Show text of moved files in Differential

Summary:
"git diff -M -C" generates useful metadata (moves/copies) but (for a pure move) no diff text. Synthetically build the diff text after the fact so this information is available in Differential.

This patch is kind of nasty but I couldn't see a cleaner way to do it. :/

This also needs some UI changes in Differential: we get a full-green new file right now, but it would be better to default-hide it with "This file was moved. Show More" or similar.

Test Plan: Moved a file, ran "arc diff", got textual diff.

Reviewers: aran, tuomaspelkonen, jungejason, btrahan, vrana

Reviewed By: vrana

CC: aran, epriestley, vrana

Maniphest Tasks: T230

Differential Revision: https://secure.phabricator.com/D479

src/parser/diff/ArcanistDiffParser.php

@@ -493,6 +493,8 @@ final class ArcanistDiffParser {
     $is_mercurial = $this->getIsMercurial();
     $is_svn = (!$is_git && !$is_mercurial);
 
+    $move_source = null;
+
     $line = $this->getLine();
     if ($is_git) {
       do {
@@ -524,7 +526,21 @@ final class ArcanistDiffParser {
           if ($line === null ||
               preg_match('/^(diff --git|commit) /', $line)) {
             // In this case, there are ONLY file mode changes, or this is a
-            // pure move.
+            // pure move. If it's a move, flag these changesets so we can build
+            // synthetic changes later, enabling us to show file contents in
+            // Differential -- git only gives us a block like this:
+            //
+            //   diff --git a/README b/READYOU
+            //   similarity index 100%
+            //   rename from README
+            //   rename to READYOU
+            //
+            // ...i.e., there is no associated diff.
+
+            $change->setNeedsSyntheticGitHunks(true);
+            if ($move_source) {
+              $move_source->setNeedsSyntheticGitHunks(true);
+            }
             return;
           }
           break;
@@ -591,6 +607,9 @@ final class ArcanistDiffParser {
             $old->setType(ArcanistDiffChangeType::TYPE_MOVE_AWAY);
           }
 
+          // We'll reference this above.
+          $move_source = $old;
+
           $old->addAwayPath($change->getCurrentPath());
         }
 

src/parser/diff/change/ArcanistDiffChange.php

@@ -38,6 +38,8 @@ final class ArcanistDiffChange {
 
   protected $hunks = array();
 
+  private $needsSyntheticGitHunks;
+
   public function toDictionary() {
     $hunks = array();
     foreach ($this->hunks as $hunk) {
@@ -239,4 +241,13 @@ final class ArcanistDiffChange {
     return trim($match[1]);
   }
 
+  public function setNeedsSyntheticGitHunks($needs_synthetic_git_hunks) {
+    $this->needsSyntheticGitHunks = $needs_synthetic_git_hunks;
+    return $this;
+  }
+
+  public function getNeedsSyntheticGitHunks() {
+    return $this->needsSyntheticGitHunks;
+  }
+
 }

src/repository/api/git/ArcanistGitAPI.php

@@ -210,16 +210,20 @@ final class ArcanistGitAPI extends ArcanistRepositoryAPI {
     return $this->relativeCommit;
   }
 
-  private function getDiffFullOptions() {
+  private function getDiffFullOptions($detect_moves_and_renames = true) {
     $options = array(
       self::getDiffBaseOptions(),
-      '-M',
-      '-C',
       '--no-color',
       '--src-prefix=a/',
       '--dst-prefix=b/',
       '-U'.$this->getDiffLinesOfContext(),
     );
+
+    if ($detect_moves_and_renames) {
+      $options[] = '-M';
+      $options[] = '-C';
+    }
+
     return implode(' ', $options);
   }
 
@@ -245,8 +249,14 @@ final class ArcanistGitAPI extends ArcanistRepositoryAPI {
     return $stdout;
   }
 
-  public function getRawDiffText($path) {
-    $options = $this->getDiffFullOptions();
+  /**
+   * @param string Path to generate a diff for.
+   * @param bool   If true, detect moves and renames. Otherwise, ignore
+   *               moves/renames; this is useful because it prompts git to
+   *               generate real diff text.
+   */
+  public function getRawDiffText($path, $detect_moves_and_renames = true) {
+    $options = $this->getDiffFullOptions($detect_moves_and_renames);
     list($stdout) = $this->execxLocal(
       "diff {$options} %s -- %s",
       $this->getRelativeCommit(),

src/workflow/diff/ArcanistDiffWorkflow.php

@@ -855,11 +855,32 @@ EOTEXT
     }
 
     foreach ($changes as $change) {
+      $path = $change->getCurrentPath();
+
+      // Certain types of changes (moves and copies) don't contain change data
+      // when expressed in raw "git diff" form. Augment any such diffs with
+      // textual data.
+      if ($change->getNeedsSyntheticGitHunks()) {
+        $diff = $repository_api->getRawDiffText($path, $moves = false);
+        $parser = new ArcanistDiffParser();
+        $raw_changes = $parser->parseDiff($diff);
+        foreach ($raw_changes as $raw_change) {
+          if ($raw_change->getCurrentPath() == $path) {
+            $change->setFileType($raw_change->getFileType());
+            foreach ($raw_change->getHunks() as $hunk) {
+              $change->addHunk($hunk);
+            }
+            break;
+          }
+        }
+
+        $change->setNeedsSyntheticGitHunks(false);
+      }
+
       if ($change->getFileType() != ArcanistDiffChangeType::FILE_BINARY) {
         continue;
       }
 
-      $path = $change->getCurrentPath();
       $name = basename($path);
 
       $old_file = $repository_api->getOriginalFileData($path);