diff --git a/src/Composer/Factory.php b/src/Composer/Factory.php
index 7e9fd1bd1..8a0ff1e2d 100644
--- a/src/Composer/Factory.php
+++ b/src/Composer/Factory.php
@@ -347,7 +347,7 @@ class Factory
         // load package
         $parser = new VersionParser;
         $guesser = new VersionGuesser($config, new ProcessExecutor($io), $parser);
-        $loader = new Package\Loader\RootPackageLoader($rm, $config, $parser, $guesser);
+        $loader = new Package\Loader\RootPackageLoader($rm, $config, $parser, $guesser, $io);
         $package = $loader->load($localConfig, 'Composer\Package\RootPackage', $cwd);
         $composer->setPackage($package);
 
diff --git a/src/Composer/Package/Loader/RootPackageLoader.php b/src/Composer/Package/Loader/RootPackageLoader.php
index f917eb838..84e99a857 100644
--- a/src/Composer/Package/Loader/RootPackageLoader.php
+++ b/src/Composer/Package/Loader/RootPackageLoader.php
@@ -15,6 +15,7 @@ namespace Composer\Package\Loader;
 use Composer\Package\BasePackage;
 use Composer\Package\AliasPackage;
 use Composer\Config;
+use Composer\IO\IOInterface;
 use Composer\Package\RootPackageInterface;
 use Composer\Repository\RepositoryFactory;
 use Composer\Package\Version\VersionGuesser;
@@ -46,13 +47,19 @@ class RootPackageLoader extends ArrayLoader
      */
     private $versionGuesser;
 
-    public function __construct(RepositoryManager $manager, Config $config, VersionParser $parser = null, VersionGuesser $versionGuesser = null)
+    /**
+     * @var IOInterface
+     */
+    private $io;
+
+    public function __construct(RepositoryManager $manager, Config $config, VersionParser $parser = null, VersionGuesser $versionGuesser = null, IOInterface $io = null)
     {
         parent::__construct($parser);
 
         $this->manager = $manager;
         $this->config = $config;
         $this->versionGuesser = $versionGuesser ?: new VersionGuesser($config, new ProcessExecutor(), $this->versionParser);
+        $this->io = $io;
     }
 
     /**
@@ -65,6 +72,10 @@ class RootPackageLoader extends ArrayLoader
     {
         if (!isset($config['name'])) {
             $config['name'] = '__root__';
+        } elseif ($this->io) {
+            if ($err = ValidatingArrayLoader::hasPackageNamingError($config['name'])) {
+                $this->io->writeError('<warning>Deprecation warning: Your package name '.$err.' Make sure you fix this as Composer 2.0 will error.</warning>');
+            }
         }
         $autoVersioned = false;
         if (!isset($config['version'])) {
@@ -131,6 +142,18 @@ class RootPackageLoader extends ArrayLoader
             }
         }
 
+        if ($this->io) {
+            foreach (array_keys(BasePackage::$supportedLinkTypes) as $linkType) {
+                if (isset($config[$linkType])) {
+                    foreach ($config[$linkType] as $linkName => $constraint) {
+                        if ($err = ValidatingArrayLoader::hasPackageNamingError($linkName, true)) {
+                            $this->io->writeError('<warning>Deprecation warning: '.$linkType.'.'.$err.' Make sure you fix this as Composer 2.0 will error.</warning>');
+                        }
+                    }
+                }
+            }
+        }
+
         if (isset($links[$config['name']])) {
             throw new \InvalidArgumentException(sprintf('Root package \'%s\' cannot require itself in its composer.json' . PHP_EOL .
                         'Did you accidentally name your root package after an external package?', $config['name']));
diff --git a/src/Composer/Package/Loader/ValidatingArrayLoader.php b/src/Composer/Package/Loader/ValidatingArrayLoader.php
index f4753025b..405e567f0 100644
--- a/src/Composer/Package/Loader/ValidatingArrayLoader.php
+++ b/src/Composer/Package/Loader/ValidatingArrayLoader.php
@@ -336,6 +336,38 @@ class ValidatingArrayLoader implements LoaderInterface
         return $this->errors;
     }
 
+    public static function hasPackageNamingError($name, $isLink = false)
+    {
+        if (preg_match(PlatformRepository::PLATFORM_PACKAGE_REGEX, $name)) {
+            return;
+        }
+
+        if (!preg_match('{^[a-z0-9]([_.-]?[a-z0-9]+)*/[a-z0-9]([_.-]?[a-z0-9]+)*$}iD', $name)) {
+            return $name.' is invalid, it should have a vendor name, a forward slash, and a package name. The vendor and package name can be words separated by -, . or _. The complete name should match "[a-z0-9]([_.-]?[a-z0-9]+)*/[a-z0-9]([_.-]?[a-z0-9]+)*".';
+        }
+
+        $reservedNames = array('nul', 'con', 'prn', 'aux', 'com1', 'com2', 'com3', 'com4', 'com5', 'com6', 'com7', 'com8', 'com9', 'lpt1', 'lpt2', 'lpt3', 'lpt4', 'lpt5', 'lpt6', 'lpt7', 'lpt8', 'lpt9');
+        $bits = explode('/', strtolower($name));
+        if (in_array($bits[0], $reservedNames, true) || in_array($bits[1], $reservedNames, true)) {
+            return $name.' is reserved, package and vendor names can not match any of: '.implode(', ', $reservedNames).'.';
+        }
+
+        if (preg_match('{\.json$}', $name)) {
+            return $name.' is invalid, package names can not end in .json, consider renaming it or perhaps using a -json suffix instead.';
+        }
+
+        if (preg_match('{[A-Z]}', $name)) {
+            if ($isLink) {
+                return $name.' is invalid, it should not contain uppercase characters. Please use '.strtolower($name).' instead.';
+            }
+
+            $suggestName = preg_replace('{(?:([a-z])([A-Z])|([A-Z])([A-Z][a-z]))}', '\\1\\3-\\2\\4', $name);
+            $suggestName = strtolower($suggestName);
+
+            return $name.' is invalid, it should not contain uppercase characters. We suggest using '.$suggestName.' instead.';
+        }
+    }
+
     private function validateRegex($property, $regex, $mandatory = false)
     {
         if (!$this->validateString($property, $mandatory)) {
diff --git a/src/Composer/Repository/PlatformRepository.php b/src/Composer/Repository/PlatformRepository.php
index 6d6e04d2f..4d74d8ed2 100644
--- a/src/Composer/Repository/PlatformRepository.php
+++ b/src/Composer/Repository/PlatformRepository.php
@@ -24,7 +24,7 @@ use Composer\XdebugHandler\XdebugHandler;
  */
 class PlatformRepository extends ArrayRepository
 {
-    const PLATFORM_PACKAGE_REGEX = '{^(?:php(?:-64bit|-ipv6|-zts|-debug)?|hhvm|(?:ext|lib)-[^/ ]+)$}i';
+    const PLATFORM_PACKAGE_REGEX = '{^(?:php(?:-64bit|-ipv6|-zts|-debug)?|hhvm|(?:ext|lib)-[a-z0-9](?:-?[a-z0-9]+)*)$}iD';
 
     private $versionParser;
 
diff --git a/tests/Composer/Test/Fixtures/installer/github-issues-4319.test b/tests/Composer/Test/Fixtures/installer/github-issues-4319.test
index d97aefc8d..ee221dab0 100644
--- a/tests/Composer/Test/Fixtures/installer/github-issues-4319.test
+++ b/tests/Composer/Test/Fixtures/installer/github-issues-4319.test
@@ -13,12 +13,12 @@ Present a clear error message when config.platform.php version results in a conf
         {
             "type": "package",
             "package": [
-                { "name": "a", "version": "1.0.0", "require": { "php": "5.5" } }
+                { "name": "a/a", "version": "1.0.0", "require": { "php": "5.5" } }
             ]
         }
     ],
     "require": {
-        "a": "~1.0"
+        "a/a": "~1.0"
     },
     "config": {
         "platform": {
@@ -36,8 +36,8 @@ Updating dependencies (including require-dev)
 Your requirements could not be resolved to an installable set of packages.
 
   Problem 1
-    - Installation request for a ~1.0 -> satisfiable by a[1.0.0].
-    - a 1.0.0 requires php 5.5 -> your PHP version (%s) overridden by "config.platform.php" version (5.3) does not satisfy that requirement.
+    - Installation request for a/a ~1.0 -> satisfiable by a/a[1.0.0].
+    - a/a 1.0.0 requires php 5.5 -> your PHP version (%s) overridden by "config.platform.php" version (5.3) does not satisfy that requirement.
 
 --EXPECT--
 
diff --git a/tests/Composer/Test/Fixtures/installer/github-issues-4795-2.test b/tests/Composer/Test/Fixtures/installer/github-issues-4795-2.test
index d807c6df8..877ac3653 100644
--- a/tests/Composer/Test/Fixtures/installer/github-issues-4795-2.test
+++ b/tests/Composer/Test/Fixtures/installer/github-issues-4795-2.test
@@ -11,27 +11,27 @@ that are also a root package, when that root package is also explicitly whitelis
         {
             "type": "package",
             "package": [
-                { "name": "a", "version": "1.0.0" },
-                { "name": "a", "version": "1.1.0" },
-                { "name": "b", "version": "1.0.0", "require": { "a": "~1.0" } },
-                { "name": "b", "version": "1.1.0", "require": { "a": "~1.1" } }
+                { "name": "a/a", "version": "1.0.0" },
+                { "name": "a/a", "version": "1.1.0" },
+                { "name": "b/b", "version": "1.0.0", "require": { "a/a": "~1.0" } },
+                { "name": "b/b", "version": "1.1.0", "require": { "a/a": "~1.1" } }
             ]
         }
     ],
     "require": {
-        "a": "~1.0",
-        "b": "~1.0"
+        "a/a": "~1.0",
+        "b/b": "~1.0"
     }
 }
 
 --INSTALLED--
 [
-    { "name": "a", "version": "1.0.0" },
-    { "name": "b", "version": "1.0.0", "require": { "a": "~1.0" } }
+    { "name": "a/a", "version": "1.0.0" },
+    { "name": "b/b", "version": "1.0.0", "require": { "a/a": "~1.0" } }
 ]
 
 --RUN--
-update a b --with-dependencies
+update a/a b/b --with-dependencies
 
 --EXPECT-OUTPUT--
 Loading composer repositories with package information
@@ -41,5 +41,5 @@ Writing lock file
 Generating autoload files
 
 --EXPECT--
-Updating a (1.0.0) to a (1.1.0)
-Updating b (1.0.0) to b (1.1.0)
+Updating a/a (1.0.0) to a/a (1.1.0)
+Updating b/b (1.0.0) to b/b (1.1.0)
diff --git a/tests/Composer/Test/Fixtures/installer/github-issues-4795.test b/tests/Composer/Test/Fixtures/installer/github-issues-4795.test
index 5a1158f26..1f4b1af27 100644
--- a/tests/Composer/Test/Fixtures/installer/github-issues-4795.test
+++ b/tests/Composer/Test/Fixtures/installer/github-issues-4795.test
@@ -11,30 +11,30 @@ dependency of one the requirements that is whitelisted for update.
         {
             "type": "package",
             "package": [
-                { "name": "a", "version": "1.0.0" },
-                { "name": "a", "version": "1.1.0" },
-                { "name": "b", "version": "1.0.0", "require": { "a": "~1.0" } },
-                { "name": "b", "version": "1.1.0", "require": { "a": "~1.1" } }
+                { "name": "a/a", "version": "1.0.0" },
+                { "name": "a/a", "version": "1.1.0" },
+                { "name": "b/b", "version": "1.0.0", "require": { "a/a": "~1.0" } },
+                { "name": "b/b", "version": "1.1.0", "require": { "a/b": "~1.1" } }
             ]
         }
     ],
     "require": {
-        "a": "~1.0",
-        "b": "~1.0"
+        "a/a": "~1.0",
+        "b/b": "~1.0"
     }
 }
 
 --INSTALLED--
 [
-    { "name": "a", "version": "1.0.0" },
-    { "name": "b", "version": "1.0.0", "require": { "a": "~1.0" } }
+    { "name": "a/a", "version": "1.0.0" },
+    { "name": "b/b", "version": "1.0.0", "require": { "a/a": "~1.0" } }
 ]
 
 --RUN--
-update b --with-dependencies
+update b/b --with-dependencies
 
 --EXPECT-OUTPUT--
-<warning>Dependency "a" is also a root requirement, but is not explicitly whitelisted. Ignoring.</warning>
+<warning>Dependency "a/a" is also a root requirement, but is not explicitly whitelisted. Ignoring.</warning>
 Loading composer repositories with package information
 Updating dependencies (including require-dev)
 Nothing to install or update
diff --git a/tests/Composer/Test/Fixtures/installer/solver-problems.test b/tests/Composer/Test/Fixtures/installer/solver-problems.test
index e0359a151..cab45f9dc 100644
--- a/tests/Composer/Test/Fixtures/installer/solver-problems.test
+++ b/tests/Composer/Test/Fixtures/installer/solver-problems.test
@@ -8,30 +8,30 @@ Test the error output of solver problems.
             "package": [
                 { "name": "unstable/package", "version": "2.0.0-alpha" },
                 { "name": "unstable/package", "version": "1.0.0" },
-                { "name": "requirer", "version": "1.0.0", "require": {"dependency": "1.0.0" } },
-                { "name": "dependency", "version": "2.0.0" },
-                { "name": "dependency", "version": "1.0.0" },
-                { "name": "stable-requiree-excluded", "version": "1.0.1" },
-                { "name": "stable-requiree-excluded", "version": "1.0.0" }
+                { "name": "requirer/pkg", "version": "1.0.0", "require": {"dependency/pkg": "1.0.0" } },
+                { "name": "dependency/pkg", "version": "2.0.0" },
+                { "name": "dependency/pkg", "version": "1.0.0" },
+                { "name": "stable-requiree-excluded/pkg", "version": "1.0.1" },
+                { "name": "stable-requiree-excluded/pkg", "version": "1.0.0" }
             ]
         }
     ],
     "require": {
         "unstable/package": "2.*",
-        "bogus": "1.*",
-        "requirer": "1.*",
-        "dependency": "2.*",
-        "stable-requiree-excluded": "1.0.1"
+        "bogus/pkg": "1.*",
+        "requirer/pkg": "1.*",
+        "dependency/pkg": "2.*",
+        "stable-requiree-excluded/pkg": "1.0.1"
     }
 }
 
 --INSTALLED--
 [
-    { "name": "stable-requiree-excluded", "version": "1.0.0" }
+    { "name": "stable-requiree-excluded/pkg", "version": "1.0.0" }
 ]
 
 --RUN--
-update unstable/package requirer dependency
+update unstable/package requirer/pkg dependency/pkg
 
 --EXPECT-EXIT-CODE--
 2
@@ -44,12 +44,12 @@ Your requirements could not be resolved to an installable set of packages.
   Problem 1
     - The requested package unstable/package 2.* exists as unstable/package[1.0.0] but these are rejected by your constraint.
   Problem 2
-    - The requested package bogus could not be found in any version, there may be a typo in the package name.
+    - The requested package bogus/pkg could not be found in any version, there may be a typo in the package name.
   Problem 3
-    - The requested package stable-requiree-excluded (installed at 1.0.0, required as 1.0.1) is satisfiable by stable-requiree-excluded[1.0.0] but these conflict with your requirements or minimum-stability.
+    - The requested package stable-requiree-excluded/pkg (installed at 1.0.0, required as 1.0.1) is satisfiable by stable-requiree-excluded/pkg[1.0.0] but these conflict with your requirements or minimum-stability.
   Problem 4
-    - Installation request for requirer 1.* -> satisfiable by requirer[1.0.0].
-    - requirer 1.0.0 requires dependency 1.0.0 -> satisfiable by dependency[1.0.0] but these conflict with your requirements or minimum-stability.
+    - Installation request for requirer/pkg 1.* -> satisfiable by requirer/pkg[1.0.0].
+    - requirer/pkg 1.0.0 requires dependency/pkg 1.0.0 -> satisfiable by dependency/pkg[1.0.0] but these conflict with your requirements or minimum-stability.
 
 Potential causes:
  - A typo in the package name
diff --git a/tests/Composer/Test/Fixtures/installer/update-with-all-dependencies.test b/tests/Composer/Test/Fixtures/installer/update-with-all-dependencies.test
index f4fbfce9b..c0019e6ca 100644
--- a/tests/Composer/Test/Fixtures/installer/update-with-all-dependencies.test
+++ b/tests/Composer/Test/Fixtures/installer/update-with-all-dependencies.test
@@ -10,27 +10,27 @@ When `--with-all-dependencies` is used, Composer\Installer::whitelistUpdateDepen
         {
             "type": "package",
             "package": [
-                { "name": "a", "version": "1.0.0" },
-                { "name": "a", "version": "1.1.0" },
-                { "name": "b", "version": "1.0.0", "require": { "a": "~1.0" } },
-                { "name": "b", "version": "1.1.0", "require": { "a": "~1.1" } }
+                { "name": "a/a", "version": "1.0.0" },
+                { "name": "a/a", "version": "1.1.0" },
+                { "name": "b/b", "version": "1.0.0", "require": { "a/a": "~1.0" } },
+                { "name": "b/b", "version": "1.1.0", "require": { "a/a": "~1.1" } }
             ]
         }
     ],
     "require": {
-        "a": "~1.0",
-        "b": "~1.0"
+        "a/a": "~1.0",
+        "b/b": "~1.0"
     }
 }
 
 --INSTALLED--
 [
-    { "name": "a", "version": "1.0.0" },
-    { "name": "b", "version": "1.0.0", "require": { "a": "~1.0" } }
+    { "name": "a/a", "version": "1.0.0" },
+    { "name": "b/b", "version": "1.0.0", "require": { "a/a": "~1.0" } }
 ]
 
 --RUN--
-update b --with-all-dependencies
+update b/b --with-all-dependencies
 
 --EXPECT-OUTPUT--
 Loading composer repositories with package information
@@ -40,5 +40,5 @@ Writing lock file
 Generating autoload files
 
 --EXPECT--
-Updating a (1.0.0) to a (1.1.0)
-Updating b (1.0.0) to b (1.1.0)
\ No newline at end of file
+Updating a/a (1.0.0) to a/a (1.1.0)
+Updating b/b (1.0.0) to b/b (1.1.0)