Select default branches more effectively in Diffusion

Summary: If you have an empty value saved in the "default branch" field, we default to empty string (or null, or whatever) instead of the correct default.

Test Plan:
  - Looked at a Git repo with an empty default branch, got a default to "master" instead of an error.
  - Looked at a Mercurial repo with an empty default branch, got a default to "default" instead of an error.

Reviewers: btrahan, csilvers

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T1237

Differential Revision: https://secure.phabricator.com/D2512

src/applications/diffusion/request/git/DiffusionGitRequest.php

@@ -83,7 +83,7 @@ final class DiffusionGitRequest extends DiffusionRequest {
       return $this->branch;
     }
     if ($this->repository) {
-      return $this->repository->getDetail('default-branch', 'master');
+      return $this->repository->getDefaultBranch();
     }
     throw new Exception("Unable to determine branch!");
   }

src/applications/diffusion/request/mercurial/DiffusionMercurialRequest.php

@@ -41,7 +41,7 @@ final class DiffusionMercurialRequest extends DiffusionRequest {
     }
 
     if ($this->repository) {
-      return $this->repository->getDetail('default-branch', 'default');
+      return $this->repository->getDefaultBranch();
     }
 
     throw new Exception("Unable to determine branch!");

src/applications/repository/controller/edit/PhabricatorRepositoryEditController.php

@@ -588,23 +588,12 @@ final class PhabricatorRepositoryEditController
     $inset->setTitle('Application Configuration');
 
     if ($has_branches) {
-
-      $default_branch_name = null;
-      if ($is_mercurial) {
-        $default_branch_name = 'default';
-      } else if ($is_git) {
-        $default_branch_name = 'master';
-      }
-
       $inset
         ->appendChild(
           id(new AphrontFormTextControl())
             ->setName('default-branch')
             ->setLabel('Default Branch')
-            ->setValue(
-              $repository->getDetail(
-                'default-branch',
-                $default_branch_name))
+            ->setValue($repository->getDefaultBranch())
             ->setError($e_branch)
             ->setCaption(
               'Default branch to show in Diffusion.'));

src/applications/repository/storage/repository/PhabricatorRepository.php

@@ -347,6 +347,20 @@ final class PhabricatorRepository extends PhabricatorRepositoryDAO {
     return $this->getDetail('tracking-enabled', false);
   }
 
+  public function getDefaultBranch() {
+    $default = $this->getDetail('default-branch');
+    if (strlen($default)) {
+      return $default;
+    }
+
+    $default_branches = array(
+      PhabricatorRepositoryType::REPOSITORY_TYPE_GIT        => 'master',
+      PhabricatorRepositoryType::REPOSITORY_TYPE_MERCURIAL  => 'default',
+    );
+
+    return idx($default_branches, $this->getVersionControlSystem());
+  }
+
   public function shouldTrackBranch($branch) {
     $vcs = $this->getVersionControlSystem();