Add new options to pull-request:merge command

src/Command/PullRequest/PullRequestMergeCommand.php

@@ -40,6 +40,8 @@ protected function configure()
             ->addOption('fast-forward', null, InputOption::VALUE_NONE, 'Merge pull-request using fast forward (no merge commit will be created)')
             ->addOption('squash', null, InputOption::VALUE_NONE, 'Squash the PR before merging')
             ->addOption('force-squash', null, InputOption::VALUE_NONE, 'Force squashing the PR, even if there are multiple authors (this will implicitly use --squash)')
+            ->addOption('rebase', null, InputOption::VALUE_NONE, 'Rebase the PR before merging')
+            ->addOption('ensure-sync', null, InputOption::VALUE_NONE, 'Ensure that the pull request history is up to date before merging')
             ->addOption('switch', null, InputOption::VALUE_REQUIRED, 'Switch the base of the pull request before merging')
             ->addOption('pat', null, InputOption::VALUE_REQUIRED, 'Give the PR\'s author a pat on the back after the merge')
             ->setHelp(
@@ -79,6 +81,16 @@ protected function configure()
 
     <info>$ gush %command.name% --fast-forward 12</info>
 
+If you want to perform an automatic rebase against the base branch before merging, the <comment>--rebase</comment> option can be used
+in order to try that operation:
+
+    <info>$ gush %command.name% --rebase 12</info>
+
+A synchronization check against the base branch can be done before the merge, passing the <comment>--ensure-sync</comment> option; so
+if this check fails, the operation will be aborted:
+
+    <info>$ gush %command.name% --ensure-sync 12</info>
+
 After the pull request is merged, you can give a pat on the back to its author using the <comment>--pat</comment>.
 This option accepts the name of any configured pat's name:
 
@@ -173,6 +185,8 @@ protected function execute(InputInterface $input, OutputInterface $output)
             $mergeOperation->setTarget($targetRemote, $targetBranch);
             $mergeOperation->setSource($sourceRemote, $sourceBranch);
             $mergeOperation->squashCommits($squash, $input->getOption('force-squash'));
+            $mergeOperation->guardSync($input->getOption('ensure-sync'));
+            $mergeOperation->rebase($input->getOption('rebase'));
             $mergeOperation->switchBase($input->getOption('switch'));
             $mergeOperation->setMergeMessage($messageCallback);
             $mergeOperation->useFastForward($input->getOption('fast-forward'));

src/Helper/GitHelper.php

@@ -615,13 +615,6 @@ public function squashCommits($base, $branchName, $ignoreMultipleAuthors = false
             $base.'..'.$branchName,
         ]))[0];
 
-        $currentBaseHeadCommit = $this->processHelper->runCommand(['git', 'rev-parse', $base]);
-        $lastKnownCommonCommit = $this->processHelper->runCommand(['git', 'merge-base', '--fork-point', $base, $branchName]);
-
-        if ($currentBaseHeadCommit !== $lastKnownCommonCommit) {
-            throw new MergeWorkflowException(sprintf('Failed while trying to perform merge against "%s", history is out of sync.', $base));
-        }
-
         // 0=author anything higher then 0 is the full body
         $commitData = StringUtil::splitLines(
             $this->processHelper->runCommand(

src/Operation/RemoteMergeOperation.php

@@ -31,6 +31,8 @@ class RemoteMergeOperation
     private $performed = false;
     private $fastForward = false;
     private $withLog = false;
+    private $rebase = false;
+    private $guardSync = false;
 
     public function __construct(GitHelper $gitHelper, FilesystemHelper $filesystemHelper)
     {
@@ -80,6 +82,8 @@ public function setMergeMessage($message, $withLog = false)
     public function useFastForward($fastForward = true)
     {
         $this->fastForward = (bool) $fastForward;
+
+        return $this;
     }
 
     public function performMerge()
@@ -143,6 +147,21 @@ public function pushToRemote()
         $this->gitHelper->pushToRemote($this->targetRemote, $target);
     }
 
+    public function rebase(bool $rebase = false)
+    {
+        $this->rebase = $rebase;
+        $this->guardSync = !$rebase;
+
+        return $this;
+    }
+
+    public function guardSync(bool $guardSync = false)
+    {
+        $this->guardSync = $guardSync;
+
+        return $this;
+    }
+
     private function createBaseBranch()
     {
         $targetBranch = null !== $this->switchBase ? $this->switchBase : $this->targetBranch;
@@ -171,7 +190,31 @@ private function createSourceBranch()
         }
 
         if ($this->squash) {
-            $this->gitHelper->squashCommits($this->targetBase, $sourceBranch, $this->forceSquash);
+            $this->gitHelper->squashCommits($this->targetBase, $sourceBranch, $this->forceSquash, $this->guardSync);
+        }
+
+        $currentBaseHeadCommit = $this->processHelper->runCommand(['git', 'rev-parse', $this->targetBase]);
+        $lastKnownCommonCommit = $this->processHelper->runCommand(['git', 'merge-base', '--fork-point', $this->targetBase, $sourceBranch]);
+
+        if ($currentBaseHeadCommit !== $lastKnownCommonCommit) {
+            if ($this->rebase) {
+                try {
+                    $this->processHelper->runCommand(['git', 'pull', '--rebase', $this->targetBase]);
+                } catch (\Exception $e) {
+                    // Error, abort the rebase operation
+                    $this->processHelper->runCommand(['git', 'rebase', '--abort'], true);
+
+                    throw new MergeWorkflowException(sprintf('Git rebase failed while trying to synchronize history against "%s".', $this->targetBase), 0, $e);
+                }
+
+                // Retrieve the commits again
+                $currentBaseHeadCommit = $this->processHelper->runCommand(['git', 'rev-parse', $this->targetBase]);
+                $lastKnownCommonCommit = $this->processHelper->runCommand(['git', 'merge-base', '--fork-point', $this->targetBase, $sourceBranch]);
+            }
+
+            if ($this->guardSync && $currentBaseHeadCommit !== $lastKnownCommonCommit) {
+                throw new MergeWorkflowException(sprintf('Failed while trying to perform merge against "%s", history is out of sync.', $this->targetBase));
+            }
         }
 
         // Allow a callback to allow late commits list composition

tests/Command/PullRequest/PullRequestMergeCommandTest.php

@@ -455,7 +455,7 @@ protected function getGitConfigHelper($notes = true)
         return $helper;
     }
 
-    private function getLocalGitHelper($message = null, $squash = false, $forceSquash = false, $switch = null, $withComments = true, $fastForward = false)
+    private function getLocalGitHelper($message = null, $squash = false, $forceSquash = false, $switch = null, $withComments = true, $fastForward = false, $guardSync = false, $rebase = false)
     {
         $helper = parent::getGitHelper();
 
@@ -470,6 +470,8 @@ private function getLocalGitHelper($message = null, $squash = false, $forceSquas
             $mergeOperation->setTarget('gushphp', 'base_ref')->shouldBeCalled();
             $mergeOperation->setSource('cordoval', 'head_ref')->shouldBeCalled();
             $mergeOperation->squashCommits($squash, $forceSquash)->shouldBeCalled();
+            $mergeOperation->guardSync($guardSync)->shouldBeCalled();
+            $mergeOperation->rebase($rebase)->shouldBeCalled();
             $mergeOperation->switchBase($switch)->shouldBeCalled();
             $mergeOperation->useFastForward($fastForward)->shouldBeCalled();
             $mergeOperation->setMergeMessage(