Solver: analyze multi conflict rules in conflict resolution correctly

src/Composer/DependencyResolver/Pool.php

@@ -189,4 +189,15 @@ class Pool implements \Countable
     {
         return \in_array($package, $this->unacceptableFixedPackages, true);
     }
+
+    public function __toString()
+    {
+        $str = "Pool:\n";
+
+        foreach ($this->packages as $package) {
+            $str .= '- '.str_pad($package->id, 6, ' ', STR_PAD_LEFT).': '.$package->getName()."\n";
+        }
+
+        return $str;
+    }
 }

src/Composer/DependencyResolver/Solver.php

@@ -15,6 +15,7 @@ namespace Composer\DependencyResolver;
 use Composer\IO\IOInterface;
 use Composer\Package\PackageInterface;
 use Composer\Repository\PlatformRepository;
+use Composer\Semver\Constraint\MultiConstraint;
 
 /**
  * @author Nils Adermann <naderman@naderman.de>
@@ -385,6 +386,10 @@ class Solver
             $this->learnedPool[\count($this->learnedPool) - 1][] = $rule;
 
             foreach ($rule->getLiterals() as $literal) {
+                if (!$this->decisions->decided($literal)) {
+                    continue;
+                }
+
                 // skip the one true literal
                 if ($this->decisions->satisfy($literal)) {
                     continue;
@@ -412,6 +417,16 @@ class Solver
             }
             unset($literal);
 
+            $decision = $this->decisions->atOffset($decisionId-1);
+            if ($rule !== $decision[Decisions::DECISION_REASON] && $decision[Decisions::DECISION_REASON] instanceof MultiConflictRule) {
+                $num++;
+                foreach ($decision[Decisions::DECISION_REASON]->getLiterals() as $literal) {
+                    if (!$this->decisions->satisfy($literal)) {
+                        $seen[abs($literal)] = true;
+                    }
+                }
+            }
+
             $l1retry = true;
             while ($l1retry) {
                 $l1retry = false;
@@ -459,6 +474,13 @@ class Solver
                     $l1num++;
                     $l1retry = true;
                 }
+
+                $decision = $this->decisions->atOffset($decisionId);
+                $rule = $decision[Decisions::DECISION_REASON];
+
+                if ($rule instanceof MultiConflictRule) {
+                    $l1retry = true;
+                }
             }
 
             $decision = $this->decisions->atOffset($decisionId);