Replace "arc merge" with "arc land --merge" for git

Summary:
I think "arc land" is better than "arc merge" in every case? Make "arc merge"
hg-only (possibly nuke it later, see T614) and point users at "arc land".

Add an explicit "--merge" flag to force --no-ff behavior in mutable reposiories.

Test Plan:
Ran "arc land --hold --merge <feature>" on this branch, got a clean
merge.

Reviewers: fratrik, btrahan

Reviewed By: btrahan

CC: aran, epriestley

Differential Revision: https://secure.phabricator.com/D1647

src/workflow/land/ArcanistLandWorkflow.php

@@ -25,7 +25,7 @@ final class ArcanistLandWorkflow extends ArcanistBaseWorkflow {
 
   public function getCommandHelp() {
     return phutil_console_format(<<<EOTEXT
-      **land** __branch__ [--onto __master__]
+      **land** [__options__] __branch__ [--onto __master__]
           Supports: git
 
           Land an accepted change (currently sitting in local feature branch
@@ -34,8 +34,9 @@ final class ArcanistLandWorkflow extends ArcanistBaseWorkflow {
 
           In mutable repositories, this will perform a --squash merge (the
           entire branch will be represented by one commit on __master__). In
-          immutable repositories, it will perform a --no-ff merge (the branch
+          immutable repositories (or when --merge is provided), it will perform
-          will always be merged into __master__ with a merge commit).
+          a --no-ff merge (the branch will always be merged into __master__ with
+          a merge commit).
 
 EOTEXT
       );
@@ -76,6 +77,11 @@ EOTEXT
         'param' => 'origin',
         'help' => "Push to a remote other than 'origin' (default).",
       ),
+      'merge' => array(
+        'help' => 'Perform a --no-ff merge, not a --squash merge. If the '.
+                  'project is marked as having an immutable history, this is '.
+                  'the default behavior.',
+      ),
       '*' => 'branch',
     );
   }
@@ -90,7 +96,8 @@ EOTEXT
 
     $remote = $this->getArgument('remote', 'origin');
     $onto = $this->getArgument('onto', 'master');
-    $is_immutable = $this->isHistoryImmutable();
+    $is_immutable = $this->isHistoryImmutable() ||
+      $this->getArgument('merge');
 
     $repository_api = $this->getRepositoryAPI();
     if (!($repository_api instanceof ArcanistGitAPI)) {
@@ -192,7 +199,7 @@ EOTEXT
 
     if ($revision['status'] != ArcanistDifferentialRevisionStatus::ACCEPTED) {
       $ok = phutil_console_confirm(
-        "Revision 'D{$id}: {$rev_title}' has not been accepted. Continue ".
+        "Revision 'D{$rev_id}: {$rev_title}' has not been accepted. Continue ".
         "anyway?");
       if (!$ok) {
         throw new ArcanistUserAbortException();
@@ -224,7 +231,7 @@ EOTEXT
         throw new ArcanistUsageException(
           "'git merge' failed. Your working copy has been left in a partially ".
           "merged state. You can: abort with 'git merge --abort'; or follow ".
-          "the instructions to complete the merge, and then push.");
+          "the instructions to complete the merge.");
       }
     } else {
       // In mutable histories, do a --squash merge.

src/workflow/merge/ArcanistMergeWorkflow.php

@@ -27,19 +27,15 @@ final class ArcanistMergeWorkflow extends ArcanistBaseWorkflow {
   public function getCommandHelp() {
     return phutil_console_format(<<<EOTEXT
       **merge** [__branch__] [--revision __revision_id__] [--show]
-          Supports: git, hg
+          Supports: hg
-          Execute a "git merge <branch>" or "hg merge --rev <branch>" of a
+          Execute a "hg merge --rev <branch>" of a reviewed branch, but give the
-          reviewed branch, but give the merge commit a useful commit message
+          merge commit a useful commit message with information from
-          with information from Differential.
+          Differential.
 
-          In Git, this operates like "git merge <branch>" and should be executed
+          Tthis operates like "hg merge" (default) or "hg merge --rev <branch>"
-          from the branch you want to merge __into__, just like "git merge".
+          and should be executed from the branch you want to merge __from__,
-          Branch is required.
+          just like "hg merge". It will also effect an "hg commit" with a rich
-
+          commit message if possible.
-          In Mercurial, this operates like "hg merge" (default) or
-          "hg merge --rev <branch>" and should be executed from the branch you
-          want to merge __from__, just like "hg merge". It will also effect an
-          "hg commit" with a rich commit message.
 
 EOTEXT
       );
@@ -78,11 +74,19 @@ EOTEXT
   }
 
   public function run() {
+    $repository_api = $this->getRepositoryAPI();
+
+    if ($repository_api instanceof ArcanistGitAPI) {
+      throw new ArcanistUsageException(
+        "'arc merge' no longer supports git. Use ".
+        "'arc land --keep-branch --hold --merge <feature_branch>' instead.");
+    }
+
     $this->writeStatusMessage(
       phutil_console_format(
         "**WARNING:** 'arc merge' is new and experimental.\n"));
 
-    $repository_api = $this->getRepositoryAPI();
+
     if (!$repository_api->supportsLocalBranchMerge()) {
       $name = $repository_api->getSourceControlSystemName();
       throw new ArcanistUsageException(
@@ -157,7 +161,7 @@ EOTEXT
   }
 
   protected function getSupportedRevisionControlSystems() {
-    return array('git', 'hg');
+    return array('hg');
   }
 
 }