Correctly generate conflict and alias rules for installed packages

src/Composer/DependencyResolver/RuleSetGenerator.php

@@ -190,10 +190,6 @@ class RuleSetGenerator
                 }
             }
 
-            // check implicit obsoletes
-            // for installed packages we only need to check installed/installed problems,
-            // as the others are picked up when looking at the uninstalled package.
-            if (!$isInstalled) {
             $obsoleteProviders = $this->pool->whatProvides($package->getName(), null);
 
             foreach ($obsoleteProviders as $provider) {
@@ -210,7 +206,6 @@ class RuleSetGenerator
             }
         }
     }
-    }
 
     protected function obsoleteImpossibleForAlias($package, $provider)
     {