/Composer/Command/DiagnoseCommand.php
@@ -260,7 +260,8 @@ EOT
         try {
             $this->httpDownloader->get($proto . '://repo.packagist.org/packages.json');
         } catch (TransportException $e) {
-            if ($hints = HttpDownloader::getExceptionHints($e)) {
+            $hints = HttpDownloader::getExceptionHints($e);
+            if (null !== $hints && count($hints) > 0) {
                 foreach ($hints as $hint) {
                     $result[] = $hint;
                 }
@@ -436,7 +437,7 @@ EOT
     /**
      * @return string
      */
-    private function getCurlVersion()
+    private function getCurlVersion(): string
     {
         if (extension_loaded('curl')) {
             if (!HttpDownloader::isCurlEnabled()) {
@@ -458,7 +459,7 @@ EOT
      *
      * @return void
      */
-    private function outputResult($result)
+    private function outputResult($result): void
     {
         $io = $this->getIO();
         if (true === $result) {
diff --git a/src/Composer/Command/FundCommand.php b/src/Composer/Command/FundCommand.php
index 5d397f058..c6287dac9 100644
--- a/src/Composer/Command/FundCommand.php
+++ b/src/Composer/Command/FundCommand.php
@@ -134,7 +134,7 @@ class FundCommand extends BaseCommand
      * @param mixed[] $fundings
      * @return mixed[]
      */
-    private function insertFundingData(array $fundings, CompletePackageInterface $package)
+    private function insertFundingData(array $fundings, CompletePackageInterface $package): array
     {
         foreach ($package->getFunding() as $fundingOption) {
             list($vendor, $packageName) = explode('/', $package->getPrettyName());
diff --git a/src/Composer/Command/HomeCommand.php b/src/Composer/Command/HomeCommand.php
index eaab9fdab..b83f31e03 100644
--- a/src/Composer/Command/HomeCommand.php
+++ b/src/Composer/Command/HomeCommand.php
@@ -101,7 +101,7 @@ EOT
      * @param bool $showOnly
      * @return bool
      */
-    private function handlePackage(CompletePackageInterface $package, $showHomepage, $showOnly)
+    private function handlePackage(CompletePackageInterface $package, $showHomepage, $showOnly): bool
     {
         $support = $package->getSupport();
         $url = $support['source'] ?? $package->getSourceUrl();
@@ -158,7 +158,7 @@ EOT
      *
      * @return RepositoryInterface[]
      */
-    private function initializeRepos()
+    private function initializeRepos(): array
     {
         $composer = $this->tryComposer();
 
diff --git a/src/Composer/Command/InitCommand.php b/src/Composer/Command/InitCommand.php
index 6869d4068..6a52fd246 100644
--- a/src/Composer/Command/InitCommand.php
+++ b/src/Composer/Command/InitCommand.php
@@ -623,7 +623,7 @@ EOT
     /**
      * @return void
      */
-    private function updateDependencies(OutputInterface $output)
+    private function updateDependencies(OutputInterface $output): void
     {
         try {
             $updateCommand = $this->getApplication()->find('update');
@@ -637,7 +637,7 @@ EOT
     /**
      * @return void
      */
-    private function runDumpAutoloadCommand(OutputInterface $output)
+    private function runDumpAutoloadCommand(OutputInterface $output): void
     {
         try {
             $command = $this->getApplication()->find('dump-autoload');
@@ -652,7 +652,7 @@ EOT
      * @param array<string, string|array<string>> $options
      * @return bool
      */
-    private function hasDependencies($options)
+    private function hasDependencies($options): bool
     {
         $requires = (array) $options['require'];
         $devRequires = isset($options['require-dev']) ? (array) $options['require-dev'] : array();
diff --git a/src/Composer/Command/LicensesCommand.php b/src/Composer/Command/LicensesCommand.php
index de51bba87..49a54c2fb 100644
--- a/src/Composer/Command/LicensesCommand.php
+++ b/src/Composer/Command/LicensesCommand.php
@@ -163,7 +163,7 @@ EOT
      * @param  array<string, PackageInterface> $bucket
      * @return array<string, PackageInterface>
      */
-    private function filterRequiredPackages(RepositoryInterface $repo, PackageInterface $package, $bucket = array())
+    private function filterRequiredPackages(RepositoryInterface $repo, PackageInterface $package, $bucket = array()): array
     {
         $requires = array_keys($package->getRequires());
 
diff --git a/src/Composer/Command/RequireCommand.php b/src/Composer/Command/RequireCommand.php
index c46a96518..5ad66a794 100644
--- a/src/Composer/Command/RequireCommand.php
+++ b/src/Composer/Command/RequireCommand.php
@@ -296,7 +296,7 @@ EOT
      * @param string $requireKey
      * @return string[]
      */
-    private function getInconsistentRequireKeys(array $newRequirements, $requireKey)
+    private function getInconsistentRequireKeys(array $newRequirements, $requireKey): array
     {
         $requireKeys = $this->getPackagesByRequireKey();
         $inconsistentRequirements = array();
@@ -315,7 +315,7 @@ EOT
     /**
      * @return array<string, string>
      */
-    private function getPackagesByRequireKey()
+    private function getPackagesByRequireKey(): array
     {
         $composerDefinition = $this->json->read();
         $require = array();
@@ -351,7 +351,7 @@ EOT
      * @return int
      * @throws \Exception
      */
-    private function doUpdate(InputInterface $input, OutputInterface $output, IOInterface $io, array $requirements, $requireKey, $removeKey)
+    private function doUpdate(InputInterface $input, OutputInterface $output, IOInterface $io, array $requirements, $requireKey, $removeKey): int
     {
         // Update packages
         $this->resetComposer();
@@ -449,7 +449,7 @@ EOT
      * @param bool $sortPackages
      * @return bool
      */
-    private function updateFileCleanly(JsonFile $json, array $new, $requireKey, $removeKey, $sortPackages)
+    private function updateFileCleanly(JsonFile $json, array $new, $requireKey, $removeKey, $sortPackages): bool
     {
         $contents = file_get_contents($json->getPath());
 
diff --git a/src/Composer/Command/ShowCommand.php b/src/Composer/Command/ShowCommand.php
index 5a80f1db9..ab8861031 100644
--- a/src/Composer/Command/ShowCommand.php
+++ b/src/Composer/Command/ShowCommand.php
@@ -923,7 +923,7 @@ EOT
      * @param array<string, string> $versions
      * @return array<string, string|string[]|null>
      */
-    private function appendVersions($json, array $versions)
+    private function appendVersions($json, array $versions): array
     {
         uasort($versions, 'version_compare');
         $versions = array_keys(array_reverse($versions));
@@ -936,7 +936,7 @@ EOT
      * @param array<string, string|string[]|null> $json
      * @return array<string, string|string[]|null>
      */
-    private function appendLicenses($json, CompletePackageInterface $package)
+    private function appendLicenses($json, CompletePackageInterface $package): array
     {
         if ($licenses = $package->getLicense()) {
             $spdxLicenses = new SpdxLicenses();
@@ -963,7 +963,7 @@ EOT
      * @param array<string, string|string[]|null> $json
      * @return array<string, string|string[]|null>
      */
-    private function appendAutoload($json, CompletePackageInterface $package)
+    private function appendAutoload($json, CompletePackageInterface $package): array
     {
         if ($package->getAutoload()) {
             $autoload = array();
@@ -996,7 +996,7 @@ EOT
      * @param array<string, string|string[]|null> $json
      * @return array<string, string|string[]|null>
      */
-    private function appendLinks($json, CompletePackageInterface $package)
+    private function appendLinks($json, CompletePackageInterface $package): array
     {
         foreach (Link::$TYPES as $linkType) {
             $json = $this->appendLink($json, $package, $linkType);
@@ -1010,7 +1010,7 @@ EOT
      * @param string $linkType
      * @return array<string, string|string[]|null>
      */
-    private function appendLink($json, CompletePackageInterface $package, $linkType)
+    private function appendLink($json, CompletePackageInterface $package, $linkType): array
     {
         $links = $package->{'get' . ucfirst($linkType)}();
 
@@ -1240,7 +1240,7 @@ EOT
      * @param string $updateStatus
      * @return string
      */
-    private function updateStatusToVersionStyle($updateStatus)
+    private function updateStatusToVersionStyle($updateStatus): string
     {
         // 'up-to-date' is printed green
         // 'semver-safe-update' is printed red
@@ -1251,7 +1251,7 @@ EOT
     /**
      * @return string
      */
-    private function getUpdateStatus(PackageInterface $latestPackage, PackageInterface $package)
+    private function getUpdateStatus(PackageInterface $latestPackage, PackageInterface $package): string
     {
         if ($latestPackage->getFullPrettyVersion() === $package->getFullPrettyVersion()) {
             return 'up-to-date';
@@ -1275,7 +1275,7 @@ EOT
      *
      * @return void
      */
-    private function writeTreeLine($line)
+    private function writeTreeLine($line): void
     {
         $io = $this->getIO();
         if (!$io->isDecorated()) {
@@ -1326,7 +1326,7 @@ EOT
     /**
      * @return RepositorySet
      */
-    private function getRepositorySet(Composer $composer)
+    private function getRepositorySet(Composer $composer): RepositorySet
     {
         if (!$this->repositorySet) {
             $this->repositorySet = new RepositorySet($composer->getPackage()->getMinimumStability(), $composer->getPackage()->getStabilityFlags());
@@ -1342,7 +1342,7 @@ EOT
      * @param  array<PackageInterface> $bucket
      * @return array<PackageInterface>
      */
-    private function filterRequiredPackages(RepositoryInterface $repo, PackageInterface $package, $bucket = array())
+    private function filterRequiredPackages(RepositoryInterface $repo, PackageInterface $package, $bucket = array()): array
     {
         $requires = $package->getRequires();
 
diff --git a/src/Composer/Command/StatusCommand.php b/src/Composer/Command/StatusCommand.php
index 99cd983d1..4a7bfe223 100644
--- a/src/Composer/Command/StatusCommand.php
+++ b/src/Composer/Command/StatusCommand.php
@@ -80,7 +80,7 @@ EOT
     /**
      * @return int
      */
-    private function doExecute(InputInterface $input)
+    private function doExecute(InputInterface $input): int
     {
         // init repos
         $composer = $this->requireComposer();
diff --git a/src/Composer/Command/UpdateCommand.php b/src/Composer/Command/UpdateCommand.php
index c2efd014b..119fab20e 100644
--- a/src/Composer/Command/UpdateCommand.php
+++ b/src/Composer/Command/UpdateCommand.php
@@ -245,7 +245,7 @@ EOT
      * @param array<string> $packages
      * @return array<string>
      */
-    private function getPackagesInteractively(IOInterface $io, InputInterface $input, OutputInterface $output, Composer $composer, array $packages)
+    private function getPackagesInteractively(IOInterface $io, InputInterface $input, OutputInterface $output, Composer $composer, array $packages): array
     {
         if (!$input->isInteractive()) {
             throw new \InvalidArgumentException('--interactive cannot be used in non-interactive terminals.');
@@ -312,7 +312,7 @@ EOT
      * @param string $constraint
      * @return Link
      */
-    private function appendConstraintToLink(Link $link, $constraint)
+    private function appendConstraintToLink(Link $link, $constraint): Link
     {
         $parser = new VersionParser;
         $oldPrettyString = $link->getConstraint()->getPrettyString();
diff --git a/src/Composer/Compiler.php b/src/Composer/Compiler.php
index 619ac4ea8..6c30d2b6d 100644
--- a/src/Composer/Compiler.php
+++ b/src/Composer/Compiler.php
@@ -201,7 +201,7 @@ class Compiler
      * @param  \SplFileInfo $file
      * @return string
      */
-    private function getRelativeFilePath($file)
+    private function getRelativeFilePath($file): string
     {
         $realPath = $file->getRealPath();
         $pathPrefix = dirname(__DIR__, 2).DIRECTORY_SEPARATOR;
@@ -258,7 +258,7 @@ class Compiler
      * @param  string $source A PHP string
      * @return string The PHP string with the whitespace removed
      */
-    private function stripWhitespace($source)
+    private function stripWhitespace($source): string
     {
         if (!function_exists('token_get_all')) {
             return $source;
@@ -289,7 +289,7 @@ class Compiler
     /**
      * @return string
      */
-    private function getStub()
+    private function getStub(): string
     {
         $stub = <<<'EOF'
 #!/usr/bin/env php
diff --git a/src/Composer/Config.php b/src/Composer/Config.php
index 1dd2f0773..d6b3da4e8 100644
--- a/src/Composer/Config.php
+++ b/src/Composer/Config.php
@@ -531,7 +531,7 @@ class Config
      * @param  string $path
      * @return string
      */
-    private function realpath($path)
+    private function realpath($path): string
     {
         if (Preg::isMatch('{^(?:/|[a-z]:|[a-z0-9.]+://)}i', $path)) {
             return $path;
diff --git a/src/Composer/Config/JsonConfigSource.php b/src/Composer/Config/JsonConfigSource.php
index 604c41f9a..798e0af1c 100644
--- a/src/Composer/Config/JsonConfigSource.php
+++ b/src/Composer/Config/JsonConfigSource.php
@@ -214,7 +214,7 @@ class JsonConfigSource implements ConfigSourceInterface
      *
      * @return void
      */
-    private function manipulateJson($method, $fallback, ...$args)
+    private function manipulateJson($method, $fallback, ...$args): void
     {
         if ($this->file->exists()) {
             if (!is_writable($this->file->getPath())) {
@@ -297,7 +297,7 @@ class JsonConfigSource implements ConfigSourceInterface
      * @param  mixed $value
      * @return int
      */
-    private function arrayUnshiftRef(&$array, &$value)
+    private function arrayUnshiftRef(&$array, &$value): int
     {
         $return = array_unshift($array, '');
         $array[0] = &$value;
diff --git a/src/Composer/Console/Application.php b/src/Composer/Console/Application.php
index 4762396af..24811b34b 100644
--- a/src/Composer/Console/Application.php
+++ b/src/Composer/Console/Application.php
@@ -358,7 +358,7 @@ class Application extends BaseApplication
      * @throws \RuntimeException
      * @return string
      */
-    private function getNewWorkingDir(InputInterface $input)
+    private function getNewWorkingDir(InputInterface $input): string
     {
         $workingDir = $input->getParameterOption(array('--working-dir', '-d'));
         if (false !== $workingDir && !is_dir($workingDir)) {
@@ -371,7 +371,7 @@ class Application extends BaseApplication
     /**
      * @return void
      */
-    private function hintCommonErrors(\Exception $exception)
+    private function hintCommonErrors(\Exception $exception): void
     {
         $io = $this->getIO();
 
@@ -408,7 +408,8 @@ class Application extends BaseApplication
             $io->writeError('<error>Check https://getcomposer.org/doc/06-config.md#process-timeout for details</error>', true, IOInterface::QUIET);
         }
 
-        if ($hints = HttpDownloader::getExceptionHints($exception)) {
+        $hints = HttpDownloader::getExceptionHints($exception);
+        if (null !== $hints && count($hints) > 0) {
             foreach ($hints as $hint) {
                 $io->writeError($hint, true, IOInterface::QUIET);
             }
@@ -553,7 +554,7 @@ class Application extends BaseApplication
     /**
      * @return Command\BaseCommand[]
      */
-    private function getPluginCommands()
+    private function getPluginCommands(): array
     {
         $commands = array();
 
diff --git a/src/Composer/Console/GithubActionError.php b/src/Composer/Console/GithubActionError.php
index 6f8710261..578ac8eca 100644
--- a/src/Composer/Console/GithubActionError.php
+++ b/src/Composer/Console/GithubActionError.php
@@ -55,7 +55,7 @@ final class GithubActionError
      * @param string $data
      * @return string
      */
-    private function escapeData($data)
+    private function escapeData($data): string
     {
         // see https://github.com/actions/toolkit/blob/4f7fb6513a355689f69f0849edeb369a4dc81729/packages/core/src/command.ts#L80-L85
         $data = str_replace("%", '%25', $data);
@@ -69,7 +69,7 @@ final class GithubActionError
      * @param string $property
      * @return string
      */
-    private function escapeProperty($property)
+    private function escapeProperty($property): string
     {
         // see https://github.com/actions/toolkit/blob/4f7fb6513a355689f69f0849edeb369a4dc81729/packages/core/src/command.ts#L87-L94
         $property = str_replace("%", '%25', $property);
diff --git a/src/Composer/DependencyResolver/LockTransaction.php b/src/Composer/DependencyResolver/LockTransaction.php
index e46b66c1a..75da918ae 100644
--- a/src/Composer/DependencyResolver/LockTransaction.php
+++ b/src/Composer/DependencyResolver/LockTransaction.php
@@ -106,7 +106,7 @@ class LockTransaction extends Transaction
      * @param bool $updateMirrors
      * @return BasePackage[]
      */
-    public function getNewLockPackages($devMode, $updateMirrors = false)
+    public function getNewLockPackages($devMode, $updateMirrors = false): array
     {
         $packages = array();
         foreach ($this->resultPackages[$devMode ? 'dev' : 'non-dev'] as $package) {
@@ -137,7 +137,7 @@ class LockTransaction extends Transaction
      * @param array<array{package: string, version: string, alias: string, alias_normalized: string}> $aliases
      * @return array<array{package: string, version: string, alias: string, alias_normalized: string}>
      */
-    public function getAliases($aliases)
+    public function getAliases($aliases): array
     {
         $usedAliases = array();
 
diff --git a/src/Composer/DependencyResolver/Pool.php b/src/Composer/DependencyResolver/Pool.php
index 3888ef8a5..981e40fe6 100644
--- a/src/Composer/DependencyResolver/Pool.php
+++ b/src/Composer/DependencyResolver/Pool.php
@@ -159,7 +159,7 @@ class Pool implements \Countable
      *                                          packages must match or null to return all
      * @return BasePackage[]
      */
-    private function computeWhatProvides($name, ConstraintInterface $constraint = null)
+    private function computeWhatProvides($name, ConstraintInterface $constraint = null): array
     {
         if (!isset($this->packageByName[$name])) {
             return array();
diff --git a/src/Composer/DependencyResolver/PoolBuilder.php b/src/Composer/DependencyResolver/PoolBuilder.php
index c0b2ed4d2..b80ff7a44 100644
--- a/src/Composer/DependencyResolver/PoolBuilder.php
+++ b/src/Composer/DependencyResolver/PoolBuilder.php
@@ -499,7 +499,7 @@ class PoolBuilder
      * @param string $name packageName
      * @return bool
      */
-    private function isRootRequire(Request $request, $name)
+    private function isRootRequire(Request $request, $name): bool
     {
         $rootRequires = $request->getRequires();
 
@@ -510,7 +510,7 @@ class PoolBuilder
      * @param  string $name
      * @return string[]
      */
-    private function getSkippedRootRequires(Request $request, $name)
+    private function getSkippedRootRequires(Request $request, $name): array
     {
         if (!isset($this->skippedLoad[$name])) {
             return array();
@@ -553,7 +553,7 @@ class PoolBuilder
      *
      * @return bool
      */
-    private function isUpdateAllowed(BasePackage $package)
+    private function isUpdateAllowed(BasePackage $package): bool
     {
         foreach ($this->updateAllowList as $pattern => $void) {
             $patternRegexp = BasePackage::packageNameToRegexp($pattern);
@@ -684,7 +684,7 @@ class PoolBuilder
     /**
      * @return Pool
      */
-    private function runOptimizer(Request $request, Pool $pool)
+    private function runOptimizer(Request $request, Pool $pool): Pool
     {
         if (null === $this->poolOptimizer) {
             return $pool;
diff --git a/src/Composer/DependencyResolver/PoolOptimizer.php b/src/Composer/DependencyResolver/PoolOptimizer.php
index 420c1ec66..3ae0c61c7 100644
--- a/src/Composer/DependencyResolver/PoolOptimizer.php
+++ b/src/Composer/DependencyResolver/PoolOptimizer.php
@@ -173,7 +173,7 @@ class PoolOptimizer
     /**
      * @return Pool Optimized pool
      */
-    private function applyRemovalsToPool(Pool $pool)
+    private function applyRemovalsToPool(Pool $pool): Pool
     {
         $packages = array();
         $removedVersions = array();
@@ -278,7 +278,7 @@ class PoolOptimizer
     /**
      * @return string
      */
-    private function calculateDependencyHash(BasePackage $package)
+    private function calculateDependencyHash(BasePackage $package): string
     {
         $hash = '';
 
diff --git a/src/Composer/DependencyResolver/Problem.php b/src/Composer/DependencyResolver/Problem.php
index 124a544cb..101187e16 100644
--- a/src/Composer/DependencyResolver/Problem.php
+++ b/src/Composer/DependencyResolver/Problem.php
@@ -117,7 +117,7 @@ class Problem
      * @return string
      * @internal
      */
-    public static function formatDeduplicatedRules($rules, $indent, RepositorySet $repositorySet, Request $request, Pool $pool, $isVerbose, array $installedMap = array(), array $learnedPool = array())
+    public static function formatDeduplicatedRules($rules, $indent, RepositorySet $repositorySet, Request $request, Pool $pool, $isVerbose, array $installedMap = array(), array $learnedPool = array()): string
     {
         $messages = array();
         $templates = array();
@@ -210,7 +210,7 @@ class Problem
      * @param string $packageName
      * @return array{0: string, 1: string}
      */
-    public static function getMissingPackageReason(RepositorySet $repositorySet, Request $request, Pool $pool, $isVerbose, $packageName, ConstraintInterface $constraint = null)
+    public static function getMissingPackageReason(RepositorySet $repositorySet, Request $request, Pool $pool, $isVerbose, $packageName, ConstraintInterface $constraint = null): array
     {
         if (PlatformRepository::isPlatformPackage($packageName)) {
             // handle php/php-*/hhvm
@@ -382,7 +382,7 @@ class Problem
      * @param bool $useRemovedVersionGroup
      * @return string
      */
-    public static function getPackageList(array $packages, $isVerbose, Pool $pool = null, ConstraintInterface $constraint = null, $useRemovedVersionGroup = false)
+    public static function getPackageList(array $packages, $isVerbose, Pool $pool = null, ConstraintInterface $constraint = null, $useRemovedVersionGroup = false): string
     {
         $prepared = array();
         $hasDefaultBranch = array();
@@ -427,7 +427,7 @@ class Problem
      * @param  string $version the effective runtime version of the platform package
      * @return ?string a version string or null if it appears the package was artificially disabled
      */
-    private static function getPlatformPackageVersion(Pool $pool, $packageName, $version)
+    private static function getPlatformPackageVersion(Pool $pool, $packageName, $version): ?string
     {
         $available = $pool->whatProvides($packageName);
 
@@ -471,7 +471,7 @@ class Problem
      * @param int $maxDev
      * @return list<string> a list of pretty versions and '...' where versions were removed
      */
-    private static function condenseVersionList(array $versions, $max, $maxDev = 16)
+    private static function condenseVersionList(array $versions, $max, $maxDev = 16): array
     {
         if (count($versions) <= $max) {
             return $versions;
@@ -505,7 +505,7 @@ class Problem
      * @param PackageInterface[] $packages
      * @return bool
      */
-    private static function hasMultipleNames(array $packages)
+    private static function hasMultipleNames(array $packages): bool
     {
         $name = null;
         foreach ($packages as $package) {
@@ -527,7 +527,7 @@ class Problem
      * @param string $reason
      * @return array{0: string, 1: string}
      */
-    private static function computeCheckForLowerPrioRepo(Pool $pool, $isVerbose, $packageName, array $higherRepoPackages, array $allReposPackages, $reason, ConstraintInterface $constraint = null)
+    private static function computeCheckForLowerPrioRepo(Pool $pool, $isVerbose, $packageName, array $higherRepoPackages, array $allReposPackages, $reason, ConstraintInterface $constraint = null): array
     {
         $nextRepoPackages = array();
         $nextRepo = null;
diff --git a/src/Composer/DependencyResolver/Rule.php b/src/Composer/DependencyResolver/Rule.php
index c5f324038..4a1ba886e 100644
--- a/src/Composer/DependencyResolver/Rule.php
+++ b/src/Composer/DependencyResolver/Rule.php
@@ -232,7 +232,7 @@ abstract class Rule
      * @internal
      * @return BasePackage
      */
-    public function getSourcePackage(Pool $pool)
+    public function getSourcePackage(Pool $pool): BasePackage
     {
         $literals = $this->getLiterals();
 
@@ -498,7 +498,7 @@ abstract class Rule
     /**
      * @return BasePackage
      */
-    private function deduplicateDefaultBranchAlias(BasePackage $package)
+    private function deduplicateDefaultBranchAlias(BasePackage $package): BasePackage
     {
         if ($package instanceof AliasPackage && $package->getPrettyVersion() === VersionParser::DEFAULT_BRANCH_ALIAS) {
             $package = $package->getAliasOf();
diff --git a/src/Composer/DependencyResolver/Solver.php b/src/Composer/DependencyResolver/Solver.php
index 45814c36e..37f079d68 100644
--- a/src/Composer/DependencyResolver/Solver.php
+++ b/src/Composer/DependencyResolver/Solver.php
@@ -302,7 +302,7 @@ class Solver
      * @param  string|int $literal
      * @return int
      */
-    private function setPropagateLearn($level, $literal, Rule $rule)
+    private function setPropagateLearn($level, $literal, Rule $rule): int
     {
         $level++;
 
@@ -351,7 +351,7 @@ class Solver
      * @param  int[] $decisionQueue
      * @return int
      */
-    private function selectAndInstall($level, array $decisionQueue, Rule $rule)
+    private function selectAndInstall($level, array $decisionQueue, Rule $rule): int
     {
         // choose best package to install from decisionQueue
         $literals = $this->policy->selectPreferredPackages($this->pool, $decisionQueue, $rule->getRequiredPackage());
@@ -548,7 +548,7 @@ class Solver
     /**
      * @return int
      */
-    private function analyzeUnsolvable(Rule $conflictRule)
+    private function analyzeUnsolvable(Rule $conflictRule): int
     {
         $problem = new Problem();
         $problem->addRule($conflictRule);
diff --git a/src/Composer/DependencyResolver/SolverProblemsException.php b/src/Composer/DependencyResolver/SolverProblemsException.php
index deaec7d24..12196b561 100644
--- a/src/Composer/DependencyResolver/SolverProblemsException.php
+++ b/src/Composer/DependencyResolver/SolverProblemsException.php
@@ -109,7 +109,7 @@ class SolverProblemsException extends \RuntimeException
      * @param string[] $missingExtensions
      * @return string
      */
-    private function createExtensionHint(array $missingExtensions)
+    private function createExtensionHint(array $missingExtensions): string
     {
         $paths = IniHelper::getAll();
 
@@ -133,7 +133,7 @@ class SolverProblemsException extends \RuntimeException
      * @param Rule[][] $reasonSets
      * @return string[]
      */
-    private function getExtensionProblems(array $reasonSets)
+    private function getExtensionProblems(array $reasonSets): array
     {
         $missingExtensions = array();
         foreach ($reasonSets as $reasonSet) {
diff --git a/src/Composer/DependencyResolver/Transaction.php b/src/Composer/DependencyResolver/Transaction.php
index 265474123..2e6640eee 100644
--- a/src/Composer/DependencyResolver/Transaction.php
+++ b/src/Composer/DependencyResolver/Transaction.php
@@ -60,7 +60,7 @@ class Transaction
     /**
      * @return OperationInterface[]
      */
-    public function getOperations()
+    public function getOperations(): array
     {
         return $this->operations;
     }
@@ -101,7 +101,7 @@ class Transaction
     /**
      * @return OperationInterface[]
      */
-    protected function calculateOperations()
+    protected function calculateOperations(): array
     {
         $operations = array();
 
@@ -218,7 +218,7 @@ class Transaction
      *
      * @return array<string, PackageInterface>
      */
-    protected function getRootPackages()
+    protected function getRootPackages(): array
     {
         $roots = $this->resultPackageMap;
 
@@ -244,7 +244,7 @@ class Transaction
     /**
      * @return PackageInterface[]
      */
-    protected function getProvidersInResult(Link $link)
+    protected function getProvidersInResult(Link $link): array
     {
         if (!isset($this->resultPackagesByName[$link->getTarget()])) {
             return array();
@@ -266,7 +266,7 @@ class Transaction
      * @param  OperationInterface[] $operations
      * @return OperationInterface[] reordered operation list
      */
-    private function movePluginsToFront(array $operations)
+    private function movePluginsToFront(array $operations): array
     {
         $dlModifyingPluginsNoDeps = array();
         $dlModifyingPluginsWithDeps = array();
@@ -343,7 +343,7 @@ class Transaction
      * @param  OperationInterface[] $operations
      * @return OperationInterface[] reordered operation list
      */
-    private function moveUninstallsToFront(array $operations)
+    private function moveUninstallsToFront(array $operations): array
     {
         $uninstOps = array();
         foreach ($operations as $idx => $op) {
diff --git a/src/Composer/Downloader/DownloadManager.php b/src/Composer/Downloader/DownloadManager.php
index 71eb87ee6..7b40784f4 100644
--- a/src/Composer/Downloader/DownloadManager.php
+++ b/src/Composer/Downloader/DownloadManager.php
@@ -406,7 +406,7 @@ class DownloadManager
      * @return string[]
      * @phpstan-return array<'dist'|'source'>&non-empty-array
      */
-    private function getAvailableSources(PackageInterface $package, PackageInterface $prevPackage = null)
+    private function getAvailableSources(PackageInterface $package, PackageInterface $prevPackage = null): array
     {
         $sourceType = $package->getSourceType();
         $distType = $package->getDistType();
@@ -456,7 +456,7 @@ class DownloadManager
      *
      * @return string
      */
-    private function normalizeTargetDir($dir)
+    private function normalizeTargetDir($dir): string
     {
         if ($dir === '\\' || $dir === '/') {
             return $dir;
diff --git a/src/Composer/Downloader/PathDownloader.php b/src/Composer/Downloader/PathDownloader.php
index 74c36f136..122e5a9b6 100644
--- a/src/Composer/Downloader/PathDownloader.php
+++ b/src/Composer/Downloader/PathDownloader.php
@@ -295,7 +295,7 @@ class PathDownloader extends FileDownloader implements VcsCapableDownloaderInter
      *
      * @return bool
      */
-    private function safeJunctions()
+    private function safeJunctions(): bool
     {
         // We need to call mklink, and rmdir on Windows 7 (version 6.1)
         return function_exists('proc_open') &&
diff --git a/src/Composer/Downloader/PerforceDownloader.php b/src/Composer/Downloader/PerforceDownloader.php
index 8f2427727..0a4e59413 100644
--- a/src/Composer/Downloader/PerforceDownloader.php
+++ b/src/Composer/Downloader/PerforceDownloader.php
@@ -57,7 +57,7 @@ class PerforceDownloader extends VcsDownloader
      *
      * @return string|null
      */
-    private function getLabelFromSourceReference($ref)
+    private function getLabelFromSourceReference($ref): ?string
     {
         $pos = strpos($ref, '@');
         if (false !== $pos) {
@@ -92,7 +92,7 @@ class PerforceDownloader extends VcsDownloader
     /**
      * @return array<string, mixed>
      */
-    private function getRepoConfig(VcsRepository $repository)
+    private function getRepoConfig(VcsRepository $repository): array
     {
         return $repository->getRepoConfig();
     }
diff --git a/src/Composer/Downloader/VcsDownloader.php b/src/Composer/Downloader/VcsDownloader.php
index eaea3d9da..b87deb044 100644
--- a/src/Composer/Downloader/VcsDownloader.php
+++ b/src/Composer/Downloader/VcsDownloader.php
@@ -346,7 +346,7 @@ abstract class VcsDownloader implements DownloaderInterface, ChangeReportInterfa
      *
      * @return string[]
      */
-    private function prepareUrls(array $urls)
+    private function prepareUrls(array $urls): array
     {
         foreach ($urls as $index => $url) {
             if (Filesystem::isLocalPath($url)) {
diff --git a/src/Composer/Downloader/ZipDownloader.php b/src/Composer/Downloader/ZipDownloader.php
index 23ad6db76..1347f296d 100644
--- a/src/Composer/Downloader/ZipDownloader.php
+++ b/src/Composer/Downloader/ZipDownloader.php
@@ -105,7 +105,7 @@ class ZipDownloader extends ArchiveDownloader
      * @param  string           $path Path where to extract file
      * @return PromiseInterface
      */
-    private function extractWithSystemUnzip(PackageInterface $package, $file, $path)
+    private function extractWithSystemUnzip(PackageInterface $package, $file, $path): PromiseInterface
     {
         // Force Exception throwing if the other alternative extraction method is not available
         $isLastChance = !self::$hasZipArchive;
@@ -172,7 +172,7 @@ class ZipDownloader extends ArchiveDownloader
      * @param  string           $path Path where to extract file
      * @return PromiseInterface
      */
-    private function extractWithZipArchive(PackageInterface $package, $file, $path)
+    private function extractWithZipArchive(PackageInterface $package, $file, $path): PromiseInterface
     {
         $processError = null;
         $zipArchive = $this->zipArchiveObject ?: new ZipArchive();
diff --git a/src/Composer/EventDispatcher/EventDispatcher.php b/src/Composer/EventDispatcher/EventDispatcher.php
index 29b1f5de7..704c1e403 100644
--- a/src/Composer/EventDispatcher/EventDispatcher.php
+++ b/src/Composer/EventDispatcher/EventDispatcher.php
@@ -556,7 +556,7 @@ class EventDispatcher
     /**
      * @return void
      */
-    private function ensureBinDirIsInPath()
+    private function ensureBinDirIsInPath(): void
     {
         $pathEnv = 'PATH';
         if (false === Platform::getEnv('PATH') && false !== Platform::getEnv('Path')) {
diff --git a/src/Composer/Factory.php b/src/Composer/Factory.php
index 5911b6633..4f7c6fb2d 100644
--- a/src/Composer/Factory.php
+++ b/src/Composer/Factory.php
@@ -696,7 +696,7 @@ class Factory
     /**
      * @return bool
      */
-    private static function useXdg()
+    private static function useXdg(): bool
     {
         foreach (array_keys($_SERVER) as $key) {
             if (strpos($key, 'XDG_') === 0) {
@@ -715,7 +715,7 @@ class Factory
      * @throws \RuntimeException
      * @return string
      */
-    private static function getUserDir()
+    private static function getUserDir(): string
     {
         $home = Platform::getEnv('HOME');
         if (!$home) {
diff --git a/src/Composer/Filter/PlatformRequirementFilter/IgnoreAllPlatformRequirementFilter.php b/src/Composer/Filter/PlatformRequirementFilter/IgnoreAllPlatformRequirementFilter.php
index d1fb51b8f..ca37baea4 100644
--- a/src/Composer/Filter/PlatformRequirementFilter/IgnoreAllPlatformRequirementFilter.php
+++ b/src/Composer/Filter/PlatformRequirementFilter/IgnoreAllPlatformRequirementFilter.php
@@ -20,7 +20,7 @@ final class IgnoreAllPlatformRequirementFilter implements PlatformRequirementFil
      * @param string $req
      * @return bool
      */
-    public function isIgnored($req)
+    public function isIgnored($req): bool
     {
         return PlatformRepository::isPlatformPackage($req);
     }
diff --git a/src/Composer/Filter/PlatformRequirementFilter/IgnoreListPlatformRequirementFilter.php b/src/Composer/Filter/PlatformRequirementFilter/IgnoreListPlatformRequirementFilter.php
index 6c3adf14b..e51d59b39 100644
--- a/src/Composer/Filter/PlatformRequirementFilter/IgnoreListPlatformRequirementFilter.php
+++ b/src/Composer/Filter/PlatformRequirementFilter/IgnoreListPlatformRequirementFilter.php
@@ -55,7 +55,7 @@ final class IgnoreListPlatformRequirementFilter implements PlatformRequirementFi
      * @param string $req
      * @return bool
      */
-    public function isIgnored($req)
+    public function isIgnored($req): bool
     {
         if (!PlatformRepository::isPlatformPackage($req)) {
             return false;
@@ -68,7 +68,7 @@ final class IgnoreListPlatformRequirementFilter implements PlatformRequirementFi
      * @param string $req
      * @return ConstraintInterface
      */
-    public function filterConstraint($req, ConstraintInterface $constraint)
+    public function filterConstraint($req, ConstraintInterface $constraint): ConstraintInterface
     {
         if (!PlatformRepository::isPlatformPackage($req)) {
             return $constraint;
diff --git a/src/Composer/Filter/PlatformRequirementFilter/IgnoreNothingPlatformRequirementFilter.php b/src/Composer/Filter/PlatformRequirementFilter/IgnoreNothingPlatformRequirementFilter.php
index 7c4bddbab..2262326c3 100644
--- a/src/Composer/Filter/PlatformRequirementFilter/IgnoreNothingPlatformRequirementFilter.php
+++ b/src/Composer/Filter/PlatformRequirementFilter/IgnoreNothingPlatformRequirementFilter.php
@@ -18,7 +18,7 @@ final class IgnoreNothingPlatformRequirementFilter implements PlatformRequiremen
      * @param string $req
      * @return false
      */
-    public function isIgnored($req)
+    public function isIgnored($req): bool
     {
         return false;
     }
diff --git a/src/Composer/Filter/PlatformRequirementFilter/PlatformRequirementFilterFactory.php b/src/Composer/Filter/PlatformRequirementFilter/PlatformRequirementFilterFactory.php
index ac8a83cd7..302bdd915 100644
--- a/src/Composer/Filter/PlatformRequirementFilter/PlatformRequirementFilterFactory.php
+++ b/src/Composer/Filter/PlatformRequirementFilter/PlatformRequirementFilterFactory.php
@@ -19,7 +19,7 @@ final class PlatformRequirementFilterFactory
      *
      * @return PlatformRequirementFilterInterface
      */
-    public static function fromBoolOrList($boolOrList)
+    public static function fromBoolOrList($boolOrList): PlatformRequirementFilterInterface
     {
         if (is_bool($boolOrList)) {
             return $boolOrList ? self::ignoreAll() : self::ignoreNothing();
@@ -40,7 +40,7 @@ final class PlatformRequirementFilterFactory
     /**
      * @return PlatformRequirementFilterInterface
      */
-    public static function ignoreAll()
+    public static function ignoreAll(): PlatformRequirementFilterInterface
     {
         return new IgnoreAllPlatformRequirementFilter();
     }
@@ -48,7 +48,7 @@ final class PlatformRequirementFilterFactory
     /**
      * @return PlatformRequirementFilterInterface
      */
-    public static function ignoreNothing()
+    public static function ignoreNothing(): PlatformRequirementFilterInterface
     {
         return new IgnoreNothingPlatformRequirementFilter();
     }
diff --git a/src/Composer/IO/ConsoleIO.php b/src/Composer/IO/ConsoleIO.php
index 63337ec93..b4e19846f 100644
--- a/src/Composer/IO/ConsoleIO.php
+++ b/src/Composer/IO/ConsoleIO.php
@@ -157,7 +157,7 @@ class ConsoleIO extends BaseIO
      *
      * @return void
      */
-    private function doWrite($messages, $newline, $stderr, $verbosity, $raw = false)
+    private function doWrite($messages, $newline, $stderr, $verbosity, $raw = false): void
     {
         $sfVerbosity = $this->verbosityMap[$verbosity];
         if ($sfVerbosity > $this->output->getVerbosity()) {
@@ -216,7 +216,7 @@ class ConsoleIO extends BaseIO
      *
      * @return void
      */
-    private function doOverwrite($messages, $newline, $size, $stderr, $verbosity)
+    private function doOverwrite($messages, $newline, $size, $stderr, $verbosity): void
     {
         // messages can be an array, let's convert it to string anyway
         $messages = implode($newline ? "\n" : '', (array) $messages);
@@ -345,7 +345,7 @@ class ConsoleIO extends BaseIO
     /**
      * @return OutputInterface
      */
-    private function getErrorOutput()
+    private function getErrorOutput(): OutputInterface
     {
         if ($this->output instanceof ConsoleOutputInterface) {
             return $this->output->getErrorOutput();
diff --git a/src/Composer/Installer.php b/src/Composer/Installer.php
index 43af3fde5..8e397d603 100644
--- a/src/Composer/Installer.php
+++ b/src/Composer/Installer.php
@@ -789,7 +789,7 @@ class Installer
      *
      * @phpstan-param list<array{package: string, version: string, alias: string, alias_normalized: string}> $rootAliases
      */
-    private function createRepositorySet($forUpdate, PlatformRepository $platformRepo, array $rootAliases = array(), $lockedRepository = null)
+    private function createRepositorySet($forUpdate, PlatformRepository $platformRepo, array $rootAliases = array(), $lockedRepository = null): RepositorySet
     {
         if ($forUpdate) {
             $minimumStability = $this->package->getMinimumStability();
@@ -858,7 +858,7 @@ class Installer
      *
      * @return DefaultPolicy
      */
-    private function createPolicy($forUpdate)
+    private function createPolicy($forUpdate): DefaultPolicy
     {
         $preferStable = null;
         $preferLowest = null;
@@ -882,7 +882,7 @@ class Installer
      * @param RootPackageInterface&BasePackage $rootPackage
      * @return Request
      */
-    private function createRequest(RootPackageInterface $rootPackage, PlatformRepository $platformRepo, LockArrayRepository $lockedRepository = null)
+    private function createRequest(RootPackageInterface $rootPackage, PlatformRepository $platformRepo, LockArrayRepository $lockedRepository = null): Request
     {
         $request = new Request($lockedRepository);
 
@@ -953,7 +953,7 @@ class Installer
      *
      * @phpstan-return list<array{package: string, version: string, alias: string, alias_normalized: string}>
      */
-    private function getRootAliases($forUpdate)
+    private function getRootAliases($forUpdate): array
     {
         if ($forUpdate) {
             $aliases = $this->package->getAliases();
@@ -969,7 +969,7 @@ class Installer
      *
      * @return array<string, string>
      */
-    private function extractPlatformRequirements(array $links)
+    private function extractPlatformRequirements(array $links): array
     {
         $platformReqs = array();
         foreach ($links as $link) {
@@ -1009,7 +1009,7 @@ class Installer
     /**
      * @return PoolOptimizer|null
      */
-    private function createPoolOptimizer(PolicyInterface $policy)
+    private function createPoolOptimizer(PolicyInterface $policy): ?PoolOptimizer
     {
         // Not the best architectural decision here, would need to be able
         // to configure from the outside of Installer but this is only
diff --git a/src/Composer/Installer/InstallationManager.php b/src/Composer/Installer/InstallationManager.php
index 71aa3d986..cb3aafbd8 100644
--- a/src/Composer/Installer/InstallationManager.php
+++ b/src/Composer/Installer/InstallationManager.php
@@ -316,7 +316,7 @@ class InstallationManager
      *
      * @return void
      */
-    private function downloadAndExecuteBatch(InstalledRepositoryInterface $repo, array $operations, array &$cleanupPromises, $devMode, $runScripts, array $allOperations)
+    private function downloadAndExecuteBatch(InstalledRepositoryInterface $repo, array $operations, array &$cleanupPromises, $devMode, $runScripts, array $allOperations): void
     {
         $promises = array();
 
@@ -400,7 +400,7 @@ class InstallationManager
      *
      * @return void
      */
-    private function executeBatch(InstalledRepositoryInterface $repo, array $operations, array $cleanupPromises, $devMode, $runScripts, array $allOperations)
+    private function executeBatch(InstalledRepositoryInterface $repo, array $operations, array $cleanupPromises, $devMode, $runScripts, array $allOperations): void
     {
         $promises = array();
         $postExecCallbacks = array();
@@ -481,7 +481,7 @@ class InstallationManager
      *
      * @return void
      */
-    private function waitOnPromises(array $promises)
+    private function waitOnPromises(array $promises): void
     {
         $progress = null;
         if (
@@ -700,7 +700,7 @@ class InstallationManager
     /**
      * @return void
      */
-    private function markForNotification(PackageInterface $package)
+    private function markForNotification(PackageInterface $package): void
     {
         if ($package->getNotificationUrl()) {
             $this->notifiablePackages[$package->getNotificationUrl()][$package->getName()] = $package;
diff --git a/src/Composer/Installer/SuggestedPackagesReporter.php b/src/Composer/Installer/SuggestedPackagesReporter.php
index 840e63f51..15e86b6d2 100644
--- a/src/Composer/Installer/SuggestedPackagesReporter.php
+++ b/src/Composer/Installer/SuggestedPackagesReporter.php
@@ -183,7 +183,7 @@ class SuggestedPackagesReporter
      * @param  PackageInterface|null    $onlyDependentsOf If passed in, only the suggestions from direct dependents of that package, or from the package itself, will be shown
      * @return mixed[]
      */
-    private function getFilteredSuggestions(InstalledRepository $installedRepo = null, PackageInterface $onlyDependentsOf = null)
+    private function getFilteredSuggestions(InstalledRepository $installedRepo = null, PackageInterface $onlyDependentsOf = null): array
     {
         $suggestedPackages = $this->getPackages();
         $installedNames = array();
@@ -220,7 +220,7 @@ class SuggestedPackagesReporter
      * @param  string $string
      * @return string
      */
-    private function escapeOutput($string)
+    private function escapeOutput($string): string
     {
         return OutputFormatter::escape(
             $this->removeControlCharacters($string)
@@ -231,7 +231,7 @@ class SuggestedPackagesReporter
      * @param  string $string
      * @return string
      */
-    private function removeControlCharacters($string)
+    private function removeControlCharacters($string): string
     {
         return Preg::replace(
             '/[[:cntrl:]]/',
diff --git a/src/Composer/Json/JsonFile.php b/src/Composer/Json/JsonFile.php
index 35661c925..aa81fb61a 100644
--- a/src/Composer/Json/JsonFile.php
+++ b/src/Composer/Json/JsonFile.php
@@ -256,7 +256,7 @@ class JsonFile
      * @throws \RuntimeException
      * @return void
      */
-    private static function throwEncodeError($code)
+    private static function throwEncodeError($code): void
     {
         switch ($code) {
             case JSON_ERROR_DEPTH:
diff --git a/src/Composer/Json/JsonManipulator.php b/src/Composer/Json/JsonManipulator.php
index 1e51f4dcc..60cbef0c1 100644
--- a/src/Composer/Json/JsonManipulator.php
+++ b/src/Composer/Json/JsonManipulator.php
@@ -133,7 +133,7 @@ class JsonManipulator
      * @param array<string> $packages
      * @return void
      */
-    private function sortPackages(array &$packages = array())
+    private function sortPackages(array &$packages = array()): void
     {
         $prefix = function ($requirement) {
             if (PlatformRepository::isPlatformPackage($requirement)) {
diff --git a/src/Composer/Package/Archiver/ZipArchiver.php b/src/Composer/Package/Archiver/ZipArchiver.php
index 4e83a2f4d..036e353a8 100644
--- a/src/Composer/Package/Archiver/ZipArchiver.php
+++ b/src/Composer/Package/Archiver/ZipArchiver.php
@@ -86,7 +86,7 @@ class ZipArchiver implements ArchiverInterface
     /**
      * @return bool
      */
-    private function compressionAvailable()
+    private function compressionAvailable(): bool
     {
         return class_exists('ZipArchive');
     }
diff --git a/src/Composer/Package/Dumper/ArrayDumper.php b/src/Composer/Package/Dumper/ArrayDumper.php
index 9b6e40946..31655d73b 100644
--- a/src/Composer/Package/Dumper/ArrayDumper.php
+++ b/src/Composer/Package/Dumper/ArrayDumper.php
@@ -148,7 +148,7 @@ class ArrayDumper
      *
      * @return array<string, mixed>
      */
-    private function dumpValues(PackageInterface $package, array $keys, array $data)
+    private function dumpValues(PackageInterface $package, array $keys, array $data): array
     {
         foreach ($keys as $method => $key) {
             if (is_numeric($method)) {
diff --git a/src/Composer/Package/Loader/ArrayLoader.php b/src/Composer/Package/Loader/ArrayLoader.php
index 403da9a45..16cede400 100644
--- a/src/Composer/Package/Loader/ArrayLoader.php
+++ b/src/Composer/Package/Loader/ArrayLoader.php
@@ -321,7 +321,7 @@ class ArrayLoader implements LoaderInterface
      *
      * @return void
      */
-    private function configureCachedLinks(&$linkCache, $package, array $config)
+    private function configureCachedLinks(&$linkCache, $package, array $config): void
     {
         $name = $package->getName();
         $prettyVersion = $package->getPrettyVersion();
@@ -385,7 +385,7 @@ class ArrayLoader implements LoaderInterface
      * @param  string       $prettyConstraint constraint string
      * @return Link
      */
-    private function createLink($source, $sourceVersion, $description, $target, $prettyConstraint)
+    private function createLink($source, $sourceVersion, $description, $target, $prettyConstraint): Link
     {
         if (!\is_string($prettyConstraint)) {
             throw new \UnexpectedValueException('Link constraint in '.$source.' '.$description.' > '.$target.' should be a string, got '.\gettype($prettyConstraint) . ' (' . var_export($prettyConstraint, true) . ')');
diff --git a/src/Composer/Package/Loader/RootPackageLoader.php b/src/Composer/Package/Loader/RootPackageLoader.php
index cd061941c..9c0c47c8f 100644
--- a/src/Composer/Package/Loader/RootPackageLoader.php
+++ b/src/Composer/Package/Loader/RootPackageLoader.php
@@ -194,7 +194,7 @@ class RootPackageLoader extends ArrayLoader
      *
      * @return list<array{package: string, version: string, alias: string, alias_normalized: string}>
      */
-    private function extractAliases(array $requires, array $aliases)
+    private function extractAliases(array $requires, array $aliases): array
     {
         foreach ($requires as $reqName => $reqVersion) {
             if (Preg::isMatch('{^([^,\s#]+)(?:#[^ ]+)? +as +([^,\s]+)$}', $reqVersion, $match)) {
@@ -224,7 +224,7 @@ class RootPackageLoader extends ArrayLoader
      * @phpstan-param array<string, BasePackage::STABILITY_*> $stabilityFlags
      * @phpstan-return array<string, BasePackage::STABILITY_*>
      */
-    public static function extractStabilityFlags(array $requires, $minimumStability, array $stabilityFlags)
+    public static function extractStabilityFlags(array $requires, $minimumStability, array $stabilityFlags): array
     {
         $stabilities = BasePackage::$stabilities;
         /** @var int $minimumStability */
@@ -286,7 +286,7 @@ class RootPackageLoader extends ArrayLoader
      *
      * @return array<string, string>
      */
-    public static function extractReferences(array $requires, array $references)
+    public static function extractReferences(array $requires, array $references): array
     {
         foreach ($requires as $reqName => $reqVersion) {
             $reqVersion = Preg::replace('{^([^,\s@]+) as .+$}', '$1', $reqVersion);
diff --git a/src/Composer/Package/Loader/ValidatingArrayLoader.php b/src/Composer/Package/Loader/ValidatingArrayLoader.php
index 7fb2c3b79..662f84861 100644
--- a/src/Composer/Package/Loader/ValidatingArrayLoader.php
+++ b/src/Composer/Package/Loader/ValidatingArrayLoader.php
@@ -494,7 +494,7 @@ class ValidatingArrayLoader implements LoaderInterface
      * @phpstan-param non-empty-string $property
      * @phpstan-param non-empty-string $regex
      */
-    private function validateRegex($property, $regex, $mandatory = false)
+    private function validateRegex($property, $regex, $mandatory = false): bool
     {
         if (!$this->validateString($property, $mandatory)) {
             return false;
@@ -523,7 +523,7 @@ class ValidatingArrayLoader implements LoaderInterface
      *
      * @phpstan-param non-empty-string $property
      */
-    private function validateString($property, $mandatory = false)
+    private function validateString($property, $mandatory = false): bool
     {
         if (isset($this->config[$property]) && !is_string($this->config[$property])) {
             $this->errors[] = $property.' : should be a string, '.gettype($this->config[$property]).' given';
@@ -552,7 +552,7 @@ class ValidatingArrayLoader implements LoaderInterface
      *
      * @phpstan-param non-empty-string $property
      */
-    private function validateArray($property, $mandatory = false)
+    private function validateArray($property, $mandatory = false): bool
     {
         if (isset($this->config[$property]) && !is_array($this->config[$property])) {
             $this->errors[] = $property.' : should be an array, '.gettype($this->config[$property]).' given';
@@ -583,7 +583,7 @@ class ValidatingArrayLoader implements LoaderInterface
      * @phpstan-param non-empty-string      $property
      * @phpstan-param non-empty-string|null $regex
      */
-    private function validateFlatArray($property, $regex = null, $mandatory = false)
+    private function validateFlatArray($property, $regex = null, $mandatory = false): bool
     {
         if (!$this->validateArray($property, $mandatory)) {
             return false;
@@ -617,7 +617,7 @@ class ValidatingArrayLoader implements LoaderInterface
      *
      * @phpstan-param non-empty-string $property
      */
-    private function validateUrl($property, $mandatory = false)
+    private function validateUrl($property, $mandatory = false): bool
     {
         if (!$this->validateString($property, $mandatory)) {
             return false;
@@ -639,7 +639,7 @@ class ValidatingArrayLoader implements LoaderInterface
      *
      * @return bool
      */
-    private function filterUrl($value, array $schemes = array('http', 'https'))
+    private function filterUrl($value, array $schemes = array('http', 'https')): bool
     {
         if ($value === '') {
             return true;
diff --git a/src/Composer/Package/Locker.php b/src/Composer/Package/Locker.php
index 5a306d14d..be9466ea3 100644
--- a/src/Composer/Package/Locker.php
+++ b/src/Composer/Package/Locker.php
@@ -419,7 +419,7 @@ class Locker
      *
      * @phpstan-return list<array<string, mixed>>
      */
-    private function lockPackages(array $packages)
+    private function lockPackages(array $packages): array
     {
         $locked = array();
 
@@ -477,7 +477,7 @@ class Locker
      * @param  PackageInterface $package The package to scan.
      * @return string|null      The formatted datetime or null if none was found.
      */
-    private function getPackageTime(PackageInterface $package)
+    private function getPackageTime(PackageInterface $package): ?string
     {
         if (!function_exists('proc_open')) {
             return null;
diff --git a/src/Composer/Package/Package.php b/src/Composer/Package/Package.php
index a0be96f3d..7549c4008 100644
--- a/src/Composer/Package/Package.php
+++ b/src/Composer/Package/Package.php
@@ -788,7 +788,7 @@ class Package extends BasePackage
      * @param  string $source
      * @return array<string, Link>
      */
-    private function convertLinksToMap(array $links, $source)
+    private function convertLinksToMap(array $links, $source): array
     {
         trigger_error('Package::'.$source.' must be called with a map of lowercased package name => Link object, got a indexed array, this is deprecated and you should fix your usage.');
         $newLinks = array();
diff --git a/src/Composer/Package/Version/VersionGuesser.php b/src/Composer/Package/Version/VersionGuesser.php
index 7927fa726..d10c02951 100644
--- a/src/Composer/Package/Version/VersionGuesser.php
+++ b/src/Composer/Package/Version/VersionGuesser.php
@@ -103,7 +103,7 @@ class VersionGuesser
      * @return array
      * @phpstan-return Version
      */
-    private function postprocess(array $versionData)
+    private function postprocess(array $versionData): array
     {
         if (!empty($versionData['feature_version']) && $versionData['feature_version'] === $versionData['version'] && $versionData['feature_pretty_version'] === $versionData['pretty_version']) {
             unset($versionData['feature_version'], $versionData['feature_pretty_version']);
@@ -126,7 +126,7 @@ class VersionGuesser
      *
      * @return array{version: string|null, commit: string|null, pretty_version: string|null, feature_version?: string|null, feature_pretty_version?: string|null}
      */
-    private function guessGitVersion(array $packageConfig, $path)
+    private function guessGitVersion(array $packageConfig, $path): array
     {
         GitUtil::cleanEnv();
         $commit = null;
@@ -211,7 +211,7 @@ class VersionGuesser
      *
      * @return array{version: string, pretty_version: string}|null
      */
-    private function versionFromGitTags($path)
+    private function versionFromGitTags($path): ?array
     {
         // try to fetch current version from git tags
         if (0 === $this->process->execute('git describe --exact-match --tags', $output, $path)) {
@@ -232,7 +232,7 @@ class VersionGuesser
      *
      * @return array{version: string|null, commit: ''|null, pretty_version: string|null, feature_version?: string|null, feature_pretty_version?: string|null}|null
      */
-    private function guessHgVersion(array $packageConfig, $path)
+    private function guessHgVersion(array $packageConfig, $path): ?array
     {
         // try to fetch current version from hg branch
         if (0 === $this->process->execute('hg branch', $output, $path)) {
@@ -276,7 +276,7 @@ class VersionGuesser
      *
      * @return array{version: string|null, pretty_version: string|null}
      */
-    private function guessFeatureVersion(array $packageConfig, $version, array $branches, $scmCmdline, $path)
+    private function guessFeatureVersion(array $packageConfig, $version, array $branches, $scmCmdline, $path): array
     {
         $prettyVersion = $version;
 
@@ -340,7 +340,7 @@ class VersionGuesser
      *
      * @return bool
      */
-    private function isFeatureBranch(array $packageConfig, $branchName)
+    private function isFeatureBranch(array $packageConfig, $branchName): bool
     {
         $nonFeatureBranches = '';
         if (!empty($packageConfig['non-feature-branches'])) {
@@ -355,7 +355,7 @@ class VersionGuesser
      *
      * @return array{version: string|null, commit: '', pretty_version: string|null}
      */
-    private function guessFossilVersion($path)
+    private function guessFossilVersion($path): array
     {
         $version = null;
         $prettyVersion = null;
@@ -385,7 +385,7 @@ class VersionGuesser
      *
      * @return array{version: string, commit: '', pretty_version: string}|null
      */
-    private function guessSvnVersion(array $packageConfig, $path)
+    private function guessSvnVersion(array $packageConfig, $path): ?array
     {
         SvnUtil::cleanEnv();
 
diff --git a/src/Composer/Package/Version/VersionSelector.php b/src/Composer/Package/Version/VersionSelector.php
index 8e4b45faa..a1a6e57df 100644
--- a/src/Composer/Package/Version/VersionSelector.php
+++ b/src/Composer/Package/Version/VersionSelector.php
@@ -211,7 +211,7 @@ class VersionSelector
      *
      * @return string
      */
-    private function transformVersion($version, $prettyVersion, $stability)
+    private function transformVersion($version, $prettyVersion, $stability): string
     {
         // attempt to transform 2.1.1 to 2.1
         // this allows you to upgrade through minor versions
@@ -242,7 +242,7 @@ class VersionSelector
     /**
      * @return VersionParser
      */
-    private function getParser()
+    private function getParser(): VersionParser
     {
         if ($this->parser === null) {
             $this->parser = new VersionParser();
diff --git a/src/Composer/Platform/Version.php b/src/Composer/Platform/Version.php
index 6c9cd8fa5..7f957ae5c 100644
--- a/src/Composer/Platform/Version.php
+++ b/src/Composer/Platform/Version.php
@@ -71,7 +71,7 @@ class Version
      * @param  string $alpha
      * @return int
      */
-    private static function convertAlphaVersionToIntVersion($alpha)
+    private static function convertAlphaVersionToIntVersion($alpha): int
     {
         return strlen($alpha) * (-ord('a') + 1) + array_sum(array_map('ord', str_split($alpha)));
     }
@@ -100,7 +100,7 @@ class Version
      *
      * @return string
      */
-    private static function convertVersionId($versionId, $base)
+    private static function convertVersionId($versionId, $base): string
     {
         return sprintf(
             '%d.%d.%d',
diff --git a/src/Composer/Plugin/PluginManager.php b/src/Composer/Plugin/PluginManager.php
index 5f3390ef7..f6fa3cd73 100644
--- a/src/Composer/Plugin/PluginManager.php
+++ b/src/Composer/Plugin/PluginManager.php
@@ -530,7 +530,7 @@ class PluginManager
      *
      * @return array<string, PackageInterface> Map of package names to packages
      */
-    private function collectDependencies(InstalledRepository $installedRepo, array $collected, PackageInterface $package)
+    private function collectDependencies(InstalledRepository $installedRepo, array $collected, PackageInterface $package): array
     {
         foreach ($package->getRequires() as $requireLink) {
             foreach ($installedRepo->findPackagesWithReplacersAndProviders($requireLink->getTarget()) as $requiredPackage) {
@@ -552,7 +552,7 @@ class PluginManager
      *
      * @return string Install path
      */
-    private function getInstallPath(PackageInterface $package, $global = false)
+    private function getInstallPath(PackageInterface $package, $global = false): string
     {
         if (!$global) {
             return $this->composer->getInstallationManager()->getInstallPath($package);
@@ -647,7 +647,7 @@ class PluginManager
      * @param  array<string, bool>|bool|null $allowPluginsConfig
      * @return array<non-empty-string, bool>|null
      */
-    private function parseAllowedPlugins($allowPluginsConfig)
+    private function parseAllowedPlugins($allowPluginsConfig): ?array
     {
         if (null === $allowPluginsConfig) {
             return null;
@@ -674,7 +674,7 @@ class PluginManager
      * @param bool $isGlobalPlugin
      * @return bool
      */
-    private function isPluginAllowed($package, $isGlobalPlugin)
+    private function isPluginAllowed($package, $isGlobalPlugin): bool
     {
         static $warned = array();
         $rules = $isGlobalPlugin ? $this->allowGlobalPluginRules : $this->allowPluginRules;
diff --git a/src/Composer/Question/StrictConfirmationQuestion.php b/src/Composer/Question/StrictConfirmationQuestion.php
index 301bb91b0..5ec5577c1 100644
--- a/src/Composer/Question/StrictConfirmationQuestion.php
+++ b/src/Composer/Question/StrictConfirmationQuestion.php
@@ -53,7 +53,7 @@ class StrictConfirmationQuestion extends Question
      *
      * @return callable
      */
-    private function getDefaultNormalizer()
+    private function getDefaultNormalizer(): callable
     {
         $default = $this->getDefault();
         $trueRegex = $this->trueAnswerRegex;
@@ -84,7 +84,7 @@ class StrictConfirmationQuestion extends Question
      *
      * @return callable
      */
-    private function getDefaultValidator()
+    private function getDefaultValidator(): callable
     {
         return function ($answer) {
             if (!is_bool($answer)) {
diff --git a/src/Composer/Repository/ArtifactRepository.php b/src/Composer/Repository/ArtifactRepository.php
index e8140162c..7db28bcab 100644
--- a/src/Composer/Repository/ArtifactRepository.php
+++ b/src/Composer/Repository/ArtifactRepository.php
@@ -73,7 +73,7 @@ class ArtifactRepository extends ArrayRepository implements ConfigurableReposito
      *
      * @return void
      */
-    private function scanDirectory($path)
+    private function scanDirectory($path): void
     {
         $io = $this->io;
 
@@ -102,7 +102,7 @@ class ArtifactRepository extends ArrayRepository implements ConfigurableReposito
     /**
      * @return ?BasePackage
      */
-    private function getComposerInformation(\SplFileInfo $file)
+    private function getComposerInformation(\SplFileInfo $file): ?BasePackage
     {
         $json = null;
         $fileType = null;
diff --git a/src/Composer/Repository/ComposerRepository.php b/src/Composer/Repository/ComposerRepository.php
index 8fa6bf03b..a5a99f9f5 100644
--- a/src/Composer/Repository/ComposerRepository.php
+++ b/src/Composer/Repository/ComposerRepository.php
@@ -39,6 +39,7 @@ use Composer\Semver\Constraint\MatchAllConstraint;
 use Composer\Util\Http\Response;
 use Composer\MetadataMinifier\MetadataMinifier;
 use Composer\Util\Url;
+use React\Promise\PromiseInterface;
 
 /**
  * @author Jordi Boggiano <j.boggiano@seld.be>
@@ -399,7 +400,7 @@ class ComposerRepository extends ArrayRepository implements ConfigurableReposito
     /**
      * @return list<string>
      */
-    private function getVendorNames()
+    private function getVendorNames(): array
     {
         $cacheKey = 'vendor-list.txt';
         $cacheAge = $this->cache->getAge($cacheKey);
@@ -430,7 +431,7 @@ class ComposerRepository extends ArrayRepository implements ConfigurableReposito
      * @param string|null $packageFilter
      * @return list<string>
      */
-    private function loadPackageList($packageFilter = null)
+    private function loadPackageList($packageFilter = null): array
     {
         if (null === $this->listUrl) {
             throw new \LogicException('Make sure to call loadRootServerFile before loadPackageList');
@@ -640,7 +641,7 @@ class ComposerRepository extends ArrayRepository implements ConfigurableReposito
     /**
      * @return string[]
      */
-    private function getProviderNames()
+    private function getProviderNames(): array
     {
         $this->loadRootServerFile();
 
@@ -677,7 +678,7 @@ class ComposerRepository extends ArrayRepository implements ConfigurableReposito
     /**
      * @return bool
      */
-    private function hasProviders()
+    private function hasProviders(): bool
     {
         $this->loadRootServerFile();
 
@@ -694,7 +695,7 @@ class ComposerRepository extends ArrayRepository implements ConfigurableReposito
      *
      * @return array<string, BasePackage>
      */
-    private function whatProvides($name, array $acceptableStabilities = null, array $stabilityFlags = null, array $alreadyLoaded = array())
+    private function whatProvides($name, array $acceptableStabilities = null, array $stabilityFlags = null, array $alreadyLoaded = array()): array
     {
         $packagesSource = null;
         if (!$this->hasPartialPackages() || !isset($this->partialPackagesByName[$name])) {
@@ -862,7 +863,7 @@ class ComposerRepository extends ArrayRepository implements ConfigurableReposito
      *
      * @return array{namesFound: array<string, true>, packages: array<string, BasePackage>}
      */
-    private function loadAsyncPackages(array $packageNames, array $acceptableStabilities = null, array $stabilityFlags = null, array $alreadyLoaded = array())
+    private function loadAsyncPackages(array $packageNames, array $acceptableStabilities = null, array $stabilityFlags = null, array $alreadyLoaded = array()): array
     {
         $this->loadRootServerFile();
 
@@ -972,7 +973,7 @@ class ComposerRepository extends ArrayRepository implements ConfigurableReposito
      *
      * @return bool
      */
-    private function isVersionAcceptable($constraint, $name, $versionData, array $acceptableStabilities = null, array $stabilityFlags = null)
+    private function isVersionAcceptable($constraint, $name, $versionData, array $acceptableStabilities = null, array $stabilityFlags = null): bool
     {
         $versions = array($versionData['version_normalized']);
 
@@ -998,7 +999,7 @@ class ComposerRepository extends ArrayRepository implements ConfigurableReposito
     /**
      * @return string
      */
-    private function getPackagesJsonUrl()
+    private function getPackagesJsonUrl(): string
     {
         $jsonUrlParts = parse_url($this->url);
 
@@ -1135,7 +1136,7 @@ class ComposerRepository extends ArrayRepository implements ConfigurableReposito
      *
      * @return string
      */
-    private function canonicalizeUrl($url)
+    private function canonicalizeUrl($url): string
     {
         if ('/' === $url[0]) {
             if (Preg::isMatch('{^[^:]++://[^/]*+}', $this->url, $matches)) {
@@ -1151,7 +1152,7 @@ class ComposerRepository extends ArrayRepository implements ConfigurableReposito
     /**
      * @return mixed[]
      */
-    private function loadDataFromServer()
+    private function loadDataFromServer(): array
     {
         $data = $this->loadRootServerFile();
 
@@ -1161,7 +1162,7 @@ class ComposerRepository extends ArrayRepository implements ConfigurableReposito
     /**
      * @return bool
      */
-    private function hasPartialPackages()
+    private function hasPartialPackages(): bool
     {
         if ($this->hasPartialPackages && null === $this->partialPackagesByName) {
             $this->initializePartialPackages();
@@ -1175,7 +1176,7 @@ class ComposerRepository extends ArrayRepository implements ConfigurableReposito
      *
      * @return void
      */
-    private function loadProviderListings($data)
+    private function loadProviderListings($data): void
     {
         if (isset($data['providers'])) {
             if (!is_array($this->providerListing)) {
@@ -1205,7 +1206,7 @@ class ComposerRepository extends ArrayRepository implements ConfigurableReposito
      *
      * @return mixed[]
      */
-    private function loadIncludes($data)
+    private function loadIncludes($data): array
     {
         $packages = array();
 
@@ -1250,7 +1251,7 @@ class ComposerRepository extends ArrayRepository implements ConfigurableReposito
      *
      * @return list<CompletePackage|CompleteAliasPackage>
      */
-    private function createPackages(array $packages, $source = null)
+    private function createPackages(array $packages, $source = null): array
     {
         if (!$packages) {
             return array();
@@ -1457,10 +1458,8 @@ class ComposerRepository extends ArrayRepository implements ConfigurableReposito
      * @param string $filename
      * @param string $cacheKey
      * @param string|null $lastModifiedTime
-     *
-     * @return \React\Promise\PromiseInterface
      */
-    private function asyncFetchFile($filename, $cacheKey, $lastModifiedTime = null)
+    private function asyncFetchFile($filename, $cacheKey, $lastModifiedTime = null): PromiseInterface
     {
         if (isset($this->packagesNotFoundCache[$filename])) {
             return \React\Promise\resolve(array('packages' => array()));
@@ -1566,7 +1565,7 @@ class ComposerRepository extends ArrayRepository implements ConfigurableReposito
      *
      * @return void
      */
-    private function initializePartialPackages()
+    private function initializePartialPackages(): void
     {
         $rootData = $this->loadRootServerFile();
 
diff --git a/src/Composer/Repository/FilesystemRepository.php b/src/Composer/Repository/FilesystemRepository.php
index 6138514fc..a6e949445 100644
--- a/src/Composer/Repository/FilesystemRepository.php
+++ b/src/Composer/Repository/FilesystemRepository.php
@@ -173,7 +173,7 @@ class FilesystemRepository extends WritableArrayRepository
      *
      * @return string
      */
-    private function dumpToPhpCode(array $array = array(), $level = 0)
+    private function dumpToPhpCode(array $array = array(), $level = 0): string
     {
         $lines = "array(\n";
         $level++;
@@ -211,7 +211,7 @@ class FilesystemRepository extends WritableArrayRepository
      *
      * @return ?array<mixed>
      */
-    private function generateInstalledVersions(InstallationManager $installationManager, array $installPaths, $devMode, $repoDir)
+    private function generateInstalledVersions(InstallationManager $installationManager, array $installPaths, $devMode, $repoDir): ?array
     {
         if (!$this->dumpVersions) {
             return null;
diff --git a/src/Composer/Repository/FilterRepository.php b/src/Composer/Repository/FilterRepository.php
index 078f66f8f..72b041582 100644
--- a/src/Composer/Repository/FilterRepository.php
+++ b/src/Composer/Repository/FilterRepository.php
@@ -195,7 +195,7 @@ class FilterRepository implements RepositoryInterface
      *
      * @return bool
      */
-    private function isAllowed($name)
+    private function isAllowed($name): bool
     {
         if (!$this->only && !$this->exclude) {
             return true;
diff --git a/src/Composer/Repository/PathRepository.php b/src/Composer/Repository/PathRepository.php
index bc86a9201..8a262c858 100644
--- a/src/Composer/Repository/PathRepository.php
+++ b/src/Composer/Repository/PathRepository.php
@@ -240,7 +240,7 @@ class PathRepository extends ArrayRepository implements ConfigurableRepositoryIn
      *
      * @return string[]
      */
-    private function getUrlMatches()
+    private function getUrlMatches(): array
     {
         $flags = GLOB_MARK | GLOB_ONLYDIR;
 
diff --git a/src/Composer/Repository/PlatformRepository.php b/src/Composer/Repository/PlatformRepository.php
index c1495f64d..e43fd3c93 100644
--- a/src/Composer/Repository/PlatformRepository.php
+++ b/src/Composer/Repository/PlatformRepository.php
@@ -586,7 +586,7 @@ class PlatformRepository extends ArrayRepository
      *
      * @return CompletePackage
      */
-    private function addOverriddenPackage(array $override, $name = null)
+    private function addOverriddenPackage(array $override, $name = null): CompletePackage
     {
         $version = $this->versionParser->normalize($override['version']);
         $package = new CompletePackage($name ?: $override['name'], $version, $override['version']);
@@ -653,7 +653,7 @@ class PlatformRepository extends ArrayRepository
      * @param  string $name
      * @return string
      */
-    private function buildPackageName($name)
+    private function buildPackageName($name): string
     {
         return 'ext-' . str_replace(' ', '-', strtolower($name));
     }
@@ -725,7 +725,7 @@ class PlatformRepository extends ArrayRepository
      * @internal
      * @return string|null
      */
-    public static function getPlatformPhpVersion()
+    public static function getPlatformPhpVersion(): ?string
     {
         return self::$lastSeenPlatformPhp;
     }
diff --git a/src/Composer/Repository/RepositoryFactory.php b/src/Composer/Repository/RepositoryFactory.php
index 5891d0f7a..09568a18a 100644
--- a/src/Composer/Repository/RepositoryFactory.php
+++ b/src/Composer/Repository/RepositoryFactory.php
@@ -145,7 +145,7 @@ class RepositoryFactory
      *
      * @return RepositoryInterface[]
      */
-    private static function createRepos(RepositoryManager $rm, array $repoConfigs)
+    private static function createRepos(RepositoryManager $rm, array $repoConfigs): array
     {
         $repos = array();
 
diff --git a/src/Composer/Repository/RepositorySet.php b/src/Composer/Repository/RepositorySet.php
index 18b988b46..beb237edc 100644
--- a/src/Composer/Repository/RepositorySet.php
+++ b/src/Composer/Repository/RepositorySet.php
@@ -336,7 +336,7 @@ class RepositorySet
      *
      * @return array<string, array<string, array{alias: string, alias_normalized: string}>>
      */
-    private static function getRootAliasesPerPackage(array $aliases)
+    private static function getRootAliasesPerPackage(array $aliases): array
     {
         $normalizedAliases = array();
 
diff --git a/src/Composer/Repository/Vcs/GitLabDriver.php b/src/Composer/Repository/Vcs/GitLabDriver.php
index 795f29e14..6d2e99e67 100644
--- a/src/Composer/Repository/Vcs/GitLabDriver.php
+++ b/src/Composer/Repository/Vcs/GitLabDriver.php
@@ -333,7 +333,7 @@ class GitLabDriver extends VcsDriver
      * @param  string $string
      * @return string
      */
-    private function urlEncodeAll($string)
+    private function urlEncodeAll($string): string
     {
         $encoded = '';
         for ($i = 0; isset($string[$i]); $i++) {
diff --git a/src/Composer/Repository/Vcs/PerforceDriver.php b/src/Composer/Repository/Vcs/PerforceDriver.php
index 75a61037c..b178257f2 100644
--- a/src/Composer/Repository/Vcs/PerforceDriver.php
+++ b/src/Composer/Repository/Vcs/PerforceDriver.php
@@ -55,7 +55,7 @@ class PerforceDriver extends VcsDriver
      *
      * @return void
      */
-    private function initPerforce($repoConfig)
+    private function initPerforce($repoConfig): void
     {
         if (!empty($this->perforce)) {
             return;
diff --git a/src/Composer/Repository/VcsRepository.php b/src/Composer/Repository/VcsRepository.php
index b5b85cd14..11d8df0e9 100644
--- a/src/Composer/Repository/VcsRepository.php
+++ b/src/Composer/Repository/VcsRepository.php
@@ -542,7 +542,7 @@ class VcsRepository extends ArrayRepository implements ConfigurableRepositoryInt
     /**
      * @return bool
      */
-    private function shouldRethrowTransportException(TransportException $e)
+    private function shouldRethrowTransportException(TransportException $e): bool
     {
         return in_array($e->getCode(), array(401, 403, 429), true) || $e->getCode() >= 500;
     }
diff --git a/src/Composer/Script/Event.php b/src/Composer/Script/Event.php
index 83aef267a..3ddf2eae0 100644
--- a/src/Composer/Script/Event.php
+++ b/src/Composer/Script/Event.php
@@ -121,7 +121,7 @@ class Event extends BaseEvent
      * @param  BaseEvent $event
      * @return BaseEvent
      */
-    private function calculateOriginatingEvent(BaseEvent $event)
+    private function calculateOriginatingEvent(BaseEvent $event): BaseEvent
     {
         if ($event instanceof Event && $event->getOriginatingEvent()) {
             return $this->calculateOriginatingEvent($event->getOriginatingEvent());
diff --git a/src/Composer/SelfUpdate/Versions.php b/src/Composer/SelfUpdate/Versions.php
index b6ba9c48f..2197e855a 100644
--- a/src/Composer/SelfUpdate/Versions.php
+++ b/src/Composer/SelfUpdate/Versions.php
@@ -95,7 +95,7 @@ class Versions
     /**
      * @return array<string, array<int, array{path: string, version: string, min-php: int}>>
      */
-    private function getVersionsData()
+    private function getVersionsData(): array
     {
         if (!$this->versionsData) {
             if ($this->config->get('disable-tls') === true) {
diff --git a/src/Composer/Util/Bitbucket.php b/src/Composer/Util/Bitbucket.php
index e0104a64b..abbb8cd45 100644
--- a/src/Composer/Util/Bitbucket.php
+++ b/src/Composer/Util/Bitbucket.php
@@ -92,7 +92,7 @@ class Bitbucket
     /**
      * @return bool
      */
-    private function requestAccessToken()
+    private function requestAccessToken(): bool
     {
         try {
             $response = $this->httpDownloader->get(self::OAUTH2_ACCESS_TOKEN_URL, array(
@@ -246,7 +246,7 @@ class Bitbucket
      * @param  string $originUrl
      * @return bool
      */
-    private function getTokenFromConfig($originUrl)
+    private function getTokenFromConfig($originUrl): bool
     {
         $authConfig = $this->config->get('bitbucket-oauth');
 
diff --git a/src/Composer/Util/Filesystem.php b/src/Composer/Util/Filesystem.php
index 3bd1c86fa..99aa803c9 100644
--- a/src/Composer/Util/Filesystem.php
+++ b/src/Composer/Util/Filesystem.php
@@ -177,7 +177,7 @@ class Filesystem
      *
      * @return bool|null Returns null, when no edge case was hit. Otherwise a bool whether removal was successful
      */
-    private function removeEdgeCases($directory, $fallbackToPhp = true)
+    private function removeEdgeCases($directory, $fallbackToPhp = true): ?bool
     {
         if ($this->isSymlinkedDirectory($directory)) {
             return $this->unlinkSymlinkedDirectory($directory);
@@ -711,7 +711,7 @@ class Filesystem
      *
      * @return bool
      */
-    private function unlinkImplementation($path)
+    private function unlinkImplementation($path): bool
     {
         if (Platform::isWindows() && is_dir($path) && is_link($path)) {
             return rmdir($path);
@@ -767,7 +767,7 @@ class Filesystem
      *
      * @return bool
      */
-    private function unlinkSymlinkedDirectory($directory)
+    private function unlinkSymlinkedDirectory($directory): bool
     {
         $resolved = $this->resolveSymlinkedDirectorySymlink($directory);
 
@@ -781,7 +781,7 @@ class Filesystem
      *
      * @return string resolved path to symbolic link or original pathname (unresolved)
      */
-    private function resolveSymlinkedDirectorySymlink($pathname)
+    private function resolveSymlinkedDirectorySymlink($pathname): string
     {
         if (!is_dir($pathname)) {
             return $pathname;
@@ -926,7 +926,7 @@ class Filesystem
      *
      * @return bool
      */
-    private function filesAreEqual($a, $b)
+    private function filesAreEqual($a, $b): bool
     {
         // Check if filesize is different
         if (filesize($a) !== filesize($b)) {
diff --git a/src/Composer/Util/Git.php b/src/Composer/Util/Git.php
index f2ea4dc24..4b92c2f77 100644
--- a/src/Composer/Util/Git.php
+++ b/src/Composer/Util/Git.php
@@ -349,7 +349,7 @@ class Git
      *
      * @return bool
      */
-    private function checkRefIsInMirror($dir, $ref)
+    private function checkRefIsInMirror($dir, $ref): bool
     {
         if (is_dir($dir) && 0 === $this->process->execute('git rev-parse --git-dir', $output, $dir) && trim($output) === '.') {
             $escapedRef = ProcessExecutor::escape($ref.'^{commit}');
@@ -368,7 +368,7 @@ class Git
      *
      * @return bool
      */
-    private function isAuthenticationFailure($url, &$match)
+    private function isAuthenticationFailure($url, &$match): bool
     {
         if (!Preg::isMatch('{^(https?://)([^/]+)(.*)$}i', $url, $match)) {
             return false;
@@ -441,7 +441,7 @@ class Git
      *
      * @return never
      */
-    private function throwException($message, $url)
+    private function throwException($message, $url): void
     {
         // git might delete a directory when it fails and php will not know
         clearstatcache();
@@ -476,7 +476,7 @@ class Git
      *
      * @return string
      */
-    private function maskCredentials($error, array $credentials)
+    private function maskCredentials($error, array $credentials): string
     {
         $maskedCredentials = array();
 
diff --git a/src/Composer/Util/GitLab.php b/src/Composer/Util/GitLab.php
index 4c1376ad4..86800dc33 100644
--- a/src/Composer/Util/GitLab.php
+++ b/src/Composer/Util/GitLab.php
@@ -169,7 +169,7 @@ class GitLab
      *
      * @see https://docs.gitlab.com/ee/api/oauth2.html#resource-owner-password-credentials-flow
      */
-    private function createToken($scheme, $originUrl)
+    private function createToken($scheme, $originUrl): array
     {
         $username = $this->io->ask('Username: ');
         $password = $this->io->askAndHideAnswer('Password: ');
diff --git a/src/Composer/Util/Hg.php b/src/Composer/Util/Hg.php
index 34dc00623..aa82bb323 100644
--- a/src/Composer/Util/Hg.php
+++ b/src/Composer/Util/Hg.php
@@ -89,7 +89,7 @@ class Hg
      *
      * @return never
      */
-    private function throwException($message, $url)
+    private function throwException($message, $url): void
     {
         if (null === self::getVersion($this->process)) {
             throw new \RuntimeException(Url::sanitize('Failed to clone ' . $url . ', hg was not found, check that it is installed and in your PATH env.' . "\n\n" . $this->process->getErrorOutput()));
diff --git a/src/Composer/Util/Http/CurlDownloader.php b/src/Composer/Util/Http/CurlDownloader.php
index 8ae18ee4c..eeff04e1f 100644
--- a/src/Composer/Util/Http/CurlDownloader.php
+++ b/src/Composer/Util/Http/CurlDownloader.php
@@ -133,7 +133,7 @@ class CurlDownloader
      *
      * @return int internal job id
      */
-    public function download($resolve, $reject, $origin, $url, $options, $copyTo = null)
+    public function download($resolve, $reject, $origin, $url, $options, $copyTo = null): int
     {
         $attributes = array();
         if (isset($options['retry-auth-failure'])) {
@@ -156,7 +156,7 @@ class CurlDownloader
      *
      * @return int internal job id
      */
-    private function initDownload($resolve, $reject, $origin, $url, $options, $copyTo = null, array $attributes = array())
+    private function initDownload($resolve, $reject, $origin, $url, $options, $copyTo = null, array $attributes = array()): int
     {
         // set defaults in a PHPStan-happy way (array_merge is not well supported)
         $attributes['retryAuthFailure'] = $attributes['retryAuthFailure'] ?? true;
@@ -489,7 +489,7 @@ class CurlDownloader
      * @param  Job    $job
      * @return string
      */
-    private function handleRedirect(array $job, Response $response)
+    private function handleRedirect(array $job, Response $response): string
     {
         if ($locationHeader = $response->getHeader('location')) {
             if (parse_url($locationHeader, PHP_URL_SCHEME)) {
@@ -524,7 +524,7 @@ class CurlDownloader
      * @param  Job                                        $job
      * @return array{retry: bool, storeAuth: string|bool}
      */
-    private function isAuthenticatedRetryNeeded(array $job, Response $response)
+    private function isAuthenticatedRetryNeeded(array $job, Response $response): array
     {
         if (in_array($response->getStatusCode(), array(401, 403)) && $job['attributes']['retryAuthFailure']) {
             $result = $this->authHelper->promptAuthIfNeeded($job['url'], $job['origin'], $response->getStatusCode(), $response->getStatusMessage(), $response->getHeaders());
@@ -596,7 +596,7 @@ class CurlDownloader
      * @param  string             $errorMessage
      * @return TransportException
      */
-    private function failResponse(array $job, Response $response, $errorMessage)
+    private function failResponse(array $job, Response $response, $errorMessage): TransportException
     {
         if (null !== $job['filename']) {
             @unlink($job['filename'].'~');
diff --git a/src/Composer/Util/Http/ProxyHelper.php b/src/Composer/Util/Http/ProxyHelper.php
index bfdfe2e4a..db19db62d 100644
--- a/src/Composer/Util/Http/ProxyHelper.php
+++ b/src/Composer/Util/Http/ProxyHelper.php
@@ -27,7 +27,7 @@ class ProxyHelper
      *
      * @throws \RuntimeException on malformed url
      */
-    public static function getProxyData()
+    public static function getProxyData(): array
     {
         $httpProxy = null;
         $httpsProxy = null;
@@ -64,7 +64,7 @@ class ProxyHelper
      *
      * @return array{http: array{proxy: string, header?: string}}
      */
-    public static function getContextOptions($proxyUrl)
+    public static function getContextOptions($proxyUrl): array
     {
         $proxy = parse_url($proxyUrl);
 
@@ -114,7 +114,7 @@ class ProxyHelper
      *
      * @return string|null The found value
      */
-    private static function getProxyEnv(array $names, &$name)
+    private static function getProxyEnv(array $names, &$name): ?string
     {
         foreach ($names as $name) {
             if (!empty($_SERVER[$name])) {
@@ -133,7 +133,7 @@ class ProxyHelper
      * @throws \RuntimeException on malformed url
      * @return string            The formatted proxy url
      */
-    private static function checkProxy($proxyUrl, $envName)
+    private static function checkProxy($proxyUrl, $envName): string
     {
         $error = sprintf('malformed %s url', $envName);
         $proxy = parse_url($proxyUrl);
@@ -161,7 +161,7 @@ class ProxyHelper
      *
      * @return string The formatted value
      */
-    private static function formatParsedUrl(array $proxy, $includeAuth)
+    private static function formatParsedUrl(array $proxy, $includeAuth): string
     {
         $proxyUrl = isset($proxy['scheme']) ? strtolower($proxy['scheme']) . '://' : '';
 
diff --git a/src/Composer/Util/Http/ProxyManager.php b/src/Composer/Util/Http/ProxyManager.php
index 43bcea749..5f11c8242 100644
--- a/src/Composer/Util/Http/ProxyManager.php
+++ b/src/Composer/Util/Http/ProxyManager.php
@@ -58,7 +58,7 @@ class ProxyManager
     /**
      * @return ProxyManager
      */
-    public static function getInstance()
+    public static function getInstance(): ProxyManager
     {
         if (!self::$instance) {
             self::$instance = new self();
@@ -83,7 +83,7 @@ class ProxyManager
      * @param  string       $requestUrl
      * @return RequestProxy
      */
-    public function getProxyForRequest($requestUrl)
+    public function getProxyForRequest($requestUrl): RequestProxy
     {
         if ($this->error) {
             throw new TransportException('Unable to use a proxy: '.$this->error);
@@ -113,7 +113,7 @@ class ProxyManager
      *
      * @return bool If false any error will be in $message
      */
-    public function isProxying()
+    public function isProxying(): bool
     {
         return $this->hasProxy;
     }
@@ -123,7 +123,7 @@ class ProxyManager
      *
      * @return string|null Safe proxy URL or an error message if setting up proxy failed or null if no proxy was configured
      */
-    public function getFormattedProxy()
+    public function getFormattedProxy(): ?string
     {
         return $this->hasProxy ? $this->info : $this->error;
     }
@@ -167,7 +167,7 @@ class ProxyManager
      *
      * @return non-empty-string
      */
-    private function setData($url, $scheme)
+    private function setData($url, $scheme): string
     {
         $safeProxy = Url::sanitize($url);
         $this->fullProxy[$scheme] = $url;
@@ -184,7 +184,7 @@ class ProxyManager
      * @param  string $requestUrl
      * @return bool
      */
-    private function noProxy($requestUrl)
+    private function noProxy($requestUrl): bool
     {
         return $this->noProxyHandler && $this->noProxyHandler->test($requestUrl);
     }
diff --git a/src/Composer/Util/Http/RequestProxy.php b/src/Composer/Util/Http/RequestProxy.php
index 5a832706f..e60c1a19c 100644
--- a/src/Composer/Util/Http/RequestProxy.php
+++ b/src/Composer/Util/Http/RequestProxy.php
@@ -47,7 +47,7 @@ class RequestProxy
      *
      * @return mixed[]
      */
-    public function getContextOptions()
+    public function getContextOptions(): array
     {
         return $this->contextOptions;
     }
@@ -58,7 +58,7 @@ class RequestProxy
      * @param  string|null $format Output format specifier
      * @return string      Safe proxy, no proxy or empty
      */
-    public function getFormattedUrl($format = '')
+    public function getFormattedUrl($format = ''): string
     {
         $result = '';
         if ($this->formattedUrl) {
@@ -74,7 +74,7 @@ class RequestProxy
      *
      * @return string Proxy url or empty
      */
-    public function getUrl()
+    public function getUrl(): string
     {
         return $this->url;
     }
@@ -84,7 +84,7 @@ class RequestProxy
      *
      * @return bool False if not secure or there is no proxy
      */
-    public function isSecure()
+    public function isSecure(): bool
     {
         return $this->isSecure;
     }
diff --git a/src/Composer/Util/HttpDownloader.php b/src/Composer/Util/HttpDownloader.php
index d1c8c1fbd..dcebffa4b 100644
--- a/src/Composer/Util/HttpDownloader.php
+++ b/src/Composer/Util/HttpDownloader.php
@@ -191,7 +191,7 @@ class HttpDownloader
      *
      * @return array{Job, PromiseInterface}
      */
-    private function addJob($request, $sync = false)
+    private function addJob($request, $sync = false): array
     {
         $request['options'] = array_replace_recursive($this->options, $request['options']);
 
@@ -291,7 +291,7 @@ class HttpDownloader
      * @param  int  $id
      * @return void
      */
-    private function startJob($id)
+    private function startJob($id): void
     {
         $job = &$this->jobs[$id];
         if ($job['status'] !== self::STATUS_QUEUED) {
@@ -355,7 +355,7 @@ class HttpDownloader
      *
      * @return void
      */
-    public function enableAsync()
+    public function enableAsync(): void
     {
         $this->allowAsync = true;
     }
@@ -366,7 +366,7 @@ class HttpDownloader
      * @param  int|null $index For internal use only, the job id
      * @return int      number of active (queued or started) jobs
      */
-    public function countActiveJobs($index = null)
+    public function countActiveJobs($index = null): int
     {
         if ($this->runningJobs < $this->maxJobs) {
             foreach ($this->jobs as $job) {
@@ -400,7 +400,7 @@ class HttpDownloader
      * @param  int $index Job id
      * @return Response
      */
-    private function getResponse($index)
+    private function getResponse($index): Response
     {
         if (!isset($this->jobs[$index])) {
             throw new \LogicException('Invalid request id');
@@ -428,7 +428,7 @@ class HttpDownloader
      * @param  array{warning?: string, info?: string, warning-versions?: string, info-versions?: string, warnings?: array<array{versions: string, message: string}>, infos?: array<array{versions: string, message: string}>} $data
      * @return void
      */
-    public static function outputWarnings(IOInterface $io, $url, $data)
+    public static function outputWarnings(IOInterface $io, $url, $data): void
     {
         // legacy warning/info keys
         foreach (array('warning', 'info') as $type) {
@@ -473,7 +473,7 @@ class HttpDownloader
      *
      * @return ?string[]
      */
-    public static function getExceptionHints(\Exception $e)
+    public static function getExceptionHints(\Exception $e): ?array
     {
         if (!$e instanceof TransportException) {
             return null;
@@ -507,7 +507,7 @@ class HttpDownloader
      * @param  Job  $job
      * @return bool
      */
-    private function canUseCurl(array $job)
+    private function canUseCurl(array $job): bool
     {
         if (!$this->curl) {
             return false;
@@ -528,7 +528,7 @@ class HttpDownloader
      * @internal
      * @return bool
      */
-    public static function isCurlEnabled()
+    public static function isCurlEnabled(): bool
     {
         return \extension_loaded('curl') && \function_exists('curl_multi_exec') && \function_exists('curl_multi_init');
     }
diff --git a/src/Composer/Util/NoProxyPattern.php b/src/Composer/Util/NoProxyPattern.php
index e8f14997b..20bddfe4a 100644
--- a/src/Composer/Util/NoProxyPattern.php
+++ b/src/Composer/Util/NoProxyPattern.php
@@ -186,7 +186,7 @@ class NoProxyPattern
      *
      * @return null|stdClass Null if the hostname is invalid
      */
-    private function getRule($index, $hostName)
+    private function getRule($index, $hostName): ?stdClass
     {
         if (array_key_exists($index, $this->rules)) {
             return $this->rules[$index];
@@ -213,7 +213,7 @@ class NoProxyPattern
      *
      * @return bool False if the host contains invalid data
      */
-    private function ipCheckData($host, &$ipdata, $allowPrefix = false)
+    private function ipCheckData($host, &$ipdata, $allowPrefix = false): bool
     {
         $ipdata = null;
         $netmask = null;
@@ -262,7 +262,7 @@ class NoProxyPattern
      *
      * @return mixed[] in_addr, size
      */
-    private function ipGetAddr($host)
+    private function ipGetAddr($host): array
     {
         $ip = inet_pton($host);
         $size = strlen($ip);
@@ -279,7 +279,7 @@ class NoProxyPattern
      *
      * @return string
      */
-    private function ipGetMask($prefix, $size)
+    private function ipGetMask($prefix, $size): string
     {
         $mask = '';
 
@@ -305,7 +305,7 @@ class NoProxyPattern
      *
      * @return string[] network in_addr, binary mask
      */
-    private function ipGetNetwork($rangeIp, $size, $prefix)
+    private function ipGetNetwork($rangeIp, $size, $prefix): array
     {
         $netmask = $this->ipGetMask($prefix, $size);
 
@@ -335,7 +335,7 @@ class NoProxyPattern
      *
      * @return string Mapped or existing in_addr
      */
-    private function ipMapTo6($binary, $size)
+    private function ipMapTo6($binary, $size): string
     {
         if ($size === 4) {
             $prefix = str_repeat(chr(0), 10) . str_repeat(chr(255), 2);
@@ -354,7 +354,7 @@ class NoProxyPattern
      *
      * @return stdClass
      */
-    private function makeData($host, $port, $ipdata)
+    private function makeData($host, $port, $ipdata): stdClass
     {
         return (object) array(
             'host' => $host,
@@ -373,7 +373,7 @@ class NoProxyPattern
      *
      * @return stdClass
      */
-    private function makeIpData($ip, $size, $netmask)
+    private function makeIpData($ip, $size, $netmask): stdClass
     {
         return (object) array(
             'ip' => $ip,
@@ -389,7 +389,7 @@ class NoProxyPattern
      *
      * @return mixed[] host, port, if there was error
      */
-    private function splitHostPort($hostName)
+    private function splitHostPort($hostName): array
     {
         // host, port, err
         $error = array('', '', true);
@@ -439,7 +439,7 @@ class NoProxyPattern
      *
      * @return bool
      */
-    private function validateInt($int, $min, $max)
+    private function validateInt($int, $min, $max): bool
     {
         $options = array(
             'options' => array(
diff --git a/src/Composer/Util/Platform.php b/src/Composer/Util/Platform.php
index b57b7dda8..39d5ac2cf 100644
--- a/src/Composer/Util/Platform.php
+++ b/src/Composer/Util/Platform.php
@@ -216,7 +216,7 @@ class Platform
      *
      * @return bool
      */
-    private static function isVirtualBoxGuest()
+    private static function isVirtualBoxGuest(): bool
     {
         if (null === self::$isVirtualBoxGuest) {
             self::$isVirtualBoxGuest = false;
diff --git a/src/Composer/Util/ProcessExecutor.php b/src/Composer/Util/ProcessExecutor.php
index cb9cdd225..809de9810 100644
--- a/src/Composer/Util/ProcessExecutor.php
+++ b/src/Composer/Util/ProcessExecutor.php
@@ -100,7 +100,7 @@ class ProcessExecutor
      * @param  mixed   $output
      * @return int
      */
-    private function doExecute($command, $cwd, $tty, &$output = null)
+    private function doExecute($command, $cwd, $tty, &$output = null): int
     {
         $this->outputCommandRun($command, $cwd, false);
 
@@ -210,7 +210,7 @@ class ProcessExecutor
      * @param  int  $id
      * @return void
      */
-    private function startJob($id)
+    private function startJob($id): void
     {
         $job = &$this->jobs[$id];
         if ($job['status'] !== self::STATUS_QUEUED) {
@@ -269,7 +269,7 @@ class ProcessExecutor
      *
      * @return void
      */
-    public function enableAsync()
+    public function enableAsync(): void
     {
         $this->allowAsync = true;
     }
@@ -280,7 +280,7 @@ class ProcessExecutor
      * @param  ?int $index job id
      * @return int         number of active (queued or started) jobs
      */
-    public function countActiveJobs($index = null)
+    public function countActiveJobs($index = null): int
     {
         // tick
         foreach ($this->jobs as $job) {
@@ -437,7 +437,7 @@ class ProcessExecutor
      *
      * @return string
      */
-    private static function escapeArgument($argument)
+    private static function escapeArgument($argument): string
     {
         if ('' === ($argument = (string) $argument)) {
             return escapeshellarg($argument);
diff --git a/src/Composer/Util/RemoteFilesystem.php b/src/Composer/Util/RemoteFilesystem.php
index 28982a8e9..464198f57 100644
--- a/src/Composer/Util/RemoteFilesystem.php
+++ b/src/Composer/Util/RemoteFilesystem.php
@@ -106,7 +106,7 @@ class RemoteFilesystem
      *
      * @return bool true
      */
-    public function copy($originUrl, $fileUrl, $fileName, $progress = true, $options = array())
+    public function copy($originUrl, $fileUrl, $fileName, $progress = true, $options = array()): bool
     {
         return $this->get($originUrl, $fileUrl, $options, $fileName, $progress);
     }
@@ -131,7 +131,7 @@ class RemoteFilesystem
      *
      * @return mixed[] Options
      */
-    public function getOptions()
+    public function getOptions(): array
     {
         return $this->options;
     }
@@ -142,7 +142,7 @@ class RemoteFilesystem
      * @param  mixed[] $options
      * @return void
      */
-    public function setOptions(array $options)
+    public function setOptions(array $options): void
     {
         $this->options = array_replace_recursive($this->options, $options);
     }
@@ -152,7 +152,7 @@ class RemoteFilesystem
      *
      * @return bool
      */
-    public function isTlsDisabled()
+    public function isTlsDisabled(): bool
     {
         return $this->disableTls === true;
     }
@@ -162,7 +162,7 @@ class RemoteFilesystem
      *
      * @return string[]
      */
-    public function getLastHeaders()
+    public function getLastHeaders(): array
     {
         return $this->lastHeaders;
     }
@@ -171,7 +171,7 @@ class RemoteFilesystem
      * @param  string[] $headers array of returned headers like from getLastHeaders()
      * @return int|null
      */
-    public static function findStatusCode(array $headers)
+    public static function findStatusCode(array $headers): ?int
     {
         $value = null;
         foreach ($headers as $header) {
@@ -189,7 +189,7 @@ class RemoteFilesystem
      * @param  string[]    $headers array of returned headers like from getLastHeaders()
      * @return string|null
      */
-    public function findStatusMessage(array $headers)
+    public function findStatusMessage(array $headers): ?string
     {
         $value = null;
         foreach ($headers as $header) {
@@ -554,7 +554,7 @@ class RemoteFilesystem
      *
      * @throws TransportException
      */
-    protected function callbackGet($notificationCode, $severity, $message, $messageCode, $bytesTransferred, $bytesMax)
+    protected function callbackGet($notificationCode, $severity, $message, $messageCode, $bytesTransferred, $bytesMax): void
     {
         switch ($notificationCode) {
             case STREAM_NOTIFY_FAILURE:
@@ -592,7 +592,7 @@ class RemoteFilesystem
      *
      * @return void
      */
-    protected function promptAuthAndRetry($httpStatus, $reason = null, $headers = array())
+    protected function promptAuthAndRetry($httpStatus, $reason = null, $headers = array()): void
     {
         $result = $this->authHelper->promptAuthIfNeeded($this->fileUrl, $this->originUrl, $httpStatus, $reason, $headers);
 
@@ -610,7 +610,7 @@ class RemoteFilesystem
      *
      * @return mixed[]
      */
-    protected function getOptionsForUrl($originUrl, $additionalOptions)
+    protected function getOptionsForUrl($originUrl, $additionalOptions): array
     {
         $tlsOptions = array();
         $headers = array();
@@ -698,7 +698,7 @@ class RemoteFilesystem
      *
      * @return string|null
      */
-    private function decodeResult($result, $http_response_header)
+    private function decodeResult($result, $http_response_header): ?string
     {
         // decode gzip
         if ($result && extension_loaded('zlib')) {
@@ -722,7 +722,7 @@ class RemoteFilesystem
      *
      * @return string|null
      */
-    private function normalizeResult($result)
+    private function normalizeResult($result): ?string
     {
         if ($result === false) {
             return null;
diff --git a/src/Composer/Util/StreamContextFactory.php b/src/Composer/Util/StreamContextFactory.php
index 852d72946..f0d8bbe93 100644
--- a/src/Composer/Util/StreamContextFactory.php
+++ b/src/Composer/Util/StreamContextFactory.php
@@ -63,7 +63,7 @@ final class StreamContextFactory
      * @phpstan-return array{http: array{header: string[], proxy?: string, request_fulluri: bool}, ssl?: mixed[]}
      * @return array formatted as a stream context array
      */
-    public static function initOptions($url, array $options, $forCurl = false)
+    public static function initOptions($url, array $options, $forCurl = false): array
     {
         // Make sure the headers are in an array form
         if (!isset($options['http']['header'])) {
@@ -134,7 +134,7 @@ final class StreamContextFactory
      *
      * @return mixed[]
      */
-    public static function getTlsDefaults(array $options, LoggerInterface $logger = null)
+    public static function getTlsDefaults(array $options, LoggerInterface $logger = null): array
     {
         $ciphers = implode(':', array(
             'ECDHE-RSA-AES128-GCM-SHA256',
@@ -240,7 +240,7 @@ final class StreamContextFactory
      * @param  string|string[] $header
      * @return string[]
      */
-    private static function fixHttpHeaderField($header)
+    private static function fixHttpHeaderField($header): array
     {
         if (!is_array($header)) {
             $header = explode("\r\n", $header);
diff --git a/src/Composer/Util/Svn.php b/src/Composer/Util/Svn.php
index c04f075df..8b1078a12 100644
--- a/src/Composer/Util/Svn.php
+++ b/src/Composer/Util/Svn.php
@@ -140,7 +140,7 @@ class Svn
      *
      * @return ?string
      */
-    private function executeWithAuthRetry($svnCommand, $cwd, $url, $path, $verbose)
+    private function executeWithAuthRetry($svnCommand, $cwd, $url, $path, $verbose): ?string
     {
         // Regenerate the command at each try, to use the newly user-provided credentials
         $command = $this->getCommand($svnCommand, $url, $path);
@@ -337,7 +337,7 @@ class Svn
      *
      * @return bool
      */
-    private function createAuthFromConfig()
+    private function createAuthFromConfig(): bool
     {
         if (!$this->config->has('http-basic')) {
             return $this->hasAuth = false;
@@ -363,7 +363,7 @@ class Svn
      *
      * @return bool
      */
-    private function createAuthFromUrl()
+    private function createAuthFromUrl(): bool
     {
         $uri = parse_url($this->url);
         if (empty($uri['user'])) {
diff --git a/src/Composer/Util/Tar.php b/src/Composer/Util/Tar.php
index cae69c906..250a01c2c 100644
--- a/src/Composer/Util/Tar.php
+++ b/src/Composer/Util/Tar.php
@@ -40,7 +40,7 @@ class Tar
      *
      * @return string
      */
-    private static function extractComposerJsonFromFolder(\PharData $phar)
+    private static function extractComposerJsonFromFolder(\PharData $phar): string
     {
         if (isset($phar['composer.json'])) {
             return $phar['composer.json']->getContent();
diff --git a/src/Composer/Util/TlsHelper.php b/src/Composer/Util/TlsHelper.php
index 3fe329d4a..bf3aa1ea3 100644
--- a/src/Composer/Util/TlsHelper.php
+++ b/src/Composer/Util/TlsHelper.php
@@ -30,7 +30,7 @@ final class TlsHelper
      *
      * @return bool
      */
-    public static function checkCertificateHost($certificate, $hostname, &$cn = null)
+    public static function checkCertificateHost($certificate, $hostname, &$cn = null): bool
     {
         $names = self::getCertificateNames($certificate);
 
@@ -61,7 +61,7 @@ final class TlsHelper
      *
      * @return array{cn: string, san: string[]}|null
      */
-    public static function getCertificateNames($certificate)
+    public static function getCertificateNames($certificate): ?array
     {
         if (is_array($certificate)) {
             $info = $certificate;
@@ -136,7 +136,7 @@ final class TlsHelper
      * @param string $certificate
      * @return string
      */
-    public static function getCertificateFingerprint($certificate)
+    public static function getCertificateFingerprint($certificate): string
     {
         $pubkey = openssl_get_publickey($certificate);
         if ($pubkey === false) {
@@ -161,7 +161,7 @@ final class TlsHelper
      *
      * @return bool
      */
-    public static function isOpensslParseSafe()
+    public static function isOpensslParseSafe(): bool
     {
         return CaBundle::isOpensslParseSafe();
     }
@@ -173,7 +173,7 @@ final class TlsHelper
      *
      * @return callable|null
      */
-    private static function certNameMatcher($certName)
+    private static function certNameMatcher($certName): ?callable
     {
         $wildcards = substr_count($certName, '*');
 
diff --git a/src/Composer/Util/Zip.php b/src/Composer/Util/Zip.php
index 7b1f6285c..f49ccdc25 100644
--- a/src/Composer/Util/Zip.php
+++ b/src/Composer/Util/Zip.php
@@ -65,7 +65,7 @@ class Zip
      *
      * @return int
      */
-    private static function locateFile(\ZipArchive $zip, $filename)
+    private static function locateFile(\ZipArchive $zip, $filename): int
     {
         // return root composer.json if it is there and is a file
         if (false !== ($index = $zip->locateName($filename)) && $zip->getFromIndex($index) !== false) {
diff --git a/tests/Composer/Test/AllFunctionalTest.php b/tests/Composer/Test/AllFunctionalTest.php
index 896079f89..12bd95e3d 100644
--- a/tests/Composer/Test/AllFunctionalTest.php
+++ b/tests/Composer/Test/AllFunctionalTest.php
@@ -179,7 +179,7 @@ class AllFunctionalTest extends TestCase
     /**
      * @return array<string, array<string>>
      */
-    public function getTestFiles()
+    public function getTestFiles(): array
     {
         $tests = array();
         foreach (Finder::create()->in(__DIR__.'/Fixtures/functional')->name('*.test')->files() as $file) {
@@ -193,7 +193,7 @@ class AllFunctionalTest extends TestCase
      * @param string $file
      * @return array{RUN: string, EXPECT?: string, EXPECT-EXIT-CODE?: int, EXPECT-REGEX?: string, EXPECT-REGEXES?: string, TEST?: string}
      */
-    private function parseTestFile($file)
+    private function parseTestFile($file): array
     {
         $tokens = Preg::split('#(?:^|\n*)--([A-Z-]+)--\n#', file_get_contents($file), -1, PREG_SPLIT_DELIM_CAPTURE);
         $data = array();
@@ -255,7 +255,7 @@ class AllFunctionalTest extends TestCase
      * @param string $output
      * @return string
      */
-    private function cleanOutput($output)
+    private function cleanOutput($output): string
     {
         $processed = '';
 
diff --git a/tests/Composer/Test/Autoload/AutoloadGeneratorTest.php b/tests/Composer/Test/Autoload/AutoloadGeneratorTest.php
index ca5af8273..48ab276c1 100644
--- a/tests/Composer/Test/Autoload/AutoloadGeneratorTest.php
+++ b/tests/Composer/Test/Autoload/AutoloadGeneratorTest.php
@@ -1741,7 +1741,7 @@ EOF;
     /**
      * @return array<string, mixed[]>
      */
-    public function platformCheckProvider()
+    public function platformCheckProvider(): array
     {
         $versionParser = new VersionParser();
 
diff --git a/tests/Composer/Test/Autoload/ClassLoaderTest.php b/tests/Composer/Test/Autoload/ClassLoaderTest.php
index 7b1f7ab7b..d11c522a9 100644
--- a/tests/Composer/Test/Autoload/ClassLoaderTest.php
+++ b/tests/Composer/Test/Autoload/ClassLoaderTest.php
@@ -42,7 +42,7 @@ class ClassLoaderTest extends TestCase
      *
      * @return array<array<string>> Array of parameter sets to test with.
      */
-    public function getLoadClassTests()
+    public function getLoadClassTests(): array
     {
         return array(
             array('Namespaced\\Foo'),
diff --git a/tests/Composer/Test/Autoload/ClassMapGeneratorTest.php b/tests/Composer/Test/Autoload/ClassMapGeneratorTest.php
index 8f4fd1395..5315c4b33 100644
--- a/tests/Composer/Test/Autoload/ClassMapGeneratorTest.php
+++ b/tests/Composer/Test/Autoload/ClassMapGeneratorTest.php
@@ -38,7 +38,7 @@ class ClassMapGeneratorTest extends TestCase
     /**
      * @return array<array<string|array<string>>>
      */
-    public function getTestCreateMapTests()
+    public function getTestCreateMapTests(): array
     {
         $classmap = array(
             'Foo\\Bar\\A' => realpath(__DIR__) . '/Fixtures/classmap/sameNsMultipleClasses.php',
diff --git a/tests/Composer/Test/Command/RunScriptCommandTest.php b/tests/Composer/Test/Command/RunScriptCommandTest.php
index fcae19051..97d5b2ad6 100644
--- a/tests/Composer/Test/Command/RunScriptCommandTest.php
+++ b/tests/Composer/Test/Command/RunScriptCommandTest.php
@@ -89,7 +89,7 @@ class RunScriptCommandTest extends TestCase
     }
 
     /** @return bool[][] **/
-    public function getDevOptions()
+    public function getDevOptions(): array
     {
         return array(
             array(true, true),
@@ -100,7 +100,7 @@ class RunScriptCommandTest extends TestCase
     }
 
     /** @return Composer **/
-    private function createComposerInstance()
+    private function createComposerInstance(): Composer
     {
         $composer = new Composer;
         $config = new Config;
diff --git a/tests/Composer/Test/Config/JsonConfigSourceTest.php b/tests/Composer/Test/Config/JsonConfigSourceTest.php
index bcc193662..f23d5d958 100644
--- a/tests/Composer/Test/Config/JsonConfigSourceTest.php
+++ b/tests/Composer/Test/Config/JsonConfigSourceTest.php
@@ -29,7 +29,7 @@ class JsonConfigSourceTest extends TestCase
      *
      * @return string
      */
-    protected function fixturePath($name)
+    protected function fixturePath($name): string
     {
         return __DIR__.'/Fixtures/'.$name;
     }
@@ -160,7 +160,7 @@ class JsonConfigSourceTest extends TestCase
      *
      * @phpstan-return array{string, string, string, string, string}
      */
-    protected function addLinkDataArguments($type, $name, $value, $fixtureBasename, $before)
+    protected function addLinkDataArguments($type, $name, $value, $fixtureBasename, $before): array
     {
         return array(
             $before,
@@ -217,7 +217,7 @@ class JsonConfigSourceTest extends TestCase
      *
      * @phpstan-return array{string, string, string, string}
      */
-    protected function removeLinkDataArguments($type, $name, $fixtureBasename, $after = null)
+    protected function removeLinkDataArguments($type, $name, $fixtureBasename, $after = null): array
     {
         return array(
             $this->fixturePath('removeLink/'.$fixtureBasename.'.json'),
diff --git a/tests/Composer/Test/ConfigTest.php b/tests/Composer/Test/ConfigTest.php
index 0aad6141c..ded833967 100644
--- a/tests/Composer/Test/ConfigTest.php
+++ b/tests/Composer/Test/ConfigTest.php
@@ -269,7 +269,7 @@ class ConfigTest extends TestCase
     /**
      * @return string[][] List of test URLs that should pass strict security
      */
-    public function allowedUrlProvider()
+    public function allowedUrlProvider(): array
     {
         $urls = array(
             'https://packagist.org',
@@ -290,7 +290,7 @@ class ConfigTest extends TestCase
     /**
      * @return string[][] List of test URLs that should not pass strict security
      */
-    public function prohibitedUrlProvider()
+    public function prohibitedUrlProvider(): array
     {
         $urls = array(
             'http://packagist.org',
diff --git a/tests/Composer/Test/DependencyResolver/PoolBuilderTest.php b/tests/Composer/Test/DependencyResolver/PoolBuilderTest.php
index 3939fcdd2..60ee193c3 100644
--- a/tests/Composer/Test/DependencyResolver/PoolBuilderTest.php
+++ b/tests/Composer/Test/DependencyResolver/PoolBuilderTest.php
@@ -149,7 +149,7 @@ class PoolBuilderTest extends TestCase
      * @param array<int, BasePackage> $packageIds
      * @return string[]
      */
-    private function getPackageResultSet(Pool $pool, $packageIds)
+    private function getPackageResultSet(Pool $pool, $packageIds): array
     {
         $result = array();
         for ($i = 1, $count = count($pool); $i <= $count; $i++) {
@@ -184,7 +184,7 @@ class PoolBuilderTest extends TestCase
     /**
      * @return array<string, array<string>>
      */
-    public function getIntegrationTests()
+    public function getIntegrationTests(): array
     {
         $fixturesDir = realpath(__DIR__.'/Fixtures/poolbuilder/');
         $tests = array();
@@ -223,7 +223,7 @@ class PoolBuilderTest extends TestCase
      * @param string $fixturesDir
      * @return array<string, string>
      */
-    protected function readTestFile(\SplFileInfo $file, $fixturesDir)
+    protected function readTestFile(\SplFileInfo $file, $fixturesDir): array
     {
         $tokens = Preg::split('#(?:^|\n*)--([A-Z-]+)--\n#', file_get_contents($file->getRealPath()), -1, PREG_SPLIT_DELIM_CAPTURE);
 
diff --git a/tests/Composer/Test/DependencyResolver/PoolOptimizerTest.php b/tests/Composer/Test/DependencyResolver/PoolOptimizerTest.php
index 6b3e863bb..3455e325b 100644
--- a/tests/Composer/Test/DependencyResolver/PoolOptimizerTest.php
+++ b/tests/Composer/Test/DependencyResolver/PoolOptimizerTest.php
@@ -100,7 +100,7 @@ class PoolOptimizerTest extends TestCase
      * @param  string $fixturesDir
      * @return mixed[]
      */
-    protected function readTestFile(\SplFileInfo $file, $fixturesDir)
+    protected function readTestFile(\SplFileInfo $file, $fixturesDir): array
     {
         $tokens = Preg::split('#(?:^|\n*)--([A-Z-]+)--\n#', file_get_contents($file->getRealPath()), -1, PREG_SPLIT_DELIM_CAPTURE);
 
@@ -154,7 +154,7 @@ class PoolOptimizerTest extends TestCase
      * @param BasePackage[] $packages
      * @return string[]
      */
-    private function reducePackagesInfoForComparison(array $packages)
+    private function reducePackagesInfoForComparison(array $packages): array
     {
         $packagesInfo = array();
 
@@ -171,7 +171,7 @@ class PoolOptimizerTest extends TestCase
      * @param mixed[][] $packagesData
      * @return BasePackage[]
      */
-    private function loadPackages(array $packagesData)
+    private function loadPackages(array $packagesData): array
     {
         $packages = array();
 
@@ -189,7 +189,7 @@ class PoolOptimizerTest extends TestCase
      * @param mixed[] $packageData
      * @return BasePackage
      */
-    private function loadPackage(array $packageData)
+    private function loadPackage(array $packageData): BasePackage
     {
         $loader = new ArrayLoader();
 
diff --git a/tests/Composer/Test/DependencyResolver/PoolTest.php b/tests/Composer/Test/DependencyResolver/PoolTest.php
index 1e7fd5724..c4c5185ae 100644
--- a/tests/Composer/Test/DependencyResolver/PoolTest.php
+++ b/tests/Composer/Test/DependencyResolver/PoolTest.php
@@ -61,7 +61,7 @@ class PoolTest extends TestCase
      * @param array<\Composer\Package\BasePackage>|null $packages
      * @return \Composer\DependencyResolver\Pool
      */
-    protected function createPool($packages = array())
+    protected function createPool($packages = array()): \Composer\DependencyResolver\Pool
     {
         return new Pool($packages);
     }
diff --git a/tests/Composer/Test/Downloader/FileDownloaderTest.php b/tests/Composer/Test/Downloader/FileDownloaderTest.php
index 691a38a72..73c92b183 100644
--- a/tests/Composer/Test/Downloader/FileDownloaderTest.php
+++ b/tests/Composer/Test/Downloader/FileDownloaderTest.php
@@ -43,7 +43,7 @@ class FileDownloaderTest extends TestCase
      * @param \Composer\Util\Filesystem $filesystem
      * @return \Composer\Downloader\FileDownloader
      */
-    protected function getDownloader($io = null, $config = null, $eventDispatcher = null, $cache = null, $httpDownloader = null, $filesystem = null)
+    protected function getDownloader($io = null, $config = null, $eventDispatcher = null, $cache = null, $httpDownloader = null, $filesystem = null): \Composer\Downloader\FileDownloader
     {
         $io = $io ?: $this->getMockBuilder('Composer\IO\IOInterface')->getMock();
         $config = $config ?: $this->config;
diff --git a/tests/Composer/Test/Downloader/FossilDownloaderTest.php b/tests/Composer/Test/Downloader/FossilDownloaderTest.php
index a59ee038c..2ba0e33f0 100644
--- a/tests/Composer/Test/Downloader/FossilDownloaderTest.php
+++ b/tests/Composer/Test/Downloader/FossilDownloaderTest.php
@@ -42,7 +42,7 @@ class FossilDownloaderTest extends TestCase
      * @param \Composer\Util\Filesystem $filesystem
      * @return FossilDownloader
      */
-    protected function getDownloaderMock($io = null, $config = null, $executor = null, $filesystem = null)
+    protected function getDownloaderMock($io = null, $config = null, $executor = null, $filesystem = null): FossilDownloader
     {
         $io = $io ?: $this->getMockBuilder('Composer\IO\IOInterface')->getMock();
         $config = $config ?: $this->getMockBuilder('Composer\Config')->getMock();
diff --git a/tests/Composer/Test/Downloader/GitDownloaderTest.php b/tests/Composer/Test/Downloader/GitDownloaderTest.php
index 57d55da1b..01a1397b8 100644
--- a/tests/Composer/Test/Downloader/GitDownloaderTest.php
+++ b/tests/Composer/Test/Downloader/GitDownloaderTest.php
@@ -62,7 +62,7 @@ class GitDownloaderTest extends TestCase
      * @param ?\Composer\Config $config
      * @return \Composer\Config
      */
-    protected function setupConfig($config = null)
+    protected function setupConfig($config = null): \Composer\Config
     {
         if (!$config) {
             $config = new Config();
@@ -82,7 +82,7 @@ class GitDownloaderTest extends TestCase
      * @param \Composer\Util\Filesystem $filesystem
      * @return GitDownloader
      */
-    protected function getDownloaderMock($io = null, $config = null, $executor = null, $filesystem = null)
+    protected function getDownloaderMock($io = null, $config = null, $executor = null, $filesystem = null): GitDownloader
     {
         $io = $io ?: $this->getMockBuilder('Composer\IO\IOInterface')->getMock();
         $executor = $executor ?: $this->getProcessExecutorMock();
@@ -647,7 +647,7 @@ composer https://github.com/old/url (push)
      * @param string $cmd
      * @return string
      */
-    private function winCompat($cmd)
+    private function winCompat($cmd): string
     {
         if (Platform::isWindows()) {
             $cmd = str_replace('cd ', 'cd /D ', $cmd);
diff --git a/tests/Composer/Test/Downloader/HgDownloaderTest.php b/tests/Composer/Test/Downloader/HgDownloaderTest.php
index f3a839303..81a039a24 100644
--- a/tests/Composer/Test/Downloader/HgDownloaderTest.php
+++ b/tests/Composer/Test/Downloader/HgDownloaderTest.php
@@ -42,7 +42,7 @@ class HgDownloaderTest extends TestCase
      * @param \Composer\Util\Filesystem $filesystem
      * @return HgDownloader
      */
-    protected function getDownloaderMock($io = null, $config = null, $executor = null, $filesystem = null)
+    protected function getDownloaderMock($io = null, $config = null, $executor = null, $filesystem = null): HgDownloader
     {
         $io = $io ?: $this->getMockBuilder('Composer\IO\IOInterface')->getMock();
         $config = $config ?: $this->getMockBuilder('Composer\Config')->getMock();
diff --git a/tests/Composer/Test/Downloader/PerforceDownloaderTest.php b/tests/Composer/Test/Downloader/PerforceDownloaderTest.php
index c6b99b5a6..16bd4d128 100644
--- a/tests/Composer/Test/Downloader/PerforceDownloaderTest.php
+++ b/tests/Composer/Test/Downloader/PerforceDownloaderTest.php
@@ -56,7 +56,7 @@ class PerforceDownloaderTest extends TestCase
     /**
      * @return \Composer\Config
      */
-    protected function getConfig()
+    protected function getConfig(): \Composer\Config
     {
         $config = new Config();
         $settings = array('config' => array('home' => $this->testPath));
@@ -87,7 +87,7 @@ class PerforceDownloaderTest extends TestCase
     /**
      * @return string[]
      */
-    protected function getRepoConfig()
+    protected function getRepoConfig(): array
     {
         return array('url' => 'TEST_URL', 'p4user' => 'TEST_USER');
     }
diff --git a/tests/Composer/Test/Downloader/ZipDownloaderTest.php b/tests/Composer/Test/Downloader/ZipDownloaderTest.php
index 92b9ab5e2..49e9dcda4 100644
--- a/tests/Composer/Test/Downloader/ZipDownloaderTest.php
+++ b/tests/Composer/Test/Downloader/ZipDownloaderTest.php
@@ -12,6 +12,7 @@
 
 namespace Composer\Test\Downloader;
 
+use React\Promise\PromiseInterface;
 use Composer\Downloader\ZipDownloader;
 use Composer\Package\PackageInterface;
 use Composer\Test\TestCase;
@@ -334,17 +335,17 @@ class ZipDownloaderTest extends TestCase
 
 class MockedZipDownloader extends ZipDownloader
 {
-    public function download(PackageInterface $package, $path, PackageInterface $prevPackage = null, $output = true)
+    public function download(PackageInterface $package, $path, PackageInterface $prevPackage = null, $output = true): ?PromiseInterface
     {
         return \React\Promise\resolve();
     }
 
-    public function install(PackageInterface $package, $path, $output = true)
+    public function install(PackageInterface $package, $path, $output = true): PromiseInterface
     {
         return \React\Promise\resolve();
     }
 
-    public function extract(PackageInterface $package, $file, $path)
+    public function extract(PackageInterface $package, $file, $path): ?PromiseInterface
     {
         return parent::extract($package, $file, $path);
     }
diff --git a/tests/Composer/Test/EventDispatcher/EventDispatcherTest.php b/tests/Composer/Test/EventDispatcher/EventDispatcherTest.php
index 7a37a92c2..e6b960acf 100644
--- a/tests/Composer/Test/EventDispatcher/EventDispatcherTest.php
+++ b/tests/Composer/Test/EventDispatcher/EventDispatcherTest.php
@@ -603,7 +603,7 @@ class EventDispatcherTest extends TestCase
     /**
      * @return true
      */
-    public static function someMethod()
+    public static function someMethod(): bool
     {
         return true;
     }
@@ -611,7 +611,7 @@ class EventDispatcherTest extends TestCase
     /**
      * @return true
      */
-    public static function someMethod2()
+    public static function someMethod2(): bool
     {
         return true;
     }
@@ -619,7 +619,7 @@ class EventDispatcherTest extends TestCase
     /**
      * @return Composer
      */
-    private function createComposerInstance()
+    private function createComposerInstance(): Composer
     {
         $composer = new Composer;
         $config = new Config();
diff --git a/tests/Composer/Test/Filter/PlatformRequirementFilter/IgnoreAllPlatformRequirementFilterTest.php b/tests/Composer/Test/Filter/PlatformRequirementFilter/IgnoreAllPlatformRequirementFilterTest.php
index 767b50747..d7dcd9b33 100644
--- a/tests/Composer/Test/Filter/PlatformRequirementFilter/IgnoreAllPlatformRequirementFilterTest.php
+++ b/tests/Composer/Test/Filter/PlatformRequirementFilter/IgnoreAllPlatformRequirementFilterTest.php
@@ -33,7 +33,7 @@ final class IgnoreAllPlatformRequirementFilterTest extends TestCase
     /**
      * @return array<string, mixed[]>
      */
-    public function dataIsIgnored()
+    public function dataIsIgnored(): array
     {
         return array(
             'php is ignored' => array('php', true),
diff --git a/tests/Composer/Test/Filter/PlatformRequirementFilter/IgnoreListPlatformRequirementFilterTest.php b/tests/Composer/Test/Filter/PlatformRequirementFilter/IgnoreListPlatformRequirementFilterTest.php
index 685e97810..47af67fd2 100644
--- a/tests/Composer/Test/Filter/PlatformRequirementFilter/IgnoreListPlatformRequirementFilterTest.php
+++ b/tests/Composer/Test/Filter/PlatformRequirementFilter/IgnoreListPlatformRequirementFilterTest.php
@@ -34,7 +34,7 @@ final class IgnoreListPlatformRequirementFilterTest extends TestCase
     /**
      * @return array<string, mixed[]>
      */
-    public function dataIsIgnored()
+    public function dataIsIgnored(): array
     {
         return array(
             'ext-json is ignored if listed' => array(array('ext-json', 'monolog/monolog'), 'ext-json', true),
diff --git a/tests/Composer/Test/Filter/PlatformRequirementFilter/IgnoreNothingPlatformRequirementFilterTest.php b/tests/Composer/Test/Filter/PlatformRequirementFilter/IgnoreNothingPlatformRequirementFilterTest.php
index 02b7da85c..8b5b1f897 100644
--- a/tests/Composer/Test/Filter/PlatformRequirementFilter/IgnoreNothingPlatformRequirementFilterTest.php
+++ b/tests/Composer/Test/Filter/PlatformRequirementFilter/IgnoreNothingPlatformRequirementFilterTest.php
@@ -32,7 +32,7 @@ final class IgnoreNothingPlatformRequirementFilterTest extends TestCase
     /**
      * @return array<string, mixed[]>
      */
-    public function dataIsIgnored()
+    public function dataIsIgnored(): array
     {
         return array(
             'php is not ignored' => array('php'),
diff --git a/tests/Composer/Test/Filter/PlatformRequirementFilter/PlatformRequirementFilterFactoryTest.php b/tests/Composer/Test/Filter/PlatformRequirementFilter/PlatformRequirementFilterFactoryTest.php
index c7e462b92..d443532e3 100644
--- a/tests/Composer/Test/Filter/PlatformRequirementFilter/PlatformRequirementFilterFactoryTest.php
+++ b/tests/Composer/Test/Filter/PlatformRequirementFilter/PlatformRequirementFilterFactoryTest.php
@@ -31,7 +31,7 @@ final class PlatformRequirementFilterFactoryTest extends TestCase
     /**
      * @return array<string, mixed[]>
      */
-    public function dataFromBoolOrList()
+    public function dataFromBoolOrList(): array
     {
         return array(
             'true creates IgnoreAllFilter' => array(true, 'Composer\Filter\PlatformRequirementFilter\IgnoreAllPlatformRequirementFilter'),
diff --git a/tests/Composer/Test/Installer/SuggestedPackagesReporterTest.php b/tests/Composer/Test/Installer/SuggestedPackagesReporterTest.php
index fc83c7261..5cd693d4f 100644
--- a/tests/Composer/Test/Installer/SuggestedPackagesReporterTest.php
+++ b/tests/Composer/Test/Installer/SuggestedPackagesReporterTest.php
@@ -271,7 +271,7 @@ class SuggestedPackagesReporterTest extends TestCase
     /**
      * @return array<string, string>
      */
-    private function getSuggestedPackageArray()
+    private function getSuggestedPackageArray(): array
     {
         return array(
             'source' => 'a',
diff --git a/tests/Composer/Test/InstallerTest.php b/tests/Composer/Test/InstallerTest.php
index 959ec7a33..3d1c78c20 100644
--- a/tests/Composer/Test/InstallerTest.php
+++ b/tests/Composer/Test/InstallerTest.php
@@ -160,7 +160,7 @@ class InstallerTest extends TestCase
      * @param  PackageInterface[] $packages
      * @return mixed[]
      */
-    protected function makePackagesComparable($packages)
+    protected function makePackagesComparable($packages): array
     {
         $dumper = new ArrayDumper();
 
@@ -516,7 +516,7 @@ class InstallerTest extends TestCase
      * @param  string $path
      * @return mixed[]
      */
-    public function loadIntegrationTests($path)
+    public function loadIntegrationTests($path): array
     {
         $fixturesDir = realpath(__DIR__.'/Fixtures/'.$path);
         $tests = array();
@@ -602,7 +602,7 @@ class InstallerTest extends TestCase
      * @param  string $fixturesDir
      * @return mixed[]
      */
-    protected function readTestFile(\SplFileInfo $file, $fixturesDir)
+    protected function readTestFile(\SplFileInfo $file, $fixturesDir): array
     {
         $tokens = Preg::split('#(?:^|\n*)--([A-Z-]+)--\n#', file_get_contents($file->getRealPath()), -1, PREG_SPLIT_DELIM_CAPTURE);
 
diff --git a/tests/Composer/Test/Mock/FactoryMock.php b/tests/Composer/Test/Mock/FactoryMock.php
index ad2a14b9a..127720666 100644
--- a/tests/Composer/Test/Mock/FactoryMock.php
+++ b/tests/Composer/Test/Mock/FactoryMock.php
@@ -12,6 +12,8 @@
 
 namespace Composer\Test\Mock;
 
+use Composer\Installer\InstallationManager;
+use Composer\Package\Loader\RootPackageLoader;
 use Composer\Composer;
 use Composer\Config;
 use Composer\Factory;
@@ -30,7 +32,7 @@ use Composer\Util\ProcessExecutor;
 
 class FactoryMock extends Factory
 {
-    public static function createConfig(IOInterface $io = null, $cwd = null)
+    public static function createConfig(IOInterface $io = null, $cwd = null): Config
     {
         $config = new Config(true, $cwd);
 
@@ -42,7 +44,7 @@ class FactoryMock extends Factory
         return $config;
     }
 
-    protected function loadRootPackage(RepositoryManager $rm, Config $config, VersionParser $parser, VersionGuesser $guesser, IOInterface $io)
+    protected function loadRootPackage(RepositoryManager $rm, Config $config, VersionParser $parser, VersionGuesser $guesser, IOInterface $io): RootPackageLoader
     {
         return new \Composer\Package\Loader\RootPackageLoader($rm, $config, $parser, new VersionGuesserMock(), $io);
     }
@@ -52,16 +54,16 @@ class FactoryMock extends Factory
         $rm->setLocalRepository(new InstalledArrayRepository);
     }
 
-    public function createInstallationManager(Loop $loop, IOInterface $io, EventDispatcher $dispatcher = null)
+    public function createInstallationManager(Loop $loop, IOInterface $io, EventDispatcher $dispatcher = null): InstallationManager
     {
         return new InstallationManagerMock();
     }
 
-    protected function createDefaultInstallers(Installer\InstallationManager $im, Composer $composer, IOInterface $io, ProcessExecutor $process = null): void
+    protected function createDefaultInstallers(InstallationManager $im, Composer $composer, IOInterface $io, ProcessExecutor $process = null): void
     {
     }
 
-    protected function purgePackages(InstalledRepositoryInterface $repo, Installer\InstallationManager $im): void
+    protected function purgePackages(InstalledRepositoryInterface $repo, InstallationManager $im): void
     {
     }
 }
diff --git a/tests/Composer/Test/Mock/InstallationManagerMock.php b/tests/Composer/Test/Mock/InstallationManagerMock.php
index 95fe5ecd5..ed4eaa873 100644
--- a/tests/Composer/Test/Mock/InstallationManagerMock.php
+++ b/tests/Composer/Test/Mock/InstallationManagerMock.php
@@ -12,6 +12,7 @@
 
 namespace Composer\Test\Mock;
 
+use React\Promise\PromiseInterface;
 use Composer\Installer\InstallationManager;
 use Composer\Repository\InstalledRepositoryInterface;
 use Composer\Package\PackageInterface;
@@ -54,12 +55,12 @@ class InstallationManagerMock extends InstallationManager
         }
     }
 
-    public function getInstallPath(PackageInterface $package)
+    public function getInstallPath(PackageInterface $package): string
     {
         return '';
     }
 
-    public function isPackageInstalled(InstalledRepositoryInterface $repo, PackageInterface $package)
+    public function isPackageInstalled(InstalledRepositoryInterface $repo, PackageInterface $package): bool
     {
         return $repo->hasPackage($package);
     }
@@ -67,7 +68,7 @@ class InstallationManagerMock extends InstallationManager
     /**
      * @inheritDoc
      */
-    public function install(InstalledRepositoryInterface $repo, InstallOperation $operation)
+    public function install(InstalledRepositoryInterface $repo, InstallOperation $operation): ?PromiseInterface
     {
         $this->installed[] = $operation->getPackage();
         $this->trace[] = strip_tags((string) $operation);
@@ -79,7 +80,7 @@ class InstallationManagerMock extends InstallationManager
     /**
      * @inheritDoc
      */
-    public function update(InstalledRepositoryInterface $repo, UpdateOperation $operation)
+    public function update(InstalledRepositoryInterface $repo, UpdateOperation $operation): ?PromiseInterface
     {
         $this->updated[] = array($operation->getInitialPackage(), $operation->getTargetPackage());
         $this->trace[] = strip_tags((string) $operation);
@@ -94,7 +95,7 @@ class InstallationManagerMock extends InstallationManager
     /**
      * @inheritDoc
      */
-    public function uninstall(InstalledRepositoryInterface $repo, UninstallOperation $operation)
+    public function uninstall(InstalledRepositoryInterface $repo, UninstallOperation $operation): ?PromiseInterface
     {
         $this->uninstalled[] = $operation->getPackage();
         $this->trace[] = strip_tags((string) $operation);
@@ -122,25 +123,25 @@ class InstallationManagerMock extends InstallationManager
     }
 
     /** @return string[] */
-    public function getTrace()
+    public function getTrace(): array
     {
         return $this->trace;
     }
 
     /** @return PackageInterface[] */
-    public function getInstalledPackages()
+    public function getInstalledPackages(): array
     {
         return $this->installed;
     }
 
     /** @return PackageInterface[][] */
-    public function getUpdatedPackages()
+    public function getUpdatedPackages(): array
     {
         return $this->updated;
     }
 
     /** @return PackageInterface[] */
-    public function getUninstalledPackages()
+    public function getUninstalledPackages(): array
     {
         return $this->uninstalled;
     }
@@ -151,7 +152,7 @@ class InstallationManagerMock extends InstallationManager
     }
 
     /** @return PackageInterface[] */
-    public function getInstalledPackagesByType()
+    public function getInstalledPackagesByType(): array
     {
         return $this->installed;
     }
diff --git a/tests/Composer/Test/Mock/ProcessExecutorMock.php b/tests/Composer/Test/Mock/ProcessExecutorMock.php
index cf9733ee1..dbd4f0bfc 100644
--- a/tests/Composer/Test/Mock/ProcessExecutorMock.php
+++ b/tests/Composer/Test/Mock/ProcessExecutorMock.php
@@ -12,6 +12,7 @@
 
 namespace Composer\Test\Mock;
 
+use React\Promise\PromiseInterface;
 use Composer\Util\ProcessExecutor;
 use Composer\Util\Platform;
 use PHPUnit\Framework\Assert;
@@ -102,7 +103,7 @@ class ProcessExecutorMock extends ProcessExecutor
         Assert::assertTrue(true); // @phpstan-ignore-line
     }
 
-    public function execute($command, &$output = null, $cwd = null)
+    public function execute($command, &$output = null, $cwd = null): int
     {
         if (func_num_args() > 1) {
             return $this->doExecute($command, $cwd, false, $output);
@@ -111,7 +112,7 @@ class ProcessExecutorMock extends ProcessExecutor
         return $this->doExecute($command, $cwd, false);
     }
 
-    public function executeTty($command, $cwd = null)
+    public function executeTty($command, $cwd = null): int
     {
         if (Platform::isTty()) {
             return $this->doExecute($command, $cwd, true);
@@ -173,7 +174,7 @@ class ProcessExecutorMock extends ProcessExecutor
         return $return;
     }
 
-    public function executeAsync($command, $cwd = null)
+    public function executeAsync($command, $cwd = null): PromiseInterface
     {
         $resolver = function ($resolve, $reject): void {
             // TODO strictly speaking this should resolve with a mock Process instance here
@@ -187,7 +188,7 @@ class ProcessExecutorMock extends ProcessExecutor
         return new Promise($resolver, $canceler);
     }
 
-    public function getErrorOutput()
+    public function getErrorOutput(): string
     {
         return $this->errorOutput;
     }
diff --git a/tests/Composer/Test/Mock/VersionGuesserMock.php b/tests/Composer/Test/Mock/VersionGuesserMock.php
index d2fe1236c..b634b0297 100644
--- a/tests/Composer/Test/Mock/VersionGuesserMock.php
+++ b/tests/Composer/Test/Mock/VersionGuesserMock.php
@@ -20,7 +20,7 @@ class VersionGuesserMock extends VersionGuesser
     {
     }
 
-    public function guessVersion(array $packageConfig, $path)
+    public function guessVersion(array $packageConfig, $path): ?array
     {
         return null;
     }
diff --git a/tests/Composer/Test/Package/Archiver/ArchivableFilesFinderTest.php b/tests/Composer/Test/Package/Archiver/ArchivableFilesFinderTest.php
index 384623879..ad9bce604 100644
--- a/tests/Composer/Test/Package/Archiver/ArchivableFilesFinderTest.php
+++ b/tests/Composer/Test/Package/Archiver/ArchivableFilesFinderTest.php
@@ -260,7 +260,7 @@ class ArchivableFilesFinderTest extends TestCase
     /**
      * @return string[]
      */
-    protected function getArchivableFiles()
+    protected function getArchivableFiles(): array
     {
         $files = array();
         foreach ($this->finder as $file) {
@@ -279,7 +279,7 @@ class ArchivableFilesFinderTest extends TestCase
      *
      * @return string[]
      */
-    protected function getArchivedFiles($command)
+    protected function getArchivedFiles($command): array
     {
         $process = Process::fromShellCommandline($command, $this->sources);
         $process->run();
diff --git a/tests/Composer/Test/Package/Archiver/ArchiveManagerTest.php b/tests/Composer/Test/Package/Archiver/ArchiveManagerTest.php
index af8166576..8d620fbc9 100644
--- a/tests/Composer/Test/Package/Archiver/ArchiveManagerTest.php
+++ b/tests/Composer/Test/Package/Archiver/ArchiveManagerTest.php
@@ -104,7 +104,7 @@ class ArchiveManagerTest extends ArchiverTest
      *
      * @return string
      */
-    protected function getTargetName(CompletePackage $package, $format, $fileName = null)
+    protected function getTargetName(CompletePackage $package, $format, $fileName = null): string
     {
         if (null === $fileName) {
             $packageName = $this->manager->getPackageFilename($package);
diff --git a/tests/Composer/Test/Package/Archiver/ArchiverTest.php b/tests/Composer/Test/Package/Archiver/ArchiverTest.php
index 9601fa1c6..5ac901d1b 100644
--- a/tests/Composer/Test/Package/Archiver/ArchiverTest.php
+++ b/tests/Composer/Test/Package/Archiver/ArchiverTest.php
@@ -52,7 +52,7 @@ abstract class ArchiverTest extends TestCase
      *
      * @return CompletePackage
      */
-    protected function setupPackage()
+    protected function setupPackage(): CompletePackage
     {
         $package = new CompletePackage('archivertest/archivertest', 'master', 'master');
         $package->setSourceUrl(realpath($this->testDir));
diff --git a/tests/Composer/Test/Package/BasePackageTest.php b/tests/Composer/Test/Package/BasePackageTest.php
index 0818ee358..b7ec37ce8 100644
--- a/tests/Composer/Test/Package/BasePackageTest.php
+++ b/tests/Composer/Test/Package/BasePackageTest.php
@@ -109,7 +109,7 @@ class BasePackageTest extends TestCase
     /**
      * @return mixed[][]
      */
-    public function dataPackageNamesToRegexp()
+    public function dataPackageNamesToRegexp(): array
     {
         return array(
             array(
diff --git a/tests/Composer/Test/Package/Dumper/ArrayDumperTest.php b/tests/Composer/Test/Package/Dumper/ArrayDumperTest.php
index 624347bd6..6a08d7b99 100644
--- a/tests/Composer/Test/Package/Dumper/ArrayDumperTest.php
+++ b/tests/Composer/Test/Package/Dumper/ArrayDumperTest.php
@@ -250,7 +250,7 @@ class ArrayDumperTest extends TestCase
      *
      * @return self
      */
-    private function packageExpects($method, $value)
+    private function packageExpects($method, $value): \Composer\Test\Package\Dumper\ArrayDumperTest
     {
         $this->package
             ->expects($this->any())
diff --git a/tests/Composer/Test/Package/Loader/ArrayLoaderTest.php b/tests/Composer/Test/Package/Loader/ArrayLoaderTest.php
index cfe12caa9..70f79bbbe 100644
--- a/tests/Composer/Test/Package/Loader/ArrayLoaderTest.php
+++ b/tests/Composer/Test/Package/Loader/ArrayLoaderTest.php
@@ -139,7 +139,7 @@ class ArrayLoaderTest extends TestCase
      *
      * @return array<string, mixed>
      */
-    protected function fixConfigWhenLoadConfigIsFalse($config)
+    protected function fixConfigWhenLoadConfigIsFalse($config): array
     {
         $expectedConfig = $config;
         unset($expectedConfig['transport-options']);
diff --git a/tests/Composer/Test/Package/Version/VersionSelectorTest.php b/tests/Composer/Test/Package/Version/VersionSelectorTest.php
index 05c2d6e0d..7a8fbf943 100644
--- a/tests/Composer/Test/Package/Version/VersionSelectorTest.php
+++ b/tests/Composer/Test/Package/Version/VersionSelectorTest.php
@@ -362,7 +362,7 @@ class VersionSelectorTest extends TestCase
      *
      * @return Package
      */
-    private function createPackage($version)
+    private function createPackage($version): Package
     {
         $parser = new VersionParser();
 
diff --git a/tests/Composer/Test/Platform/HhvmDetectorTest.php b/tests/Composer/Test/Platform/HhvmDetectorTest.php
index d3881a74d..eaf93c982 100644
--- a/tests/Composer/Test/Platform/HhvmDetectorTest.php
+++ b/tests/Composer/Test/Platform/HhvmDetectorTest.php
@@ -71,7 +71,7 @@ class HhvmDetectorTest extends TestCase
     /**
      * @return ?string
      */
-    private static function versionIdToVersion()
+    private static function versionIdToVersion(): ?string
     {
         if (!defined('HHVM_VERSION_ID')) {
             return null;
diff --git a/tests/Composer/Test/Plugin/PluginInstallerTest.php b/tests/Composer/Test/Plugin/PluginInstallerTest.php
index 0bba37da8..fc0229527 100644
--- a/tests/Composer/Test/Plugin/PluginInstallerTest.php
+++ b/tests/Composer/Test/Plugin/PluginInstallerTest.php
@@ -407,7 +407,7 @@ class PluginInstallerTest extends TestCase
     }
 
     /** @return mixed[] */
-    public function invalidImplementationClassNames()
+    public function invalidImplementationClassNames(): array
     {
         return array(
             array(null),
@@ -422,7 +422,7 @@ class PluginInstallerTest extends TestCase
     }
 
     /** @return mixed[] */
-    public function nonExistingOrInvalidImplementationClassTypes()
+    public function nonExistingOrInvalidImplementationClassTypes(): array
     {
         return array(
             array('\stdClass'),
diff --git a/tests/Composer/Test/Question/StrictConfirmationQuestionTest.php b/tests/Composer/Test/Question/StrictConfirmationQuestionTest.php
index ed996717d..7d9c94a75 100644
--- a/tests/Composer/Test/Question/StrictConfirmationQuestionTest.php
+++ b/tests/Composer/Test/Question/StrictConfirmationQuestionTest.php
@@ -30,7 +30,7 @@ class StrictConfirmationQuestionTest extends TestCase
      *
      * @phpstan-return list<array{non-empty-string}>
      */
-    public function getAskConfirmationBadData()
+    public function getAskConfirmationBadData(): array
     {
         return array(
             array('not correct'),
@@ -77,7 +77,7 @@ class StrictConfirmationQuestionTest extends TestCase
      *
      * @phpstan-return list<array{string, bool}>|list<array{string, bool, bool}>
      */
-    public function getAskConfirmationData()
+    public function getAskConfirmationData(): array
     {
         return array(
             array('', true),
@@ -119,7 +119,7 @@ class StrictConfirmationQuestionTest extends TestCase
     /**
      * @return StreamOutput
      */
-    protected function createOutputInterface()
+    protected function createOutputInterface(): StreamOutput
     {
         return new StreamOutput(fopen('php://memory', 'r+', false));
     }
@@ -131,7 +131,7 @@ class StrictConfirmationQuestionTest extends TestCase
      *
      * @phpstan-return array{ArrayInput, QuestionHelper}
      */
-    protected function createInput($entry)
+    protected function createInput($entry): array
     {
         $input = new ArrayInput(array('--no-interaction'));
         $input->setStream($this->getInputStream($entry));
diff --git a/tests/Composer/Test/Repository/PlatformRepositoryTest.php b/tests/Composer/Test/Repository/PlatformRepositoryTest.php
index 96cdaa21a..f8c5946f8 100644
--- a/tests/Composer/Test/Repository/PlatformRepositoryTest.php
+++ b/tests/Composer/Test/Repository/PlatformRepositoryTest.php
@@ -1285,7 +1285,7 @@ class ResourceBundleStub
      *
      * @return ResourceBundleStub
      */
-    public static function create($locale, $bundleName, $fallback)
+    public static function create($locale, $bundleName, $fallback): ResourceBundleStub
     {
         Assert::assertSame(3, func_num_args());
         Assert::assertSame('root', $locale);
@@ -1300,7 +1300,7 @@ class ResourceBundleStub
      *
      * @return string
      */
-    public function get($field)
+    public function get($field): string
     {
         Assert::assertSame(1, func_num_args());
         Assert::assertSame('Version', $field);
@@ -1328,7 +1328,7 @@ class ImagickStub
      * @return array<string, string>
      * @phpstan-return array{versionString: string}
      */
-    public function getVersion()
+    public function getVersion(): array
     {
         Assert::assertSame(0, func_num_args());
 
diff --git a/tests/Composer/Test/Repository/Vcs/GitBitbucketDriverTest.php b/tests/Composer/Test/Repository/Vcs/GitBitbucketDriverTest.php
index 1643769ae..95fd969aa 100644
--- a/tests/Composer/Test/Repository/Vcs/GitBitbucketDriverTest.php
+++ b/tests/Composer/Test/Repository/Vcs/GitBitbucketDriverTest.php
@@ -64,7 +64,7 @@ class GitBitbucketDriverTest extends TestCase
      *
      * @phpstan-param array{url: string}&array<string, mixed> $repoConfig
      */
-    private function getDriver(array $repoConfig)
+    private function getDriver(array $repoConfig): GitBitbucketDriver
     {
         $driver = new GitBitbucketDriver(
             $repoConfig,
diff --git a/tests/Composer/Test/Repository/Vcs/GitHubDriverTest.php b/tests/Composer/Test/Repository/Vcs/GitHubDriverTest.php
index 74576d98a..8482b28bd 100644
--- a/tests/Composer/Test/Repository/Vcs/GitHubDriverTest.php
+++ b/tests/Composer/Test/Repository/Vcs/GitHubDriverTest.php
@@ -337,7 +337,7 @@ class GitHubDriverTest extends TestCase
     /**
      * @return list<array{bool, string}>
      */
-    public function supportsProvider()
+    public function supportsProvider(): array
     {
         return array(
             array(false, 'https://github.com/acme'),
diff --git a/tests/Composer/Test/Repository/Vcs/PerforceDriverTest.php b/tests/Composer/Test/Repository/Vcs/PerforceDriverTest.php
index 058bbc4c7..00acd67df 100644
--- a/tests/Composer/Test/Repository/Vcs/PerforceDriverTest.php
+++ b/tests/Composer/Test/Repository/Vcs/PerforceDriverTest.php
@@ -102,7 +102,7 @@ class PerforceDriverTest extends TestCase
      *
      * @return Config
      */
-    protected function getTestConfig($testPath)
+    protected function getTestConfig($testPath): Config
     {
         $config = new Config();
         $config->merge(array('config' => array('home' => $testPath)));
diff --git a/tests/Composer/Test/Script/EventTest.php b/tests/Composer/Test/Script/EventTest.php
index 561d0b300..724d0e886 100644
--- a/tests/Composer/Test/Script/EventTest.php
+++ b/tests/Composer/Test/Script/EventTest.php
@@ -71,7 +71,7 @@ class EventTest extends TestCase
     /**
      * @return Composer
      */
-    private function createComposerInstance()
+    private function createComposerInstance(): Composer
     {
         $composer = new Composer;
         $config = new Config;
diff --git a/tests/Composer/Test/TestCase.php b/tests/Composer/Test/TestCase.php
index 380bd2550..a7a9d5c29 100644
--- a/tests/Composer/Test/TestCase.php
+++ b/tests/Composer/Test/TestCase.php
@@ -67,7 +67,7 @@ abstract class TestCase extends \PHPUnit\Framework\TestCase
     /**
      * @return string
      */
-    public static function getUniqueTmpDirectory()
+    public static function getUniqueTmpDirectory(): string
     {
         $attempts = 5;
         $root = sys_get_temp_dir();
@@ -86,7 +86,7 @@ abstract class TestCase extends \PHPUnit\Framework\TestCase
     /**
      * @return VersionParser
      */
-    protected static function getVersionParser()
+    protected static function getVersionParser(): VersionParser
     {
         if (!self::$parser) {
             self::$parser = new VersionParser();
@@ -100,7 +100,7 @@ abstract class TestCase extends \PHPUnit\Framework\TestCase
      * @param string $version
      * @return Constraint
      */
-    protected function getVersionConstraint($operator, $version)
+    protected function getVersionConstraint($operator, $version): Constraint
     {
         $constraint = new Constraint(
             $operator,
@@ -214,7 +214,7 @@ abstract class TestCase extends \PHPUnit\Framework\TestCase
      *
      * @return string The transformed command
      */
-    protected function getCmd($cmd)
+    protected function getCmd($cmd): string
     {
         if (Platform::isWindows()) {
             $cmd = Preg::replaceCallback("/('[^']*')/", function ($m) {
diff --git a/tests/Composer/Test/Util/NoProxyPatternTest.php b/tests/Composer/Test/Util/NoProxyPatternTest.php
index 9a02d7e54..2a09261a7 100644
--- a/tests/Composer/Test/Util/NoProxyPatternTest.php
+++ b/tests/Composer/Test/Util/NoProxyPatternTest.php
@@ -140,7 +140,7 @@ class NoProxyPatternTest extends TestCase
      *
      * @return string
      */
-    private function getUrl($url)
+    private function getUrl($url): string
     {
         if (parse_url($url, PHP_URL_SCHEME)) {
             return $url;
diff --git a/tests/Composer/Test/Util/PackageSorterTest.php b/tests/Composer/Test/Util/PackageSorterTest.php
index e11d1b89f..7c3eb7671 100644
--- a/tests/Composer/Test/Util/PackageSorterTest.php
+++ b/tests/Composer/Test/Util/PackageSorterTest.php
@@ -124,7 +124,7 @@ class PackageSorterTest extends TestCase
      *
      * @return Package
      */
-    private function createPackage($name, $requires)
+    private function createPackage($name, $requires): Package
     {
         $package = new Package($name, '1.0.0.0', '1.0.0');
 
diff --git a/tests/Composer/Test/Util/PerforceTest.php b/tests/Composer/Test/Util/PerforceTest.php
index 764d1a68c..4e3f7d5b9 100644
--- a/tests/Composer/Test/Util/PerforceTest.php
+++ b/tests/Composer/Test/Util/PerforceTest.php
@@ -50,7 +50,7 @@ class PerforceTest extends TestCase
     /**
      * @return array<string, string>
      */
-    public function getTestRepoConfig()
+    public function getTestRepoConfig(): array
     {
         return array(
             'depot' => self::TEST_DEPOT,
@@ -598,7 +598,7 @@ class PerforceTest extends TestCase
     /**
      * @return string
      */
-    public static function getComposerJson()
+    public static function getComposerJson(): string
     {
         return JsonFile::encode([
             'name' => 'test/perforce',
@@ -615,7 +615,7 @@ class PerforceTest extends TestCase
      *
      * @return string[]
      */
-    private function getExpectedClientSpec($withStream)
+    private function getExpectedClientSpec($withStream): array
     {
         $expectedArray = array(
             'Client: composer_perforce_TEST_depot',
diff --git a/tests/Composer/Test/Util/RemoteFilesystemTest.php b/tests/Composer/Test/Util/RemoteFilesystemTest.php
index 667e6d17f..26e76982e 100644
--- a/tests/Composer/Test/Util/RemoteFilesystemTest.php
+++ b/tests/Composer/Test/Util/RemoteFilesystemTest.php
@@ -265,7 +265,7 @@ class RemoteFilesystemTest extends TestCase
      *
      * @return string[][]
      */
-    public function provideBitbucketPublicDownloadUrls()
+    public function provideBitbucketPublicDownloadUrls(): array
     {
         return array(
             array('https://bitbucket.org/seldaek/composer-live-test-repo/downloads/composer-unit-test-download-me.txt', '1234'),
@@ -343,7 +343,7 @@ class RemoteFilesystemTest extends TestCase
      *
      * @return mixed[]
      */
-    private function callGetOptionsForUrl(IOInterface $io, array $args = array(), array $options = array(), $fileUrl = '')
+    private function callGetOptionsForUrl(IOInterface $io, array $args = array(), array $options = array(), $fileUrl = ''): array
     {
         $fs = new RemoteFilesystem($io, $this->getConfigMock(), $options);
         $ref = new ReflectionMethod($fs, 'getOptionsForUrl');