Validate: Warn about providing or replacing packages you require

src/Composer/Util/ConfigValidator.php

@@ -138,6 +138,22 @@ class ConfigValidator
             }
         }
 
+
+        // check for meaningless provide/replace satisfying requirements
+        foreach (array('provide', 'replace') as $linkType) {
+            if (isset($manifest[$linkType])) {
+                foreach (array('require', 'require-dev') as $requireType) {
+                    if (isset($manifest[$requireType])) {
+                        foreach ($manifest[$linkType] as $provide => $constraint) {
+                            if (isset($manifest[$requireType][$provide])) {
+                                $warnings[] = 'The package ' . $provide . ' in '.$requireType.' is also listed in '.$linkType.' which satisfies the requirement. Remove it from '.$linkType.' if you wish to install it.';
+                            }
+                        }
+                    }
+                }
+            }
+        }
+
         // check for commit references
         $require = isset($manifest['require']) ? $manifest['require'] : array();
         $requireDev = isset($manifest['require-dev']) ? $manifest['require-dev'] : array();

tests/Composer/Test/Util/ConfigValidatorTest.php

@@ -45,4 +45,23 @@ class ConfigValidatorTest extends TestCase
             $warnings
         );
     }
+
+    public function testConfigValidatorWarnsOnUnnecessaryProvideReplace()
+    {
+        $configValidator = new ConfigValidator(new NullIO());
+        list(, , $warnings) = $configValidator->validate(__DIR__ . '/Fixtures/composer_provide-replace-requirements.json');
+
+        $this->assertContains(
+            'The package a/a in require is also listed in provide which satisfies the requirement. Remove it from provide if you wish to install it.',
+            $warnings
+        );
+        $this->assertContains(
+            'The package b/b in require is also listed in replace which satisfies the requirement. Remove it from replace if you wish to install it.',
+            $warnings
+        );
+        $this->assertContains(
+            'The package c/c in require-dev is also listed in provide which satisfies the requirement. Remove it from provide if you wish to install it.',
+            $warnings
+        );
+    }
 }

tests/Composer/Test/Util/Fixtures/composer_provide-replace-requirements.json

@@ -0,0 +1,17 @@
+{
+    "license": "MIT",
+    "require": {
+        "a/a": "^1.0",
+        "b/b": "^2.0"
+    },
+    "require-dev": {
+        "c/c": "^2.0"
+    },
+    "provide": {
+        "a/a": "1.0.0",
+        "c/c": "1.0.0"
+    },
+    "replace": {
+        "b/b": "3.0.0"
+    }
+}