Add trailing tabs when generating synthetic Git diffs for files with spaces

Summary:
Fixes T8768. See PHI294. See that task for more details.

Git, Mercurial, `diff`, and `patch` have conspired to make things weird. To correctly handle files with spaces in the way everything else does and expects, we need to emit semantic trailing whitespace literals.

Test Plan:
- Created a file with spaces in it in a Mercurial repositroy, committed it, diffed it into a revision.
- Used `arc patch` to apply the change to a clean copy of the repository.
- Before patch: Mercurial incorrectly creates a file named `X`, not a file named `X Y.txt`.
- After patch: `arc patch` commit is identical to genuine commit.
- Also added test coverage. The other general behaviors here are fairly well covered already.

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T8768

Differential Revision: https://secure.phabricator.com/D18869

src/parser/ArcanistBundle.php

@@ -424,6 +424,9 @@ final class ArcanistBundle extends Phobject {
         $cur_target  = 'b/'.$cur_path;
       }
 
+      $old_target = $this->encodeGitTargetPath($old_target);
+      $cur_target = $this->encodeGitTargetPath($cur_target);
+
       $result[] = "diff --git {$old_index} {$cur_index}".$eol;
 
       if ($type == ArcanistDiffChangeType::TYPE_ADD) {
@@ -591,6 +594,24 @@ final class ArcanistBundle extends Phobject {
     return $results;
   }
 
+  private function encodeGitTargetPath($path) {
+    // See T8768. If a target path contains spaces, it must be terminated with
+    // a tab. If we don't do this, Mercurial has the wrong behavior when
+    // applying the patch. This results in a semantic trailing whitespace
+    // character:
+    //
+    //   +++ b/X Y.txt\t
+    //
+    // Everyone is at fault here and there are no winners.
+
+    if (strpos($path, ' ') !== false) {
+      $path = $path."\t";
+    }
+
+    return $path;
+  }
+
+
   private function getOldPath(ArcanistDiffChange $change) {
     $old_path = $change->getOldPath();
     $type = $change->getType();

src/parser/__tests__/ArcanistBundleTestCase.php

@@ -33,6 +33,37 @@ final class ArcanistBundleTestCase extends PhutilTestCase {
     return ArcanistBundle::newFromDiff($diff);
   }
 
+  public function testTabEncoding() {
+    // See T8768. Test that we add semantic trailing tab literals to diffs
+    // touching files with spaces in them. This is a pain to encode using the
+    // support toolset here so just do it manually.
+
+    // Note that the "b/X Y.txt" line has a trailing tab literal.
+
+    $diff = <<<EODIFF
+diff --git a/X Y.txt b/X Y.txt
+new file mode 100644
+--- /dev/null
++++ b/X Y.txt\t
+@@ -0,0 +1 @@
++quack
+
+
+EODIFF;
+
+    $bundle = ArcanistBundle::newFromDiff($diff);
+
+    $changes = $bundle->getChanges();
+    $this->assertEqual(1, count($changes));
+
+    // The path should parse as "X Y.txt" despite the trailing tab.
+    $change = head($changes);
+    $this->assertEqual('X Y.txt', $change->getCurrentPath());
+
+    // The tab should be restored when the diff is output again.
+    $this->assertEqual($diff, $bundle->toGitPatch());
+  }
+
   /**
    * Unarchive a saved git repository and apply each commit as though via
    * "arc patch", verifying that the resulting tree hash is identical to the