diff --git a/src/Composer/DependencyResolver/PoolBuilder.php b/src/Composer/DependencyResolver/PoolBuilder.php
index 1ccd3a80c..3c4547be7 100644
--- a/src/Composer/DependencyResolver/PoolBuilder.php
+++ b/src/Composer/DependencyResolver/PoolBuilder.php
@@ -27,6 +27,7 @@ use Composer\Semver\Constraint\Constraint;
 use Composer\Semver\Constraint\ConstraintInterface;
 use Composer\Semver\Constraint\MatchAllConstraint;
 use Composer\Semver\Constraint\MultiConstraint;
+use Composer\Semver\Intervals;
 
 /**
  * @author Nils Adermann <naderman@naderman.de>
@@ -57,16 +58,22 @@ class PoolBuilder
      * @var IOInterface
      */
     private $io;
-
     /**
      * @psalm-var array<string, AliasPackage>
      */
     private $aliasMap = array();
     /**
-     * @psalm-var array<string, ConstraintInterface[]|null>
+     * @psalm-var array<string, ConstraintInterface>
+     */
+    private $packagesToLoad = array();
+    /**
+     * @psalm-var array<string, ConstraintInterface>
+     */
+    private $loadedPackages = array();
+    /**
+     * @psalm-var array<int, array<string, array<string, PackageInterface>>>
      */
-    private $nameConstraints = array();
-    private $loadedNames = array();
+    private $loadedPerRepo = array();
     /**
      * @psalm-var Package[]
      */
@@ -77,11 +84,23 @@ class PoolBuilder
     private $unacceptableFixedPackages = array();
     private $updateAllowList = array();
     private $skippedLoad = array();
+
+    /**
+     * Keeps a list of dependencies which are root requirements, and as such
+     * have already their maximum required range loaded and can not be
+     * extended by markPackageNameForLoading
+     *
+     * Packages get cleared from this list if they get unfixed as in that case
+     * we need to actually load them
+     */
+    private $maxExtendedReqs = array();
     /**
      * @psalm-var array<string, bool>
      */
     private $updateAllowWarned = array();
 
+    private $indexCounter = 0;
+
     /**
      * @param int[] $acceptableStabilities array of stability => BasePackage::STABILITY_* value
      * @psalm-param array<string, BasePackage::STABILITY_*> $acceptableStabilities
@@ -121,15 +140,14 @@ class PoolBuilder
             }
         }
 
-        $loadNames = array();
         foreach ($request->getFixedPackages() as $package) {
-            $this->nameConstraints[$package->getName()] = null;
-            $this->loadedNames[$package->getName()] = true;
+            // using MatchAllConstraint here because fixed packages do not need to retrigger
+            // loading any packages
+            $this->loadedPackages[$package->getName()] = new MatchAllConstraint();
 
             // replace means conflict, so if a fixed package replaces a name, no need to load that one, packages would conflict anyways
             foreach ($package->getReplaces() as $link) {
-                $this->nameConstraints[$package->getName()] = null;
-                $this->loadedNames[$link->getTarget()] = true;
+                $this->loadedPackages[$link->getTarget()] = new MatchAllConstraint();
             }
 
             // TODO in how far can we do the above for conflicts? It's more tricky cause conflicts can be limited to
@@ -140,7 +158,7 @@ class PoolBuilder
                 || $package->getRepository() instanceof PlatformRepository
                 || StabilityFilter::isPackageAcceptable($this->acceptableStabilities, $this->stabilityFlags, $package->getNames(), $package->getStability())
             ) {
-                $loadNames += $this->loadPackage($request, $package, false);
+                $this->loadPackage($request, $package, false);
             } else {
                 $this->unacceptableFixedPackages[] = $package;
             }
@@ -148,60 +166,30 @@ class PoolBuilder
 
         foreach ($request->getRequires() as $packageName => $constraint) {
             // fixed packages have already been added, so if a root require needs one of them, no need to do anything
-            if (isset($this->loadedNames[$packageName])) {
+            if (isset($this->loadedPackages[$packageName])) {
                 continue;
             }
 
-            $loadNames[$packageName] = $constraint;
-            $this->nameConstraints[$packageName] = $constraint && !($constraint instanceof MatchAllConstraint) ? array($constraint) : null;
+            $this->packagesToLoad[$packageName] = $constraint;
+            $this->maxExtendedReqs[$packageName] = true;
         }
 
-        // clean up loadNames for anything we manually marked loaded above
-        foreach ($loadNames as $name => $void) {
-            if (isset($this->loadedNames[$name])) {
-                unset($loadNames[$name]);
+        // clean up packagesToLoad for anything we manually marked loaded above
+        foreach ($this->packagesToLoad as $name => $constraint) {
+            if (isset($this->loadedPackages[$name])) {
+                unset($this->packagesToLoad[$name]);
             }
         }
 
-        while (!empty($loadNames)) {
-            foreach ($loadNames as $name => $void) {
-                $this->loadedNames[$name] = true;
-            }
-
-            $newLoadNames = array();
-            foreach ($repositories as $repository) {
-                // these repos have their packages fixed if they need to be loaded so we
-                // never need to load anything else from them
-                if ($repository instanceof PlatformRepository || $repository === $request->getLockedRepository()) {
-                    continue;
-                }
-                $result = $repository->loadPackages($loadNames, $this->acceptableStabilities, $this->stabilityFlags);
-
-                foreach ($result['namesFound'] as $name) {
-                    // avoid loading the same package again from other repositories once it has been found
-                    unset($loadNames[$name]);
-                }
-                foreach ($result['packages'] as $package) {
-                    $newLoadNames += $this->loadPackage($request, $package);
-                }
-            }
-
-            $loadNames = $newLoadNames;
+        while (!empty($this->packagesToLoad)) {
+            $this->loadPackagesMarkedForLoading($request, $repositories);
         }
 
-        // filter packages according to all the require statements collected for each package
-        $nameConstraints = array();
-        foreach ($this->nameConstraints as $name => $constraints) {
-            if (\is_array($constraints)) {
-                $nameConstraints[$name] = MultiConstraint::create(array_values(array_unique($constraints)), false);
-            }
-        }
         foreach ($this->packages as $i => $package) {
             // we check all alias related packages at once, so no need to check individual aliases
             // isset also checks non-null value
-            if (!$package instanceof AliasPackage && isset($nameConstraints[$package->getName()])) {
-                $constraint = $nameConstraints[$package->getName()];
-
+            if (!$package instanceof AliasPackage) {
+                $constraint = new Constraint('==', $package->getVersion());
                 $aliasedPackages = array($i => $package);
                 if (isset($this->aliasMap[spl_object_hash($package)])) {
                     $aliasedPackages += $this->aliasMap[spl_object_hash($package)];
@@ -241,19 +229,111 @@ class PoolBuilder
         $pool = new Pool($this->packages, $this->unacceptableFixedPackages);
 
         $this->aliasMap = array();
-        $this->nameConstraints = array();
-        $this->loadedNames = array();
+        $this->packagesToLoad = array();
+        $this->loadedPackages = array();
+        $this->loadedPerRepo = array();
         $this->packages = array();
         $this->unacceptableFixedPackages = array();
+        $this->maxExtendedReqs = array();
+        $this->skippedLoad = array();
+        $this->indexCounter = 0;
+
+        Intervals::clear();
 
         return $pool;
     }
 
+    private function markPackageNameForLoading(Request $request, $name, ConstraintInterface $constraint)
+    {
+        // Skip platform requires at this stage
+        if (PlatformRepository::isPlatformPackage($name)) {
+            return;
+        }
+
+        // Root require (which was not unfixed) already loaded the maximum range so no
+        // need to check anything here
+        if (isset($this->maxExtendedReqs[$name])) {
+            return;
+        }
+
+        // Root requires can not be overruled by dependencies so there is no point in
+        // extending the loaded constraint for those.
+        // This is triggered when loading a root require which was fixed but got unfixed, then
+        // we make sure that we load at most the intervals covered by the root constraint.
+        $rootRequires = $request->getRequires();
+        if (isset($rootRequires[$name]) && !Intervals::isSubsetOf($constraint, $rootRequires[$name])) {
+            $constraint = $rootRequires[$name];
+        }
+
+        // Not yet loaded or already marked for a reload, override the existing constraint
+        // (either it's a new one to load, or it has already been extended above)
+        if (!isset($this->loadedPackages[$name])) {
+            // Maybe it was already marked before but not loaded yet. In that case
+            // we have to extend the constraint (we don't check if they are identical because
+            // MultiConstraint::create() will optimize anyway)
+            if (isset($this->packagesToLoad[$name])) {
+                // Already marked for loading and this does not expand the constraint to be loaded, nothing to do
+                if (Intervals::isSubsetOf($constraint, $this->packagesToLoad[$name])) {
+                    return;
+                }
+
+                // extend the constraint to be loaded
+                $constraint = Intervals::compactConstraint(MultiConstraint::create(array($this->packagesToLoad[$name], $constraint), false));
+            }
+
+            $this->packagesToLoad[$name] = $constraint;
+            return;
+        }
+
+        // No need to load this package with this constraint because it is
+        // a subset of the constraint with which we have already loaded packages
+        if (Intervals::isSubsetOf($constraint, $this->loadedPackages[$name])) {
+            return;
+        }
+
+        // We have already loaded that package but not in the constraint that's
+        // required. We extend the constraint and mark that package as not being loaded
+        // yet so we get the required package versions
+        $this->packagesToLoad[$name] = Intervals::compactConstraint(MultiConstraint::create(array($this->loadedPackages[$name], $constraint), false));
+        unset($this->loadedPackages[$name]);
+    }
+
+    private function loadPackagesMarkedForLoading(Request $request, $repositories)
+    {
+        foreach ($this->packagesToLoad as $name => $constraint) {
+            $this->loadedPackages[$name] = $constraint;
+        }
+
+        $packageBatch = $this->packagesToLoad;
+        $this->packagesToLoad = array();
+
+        foreach ($repositories as $repoIndex => $repository) {
+            if (empty($packageBatch)) {
+                break;
+            }
+
+            // these repos have their packages fixed if they need to be loaded so we
+            // never need to load anything else from them
+            if ($repository instanceof PlatformRepository || $repository === $request->getLockedRepository()) {
+                continue;
+            }
+            $result = $repository->loadPackages($packageBatch, $this->acceptableStabilities, $this->stabilityFlags, isset($this->loadedPerRepo[$repoIndex]) ? $this->loadedPerRepo[$repoIndex] : array());
+
+            foreach ($result['namesFound'] as $name) {
+                // avoid loading the same package again from other repositories once it has been found
+                unset($packageBatch[$name]);
+            }
+            foreach ($result['packages'] as $package) {
+                $this->loadedPerRepo[$repoIndex][$package->getName()][$package->getVersion()] = $package;
+                $this->loadPackage($request, $package);
+            }
+        }
+    }
+
     private function loadPackage(Request $request, PackageInterface $package, $propagateUpdate = true)
     {
-        end($this->packages);
-        $index = key($this->packages) + 1;
-        $this->packages[] = $package;
+        $index = $this->indexCounter++;
+        $this->packages[$index] = $package;
 
         if ($package instanceof AliasPackage) {
             $this->aliasMap[spl_object_hash($package->getAliasOf())][$index] = $package;
@@ -283,37 +363,35 @@ class PoolBuilder
             $aliasPackage = new AliasPackage($basePackage, $alias['alias_normalized'], $alias['alias']);
             $aliasPackage->setRootPackageAlias(true);
 
-            $this->packages[] = $aliasPackage;
-            $this->aliasMap[spl_object_hash($aliasPackage->getAliasOf())][$index+1] = $aliasPackage;
+            $newIndex = $this->indexCounter++;
+            $this->packages[$newIndex] = $aliasPackage;
+            $this->aliasMap[spl_object_hash($aliasPackage->getAliasOf())][$newIndex] = $aliasPackage;
         }
 
-        $loadNames = array();
         foreach ($package->getRequires() as $link) {
             $require = $link->getTarget();
-            if (!isset($this->loadedNames[$require])) {
-                $loadNames[$require] = null;
-            // if this is a partial update with transitive dependencies we need to unfix the package we now know is a
-            // dependency of another package which we are trying to update, and then attempt to load it again
-            } elseif ($propagateUpdate && $request->getUpdateAllowTransitiveDependencies() && isset($this->skippedLoad[$require])) {
-                if ($request->getUpdateAllowTransitiveRootDependencies() || !$this->isRootRequire($request, $this->skippedLoad[$require])) {
-                    $this->unfixPackage($request, $require);
-                    $loadNames[$require] = null;
-                } elseif (!$request->getUpdateAllowTransitiveRootDependencies() && $this->isRootRequire($request, $require) && !isset($this->updateAllowWarned[$require])) {
-                    $this->updateAllowWarned[$require] = true;
-                    $this->io->writeError('<warning>Dependency "'.$require.'" is also a root requirement. Package has not been listed as an update argument, so keeping locked at old version. Use --with-all-dependencies to include root dependencies.</warning>');
-                }
-            }
-
             $linkConstraint = $link->getConstraint();
-            if ($linkConstraint && !($linkConstraint instanceof MatchAllConstraint)) {
-                if (!\array_key_exists($require, $this->nameConstraints)) {
-                    $this->nameConstraints[$require] = array($linkConstraint);
-                } elseif (\is_array($this->nameConstraints[$require])) {
-                    $this->nameConstraints[$require][] = $linkConstraint;
+
+            if ($propagateUpdate) {
+                // if this is a partial update with transitive dependencies we need to unfix the package we now know is a
+                // dependency of another package which we are trying to update, and then attempt to load it again
+                if ($request->getUpdateAllowTransitiveDependencies() && isset($this->skippedLoad[$require])) {
+                    if ($request->getUpdateAllowTransitiveRootDependencies() || !$this->isRootRequire($request, $this->skippedLoad[$require])) {
+                        $this->unfixPackage($request, $require);
+                        $this->markPackageNameForLoading($request, $require, $linkConstraint);
+                    } elseif (!$request->getUpdateAllowTransitiveRootDependencies() && $this->isRootRequire($request, $require) && !isset($this->updateAllowWarned[$require])) {
+                        $this->updateAllowWarned[$require] = true;
+                        $this->io->writeError('<warning>Dependency "'.$require.'" is also a root requirement. Package has not been listed as an update argument, so keeping locked at old version. Use --with-all-dependencies to include root dependencies.</warning>');
+                    }
+                } else {
+                    $this->markPackageNameForLoading($request, $require, $linkConstraint);
                 }
-                // else it is null and should stay null
             } else {
-                $this->nameConstraints[$require] = null;
+                // We also need to load the requirements of a fixed package
+                // unless it was skipped
+                if (!isset($this->skippedLoad[$require])) {
+                    $this->markPackageNameForLoading($request, $require, $linkConstraint);
+                }
             }
         }
 
@@ -322,12 +400,10 @@ class PoolBuilder
         if ($propagateUpdate && $request->getUpdateAllowTransitiveDependencies()) {
             foreach ($package->getReplaces() as $link) {
                 $replace = $link->getTarget();
-                if (isset($this->loadedNames[$replace]) && isset($this->skippedLoad[$replace])) {
+                if (isset($this->loadedPackages[$replace]) && isset($this->skippedLoad[$replace])) {
                     if ($request->getUpdateAllowTransitiveRootDependencies() || !$this->isRootRequire($request, $this->skippedLoad[$replace])) {
                         $this->unfixPackage($request, $replace);
-                        $loadNames[$replace] = null;
-                        // TODO should we try to merge constraints here?
-                        $this->nameConstraints[$replace] = null;
+                        $this->markPackageNameForLoading($request, $replace, $link->getConstraint());
                     } elseif (!$request->getUpdateAllowTransitiveRootDependencies() && $this->isRootRequire($request, $replace) && !isset($this->updateAllowWarned[$replace])) {
                         $this->updateAllowWarned[$replace] = true;
                         $this->io->writeError('<warning>Dependency "'.$replace.'" is also a root requirement. Package has not been listed as an update argument, so keeping locked at old version. Use --with-all-dependencies to include root dependencies.</warning>');
@@ -335,8 +411,6 @@ class PoolBuilder
                 }
             }
         }
-
-        return $loadNames;
     }
 
     /**
@@ -401,14 +475,7 @@ class PoolBuilder
             if (!($lockedPackage instanceof AliasPackage) && $lockedPackage->getName() === $name) {
                 if (false !== $index = array_search($lockedPackage, $this->packages, true)) {
                     $request->unfixPackage($lockedPackage);
-                    unset($this->packages[$index]);
-                    if (isset($this->aliasMap[spl_object_hash($lockedPackage)])) {
-                        foreach ($this->aliasMap[spl_object_hash($lockedPackage)] as $aliasIndex => $aliasPackage) {
-                            $request->unfixPackage($aliasPackage);
-                            unset($this->packages[$aliasIndex]);
-                        }
-                        unset($this->aliasMap[spl_object_hash($lockedPackage)]);
-                    }
+                    $this->removeLoadedPackage($request, $lockedPackage, $index);
                 }
             }
         }
@@ -423,7 +490,20 @@ class PoolBuilder
         }
 
         unset($this->skippedLoad[$name]);
-        unset($this->loadedNames[$name]);
+        unset($this->loadedPackages[$name]);
+        unset($this->maxExtendedReqs[$name]);
+    }
+
+    private function removeLoadedPackage(Request $request, PackageInterface $package, $index)
+    {
+        unset($this->packages[$index]);
+        if (isset($this->aliasMap[spl_object_hash($package)])) {
+            foreach ($this->aliasMap[spl_object_hash($package)] as $aliasIndex => $aliasPackage) {
+                $request->unfixPackage($aliasPackage);
+                unset($this->packages[$aliasIndex]);
+            }
+            unset($this->aliasMap[spl_object_hash($package)]);
+        }
     }
 }
 
diff --git a/src/Composer/DependencyResolver/Request.php b/src/Composer/DependencyResolver/Request.php
index 5782c3ff1..c3367e3d9 100644
--- a/src/Composer/DependencyResolver/Request.php
+++ b/src/Composer/DependencyResolver/Request.php
@@ -17,6 +17,7 @@ use Composer\Package\PackageInterface;
 use Composer\Package\RootAliasPackage;
 use Composer\Repository\LockArrayRepository;
 use Composer\Semver\Constraint\ConstraintInterface;
+use Composer\Semver\Constraint\MatchAllConstraint;
 
 /**
  * @author Nils Adermann <naderman@naderman.de>
@@ -55,6 +56,13 @@ class Request
     public function requireName($packageName, ConstraintInterface $constraint = null)
     {
         $packageName = strtolower($packageName);
+
+        if ($constraint === null) {
+            $constraint = new MatchAllConstraint();
+        }
+        if (isset($this->requires[$packageName])) {
+            throw new \LogicException('Overwriting requires seems like a bug ('.$packageName.' '.$this->requires[$packageName]->getPrettyConstraint().' => '.$constraint->getPrettyConstraint().', check why it is happening, might be a root alias');
+        }
         $this->requires[$packageName] = $constraint;
     }
 
diff --git a/src/Composer/Package/Link.php b/src/Composer/Package/Link.php
index 5a6c683cc..4af6a5a6a 100644
--- a/src/Composer/Package/Link.php
+++ b/src/Composer/Package/Link.php
@@ -32,7 +32,7 @@ class Link
     protected $target;
 
     /**
-     * @var ConstraintInterface|null
+     * @var ConstraintInterface
      */
     protected $constraint;
 
@@ -49,13 +49,13 @@ class Link
     /**
      * Creates a new package link.
      *
-     * @param string                   $source
-     * @param string                   $target
-     * @param ConstraintInterface|null $constraint       Constraint applying to the target of this link
-     * @param string                   $description      Used to create a descriptive string representation
-     * @param string|null              $prettyConstraint
+     * @param string              $source
+     * @param string              $target
+     * @param ConstraintInterface $constraint       Constraint applying to the target of this link
+     * @param string              $description      Used to create a descriptive string representation
+     * @param string|null         $prettyConstraint
      */
-    public function __construct($source, $target, ConstraintInterface $constraint = null, $description = 'relates to', $prettyConstraint = null)
+    public function __construct($source, $target, ConstraintInterface $constraint, $description = 'relates to', $prettyConstraint = null)
     {
         $this->source = strtolower($source);
         $this->target = strtolower($target);
@@ -89,7 +89,7 @@ class Link
     }
 
     /**
-     * @return ConstraintInterface|null
+     * @return ConstraintInterface
      */
     public function getConstraint()
     {
diff --git a/src/Composer/Repository/ArrayRepository.php b/src/Composer/Repository/ArrayRepository.php
index 37a241cbc..24a7a38d8 100644
--- a/src/Composer/Repository/ArrayRepository.php
+++ b/src/Composer/Repository/ArrayRepository.php
@@ -50,7 +50,7 @@ class ArrayRepository implements RepositoryInterface
     /**
      * {@inheritDoc}
      */
-    public function loadPackages(array $packageMap, array $acceptableStabilities, array $stabilityFlags)
+    public function loadPackages(array $packageMap, array $acceptableStabilities, array $stabilityFlags, array $alreadyLoaded = array())
     {
         $packages = $this->getPackages();
 
@@ -61,6 +61,7 @@ class ArrayRepository implements RepositoryInterface
                 if (
                     (!$packageMap[$package->getName()] || $packageMap[$package->getName()]->matches(new Constraint('==', $package->getVersion())))
                     && StabilityFilter::isPackageAcceptable($acceptableStabilities, $stabilityFlags, $package->getNames(), $package->getStability())
+                    && !isset($alreadyLoaded[$package->getName()][$package->getVersion()])
                 ) {
                     // add selected packages which match stability requirements
                     $result[spl_object_hash($package)] = $package;
diff --git a/src/Composer/Repository/ComposerRepository.php b/src/Composer/Repository/ComposerRepository.php
index 9b244f397..f9018136b 100644
--- a/src/Composer/Repository/ComposerRepository.php
+++ b/src/Composer/Repository/ComposerRepository.php
@@ -341,13 +341,13 @@ class ComposerRepository extends ArrayRepository implements ConfigurableReposito
         return $names;
     }
 
-    public function loadPackages(array $packageNameMap, array $acceptableStabilities, array $stabilityFlags)
+    public function loadPackages(array $packageNameMap, array $acceptableStabilities, array $stabilityFlags, array $alreadyLoaded = array())
     {
         // this call initializes loadRootServerFile which is needed for the rest below to work
         $hasProviders = $this->hasProviders();
 
         if (!$hasProviders && !$this->hasPartialPackages() && !$this->lazyProvidersUrl) {
-            return parent::loadPackages($packageNameMap, $acceptableStabilities, $stabilityFlags);
+            return parent::loadPackages($packageNameMap, $acceptableStabilities, $stabilityFlags, $alreadyLoaded);
         }
 
         $packages = array();
@@ -363,12 +363,13 @@ class ComposerRepository extends ArrayRepository implements ConfigurableReposito
                     continue;
                 }
 
-                $candidates = $this->whatProvides($name, $acceptableStabilities, $stabilityFlags);
+                $candidates = $this->whatProvides($name, $acceptableStabilities, $stabilityFlags, $alreadyLoaded);
                 foreach ($candidates as $candidate) {
                     if ($candidate->getName() !== $name) {
                         throw new \LogicException('whatProvides should never return a package with a different name than the requested one');
                     }
                     $namesFound[$name] = true;
+
                     if (!$constraint || $constraint->matches(new Constraint('==', $candidate->getVersion()))) {
                         $matches[spl_object_hash($candidate)] = $candidate;
                         if ($candidate instanceof AliasPackage && !isset($matches[spl_object_hash($candidate->getAliasOf())])) {
@@ -401,7 +402,7 @@ class ComposerRepository extends ArrayRepository implements ConfigurableReposito
                 }
             }
 
-            $result = $this->loadAsyncPackages($packageNameMap, $acceptableStabilities, $stabilityFlags);
+            $result = $this->loadAsyncPackages($packageNameMap, $acceptableStabilities, $stabilityFlags, $alreadyLoaded);
             $packages = array_merge($packages, $result['packages']);
             $namesFound = array_merge($namesFound, $result['namesFound']);
         }
@@ -531,7 +532,7 @@ class ComposerRepository extends ArrayRepository implements ConfigurableReposito
      * @param string $name package name
      * @return array|mixed
      */
-    private function whatProvides($name, array $acceptableStabilities = null, array $stabilityFlags = null)
+    private function whatProvides($name, array $acceptableStabilities = null, array $stabilityFlags = null, array $alreadyLoaded = array())
     {
         if (!$this->hasPartialPackages() || !isset($this->partialPackagesByName[$name])) {
             // skip platform packages, root package and composer-plugin-api
@@ -623,6 +624,11 @@ class ComposerRepository extends ArrayRepository implements ConfigurableReposito
                         $version['version_normalized'] = $this->versionParser->normalize($version['version']);
                     }
 
+                    // avoid loading packages which have already been loaded
+                    if (isset($alreadyLoaded[$name][$version['version_normalized']])) {
+                        continue;
+                    }
+
                     if ($this->isVersionAcceptable(null, $normalizedName, $version, $acceptableStabilities, $stabilityFlags)) {
                         $versionsToLoad[$version['uid']] = $version;
                     }
@@ -680,7 +686,7 @@ class ComposerRepository extends ArrayRepository implements ConfigurableReposito
     /**
      * @param array $packageNames array of package name => ConstraintInterface|null - if a constraint is provided, only packages matching it will be loaded
      */
-    private function loadAsyncPackages(array $packageNames, array $acceptableStabilities = null, array $stabilityFlags = null)
+    private function loadAsyncPackages(array $packageNames, array $acceptableStabilities = null, array $stabilityFlags = null, array $alreadyLoaded = array())
     {
         $this->loadRootServerFile();
 
@@ -723,7 +729,7 @@ class ComposerRepository extends ArrayRepository implements ConfigurableReposito
             }
 
             $promises[] = $this->asyncFetchFile($url, $cacheKey, $lastModified)
-                ->then(function ($response) use (&$packages, &$namesFound, $contents, $realName, $constraint, $repo, $acceptableStabilities, $stabilityFlags) {
+                ->then(function ($response) use (&$packages, &$namesFound, $contents, $realName, $constraint, $repo, $acceptableStabilities, $stabilityFlags, $alreadyLoaded) {
                     if (true === $response) {
                         $response = $contents;
                     }
@@ -748,6 +754,11 @@ class ComposerRepository extends ArrayRepository implements ConfigurableReposito
                             $version['version_normalized'] = $repo->versionParser->normalize($version['version']);
                         }
 
+                        // avoid loading packages which have already been loaded
+                        if (isset($alreadyLoaded[$realName][$version['version_normalized']])) {
+                            continue;
+                        }
+
                         if ($repo->isVersionAcceptable($constraint, $realName, $version, $acceptableStabilities, $stabilityFlags)) {
                             $versionsToLoad[] = $version;
                         }
diff --git a/src/Composer/Repository/CompositeRepository.php b/src/Composer/Repository/CompositeRepository.php
index acabaffb0..eaa70db2b 100644
--- a/src/Composer/Repository/CompositeRepository.php
+++ b/src/Composer/Repository/CompositeRepository.php
@@ -102,13 +102,13 @@ class CompositeRepository implements RepositoryInterface
     /**
      * {@inheritDoc}
      */
-    public function loadPackages(array $packageMap, array $acceptableStabilities, array $stabilityFlags)
+    public function loadPackages(array $packageMap, array $acceptableStabilities, array $stabilityFlags, array $alreadyLoaded = array())
     {
         $packages = array();
         $namesFound = array();
         foreach ($this->repositories as $repository) {
             /* @var $repository RepositoryInterface */
-            $result = $repository->loadPackages($packageMap, $acceptableStabilities, $stabilityFlags);
+            $result = $repository->loadPackages($packageMap, $acceptableStabilities, $stabilityFlags, $alreadyLoaded);
             $packages[] = $result['packages'];
             $namesFound[] = $result['namesFound'];
         }
diff --git a/src/Composer/Repository/FilterRepository.php b/src/Composer/Repository/FilterRepository.php
index 5221e55cb..361c2fe67 100644
--- a/src/Composer/Repository/FilterRepository.php
+++ b/src/Composer/Repository/FilterRepository.php
@@ -108,7 +108,7 @@ class FilterRepository implements RepositoryInterface
     /**
      * {@inheritDoc}
      */
-    public function loadPackages(array $packageMap, array $acceptableStabilities, array $stabilityFlags)
+    public function loadPackages(array $packageMap, array $acceptableStabilities, array $stabilityFlags, array $alreadyLoaded = array())
     {
         foreach ($packageMap as $name => $constraint) {
             if (!$this->isAllowed($name)) {
@@ -120,7 +120,7 @@ class FilterRepository implements RepositoryInterface
             return array('namesFound' => array(), 'packages' => array());
         }
 
-        $result = $this->repo->loadPackages($packageMap, $acceptableStabilities, $stabilityFlags);
+        $result = $this->repo->loadPackages($packageMap, $acceptableStabilities, $stabilityFlags, $alreadyLoaded);
         if (!$this->canonical) {
             $result['namesFound'] = array();
         }
diff --git a/src/Composer/Repository/PlatformRepository.php b/src/Composer/Repository/PlatformRepository.php
index ac6d49525..f6ec91864 100644
--- a/src/Composer/Repository/PlatformRepository.php
+++ b/src/Composer/Repository/PlatformRepository.php
@@ -593,4 +593,21 @@ class PlatformRepository extends ArrayRepository
 
         $this->addPackage($lib);
     }
+
+    /**
+     * Check if a package name is a platform package.
+     *
+     * @param $name
+     * @return bool
+     */
+    public static function isPlatformPackage($name)
+    {
+        static $cache = array();
+
+        if (isset($cache[$name])) {
+            return $cache[$name];
+        }
+
+        return $cache[$name] = (bool) preg_match(PlatformRepository::PLATFORM_PACKAGE_REGEX, $name);
+    }
 }
diff --git a/src/Composer/Repository/RepositoryInterface.php b/src/Composer/Repository/RepositoryInterface.php
index afb99ca62..54e6e04a6 100644
--- a/src/Composer/Repository/RepositoryInterface.php
+++ b/src/Composer/Repository/RepositoryInterface.php
@@ -75,11 +75,13 @@ interface RepositoryInterface extends \Countable
      * @psalm-param array<string, BasePackage::STABILITY_*> $acceptableStabilities
      * @param int[] $stabilityFlags an array of package name => BasePackage::STABILITY_* value
      * @psalm-param array<string, BasePackage::STABILITY_*> $stabilityFlags
+     * @param array[] $alreadyLoaded an array of package name => package version => package
+     * @psalm-param array<string, array<string, PackageInterface>> $alreadyLoaded
      *
      * @return array [namesFound => string[], packages => PackageInterface[]]
      * @psalm-return array{namesFound: string[], packages: PackageInterface[]}
      */
-    public function loadPackages(array $packageNameMap, array $acceptableStabilities, array $stabilityFlags);
+    public function loadPackages(array $packageNameMap, array $acceptableStabilities, array $stabilityFlags, array $alreadyLoaded = array());
 
     /**
      * Searches the repository for packages containing the query
diff --git a/tests/Composer/Test/Autoload/AutoloadGeneratorTest.php b/tests/Composer/Test/Autoload/AutoloadGeneratorTest.php
index c178e93d8..35dcd37da 100644
--- a/tests/Composer/Test/Autoload/AutoloadGeneratorTest.php
+++ b/tests/Composer/Test/Autoload/AutoloadGeneratorTest.php
@@ -16,6 +16,7 @@ use Composer\Autoload\AutoloadGenerator;
 use Composer\Package\Link;
 use Composer\Package\Version\VersionParser;
 use Composer\Semver\Constraint\Constraint;
+use Composer\Semver\Constraint\MatchAllConstraint;
 use Composer\Util\Filesystem;
 use Composer\Package\AliasPackage;
 use Composer\Package\Package;
@@ -366,8 +367,8 @@ class AutoloadGeneratorTest extends TestCase
     {
         $package = new Package('a', '1.0', '1.0');
         $package->setRequires(array(
-            new Link('a', 'a/a'),
-            new Link('a', 'b/b'),
+            new Link('a', 'a/a', new MatchAllConstraint()),
+            new Link('a', 'b/b', new MatchAllConstraint()),
         ));
 
         $packages = array();
@@ -395,7 +396,7 @@ class AutoloadGeneratorTest extends TestCase
     {
         $package = new Package('a', '1.0', '1.0');
         $package->setRequires(array(
-            new Link('a', 'a/a'),
+            new Link('a', 'a/a', new MatchAllConstraint()),
         ));
 
         $packages = array();
@@ -403,11 +404,11 @@ class AutoloadGeneratorTest extends TestCase
         $packages[] = $b = new Package('b/b', '1.0', '1.0');
         $a->setAutoload(array('psr-0' => array('A' => 'src/', 'A\\B' => 'lib/')));
         $a->setRequires(array(
-            new Link('a/a', 'b/b'),
+            new Link('a/a', 'b/b', new MatchAllConstraint()),
         ));
         $b->setAutoload(array('psr-0' => array('B\\Sub\\Name' => 'src/')));
         $b->setRequires(array(
-            new Link('b/b', 'a/a'),
+            new Link('b/b', 'a/a', new MatchAllConstraint()),
         ));
 
         $this->repository->expects($this->once())
@@ -427,13 +428,13 @@ class AutoloadGeneratorTest extends TestCase
     public function testNonDevAutoloadShouldIncludeReplacedPackages()
     {
         $package = new Package('a', '1.0', '1.0');
-        $package->setRequires(array(new Link('a', 'a/a')));
+        $package->setRequires(array(new Link('a', 'a/a', new MatchAllConstraint())));
 
         $packages = array();
         $packages[] = $a = new Package('a/a', '1.0', '1.0');
         $packages[] = $b = new Package('b/b', '1.0', '1.0');
 
-        $a->setRequires(array(new Link('a/a', 'b/c')));
+        $a->setRequires(array(new Link('a/a', 'b/c', new MatchAllConstraint())));
 
         $b->setAutoload(array('psr-4' => array('B\\' => 'src/')));
         $b->setReplaces(
@@ -462,7 +463,7 @@ class AutoloadGeneratorTest extends TestCase
     {
         $package = new Package('a', '1.0', '1.0');
         $package->setRequires(array(
-            new Link('a', 'a/a'),
+            new Link('a', 'a/a', new MatchAllConstraint()),
         ));
 
         $packages = array();
@@ -470,11 +471,11 @@ class AutoloadGeneratorTest extends TestCase
         $packages[] = $b = new Package('b/b', '1.0', '1.0');
         $a->setAutoload(array('psr-0' => array('A' => 'src/', 'A\\B' => 'lib/')));
         $a->setRequires(array(
-            new Link('a/a', 'c/c'),
+            new Link('a/a', 'c/c', new MatchAllConstraint()),
         ));
         $b->setAutoload(array('psr-0' => array('B\\Sub\\Name' => 'src/')));
         $b->setReplaces(array(
-            new Link('b/b', 'c/c'),
+            new Link('b/b', 'c/c', new MatchAllConstraint()),
         ));
 
         $this->repository->expects($this->once())
@@ -495,7 +496,7 @@ class AutoloadGeneratorTest extends TestCase
     {
         $package = new Package('a', '1.0', '1.0');
         $package->setRequires(array(
-            new Link('a', 'a/a')
+            new Link('a', 'a/a', new MatchAllConstraint())
         ));
 
         $packages = array();
@@ -506,18 +507,18 @@ class AutoloadGeneratorTest extends TestCase
         $packages[] = $e = new Package('e/e', '1.0', '1.0');
         $a->setAutoload(array('classmap' => array('src/A.php')));
         $a->setRequires(array(
-            new Link('a/a', 'b/b')
+            new Link('a/a', 'b/b', new MatchAllConstraint())
         ));
         $b->setAutoload(array('classmap' => array('src/B.php')));
         $b->setRequires(array(
-            new Link('b/b', 'e/e')
+            new Link('b/b', 'e/e', new MatchAllConstraint())
         ));
         $c->setAutoload(array('classmap' => array('src/C.php')));
         $c->setReplaces(array(
-            new Link('c/c', 'b/b')
+            new Link('c/c', 'b/b', new MatchAllConstraint())
         ));
         $c->setRequires(array(
-            new Link('c/c', 'd/d')
+            new Link('c/c', 'd/d', new MatchAllConstraint())
         ));
         $d->setAutoload(array('classmap' => array('src/D.php')));
         $e->setAutoload(array('classmap' => array('src/E.php')));
@@ -547,7 +548,7 @@ class AutoloadGeneratorTest extends TestCase
     {
         $package = new Package('a', '1.0', '1.0');
         $package->setRequires(array(
-            new Link('a', 'a/a'),
+            new Link('a', 'a/a', new MatchAllConstraint()),
         ));
 
         $package->setAutoload(array(
@@ -652,8 +653,8 @@ EOF;
     {
         $package = new Package('a', '1.0', '1.0');
         $package->setRequires(array(
-            new Link('a', 'a/a'),
-            new Link('a', 'b/b'),
+            new Link('a', 'a/a', new MatchAllConstraint()),
+            new Link('a', 'b/b', new MatchAllConstraint()),
         ));
 
         $packages = array();
@@ -692,8 +693,8 @@ EOF;
     {
         $package = new Package('a', '1.0', '1.0');
         $package->setRequires(array(
-            new Link('a', 'a/a'),
-            new Link('a', 'b/b'),
+            new Link('a', 'a/a', new MatchAllConstraint()),
+            new Link('a', 'b/b', new MatchAllConstraint()),
         ));
 
         $packages = array();
@@ -732,9 +733,9 @@ EOF;
     {
         $package = new Package('a', '1.0', '1.0');
         $package->setRequires(array(
-            new Link('a', 'a/a'),
-            new Link('a', 'b/b'),
-            new Link('a', 'c/c'),
+            new Link('a', 'a/a', new MatchAllConstraint()),
+            new Link('a', 'b/b', new MatchAllConstraint()),
+            new Link('a', 'c/c', new MatchAllConstraint()),
         ));
 
         $packages = array();
@@ -777,9 +778,9 @@ EOF;
     {
         $package = new Package('a', '1.0', '1.0');
         $package->setRequires(array(
-            new Link('a', 'a/a'),
-            new Link('a', 'b/b'),
-            new Link('a', 'c/c'),
+            new Link('a', 'a/a', new MatchAllConstraint()),
+            new Link('a', 'b/b', new MatchAllConstraint()),
+            new Link('a', 'c/c', new MatchAllConstraint()),
         ));
 
         $packages = array();
@@ -827,9 +828,9 @@ EOF;
         $package = new Package('a', '1.0', '1.0');
         $package->setAutoload(array('files' => array('root.php')));
         $package->setRequires(array(
-            new Link('a', 'a/a'),
-            new Link('a', 'b/b'),
-            new Link('a', 'c/c'),
+            new Link('a', 'a/a', new MatchAllConstraint()),
+            new Link('a', 'b/b', new MatchAllConstraint()),
+            new Link('a', 'c/c', new MatchAllConstraint()),
         ));
 
         $packages = array();
@@ -878,9 +879,9 @@ EOF;
         $notAutoloadPackage = new Package('a', '1.0', '1.0');
 
         $requires = array(
-            new Link('a', 'a/a'),
-            new Link('a', 'b/b'),
-            new Link('a', 'c/c'),
+            new Link('a', 'a/a', new MatchAllConstraint()),
+            new Link('a', 'b/b', new MatchAllConstraint()),
+            new Link('a', 'c/c', new MatchAllConstraint()),
         );
         $autoloadPackage->setRequires($requires);
         $notAutoloadPackage->setRequires($requires);
@@ -949,10 +950,10 @@ EOF;
         $package = new Package('a', '1.0', '1.0');
         $package->setAutoload(array('files' => array('root2.php')));
         $package->setRequires(array(
-            new Link('a', 'z/foo'),
-            new Link('a', 'b/bar'),
-            new Link('a', 'd/d'),
-            new Link('a', 'e/e'),
+            new Link('a', 'z/foo', new MatchAllConstraint()),
+            new Link('a', 'b/bar', new MatchAllConstraint()),
+            new Link('a', 'd/d', new MatchAllConstraint()),
+            new Link('a', 'e/e', new MatchAllConstraint()),
         ));
 
         $packages = array();
@@ -963,18 +964,18 @@ EOF;
         $packages[] = $e = new Package('e/e', '1.0', '1.0');
 
         $z->setAutoload(array('files' => array('testA.php')));
-        $z->setRequires(array(new Link('z/foo', 'c/lorem')));
+        $z->setRequires(array(new Link('z/foo', 'c/lorem', new MatchAllConstraint())));
 
         $b->setAutoload(array('files' => array('testB.php')));
-        $b->setRequires(array(new Link('b/bar', 'c/lorem'), new Link('b/bar', 'd/d')));
+        $b->setRequires(array(new Link('b/bar', 'c/lorem', new MatchAllConstraint()), new Link('b/bar', 'd/d', new MatchAllConstraint())));
 
         $c->setAutoload(array('files' => array('testC.php')));
 
         $d->setAutoload(array('files' => array('testD.php')));
-        $d->setRequires(array(new Link('d/d', 'c/lorem')));
+        $d->setRequires(array(new Link('d/d', 'c/lorem', new MatchAllConstraint())));
 
         $e->setAutoload(array('files' => array('testE.php')));
-        $e->setRequires(array(new Link('e/e', 'c/lorem')));
+        $e->setRequires(array(new Link('e/e', 'c/lorem', new MatchAllConstraint())));
 
         $this->repository->expects($this->once())
             ->method('getCanonicalPackages')
@@ -1022,8 +1023,8 @@ EOF;
             'classmap' => array($this->workingDir.'/src'),
         ));
         $mainPackage->setRequires(array(
-            new Link('z', 'a/a'),
-            new Link('z', 'b/b'),
+            new Link('z', 'a/a', new MatchAllConstraint()),
+            new Link('z', 'b/b', new MatchAllConstraint()),
         ));
 
         $packages = array();
@@ -1285,7 +1286,7 @@ EOF;
             'files' => array('test.php'),
         ));
         $package->setRequires(array(
-            new Link('a', 'b/b'),
+            new Link('a', 'b/b', new MatchAllConstraint()),
         ));
 
         $vendorPackage = new Package('b/b', '1.0', '1.0');
diff --git a/tests/Composer/Test/DependencyResolver/Fixtures/poolbuilder/alias-priority-conflicting.test b/tests/Composer/Test/DependencyResolver/Fixtures/poolbuilder/alias-priority-conflicting.test
new file mode 100644
index 000000000..5456f0baf
--- /dev/null
+++ b/tests/Composer/Test/DependencyResolver/Fixtures/poolbuilder/alias-priority-conflicting.test
@@ -0,0 +1,62 @@
+--TEST--
+Check root aliases are loaded
+
+--ROOT--
+{
+    "minimum-stability": "dev",
+    "aliases": [
+        {
+            "package": "req/pkg",
+            "version": "dev-feature-foo",
+            "alias": "dev-master"
+        }
+    ]
+}
+
+
+--REQUEST--
+{
+    "require": {
+        "package/a": "dev-master",
+        "req/pkg": "dev-feature-foo"
+    }
+}
+
+--FIXED--
+[
+]
+
+--PACKAGE-REPOS--
+[
+    [
+        {
+            "name": "req/pkg", "version": "dev-feature-foo",
+            "source": { "reference": "feat.f", "type": "git", "url": "" }
+        },
+        {
+            "name": "req/pkg", "version": "dev-master",
+            "extra": { "branch-alias": { "dev-master": "1.0.x-dev" } },
+            "source": { "reference": "forked", "type": "git", "url": "" },
+            "default-branch": true
+        },
+        {
+            "name": "req/pkg", "version": "dev-master",
+            "extra": { "branch-alias": { "dev-master": "1.0.x-dev" } },
+            "source": { "reference": "master", "type": "git", "url": "" },
+            "default-branch": true
+        },
+        {
+            "name": "package/a", "version": "dev-master",
+            "require": { "req/pkg": "dev-master" },
+            "default-branch": true
+        }
+    ]
+]
+
+--EXPECT--
+[
+    "req/pkg-dev-feature-foo#feat.f",
+    "req/pkg-dev-master#feat.f (alias of dev-feature-foo)",
+    "package/a-dev-master",
+    "package/a-9999999-dev (alias of dev-master)"
+]
diff --git a/tests/Composer/Test/DependencyResolver/Fixtures/poolbuilder/alias-with-reference.test b/tests/Composer/Test/DependencyResolver/Fixtures/poolbuilder/alias-with-reference.test
new file mode 100644
index 000000000..f3cbca7f1
--- /dev/null
+++ b/tests/Composer/Test/DependencyResolver/Fixtures/poolbuilder/alias-with-reference.test
@@ -0,0 +1,59 @@
+--TEST--
+Check root aliases get selected correctly
+
+--ROOT--
+{
+    "stability-flags": {
+        "a/aliased": "dev"
+    },
+    "aliases": [
+        {
+            "package": "a/aliased",
+            "version": "dev-master",
+            "alias": "1.0.0"
+        }
+    ],
+    "references": {
+        "a/aliased": "abcd"
+    }
+}
+
+
+--REQUEST--
+{
+    "require": {
+        "a/aliased": "dev-master",
+        "b/requirer": "*"
+    }
+}
+
+--FIXED--
+[
+]
+
+--PACKAGE-REPOS--
+[
+    [
+        {
+            "name": "a/aliased", "version": "dev-master",
+            "source": { "reference": "orig", "type": "git", "url": "" },
+            "default-branch": true
+        },
+        {
+            "name": "a/aliased", "version": "1.0"
+        },
+        {
+            "name": "b/requirer", "version": "1.0.0",
+            "require": { "a/aliased": "1.0.0" },
+            "source": { "reference": "1.0.0", "type": "git", "url": "" }
+        }
+    ]
+]
+
+--EXPECT--
+[
+    "a/aliased-dev-master#abcd",
+    "a/aliased-1.0.0.0#abcd (alias of dev-master)",
+    "b/requirer-1.0.0.0#1.0.0",
+    "a/aliased-9999999-dev#abcd (alias of dev-master)"
+]
diff --git a/tests/Composer/Test/DependencyResolver/Fixtures/poolbuilder/constraint-expansion-works-with-exact-versions.test b/tests/Composer/Test/DependencyResolver/Fixtures/poolbuilder/constraint-expansion-works-with-exact-versions.test
new file mode 100644
index 000000000..908b3602c
--- /dev/null
+++ b/tests/Composer/Test/DependencyResolver/Fixtures/poolbuilder/constraint-expansion-works-with-exact-versions.test
@@ -0,0 +1,31 @@
+--TEST--
+Tests if version constraint is expanded. If not, dep/dep 3.0.0 would not be loaded here.
+
+--REQUEST--
+{
+    "require": {
+        "root/req": "*"
+    }
+}
+
+--FIXED--
+[
+]
+
+--PACKAGE-REPOS--
+[
+    [
+        {"name": "root/req", "version": "1.0.0", "require": {"dep/dep": "2.3.4"}},
+        {"name": "dep/dep", "version": "2.3.4", "require": {"dep/dep2": "2.*"}},
+        {"name": "dep/dep", "version": "2.3.5"},
+        {"name": "dep/dep2", "version": "2.3.4", "require": {"dep/dep": "2.*"}}
+    ]
+]
+
+--EXPECT--
+[
+    "root/req-1.0.0.0",
+    "dep/dep-2.3.4.0",
+    "dep/dep2-2.3.4.0",
+    "dep/dep-2.3.5.0"
+]
diff --git a/tests/Composer/Test/DependencyResolver/Fixtures/poolbuilder/fixed-packages-do-not-load-from-repos.test b/tests/Composer/Test/DependencyResolver/Fixtures/poolbuilder/fixed-packages-do-not-load-from-repos.test
index f1dbd69fe..fb52a9b6d 100644
--- a/tests/Composer/Test/DependencyResolver/Fixtures/poolbuilder/fixed-packages-do-not-load-from-repos.test
+++ b/tests/Composer/Test/DependencyResolver/Fixtures/poolbuilder/fixed-packages-do-not-load-from-repos.test
@@ -3,21 +3,34 @@ Fixed packages do not get loaded from the repos
 
 --REQUEST--
 {
-    "some/pkg": "*"
+    "require": {
+        "some/pkg": "*",
+        "root/req": "*"
+    }
 }
 
 --FIXED--
 [
-    {"name": "some/pkg", "version": "1.0.3", "id": 1}
+    {"name": "some/pkg", "version": "1.0.3", "id": 1},
+    {"name": "dep/dep", "version": "2.1.5", "id": 2}
 ]
 
---PACKAGES--
+--PACKAGE-REPOS--
 [
-    {"name": "some/pkg", "version": "1.0.0"},
-    {"name": "some/pkg", "version": "1.1.0"}
+    [
+        {"name": "some/pkg", "version": "1.0.0"},
+        {"name": "some/pkg", "version": "1.1.0"},
+        {"name": "root/req", "version": "1.0.0", "require": {"dep/dep": "2.*"}},
+        {"name": "root/req", "version": "2.0.0", "require": {"dep/dep": "3.*"}},
+        {"name": "dep/dep", "version": "2.3.4"},
+        {"name": "dep/dep", "version": "3.0.1"}
+    ]
 ]
 
 --EXPECT--
 [
-    1
+    1,
+    2,
+    "root/req-1.0.0.0",
+    "root/req-2.0.0.0"
 ]
diff --git a/tests/Composer/Test/DependencyResolver/Fixtures/poolbuilder/fixed-packages-replaced-do-not-load-from-repos.test b/tests/Composer/Test/DependencyResolver/Fixtures/poolbuilder/fixed-packages-replaced-do-not-load-from-repos.test
new file mode 100644
index 000000000..4847411ef
--- /dev/null
+++ b/tests/Composer/Test/DependencyResolver/Fixtures/poolbuilder/fixed-packages-replaced-do-not-load-from-repos.test
@@ -0,0 +1,33 @@
+--TEST--
+Packages replaced by fixed packages do not get loaded from the repos
+
+--REQUEST--
+{
+    "require": {
+        "some/pkg": "*",
+        "root/req": "*"
+    }
+}
+
+--FIXED--
+[
+    {"name": "some/pkg", "version": "1.0.3", "replace": {"dep/dep": "2.1.0"}, "id": 1}
+]
+
+--PACKAGE-REPOS--
+[
+    [
+        {"name": "some/pkg", "version": "1.0.0"},
+        {"name": "root/req", "version": "1.0.0", "require": {"dep/dep": "2.*"}},
+        {"name": "root/req", "version": "2.0.0", "require": {"dep/dep": "3.*"}},
+        {"name": "dep/dep", "version": "2.3.4"},
+        {"name": "dep/dep", "version": "3.0.1"}
+    ]
+]
+
+--EXPECT--
+[
+    1,
+    "root/req-1.0.0.0",
+    "root/req-2.0.0.0"
+]
diff --git a/tests/Composer/Test/DependencyResolver/Fixtures/poolbuilder/multi-repo-replace-partial-update.test b/tests/Composer/Test/DependencyResolver/Fixtures/poolbuilder/multi-repo-replace-partial-update.test
new file mode 100644
index 000000000..01eda5215
--- /dev/null
+++ b/tests/Composer/Test/DependencyResolver/Fixtures/poolbuilder/multi-repo-replace-partial-update.test
@@ -0,0 +1,107 @@
+--TEST--
+Check that replacers from additional repositories are loaded when doing a partial update
+
+--REQUEST--
+{
+    "require": {
+        "base/package": "^1.0",
+        "indirect/replacer": "^1.0"
+    },
+    "locked": [
+        {"name": "shared/dep", "version": "1.2.0", "id": 1},
+        {"name": "indirect/replacer", "version": "1.2.0", "require": {"replacer/package": "^1.2"}, "id": 2},
+        {"name": "replacer/package", "version": "1.2.0", "require": {"shared/dep": "^1.1"}, "replace": {"base/package": "1.2.0"}, "id": 3}
+    ],
+    "allowList": [
+        "indirect/replacer"
+    ],
+    "allowTransitiveDepsNoRootRequire": true
+}
+
+--FIXED--
+[
+]
+
+--PACKAGE-REPOS--
+[
+    [
+        {
+            "name": "base/package",
+            "version": "1.0.0",
+            "require": {
+                "shared/dep": "^1.2"
+            }
+        },
+        {
+            "name": "shared/dep",
+            "version": "1.0.0"
+        },
+        {
+            "name": "shared/dep",
+            "version": "1.2.0"
+        }
+    ],
+    [
+        {
+            "name": "base/package",
+            "version": "1.1.0"
+        },
+        {
+            "name": "shared/dep",
+            "version": "1.3.0"
+        }
+    ],
+    {
+        "canonical": false,
+        "packages": [
+            {
+                "name": "indirect/replacer",
+                "version": "1.2.0",
+                "require": {
+                    "replacer/package": "^1.2"
+                }
+            },
+            {
+                "name": "replacer/package",
+                "version": "1.2.0",
+                "require": {
+                    "shared/dep": "^1.1"
+                }
+            },
+            {
+                "name": "shared/dep",
+                "version": "1.1.0"
+            }
+        ]
+    },
+    [
+        {
+            "name": "replacer/package",
+            "version": "1.0.0",
+            "require": {
+                "shared/dep": "^1.0"
+            },
+            "replace": {
+                "base/package": "1.0.0"
+            }
+        },
+        {
+            "name": "indirect/replacer",
+            "version": "1.0.0",
+            "require": {
+                "replacer/package": "^1.0"
+            }
+        }
+    ]
+]
+
+--EXPECT--
+[
+    "indirect/replacer-1.2.0.0",
+    "indirect/replacer-1.0.0.0",
+    "replacer/package-1.2.0.0",
+    "replacer/package-1.0.0.0",
+    "base/package-1.0.0.0",
+    "shared/dep-1.0.0.0",
+    "shared/dep-1.2.0.0"
+]
diff --git a/tests/Composer/Test/DependencyResolver/Fixtures/poolbuilder/multi-repo-replace.test b/tests/Composer/Test/DependencyResolver/Fixtures/poolbuilder/multi-repo-replace.test
new file mode 100644
index 000000000..00c63e4f5
--- /dev/null
+++ b/tests/Composer/Test/DependencyResolver/Fixtures/poolbuilder/multi-repo-replace.test
@@ -0,0 +1,98 @@
+--TEST--
+Check that replacers from additional repositories are loaded
+
+--REQUEST--
+{
+    "require": {
+        "base/package": "^1.0",
+        "indirect/replacer": "^1.0"
+    }
+}
+
+--FIXED--
+[
+]
+
+--PACKAGE-REPOS--
+[
+    [
+        {
+            "name": "base/package",
+            "version": "1.0.0",
+            "require": {
+                "shared/dep": "^1.2"
+            }
+        },
+        {
+            "name": "shared/dep",
+            "version": "1.0.0"
+        },
+        {
+            "name": "shared/dep",
+            "version": "1.2.0"
+        }
+    ],
+    [
+        {
+            "name": "base/package",
+            "version": "1.1.0"
+        },
+        {
+            "name": "shared/dep",
+            "version": "1.3.0"
+        }
+    ],
+    {
+        "canonical": false,
+        "packages": [
+            {
+                "name": "indirect/replacer",
+                "version": "1.2.0",
+                "require": {
+                    "replacer/package": "^1.2"
+                }
+            },
+            {
+                "name": "replacer/package",
+                "version": "1.2.0",
+                "require": {
+                    "shared/dep": "^1.1"
+                }
+            },
+            {
+                "name": "shared/dep",
+                "version": "1.1.0"
+            }
+        ]
+    },
+    [
+        {
+            "name": "replacer/package",
+            "version": "1.0.0",
+            "require": {
+                "shared/dep": "^1.0"
+            },
+            "replace": {
+                "base/package": "1.2.0"
+            }
+        },
+        {
+            "name": "indirect/replacer",
+            "version": "1.0.0",
+            "require": {
+                "replacer/package": "^1.0"
+            }
+        }
+    ]
+]
+
+--EXPECT--
+[
+    "base/package-1.0.0.0",
+    "indirect/replacer-1.2.0.0",
+    "indirect/replacer-1.0.0.0",
+    "shared/dep-1.2.0.0",
+    "replacer/package-1.2.0.0",
+    "replacer/package-1.0.0.0",
+    "shared/dep-1.0.0.0"
+]
diff --git a/tests/Composer/Test/DependencyResolver/Fixtures/poolbuilder/must-expand-root-reqs.test b/tests/Composer/Test/DependencyResolver/Fixtures/poolbuilder/must-expand-root-reqs.test
new file mode 100644
index 000000000..fb52a9b6d
--- /dev/null
+++ b/tests/Composer/Test/DependencyResolver/Fixtures/poolbuilder/must-expand-root-reqs.test
@@ -0,0 +1,36 @@
+--TEST--
+Fixed packages do not get loaded from the repos
+
+--REQUEST--
+{
+    "require": {
+        "some/pkg": "*",
+        "root/req": "*"
+    }
+}
+
+--FIXED--
+[
+    {"name": "some/pkg", "version": "1.0.3", "id": 1},
+    {"name": "dep/dep", "version": "2.1.5", "id": 2}
+]
+
+--PACKAGE-REPOS--
+[
+    [
+        {"name": "some/pkg", "version": "1.0.0"},
+        {"name": "some/pkg", "version": "1.1.0"},
+        {"name": "root/req", "version": "1.0.0", "require": {"dep/dep": "2.*"}},
+        {"name": "root/req", "version": "2.0.0", "require": {"dep/dep": "3.*"}},
+        {"name": "dep/dep", "version": "2.3.4"},
+        {"name": "dep/dep", "version": "3.0.1"}
+    ]
+]
+
+--EXPECT--
+[
+    1,
+    2,
+    "root/req-1.0.0.0",
+    "root/req-2.0.0.0"
+]
diff --git a/tests/Composer/Test/DependencyResolver/Fixtures/poolbuilder/package-versions-are-not-loaded-if-not-required-expansion.test b/tests/Composer/Test/DependencyResolver/Fixtures/poolbuilder/package-versions-are-not-loaded-if-not-required-expansion.test
new file mode 100644
index 000000000..a41f4d1aa
--- /dev/null
+++ b/tests/Composer/Test/DependencyResolver/Fixtures/poolbuilder/package-versions-are-not-loaded-if-not-required-expansion.test
@@ -0,0 +1,34 @@
+--TEST--
+Tests if version constraint is expanded. If not, dep/dep 3.0.0 would not be loaded here.
+
+--REQUEST--
+{
+    "require": {
+        "root/req": "*"
+    }
+}
+
+--FIXED--
+[
+]
+
+--PACKAGE-REPOS--
+[
+    [
+        {"name": "root/req", "version": "1.0.0", "require": {"dep/dep": "2.*"}},
+        {"name": "dep/dep", "version": "2.3.4", "require": {"dep/dep2": "2.*"}},
+        {"name": "dep/dep", "version": "2.3.5"},
+        {"name": "dep/dep", "version": "3.0.0"},
+        {"name": "dep/dep", "version": "4.0.0"},
+        {"name": "dep/dep2", "version": "2.3.4", "require": {"dep/dep": "3.*"}}
+    ]
+]
+
+--EXPECT--
+[
+    "root/req-1.0.0.0",
+    "dep/dep-2.3.4.0",
+    "dep/dep-2.3.5.0",
+    "dep/dep2-2.3.4.0",
+    "dep/dep-3.0.0.0"
+]
diff --git a/tests/Composer/Test/DependencyResolver/Fixtures/poolbuilder/package-versions-are-not-loaded-if-not-required-recursive.test b/tests/Composer/Test/DependencyResolver/Fixtures/poolbuilder/package-versions-are-not-loaded-if-not-required-recursive.test
new file mode 100644
index 000000000..0eb8bbb69
--- /dev/null
+++ b/tests/Composer/Test/DependencyResolver/Fixtures/poolbuilder/package-versions-are-not-loaded-if-not-required-recursive.test
@@ -0,0 +1,31 @@
+--TEST--
+Test irrelevant package versions are not loaded recursively
+
+--REQUEST--
+{
+    "require": {
+        "root/req": "*"
+    }
+}
+
+--FIXED--
+[
+]
+
+--PACKAGE-REPOS--
+[
+    [
+        {"name": "root/req", "version": "1.0.0", "require": {"dep/dep": "2.*"}},
+        {"name": "dep/dep", "version": "2.3.4", "require": {"dep/dep2": "2.*"}},
+        {"name": "dep/dep", "version": "3.0.1"},
+        {"name": "dep/dep2", "version": "2.3.4"},
+        {"name": "dep/dep2", "version": "3.0.1"}
+    ]
+]
+
+--EXPECT--
+[
+    "root/req-1.0.0.0",
+    "dep/dep-2.3.4.0",
+    "dep/dep2-2.3.4.0"
+]
diff --git a/tests/Composer/Test/DependencyResolver/Fixtures/poolbuilder/packages-that-do-not-exist.test b/tests/Composer/Test/DependencyResolver/Fixtures/poolbuilder/packages-that-do-not-exist.test
new file mode 100644
index 000000000..bcf041002
--- /dev/null
+++ b/tests/Composer/Test/DependencyResolver/Fixtures/poolbuilder/packages-that-do-not-exist.test
@@ -0,0 +1,27 @@
+--TEST--
+Test package is not found
+
+--REQUEST--
+{
+    "require": {
+        "root/req": "*"
+    }
+}
+
+--FIXED--
+[
+]
+
+--PACKAGE-REPOS--
+[
+    [
+        {"name": "root/req", "version": "1.0.0", "require": {"dep/dep": "2.*"}},
+        {"name": "dep/dep", "version": "2.3.4", "require": {"dep/dep3": "2.*"}}
+    ]
+]
+
+--EXPECT--
+[
+    "root/req-1.0.0.0",
+    "dep/dep-2.3.4.0"
+]
diff --git a/tests/Composer/Test/DependencyResolver/Fixtures/poolbuilder/partial-update-transitive-deps-no-root-unfix.test b/tests/Composer/Test/DependencyResolver/Fixtures/poolbuilder/partial-update-transitive-deps-no-root-unfix.test
new file mode 100644
index 000000000..4f3f3c8c0
--- /dev/null
+++ b/tests/Composer/Test/DependencyResolver/Fixtures/poolbuilder/partial-update-transitive-deps-no-root-unfix.test
@@ -0,0 +1,49 @@
+--TEST--
+Partially updating one root requirement with transitive deps without root requirements keeps the other root requirement fixed.
+
+--REQUEST--
+{
+    "require": {
+        "root/update": "*",
+        "root/fix": "*"
+    },
+    "locked": [
+        {"name": "root/update", "version": "1.0.1", "require": {"dep/dep": "1.*", "dep2/dep2": "1.*"}, "id": 1},
+        {"name": "dep/dep", "version": "1.0.2", "require": {"root/fix": "1.*"}, "id": 2},
+        {"name": "dep2/dep2", "version": "1.0.2", "require": {"dep/dep": "1.*"}, "id": 3},
+        {"name": "root/fix", "version": "1.0.3", "id": 4}
+    ],
+    "allowList": [
+        "root/update"
+    ],
+    "allowTransitiveDepsNoRootRequire": true
+}
+
+--FIXED--
+[
+]
+
+--PACKAGE-REPOS--
+[
+    [
+        {"name": "root/update", "version": "1.0.4", "require": {"dep/dep": "1.*", "dep2/dep2": "1.*"}},
+        {"name": "root/update", "version": "1.0.5", "require": {"dep/dep": "2.*", "dep2/dep2": "2.*"}},
+        {"name": "root/fix", "version": "1.0.6"},
+        {"name": "root/fix", "version": "2.0.7"},
+        {"name": "dep/dep", "version": "1.0.8", "require": {"root/fix": "1.*"}},
+        {"name": "dep/dep", "version": "2.0.9", "require": {"root/fix": "2.*"}},
+        {"name": "dep2/dep2", "version": "1.0.8", "require": {"dep/dep": "1.*"}},
+        {"name": "dep2/dep2", "version": "2.0.9", "require": {"dep/dep": "2.*"}}
+    ]
+]
+
+--EXPECT--
+[
+    4,
+   "root/update-1.0.4.0",
+   "root/update-1.0.5.0",
+   "dep/dep-1.0.8.0",
+   "dep/dep-2.0.9.0",
+   "dep2/dep2-1.0.8.0",
+   "dep2/dep2-2.0.9.0"
+]
diff --git a/tests/Composer/Test/DependencyResolver/Fixtures/poolbuilder/partial-update-transitive-deps-unfix.test b/tests/Composer/Test/DependencyResolver/Fixtures/poolbuilder/partial-update-transitive-deps-unfix.test
new file mode 100644
index 000000000..2db47d1bd
--- /dev/null
+++ b/tests/Composer/Test/DependencyResolver/Fixtures/poolbuilder/partial-update-transitive-deps-unfix.test
@@ -0,0 +1,50 @@
+--TEST--
+Partially updating one root requirement with transitive deps fully updates another one too.
+
+--REQUEST--
+{
+    "require": {
+        "root/update": "*",
+        "root/dep": "1.0.*",
+        "root/dep2": "*"
+    },
+    "locked": [
+        {"name": "root/update", "version": "1.0.1", "require": {"dep/dep": "1.*"}},
+        {"name": "dep/dep", "version": "1.0.2", "require": {"root/dep": "1.*", "root/dep2": "1.*"}},
+        {"name": "root/dep", "version": "1.0.3"},
+        {"name": "root/dep2", "version": "1.0.3"}
+    ],
+    "allowList": [
+        "root/update"
+    ],
+    "allowTransitiveDeps": true
+}
+
+--FIXED--
+[
+]
+
+--PACKAGE-REPOS--
+[
+    [
+        {"name": "root/update", "version": "1.0.4", "require": {"dep/dep": "1.*"}},
+        {"name": "root/update", "version": "1.0.5", "require": {"dep/dep": "2.*"}},
+        {"name": "root/dep", "version": "1.0.6"},
+        {"name": "root/dep", "version": "2.0.7"},
+        {"name": "root/dep2", "version": "1.0.6"},
+        {"name": "root/dep2", "version": "2.0.7"},
+        {"name": "dep/dep", "version": "1.0.8", "require": {"root/dep": "1.*", "root/dep2": "1.*"}},
+        {"name": "dep/dep", "version": "2.0.9", "require": {"root/dep": "2.*", "root/dep2": "2.*"}}
+    ]
+]
+
+--EXPECT--
+[
+   "root/update-1.0.4.0",
+   "root/update-1.0.5.0",
+   "dep/dep-1.0.8.0",
+   "dep/dep-2.0.9.0",
+   "root/dep-1.0.6.0",
+   "root/dep2-1.0.6.0",
+   "root/dep2-2.0.7.0"
+]
diff --git a/tests/Composer/Test/DependencyResolver/Fixtures/poolbuilder/partial-update-unfixing-with-replacers.test b/tests/Composer/Test/DependencyResolver/Fixtures/poolbuilder/partial-update-unfixing-with-replacers.test
new file mode 100644
index 000000000..c4148d5ba
--- /dev/null
+++ b/tests/Composer/Test/DependencyResolver/Fixtures/poolbuilder/partial-update-unfixing-with-replacers.test
@@ -0,0 +1,52 @@
+--TEST--
+Fixed packages and replacers get unfixed correctly (refs https://github.com/composer/composer/pull/8942)
+
+--REQUEST--
+{
+    "require": {
+        "root/req1": "*",
+        "root/req3": "*"
+    },
+    "locked": [
+        {"name": "root/req1", "version": "1.0.0", "require": {"replacer/pkg": "1.*"}},
+        {"name": "root/req3", "version": "1.0.0", "require": {"replaced/pkg": "1.*", "dep/dep": "2.*"}},
+        {"name": "replacer/pkg", "version": "1.0.0", "replace": {"replaced/pkg": "*"}},
+        {"name": "dep/dep", "version": "2.3.5"}
+    ],
+    "allowList": [
+        "root/req1"
+    ],
+    "allowTransitiveDeps": true
+}
+
+--FIXED--
+[
+]
+
+--PACKAGE-REPOS--
+[
+    [
+        {"name": "root/req1", "version": "1.0.0", "require": {"replacer/pkg": "1.*"}},
+        {"name": "root/req1", "version": "1.1.0", "require": {"replacer/pkg": "1.*"}},
+        {"name": "root/req3", "version": "1.0.0", "require": {"replaced/pkg": "1.*"}},
+        {"name": "root/req3", "version": "1.1.0", "require": {"replaced/pkg": "1.*"}},
+        {"name": "replacer/pkg", "version": "1.0.0", "replace": {"replaced/pkg": "*"}},
+        {"name": "replacer/pkg", "version": "1.1.0", "replace": {"replaced/pkg": "*"}},
+        {"name": "replaced/pkg", "version": "1.2.3"},
+        {"name": "replaced/pkg", "version": "1.2.4"},
+        {"name": "dep/dep", "version": "2.3.5"},
+        {"name": "dep/dep", "version": "2.3.6"}
+    ]
+]
+
+--EXPECT--
+[
+    "root/req3-1.0.0.0 (locked)",
+    "dep/dep-2.3.5.0 (locked)",
+    "root/req1-1.0.0.0",
+    "root/req1-1.1.0.0",
+    "replacer/pkg-1.0.0.0",
+    "replacer/pkg-1.1.0.0",
+    "replaced/pkg-1.2.3.0",
+    "replaced/pkg-1.2.4.0"
+]
diff --git a/tests/Composer/Test/DependencyResolver/Fixtures/poolbuilder/partial-update.test b/tests/Composer/Test/DependencyResolver/Fixtures/poolbuilder/partial-update.test
new file mode 100644
index 000000000..a4d04ced5
--- /dev/null
+++ b/tests/Composer/Test/DependencyResolver/Fixtures/poolbuilder/partial-update.test
@@ -0,0 +1,39 @@
+--TEST--
+Partially updating a root requirement without deps, still selects a new dependency if the update results in a replacement missing for another locked package.
+
+--REQUEST--
+{
+    "require": {
+        "some/pkg": "*",
+        "root/req": "*"
+    },
+    "locked": [
+        {"name": "some/pkg", "version": "1.0.3", "replace": {"dep/dep": "2.1.0"}, "id": 1},
+        {"name": "root/req", "version": "1.0.0", "require": {"dep/dep": "2.*"}, "id": 2}
+    ],
+    "allowList": [
+        "some/pkg"
+    ]
+}
+
+--FIXED--
+[
+]
+
+--PACKAGE-REPOS--
+[
+    [
+        {"name": "some/pkg", "version": "1.0.4"},
+        {"name": "root/req", "version": "1.0.0", "require": {"dep/dep": "2.*"}},
+        {"name": "root/req", "version": "2.0.0", "require": {"dep/dep": "3.*"}},
+        {"name": "dep/dep", "version": "2.3.4"},
+        {"name": "dep/dep", "version": "3.0.1"}
+    ]
+]
+
+--EXPECT--
+[
+    2,
+   "some/pkg-1.0.4.0",
+   "dep/dep-2.3.4.0"
+]
diff --git a/tests/Composer/Test/DependencyResolver/Fixtures/poolbuilder/stability-flags-take-over-minimum-stability-and-filter-packages.test b/tests/Composer/Test/DependencyResolver/Fixtures/poolbuilder/stability-flags-take-over-minimum-stability-and-filter-packages.test
index 5a6ca8f2f..849033dcb 100644
--- a/tests/Composer/Test/DependencyResolver/Fixtures/poolbuilder/stability-flags-take-over-minimum-stability-and-filter-packages.test
+++ b/tests/Composer/Test/DependencyResolver/Fixtures/poolbuilder/stability-flags-take-over-minimum-stability-and-filter-packages.test
@@ -18,19 +18,23 @@ Stability flags apply
 
 --REQUEST--
 {
-    "flagged/pkg": "*",
-    "default/pkg": "*"
+    "require": {
+        "flagged/pkg": "*",
+        "default/pkg": "*"
+    }
 }
 
---PACKAGES--
+--PACKAGE-REPOS--
 [
-    {"name": "flagged/pkg", "version": "1.0.0", "id": 1},
-    {"name": "flagged/pkg", "version": "1.0.0-beta", "id": 2},
-    {"name": "flagged/pkg", "version": "1.0.0-dev", "id": 3},
-    {"name": "flagged/pkg", "version": "1.0.0-RC", "id": 4},
-    {"name": "default/pkg", "version": "1.0.0", "id": 5},
-    {"name": "default/pkg", "version": "1.0.0-RC", "id": 6},
-    {"name": "default/pkg", "version": "1.0.0-alpha", "id": 7}
+    [
+        {"name": "flagged/pkg", "version": "1.0.0", "id": 1},
+        {"name": "flagged/pkg", "version": "1.0.0-beta", "id": 2},
+        {"name": "flagged/pkg", "version": "1.0.0-dev", "id": 3},
+        {"name": "flagged/pkg", "version": "1.0.0-RC", "id": 4},
+        {"name": "default/pkg", "version": "1.0.0", "id": 5},
+        {"name": "default/pkg", "version": "1.0.0-RC", "id": 6},
+        {"name": "default/pkg", "version": "1.0.0-alpha", "id": 7}
+    ]
 ]
 
 --EXPECT--
@@ -40,5 +44,5 @@ Stability flags apply
     4,
     5,
     6,
-    "default/pkg-1.2.0.0 alias of 6"
+    "default/pkg-1.2.0.0 (alias of 6)"
 ]
diff --git a/tests/Composer/Test/DependencyResolver/PoolBuilderTest.php b/tests/Composer/Test/DependencyResolver/PoolBuilderTest.php
index 647ee2c2d..a72e42c96 100644
--- a/tests/Composer/Test/DependencyResolver/PoolBuilderTest.php
+++ b/tests/Composer/Test/DependencyResolver/PoolBuilderTest.php
@@ -14,6 +14,7 @@ namespace Composer\Test\DependencyResolver;
 
 use Composer\IO\NullIO;
 use Composer\Repository\ArrayRepository;
+use Composer\Repository\FilterRepository;
 use Composer\Repository\LockArrayRepository;
 use Composer\DependencyResolver\DefaultPolicy;
 use Composer\DependencyResolver\Pool;
@@ -36,11 +37,12 @@ class PoolBuilderTest extends TestCase
     /**
      * @dataProvider getIntegrationTests
      */
-    public function testPoolBuilder($file, $message, $expect, $root, $requestData, $packages, $fixed)
+    public function testPoolBuilder($file, $message, $expect, $root, $requestData, $packageRepos, $fixed)
     {
         $rootAliases = !empty($root['aliases']) ? $root['aliases'] : array();
         $minimumStability = !empty($root['minimum-stability']) ? $root['minimum-stability'] : 'stable';
         $stabilityFlags = !empty($root['stability-flags']) ? $root['stability-flags'] : array();
+        $rootReferences = !empty($root['references']) ? $root['references'] : array();
         $stabilityFlags = array_map(function ($stability) {
             return BasePackage::$stabilities[$stability];
         }, $stabilityFlags);
@@ -71,16 +73,42 @@ class PoolBuilderTest extends TestCase
             return $pkg;
         };
 
-        $repositorySet = new RepositorySet($minimumStability, $stabilityFlags, $rootAliases);
-        $repositorySet->addRepository($repo = new ArrayRepository());
-        foreach ($packages as $package) {
-            $repo->addPackage($loadPackage($package));
+        $repositorySet = new RepositorySet($minimumStability, $stabilityFlags, $rootAliases, $rootReferences);
+        foreach ($packageRepos as $packages) {
+            $repo = new ArrayRepository();
+            if (isset($packages['canonical']) || isset($packages['only']) || isset($packages['exclude'])) {
+                $options = $packages;
+                $packages = $options['packages'];
+                unset($options['packages']);
+                $repositorySet->addRepository(new FilterRepository($repo, $options));
+            } else {
+                $repositorySet->addRepository($repo);
+            }
+            foreach ($packages as $package) {
+                $repo->addPackage($loadPackage($package));
+            }
         }
+        $repositorySet->addRepository($lockedRepo = new LockArrayRepository());
 
-        $request = new Request();
-        foreach ($requestData as $package => $constraint) {
+        if (isset($requestData['locked'])) {
+            foreach ($requestData['locked'] as $package) {
+                $lockedRepo->addPackage($loadPackage($package));
+            }
+        }
+        $request = new Request($lockedRepo);
+        foreach ($requestData['require'] as $package => $constraint) {
             $request->requireName($package, $parser->parseConstraints($constraint));
         }
+        if (isset($requestData['allowList'])) {
+            $transitiveDeps = Request::UPDATE_ONLY_LISTED;
+            if (isset($requestData['allowTransitiveDepsNoRootRequire']) && $requestData['allowTransitiveDepsNoRootRequire']) {
+                $transitiveDeps = Request::UPDATE_LISTED_WITH_TRANSITIVE_DEPS_NO_ROOT_REQUIRE;
+            }
+            if (isset($requestData['allowTransitiveDeps']) && $requestData['allowTransitiveDeps']) {
+                $transitiveDeps = Request::UPDATE_LISTED_WITH_TRANSITIVE_DEPS;
+            }
+            $request->setUpdateAllowList(array_flip($requestData['allowList']), $transitiveDeps);
+        }
 
         foreach ($fixed as $fixedPackage) {
             $request->fixPackage($loadPackage($fixedPackage));
@@ -97,11 +125,23 @@ class PoolBuilderTest extends TestCase
                 return $id;
             }
 
-            if ($package instanceof AliasPackage && $id = array_search($package->getAliasOf(), $packageIds, true)) {
-                return (string) $package->getName().'-'.$package->getVersion() .' alias of '.$id;
+            $suffix = '';
+            if ($package->getSourceReference()) {
+                $suffix = '#'.$package->getSourceReference();
+            }
+            if ($package->getRepository() instanceof LockArrayRepository) {
+                $suffix .= ' (locked)';
+            }
+
+            if ($package instanceof AliasPackage) {
+                if ($id = array_search($package->getAliasOf(), $packageIds, true)) {
+                    return (string) $package->getName().'-'.$package->getVersion() . $suffix . ' (alias of '.$id . ')';
+                }
+
+                return (string) $package->getName().'-'.$package->getVersion() . $suffix . ' (alias of '.$package->getAliasOf()->getVersion().')';
             }
 
-            return (string) $package;
+            return (string) $package->getName().'-'.$package->getVersion() . $suffix;
         }, $result);
 
         $this->assertSame($expect, $result);
@@ -124,7 +164,7 @@ class PoolBuilderTest extends TestCase
                 $request = JsonFile::parseJson($testData['REQUEST']);
                 $root = !empty($testData['ROOT']) ? JsonFile::parseJson($testData['ROOT']) : array();
 
-                $packages = JsonFile::parseJson($testData['PACKAGES']);
+                $packageRepos = JsonFile::parseJson($testData['PACKAGE-REPOS']);
                 $fixed = array();
                 if (!empty($testData['FIXED'])) {
                     $fixed = JsonFile::parseJson($testData['FIXED']);
@@ -134,7 +174,7 @@ class PoolBuilderTest extends TestCase
                 die(sprintf('Test "%s" is not valid: '.$e->getMessage(), str_replace($fixturesDir.'/', '', $file)));
             }
 
-            $tests[basename($file)] = array(str_replace($fixturesDir.'/', '', $file), $message, $expect, $root, $request, $packages, $fixed);
+            $tests[basename($file)] = array(str_replace($fixturesDir.'/', '', $file), $message, $expect, $root, $request, $packageRepos, $fixed);
         }
 
         return $tests;
@@ -149,7 +189,7 @@ class PoolBuilderTest extends TestCase
             'ROOT' => false,
             'REQUEST' => true,
             'FIXED' => false,
-            'PACKAGES' => true,
+            'PACKAGE-REPOS' => true,
             'EXPECT' => true,
         );
 
diff --git a/tests/Composer/Test/DependencyResolver/RequestTest.php b/tests/Composer/Test/DependencyResolver/RequestTest.php
index e2a3ce9e6..a93bc404b 100644
--- a/tests/Composer/Test/DependencyResolver/RequestTest.php
+++ b/tests/Composer/Test/DependencyResolver/RequestTest.php
@@ -14,6 +14,7 @@ namespace Composer\Test\DependencyResolver;
 
 use Composer\DependencyResolver\Request;
 use Composer\Repository\ArrayRepository;
+use Composer\Semver\Constraint\MatchAllConstraint;
 use Composer\Test\TestCase;
 
 class RequestTest extends TestCase
@@ -34,7 +35,7 @@ class RequestTest extends TestCase
 
         $this->assertEquals(
             array(
-                'foo' => null,
+                'foo' => new MatchAllConstraint(),
             ),
             $request->getRequires()
         );
diff --git a/tests/Composer/Test/DependencyResolver/RuleTest.php b/tests/Composer/Test/DependencyResolver/RuleTest.php
index 2e1a9921d..ebf15fcac 100644
--- a/tests/Composer/Test/DependencyResolver/RuleTest.php
+++ b/tests/Composer/Test/DependencyResolver/RuleTest.php
@@ -19,6 +19,7 @@ use Composer\DependencyResolver\Pool;
 use Composer\Package\BasePackage;
 use Composer\Package\Link;
 use Composer\Repository\ArrayRepository;
+use Composer\Semver\Constraint\MatchAllConstraint;
 use Composer\Test\TestCase;
 
 class RuleTest extends TestCase
@@ -102,8 +103,11 @@ class RuleTest extends TestCase
         $repositorySetMock = $this->getMockBuilder('Composer\Repository\RepositorySet')->disableOriginalConstructor()->getMock();
         $requestMock = $this->getMockBuilder('Composer\DependencyResolver\Request')->disableOriginalConstructor()->getMock();
 
-        $rule = new GenericRule(array($p1->getId(), -$p2->getId()), Rule::RULE_PACKAGE_REQUIRES, new Link('baz', 'foo'));
+        $emptyConstraint = new MatchAllConstraint();
+        $emptyConstraint->setPrettyString('*');
 
-        $this->assertEquals('baz 1.1 relates to foo -> satisfiable by foo[2.1].', $rule->getPrettyString($repositorySetMock, $requestMock, $pool, false));
+        $rule = new GenericRule(array($p1->getId(), -$p2->getId()), Rule::RULE_PACKAGE_REQUIRES, new Link('baz', 'foo', $emptyConstraint));
+
+        $this->assertEquals('baz 1.1 relates to foo * -> satisfiable by foo[2.1].', $rule->getPrettyString($repositorySetMock, $requestMock, $pool, false));
     }
 }
diff --git a/tests/Composer/Test/DependencyResolver/SolverTest.php b/tests/Composer/Test/DependencyResolver/SolverTest.php
index 6fa7f1f84..6ed4c6bbd 100644
--- a/tests/Composer/Test/DependencyResolver/SolverTest.php
+++ b/tests/Composer/Test/DependencyResolver/SolverTest.php
@@ -235,8 +235,8 @@ class SolverTest extends TestCase
         $this->repo->addPackage($newPackageA = $this->getPackage('A', '1.1'));
         $this->repo->addPackage($newPackageB = $this->getPackage('B', '1.1'));
 
-        $packageA->setRequires(array('b' => new Link('A', 'B', null, 'requires')));
-        $newPackageA->setRequires(array('b' => new Link('A', 'B', null, 'requires')));
+        $packageA->setRequires(array('b' => new Link('A', 'B', new MatchAllConstraint(), 'requires')));
+        $newPackageA->setRequires(array('b' => new Link('A', 'B', new MatchAllConstraint(), 'requires')));
 
         $this->reposComplete();
 
@@ -639,8 +639,11 @@ class SolverTest extends TestCase
 
         $this->reposComplete();
 
-        $this->request->requireName('A');
-        $this->request->requireName('B');
+        $emptyConstraint = new MatchAllConstraint();
+        $emptyConstraint->setPrettyString('*');
+
+        $this->request->requireName('A', $emptyConstraint);
+        $this->request->requireName('B', $emptyConstraint);
 
         $this->createSolver();
         try {
@@ -652,9 +655,9 @@ class SolverTest extends TestCase
 
             $msg = "\n";
             $msg .= "  Problem 1\n";
-            $msg .= "    - Root composer.json requires a -> satisfiable by A[1.0].\n";
+            $msg .= "    - Root composer.json requires a * -> satisfiable by A[1.0].\n";
             $msg .= "    - A 1.0 conflicts with B 1.0.\n";
-            $msg .= "    - Root composer.json requires b -> satisfiable by B[1.0].\n";
+            $msg .= "    - Root composer.json requires b * -> satisfiable by B[1.0].\n";
             $this->assertEquals($msg, $e->getPrettyString($this->repoSet, $this->request, $this->pool, false));
         }
     }
@@ -683,7 +686,7 @@ class SolverTest extends TestCase
 
             $msg = "\n";
             $msg .= "  Problem 1\n";
-            $msg .= "    - Root composer.json requires a -> satisfiable by A[1.0].\n";
+            $msg .= "    - Root composer.json requires a * -> satisfiable by A[1.0].\n";
             $msg .= "    - A 1.0 requires b >= 2.0 -> found B[1.0] but it does not match the constraint.\n";
             $this->assertEquals($msg, $e->getPrettyString($this->repoSet, $this->request, $this->pool, false));
         }
@@ -712,7 +715,10 @@ class SolverTest extends TestCase
 
         $this->reposComplete();
 
-        $this->request->requireName('A');
+        $emptyConstraint = new MatchAllConstraint();
+        $emptyConstraint->setPrettyString('*');
+
+        $this->request->requireName('A', $emptyConstraint);
 
         $this->createSolver();
         try {
@@ -729,7 +735,7 @@ class SolverTest extends TestCase
             $msg .= "    - B 1.0 requires c >= 1.0 -> satisfiable by C[1.0].\n";
             $msg .= "    - You can only install one version of a package, so only one of these can be installed: B[0.9, 1.0].\n";
             $msg .= "    - A 1.0 requires b >= 1.0 -> satisfiable by B[1.0].\n";
-            $msg .= "    - Root composer.json requires a -> satisfiable by A[1.0].\n";
+            $msg .= "    - Root composer.json requires a * -> satisfiable by A[1.0].\n";
             $this->assertEquals($msg, $e->getPrettyString($this->repoSet, $this->request, $this->pool, false));
         }
     }
diff --git a/tests/Composer/Test/Package/RootAliasPackageTest.php b/tests/Composer/Test/Package/RootAliasPackageTest.php
index a5fe9172d..459f935e5 100644
--- a/tests/Composer/Test/Package/RootAliasPackageTest.php
+++ b/tests/Composer/Test/Package/RootAliasPackageTest.php
@@ -14,6 +14,7 @@ namespace Composer\Test\Package;
 
 use Composer\Package\Link;
 use Composer\Package\RootAliasPackage;
+use Composer\Semver\Constraint\MatchAllConstraint;
 use Composer\Test\TestCase;
 use Prophecy\Argument;
 
@@ -26,7 +27,7 @@ class RootAliasPackageTest extends TestCase
 
         $alias = new RootAliasPackage($root->reveal(), '1.0', '1.0.0.0');
         $this->assertEmpty($alias->getRequires());
-        $links = array(new Link('a', 'b', null, 'foo', 'self.version'));
+        $links = array(new Link('a', 'b', new MatchAllConstraint(), 'foo', 'self.version'));
         $alias->setRequires($links);
         $this->assertNotEmpty($alias->getRequires());
     }
@@ -38,7 +39,7 @@ class RootAliasPackageTest extends TestCase
 
         $alias = new RootAliasPackage($root->reveal(), '1.0', '1.0.0.0');
         $this->assertEmpty($alias->getDevRequires());
-        $links = array(new Link('a', 'b', null, 'foo', 'self.version'));
+        $links = array(new Link('a', 'b', new MatchAllConstraint(), 'foo', 'self.version'));
         $alias->setDevRequires($links);
         $this->assertNotEmpty($alias->getDevRequires());
     }
@@ -50,7 +51,7 @@ class RootAliasPackageTest extends TestCase
 
         $alias = new RootAliasPackage($root->reveal(), '1.0', '1.0.0.0');
         $this->assertEmpty($alias->getConflicts());
-        $links = array(new Link('a', 'b', null, 'foo', 'self.version'));
+        $links = array(new Link('a', 'b', new MatchAllConstraint(), 'foo', 'self.version'));
         $alias->setConflicts($links);
         $this->assertNotEmpty($alias->getConflicts());
     }
@@ -62,7 +63,7 @@ class RootAliasPackageTest extends TestCase
 
         $alias = new RootAliasPackage($root->reveal(), '1.0', '1.0.0.0');
         $this->assertEmpty($alias->getProvides());
-        $links = array(new Link('a', 'b', null, 'foo', 'self.version'));
+        $links = array(new Link('a', 'b', new MatchAllConstraint(), 'foo', 'self.version'));
         $alias->setProvides($links);
         $this->assertNotEmpty($alias->getProvides());
     }
@@ -74,7 +75,7 @@ class RootAliasPackageTest extends TestCase
 
         $alias = new RootAliasPackage($root->reveal(), '1.0', '1.0.0.0');
         $this->assertEmpty($alias->getReplaces());
-        $links = array(new Link('a', 'b', null, 'foo', 'self.version'));
+        $links = array(new Link('a', 'b', new MatchAllConstraint(), 'foo', 'self.version'));
         $alias->setReplaces($links);
         $this->assertNotEmpty($alias->getReplaces());
     }
diff --git a/tests/Composer/Test/Repository/InstalledRepositoryTest.php b/tests/Composer/Test/Repository/InstalledRepositoryTest.php
index a37adb058..505278c3b 100644
--- a/tests/Composer/Test/Repository/InstalledRepositoryTest.php
+++ b/tests/Composer/Test/Repository/InstalledRepositoryTest.php
@@ -16,6 +16,7 @@ use Composer\Repository\InstalledRepository;
 use Composer\Repository\ArrayRepository;
 use Composer\Repository\InstalledArrayRepository;
 use Composer\Package\Link;
+use Composer\Semver\Constraint\MatchAllConstraint;
 use Composer\Test\TestCase;
 
 class InstalledRepositoryTest extends TestCase
@@ -30,8 +31,8 @@ class InstalledRepositoryTest extends TestCase
         $arrayRepoTwo->addPackage($bar = $this->getPackage('bar', '1'));
         $arrayRepoTwo->addPackage($bar2 = $this->getPackage('bar', '2'));
 
-        $foo->setReplaces(array(new Link('foo', 'provided')));
-        $bar2->setProvides(array(new Link('bar', 'provided')));
+        $foo->setReplaces(array(new Link('foo', 'provided', new MatchAllConstraint())));
+        $bar2->setProvides(array(new Link('bar', 'provided', new MatchAllConstraint())));
 
         $repo = new InstalledRepository(array($arrayRepoOne, $arrayRepoTwo));
 
diff --git a/tests/Composer/Test/Util/PackageSorterTest.php b/tests/Composer/Test/Util/PackageSorterTest.php
index e93503436..8704a3af0 100644
--- a/tests/Composer/Test/Util/PackageSorterTest.php
+++ b/tests/Composer/Test/Util/PackageSorterTest.php
@@ -16,6 +16,7 @@ use Composer\Package\Link;
 use Composer\Package\Package;
 use Composer\Test\TestCase;
 use Composer\Util\PackageSorter;
+use Composer\Semver\Constraint\MatchAllConstraint;
 
 class PackageSorterTest extends TestCase
 {
@@ -120,7 +121,7 @@ class PackageSorterTest extends TestCase
 
         $links = array();
         foreach ($requires as $requireName) {
-            $links[] = new Link($package->getName(), $requireName);
+            $links[] = new Link($package->getName(), $requireName, new MatchAllConstraint);
         }
         $package->setRequires($links);