Fix the exception when watching the first commit of a mercurial repo

Summary: Most checks were actually in place, but `ExecFuture` throws a `CommandException` which wasn't taken into account.

Test Plan: look at the first command and no longer saw an exception. Also, other commits worked as well.

Reviewers: richardvanvelzen

Reviewed By: richardvanvelzen

CC: krisbuist, Korvin, epriestley, aran

Differential Revision: https://secure.phabricator.com/D7730

src/applications/diffusion/query/rawdiff/DiffusionMercurialRawDiffQuery.php

@@ -3,23 +3,7 @@
 final class DiffusionMercurialRawDiffQuery extends DiffusionRawDiffQuery {
 
   protected function executeQuery() {
-    $raw_diff = $this->executeRawDiffCommand();
+    return $this->executeRawDiffCommand();
-
-    // the only legitimate case here is if we are looking at the first commit
-    // in the repository. no parents means first commit.
-    if (!$raw_diff) {
-      $drequest = $this->getRequest();
-      $parent_query =
-        DiffusionCommitParentsQuery::newFromDiffusionRequest($drequest);
-      $parents = $parent_query->loadParents();
-      if ($parents === array()) {
-        // mercurial likes the string null here
-        $this->setAgainstCommit('null');
-        $raw_diff = $this->executeRawDiffCommand();
-      }
-    }
-
-    return $raw_diff;
   }
 
 
@@ -34,11 +18,14 @@ final class DiffusionMercurialRawDiffQuery extends DiffusionRawDiffQuery {
 
     $against = $this->getAgainstCommit();
     if ($against === null) {
-      $against = $commit.'^';
+      // If `$commit` has no parents (usually because it's the first commit
+      // in the repository), we want to diff against `null`. This revset will
+      // do that for us automatically.
+      $against = '('.$commit.'^ or null)';
     }
 
     $future = $repository->getLocalCommandFuture(
-      'diff -U %d --git --rev %s:%s -- %s',
+      'diff -U %d --git --rev %s --rev %s -- %s',
       $this->getLinesOfContext(),
       $against,
       $commit,