Create an impossible rule when trying to install something that doesn't exist.

The rule isn't acted upon yet (hence the incomplete test) but it is there as a reminder that this case needs to be handled.

src/Composer/DependencyResolver/Solver.php

@@ -964,6 +964,12 @@ class Solver
 
 
         foreach ($this->jobs as $job) {
+            if (empty($job['packages']) && $job['cmd'] == 'install') {
+                $this->addRule(
+                    RuleSet::TYPE_JOB,
+                    $this->createImpossibleRule(static::RULE_JOB_INSTALL, $job)
+                );
+            }
             foreach ($job['packages'] as $package) {
                 switch ($job['cmd']) {
                     case 'install':

tests/Composer/Test/DependencyResolver/SolverTest.php

@@ -55,6 +55,22 @@ class SolverTest extends TestCase
         ));
     }
 
+    public function testInstallNonExistingPackageFails()
+    {
+        $this->repo->addPackage($this->getPackage('A', '1.0'));
+        $this->reposComplete();
+
+        $this->request->install('B');
+
+        try {
+            $transaction = $this->solver->solve($this->request);
+            $this->markTestIncomplete('Reporting this failure is not implemented/working yet');
+            //$this->fail('Unsolvable conflict did not resolve in exception.');
+        } catch (SolverProblemsException $e) {
+            // @todo: assert problem properties
+        }
+    }
+
     public function testSolverInstallWithDeps()
     {
         $this->repo->addPackage($packageA = $this->getPackage('A', '1.0'));