diff --git a/composer.json b/composer.json
index 20704951c..9225f2e5f 100644
--- a/composer.json
+++ b/composer.json
@@ -78,11 +78,20 @@
     ],
     "scripts": {
         "compile": "@php -dphar.readonly=0 bin/compile",
-        "test": "simple-phpunit"
+        "test": "simple-phpunit",
+        "phpstan-setup": [
+            "@composer config platform --unset",
+            "@php composer.phar update",
+            "@composer require --dev phpstan/phpstan:^0.12.93 phpstan/phpstan-phpunit:^0.12.17 phpunit/phpunit:^7.5.20 --with-all-dependencies",
+            "git checkout composer.json composer.lock"
+        ],
+        "phpstan": "@php vendor/bin/phpstan analyse --configuration=phpstan/config.neon"
     },
     "scripts-descriptions": {
         "compile": "Compile composer.phar",
-        "test": "Run all tests"
+        "test": "Run all tests",
+        "phpstan-setup": "Prepare environment to run PHPStan locally (must be run with PHP7.4)",
+        "phpstan": "Runs PHPStan (after phpstan-setup was executed, must be run with PHP7.4)"
     },
     "support": {
         "issues": "https://github.com/composer/composer/issues",
diff --git a/composer.lock b/composer.lock
index 4a9a22073..b953e70c9 100644
--- a/composer.lock
+++ b/composer.lock
@@ -608,16 +608,16 @@
         },
         {
             "name": "seld/phar-utils",
-            "version": "1.1.1",
+            "version": "1.1.2",
             "source": {
                 "type": "git",
                 "url": "https://github.com/Seldaek/phar-utils.git",
-                "reference": "8674b1d84ffb47cc59a101f5d5a3b61e87d23796"
+                "reference": "749042a2315705d2dfbbc59234dd9ceb22bf3ff0"
             },
             "dist": {
                 "type": "zip",
-                "url": "https://api.github.com/repos/Seldaek/phar-utils/zipball/8674b1d84ffb47cc59a101f5d5a3b61e87d23796",
-                "reference": "8674b1d84ffb47cc59a101f5d5a3b61e87d23796",
+                "url": "https://api.github.com/repos/Seldaek/phar-utils/zipball/749042a2315705d2dfbbc59234dd9ceb22bf3ff0",
+                "reference": "749042a2315705d2dfbbc59234dd9ceb22bf3ff0",
                 "shasum": ""
             },
             "require": {
@@ -650,9 +650,9 @@
             ],
             "support": {
                 "issues": "https://github.com/Seldaek/phar-utils/issues",
-                "source": "https://github.com/Seldaek/phar-utils/tree/master"
+                "source": "https://github.com/Seldaek/phar-utils/tree/1.1.2"
             },
-            "time": "2020-07-07T18:42:57+00:00"
+            "time": "2021-08-19T21:01:38+00:00"
         },
         {
             "name": "symfony/console",
diff --git a/phpstan/baseline.neon b/phpstan/baseline.neon
index e747a8e40..9d3580e48 100644
--- a/phpstan/baseline.neon
+++ b/phpstan/baseline.neon
@@ -1,277 +1,11 @@
 parameters:
-	ignoreErrors:
-		-
-			message: "#^Else branch is unreachable because ternary operator condition is always true\\.$#"
-			count: 1
-			path: ../src/Composer/Autoload/AutoloadGenerator.php
-
-		-
-			message: "#^Left side of && is always true\\.$#"
-			count: 1
-			path: ../src/Composer/Autoload/AutoloadGenerator.php
-
-		-
-			message: "#^If condition is always true\\.$#"
-			count: 1
-			path: ../src/Composer/Autoload/ClassMapGenerator.php
-
-		-
-			message: "#^Else branch is unreachable because previous condition is always true\\.$#"
-			count: 1
-			path: ../src/Composer/Command/BaseCommand.php
-
-		-
-			message: "#^Elseif branch is unreachable because previous condition is always true\\.$#"
-			count: 1
-			path: ../src/Composer/Command/BaseCommand.php
-
-		-
-			message: "#^Result of && is always false\\.$#"
-			count: 1
-			path: ../src/Composer/Command/DiagnoseCommand.php
-
-		-
-			message: "#^Strict comparison using \\!\\=\\= between '@package_version@' and '@package_version@' will always evaluate to false\\.$#"
-			count: 1
-			path: ../src/Composer/Command/DiagnoseCommand.php
-
-		-
-			message: "#^Ternary operator condition is always true\\.$#"
-			count: 1
-			path: ../src/Composer/Command/DiagnoseCommand.php
-
-		-
-			message: "#^Negated boolean expression is always false\\.$#"
-			count: 1
-			path: ../src/Composer/Command/InitCommand.php
-
-		-
-			message: "#^Negated boolean expression is always false\\.$#"
-			count: 1
-			path: ../src/Composer/Command/InstallCommand.php
-
-		-
-			message: "#^Call to function is_array\\(\\) with string will always evaluate to false\\.$#"
-			count: 1
-			path: ../src/Composer/Command/ShowCommand.php
-
-		-
-			message: "#^Elseif branch is unreachable because previous condition is always true\\.$#"
-			count: 1
-			path: ../src/Composer/Command/ShowCommand.php
-
-		-
-			message: "#^Negated boolean expression is always false\\.$#"
-			count: 1
-			path: ../src/Composer/Command/ShowCommand.php
-
-		-
-			message: "#^Unreachable statement \\- code above always terminates\\.$#"
-			count: 1
-			path: ../src/Composer/Composer.php
-
-		-
-			message: "#^If condition is always true\\.$#"
-			count: 1
-			path: ../src/Composer/Console/Application.php
-
-		-
-			message: "#^Left side of && is always true\\.$#"
-			count: 2
-			path: ../src/Composer/Console/Application.php
-
-		-
-			message: "#^Strict comparison using \\!\\=\\= between '@package_branch…' and '@package_branch…' will always evaluate to false\\.$#"
-			count: 1
-			path: ../src/Composer/Console/Application.php
-
-		-
-			message: "#^Strict comparison using \\=\\=\\= between null and Composer\\\\Composer will always evaluate to false\\.$#"
-			count: 1
-			path: ../src/Composer/Console/Application.php
-
-		-
-			message: "#^Instanceof between mixed and Composer\\\\Package\\\\RootAliasPackage will always evaluate to false\\.$#"
-			count: 1
-			path: ../src/Composer/DependencyResolver/LockTransaction.php
-
-		-
-			message: "#^If condition is always true\\.$#"
-			count: 1
-			path: ../src/Composer/DependencyResolver/PoolBuilder.php
-
-		-
-			message: "#^Ternary operator condition is always true\\.$#"
-			count: 1
-			path: ../src/Composer/DependencyResolver/Problem.php
-
-		-
-			message: "#^If condition is always true\\.$#"
-			count: 2
-			path: ../src/Composer/Downloader/FileDownloader.php
-
-		-
-			message: "#^Left side of && is always true\\.$#"
-			count: 3
-			path: ../src/Composer/Downloader/FileDownloader.php
-
-		-
-			message: "#^Comparison operation \"\\>\" between 0 and 6 is always false\\.$#"
-			count: 1
-			path: ../src/Composer/Downloader/PathDownloader.php
-
-		-
-			message: "#^Comparison operation \"\\>\\=\" between 0 and 1 is always false\\.$#"
-			count: 1
-			path: ../src/Composer/Downloader/PathDownloader.php
-
-		-
-			message: "#^Result of && is always false\\.$#"
-			count: 2
-			path: ../src/Composer/Downloader/PathDownloader.php
-
-		-
-			message: "#^Result of \\|\\| is always false\\.$#"
-			count: 1
-			path: ../src/Composer/Downloader/PathDownloader.php
-
-		-
-			message: "#^Strict comparison using \\=\\=\\= between 0 and 6 will always evaluate to false\\.$#"
-			count: 1
-			path: ../src/Composer/Downloader/PathDownloader.php
-
-		-
-			message: "#^If condition is always true\\.$#"
-			count: 1
-			path: ../src/Composer/Factory.php
-
-		-
-			message: "#^Left side of && is always true\\.$#"
-			count: 3
-			path: ../src/Composer/Factory.php
-
-		-
-			message: "#^Strict comparison using \\=\\=\\= between 16 and 0 will always evaluate to false\\.$#"
-			count: 1
-			path: ../src/Composer/IO/ConsoleIO.php
-
-		-
-			message: "#^Result of && is always false\\.$#"
-			count: 1
-			path: ../src/Composer/InstalledVersions.php
-
-		-
-			message: "#^If condition is always true\\.$#"
-			count: 2
-			path: ../src/Composer/Installer.php
-
-		-
-			message: "#^Negated boolean expression is always false\\.$#"
-			count: 1
-			path: ../src/Composer/Installer.php
-
-		-
-			message: "#^Empty array passed to foreach\\.$#"
-			count: 1
-			path: ../src/Composer/Installer/InstallationManager.php
-
-		-
-			message: "#^Right side of && is always true\\.$#"
-			count: 2
-			path: ../src/Composer/Installer/InstallationManager.php
-
-		-
-			message: "#^Strict comparison using \\=\\=\\= between null and string will always evaluate to false\\.$#"
-			count: 1
-			path: ../src/Composer/Json/JsonFile.php
-
-		-
-			message: "#^If condition is always true\\.$#"
-			count: 1
-			path: ../src/Composer/Package/Dumper/ArrayDumper.php
-
-		-
-			message: "#^Ternary operator condition is always true\\.$#"
-			count: 1
-			path: ../src/Composer/Package/Link.php
-
-		-
-			message: "#^Unreachable statement \\- code above always terminates\\.$#"
-			count: 1
-			path: ../src/Composer/Package/Loader/ArrayLoader.php
-
-		-
-			message: "#^Else branch is unreachable because previous condition is always true\\.$#"
-			count: 1
-			path: ../src/Composer/Package/Locker.php
-
-		-
-			message: "#^If condition is always true\\.$#"
-			count: 3
-			path: ../src/Composer/Plugin/PluginManager.php
-
-		-
-			message: "#^Left side of && is always true\\.$#"
-			count: 1
-			path: ../src/Composer/Plugin/PluginManager.php
-
-		-
-			message: "#^Ternary operator condition is always true\\.$#"
-			count: 2
-			path: ../src/Composer/Plugin/PluginManager.php
-
-		-
-			message: "#^Instanceof between string and Composer\\\\Package\\\\PackageInterface will always evaluate to false\\.$#"
-			count: 1
-			path: ../src/Composer/Plugin/PostFileDownloadEvent.php
-
-		-
-			message: "#^Result of && is always false\\.$#"
-			count: 1
-			path: ../src/Composer/Plugin/PostFileDownloadEvent.php
-
-		-
-			message: "#^Negated boolean expression is always false\\.$#"
-			count: 1
-			path: ../src/Composer/Repository/ArrayRepository.php
-
-		-
-			message: "#^Strict comparison using \\=\\=\\= between null and Composer\\\\Repository\\\\RepositoryInterface will always evaluate to false\\.$#"
-			count: 1
-			path: ../src/Composer/Repository/ArrayRepository.php
-
-		-
-			message: "#^If condition is always false\\.$#"
-			count: 1
-			path: ../src/Composer/Repository/ComposerRepository.php
-
-		-
-			message: "#^Negated boolean expression is always false\\.$#"
-			count: 1
-			path: ../src/Composer/Repository/ComposerRepository.php
-
-		-
-			message: "#^Negated boolean expression is always true\\.$#"
-			count: 1
-			path: ../src/Composer/Repository/InstalledRepository.php
-
-		-
-			message: "#^Negated boolean expression is always true\\.$#"
-			count: 1
-			path: ../src/Composer/Repository/Vcs/GitBitbucketDriver.php
-
-		-
-			message: "#^Unreachable statement \\- code above always terminates\\.$#"
-			count: 1
-			path: ../src/Composer/Repository/Vcs/GitBitbucketDriver.php
-
-		-
-			message: "#^Negated boolean expression is always false\\.$#"
-			count: 1
-			path: ../src/Composer/Repository/Vcs/GitLabDriver.php
-
-		-
-			message: "#^Right side of && is always true\\.$#"
-			count: 1
-			path: ../src/Composer/Repository/Vcs/GitLabDriver.php
+    ignoreErrors:
+        -
+            message: "#^Parameter \\#1 \\$autoload_function of function spl_autoload_register expects callable\\(string\\)\\: void, array\\(\\$this\\(Composer\\\\Autoload\\\\ClassLoader\\), 'loadClass'\\) given\\.$#"
+            count: 1
+            path: ../src/Composer/Autoload/ClassLoader.php
 
+        -
+            message: "#^Parameter \\#2 \\$capabilityClassName of method Composer\\\\Plugin\\\\PluginManager\\:\\:getPluginCapability\\(\\) expects class\\-string\\<Composer\\\\Plugin\\\\Capability\\\\Capability\\>, string given\\.$#"
+            count: 2
+            path: ../tests/Composer/Test/Plugin/PluginInstallerTest.php
diff --git a/phpstan/config.neon b/phpstan/config.neon
index 9f934ddea..6458aac46 100644
--- a/phpstan/config.neon
+++ b/phpstan/config.neon
@@ -3,7 +3,7 @@ includes:
     - ./baseline.neon
 
 parameters:
-    level: 4
+    level: 5
     excludes_analyse:
        - '../tests/Composer/Test/Fixtures/*'
        - '../tests/Composer/Test/Autoload/Fixtures/*'
@@ -42,5 +42,11 @@ parameters:
         - ../src
         - ../tests
 
+    dynamicConstantNames:
+        - Composer\Composer::BRANCH_ALIAS_VERSION
+        - Composer\Composer::VERSION
+        - Composer\Composer::RELEASE_DATE
+        - Composer\Composer::SOURCE_VERSION
+
 rules:
     - Composer\PHPStanRules\AnonymousFunctionWithThisRule
diff --git a/src/Composer/Autoload/AutoloadGenerator.php b/src/Composer/Autoload/AutoloadGenerator.php
index 6a8848976..47c888ab7 100644
--- a/src/Composer/Autoload/AutoloadGenerator.php
+++ b/src/Composer/Autoload/AutoloadGenerator.php
@@ -41,7 +41,7 @@ class AutoloadGenerator
     private $eventDispatcher;
 
     /**
-     * @var IOInterface
+     * @var ?IOInterface
      */
     private $io;
 
@@ -667,7 +667,7 @@ EOF;
             $baseDir = "'phar://' . " . $baseDir;
         }
 
-        return $baseDir . (($path !== false) ? var_export($path, true) : "");
+        return $baseDir . var_export($path, true);
     }
 
     protected function getPlatformCheck(array $packageMap, array $ignorePlatformReqs, $checkPlatform, array $devPackageNames)
diff --git a/src/Composer/Autoload/ClassMapGenerator.php b/src/Composer/Autoload/ClassMapGenerator.php
index 33c2d48c8..085136f0e 100644
--- a/src/Composer/Autoload/ClassMapGenerator.php
+++ b/src/Composer/Autoload/ClassMapGenerator.php
@@ -33,8 +33,8 @@ class ClassMapGenerator
     /**
      * Generate a class map file
      *
-     * @param \Traversable $dirs Directories or a single path to search in
-     * @param string       $file The name of the class map file
+     * @param \Traversable|array $dirs Directories or a single path to search in
+     * @param string             $file The name of the class map file
      */
     public static function dump($dirs, $file)
     {
@@ -50,11 +50,11 @@ class ClassMapGenerator
     /**
      * Iterate over all files in the given directory searching for classes
      *
-     * @param \Iterator|string $path         The path to search in or an iterator
-     * @param string           $excluded     Regex that matches file paths to be excluded from the classmap
-     * @param IOInterface      $io           IO object
-     * @param string           $namespace    Optional namespace prefix to filter by
-     * @param string           $autoloadType psr-0|psr-4 Optional autoload standard to use mapping rules
+     * @param \Traversable|string $path         The path to search in or an iterator
+     * @param string              $excluded     Regex that matches file paths to be excluded from the classmap
+     * @param ?IOInterface        $io           IO object
+     * @param ?string             $namespace    Optional namespace prefix to filter by
+     * @param ?string             $autoloadType psr-0|psr-4 Optional autoload standard to use mapping rules
      *
      * @throws \RuntimeException When the path is neither an existing file nor directory
      * @return array             A class map array
@@ -147,13 +147,13 @@ class ClassMapGenerator
     /**
      * Remove classes which could not have been loaded by namespace autoloaders
      *
-     * @param  array       $classes       found classes in given file
-     * @param  string      $filePath      current file
-     * @param  string      $baseNamespace prefix of given autoload mapping
-     * @param  string      $namespaceType psr-0|psr-4
-     * @param  string      $basePath      root directory of given autoload mapping
-     * @param  IOInterface $io            IO object
-     * @return array       valid classes
+     * @param  array        $classes       found classes in given file
+     * @param  string       $filePath      current file
+     * @param  string       $baseNamespace prefix of given autoload mapping
+     * @param  string       $namespaceType psr-0|psr-4
+     * @param  string       $basePath      root directory of given autoload mapping
+     * @param  ?IOInterface $io            IO object
+     * @return array        valid classes
      */
     private static function filterByNamespace($classes, $filePath, $baseNamespace, $namespaceType, $basePath, $io)
     {
diff --git a/src/Composer/Command/ArchiveCommand.php b/src/Composer/Command/ArchiveCommand.php
index 6f30d5f24..3acf4fd04 100644
--- a/src/Composer/Command/ArchiveCommand.php
+++ b/src/Composer/Command/ArchiveCommand.php
@@ -49,7 +49,7 @@ class ArchiveCommand extends BaseCommand
                 new InputOption('dir', null, InputOption::VALUE_REQUIRED, 'Write the archive to this directory'),
                 new InputOption('file', null, InputOption::VALUE_REQUIRED, 'Write the archive with the given file name.'
                     .' Note that the format will be appended.'),
-                new InputOption('ignore-filters', false, InputOption::VALUE_NONE, 'Ignore filters when saving package'),
+                new InputOption('ignore-filters', null, InputOption::VALUE_NONE, 'Ignore filters when saving package'),
             ))
             ->setHelp(
                 <<<EOT
diff --git a/src/Composer/Command/BaseCommand.php b/src/Composer/Command/BaseCommand.php
index 69340b91e..b473fbe80 100644
--- a/src/Composer/Command/BaseCommand.php
+++ b/src/Composer/Command/BaseCommand.php
@@ -61,6 +61,7 @@ abstract class BaseCommand extends Command
             if ($application instanceof Application) {
                 /* @var $application    Application */
                 $this->composer = $application->getComposer($required, $disablePlugins);
+            /** @phpstan-ignore-next-line */
             } elseif ($required) {
                 throw new \RuntimeException(
                     'Could not create a Composer\Composer instance, you must inject '.
@@ -109,8 +110,8 @@ abstract class BaseCommand extends Command
         if (null === $this->io) {
             $application = $this->getApplication();
             if ($application instanceof Application) {
-                /* @var $application    Application */
                 $this->io = $application->getIO();
+            /** @phpstan-ignore-next-line */
             } else {
                 $this->io = new NullIO();
             }
diff --git a/src/Composer/Command/DiagnoseCommand.php b/src/Composer/Command/DiagnoseCommand.php
index e70815fc6..2fdd99bf2 100644
--- a/src/Composer/Command/DiagnoseCommand.php
+++ b/src/Composer/Command/DiagnoseCommand.php
@@ -304,9 +304,11 @@ EOT
         try {
             $url = $domain === 'github.com' ? 'https://api.'.$domain.'/' : 'https://'.$domain.'/api/v3/';
 
-            return $this->httpDownloader->get($url, array(
+            $this->httpDownloader->get($url, array(
                 'retry-auth-failure' => false,
-            )) ? true : 'Unexpected error';
+            ));
+
+            return true;
         } catch (\Exception $e) {
             if ($e instanceof TransportException && $e->getCode() === 401) {
                 return '<comment>The oauth token for '.$domain.' seems invalid, run "composer config --global --unset github-oauth.'.$domain.'" to remove it</comment>';
diff --git a/src/Composer/Command/InitCommand.php b/src/Composer/Command/InitCommand.php
index c710c4e63..e6ebadd25 100644
--- a/src/Composer/Command/InitCommand.php
+++ b/src/Composer/Command/InitCommand.php
@@ -43,7 +43,7 @@ use Symfony\Component\Console\Helper\FormatterHelper;
  */
 class InitCommand extends BaseCommand
 {
-    /** @var CompositeRepository */
+    /** @var ?CompositeRepository */
     protected $repos;
 
     /** @var array */
@@ -705,10 +705,11 @@ EOT
         $finder = new ExecutableFinder();
         $gitBin = $finder->find('git');
 
-        // TODO in v3 always call with an array
+        // TODO in v2.3 always call with an array
         if (method_exists('Symfony\Component\Process\Process', 'fromShellCommandline')) {
             $cmd = new Process(array($gitBin, 'config', '-l'));
         } else {
+            // @phpstan-ignore-next-line
             $cmd = new Process(sprintf('%s config -l', ProcessExecutor::escape($gitBin)));
         }
         $cmd->run();
diff --git a/src/Composer/Command/RequireCommand.php b/src/Composer/Command/RequireCommand.php
index c502cabf2..094b5df55 100644
--- a/src/Composer/Command/RequireCommand.php
+++ b/src/Composer/Command/RequireCommand.php
@@ -320,7 +320,7 @@ EOT
                 'require-dev' => $rootPackage->getDevRequires(),
             );
             $loader = new ArrayLoader();
-            $newLinks = $loader->parseLinks($rootPackage->getName(), $rootPackage->getPrettyVersion(), BasePackage::$supportedLinkTypes[$requireKey]['description'], $requirements);
+            $newLinks = $loader->parseLinks($rootPackage->getName(), $rootPackage->getPrettyVersion(), BasePackage::$supportedLinkTypes[$requireKey]['method'], $requirements);
             $links[$requireKey] = array_merge($links[$requireKey], $newLinks);
             foreach ($requirements as $package => $constraint) {
                 unset($links[$removeKey][$package]);
diff --git a/src/Composer/Command/ShowCommand.php b/src/Composer/Command/ShowCommand.php
index 765788772..dd26bbe7c 100644
--- a/src/Composer/Command/ShowCommand.php
+++ b/src/Composer/Command/ShowCommand.php
@@ -54,7 +54,7 @@ class ShowCommand extends BaseCommand
     protected $versionParser;
     protected $colors;
 
-    /** @var RepositorySet */
+    /** @var ?RepositorySet */
     private $repositorySet;
 
     protected function configure()
@@ -311,12 +311,6 @@ EOT
             return 0;
         }
 
-        if ($repos instanceof CompositeRepository) {
-            $repos = $repos->getRepositories();
-        } elseif (!is_array($repos)) {
-            $repos = array($repos);
-        }
-
         // list packages
         $packages = array();
         $packageFilterRegex = null;
@@ -334,7 +328,7 @@ EOT
             $input->setOption('path', false);
         }
 
-        foreach ($repos as $repo) {
+        foreach ($repos->getRepositories() as $repo) {
             if ($repo === $platformRepo) {
                 $type = 'platform';
             } elseif ($lockedRepo !== null && $repo === $lockedRepo) {
@@ -1245,6 +1239,9 @@ EOT
         return $candidate;
     }
 
+    /**
+     * @return RepositorySet
+     */
     private function getRepositorySet(Composer $composer)
     {
         if (!$this->repositorySet) {
diff --git a/src/Composer/Command/UpdateCommand.php b/src/Composer/Command/UpdateCommand.php
index 86167c1b3..0fe582299 100644
--- a/src/Composer/Command/UpdateCommand.php
+++ b/src/Composer/Command/UpdateCommand.php
@@ -315,6 +315,7 @@ EOT
             $link->getSource(),
             $link->getTarget(),
             $newConstraint,
+            /** @phpstan-ignore-next-line */
             $link->getDescription(),
             $link->getPrettyConstraint() . ', ' . $constraint
         );
diff --git a/src/Composer/Compiler.php b/src/Composer/Compiler.php
index 1bec4a513..a0f303f9f 100644
--- a/src/Composer/Compiler.php
+++ b/src/Composer/Compiler.php
@@ -43,13 +43,25 @@ class Compiler
             unlink($pharFile);
         }
 
-        $process = new Process('git log --pretty="%H" -n1 HEAD', __DIR__);
+        // TODO in v2.3 always call with an array
+        if (method_exists('Symfony\Component\Process\Process', 'fromShellCommandline')) {
+            $process = new Process(array('git', 'log', '--pretty="%H"', '-n1', 'HEAD'), __DIR__);
+        } else {
+            // @phpstan-ignore-next-line
+            $process = new Process('git log --pretty="%H" -n1 HEAD', __DIR__);
+        }
         if ($process->run() != 0) {
             throw new \RuntimeException('Can\'t run git log. You must ensure to run compile from composer git repository clone and that git binary is available.');
         }
         $this->version = trim($process->getOutput());
 
-        $process = new Process('git log -n1 --pretty=%ci HEAD', __DIR__);
+        // TODO in v2.3 always call with an array
+        if (method_exists('Symfony\Component\Process\Process', 'fromShellCommandline')) {
+            $process = new Process(array('git', 'log', '-n1', '--pretty=%ci', 'HEAD'), __DIR__);
+        } else {
+            // @phpstan-ignore-next-line
+            $process = new Process('git log -n1 --pretty=%ci HEAD', __DIR__);
+        }
         if ($process->run() != 0) {
             throw new \RuntimeException('Can\'t run git log. You must ensure to run compile from composer git repository clone and that git binary is available.');
         }
@@ -57,7 +69,13 @@ class Compiler
         $this->versionDate = new \DateTime(trim($process->getOutput()));
         $this->versionDate->setTimezone(new \DateTimeZone('UTC'));
 
-        $process = new Process('git describe --tags --exact-match HEAD');
+        // TODO in v2.3 always call with an array
+        if (method_exists('Symfony\Component\Process\Process', 'fromShellCommandline')) {
+            $process = new Process(array('git', 'describe', '--tags', '--exact-match', 'HEAD'), __DIR__);
+        } else {
+            // @phpstan-ignore-next-line
+            $process = new Process('git describe --tags --exact-match HEAD');
+        }
         if ($process->run() == 0) {
             $this->version = trim($process->getOutput());
         } else {
diff --git a/src/Composer/Composer.php b/src/Composer/Composer.php
index 16f29f113..e2bcc0225 100644
--- a/src/Composer/Composer.php
+++ b/src/Composer/Composer.php
@@ -88,9 +88,9 @@ class Composer
     private $package;
 
     /**
-     * @var Locker
+     * @var ?Locker
      */
-    private $locker;
+    private $locker = null;
 
     /**
      * @var Loop
@@ -179,7 +179,7 @@ class Composer
     }
 
     /**
-     * @return Locker
+     * @return ?Locker
      */
     public function getLocker()
     {
diff --git a/src/Composer/Console/Application.php b/src/Composer/Console/Application.php
index 245547f6e..c4a93d10f 100644
--- a/src/Composer/Console/Application.php
+++ b/src/Composer/Console/Application.php
@@ -77,8 +77,8 @@ class Application extends BaseApplication
         static $shutdownRegistered = false;
 
         if (function_exists('ini_set') && extension_loaded('xdebug')) {
-            ini_set('xdebug.show_exception_trace', false);
-            ini_set('xdebug.scream', false);
+            ini_set('xdebug.show_exception_trace', '0');
+            ini_set('xdebug.scream', '0');
         }
 
         if (function_exists('date_default_timezone_set') && function_exists('date_default_timezone_get')) {
@@ -408,7 +408,8 @@ class Application extends BaseApplication
      * @param  bool                    $required
      * @param  bool|null               $disablePlugins
      * @throws JsonValidationException
-     * @return \Composer\Composer
+     * @throws \InvalidArgumentException
+     * @return ?\Composer\Composer If $required is true then the return value is guaranteed
      */
     public function getComposer($required = true, $disablePlugins = null)
     {
@@ -444,7 +445,7 @@ class Application extends BaseApplication
     public function resetComposer()
     {
         $this->composer = null;
-        if ($this->getIO() && method_exists($this->getIO(), 'resetAuthentications')) {
+        if (method_exists($this->getIO(), 'resetAuthentications')) {
             $this->getIO()->resetAuthentications();
         }
     }
diff --git a/src/Composer/DependencyResolver/GenericRule.php b/src/Composer/DependencyResolver/GenericRule.php
index 10ea9c335..39c4783ed 100644
--- a/src/Composer/DependencyResolver/GenericRule.php
+++ b/src/Composer/DependencyResolver/GenericRule.php
@@ -14,6 +14,7 @@ namespace Composer\DependencyResolver;
 
 use Composer\Package\BasePackage;
 use Composer\Package\Link;
+use Composer\Semver\Constraint\ConstraintInterface;
 
 /**
  * @author Nils Adermann <naderman@naderman.de>
@@ -23,9 +24,11 @@ class GenericRule extends Rule
     protected $literals;
 
     /**
-     * @param array                     $literals
-     * @param int|null                  $reason     A RULE_* constant describing the reason for generating this rule
-     * @param Link|BasePackage|int|null $reasonData
+     * @param array                           $literals
+     * @param int|null                        $reason     A RULE_* constant describing the reason for generating this rule
+     * @param Link|BasePackage|int|null|array $reasonData
+     *
+     * @phpstan-param Link|BasePackage|int|null|array{packageName: string, constraint: ConstraintInterface} $reasonData
      */
     public function __construct(array $literals, $reason, $reasonData)
     {
diff --git a/src/Composer/DependencyResolver/LockTransaction.php b/src/Composer/DependencyResolver/LockTransaction.php
index eb5dead6b..3a3d94505 100644
--- a/src/Composer/DependencyResolver/LockTransaction.php
+++ b/src/Composer/DependencyResolver/LockTransaction.php
@@ -13,7 +13,8 @@
 namespace Composer\DependencyResolver;
 
 use Composer\Package\AliasPackage;
-use Composer\Package\RootAliasPackage;
+use Composer\Package\BasePackage;
+use Composer\Package\Package;
 
 /**
  * @author Nils Adermann <naderman@naderman.de>
@@ -23,22 +24,32 @@ class LockTransaction extends Transaction
 {
     /**
      * packages in current lock file, platform repo or otherwise present
-     * @var array
+     *
+     * Indexed by spl_object_hash
+     *
+     * @var array<string, BasePackage>
      */
     protected $presentMap;
 
     /**
      * Packages which cannot be mapped, platform repo, root package, other fixed repos
-     * @var array
+     *
+     * Indexed by package id
+     *
+     * @var array<int, BasePackage>
      */
     protected $unlockableMap;
 
     /**
-     * @var array
+     * @var array{dev: BasePackage[], non-dev: BasePackage[], all: BasePackage[]}
      */
     protected $resultPackages;
 
-    public function __construct(Pool $pool, $presentMap, $unlockableMap, $decisions)
+    /**
+     * @param array<string, BasePackage> $presentMap
+     * @param array<int, BasePackage> $unlockableMap
+     */
+    public function __construct(Pool $pool, array $presentMap, array $unlockableMap, Decisions $decisions)
     {
         $this->presentMap = $presentMap;
         $this->unlockableMap = $unlockableMap;
@@ -88,7 +99,7 @@ class LockTransaction extends Transaction
     {
         $packages = array();
         foreach ($this->resultPackages[$devMode ? 'dev' : 'non-dev'] as $package) {
-            if (!($package instanceof AliasPackage) && !($package instanceof RootAliasPackage)) {
+            if (!$package instanceof AliasPackage) {
                 // if we're just updating mirrors we need to reset references to the same as currently "present" packages' references to keep the lock file as-is
                 // we do not reset references if the currently present package didn't have any, or if the type of VCS has changed
                 if ($updateMirrors && !isset($this->presentMap[spl_object_hash($package)])) {
@@ -97,7 +108,7 @@ class LockTransaction extends Transaction
                             if ($presentPackage->getSourceReference() && $presentPackage->getSourceType() === $package->getSourceType()) {
                                 $package->setSourceDistReferences($presentPackage->getSourceReference());
                             }
-                            if ($presentPackage->getReleaseDate()) {
+                            if ($presentPackage->getReleaseDate() && $package instanceof Package) {
                                 $package->setReleaseDate($presentPackage->getReleaseDate());
                             }
                         }
diff --git a/src/Composer/DependencyResolver/Pool.php b/src/Composer/DependencyResolver/Pool.php
index ceb8777ee..5fd5ff607 100644
--- a/src/Composer/DependencyResolver/Pool.php
+++ b/src/Composer/DependencyResolver/Pool.php
@@ -202,7 +202,7 @@ class Pool implements \Countable
         $str = "Pool:\n";
 
         foreach ($this->packages as $package) {
-            $str .= '- '.str_pad($package->id, 6, ' ', STR_PAD_LEFT).': '.$package->getName()."\n";
+            $str .= '- '.str_pad((string) $package->id, 6, ' ', STR_PAD_LEFT).': '.$package->getName()."\n";
         }
 
         return $str;
diff --git a/src/Composer/DependencyResolver/PoolBuilder.php b/src/Composer/DependencyResolver/PoolBuilder.php
index f4500cc0d..a8a4ecbee 100644
--- a/src/Composer/DependencyResolver/PoolBuilder.php
+++ b/src/Composer/DependencyResolver/PoolBuilder.php
@@ -17,6 +17,7 @@ use Composer\IO\IOInterface;
 use Composer\Package\AliasPackage;
 use Composer\Package\BasePackage;
 use Composer\Package\CompleteAliasPackage;
+use Composer\Package\CompletePackage;
 use Composer\Package\CompletePackageInterface;
 use Composer\Package\PackageInterface;
 use Composer\Package\Version\StabilityFilter;
@@ -38,10 +39,12 @@ class PoolBuilder
 {
     /**
      * @var int[]
+     * @phpstan-var array<string, BasePackage::STABILITY_*>
      */
     private $acceptableStabilities;
     /**
      * @var int[]
+     * @phpstan-var array<string, BasePackage::STABILITY_*>
      */
     private $stabilityFlags;
     /**
@@ -55,7 +58,7 @@ class PoolBuilder
      */
     private $rootReferences;
     /**
-     * @var EventDispatcher
+     * @var ?EventDispatcher
      */
     private $eventDispatcher;
     /**
@@ -340,7 +343,7 @@ class PoolBuilder
         }
     }
 
-    private function loadPackage(Request $request, PackageInterface $package, $propagateUpdate = true)
+    private function loadPackage(Request $request, BasePackage $package, $propagateUpdate = true)
     {
         $index = $this->indexCounter++;
         $this->packages[$index] = $package;
@@ -370,7 +373,7 @@ class PoolBuilder
             } else {
                 $basePackage = $package;
             }
-            if ($basePackage instanceof CompletePackageInterface) {
+            if ($basePackage instanceof CompletePackage) {
                 $aliasPackage = new CompleteAliasPackage($basePackage, $alias['alias_normalized'], $alias['alias']);
             } else {
                 $aliasPackage = new AliasPackage($basePackage, $alias['alias_normalized'], $alias['alias']);
diff --git a/src/Composer/DependencyResolver/Problem.php b/src/Composer/DependencyResolver/Problem.php
index 5248dbadf..6a490dd1d 100644
--- a/src/Composer/DependencyResolver/Problem.php
+++ b/src/Composer/DependencyResolver/Problem.php
@@ -18,6 +18,7 @@ use Composer\Package\RootPackageInterface;
 use Composer\Repository\RepositorySet;
 use Composer\Repository\LockArrayRepository;
 use Composer\Semver\Constraint\Constraint;
+use Composer\Semver\Constraint\ConstraintInterface;
 use Composer\Package\Version\VersionParser;
 
 /**
@@ -459,7 +460,7 @@ class Problem
     /**
      * Turns a constraint into text usable in a sentence describing a request
      *
-     * @param  \Composer\Semver\Constraint\ConstraintInterface $constraint
+     * @param  ?ConstraintInterface $constraint
      * @return string
      */
     protected static function constraintToText($constraint)
diff --git a/src/Composer/Downloader/DownloadManager.php b/src/Composer/Downloader/DownloadManager.php
index f55cb9a28..736baf920 100644
--- a/src/Composer/Downloader/DownloadManager.php
+++ b/src/Composer/Downloader/DownloadManager.php
@@ -401,7 +401,7 @@ class DownloadManager
     }
 
     /**
-     * @return string[]
+     * @return array<'dist'|'source'>&non-empty-array
      */
     private function getAvailableSources(PackageInterface $package, PackageInterface $prevPackage = null)
     {
diff --git a/src/Composer/Downloader/FileDownloader.php b/src/Composer/Downloader/FileDownloader.php
index b732cad9b..7683d3d21 100644
--- a/src/Composer/Downloader/FileDownloader.php
+++ b/src/Composer/Downloader/FileDownloader.php
@@ -51,9 +51,9 @@ class FileDownloader implements DownloaderInterface, ChangeReportInterface
     protected $httpDownloader;
     /** @var Filesystem */
     protected $filesystem;
-    /** @var Cache */
+    /** @var ?Cache */
     protected $cache;
-    /** @var EventDispatcher */
+    /** @var ?EventDispatcher */
     protected $eventDispatcher;
     /** @var ProcessExecutor */
     protected $process;
diff --git a/src/Composer/Factory.php b/src/Composer/Factory.php
index 6aed45454..d67ccf29a 100644
--- a/src/Composer/Factory.php
+++ b/src/Composer/Factory.php
@@ -38,6 +38,7 @@ use Composer\Autoload\AutoloadGenerator;
 use Composer\Package\Version\VersionParser;
 use Composer\Downloader\TransportException;
 use Composer\Json\JsonValidationException;
+use Composer\Repository\InstalledRepositoryInterface;
 use Seld\JsonLint\JsonParser;
 
 /**
@@ -434,9 +435,7 @@ class Factory
 
             // once everything is initialized we can
             // purge packages from local repos if they have been deleted on the filesystem
-            if ($rm->getLocalRepository()) {
-                $this->purgePackages($rm->getLocalRepository(), $im);
-            }
+            $this->purgePackages($rm->getLocalRepository(), $im);
         }
 
         return $composer;
@@ -585,10 +584,10 @@ class Factory
     }
 
     /**
-     * @param WritableRepositoryInterface   $repo repository to purge packages from
+     * @param InstalledRepositoryInterface   $repo repository to purge packages from
      * @param Installer\InstallationManager $im   manager to check whether packages are still installed
      */
-    protected function purgePackages(WritableRepositoryInterface $repo, Installer\InstallationManager $im)
+    protected function purgePackages(InstalledRepositoryInterface $repo, Installer\InstallationManager $im)
     {
         foreach ($repo->getPackages() as $package) {
             if (!$im->isPackageInstalled($repo, $package)) {
@@ -632,7 +631,7 @@ class Factory
         if (isset($_SERVER['argv']) && in_array('disable-tls', $_SERVER['argv']) && (in_array('conf', $_SERVER['argv']) || in_array('config', $_SERVER['argv']))) {
             $warned = true;
             $disableTls = !extension_loaded('openssl');
-        } elseif ($config && $config->get('disable-tls') === true) {
+        } elseif ($config->get('disable-tls') === true) {
             if (!$warned) {
                 $io->writeError('<warning>You are running Composer with SSL/TLS protection disabled.</warning>');
             }
@@ -644,10 +643,10 @@ class Factory
         }
         $httpDownloaderOptions = array();
         if ($disableTls === false) {
-            if ($config && $config->get('cafile')) {
+            if ($config->get('cafile')) {
                 $httpDownloaderOptions['ssl']['cafile'] = $config->get('cafile');
             }
-            if ($config && $config->get('capath')) {
+            if ($config->get('capath')) {
                 $httpDownloaderOptions['ssl']['capath'] = $config->get('capath');
             }
             $httpDownloaderOptions = array_replace_recursive($httpDownloaderOptions, $options);
diff --git a/src/Composer/IO/ConsoleIO.php b/src/Composer/IO/ConsoleIO.php
index 1b790ad5e..d6aa538c1 100644
--- a/src/Composer/IO/ConsoleIO.php
+++ b/src/Composer/IO/ConsoleIO.php
@@ -159,13 +159,6 @@ class ConsoleIO extends BaseIO
             return;
         }
 
-        // hack to keep our usage BC with symfony<2.8 versions
-        // this removes the quiet output but there is no way around it
-        // see https://github.com/composer/composer/pull/4913
-        if (OutputInterface::VERBOSITY_QUIET === 0) {
-            $sfVerbosity = OutputInterface::OUTPUT_NORMAL;
-        }
-
         if ($raw) {
             if ($sfVerbosity === OutputInterface::OUTPUT_NORMAL) {
                 $sfVerbosity = OutputInterface::OUTPUT_RAW;
diff --git a/src/Composer/InstalledVersions.php b/src/Composer/InstalledVersions.php
index b3a4e1611..9809a2190 100644
--- a/src/Composer/InstalledVersions.php
+++ b/src/Composer/InstalledVersions.php
@@ -228,7 +228,7 @@ class InstalledVersions
 
     /**
      * @return array
-     * @psalm-return array{name: string, version: string, reference: string, pretty_version: string, aliases: string[], dev: bool, install_path: string}
+     * @psalm-return array{name: string, version: string, reference: string, pretty_version: string, aliases: string[], dev: bool, install_path: string, type: string}
      */
     public static function getRootPackage()
     {
@@ -242,7 +242,7 @@ class InstalledVersions
      *
      * @deprecated Use getAllRawData() instead which returns all datasets for all autoloaders present in the process. getRawData only returns the first dataset loaded, which may not be what you expect.
      * @return array[]
-     * @psalm-return array{root: array{name: string, version: string, reference: string, pretty_version: string, aliases: string[], dev: bool, install_path: string}, versions: array<string, array{dev_requirement: bool, pretty_version?: string, version?: string, aliases?: string[], reference?: string, replaced?: string[], provided?: string[], install_path?: string}>}
+     * @psalm-return array{root: array{name: string, version: string, reference: string, pretty_version: string, aliases: string[], dev: bool, install_path: string, type: string}, versions: array<string, array{dev_requirement: bool, pretty_version?: string, version?: string, aliases?: string[], reference?: string, replaced?: string[], provided?: string[], install_path?: string, type?: string}>}
      */
     public static function getRawData()
     {
@@ -265,7 +265,7 @@ class InstalledVersions
      * Returns the raw data of all installed.php which are currently loaded for custom implementations
      *
      * @return array[]
-     * @psalm-return list<array{root: array{name: string, version: string, reference: string, pretty_version: string, aliases: string[], dev: bool, install_path: string}, versions: array<string, array{dev_requirement: bool, pretty_version?: string, version?: string, aliases?: string[], reference?: string, replaced?: string[], provided?: string[], install_path?: string}>}>
+     * @psalm-return list<array{root: array{name: string, version: string, reference: string, pretty_version: string, aliases: string[], dev: bool, install_path: string, type: string}, versions: array<string, array{dev_requirement: bool, pretty_version?: string, version?: string, aliases?: string[], reference?: string, replaced?: string[], provided?: string[], install_path?: string, type?: string}>}>
      */
     public static function getAllRawData()
     {
@@ -288,7 +288,7 @@ class InstalledVersions
      * @param  array[] $data A vendor/composer/installed.php data set
      * @return void
      *
-     * @psalm-param array{root: array{name: string, version: string, reference: string, pretty_version: string, aliases: string[], dev: bool, install_path: string}, versions: array<string, array{dev_requirement: bool, pretty_version?: string, version?: string, aliases?: string[], reference?: string, replaced?: string[], provided?: string[], install_path?: string}>} $data
+     * @psalm-param array{root: array{name: string, version: string, reference: string, pretty_version: string, aliases: string[], dev: bool, install_path: string, type: string}, versions: array<string, array{dev_requirement: bool, pretty_version?: string, version?: string, aliases?: string[], reference?: string, replaced?: string[], provided?: string[], install_path?: string, type?: string}>} $data
      */
     public static function reload($data)
     {
@@ -298,7 +298,7 @@ class InstalledVersions
 
     /**
      * @return array[]
-     * @psalm-return list<array{root: array{name: string, version: string, reference: string, pretty_version: string, aliases: string[], dev: bool, install_path: string}, versions: array<string, array{dev_requirement: bool, pretty_version?: string, version?: string, aliases?: string[], reference?: string, replaced?: string[], provided?: string[], install_path?: string}>}>
+     * @psalm-return list<array{root: array{name: string, version: string, reference: string, pretty_version: string, aliases: string[], dev: bool, install_path: string, type: string}, versions: array<string, array{dev_requirement: bool, pretty_version?: string, version?: string, aliases?: string[], reference?: string, replaced?: string[], provided?: string[], install_path?: string, type?: string}>}>
      */
     private static function getInstalled()
     {
diff --git a/src/Composer/Installer.php b/src/Composer/Installer.php
index 6cf057172..d04005132 100644
--- a/src/Composer/Installer.php
+++ b/src/Composer/Installer.php
@@ -152,7 +152,7 @@ class Installer
     protected $suggestedPackagesReporter;
 
     /**
-     * @var RepositoryInterface
+     * @var ?RepositoryInterface
      */
     protected $additionalFixedRepository;
 
@@ -180,6 +180,7 @@ class Installer
         $this->installationManager = $installationManager;
         $this->eventDispatcher = $eventDispatcher;
         $this->autoloadGenerator = $autoloadGenerator;
+        $this->suggestedPackagesReporter = new SuggestedPackagesReporter($this->io);
 
         $this->writeLock = $config->get('lock');
     }
@@ -238,10 +239,6 @@ class Installer
 
         $localRepo = $this->repositoryManager->getLocalRepository();
 
-        if (!$this->suggestedPackagesReporter) {
-            $this->suggestedPackagesReporter = new SuggestedPackagesReporter($this->io);
-        }
-
         try {
             if ($this->update) {
                 $res = $this->doUpdate($localRepo, $this->install);
diff --git a/src/Composer/Installer/InstallationManager.php b/src/Composer/Installer/InstallationManager.php
index fb3e28f78..c7f43a5bf 100644
--- a/src/Composer/Installer/InstallationManager.php
+++ b/src/Composer/Installer/InstallationManager.php
@@ -47,7 +47,7 @@ class InstallationManager
     private $loop;
     /** @var IOInterface */
     private $io;
-    /** @var EventDispatcher */
+    /** @var ?EventDispatcher */
     private $eventDispatcher;
     /** @var bool */
     private $outputProgress;
@@ -179,6 +179,7 @@ class InstallationManager
      */
     public function execute(InstalledRepositoryInterface $repo, array $operations, $devMode = true, $runScripts = true)
     {
+        /** @var PromiseInterface[] */
         $cleanupPromises = array();
 
         $loop = $this->loop;
diff --git a/src/Composer/Json/JsonFile.php b/src/Composer/Json/JsonFile.php
index 1b662fa91..53cf5534f 100644
--- a/src/Composer/Json/JsonFile.php
+++ b/src/Composer/Json/JsonFile.php
@@ -291,7 +291,7 @@ class JsonFile
     /**
      * Parses json string and returns hash.
      *
-     * @param string $json json string
+     * @param ?string $json json string
      * @param string $file the json file
      *
      * @throws ParsingException
@@ -300,7 +300,7 @@ class JsonFile
     public static function parseJson($json, $file = null)
     {
         if (null === $json) {
-            return;
+            return null;
         }
         $data = json_decode($json, true);
         if (null === $data && JSON_ERROR_NONE !== json_last_error()) {
diff --git a/src/Composer/Package/AliasPackage.php b/src/Composer/Package/AliasPackage.php
index 42d38b6b6..c993230c6 100644
--- a/src/Composer/Package/AliasPackage.php
+++ b/src/Composer/Package/AliasPackage.php
@@ -113,6 +113,7 @@ class AliasPackage extends BasePackage
 
     /**
      * {@inheritDoc}
+     * @return array<string|int, Link>
      */
     public function getConflicts()
     {
@@ -121,6 +122,7 @@ class AliasPackage extends BasePackage
 
     /**
      * {@inheritDoc}
+     * @return array<string|int, Link>
      */
     public function getProvides()
     {
@@ -129,6 +131,7 @@ class AliasPackage extends BasePackage
 
     /**
      * {@inheritDoc}
+     * @return array<string|int, Link>
      */
     public function getReplaces()
     {
@@ -167,8 +170,8 @@ class AliasPackage extends BasePackage
     }
 
     /**
-     * @param Link[] $links
-     * @param string $linkType
+     * @param Link[]       $links
+     * @param Link::TYPE_* $linkType
      *
      * @return Link[]
      */
diff --git a/src/Composer/Package/BasePackage.php b/src/Composer/Package/BasePackage.php
index f8199a0bb..04a57f5bc 100644
--- a/src/Composer/Package/BasePackage.php
+++ b/src/Composer/Package/BasePackage.php
@@ -24,6 +24,7 @@ abstract class BasePackage implements PackageInterface
 {
     /**
      * @phpstan-var array<string, array{description: string, method: Link::TYPE_*}>
+     * @internal
      */
     public static $supportedLinkTypes = array(
         'require' => array('description' => 'requires', 'method' => Link::TYPE_REQUIRE),
diff --git a/src/Composer/Package/Link.php b/src/Composer/Package/Link.php
index 955eb8e97..af08705df 100644
--- a/src/Composer/Package/Link.php
+++ b/src/Composer/Package/Link.php
@@ -26,6 +26,12 @@ class Link
     const TYPE_PROVIDE = 'provides';
     const TYPE_CONFLICT = 'conflicts';
     const TYPE_REPLACE = 'replaces';
+
+    /**
+     * Special type
+     * @internal
+     */
+    const TYPE_DOES_NOT_REQUIRE = 'does not require';
     /**
      * TODO should be marked private once 5.3 is dropped
      * @private
@@ -37,6 +43,7 @@ class Link
      *
      * @internal
      * @var string[]
+     * @phpstan-var array<self::TYPE_REQUIRE|self::TYPE_DEV_REQUIRE|self::TYPE_PROVIDE|self::TYPE_CONFLICT|self::TYPE_REPLACE>
      */
     public static $TYPES = array(
         self::TYPE_REQUIRE,
@@ -63,12 +70,12 @@ class Link
 
     /**
      * @var string
-     * @phpstan-var self::TYPE_* $description
+     * @phpstan-var string $description
      */
     protected $description;
 
     /**
-     * @var string|null
+     * @var ?string
      */
     protected $prettyConstraint;
 
@@ -91,7 +98,7 @@ class Link
         $this->source = strtolower($source);
         $this->target = strtolower($target);
         $this->constraint = $constraint;
-        $this->description = $description;
+        $this->description = self::TYPE_DEV_REQUIRE === $description ? 'requires (for development)' : $description;
         $this->prettyConstraint = $prettyConstraint;
     }
 
@@ -154,6 +161,6 @@ class Link
      */
     public function getPrettyString(PackageInterface $sourcePackage)
     {
-        return $sourcePackage->getPrettyString().' '.$this->description.' '.$this->target.($this->constraint ? ' '.$this->constraint->getPrettyString() : '');
+        return $sourcePackage->getPrettyString().' '.$this->description.' '.$this->target.' '.$this->constraint->getPrettyString();
     }
 }
diff --git a/src/Composer/Package/Loader/ArrayLoader.php b/src/Composer/Package/Loader/ArrayLoader.php
index 1f3843f3e..4367b9a3a 100644
--- a/src/Composer/Package/Loader/ArrayLoader.php
+++ b/src/Composer/Package/Loader/ArrayLoader.php
@@ -45,9 +45,12 @@ class ArrayLoader implements LoaderInterface
 
     /**
      * @template PackageClass of CompletePackageInterface
-     * @param  array                                $config package data
-     * @param  string                               $class  FQCN to be instantiated
-     * @return CompletePackage|CompleteAliasPackage
+     *
+     * @param  array  $config package data
+     * @param  string $class  FQCN to be instantiated
+     *
+     * @return CompletePackage|CompleteAliasPackage|RootPackage|RootAliasPackage
+     *
      * @phpstan-param class-string<PackageClass> $class
      */
     public function load(array $config, $class = 'Composer\Package\CompletePackage')
@@ -65,7 +68,7 @@ class ArrayLoader implements LoaderInterface
                     $this->parseLinks(
                         $package->getName(),
                         $package->getPrettyVersion(),
-                        $opts['description'],
+                        $opts['method'],
                         $config[$type]
                     )
                 );
@@ -78,23 +81,16 @@ class ArrayLoader implements LoaderInterface
     }
 
     /**
-     * @template PackageClass of CompletePackageInterface
      * @param  array                                      $versions
-     * @param  string                                     $class    FQCN to be instantiated
      * @return list<CompletePackage|CompleteAliasPackage>
-     * @phpstan-param class-string<PackageClass> $class
      */
-    public function loadPackages(array $versions, $class = 'Composer\Package\CompletePackage')
+    public function loadPackages(array $versions)
     {
-        if ($class !== 'Composer\Package\CompletePackage') {
-            trigger_error('The $class arg is deprecated, please reach out to Composer maintainers ASAP if you still need this.', E_USER_DEPRECATED);
-        }
-
         $packages = array();
         $linkCache = array();
 
         foreach ($versions as $version) {
-            $package = $this->createObject($version, $class);
+            $package = $this->createObject($version, 'Composer\Package\CompletePackage');
 
             $this->configureCachedLinks($linkCache, $package, $version);
             $package = $this->configureObject($package, $version);
@@ -137,14 +133,14 @@ class ArrayLoader implements LoaderInterface
     }
 
     /**
-     * @param  CompletePackageInterface                                          $package
+     * @param  CompletePackage                                                   $package
      * @param  array                                                             $config  package data
      * @return RootPackage|RootAliasPackage|CompletePackage|CompleteAliasPackage
      */
     private function configureObject(PackageInterface $package, array $config)
     {
-        if (!$package instanceof Package) {
-            throw new \LogicException('ArrayLoader expects instances of the Composer\Package\Package class to function correctly');
+        if (!$package instanceof CompletePackage) {
+            throw new \LogicException('ArrayLoader expects instances of the Composer\Package\CompletePackage class to function correctly');
         }
 
         $package->setType(isset($config['type']) ? strtolower($config['type']) : 'library');
@@ -302,15 +298,11 @@ class ArrayLoader implements LoaderInterface
         if ($aliasNormalized = $this->getBranchAlias($config)) {
             $prettyAlias = preg_replace('{(\.9{7})+}', '.x', $aliasNormalized);
 
-            if ($package instanceof RootPackageInterface) {
+            if ($package instanceof RootPackage) {
                 return new RootAliasPackage($package, $aliasNormalized, $prettyAlias);
             }
 
-            if ($package instanceof CompletePackageInterface) {
-                return new CompleteAliasPackage($package, $aliasNormalized, $prettyAlias);
-            }
-
-            return new AliasPackage($package, $aliasNormalized, $prettyAlias);
+            return new CompleteAliasPackage($package, $aliasNormalized, $prettyAlias);
         }
 
         return $package;
@@ -335,10 +327,10 @@ class ArrayLoader implements LoaderInterface
                 foreach ($config[$type] as $prettyTarget => $constraint) {
                     $target = strtolower($prettyTarget);
                     if ($constraint === 'self.version') {
-                        $links[$target] = $this->createLink($name, $prettyVersion, $opts['description'], $target, $constraint);
+                        $links[$target] = $this->createLink($name, $prettyVersion, $opts['method'], $target, $constraint);
                     } else {
                         if (!isset($linkCache[$name][$type][$target][$constraint])) {
-                            $linkCache[$name][$type][$target][$constraint] = array($target, $this->createLink($name, $prettyVersion, $opts['description'], $target, $constraint));
+                            $linkCache[$name][$type][$target][$constraint] = array($target, $this->createLink($name, $prettyVersion, $opts['method'], $target, $constraint));
                         }
 
                         list($target, $link) = $linkCache[$name][$type][$target][$constraint];
diff --git a/src/Composer/Package/Locker.php b/src/Composer/Package/Locker.php
index 4bbbb1d4c..2ab1e2052 100644
--- a/src/Composer/Package/Locker.php
+++ b/src/Composer/Package/Locker.php
@@ -186,11 +186,7 @@ class Locker
             if (isset($lockData['aliases'])) {
                 foreach ($lockData['aliases'] as $alias) {
                     if (isset($packageByName[$alias['package']])) {
-                        if ($packageByName[$alias['package']] instanceof CompletePackageInterface) {
-                            $aliasPkg = new CompleteAliasPackage($packageByName[$alias['package']], $alias['alias_normalized'], $alias['alias']);
-                        } else {
-                            $aliasPkg = new AliasPackage($packageByName[$alias['package']], $alias['alias_normalized'], $alias['alias']);
-                        }
+                        $aliasPkg = new CompleteAliasPackage($packageByName[$alias['package']], $alias['alias_normalized'], $alias['alias']);
                         $aliasPkg->setRootPackageAlias(true);
                         $packages->addPackage($aliasPkg);
                     }
diff --git a/src/Composer/Package/Package.php b/src/Composer/Package/Package.php
index 9afbd6429..2b3ccb1aa 100644
--- a/src/Composer/Package/Package.php
+++ b/src/Composer/Package/Package.php
@@ -22,46 +22,68 @@ use Composer\Util\ComposerMirror;
  */
 class Package extends BasePackage
 {
+    /** @var string */
     protected $type;
+    /** @var ?string */
     protected $targetDir;
+    /** @var 'source'|'dist'|null */
     protected $installationSource;
+    /** @var ?string */
     protected $sourceType;
+    /** @var ?string */
     protected $sourceUrl;
     /** @var ?string */
     protected $sourceReference;
+    /** @var ?array */
     protected $sourceMirrors;
+    /** @var ?string */
     protected $distType;
+    /** @var ?string */
     protected $distUrl;
     /** @var ?string */
     protected $distReference;
     /** @var ?string */
     protected $distSha1Checksum;
+    /** @var ?array */
     protected $distMirrors;
+    /** @var string */
     protected $version;
+    /** @var string */
     protected $prettyVersion;
+    /** @var ?\DateTime */
     protected $releaseDate;
+    /** @var mixed[] */
     protected $extra = array();
+    /** @var string[] */
     protected $binaries = array();
+    /** @var bool */
     protected $dev;
+    /** @var string */
     protected $stability;
+    /** @var ?string */
     protected $notificationUrl;
 
-    /** @var Link[] */
+    /** @var array<string, Link> */
     protected $requires = array();
-    /** @var Link[] */
+    /** @var array<string, Link> */
     protected $conflicts = array();
-    /** @var Link[] */
+    /** @var array<string, Link> */
     protected $provides = array();
-    /** @var Link[] */
+    /** @var array<string, Link> */
     protected $replaces = array();
-    /** @var Link[] */
+    /** @var array<string, Link> */
     protected $devRequires = array();
+    /** @var array<string, string> */
     protected $suggests = array();
+    /** @var array{psr-0?: array<string, string|string[]>, psr-4?: array<string, string|string[]>, classmap?: list<string>, files?: list<string>} */
     protected $autoload = array();
+    /** @var array{psr-0?: array<string, string|string[]>, psr-4?: array<string, string|string[]>, classmap?: list<string>, files?: list<string>} */
     protected $devAutoload = array();
+    /** @var string[] */
     protected $includePaths = array();
+    /** @var bool */
     protected $isDefaultBranch = false;
-    /** @var array */
+    /** @var mixed[] */
     protected $transportOptions = array();
 
     /**
@@ -395,7 +417,7 @@ class Package extends BasePackage
     /**
      * Set the required packages
      *
-     * @param Link[] $requires A set of package links
+     * @param array<string, Link> $requires A set of package links
      */
     public function setRequires(array $requires)
     {
@@ -413,7 +435,7 @@ class Package extends BasePackage
     /**
      * Set the conflicting packages
      *
-     * @param Link[] $conflicts A set of package links
+     * @param array<string, Link> $conflicts A set of package links
      */
     public function setConflicts(array $conflicts)
     {
@@ -422,6 +444,7 @@ class Package extends BasePackage
 
     /**
      * {@inheritDoc}
+     * @return array<string, Link>
      */
     public function getConflicts()
     {
@@ -431,7 +454,7 @@ class Package extends BasePackage
     /**
      * Set the provided virtual packages
      *
-     * @param Link[] $provides A set of package links
+     * @param array<string, Link> $provides A set of package links
      */
     public function setProvides(array $provides)
     {
@@ -440,6 +463,7 @@ class Package extends BasePackage
 
     /**
      * {@inheritDoc}
+     * @return array<string, Link>
      */
     public function getProvides()
     {
@@ -449,7 +473,7 @@ class Package extends BasePackage
     /**
      * Set the packages this one replaces
      *
-     * @param Link[] $replaces A set of package links
+     * @param array<string, Link> $replaces A set of package links
      */
     public function setReplaces(array $replaces)
     {
@@ -458,6 +482,7 @@ class Package extends BasePackage
 
     /**
      * {@inheritDoc}
+     * @return array<string, Link>
      */
     public function getReplaces()
     {
@@ -467,7 +492,7 @@ class Package extends BasePackage
     /**
      * Set the recommended packages
      *
-     * @param Link[] $devRequires A set of package links
+     * @param array<string, Link> $devRequires A set of package links
      */
     public function setDevRequires(array $devRequires)
     {
@@ -485,7 +510,7 @@ class Package extends BasePackage
     /**
      * Set the suggested packages
      *
-     * @param array $suggests A set of package names/comments
+     * @param array<string, string> $suggests A set of package names/comments
      */
     public function setSuggests(array $suggests)
     {
diff --git a/src/Composer/Package/PackageInterface.php b/src/Composer/Package/PackageInterface.php
index 355cf49f0..c3df0fd63 100644
--- a/src/Composer/Package/PackageInterface.php
+++ b/src/Composer/Package/PackageInterface.php
@@ -82,14 +82,14 @@ interface PackageInterface
     /**
      * Returns the package targetDir property
      *
-     * @return string|null The package targetDir
+     * @return ?string The package targetDir
      */
     public function getTargetDir();
 
     /**
      * Returns the package extra data
      *
-     * @return array The package extra data
+     * @return mixed[] The package extra data
      */
     public function getExtra();
 
@@ -97,27 +97,29 @@ interface PackageInterface
      * Sets source from which this package was installed (source/dist).
      *
      * @param string $type source/dist
+     * @phpstan-param 'source'|'dist'|null $type
      */
     public function setInstallationSource($type);
 
     /**
      * Returns source from which this package was installed (source/dist).
      *
-     * @return string source/dist
+     * @return ?string source/dist
+     * @phpstan-return 'source'|'dist'|null
      */
     public function getInstallationSource();
 
     /**
      * Returns the repository type of this package, e.g. git, svn
      *
-     * @return string The repository type
+     * @return ?string The repository type
      */
     public function getSourceType();
 
     /**
      * Returns the repository url of this package, e.g. git://github.com/naderman/composer.git
      *
-     * @return string The repository url
+     * @return ?string The repository url
      */
     public function getSourceUrl();
 
@@ -138,12 +140,12 @@ interface PackageInterface
     /**
      * Returns the source mirrors of this package
      *
-     * @return array|null
+     * @return ?array
      */
     public function getSourceMirrors();
 
     /**
-     * @param  array|null $mirrors
+     * @param  ?array $mirrors
      * @return void
      */
     public function setSourceMirrors($mirrors);
@@ -151,14 +153,14 @@ interface PackageInterface
     /**
      * Returns the type of the distribution archive of this version, e.g. zip, tarball
      *
-     * @return string The repository type
+     * @return ?string The repository type
      */
     public function getDistType();
 
     /**
      * Returns the url of the distribution archive of this version
      *
-     * @return string
+     * @return ?string
      */
     public function getDistUrl();
 
@@ -186,12 +188,12 @@ interface PackageInterface
     /**
      * Returns the dist mirrors of this package
      *
-     * @return array|null
+     * @return ?array
      */
     public function getDistMirrors();
 
     /**
-     * @param  array|null $mirrors
+     * @param  ?array $mirrors
      * @return void
      */
     public function setDistMirrors($mirrors);
@@ -226,7 +228,7 @@ interface PackageInterface
     /**
      * Returns the release date of the package
      *
-     * @return \DateTime
+     * @return ?\DateTime
      */
     public function getReleaseDate();
 
@@ -241,7 +243,7 @@ interface PackageInterface
      * Returns a set of links to packages which need to be installed before
      * this package can be installed
      *
-     * @return Link[] An array of package links defining required packages
+     * @return array<string, Link> An array of package links defining required packages
      */
     public function getRequires();
 
@@ -273,7 +275,7 @@ interface PackageInterface
      * Returns a set of links to packages which are required to develop
      * this package. These are installed if in dev mode.
      *
-     * @return Link[] An array of package links defining packages required for development
+     * @return array<string, Link> An array of package links defining packages required for development
      */
     public function getDevRequires();
 
@@ -295,7 +297,7 @@ interface PackageInterface
      * directories for autoloading using the type specified.
      *
      * @return array Mapping of autoloading rules
-     * @phpstan-return array{psr-0?: array<string, string>, psr-4?: array<string, string>, classmap?: list<string>, files?: list<string>}
+     * @phpstan-return array{psr-0?: array<string, string|string[]>, psr-4?: array<string, string|string[]>, classmap?: list<string>, files?: list<string>}
      */
     public function getAutoload();
 
@@ -308,7 +310,7 @@ interface PackageInterface
      * directories for autoloading using the type specified.
      *
      * @return array Mapping of dev autoloading rules
-     * @phpstan-return array{psr-0?: array<string, string>, psr-4?: array<string, string>, classmap?: list<string>, files?: list<string>}
+     * @phpstan-return array{psr-0?: array<string, string|string[]>, psr-4?: array<string, string|string[]>, classmap?: list<string>, files?: list<string>}
      */
     public function getDevAutoload();
 
@@ -330,7 +332,7 @@ interface PackageInterface
     /**
      * Returns a reference to the repository that owns the package
      *
-     * @return RepositoryInterface
+     * @return ?RepositoryInterface
      */
     public function getRepository();
 
@@ -351,7 +353,7 @@ interface PackageInterface
     /**
      * Returns the package notification url
      *
-     * @return string
+     * @return ?string
      */
     public function getNotificationUrl();
 
@@ -377,7 +379,7 @@ interface PackageInterface
     /**
      * Returns a list of options to download package dist files
      *
-     * @return array
+     * @return mixed[]
      */
     public function getTransportOptions();
 
diff --git a/src/Composer/Package/RootAliasPackage.php b/src/Composer/Package/RootAliasPackage.php
index 6a71ba740..78139eb02 100644
--- a/src/Composer/Package/RootAliasPackage.php
+++ b/src/Composer/Package/RootAliasPackage.php
@@ -17,23 +17,23 @@ namespace Composer\Package;
  */
 class RootAliasPackage extends CompleteAliasPackage implements RootPackageInterface
 {
-    /** @var RootPackageInterface */
+    /** @var RootPackage */
     protected $aliasOf;
 
     /**
      * All descendants' constructors should call this parent constructor
      *
-     * @param RootPackageInterface $aliasOf       The package this package is an alias of
-     * @param string               $version       The version the alias must report
-     * @param string               $prettyVersion The alias's non-normalized version
+     * @param RootPackage $aliasOf       The package this package is an alias of
+     * @param string      $version       The version the alias must report
+     * @param string      $prettyVersion The alias's non-normalized version
      */
-    public function __construct(RootPackageInterface $aliasOf, $version, $prettyVersion)
+    public function __construct(RootPackage $aliasOf, $version, $prettyVersion)
     {
         parent::__construct($aliasOf, $version, $prettyVersion);
     }
 
     /**
-     * @return RootPackageInterface
+     * @return RootPackage
      */
     public function getAliasOf()
     {
diff --git a/src/Composer/Plugin/PluginManager.php b/src/Composer/Plugin/PluginManager.php
index cd85ac2d3..eb13aad0e 100644
--- a/src/Composer/Plugin/PluginManager.php
+++ b/src/Composer/Plugin/PluginManager.php
@@ -39,7 +39,7 @@ class PluginManager
     protected $composer;
     /** @var IOInterface */
     protected $io;
-    /** @var Composer */
+    /** @var ?Composer */
     protected $globalComposer;
     /** @var VersionParser */
     protected $versionParser;
@@ -82,9 +82,7 @@ class PluginManager
 
         $repo = $this->composer->getRepositoryManager()->getLocalRepository();
         $globalRepo = $this->globalComposer ? $this->globalComposer->getRepositoryManager()->getLocalRepository() : null;
-        if ($repo) {
-            $this->loadRepository($repo, false);
-        }
+        $this->loadRepository($repo, false);
         if ($globalRepo) {
             $this->loadRepository($globalRepo, true);
         }
@@ -259,6 +257,7 @@ class PluginManager
         }
 
         if ($oldInstallerPlugin) {
+            /** @var \Composer\Installer\InstallerInterface $installer */
             $installer = $this->registeredPlugins[$package->getName()];
             unset($this->registeredPlugins[$package->getName()]);
             $this->composer->getInstallationManager()->removeInstaller($installer);
@@ -469,7 +468,7 @@ class PluginManager
             array_key_exists($capability, $capabilities)
             && (empty($capabilities[$capability]) || !is_string($capabilities[$capability]) || !trim($capabilities[$capability]))
         ) {
-            throw new \UnexpectedValueException('Plugin '.get_class($plugin).' provided invalid capability class name(s), got '.var_export($capabilities[$capability], 1));
+            throw new \UnexpectedValueException('Plugin '.get_class($plugin).' provided invalid capability class name(s), got '.var_export($capabilities[$capability], true));
         }
 
         return null;
diff --git a/src/Composer/Plugin/PostFileDownloadEvent.php b/src/Composer/Plugin/PostFileDownloadEvent.php
index c30e00c89..7be34d728 100644
--- a/src/Composer/Plugin/PostFileDownloadEvent.php
+++ b/src/Composer/Plugin/PostFileDownloadEvent.php
@@ -59,6 +59,7 @@ class PostFileDownloadEvent extends Event
      */
     public function __construct($name, $fileName, $checksum, $url, $type, $context = null)
     {
+        /** @phpstan-ignore-next-line */
         if ($context === null && $type instanceof PackageInterface) {
             $context = $type;
             $type = 'package';
diff --git a/src/Composer/Repository/ArrayRepository.php b/src/Composer/Repository/ArrayRepository.php
index 07aa04db1..8b44547a1 100644
--- a/src/Composer/Repository/ArrayRepository.php
+++ b/src/Composer/Repository/ArrayRepository.php
@@ -13,7 +13,9 @@
 namespace Composer\Repository;
 
 use Composer\Package\AliasPackage;
+use Composer\Package\BasePackage;
 use Composer\Package\CompleteAliasPackage;
+use Composer\Package\CompletePackage;
 use Composer\Package\PackageInterface;
 use Composer\Package\CompletePackageInterface;
 use Composer\Package\Version\VersionParser;
@@ -28,11 +30,11 @@ use Composer\Semver\Constraint\Constraint;
  */
 class ArrayRepository implements RepositoryInterface
 {
-    /** @var ?PackageInterface[] */
+    /** @var ?array<PackageInterface&BasePackage> */
     protected $packages = null;
 
     /**
-     * @var ?PackageInterface[] indexed by package unique name and used to cache hasPackage calls
+     * @var ?array<PackageInterface&BasePackage> indexed by package unique name and used to cache hasPackage calls
      */
     protected $packageMap = null;
 
@@ -232,13 +234,17 @@ class ArrayRepository implements RepositoryInterface
         return $result;
     }
 
+    /**
+     * @phpstan-param PackageInterface&BasePackage $package
+     * @return AliasPackage|CompleteAliasPackage
+     */
     protected function createAliasPackage(PackageInterface $package, $alias, $prettyAlias)
     {
         while ($package instanceof AliasPackage) {
             $package = $package->getAliasOf();
         }
 
-        if ($package instanceof CompletePackageInterface) {
+        if ($package instanceof CompletePackage) {
             return new CompleteAliasPackage($package, $alias, $prettyAlias);
         }
 
@@ -275,6 +281,10 @@ class ArrayRepository implements RepositoryInterface
             $this->initialize();
         }
 
+        if (null === $this->packages) {
+            throw new \LogicException('initialize failed to initialize the packages array');
+        }
+
         return $this->packages;
     }
 
diff --git a/src/Composer/Repository/ComposerRepository.php b/src/Composer/Repository/ComposerRepository.php
index b5dea04b4..0aaf458db 100644
--- a/src/Composer/Repository/ComposerRepository.php
+++ b/src/Composer/Repository/ComposerRepository.php
@@ -49,6 +49,7 @@ class ComposerRepository extends ArrayRepository implements ConfigurableReposito
     private $url;
     private $baseUrl;
     private $io;
+    /** @var HttpDownloader */
     private $httpDownloader;
     private $loop;
     protected $cache;
diff --git a/src/Composer/Repository/InstalledRepository.php b/src/Composer/Repository/InstalledRepository.php
index 7405a30bb..13c5fddbb 100644
--- a/src/Composer/Repository/InstalledRepository.php
+++ b/src/Composer/Repository/InstalledRepository.php
@@ -114,7 +114,7 @@ class InstalledRepository extends CompositeRepository
                 foreach ($package->getReplaces() as $link) {
                     foreach ($needles as $needle) {
                         if ($link->getSource() === $needle) {
-                            if ($constraint === null || ($link->getConstraint()->matches($constraint) === !$invert)) {
+                            if ($constraint === null || ($link->getConstraint()->matches($constraint) === true)) {
                                 // already displayed this node's dependencies, cutting short
                                 if (in_array($link->getTarget(), $packagesInTree)) {
                                     $results[] = array($package, $link, false);
@@ -221,7 +221,7 @@ class InstalledRepository extends CompositeRepository
                                 }
 
                                 $results[] = array($package, $link, false);
-                                $results[] = array($rootPackage, new Link($rootPackage->getName(), $link->getTarget(), new MatchAllConstraint, 'does not require', 'but ' . $pkg->getPrettyVersion() . ' is installed'), false);
+                                $results[] = array($rootPackage, new Link($rootPackage->getName(), $link->getTarget(), new MatchAllConstraint, Link::TYPE_DOES_NOT_REQUIRE, 'but ' . $pkg->getPrettyVersion() . ' is installed'), false);
                             } else {
                                 // no root so let's just print whatever we found
                                 $results[] = array($package, $link, false);
diff --git a/src/Composer/Repository/PlatformRepository.php b/src/Composer/Repository/PlatformRepository.php
index 3b08b3e2c..095c86a8a 100644
--- a/src/Composer/Repository/PlatformRepository.php
+++ b/src/Composer/Repository/PlatformRepository.php
@@ -566,7 +566,7 @@ class PlatformRepository extends ArrayRepository
 
         if ($name === 'uuid') {
             $ext->setReplaces(array(
-                new Link('ext-uuid', 'lib-uuid', new Constraint('=', $version), Link::TYPE_REPLACE, $ext->getPrettyVersion()),
+                'lib-uuid' => new Link('ext-uuid', 'lib-uuid', new Constraint('=', $version), Link::TYPE_REPLACE, $ext->getPrettyVersion()),
             ));
         }
 
diff --git a/src/Composer/Repository/RepositoryInterface.php b/src/Composer/Repository/RepositoryInterface.php
index f5f1204d0..3b0760e0e 100644
--- a/src/Composer/Repository/RepositoryInterface.php
+++ b/src/Composer/Repository/RepositoryInterface.php
@@ -44,6 +44,7 @@ interface RepositoryInterface extends \Countable
      * @param string|ConstraintInterface $constraint package version or version constraint to match against
      *
      * @return PackageInterface|null
+     * @phpstan-return (BasePackage&PackageInterface)|null
      */
     public function findPackage($name, $constraint);
 
@@ -54,6 +55,7 @@ interface RepositoryInterface extends \Countable
      * @param string|ConstraintInterface $constraint package version or version constraint to match against
      *
      * @return PackageInterface[]
+     * @phpstan-return array<BasePackage&PackageInterface>
      */
     public function findPackages($name, $constraint = null);
 
@@ -61,6 +63,7 @@ interface RepositoryInterface extends \Countable
      * Returns list of registered packages.
      *
      * @return PackageInterface[]
+     * @phpstan-return array<BasePackage&PackageInterface>
      */
     public function getPackages();
 
@@ -75,7 +78,10 @@ interface RepositoryInterface extends \Countable
      * @param array<string, BasePackage::STABILITY_*>        $stabilityFlags        an array of package name => BasePackage::STABILITY_* value
      * @param array<string, array<string, PackageInterface>> $alreadyLoaded         an array of package name => package version => package
      *
-     * @return array{namesFound: string[], packages: PackageInterface[]}
+     * @return array
+     *
+     * @phpstan-param  array<string, ConstraintInterface|null> $packageNameMap
+     * @phpstan-return array{namesFound: string[], packages: array<BasePackage&PackageInterface>}
      */
     public function loadPackages(array $packageNameMap, array $acceptableStabilities, array $stabilityFlags, array $alreadyLoaded = array());
 
diff --git a/src/Composer/Repository/RepositorySet.php b/src/Composer/Repository/RepositorySet.php
index 66db56833..ae7e2cba8 100644
--- a/src/Composer/Repository/RepositorySet.php
+++ b/src/Composer/Repository/RepositorySet.php
@@ -21,6 +21,7 @@ use Composer\IO\NullIO;
 use Composer\Package\BasePackage;
 use Composer\Package\AliasPackage;
 use Composer\Package\CompleteAliasPackage;
+use Composer\Package\CompletePackage;
 use Composer\Package\CompletePackageInterface;
 use Composer\Semver\Constraint\ConstraintInterface;
 use Composer\Package\Version\StabilityFilter;
@@ -56,13 +57,13 @@ class RepositorySet
 
     /**
      * @var int[] array of stability => BasePackage::STABILITY_* value
-     * @phpstan-var array<string, int>
+     * @phpstan-var array<string, BasePackage::STABILITY_*>
      */
     private $acceptableStabilities;
 
     /**
      * @var int[] array of package name => BasePackage::STABILITY_* value
-     * @phpstan-var array<string, int>
+     * @phpstan-var array<string, BasePackage::STABILITY_*>
      */
     private $stabilityFlags;
 
@@ -80,7 +81,7 @@ class RepositorySet
      *
      * @param string $minimumStability
      * @param int[]  $stabilityFlags   an array of package name => BasePackage::STABILITY_* value
-     * @phpstan-param array<string, int> $stabilityFlags
+     * @phpstan-param array<string, BasePackage::STABILITY_*> $stabilityFlags
      * @param array[] $rootAliases
      * @phpstan-param list<array{package: string, version: string, alias: string, alias_normalized: string}> $rootAliases
      * @param string[] $rootReferences an array of package name => source reference
@@ -254,7 +255,7 @@ class RepositorySet
                     while ($package instanceof AliasPackage) {
                         $package = $package->getAliasOf();
                     }
-                    if ($package instanceof CompletePackageInterface) {
+                    if ($package instanceof CompletePackage) {
                         $aliasPackage = new CompleteAliasPackage($package, $alias['alias_normalized'], $alias['alias']);
                     } else {
                         $aliasPackage = new AliasPackage($package, $alias['alias_normalized'], $alias['alias']);
diff --git a/src/Composer/Repository/Vcs/BitbucketDriver.php b/src/Composer/Repository/Vcs/BitbucketDriver.php
index 1a9a8f6d8..96b4c3298 100644
--- a/src/Composer/Repository/Vcs/BitbucketDriver.php
+++ b/src/Composer/Repository/Vcs/BitbucketDriver.php
@@ -77,6 +77,7 @@ abstract class BitbucketDriver extends VcsDriver
      * sets some parameters which are used in other methods
      *
      * @return bool
+     * @phpstan-impure
      */
     protected function getRepoData()
     {
@@ -363,6 +364,8 @@ abstract class BitbucketDriver extends VcsDriver
      * @param bool   $fetchingRepoData
      *
      * @return Response The result
+     *
+     * @phpstan-impure
      */
     protected function fetchWithOAuthCredentials($url, $fetchingRepoData = false)
     {
@@ -396,6 +399,9 @@ abstract class BitbucketDriver extends VcsDriver
      */
     abstract protected function generateSshUrl();
 
+    /**
+     * @phpstan-impure
+     */
     protected function attemptCloneFallback()
     {
         try {
diff --git a/src/Composer/Repository/Vcs/HgBitbucketDriver.php b/src/Composer/Repository/Vcs/HgBitbucketDriver.php
index 42adcb918..71505cf52 100644
--- a/src/Composer/Repository/Vcs/HgBitbucketDriver.php
+++ b/src/Composer/Repository/Vcs/HgBitbucketDriver.php
@@ -31,12 +31,10 @@ class HgBitbucketDriver extends BitbucketDriver
 
         if (null === $this->rootIdentifier) {
             if (!$this->getRepoData()) {
-                // @phpstan-ignore-next-line
                 if (!$this->fallbackDriver) {
                     throw new \LogicException('A fallback driver should be setup if getRepoData returns false');
                 }
 
-                // @phpstan-ignore-next-line
                 return $this->fallbackDriver->getRootIdentifier();
             }
 
diff --git a/src/Composer/Repository/Vcs/VcsDriver.php b/src/Composer/Repository/Vcs/VcsDriver.php
index 8927a0dcc..ae86e44a7 100644
--- a/src/Composer/Repository/Vcs/VcsDriver.php
+++ b/src/Composer/Repository/Vcs/VcsDriver.php
@@ -157,6 +157,7 @@ abstract class VcsDriver implements VcsDriverInterface
      * @param string $url The URL of content
      *
      * @return Response
+     * @throws TransportException
      */
     protected function getContents($url)
     {
diff --git a/src/Composer/Util/Http/CurlDownloader.php b/src/Composer/Util/Http/CurlDownloader.php
index e8c57908e..e412f52e6 100644
--- a/src/Composer/Util/Http/CurlDownloader.php
+++ b/src/Composer/Util/Http/CurlDownloader.php
@@ -142,6 +142,7 @@ class CurlDownloader
 
         if ($copyTo) {
             $errorMessage = '';
+            // @phpstan-ignore-next-line
             set_error_handler(function ($code, $msg) use (&$errorMessage) {
                 if ($errorMessage) {
                     $errorMessage .= "\n";
diff --git a/src/Composer/Util/HttpDownloader.php b/src/Composer/Util/HttpDownloader.php
index 4610a29b2..809ac2b1a 100644
--- a/src/Composer/Util/HttpDownloader.php
+++ b/src/Composer/Util/HttpDownloader.php
@@ -481,6 +481,7 @@ class HttpDownloader
 
     /**
      * @internal
+     * @return bool
      */
     public static function isCurlEnabled()
     {
diff --git a/src/Composer/Util/NoProxyPattern.php b/src/Composer/Util/NoProxyPattern.php
index b8175f3c9..7e0b5cce0 100644
--- a/src/Composer/Util/NoProxyPattern.php
+++ b/src/Composer/Util/NoProxyPattern.php
@@ -264,8 +264,8 @@ class NoProxyPattern
     /**
      * Returns the binary network mask mapped to IPv6
      *
-     * @param string $prefix CIDR prefix-length
-     * @param int    $size   Byte size of in_addr
+     * @param int $prefix CIDR prefix-length
+     * @param int $size   Byte size of in_addr
      *
      * @return string
      */
@@ -274,7 +274,7 @@ class NoProxyPattern
         $mask = '';
 
         if ($ones = floor($prefix / 8)) {
-            $mask = str_repeat(chr(255), $ones);
+            $mask = str_repeat(chr(255), (int) $ones);
         }
 
         if ($remainder = $prefix % 8) {
@@ -291,7 +291,7 @@ class NoProxyPattern
      *
      * @param string $rangeIp IP in_addr
      * @param int    $size    Byte size of in_addr
-     * @param string $prefix  CIDR prefix-length
+     * @param int    $prefix  CIDR prefix-length
      *
      * @return string[] network in_addr, binary mask
      */
diff --git a/src/Composer/Util/StreamContextFactory.php b/src/Composer/Util/StreamContextFactory.php
index 3542d55ed..4e6997155 100644
--- a/src/Composer/Util/StreamContextFactory.php
+++ b/src/Composer/Util/StreamContextFactory.php
@@ -31,7 +31,7 @@ final class StreamContextFactory
      * Creates a context supporting HTTP proxies
      *
      * @param string $url URL the context is to be used for
-     * @phpstan-param array{http?: array{follow_location?: int, max_redirects?: int, header?: string|array<string, string|int>}} $defaultOptions
+     * @phpstan-param array{http?: array{follow_location?: int, max_redirects?: int, header?: string|array<string>}} $defaultOptions
      * @param  array             $defaultOptions Options to merge with the default
      * @param  array             $defaultParams  Parameters to specify on the context
      * @throws \RuntimeException if https proxy required and OpenSSL uninstalled
diff --git a/src/Composer/Util/SyncHelper.php b/src/Composer/Util/SyncHelper.php
index a970028a9..9db7f3365 100644
--- a/src/Composer/Util/SyncHelper.php
+++ b/src/Composer/Util/SyncHelper.php
@@ -39,7 +39,7 @@ class SyncHelper
             self::await($loop, $downloader->prepare($type, $package, $path, $prevPackage));
 
             if ($type === 'update') {
-                self::await($loop, $downloader->update($package, $path, $prevPackage));
+                self::await($loop, $downloader->update($package, $prevPackage, $path));
             } else {
                 self::await($loop, $downloader->install($package, $path));
             }
diff --git a/tests/Composer/Test/AllFunctionalTest.php b/tests/Composer/Test/AllFunctionalTest.php
index 1cbf16ecc..22cea755d 100644
--- a/tests/Composer/Test/AllFunctionalTest.php
+++ b/tests/Composer/Test/AllFunctionalTest.php
@@ -78,7 +78,13 @@ class AllFunctionalTest extends TestCase
             }
         }
 
-        $proc = new Process((defined('PHP_BINARY') ? escapeshellcmd(PHP_BINARY) : 'php').' -dphar.readonly=0 '.escapeshellarg('./bin/compile'), $target);
+        // TODO in v2.3 always call with an array
+        if (method_exists('Symfony\Component\Process\Process', 'fromShellCommandline')) {
+            $proc = new Process(array((defined('PHP_BINARY') ? PHP_BINARY : 'php'), '-dphar.readonly=0', './bin/compile'), $target);
+        } else {
+            // @phpstan-ignore-next-line
+            $proc = new Process((defined('PHP_BINARY') ? escapeshellcmd(PHP_BINARY) : 'php').' -dphar.readonly=0 '.escapeshellarg('./bin/compile'), $target);
+        }
         $exitcode = $proc->run();
 
         if ($exitcode !== 0 || trim($proc->getOutput())) {
@@ -110,8 +116,15 @@ class AllFunctionalTest extends TestCase
             'COMPOSER_CACHE_DIR' => $this->testDir.'cache',
         );
 
-        $cmd = (defined('PHP_BINARY') ? escapeshellcmd(PHP_BINARY) : 'php') .' '.escapeshellarg(self::$pharPath).' --no-ansi '.$testData['RUN'];
-        $proc = new Process($cmd, $this->testDir, $env, null, 300);
+        // TODO in v2.3 always call with an array
+        if (method_exists('Symfony\Component\Process\Process', 'fromShellCommandline')) {
+            $cmd = array((defined('PHP_BINARY') ? PHP_BINARY : 'php'), self::$pharPath, '--no-ansi', $testData['RUN']);
+            $proc = new Process($cmd, $this->testDir, $env, null, 300);
+        } else {
+            $cmd = (defined('PHP_BINARY') ? escapeshellcmd(PHP_BINARY) : 'php') .' '.escapeshellarg(self::$pharPath).' --no-ansi '.$testData['RUN'];
+            // @phpstan-ignore-next-line
+            $proc = new Process($cmd, $this->testDir, $env, null, 300);
+        }
         $output = '';
 
         $exitcode = $proc->run(function ($type, $buffer) use (&$output) {
diff --git a/tests/Composer/Test/Autoload/AutoloadGeneratorTest.php b/tests/Composer/Test/Autoload/AutoloadGeneratorTest.php
index 134ebd6b8..0e571f81a 100644
--- a/tests/Composer/Test/Autoload/AutoloadGeneratorTest.php
+++ b/tests/Composer/Test/Autoload/AutoloadGeneratorTest.php
@@ -371,8 +371,8 @@ class AutoloadGeneratorTest extends TestCase
     {
         $package = new RootPackage('root/a', '1.0', '1.0');
         $package->setRequires(array(
-            new Link('a', 'a/a', new MatchAllConstraint()),
-            new Link('a', 'b/b', new MatchAllConstraint()),
+            'a/a' => new Link('a', 'a/a', new MatchAllConstraint()),
+            'b/b' => new Link('a', 'b/b', new MatchAllConstraint()),
         ));
 
         $packages = array();
@@ -400,7 +400,7 @@ class AutoloadGeneratorTest extends TestCase
     {
         $package = new RootPackage('root/a', '1.0', '1.0');
         $package->setRequires(array(
-            new Link('a', 'a/a', new MatchAllConstraint()),
+            'a/a' => new Link('a', 'a/a', new MatchAllConstraint()),
         ));
 
         $packages = array();
@@ -408,11 +408,11 @@ class AutoloadGeneratorTest extends TestCase
         $packages[] = $b = new Package('b/b', '1.0', '1.0');
         $a->setAutoload(array('psr-0' => array('A' => 'src/', 'A\\B' => 'lib/')));
         $a->setRequires(array(
-            new Link('a/a', 'b/b', new MatchAllConstraint()),
+            'b/b' => new Link('a/a', 'b/b', new MatchAllConstraint()),
         ));
         $b->setAutoload(array('psr-0' => array('B\\Sub\\Name' => 'src/')));
         $b->setRequires(array(
-            new Link('b/b', 'a/a', new MatchAllConstraint()),
+            'a/a' => new Link('b/b', 'a/a', new MatchAllConstraint()),
         ));
 
         $this->repository->expects($this->once())
@@ -432,17 +432,17 @@ class AutoloadGeneratorTest extends TestCase
     public function testNonDevAutoloadShouldIncludeReplacedPackages()
     {
         $package = new RootPackage('root/a', '1.0', '1.0');
-        $package->setRequires(array(new Link('a', 'a/a', new MatchAllConstraint())));
+        $package->setRequires(array('a/a' => new Link('a', 'a/a', new MatchAllConstraint())));
 
         $packages = array();
         $packages[] = $a = new Package('a/a', '1.0', '1.0');
         $packages[] = $b = new Package('b/b', '1.0', '1.0');
 
-        $a->setRequires(array(new Link('a/a', 'b/c', new MatchAllConstraint())));
+        $a->setRequires(array('b/c' => new Link('a/a', 'b/c', new MatchAllConstraint())));
 
         $b->setAutoload(array('psr-4' => array('B\\' => 'src/')));
         $b->setReplaces(
-            array(new Link('b/b', 'b/c', new Constraint('==', '1.0'), Link::TYPE_REPLACE))
+            array('b/c' => new Link('b/b', 'b/c', new Constraint('==', '1.0'), Link::TYPE_REPLACE))
         );
 
         $this->repository->expects($this->once())
@@ -467,7 +467,7 @@ class AutoloadGeneratorTest extends TestCase
     {
         $package = new RootPackage('root/a', '1.0', '1.0');
         $package->setRequires(array(
-            new Link('a', 'a/a', new MatchAllConstraint()),
+            'a/a' => new Link('a', 'a/a', new MatchAllConstraint()),
         ));
 
         $packages = array();
@@ -475,11 +475,11 @@ class AutoloadGeneratorTest extends TestCase
         $packages[] = $b = new Package('b/b', '1.0', '1.0');
         $a->setAutoload(array('psr-0' => array('A' => 'src/', 'A\\B' => 'lib/')));
         $a->setRequires(array(
-            new Link('a/a', 'c/c', new MatchAllConstraint()),
+            'c/c' => new Link('a/a', 'c/c', new MatchAllConstraint()),
         ));
         $b->setAutoload(array('psr-0' => array('B\\Sub\\Name' => 'src/')));
         $b->setReplaces(array(
-            new Link('b/b', 'c/c', new MatchAllConstraint()),
+            'c/c' => new Link('b/b', 'c/c', new MatchAllConstraint()),
         ));
 
         $this->repository->expects($this->once())
@@ -500,7 +500,7 @@ class AutoloadGeneratorTest extends TestCase
     {
         $package = new RootPackage('root/a', '1.0', '1.0');
         $package->setRequires(array(
-            new Link('a', 'a/a', new MatchAllConstraint()),
+            'a/a' => new Link('a', 'a/a', new MatchAllConstraint()),
         ));
 
         $packages = array();
@@ -511,18 +511,18 @@ class AutoloadGeneratorTest extends TestCase
         $packages[] = $e = new Package('e/e', '1.0', '1.0');
         $a->setAutoload(array('classmap' => array('src/A.php')));
         $a->setRequires(array(
-            new Link('a/a', 'b/b', new MatchAllConstraint()),
+            'b/b' => new Link('a/a', 'b/b', new MatchAllConstraint()),
         ));
         $b->setAutoload(array('classmap' => array('src/B.php')));
         $b->setRequires(array(
-            new Link('b/b', 'e/e', new MatchAllConstraint()),
+            'e/e' => new Link('b/b', 'e/e', new MatchAllConstraint()),
         ));
         $c->setAutoload(array('classmap' => array('src/C.php')));
         $c->setReplaces(array(
-            new Link('c/c', 'b/b', new MatchAllConstraint()),
+            'b/b' => new Link('c/c', 'b/b', new MatchAllConstraint()),
         ));
         $c->setRequires(array(
-            new Link('c/c', 'd/d', new MatchAllConstraint()),
+            'd/d' => new Link('c/c', 'd/d', new MatchAllConstraint()),
         ));
         $d->setAutoload(array('classmap' => array('src/D.php')));
         $e->setAutoload(array('classmap' => array('src/E.php')));
@@ -552,7 +552,7 @@ class AutoloadGeneratorTest extends TestCase
     {
         $package = new RootPackage('root/a', '1.0', '1.0');
         $package->setRequires(array(
-            new Link('a', 'a/a', new MatchAllConstraint()),
+            'a/a' => new Link('a', 'a/a', new MatchAllConstraint()),
         ));
 
         $package->setAutoload(array(
@@ -657,8 +657,8 @@ EOF;
     {
         $package = new RootPackage('root/a', '1.0', '1.0');
         $package->setRequires(array(
-            new Link('a', 'a/a', new MatchAllConstraint()),
-            new Link('a', 'b/b', new MatchAllConstraint()),
+            'a/a' => new Link('a', 'a/a', new MatchAllConstraint()),
+            'b/b' => new Link('a', 'b/b', new MatchAllConstraint()),
         ));
 
         $packages = array();
@@ -697,8 +697,8 @@ EOF;
     {
         $package = new RootPackage('root/a', '1.0', '1.0');
         $package->setRequires(array(
-            new Link('a', 'a/a', new MatchAllConstraint()),
-            new Link('a', 'b/b', new MatchAllConstraint()),
+            'a/a' => new Link('a', 'a/a', new MatchAllConstraint()),
+            'b/b' => new Link('a', 'b/b', new MatchAllConstraint()),
         ));
 
         $packages = array();
@@ -737,9 +737,9 @@ EOF;
     {
         $package = new RootPackage('root/a', '1.0', '1.0');
         $package->setRequires(array(
-            new Link('a', 'a/a', new MatchAllConstraint()),
-            new Link('a', 'b/b', new MatchAllConstraint()),
-            new Link('a', 'c/c', new MatchAllConstraint()),
+            'a/a' => new Link('a', 'a/a', new MatchAllConstraint()),
+            'b/b' => new Link('a', 'b/b', new MatchAllConstraint()),
+            'c/c' => new Link('a', 'c/c', new MatchAllConstraint()),
         ));
 
         $packages = array();
@@ -782,9 +782,9 @@ EOF;
     {
         $package = new RootPackage('root/a', '1.0', '1.0');
         $package->setRequires(array(
-            new Link('a', 'a/a', new MatchAllConstraint()),
-            new Link('a', 'b/b', new MatchAllConstraint()),
-            new Link('a', 'c/c', new MatchAllConstraint()),
+            'a/a' => new Link('a', 'a/a', new MatchAllConstraint()),
+            'b/b' => new Link('a', 'b/b', new MatchAllConstraint()),
+            'c/c' => new Link('a', 'c/c', new MatchAllConstraint()),
         ));
 
         $packages = array();
@@ -831,9 +831,9 @@ EOF;
     {
         $package = new RootPackage('root/a', '1.0', '1.0');
         $package->setRequires(array(
-            new Link('a', 'a/a', new MatchAllConstraint()),
-            new Link('a', 'b/b', new MatchAllConstraint()),
-            new Link('a', 'c/c', new MatchAllConstraint()),
+            'a/a' => new Link('a', 'a/a', new MatchAllConstraint()),
+            'b/b' => new Link('a', 'b/b', new MatchAllConstraint()),
+            'c/c' => new Link('a', 'c/c', new MatchAllConstraint()),
         ));
 
         $packages = array();
@@ -881,9 +881,9 @@ EOF;
         $package = new RootPackage('root/a', '1.0', '1.0');
         $package->setAutoload(array('files' => array('root.php')));
         $package->setRequires(array(
-            new Link('a', 'a/a', new MatchAllConstraint()),
-            new Link('a', 'b/b', new MatchAllConstraint()),
-            new Link('a', 'c/c', new MatchAllConstraint()),
+            'a/a' => new Link('a', 'a/a', new MatchAllConstraint()),
+            'b/b' => new Link('a', 'b/b', new MatchAllConstraint()),
+            'c/c' => new Link('a', 'c/c', new MatchAllConstraint()),
         ));
 
         $packages = array();
@@ -932,9 +932,9 @@ EOF;
         $notAutoloadPackage = new RootPackage('root/a', '1.0', '1.0');
 
         $requires = array(
-            new Link('a', 'a/a', new MatchAllConstraint()),
-            new Link('a', 'b/b', new MatchAllConstraint()),
-            new Link('a', 'c/c', new MatchAllConstraint()),
+            'a/a' => new Link('a', 'a/a', new MatchAllConstraint()),
+            'b/b' => new Link('a', 'b/b', new MatchAllConstraint()),
+            'c/c' => new Link('a', 'c/c', new MatchAllConstraint()),
         );
         $autoloadPackage->setRequires($requires);
         $notAutoloadPackage->setRequires($requires);
@@ -1003,10 +1003,10 @@ EOF;
         $package = new RootPackage('root/a', '1.0', '1.0');
         $package->setAutoload(array('files' => array('root2.php')));
         $package->setRequires(array(
-            new Link('a', 'z/foo', new MatchAllConstraint()),
-            new Link('a', 'b/bar', new MatchAllConstraint()),
-            new Link('a', 'd/d', new MatchAllConstraint()),
-            new Link('a', 'e/e', new MatchAllConstraint()),
+            'z/foo' => new Link('a', 'z/foo', new MatchAllConstraint()),
+            'b/bar' => new Link('a', 'b/bar', new MatchAllConstraint()),
+            'd/d' => new Link('a', 'd/d', new MatchAllConstraint()),
+            'e/e' => new Link('a', 'e/e', new MatchAllConstraint()),
         ));
 
         $packages = array();
@@ -1017,18 +1017,18 @@ EOF;
         $packages[] = $e = new Package('e/e', '1.0', '1.0');
 
         $z->setAutoload(array('files' => array('testA.php')));
-        $z->setRequires(array(new Link('z/foo', 'c/lorem', new MatchAllConstraint())));
+        $z->setRequires(array('c/lorem' => new Link('z/foo', 'c/lorem', new MatchAllConstraint())));
 
         $b->setAutoload(array('files' => array('testB.php')));
-        $b->setRequires(array(new Link('b/bar', 'c/lorem', new MatchAllConstraint()), new Link('b/bar', 'd/d', new MatchAllConstraint())));
+        $b->setRequires(array('c/lorem' => new Link('b/bar', 'c/lorem', new MatchAllConstraint()), 'd/d' => new Link('b/bar', 'd/d', new MatchAllConstraint())));
 
         $c->setAutoload(array('files' => array('testC.php')));
 
         $d->setAutoload(array('files' => array('testD.php')));
-        $d->setRequires(array(new Link('d/d', 'c/lorem', new MatchAllConstraint())));
+        $d->setRequires(array('c/lorem' => new Link('d/d', 'c/lorem', new MatchAllConstraint())));
 
         $e->setAutoload(array('files' => array('testE.php')));
-        $e->setRequires(array(new Link('e/e', 'c/lorem', new MatchAllConstraint())));
+        $e->setRequires(array('c/lorem' => new Link('e/e', 'c/lorem', new MatchAllConstraint())));
 
         $this->repository->expects($this->once())
             ->method('getCanonicalPackages')
@@ -1076,8 +1076,8 @@ EOF;
             'classmap' => array($this->workingDir.'/src'),
         ));
         $rootPackage->setRequires(array(
-            new Link('z', 'a/a', new MatchAllConstraint()),
-            new Link('z', 'b/b', new MatchAllConstraint()),
+            'a/a' => new Link('z', 'a/a', new MatchAllConstraint()),
+            'b/b' => new Link('z', 'b/b', new MatchAllConstraint()),
         ));
 
         $packages = array();
@@ -1339,7 +1339,7 @@ EOF;
             'files' => array('test.php'),
         ));
         $package->setRequires(array(
-            new Link('a', 'b/b', new MatchAllConstraint()),
+            'b/b' => new Link('a', 'b/b', new MatchAllConstraint()),
         ));
 
         $vendorPackage = new Package('b/b', '1.0', '1.0');
diff --git a/tests/Composer/Test/Command/InitCommandTest.php b/tests/Composer/Test/Command/InitCommandTest.php
index 1c2014195..8006fe106 100644
--- a/tests/Composer/Test/Command/InitCommandTest.php
+++ b/tests/Composer/Test/Command/InitCommandTest.php
@@ -110,7 +110,7 @@ class InitCommandTest extends TestCase
     public function testNamespaceFromMissingPackageName()
     {
         $command = new InitCommand;
-        $namespace = $command->namespaceFromPackageName(null);
+        $namespace = $command->namespaceFromPackageName('');
         $this->assertNull($namespace);
     }
 }
diff --git a/tests/Composer/Test/DependencyResolver/RuleSetTest.php b/tests/Composer/Test/DependencyResolver/RuleSetTest.php
index 9ccb25c09..7ffe6ac49 100644
--- a/tests/Composer/Test/DependencyResolver/RuleSetTest.php
+++ b/tests/Composer/Test/DependencyResolver/RuleSetTest.php
@@ -16,6 +16,7 @@ use Composer\DependencyResolver\GenericRule;
 use Composer\DependencyResolver\Rule;
 use Composer\DependencyResolver\RuleSet;
 use Composer\DependencyResolver\Pool;
+use Composer\Semver\Constraint\MatchNoneConstraint;
 use Composer\Test\TestCase;
 
 class RuleSetTest extends TestCase
@@ -144,7 +145,7 @@ class RuleSetTest extends TestCase
 
         $ruleSet = new RuleSet;
         $literal = $p->getId();
-        $rule = new GenericRule(array($literal), Rule::RULE_ROOT_REQUIRE, array('packageName' => 'foo/bar', 'constraint' => null));
+        $rule = new GenericRule(array($literal), Rule::RULE_ROOT_REQUIRE, array('packageName' => 'foo/bar', 'constraint' => new MatchNoneConstraint));
 
         $ruleSet->add($rule, RuleSet::TYPE_REQUEST);
 
diff --git a/tests/Composer/Test/IO/BufferIOTest.php b/tests/Composer/Test/IO/BufferIOTest.php
index 013a3c100..7b8bf2f41 100644
--- a/tests/Composer/Test/IO/BufferIOTest.php
+++ b/tests/Composer/Test/IO/BufferIOTest.php
@@ -36,8 +36,8 @@ class BufferIOTest extends TestCase
             '',
         ));
 
-        $this->assertTrue($bufferIO->askConfirmation('Please say yes!', 'no'));
-        $this->assertFalse($bufferIO->askConfirmation('Now please say no!', 'yes'));
+        $this->assertTrue($bufferIO->askConfirmation('Please say yes!', false));
+        $this->assertFalse($bufferIO->askConfirmation('Now please say no!', true));
         $this->assertSame('default', $bufferIO->ask('Empty string last', 'default'));
     }
 }
diff --git a/tests/Composer/Test/IO/ConsoleIOTest.php b/tests/Composer/Test/IO/ConsoleIOTest.php
index 1ff86170c..b89932bd4 100644
--- a/tests/Composer/Test/IO/ConsoleIOTest.php
+++ b/tests/Composer/Test/IO/ConsoleIOTest.php
@@ -191,7 +191,7 @@ class ConsoleIOTest extends TestCase
         ;
 
         $consoleIO = new ConsoleIO($inputMock, $outputMock, $setMock);
-        $consoleIO->askConfirmation('Why?', 'default');
+        $consoleIO->askConfirmation('Why?', false);
     }
 
     public function testAskAndValidate()
@@ -250,7 +250,7 @@ class ConsoleIOTest extends TestCase
         ;
 
         $consoleIO = new ConsoleIO($inputMock, $outputMock, $setMock);
-        $result = $consoleIO->select('Select item', array("item1", "item2"), null, false, "Error message", true);
+        $result = $consoleIO->select('Select item', array("item1", "item2"), 'item1', false, "Error message", true);
         $this->assertEquals(array('1'), $result);
     }
 
diff --git a/tests/Composer/Test/IO/NullIOTest.php b/tests/Composer/Test/IO/NullIOTest.php
index 11430379b..2a66807d3 100644
--- a/tests/Composer/Test/IO/NullIOTest.php
+++ b/tests/Composer/Test/IO/NullIOTest.php
@@ -58,14 +58,14 @@ class NullIOTest extends TestCase
     {
         $io = new NullIO();
 
-        $this->assertEquals('foo', $io->askConfirmation('bar', 'foo'));
+        $this->assertEquals(false, $io->askConfirmation('bar', false));
     }
 
     public function testAskAndValidate()
     {
         $io = new NullIO();
 
-        $this->assertEquals('foo', $io->askAndValidate('question', 'validator', false, 'foo'));
+        $this->assertEquals('foo', $io->askAndValidate('question', function ($x) { return true; }, null, 'foo'));
     }
 
     public function testSelect()
diff --git a/tests/Composer/Test/Installer/LibraryInstallerTest.php b/tests/Composer/Test/Installer/LibraryInstallerTest.php
index cff4fbc34..967b40db0 100644
--- a/tests/Composer/Test/Installer/LibraryInstallerTest.php
+++ b/tests/Composer/Test/Installer/LibraryInstallerTest.php
@@ -288,7 +288,7 @@ class LibraryInstallerTest extends TestCase
     protected function createPackageMock()
     {
         return $this->getMockBuilder('Composer\Package\Package')
-            ->setConstructorArgs(array(md5(mt_rand()), '1.0.0.0', '1.0.0'))
+            ->setConstructorArgs(array(md5((string) mt_rand()), '1.0.0.0', '1.0.0'))
             ->getMock();
     }
 }
diff --git a/tests/Composer/Test/Installer/MetapackageInstallerTest.php b/tests/Composer/Test/Installer/MetapackageInstallerTest.php
index 481de79da..4ba65991f 100644
--- a/tests/Composer/Test/Installer/MetapackageInstallerTest.php
+++ b/tests/Composer/Test/Installer/MetapackageInstallerTest.php
@@ -101,7 +101,7 @@ class MetapackageInstallerTest extends TestCase
     private function createPackageMock()
     {
         return $this->getMockBuilder('Composer\Package\Package')
-            ->setConstructorArgs(array(md5(mt_rand()), '1.0.0.0', '1.0.0'))
+            ->setConstructorArgs(array(md5((string) mt_rand()), '1.0.0.0', '1.0.0'))
             ->getMock();
     }
 }
diff --git a/tests/Composer/Test/Installer/SuggestedPackagesReporterTest.php b/tests/Composer/Test/Installer/SuggestedPackagesReporterTest.php
index fb8003306..fad4d1235 100644
--- a/tests/Composer/Test/Installer/SuggestedPackagesReporterTest.php
+++ b/tests/Composer/Test/Installer/SuggestedPackagesReporterTest.php
@@ -279,7 +279,7 @@ class SuggestedPackagesReporterTest extends TestCase
     private function createPackageMock()
     {
         return $this->getMockBuilder('Composer\Package\Package')
-            ->setConstructorArgs(array(md5(mt_rand()), '1.0.0.0', '1.0.0'))
+            ->setConstructorArgs(array(md5((string) mt_rand()), '1.0.0.0', '1.0.0'))
             ->getMock();
     }
 }
diff --git a/tests/Composer/Test/Mock/FactoryMock.php b/tests/Composer/Test/Mock/FactoryMock.php
index c095bc639..79b50e19d 100644
--- a/tests/Composer/Test/Mock/FactoryMock.php
+++ b/tests/Composer/Test/Mock/FactoryMock.php
@@ -16,13 +16,14 @@ use Composer\Composer;
 use Composer\Config;
 use Composer\Factory;
 use Composer\Repository\RepositoryManager;
-use Composer\Repository\WritableRepositoryInterface;
 use Composer\Package\Version\VersionGuesser;
 use Composer\Package\Version\VersionParser;
 use Composer\Package\RootPackageInterface;
 use Composer\Installer;
 use Composer\EventDispatcher\EventDispatcher;
 use Composer\IO\IOInterface;
+use Composer\Repository\InstalledArrayRepository;
+use Composer\Repository\InstalledRepositoryInterface;
 use Composer\Test\TestCase;
 use Composer\Util\Loop;
 use Composer\Util\ProcessExecutor;
@@ -48,6 +49,7 @@ class FactoryMock extends Factory
 
     protected function addLocalRepository(IOInterface $io, RepositoryManager $rm, $vendorDir, RootPackageInterface $rootPackage, ProcessExecutor $process = null)
     {
+        $rm->setLocalRepository(new InstalledArrayRepository);
     }
 
     public function createInstallationManager(Loop $loop, IOInterface $io, EventDispatcher $dispatcher = null)
@@ -59,7 +61,7 @@ class FactoryMock extends Factory
     {
     }
 
-    protected function purgePackages(WritableRepositoryInterface $repo, Installer\InstallationManager $im)
+    protected function purgePackages(InstalledRepositoryInterface $repo, Installer\InstallationManager $im)
     {
     }
 }
diff --git a/tests/Composer/Test/Mock/ProcessExecutorMock.php b/tests/Composer/Test/Mock/ProcessExecutorMock.php
index 1d1889f0f..4010e0f4c 100644
--- a/tests/Composer/Test/Mock/ProcessExecutorMock.php
+++ b/tests/Composer/Test/Mock/ProcessExecutorMock.php
@@ -30,7 +30,7 @@ class ProcessExecutorMock extends ProcessExecutor
     private $log = array();
 
     /**
-     * @param array<string|array{cmd: string, return: int, stdout?: string, stderr?: string, callback?: callable}> $expectations
+     * @param array<string|array{cmd: string, return?: int, stdout?: string, stderr?: string, callback?: callable}> $expectations
      * @param bool                                                                                                 $strict         set to true if you want to provide *all* expected commands, and not just a subset you are interested in testing
      * @param array{return: int, stdout?: string, stderr?: string}                                                 $defaultHandler default command handler for undefined commands if not in strict mode
      */
diff --git a/tests/Composer/Test/Package/Archiver/ArchiveManagerTest.php b/tests/Composer/Test/Package/Archiver/ArchiveManagerTest.php
index 2c99ac61c..a9f281975 100644
--- a/tests/Composer/Test/Package/Archiver/ArchiveManagerTest.php
+++ b/tests/Composer/Test/Package/Archiver/ArchiveManagerTest.php
@@ -15,6 +15,7 @@ namespace Composer\Test\Package\Archiver;
 use Composer\IO\NullIO;
 use Composer\Factory;
 use Composer\Package\Archiver\ArchiveManager;
+use Composer\Package\CompletePackage;
 use Composer\Package\PackageInterface;
 use Composer\Util\Loop;
 use Composer\Test\Mock\FactoryMock;
@@ -95,7 +96,7 @@ class ArchiveManagerTest extends ArchiverTest
         unlink($target);
     }
 
-    protected function getTargetName(PackageInterface $package, $format, $fileName = null)
+    protected function getTargetName(CompletePackage $package, $format, $fileName = null)
     {
         if (null === $fileName) {
             $packageName = $this->manager->getPackageFilename($package);
diff --git a/tests/Composer/Test/Package/Dumper/ArrayDumperTest.php b/tests/Composer/Test/Package/Dumper/ArrayDumperTest.php
index dbcdf848f..39f1b0a0b 100644
--- a/tests/Composer/Test/Package/Dumper/ArrayDumperTest.php
+++ b/tests/Composer/Test/Package/Dumper/ArrayDumperTest.php
@@ -178,7 +178,7 @@ class ArrayDumperTest extends TestCase
             ),
             array(
                 'require-dev',
-                array(new Link('foo', 'foo/bar', new Constraint('=', '1.0.0.0'), 'requires (for development)', '1.0.0')),
+                array(new Link('foo', 'foo/bar', new Constraint('=', '1.0.0.0'), Link::TYPE_DEV_REQUIRE, '1.0.0')),
                 'devRequires',
                 array('foo/bar' => '1.0.0'),
             ),
diff --git a/tests/Composer/Test/Package/Loader/ArrayLoaderTest.php b/tests/Composer/Test/Package/Loader/ArrayLoaderTest.php
index 1d4f8661b..285dd13e4 100644
--- a/tests/Composer/Test/Package/Loader/ArrayLoaderTest.php
+++ b/tests/Composer/Test/Package/Loader/ArrayLoaderTest.php
@@ -14,6 +14,7 @@ namespace Composer\Test\Package\Loader;
 
 use Composer\Package\Loader\ArrayLoader;
 use Composer\Package\Dumper\ArrayDumper;
+use Composer\Package\Link;
 use Composer\Test\TestCase;
 
 class ArrayLoaderTest extends TestCase
@@ -287,7 +288,7 @@ class ArrayLoaderTest extends TestCase
      */
     public function testPluginApiVersionAreKeptAsDeclared($apiVersion)
     {
-        $links = $this->loader->parseLinks('Plugin', '9.9.9', '', array('composer-plugin-api' => $apiVersion));
+        $links = $this->loader->parseLinks('Plugin', '9.9.9', Link::TYPE_REQUIRE, array('composer-plugin-api' => $apiVersion));
 
         $this->assertArrayHasKey('composer-plugin-api', $links);
         $this->assertSame($apiVersion, $links['composer-plugin-api']->getConstraint()->getPrettyString());
@@ -295,7 +296,7 @@ class ArrayLoaderTest extends TestCase
 
     public function testPluginApiVersionDoesSupportSelfVersion()
     {
-        $links = $this->loader->parseLinks('Plugin', '6.6.6', '', array('composer-plugin-api' => 'self.version'));
+        $links = $this->loader->parseLinks('Plugin', '6.6.6', Link::TYPE_REQUIRE, array('composer-plugin-api' => 'self.version'));
 
         $this->assertArrayHasKey('composer-plugin-api', $links);
         $this->assertSame('6.6.6', $links['composer-plugin-api']->getConstraint()->getPrettyString());
diff --git a/tests/Composer/Test/Package/RootAliasPackageTest.php b/tests/Composer/Test/Package/RootAliasPackageTest.php
index f3db670a7..00ca7fa05 100644
--- a/tests/Composer/Test/Package/RootAliasPackageTest.php
+++ b/tests/Composer/Test/Package/RootAliasPackageTest.php
@@ -27,7 +27,7 @@ class RootAliasPackageTest extends TestCase
 
         $alias = new RootAliasPackage($root->reveal(), '1.0', '1.0.0.0');
         $this->assertEmpty($alias->getRequires());
-        $links = array(new Link('a', 'b', new MatchAllConstraint(), 'foo', 'self.version'));
+        $links = array(new Link('a', 'b', new MatchAllConstraint(), Link::TYPE_REQUIRE, 'self.version'));
         $alias->setRequires($links);
         $this->assertNotEmpty($alias->getRequires());
     }
@@ -39,7 +39,7 @@ class RootAliasPackageTest extends TestCase
 
         $alias = new RootAliasPackage($root->reveal(), '1.0', '1.0.0.0');
         $this->assertEmpty($alias->getDevRequires());
-        $links = array(new Link('a', 'b', new MatchAllConstraint(), 'foo', 'self.version'));
+        $links = array(new Link('a', 'b', new MatchAllConstraint(), Link::TYPE_DEV_REQUIRE, 'self.version'));
         $alias->setDevRequires($links);
         $this->assertNotEmpty($alias->getDevRequires());
     }
@@ -51,7 +51,7 @@ class RootAliasPackageTest extends TestCase
 
         $alias = new RootAliasPackage($root->reveal(), '1.0', '1.0.0.0');
         $this->assertEmpty($alias->getConflicts());
-        $links = array(new Link('a', 'b', new MatchAllConstraint(), 'foo', 'self.version'));
+        $links = array(new Link('a', 'b', new MatchAllConstraint(), Link::TYPE_CONFLICT, 'self.version'));
         $alias->setConflicts($links);
         $this->assertNotEmpty($alias->getConflicts());
     }
@@ -63,7 +63,7 @@ class RootAliasPackageTest extends TestCase
 
         $alias = new RootAliasPackage($root->reveal(), '1.0', '1.0.0.0');
         $this->assertEmpty($alias->getProvides());
-        $links = array(new Link('a', 'b', new MatchAllConstraint(), 'foo', 'self.version'));
+        $links = array(new Link('a', 'b', new MatchAllConstraint(), Link::TYPE_PROVIDE, 'self.version'));
         $alias->setProvides($links);
         $this->assertNotEmpty($alias->getProvides());
     }
@@ -75,7 +75,7 @@ class RootAliasPackageTest extends TestCase
 
         $alias = new RootAliasPackage($root->reveal(), '1.0', '1.0.0.0');
         $this->assertEmpty($alias->getReplaces());
-        $links = array(new Link('a', 'b', new MatchAllConstraint(), 'foo', 'self.version'));
+        $links = array(new Link('a', 'b', new MatchAllConstraint(), Link::TYPE_REPLACE, 'self.version'));
         $alias->setReplaces($links);
         $this->assertNotEmpty($alias->getReplaces());
     }
diff --git a/tests/Composer/Test/Plugin/PluginInstallerTest.php b/tests/Composer/Test/Plugin/PluginInstallerTest.php
index 9af15a41a..2aa709e53 100644
--- a/tests/Composer/Test/Plugin/PluginInstallerTest.php
+++ b/tests/Composer/Test/Plugin/PluginInstallerTest.php
@@ -54,12 +54,12 @@ class PluginInstallerTest extends TestCase
     protected $directory;
 
     /**
-     * @var \PHPUnit\Framework\MockObject\MockObject
+     * @var \PHPUnit\Framework\MockObject\MockObject&\Composer\Installer\InstallationManager
      */
     protected $im;
 
     /**
-     * @var \PHPUnit\Framework\MockObject\MockObject
+     * @var \PHPUnit\Framework\MockObject\MockObject&\Composer\Repository\InstalledRepositoryInterface
      */
     protected $repository;
 
diff --git a/tests/Composer/Test/Repository/PlatformRepositoryTest.php b/tests/Composer/Test/Repository/PlatformRepositoryTest.php
index e2ba60806..30a464b24 100644
--- a/tests/Composer/Test/Repository/PlatformRepositoryTest.php
+++ b/tests/Composer/Test/Repository/PlatformRepositoryTest.php
@@ -13,6 +13,7 @@
 namespace Composer\Test\Repository;
 
 use Composer\Package\Package;
+use Composer\Package\PackageInterface;
 use Composer\Repository\PlatformRepository;
 use Composer\Test\TestCase;
 use PHPUnit\Framework\Assert;
@@ -1189,7 +1190,7 @@ Linked Version => 1.2.11',
         }
     }
 
-    private function assertPackageLinks($context, array $expectedLinks, Package $sourcePackage, array $links)
+    private function assertPackageLinks($context, array $expectedLinks, PackageInterface $sourcePackage, array $links)
     {
         self::assertCount(count($expectedLinks), $links, sprintf('%s: expected package count to match', $context));
 
diff --git a/tests/Composer/Test/TestCase.php b/tests/Composer/Test/TestCase.php
index c511e67bb..0b38c6d73 100644
--- a/tests/Composer/Test/TestCase.php
+++ b/tests/Composer/Test/TestCase.php
@@ -94,7 +94,7 @@ abstract class TestCase extends PolyfillTestCase
                     $arrayLoader->parseLinks(
                         $package->getName(),
                         $package->getPrettyVersion(),
-                        $opts['description'],
+                        $opts['method'],
                         $config[$type]
                     )
                 );
diff --git a/tests/Composer/Test/Util/MetadataMinifierTest.php b/tests/Composer/Test/Util/MetadataMinifierTest.php
index 043c3356c..fa69e928d 100644
--- a/tests/Composer/Test/Util/MetadataMinifierTest.php
+++ b/tests/Composer/Test/Util/MetadataMinifierTest.php
@@ -22,7 +22,7 @@ class MetadataMinifierTest extends TestCase
     public function testMinifyExpand()
     {
         $package1 = new CompletePackage('foo/bar', '2.0.0.0', '2.0.0');
-        $package1->setScripts(array('foo' => 'bar'));
+        $package1->setScripts(array('foo' => array('bar')));
         $package1->setLicense(array('MIT'));
         $package2 = new CompletePackage('foo/bar', '1.2.0.0', '1.2.0');
         $package2->setLicense(array('GPL'));
@@ -32,7 +32,7 @@ class MetadataMinifierTest extends TestCase
         $dumper = new ArrayDumper();
 
         $minified = array(
-            array('name' => 'foo/bar', 'version' => '2.0.0', 'version_normalized' => '2.0.0.0', 'type' => 'library', 'scripts' => array('foo' => 'bar'), 'license' => array('MIT')),
+            array('name' => 'foo/bar', 'version' => '2.0.0', 'version_normalized' => '2.0.0.0', 'type' => 'library', 'scripts' => array('foo' => array('bar')), 'license' => array('MIT')),
             array('version' => '1.2.0', 'version_normalized' => '1.2.0.0', 'license' => array('GPL'), 'homepage' => 'https://example.org', 'scripts' => '__unset'),
             array('version' => '1.0.0', 'version_normalized' => '1.0.0.0', 'homepage' => '__unset'),
         );
diff --git a/tests/Composer/Test/Util/PackageSorterTest.php b/tests/Composer/Test/Util/PackageSorterTest.php
index 3dc1535ec..23f5996a6 100644
--- a/tests/Composer/Test/Util/PackageSorterTest.php
+++ b/tests/Composer/Test/Util/PackageSorterTest.php
@@ -123,7 +123,7 @@ class PackageSorterTest extends TestCase
 
         $links = array();
         foreach ($requires as $requireName) {
-            $links[] = new Link($package->getName(), $requireName, new MatchAllConstraint);
+            $links[$requireName] = new Link($package->getName(), $requireName, new MatchAllConstraint);
         }
         $package->setRequires($links);