Error out on recursive links in validating loader and ignore them in regular loader

src/Composer/Package/Loader/ArrayLoader.php

@@ -327,6 +327,12 @@ class ArrayLoader implements LoaderInterface
                 $links = array();
                 foreach ($config[$type] as $prettyTarget => $constraint) {
                     $target = strtolower($prettyTarget);
+
+                    // recursive links are not supported
+                    if ($target === $name) {
+                        continue;
+                    }
+
                     if ($constraint === 'self.version') {
                         $links[$target] = $this->createLink($name, $prettyVersion, $opts['method'], $target, $constraint);
                     } else {

src/Composer/Package/Loader/ValidatingArrayLoader.php

@@ -241,6 +241,11 @@ class ValidatingArrayLoader implements LoaderInterface
         foreach (array_keys(BasePackage::$supportedLinkTypes) as $linkType) {
             if ($this->validateArray($linkType) && isset($this->config[$linkType])) {
                 foreach ($this->config[$linkType] as $package => $constraint) {
+                    if (0 === strcasecmp($package, $this->config['name'])) {
+                        $this->errors[] = $linkType.'.'.$package.' : a package cannot set a '.$linkType.' on itself';
+                        unset($this->config[$linkType][$package]);
+                        continue;
+                    }
                     if ($err = self::hasPackageNamingError($package, true)) {
                         $this->warnings[] = 'Deprecation warning: '.$linkType.'.'.$err.' Make sure you fix this as Composer 2.0 will error.';
                     } elseif (!preg_match('{^[A-Za-z0-9_./-]+$}', $package)) {

tests/Composer/Test/Fixtures/installer/circular-dependency2.test

@@ -17,7 +17,7 @@ Circular dependencies are possible between packages
                     "version": "1.0.0",
                     "source": { "reference": "some.branch", "type": "git", "url": "" },
                     "require": {
-                        "require/itself": "1.0.0"
+                        "root/pkg": "dev-master"
                     }
                 },
                 {

tests/Composer/Test/Package/Loader/ValidatingArrayLoaderTest.php

@@ -354,6 +354,15 @@ class ValidatingArrayLoaderTest extends TestCase
                     'source.url : must not start with a "-", "--foo" given',
                 ),
             ),
+            array(
+                array(
+                    'name' => 'foo/bar',
+                    'require' => array('foo/Bar' => '1.*'),
+                ),
+                array(
+                    'require.foo/Bar : a package cannot set a require on itself',
+                ),
+            ),
         ));
     }