Support mutable history in mercurial for arc diff and arc amend

Summary:
This adds basic support for mutable history for arc diff and arc amend for
mercurial. This is purely opt-in (so it shouldn't affect anyone who doesn't want
this feature) by explicitly setting

    "immutable_history" : false

in arc configuration.

This also fixes another instance of weird behaviour for multiple heads - the
first instance was fixed here:
https://github.com/facebook/arcanist/pull/28

Test Plan:
without "immutable_history" turned on)>

When ##arc diff## produces an update diff, it should list only commits that are
ancestors of the current revision - not ones from other heads.

Reviewers: epriestley

CC: csilvers, aran, Koolvin

Differential Revision: https://secure.phabricator.com/D2654

src/repository/api/ArcanistGitAPI.php

@@ -459,7 +459,7 @@ final class ArcanistGitAPI extends ArcanistRepositoryAPI {
     return $this->status;
   }
 
-  public function amendGitHeadCommit($message) {
+  public function amendCommit($message) {
     $tmp_file = new TempFile();
     Filesystem::writeFile($tmp_file, $message);
     $this->execxLocal(
@@ -681,6 +681,14 @@ final class ArcanistGitAPI extends ArcanistRepositoryAPI {
     return rtrim($stdout, "\n");
   }
 
+  public function isHistoryDefaultImmutable() {
+    return false;
+  }
+
+  public function supportsAmend() {
+    return true;
+  }
+
   public function supportsRelativeLocalCommits() {
     return true;
   }

src/repository/api/ArcanistMercurialAPI.php

@@ -406,6 +406,19 @@ final class ArcanistMercurialAPI extends ArcanistRepositoryAPI {
     return $this->workingCopyRevision;
   }
 
+  public function isHistoryDefaultImmutable() {
+    return true;
+  }
+
+  public function supportsAmend() {
+    list ($err, $stdout) = $this->execManualLocal('help commit');
+    if ($err) {
+        return false;
+    } else {
+        return (strstr($stdout, "amend") !== false);
+    }
+  }
+
   public function supportsRelativeLocalCommits() {
     return true;
   }
@@ -473,9 +486,9 @@ final class ArcanistMercurialAPI extends ArcanistRepositoryAPI {
 
   public function getCommitMessageLog() {
     list($stdout) = $this->execxLocal(
-      "log --template '{node}\\1{desc}\\0' --rev %s..%s --",
+      "log --template '{node}\\1{desc}\\0' --prune %s --rev %s --",
       $this->getRelativeCommit(),
-      $this->getWorkingCopyRevision());
+      "ancestors({$this->getWorkingCopyRevision()})");
 
     $map = array();
 
@@ -492,6 +505,37 @@ final class ArcanistMercurialAPI extends ArcanistRepositoryAPI {
     ConduitClient $conduit,
     array $query) {
 
+    $messages = $this->getCommitMessageLog();
+    $parser = new ArcanistDiffParser();
+
+    // First, try to find revisions by explicit revision IDs in commit messages.
+    $reason_map = array();
+    $revision_ids = array();
+    foreach ($messages as $node_id => $message) {
+      $object = ArcanistDifferentialCommitMessage::newFromRawCorpus($message);
+
+      if ($object->getRevisionID()) {
+        $revision_ids[] = $object->getRevisionID();
+        $reason_map[$object->getRevisionID()] = $node_id;
+      }
+    }
+
+    if ($revision_ids) {
+      $results = $conduit->callMethodSynchronous(
+        'differential.query',
+        $query + array(
+          'ids' => $revision_ids,
+        ));
+
+      foreach ($results as $key => $result) {
+        $hash = substr($reason_map[$result['id']], 0, 16);
+        $results[$key]['why'] =
+          "Commit message for '{$hash}' has explicit 'Differential Revision'.";
+      }
+
+      return $results;
+    }
+
     // Try to find revisions by hash.
     $hashes = array();
     foreach ($this->getLocalCommitInformation() as $commit) {
@@ -517,6 +561,14 @@ final class ArcanistMercurialAPI extends ArcanistRepositoryAPI {
     $this->execxLocal('up');
   }
 
+  public function amendCommit($message) {
+    $tmp_file = new TempFile();
+    Filesystem::writeFile($tmp_file, $message);
+    $this->execxLocal(
+      'commit --amend -l %s',
+      $tmp_file);
+  }
+
   public function setIncludeDirectoryStateInDiffs($include) {
     $this->includeDirectoryStateInDiffs = $include;
     return $this;

src/repository/api/ArcanistRepositoryAPI.php

@@ -170,6 +170,8 @@ abstract class ArcanistRepositoryAPI {
   abstract public function getLocalCommitInformation();
   abstract public function getSourceControlBaseRevision();
   abstract public function getCanonicalRevisionName($string);
+  abstract public function isHistoryDefaultImmutable();
+  abstract public function supportsAmend();
   abstract public function supportsRelativeLocalCommits();
   abstract public function getWorkingCopyRevision();
   abstract public function updateWorkingCopy();
@@ -177,6 +179,10 @@ abstract class ArcanistRepositoryAPI {
     ConduitClient $conduit,
     array $query);
 
+  public function amendCommit() {
+    throw new ArcanistCapabilityNotSupportedException($this);
+  }
+
   public function getAllBranches() {
     // TODO: Implement for Mercurial/SVN and make abstract.
     return array();

src/repository/api/ArcanistSubversionAPI.php

@@ -507,6 +507,14 @@ EODIFF;
     return null;
   }
 
+  public function isHistoryDefaultImmutable() {
+    return true;
+  }
+
+  public function supportsAmend() {
+    return false;
+  }
+
   public function supportsRelativeLocalCommits() {
     return false;
   }

src/workflow/ArcanistAmendWorkflow.php

@@ -32,9 +32,11 @@ EOTEXT
 
   public function getCommandHelp() {
     return phutil_console_format(<<<EOTEXT
-          Supports: git
+          Supports: git, hg
           Amend the working copy after a revision has been accepted, so commits
           can be marked 'committed' and pushed upstream.
+
+          Supported in Mercurial 2.2 and newer.
 EOTEXT
       );
   }
@@ -74,12 +76,13 @@ EOTEXT
     $is_show = $this->getArgument('show');
 
     $repository_api = $this->getRepositoryAPI();
-    if (!($repository_api instanceof ArcanistGitAPI)) {
-      throw new ArcanistUsageException(
-        "You may only run 'arc amend' in a git working copy.");
-    }
-
     if (!$is_show) {
+      if (!$repository_api->supportsAmend()) {
+        throw new ArcanistUsageException(
+          "You may only run 'arc amend' in a git or hg (version ".
+          "2.2 or newer) working copy.");
+      }
+
       if ($this->isHistoryImmutable()) {
         throw new ArcanistUsageException(
           "This project is marked as adhering to a conservative history ".
@@ -175,7 +178,8 @@ EOTEXT
       echo phutil_console_format(
         "Amending commit message to reflect revision **%s**.\n",
         "D{$revision_id}: {$revision_title}");
-      $repository_api->amendGitHeadCommit($message);
+
+      $repository_api->amendCommit($message);
 
       $mark_workflow = $this->buildChildWorkflow(
         'close-revision',
@@ -191,7 +195,7 @@ EOTEXT
 
 
   protected function getSupportedRevisionControlSystems() {
-    return array('git');
+    return array('git', 'hg');
   }
 
 }

src/workflow/ArcanistBaseWorkflow.php

@@ -1027,8 +1027,15 @@ abstract class ArcanistBaseWorkflow {
   }
 
   protected function isHistoryImmutable() {
+    $repository_api = $this->getRepositoryAPI();
     $working_copy = $this->getWorkingCopy();
-    return ($working_copy->getConfig('immutable_history') === true);
+
+    $project_config = $working_copy->getConfig('immutable_history');
+    if ($project_config !== null) {
+      return $project_config;
+    }
+
+    return $repository_api->isHistoryDefaultImmutable();
   }
 
   /**

src/workflow/ArcanistDiffWorkflow.php

@@ -473,12 +473,15 @@ EOTEXT
             'revision_id' => $result['revisionid'],
           ));
 
-        if (!$this->isRawDiffSource()) {
+        if (!$this->isRawDiffSource() && $this->shouldAmend()) {
           $repository_api = $this->getRepositoryAPI();
-          if (($repository_api instanceof ArcanistGitAPI) &&
-              $this->shouldAmend()) {
+
+          if ($repository_api->supportsAmend()) {
             echo "Updating commit message...\n";
-            $repository_api->amendGitHeadCommit($revised_message);
+            $repository_api->amendCommit($revised_message);
+          } else {
+            echo "Commit message was not amended. Amending commit message is ".
+                 "only supported in git and hg (version 2.2 or newer)";
           }
         }