Improve mercurial 'arc land' perf by avoiding updates

Summary:
Mercurial 'arc land --hold' was taking 90+ seconds on our large
repository.  Since most of arc land doesn't require any particular working
directory, I've changed the mercurial logic to avoid all updates except for
two: the one prior to finding the revision (only applies if the user specified
--branch), and the one at the end to leave the user in a good state.

Also got rid of a 'hg outgoing' call when phases are supported. Also changed
the hg-subversion detection to just look for .hg/svn instead of running 'hg
svn info', which was taking 4 seconds.

Now arc land takes about 50 seconds. Still much worse than git's 25 seconds.
One big hot spot is in the two 'hg rebase' calls, which account for 25 seconds
(versus 11 seconds of git).

Test Plan:
Tested arc land with mercurial and git. Tested with and without the --branch
options.

Reviewers: epriestley, bos, sid0, dschleimer

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D5014

src/repository/api/ArcanistMercurialAPI.php

@@ -12,6 +12,9 @@ final class ArcanistMercurialAPI extends ArcanistRepositoryAPI {
   private $includeDirectoryStateInDiffs;
   private $rawDiffCache = array();
 
+  private $supportsRebase;
+  private $supportsPhases;
+
   protected function buildLocalFuture(array $argv) {
 
     // Mercurial has a "defaults" feature which basically breaks automation by
@@ -113,8 +116,7 @@ final class ArcanistMercurialAPI extends ArcanistRepositoryAPI {
     // Mercurial 2.1 and up have phases which indicate if something is
     // published or not. To find which revs are outgoing, it's much
     // faster to check the phase instead of actually checking the server.
-    list($err) = $this->execManualLocal('help phase');
+    if (!$this->supportsPhases()) {
-    if (!$err) {
       list($err, $stdout) = $this->execManualLocal(
         'log --branch %s -r %s --style default',
         $this->getBranchName(),
@@ -445,6 +447,24 @@ final class ArcanistMercurialAPI extends ArcanistRepositoryAPI {
     }
   }
 
+  public function supportsRebase() {
+    if ($this->supportsRebase === null) {
+      list ($err) = $this->execManualLocal("help rebase");
+      $this->supportsRebase = $err === 0;
+    }
+
+    return $this->supportsRebase;
+  }
+
+  public function supportsPhases() {
+    if ($this->supportsPhases === null) {
+      list ($err) = $this->execManualLocal("help phase");
+      $this->supportsPhases = $err === 0;
+    }
+
+    return $this->supportsPhases;
+  }
+
   public function supportsCommitRanges() {
     return true;
   }
@@ -770,6 +790,10 @@ final class ArcanistMercurialAPI extends ArcanistRepositoryAPI {
 
   }
 
+  public function isHgSubversionRepo() {
+    return file_exists($this->getPath('.hg/svn'));
+  }
+
   public function getSubversionInfo() {
     $info = array();
     $base_path = null;

src/workflow/ArcanistLandWorkflow.php

@@ -189,8 +189,7 @@ EOTEXT
     }
 
     if ($this->isHg) {
-      list ($err) = $repository_api->execManualLocal('svn info');
+      $this->isHgSvn = $repository_api->isHgSubversionRepo();
-      $this->isHgSvn = !$err;
     }
 
     $branch = $this->getArgument('branch');
@@ -255,8 +254,7 @@ EOTEXT
 
     if ($this->isHg) {
       if ($this->useSquash) {
-        list ($err) = $repository_api->execManualLocal("rebase --help");
+        if (!$repository_api->supportsRebase()) {
-        if ($err) {
           throw new ArcanistUsageException(
             "You must enable the rebase extension to use ".
             "the --squash strategy.");
@@ -298,9 +296,11 @@ EOTEXT
 
   private function checkoutBranch() {
     $repository_api = $this->getRepositoryAPI();
+    if ($this->getBranchOrBookmark() != $this->branch) {
       $repository_api->execxLocal(
         'checkout %s',
         $this->branch);
+    }
 
     echo phutil_console_format(
       "Switched to branch **%s**. Identifying and merging...\n",
@@ -378,14 +378,15 @@ EOTEXT
 
   private function pullFromRemote() {
     $repository_api = $this->getRepositoryAPI();
+
+    $local_ahead_of_remote = false;
+    if ($this->isGit) {
       $repository_api->execxLocal('checkout %s', $this->onto);
 
       echo phutil_console_format(
         "Switched to branch **%s**. Updating branch...\n",
         $this->onto);
 
-    $local_ahead_of_remote = false;
-    if ($this->isGit) {
       try {
         $repository_api->execxLocal('pull --ff-only --no-stat');
       } catch (CommandException $ex) {
@@ -404,6 +405,17 @@ EOTEXT
       }
 
     } else if ($this->isHg) {
+      echo phutil_console_format(
+        "Updating **%s**...\n",
+        $this->onto);
+
+      if ($repository_api->supportsPhases()) {
+        list($out) = $repository_api->execxLocal(
+          'log -r %s --template {phase}', $this->onto);
+        if ($out != 'public') {
+          $local_ahead_of_remote = true;
+        }
+      } else {
         // execManual instead of execx because outgoing returns
         // code 1 when there is nothing outgoing
         list($err, $out) = $repository_api->execManualLocal(
@@ -413,9 +425,12 @@ EOTEXT
         // $err === 0 means something is outgoing
         if ($err === 0) {
           $local_ahead_of_remote = true;
-      } else {
+        }
+      }
+
+      if (!$local_ahead_of_remote) {
         try {
-          $repository_api->execxLocal('pull -u');
+          $repository_api->execxLocal('pull');
         } catch (CommandException $ex) {
           $err = $ex->getError();
           $stdout = $ex->getStdOut();
@@ -512,9 +527,9 @@ EOTEXT
 
   private function squash() {
     $repository_api = $this->getRepositoryAPI();
-    $repository_api->execxLocal('checkout %s', $this->onto);
 
     if ($this->isGit) {
+      $repository_api->execxLocal('checkout %s', $this->onto);
       $repository_api->execxLocal(
         'merge --squash --ff-only %s',
         $this->branch);