Allow ArcanistDiffParser to parse diff.suppress-blank-empty Git diffs

Summary: See D3963. Instead, parse these diffs so they'll work with `--raw`, etc.

Test Plan:
Generated a failing diff, added it as a test case. Fixed issue. Ran test suite. Ran `arc` against it:

  $ git -c diff.suppress-blank-empty=true diff HEAD | arc diff --raw --only --conduit-uri=http://local.aphront.com:8080/
  Reading diff from stdin...
  Created a new Differential diff:
          Diff URI: http://local.aphront.com:8080/differential/diff/103/

  Included changes:
    M       things

Reviewers: vrana, jiiix, btrahan

Reviewed By: vrana

CC: aran

Differential Revision: https://secure.phabricator.com/D3969

src/parser/ArcanistDiffParser.php

@@ -840,12 +840,17 @@ final class ArcanistDiffParser {
       $add = 0;
       $del = 0;
 
-      $advance = false;
+      $hit_next_hunk = false;
       while ((($line = $this->nextLine()) !== null)) {
-        if (strlen($line)) {
+        if (strlen(rtrim($line, "\r\n"))) {
           $char = $line[0];
         } else {
-          $char = '~';
+          // Normally, we do not encouter empty lines in diffs, because
+          // unchanged lines have an initial space. However, in Git, with
+          // the option `diff.suppress-blank-empty` set, unchanged blank lines
+          // emit as completely empty. If we encounter a completely empty line,
+          // treat it as a ' ' (i.e., unchanged empty line) line.
+          $char = ' ';
         }
         switch ($char) {
           case '\\':
@@ -861,20 +866,19 @@ final class ArcanistDiffParser {
               $hunk->setIsMissingNewNewline(true);
             }
             if (!$new_len) {
-              $advance = true;
               break 2;
             }
             break;
           case '+':
-            if (!$new_len) {
-              break 2;
-            }
             ++$add;
             --$new_len;
             $real[] = $line;
             break;
           case '-':
             if (!$old_len) {
+              // In this case, we've hit "---" from a new file. So don't
+              // advance the line cursor.
+              $hit_next_hunk = true;
               break 2;
             }
             ++$del;
@@ -889,17 +893,14 @@ final class ArcanistDiffParser {
             --$new_len;
             $real[] = $line;
             break;
-          case "\r":
-          case "\n":
-          case '~':
-            $advance = true;
-            break 2;
           default:
+            // We hit something, likely another hunk.
+            $hit_next_hunk = true;
             break 2;
         }
       }
 
-      if ($old_len != 0 || $new_len != 0) {
+      if ($old_len || $new_len) {
         $this->didFailParse("Found the wrong number of hunk lines.");
       }
 
@@ -939,7 +940,7 @@ final class ArcanistDiffParser {
         $change->addHunk($hunk);
       }
 
-      if ($advance) {
+      if (!$hit_next_hunk) {
         $line = $this->nextNonemptyLine();
       }
 

src/parser/__tests__/ArcanistDiffParserTestCase.php

@@ -536,6 +536,9 @@ EOTEXT
       case 'more-newlines.svndiff':
         $this->assertEqual(1, count($changes));
         break;
+      case 'suppress-blank-empty.gitdiff':
+        $this->assertEqual(1, count($changes));
+        break;
       default:
         throw new Exception("No test block for diff file {$diff_file}.");
         break;

src/parser/__tests__/diff/suppress-blank-empty.gitdiff

@@ -0,0 +1,11 @@
+diff --git a/things b/things
+index b6c8793..0c96a0f 100644
+--- a/things
++++ b/things
+@@ -1,5 +1,5 @@
+ apple
+
+-banana
++bananas
+
+ cherry