Use policy rule instead of stacking up another repo to prioritize aliased packages

src/Composer/Command/InstallCommand.php

@@ -106,7 +106,6 @@ EOT
         }
 
         // prepare aliased packages
-        $aliasRepo = new ArrayRepository;
         if (!$update && $composer->getLocker()->isLocked()) {
             $aliases = $composer->getLocker()->getAliases();
         } else {
@@ -114,14 +113,13 @@ EOT
         }
         foreach ($aliases as $alias) {
             foreach ($repoManager->findPackages($alias['package'], $alias['version']) as $package) {
-                $aliasRepo->addPackage(new AliasPackage($package, $alias['alias']));
+                $package->getRepository()->addPackage(new AliasPackage($package, $alias['alias']));
             }
             foreach ($repoManager->getLocalRepository()->findPackages($alias['package'], $alias['version']) as $package) {
                 $repoManager->getLocalRepository()->addPackage(new AliasPackage($package, $alias['alias']));
                 $repoManager->getLocalRepository()->removePackage($package);
             }
         }
-        $repoManager->addRepository($aliasRepo);
 
         // creating repository pool
         $pool = new Pool;

src/Composer/DependencyResolver/DefaultPolicy.php

@@ -14,6 +14,7 @@ namespace Composer\DependencyResolver;
 
 use Composer\Repository\RepositoryInterface;
 use Composer\Package\PackageInterface;
+use Composer\Package\AliasPackage;
 use Composer\Package\LinkConstraint\VersionConstraint;
 
 /**
@@ -103,6 +104,16 @@ class DefaultPolicy implements PolicyInterface
     public function compareByPriorityPreferInstalled(Pool $pool, array $installedMap, PackageInterface $a, PackageInterface $b, $ignoreReplace = false)
     {
         if ($a->getRepository() === $b->getRepository()) {
+            if ($a->getName() === $b->getName()) {
+                $aAliased = $a instanceof AliasPackage;
+                $bAliased = $b instanceof AliasPackage;
+                if ($aAliased && !$bAliased) {
+                    return -1; // use a
+                }
+                if (!$aAliased && $bAliased) {
+                    return 1; // use b
+                }
+            }
 
             if (!$ignoreReplace) {
                 // return original, not replaced