Expand abbreviated Mercurial hashes to full hashes

Summary:
If you go to `/rXnnnn` in Git, we expand the hash. If you go to `/rXnnnn` in Mercurial, we give you a confusing error message.

Reconcile Mercurial behavior with Git. Fixes T2265.

Test Plan: Viewed partial hash, full hash commit in Diffusion. Viewed very short hash, got reasonable behaviors.

Reviewers: btrahan, tido

Reviewed By: tido

CC: aran

Maniphest Tasks: T2265

Differential Revision: https://secure.phabricator.com/D4330

src/applications/diffusion/request/DiffusionMercurialRequest.php

@@ -16,6 +16,29 @@ final class DiffusionMercurialRequest extends DiffusionRequest {
       $this->raiseCloneException();
     }
 
+    // Expand abbreviated hashes to full hashes so "/rXnnnn" (i.e., fewer than
+    // 40 characters) works correctly.
+    if (!$this->commit) {
+      return;
+    }
+
+    if (strlen($this->commit) == 40) {
+      return;
+    }
+
+    list($full_hash) = $this->repository->execxLocalCommand(
+      'log --template=%s --rev %s',
+      '{node}',
+      $this->commit);
+
+    $full_hash = explode("\n", trim($full_hash));
+
+    // TODO: Show "multiple matching commits" if count is larger than 1. For
+    // now, pick the first one.
+
+    $this->commit = head($full_hash);
+
+
     return;
   }