Add an "--update <revision>" flag to Arcanist

Summary:
See T614. This flag explicitly tells Arcanist to use the message for an existing
revision, and attach the change to it directly.

Next step is to have "arc diff" automatically choose "--create" or "--update" in
the absence of "--create", "--update", "--only", "--preview" or a template
commit message.

Test Plan:
Ran "arc diff --update <n>" for various revisions. Got updates or
errors as expected.

Reviewers: btrahan, jungejason

Reviewed By: btrahan

CC: aran, btrahan, jungejason

Maniphest Tasks: T614

Differential Revision: https://secure.phabricator.com/D1346

src/differential/commitmessage/ArcanistDifferentialCommitMessage.php

@@ -1,7 +1,7 @@
 <?php
 
 /*
- * Copyright 2011 Facebook, Inc.
+ * Copyright 2012 Facebook, Inc.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -79,12 +79,11 @@ class ArcanistDifferentialCommitMessage {
   }
 
   public function pullDataFromConduit(ConduitClient $conduit) {
-    $result = $conduit->callMethod(
+    $result = $conduit->callMethodSynchronous(
       'differential.parsecommitmessage',
       array(
         'corpus' => $this->rawCorpus,
       ));
-    $result = $result->resolve();
     if (!empty($result['errors'])) {
       throw new ArcanistDifferentialCommitMessageParserException(
         $result['errors']);

src/workflow/diff/ArcanistDiffWorkflow.php

@@ -139,13 +139,19 @@ EOTEXT
         ),
       ),
       'create' => array(
-        'help' => "(EXPERIMENTAL) Create a new revision.",
+        'help' => "Always create a new revision.",
         'conflicts' => array(
           'edit'    => '--create can not be used with --edit.',
           'only'    => '--create can not be used with --only.',
           'preview' => '--create can not be used with --preview.',
+
+          'update'  => '--create can not be used with --update.',
         ),
       ),
+      'update' => array(
+        'param' => 'revision_id',
+        'help'  => "Always update a specific revision.",
+      ),
       'nounit' => array(
         'help' =>
           "Do not run unit tests.",
@@ -459,6 +465,10 @@ EOTEXT
       return false;
     }
 
+    if ($this->getArgument('update')) {
+      return false;
+    }
+
     if ($this->isRawDiffSource()) {
       return true;
     }
@@ -1061,6 +1071,7 @@ EOTEXT
    */
   private function buildCommitMessage() {
     $is_create = $this->getArgument('create');
+    $is_update = $this->getArgument('update');
     $is_raw = $this->isRawDiffSource();
 
     $message = null;
@@ -1073,6 +1084,10 @@ EOTEXT
       }
     }
 
+    if ($is_update) {
+      return $this->getCommitMessageFromRevision($is_update);
+    }
+
     if ($is_raw) {
       return null;
     }
@@ -1144,6 +1159,45 @@ EOTEXT
   }
 
 
+  /**
+   * @task message
+   */
+  private function getCommitMessageFromRevision($revision_id) {
+    $id = $this->normalizeRevisionID($revision_id);
+
+    $revision = $this->getConduit()->callMethodSynchronous(
+      'differential.query',
+      array(
+        'ids' => array($id),
+      ));
+    $revision = head($revision);
+
+    if (!$revision) {
+      throw new ArcanistUsageException(
+        "Revision '{$revision_id}' does not exist!");
+    }
+
+    if ($revision['authorPHID'] != $this->getUserPHID()) {
+      $rev_title = $revision['title'];
+      throw new ArcanistUsageException(
+        "You don't own revision D{$id} '{$rev_title}'. You can only update ".
+        "revisions you own.");
+    }
+
+    $message = $this->getConduit()->callMethodSynchronous(
+      'differential.getcommitmessage',
+      array(
+        'revision_id' => $id,
+        'edit'        => false,
+      ));
+
+    $obj = ArcanistDifferentialCommitMessage::newFromRawCorpus($message);
+    $obj->pullDataFromConduit($this->getConduit());
+
+    return $obj;
+  }
+
+
   /**
    * @task message
    */