Clean up hg --debug branches calls

Summary: Ref T1493. Consolidate these a bit; they might need some more magic once we do `--noupdate` checkouts. Mostly just trying to clean up and centralize this code a bit.

Test Plan: Viewed and `bin/repository discover`'d Mercurial repos with and without any branches.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T1493

Differential Revision: https://secure.phabricator.com/D7480

src/applications/diffusion/conduit/ConduitAPI_diffusion_branchquery_Method.php

@@ -65,17 +65,9 @@ final class ConduitAPI_diffusion_branchquery_Method
     $offset = $request->getValue('offset');
     $limit = $request->getValue('limit');
 
-    list($stdout) = $repository->execxLocalCommand(
-      '--debug branches');
-    $branch_info = ArcanistMercurialParser::parseMercurialBranches($stdout);
-
-    $branches = array();
-    foreach ($branch_info as $name => $info) {
-      $branch = new DiffusionBranchInformation();
-      $branch->setName($name);
-      $branch->setHeadCommitIdentifier($info['rev']);
-      $branches[] = $branch->toDictionary();
-    }
+    $branches = id(new DiffusionLowLevelMercurialBranchesQuery())
+      ->setRepository($repository)
+      ->execute();
 
     if ($offset) {
       $branches = array_slice($branches, $offset);
@@ -85,6 +77,6 @@ final class ConduitAPI_diffusion_branchquery_Method
       $branches = array_slice($branches, 0, $limit);
     }
 
-    return $branches;
+    return mpull($branches, 'toDictionary');
   }
 }

src/applications/diffusion/query/lowlevel/DiffusionLowLevelMercurialBranchesQuery.php

@@ -0,0 +1,28 @@
+<?php
+
+/**
+ * Execute and parse a low-level Mercurial branches query using `hg branches`.
+ */
+final class DiffusionLowLevelMercurialBranchesQuery
+  extends DiffusionLowLevelQuery {
+
+  protected function executeQuery() {
+    $repository = $this->getRepository();
+
+    // NOTE: `--debug` gives us 40-character hashes.
+    list($stdout) = $repository->execxLocalCommand(
+      '--debug branches');
+
+    $branches = array();
+
+    $lines = ArcanistMercurialParser::parseMercurialBranches($stdout);
+    foreach ($lines as $name => $spec) {
+      $branches[] = id(new DiffusionBranchInformation())
+        ->setName($name)
+        ->setHeadCommitIdentifier($spec['rev']);
+    }
+
+    return $branches;
+  }
+
+}