diff --git a/src/applications/differential/__tests__/DifferentialParseRenderTestCase.php b/src/applications/differential/__tests__/DifferentialParseRenderTestCase.php
index 259bb671de..ce93bbe65a 100644
--- a/src/applications/differential/__tests__/DifferentialParseRenderTestCase.php
+++ b/src/applications/differential/__tests__/DifferentialParseRenderTestCase.php
@@ -1,110 +1,114 @@
 <?php
 
 final class DifferentialParseRenderTestCase extends PhabricatorTestCase {
 
   private function getTestDataDirectory() {
     return dirname(__FILE__).'/data/';
   }
 
   public function testParseRender() {
     $dir = $this->getTestDataDirectory();
     foreach (Filesystem::listDirectory($dir, $show_hidden = false) as $file) {
       if (!preg_match('/\.diff$/', $file)) {
         continue;
       }
       $data = Filesystem::readFile($dir.$file);
 
+      // Strip trailing "~" characters from inputs so they may contain
+      // trailing whitespace.
+      $data = preg_replace('/~$/m', '', $data);
+
       $opt_file = $dir.$file.'.options';
       if (Filesystem::pathExists($opt_file)) {
         $options = Filesystem::readFile($opt_file);
         try {
           $options = phutil_json_decode($options);
         } catch (PhutilJSONParserException $ex) {
           throw new PhutilProxyException(
             pht('Invalid options file: %s.', $opt_file),
             $ex);
         }
       } else {
         $options = array();
       }
 
       foreach (array('one', 'two') as $type) {
         $this->runParser($type, $data, $file, 'expect');
         $this->runParser($type, $data, $file, 'unshielded');
       }
     }
   }
 
   private function runParser($type, $data, $file, $extension) {
     $dir = $this->getTestDataDirectory();
     $test_file = $dir.$file.'.'.$type.'.'.$extension;
     if (!Filesystem::pathExists($test_file)) {
       return;
     }
 
     $unshielded = false;
     switch ($extension) {
       case 'unshielded':
         $unshielded = true;
         break;
     }
 
     $parsers = $this->buildChangesetParsers($type, $data, $file);
     $actual = $this->renderParsers($parsers, $unshielded);
     $expect = Filesystem::readFile($test_file);
 
     $this->assertEqual($expect, $actual, basename($test_file));
   }
 
   private function renderParsers(array $parsers, $unshield) {
     $result = array();
     foreach ($parsers as $parser) {
       if ($unshield) {
         $s_range = 0;
         $e_range = 0xFFFF;
       } else {
         $s_range = null;
         $e_range = null;
       }
 
       $result[] = $parser->render($s_range, $e_range, array());
     }
     return implode(str_repeat('~', 80)."\n", $result);
   }
 
   private function buildChangesetParsers($type, $data, $file) {
     $parser = new ArcanistDiffParser();
     $changes = $parser->parseDiff($data);
 
     $diff = DifferentialDiff::newFromRawChanges(
       PhabricatorUser::getOmnipotentUser(),
       $changes);
 
     $changesets = $diff->getChangesets();
 
     $engine = new PhabricatorMarkupEngine();
     $engine->setViewer(new PhabricatorUser());
 
     $parsers = array();
     foreach ($changesets as $changeset) {
       $cparser = new DifferentialChangesetParser();
       $cparser->setUser(new PhabricatorUser());
       $cparser->setDisableCache(true);
       $cparser->setChangeset($changeset);
       $cparser->setMarkupEngine($engine);
 
       if ($type == 'one') {
         $cparser->setRenderer(new DifferentialChangesetOneUpTestRenderer());
       } else if ($type == 'two') {
         $cparser->setRenderer(new DifferentialChangesetTwoUpTestRenderer());
       } else {
         throw new Exception(pht('Unknown renderer type "%s"!', $type));
       }
 
       $parsers[] = $cparser;
     }
 
     return $parsers;
   }
 
 }
diff --git a/src/applications/differential/__tests__/data/generated.diff b/src/applications/differential/__tests__/data/generated.diff
index 7846c9a494..c130993cf7 100644
--- a/src/applications/differential/__tests__/data/generated.diff
+++ b/src/applications/differential/__tests__/data/generated.diff
@@ -1,10 +1,10 @@
 diff --git a/GENERATED b/GENERATED
 index 5dcff7f..eff82ef 100644
 --- a/GENERATED
 +++ b/GENERATED
 @@ -1,4 +1,4 @@
  @generated
-
+ ~
 -This is a generated file.
 +This is a generated file, full of generated code.
 
diff --git a/src/applications/differential/parser/DifferentialChangesetParser.php b/src/applications/differential/parser/DifferentialChangesetParser.php
index caa7463672..f0f952328a 100644
--- a/src/applications/differential/parser/DifferentialChangesetParser.php
+++ b/src/applications/differential/parser/DifferentialChangesetParser.php
@@ -1,1369 +1,1419 @@
 <?php
 
 final class DifferentialChangesetParser extends Phobject {
 
   const HIGHLIGHT_BYTE_LIMIT = 262144;
 
   protected $visible      = array();
   protected $new          = array();
   protected $old          = array();
   protected $intra        = array();
   protected $depthOnlyLines = array();
   protected $newRender    = null;
   protected $oldRender    = null;
 
   protected $filename     = null;
   protected $hunkStartLines = array();
 
   protected $comments     = array();
   protected $specialAttributes = array();
 
   protected $changeset;
 
   protected $renderCacheKey = null;
 
   private $handles = array();
   private $user;
 
   private $leftSideChangesetID;
   private $leftSideAttachesToNewFile;
 
   private $rightSideChangesetID;
   private $rightSideAttachesToNewFile;
 
   private $originalLeft;
   private $originalRight;
 
   private $renderingReference;
   private $isSubparser;
 
   private $isTopLevel;
 
   private $coverage;
   private $markupEngine;
   private $highlightErrors;
   private $disableCache;
   private $renderer;
   private $characterEncoding;
   private $highlightAs;
   private $highlightingDisabled;
   private $showEditAndReplyLinks = true;
   private $canMarkDone;
   private $objectOwnerPHID;
   private $offsetMode;
 
   private $rangeStart;
   private $rangeEnd;
   private $mask;
   private $linesOfContext = 8;
 
   private $highlightEngine;
 
   public function setRange($start, $end) {
     $this->rangeStart = $start;
     $this->rangeEnd = $end;
     return $this;
   }
 
   public function setMask(array $mask) {
     $this->mask = $mask;
     return $this;
   }
 
   public function renderChangeset() {
     return $this->render($this->rangeStart, $this->rangeEnd, $this->mask);
   }
 
   public function setShowEditAndReplyLinks($bool) {
     $this->showEditAndReplyLinks = $bool;
     return $this;
   }
 
   public function getShowEditAndReplyLinks() {
     return $this->showEditAndReplyLinks;
   }
 
   public function setHighlightAs($highlight_as) {
     $this->highlightAs = $highlight_as;
     return $this;
   }
 
   public function getHighlightAs() {
     return $this->highlightAs;
   }
 
   public function setCharacterEncoding($character_encoding) {
     $this->characterEncoding = $character_encoding;
     return $this;
   }
 
   public function getCharacterEncoding() {
     return $this->characterEncoding;
   }
 
   public function setRenderer(DifferentialChangesetRenderer $renderer) {
     $this->renderer = $renderer;
     return $this;
   }
 
   public function getRenderer() {
     if (!$this->renderer) {
       return new DifferentialChangesetTwoUpRenderer();
     }
     return $this->renderer;
   }
 
   public function setDisableCache($disable_cache) {
     $this->disableCache = $disable_cache;
     return $this;
   }
 
   public function getDisableCache() {
     return $this->disableCache;
   }
 
   public function setCanMarkDone($can_mark_done) {
     $this->canMarkDone = $can_mark_done;
     return $this;
   }
 
   public function getCanMarkDone() {
     return $this->canMarkDone;
   }
 
   public function setObjectOwnerPHID($phid) {
     $this->objectOwnerPHID = $phid;
     return $this;
   }
 
   public function getObjectOwnerPHID() {
     return $this->objectOwnerPHID;
   }
 
   public function setOffsetMode($offset_mode) {
     $this->offsetMode = $offset_mode;
     return $this;
   }
 
   public function getOffsetMode() {
     return $this->offsetMode;
   }
 
   public static function getDefaultRendererForViewer(PhabricatorUser $viewer) {
     $is_unified = $viewer->compareUserSetting(
       PhabricatorUnifiedDiffsSetting::SETTINGKEY,
       PhabricatorUnifiedDiffsSetting::VALUE_ALWAYS_UNIFIED);
 
     if ($is_unified) {
       return '1up';
     }
 
     return null;
   }
 
   public function readParametersFromRequest(AphrontRequest $request) {
     $this->setCharacterEncoding($request->getStr('encoding'));
     $this->setHighlightAs($request->getStr('highlight'));
 
     $renderer = null;
 
     // If the viewer prefers unified diffs, always set the renderer to unified.
     // Otherwise, we leave it unspecified and the client will choose a
     // renderer based on the screen size.
 
     if ($request->getStr('renderer')) {
       $renderer = $request->getStr('renderer');
     } else {
       $renderer = self::getDefaultRendererForViewer($request->getViewer());
     }
 
     switch ($renderer) {
       case '1up':
         $this->setRenderer(new DifferentialChangesetOneUpRenderer());
         break;
       default:
         $this->setRenderer(new DifferentialChangesetTwoUpRenderer());
         break;
     }
 
     return $this;
   }
 
   const CACHE_VERSION = 13;
   const CACHE_MAX_SIZE = 8e6;
 
   const ATTR_GENERATED  = 'attr:generated';
   const ATTR_DELETED    = 'attr:deleted';
   const ATTR_UNCHANGED  = 'attr:unchanged';
   const ATTR_MOVEAWAY   = 'attr:moveaway';
 
   public function setOldLines(array $lines) {
     $this->old = $lines;
     return $this;
   }
 
   public function setNewLines(array $lines) {
     $this->new = $lines;
     return $this;
   }
 
   public function setSpecialAttributes(array $attributes) {
     $this->specialAttributes = $attributes;
     return $this;
   }
 
   public function setIntraLineDiffs(array $diffs) {
     $this->intra = $diffs;
     return $this;
   }
 
   public function setDepthOnlyLines(array $lines) {
     $this->depthOnlyLines = $lines;
     return $this;
   }
 
   public function getDepthOnlyLines() {
     return $this->depthOnlyLines;
   }
 
   public function setVisibileLinesMask(array $mask) {
     $this->visible = $mask;
     return $this;
   }
 
   public function setLinesOfContext($lines_of_context) {
     $this->linesOfContext = $lines_of_context;
     return $this;
   }
 
   public function getLinesOfContext() {
     return $this->linesOfContext;
   }
 
 
   /**
    * Configure which Changeset comments added to the right side of the visible
    * diff will be attached to. The ID must be the ID of a real Differential
    * Changeset.
    *
    * The complexity here is that we may show an arbitrary side of an arbitrary
    * changeset as either the left or right part of a diff. This method allows
    * the left and right halves of the displayed diff to be correctly mapped to
    * storage changesets.
    *
    * @param id    The Differential Changeset ID that comments added to the right
    *              side of the visible diff should be attached to.
    * @param bool  If true, attach new comments to the right side of the storage
    *              changeset. Note that this may be false, if the left side of
    *              some storage changeset is being shown as the right side of
    *              a display diff.
    * @return this
    */
   public function setRightSideCommentMapping($id, $is_new) {
     $this->rightSideChangesetID = $id;
     $this->rightSideAttachesToNewFile = $is_new;
     return $this;
   }
 
   /**
    * See setRightSideCommentMapping(), but this sets information for the left
    * side of the display diff.
    */
   public function setLeftSideCommentMapping($id, $is_new) {
     $this->leftSideChangesetID = $id;
     $this->leftSideAttachesToNewFile = $is_new;
     return $this;
   }
 
   public function setOriginals(
     DifferentialChangeset $left,
     DifferentialChangeset $right) {
 
     $this->originalLeft = $left;
     $this->originalRight = $right;
     return $this;
   }
 
   public function diffOriginals() {
     $engine = new PhabricatorDifferenceEngine();
     $changeset = $engine->generateChangesetFromFileContent(
       implode('', mpull($this->originalLeft->getHunks(), 'getChanges')),
       implode('', mpull($this->originalRight->getHunks(), 'getChanges')));
 
     $parser = new DifferentialHunkParser();
 
     return $parser->parseHunksForHighlightMasks(
       $changeset->getHunks(),
       $this->originalLeft->getHunks(),
       $this->originalRight->getHunks());
   }
 
   /**
    * Set a key for identifying this changeset in the render cache. If set, the
    * parser will attempt to use the changeset render cache, which can improve
    * performance for frequently-viewed changesets.
    *
    * By default, there is no render cache key and parsers do not use the cache.
    * This is appropriate for rarely-viewed changesets.
    *
    * NOTE: Currently, this key must be a valid Differential Changeset ID.
    *
    * @param   string  Key for identifying this changeset in the render cache.
    * @return  this
    */
   public function setRenderCacheKey($key) {
     $this->renderCacheKey = $key;
     return $this;
   }
 
   private function getRenderCacheKey() {
     return $this->renderCacheKey;
   }
 
   public function setChangeset(DifferentialChangeset $changeset) {
     $this->changeset = $changeset;
 
     $this->setFilename($changeset->getFilename());
 
     return $this;
   }
 
   public function setRenderingReference($ref) {
     $this->renderingReference = $ref;
     return $this;
   }
 
   private function getRenderingReference() {
     return $this->renderingReference;
   }
 
   public function getChangeset() {
     return $this->changeset;
   }
 
   public function setFilename($filename) {
     $this->filename = $filename;
     return $this;
   }
 
   public function setHandles(array $handles) {
     assert_instances_of($handles, 'PhabricatorObjectHandle');
     $this->handles = $handles;
     return $this;
   }
 
   public function setMarkupEngine(PhabricatorMarkupEngine $engine) {
     $this->markupEngine = $engine;
     return $this;
   }
 
   public function setUser(PhabricatorUser $user) {
     $this->user = $user;
     return $this;
   }
 
   public function getUser() {
     return $this->user;
   }
 
   public function setCoverage($coverage) {
     $this->coverage = $coverage;
     return $this;
   }
   private function getCoverage() {
     return $this->coverage;
   }
 
   public function parseInlineComment(
     PhabricatorInlineCommentInterface $comment) {
 
     // Parse only comments which are actually visible.
     if ($this->isCommentVisibleOnRenderedDiff($comment)) {
       $this->comments[] = $comment;
     }
     return $this;
   }
 
   private function loadCache() {
     $render_cache_key = $this->getRenderCacheKey();
     if (!$render_cache_key) {
       return false;
     }
 
     $data = null;
 
     $changeset = new DifferentialChangeset();
     $conn_r = $changeset->establishConnection('r');
     $data = queryfx_one(
       $conn_r,
       'SELECT * FROM %T WHERE id = %d',
       $changeset->getTableName().'_parse_cache',
       $render_cache_key);
 
     if (!$data) {
       return false;
     }
 
     if ($data['cache'][0] == '{') {
       // This is likely an old-style JSON cache which we will not be able to
       // deserialize.
       return false;
     }
 
     $data = unserialize($data['cache']);
     if (!is_array($data) || !$data) {
       return false;
     }
 
     foreach (self::getCacheableProperties() as $cache_key) {
       if (!array_key_exists($cache_key, $data)) {
         // If we're missing a cache key, assume we're looking at an old cache
         // and ignore it.
         return false;
       }
     }
 
     if ($data['cacheVersion'] !== self::CACHE_VERSION) {
       return false;
     }
 
     // Someone displays contents of a partially cached shielded file.
     if (!isset($data['newRender']) && (!$this->isTopLevel || $this->comments)) {
       return false;
     }
 
     unset($data['cacheVersion'], $data['cacheHost']);
     $cache_prop = array_select_keys($data, self::getCacheableProperties());
     foreach ($cache_prop as $cache_key => $v) {
       $this->$cache_key = $v;
     }
 
     return true;
   }
 
   protected static function getCacheableProperties() {
     return array(
       'visible',
       'new',
       'old',
       'intra',
       'depthOnlyLines',
       'newRender',
       'oldRender',
       'specialAttributes',
       'hunkStartLines',
       'cacheVersion',
       'cacheHost',
       'highlightingDisabled',
     );
   }
 
   public function saveCache() {
     if (PhabricatorEnv::isReadOnly()) {
       return false;
     }
 
     if ($this->highlightErrors) {
       return false;
     }
 
     $render_cache_key = $this->getRenderCacheKey();
     if (!$render_cache_key) {
       return false;
     }
 
     $cache = array();
     foreach (self::getCacheableProperties() as $cache_key) {
       switch ($cache_key) {
         case 'cacheVersion':
           $cache[$cache_key] = self::CACHE_VERSION;
           break;
         case 'cacheHost':
           $cache[$cache_key] = php_uname('n');
           break;
         default:
           $cache[$cache_key] = $this->$cache_key;
           break;
       }
     }
     $cache = serialize($cache);
 
     // We don't want to waste too much space by a single changeset.
     if (strlen($cache) > self::CACHE_MAX_SIZE) {
       return;
     }
 
     $changeset = new DifferentialChangeset();
     $conn_w = $changeset->establishConnection('w');
 
     $unguarded = AphrontWriteGuard::beginScopedUnguardedWrites();
       try {
         queryfx(
           $conn_w,
           'INSERT INTO %T (id, cache, dateCreated) VALUES (%d, %B, %d)
             ON DUPLICATE KEY UPDATE cache = VALUES(cache)',
           DifferentialChangeset::TABLE_CACHE,
           $render_cache_key,
           $cache,
           time());
       } catch (AphrontQueryException $ex) {
         // Ignore these exceptions. A common cause is that the cache is
         // larger than 'max_allowed_packet', in which case we're better off
         // not writing it.
 
         // TODO: It would be nice to tailor this more narrowly.
       }
     unset($unguarded);
   }
 
   private function markGenerated($new_corpus_block = '') {
     $generated_guess = (strpos($new_corpus_block, '@'.'generated') !== false);
 
     if (!$generated_guess) {
       $generated_path_regexps = PhabricatorEnv::getEnvConfig(
         'differential.generated-paths');
       foreach ($generated_path_regexps as $regexp) {
         if (preg_match($regexp, $this->changeset->getFilename())) {
           $generated_guess = true;
           break;
         }
       }
     }
 
     $event = new PhabricatorEvent(
       PhabricatorEventType::TYPE_DIFFERENTIAL_WILLMARKGENERATED,
       array(
         'corpus' => $new_corpus_block,
         'is_generated' => $generated_guess,
       )
     );
     PhutilEventEngine::dispatchEvent($event);
 
     $generated = $event->getValue('is_generated');
 
     $attribute = $this->changeset->isGeneratedChangeset();
     if ($attribute) {
       $generated = true;
     }
 
     $this->specialAttributes[self::ATTR_GENERATED] = $generated;
   }
 
   public function isGenerated() {
     return idx($this->specialAttributes, self::ATTR_GENERATED, false);
   }
 
   public function isDeleted() {
     return idx($this->specialAttributes, self::ATTR_DELETED, false);
   }
 
   public function isUnchanged() {
     return idx($this->specialAttributes, self::ATTR_UNCHANGED, false);
   }
 
   public function isMoveAway() {
     return idx($this->specialAttributes, self::ATTR_MOVEAWAY, false);
   }
 
   private function applyIntraline(&$render, $intra, $corpus) {
 
     foreach ($render as $key => $text) {
       if (isset($intra[$key])) {
         $render[$key] = ArcanistDiffUtils::applyIntralineDiff(
           $text,
           $intra[$key]);
       }
     }
   }
 
   private function getHighlightFuture($corpus) {
     $language = $this->highlightAs;
 
     if (!$language) {
       $language = $this->highlightEngine->getLanguageFromFilename(
         $this->filename);
 
       if (($language != 'txt') &&
           (strlen($corpus) > self::HIGHLIGHT_BYTE_LIMIT)) {
         $this->highlightingDisabled = true;
         $language = 'txt';
       }
     }
 
     return $this->highlightEngine->getHighlightFuture(
       $language,
       $corpus);
   }
 
   protected function processHighlightedSource($data, $result) {
 
     $result_lines = phutil_split_lines($result);
     foreach ($data as $key => $info) {
       if (!$info) {
         unset($result_lines[$key]);
       }
     }
     return $result_lines;
   }
 
   private function tryCacheStuff() {
     $skip_cache = false;
 
     if ($this->disableCache) {
       $skip_cache = true;
     }
 
     if ($this->characterEncoding) {
       $skip_cache = true;
     }
 
     if ($this->highlightAs) {
       $skip_cache = true;
     }
 
     $changeset = $this->changeset;
 
     if ($changeset->getFileType() != DifferentialChangeType::FILE_TEXT &&
         $changeset->getFileType() != DifferentialChangeType::FILE_SYMLINK) {
 
       $this->markGenerated();
 
     } else {
       if ($skip_cache || !$this->loadCache()) {
         $this->process();
         if (!$skip_cache) {
           $this->saveCache();
         }
       }
     }
   }
 
   private function process() {
     $changeset = $this->changeset;
 
     $hunk_parser = new DifferentialHunkParser();
     $hunk_parser->parseHunksForLineData($changeset->getHunks());
+
+    $this->realignDiff($changeset, $hunk_parser);
+
     $hunk_parser->reparseHunksForSpecialAttributes();
 
     $unchanged = false;
     if (!$hunk_parser->getHasAnyChanges()) {
       $filetype = $this->changeset->getFileType();
       if ($filetype == DifferentialChangeType::FILE_TEXT ||
           $filetype == DifferentialChangeType::FILE_SYMLINK) {
         $unchanged = true;
       }
     }
 
     $moveaway = false;
     $changetype = $this->changeset->getChangeType();
     if ($changetype == DifferentialChangeType::TYPE_MOVE_AWAY) {
       $moveaway = true;
     }
 
     $this->setSpecialAttributes(array(
       self::ATTR_UNCHANGED  => $unchanged,
       self::ATTR_DELETED    => $hunk_parser->getIsDeleted(),
       self::ATTR_MOVEAWAY   => $moveaway,
     ));
 
     $lines_context = $this->getLinesOfContext();
 
     $hunk_parser->generateIntraLineDiffs();
     $hunk_parser->generateVisibileLinesMask($lines_context);
 
     $this->setOldLines($hunk_parser->getOldLines());
     $this->setNewLines($hunk_parser->getNewLines());
     $this->setIntraLineDiffs($hunk_parser->getIntraLineDiffs());
     $this->setDepthOnlyLines($hunk_parser->getDepthOnlyLines());
     $this->setVisibileLinesMask($hunk_parser->getVisibleLinesMask());
     $this->hunkStartLines = $hunk_parser->getHunkStartLines(
       $changeset->getHunks());
 
     $new_corpus = $hunk_parser->getNewCorpus();
     $new_corpus_block = implode('', $new_corpus);
     $this->markGenerated($new_corpus_block);
 
     if ($this->isTopLevel &&
         !$this->comments &&
           ($this->isGenerated() ||
            $this->isUnchanged() ||
            $this->isDeleted())) {
       return;
     }
 
     $old_corpus = $hunk_parser->getOldCorpus();
     $old_corpus_block = implode('', $old_corpus);
     $old_future = $this->getHighlightFuture($old_corpus_block);
     $new_future = $this->getHighlightFuture($new_corpus_block);
     $futures = array(
       'old' => $old_future,
       'new' => $new_future,
     );
     $corpus_blocks = array(
       'old' => $old_corpus_block,
       'new' => $new_corpus_block,
     );
 
     $this->highlightErrors = false;
     foreach (new FutureIterator($futures) as $key => $future) {
       try {
         try {
           $highlighted = $future->resolve();
         } catch (PhutilSyntaxHighlighterException $ex) {
           $this->highlightErrors = true;
           $highlighted = id(new PhutilDefaultSyntaxHighlighter())
             ->getHighlightFuture($corpus_blocks[$key])
             ->resolve();
         }
         switch ($key) {
         case 'old':
           $this->oldRender = $this->processHighlightedSource(
             $this->old,
             $highlighted);
           break;
         case 'new':
           $this->newRender = $this->processHighlightedSource(
             $this->new,
             $highlighted);
           break;
         }
       } catch (Exception $ex) {
         phlog($ex);
         throw $ex;
       }
     }
 
     $this->applyIntraline(
       $this->oldRender,
       ipull($this->intra, 0),
       $old_corpus);
     $this->applyIntraline(
       $this->newRender,
       ipull($this->intra, 1),
       $new_corpus);
   }
 
   private function shouldRenderPropertyChangeHeader($changeset) {
     if (!$this->isTopLevel) {
       // We render properties only at top level; otherwise we get multiple
       // copies of them when a user clicks "Show More".
       return false;
     }
 
     return true;
   }
 
   public function render(
     $range_start  = null,
     $range_len    = null,
     $mask_force   = array()) {
 
     // "Top level" renders are initial requests for the whole file, versus
     // requests for a specific range generated by clicking "show more". We
     // generate property changes and "shield" UI elements only for toplevel
     // requests.
     $this->isTopLevel = (($range_start === null) && ($range_len === null));
     $this->highlightEngine = PhabricatorSyntaxHighlighter::newEngine();
 
     $encoding = null;
     if ($this->characterEncoding) {
       // We are forcing this changeset to be interpreted with a specific
       // character encoding, so force all the hunks into that encoding and
       // propagate it to the renderer.
       $encoding = $this->characterEncoding;
       foreach ($this->changeset->getHunks() as $hunk) {
         $hunk->forceEncoding($this->characterEncoding);
       }
     } else {
       // We're just using the default, so tell the renderer what that is
       // (by reading the encoding from the first hunk).
       foreach ($this->changeset->getHunks() as $hunk) {
         $encoding = $hunk->getDataEncoding();
         break;
       }
     }
 
     $this->tryCacheStuff();
 
     // If we're rendering in an offset mode, treat the range numbers as line
     // numbers instead of rendering offsets.
     $offset_mode = $this->getOffsetMode();
     if ($offset_mode) {
       if ($offset_mode == 'new') {
         $offset_map = $this->new;
       } else {
         $offset_map = $this->old;
       }
 
       // NOTE: Inline comments use zero-based lengths. For example, a comment
       // that starts and ends on line 123 has length 0. Rendering considers
       // this range to have length 1. Probably both should agree, but that
       // ship likely sailed long ago. Tweak things here to get the two systems
       // to agree. See PHI985, where this affected mail rendering of inline
       // comments left on the final line of a file.
 
       $range_end = $this->getOffset($offset_map, $range_start + $range_len);
       $range_start = $this->getOffset($offset_map, $range_start);
       $range_len = ($range_end - $range_start) + 1;
     }
 
     $render_pch = $this->shouldRenderPropertyChangeHeader($this->changeset);
 
     $rows = max(
       count($this->old),
       count($this->new));
 
     $renderer = $this->getRenderer()
       ->setUser($this->getUser())
       ->setChangeset($this->changeset)
       ->setRenderPropertyChangeHeader($render_pch)
       ->setIsTopLevel($this->isTopLevel)
       ->setOldRender($this->oldRender)
       ->setNewRender($this->newRender)
       ->setHunkStartLines($this->hunkStartLines)
       ->setOldChangesetID($this->leftSideChangesetID)
       ->setNewChangesetID($this->rightSideChangesetID)
       ->setOldAttachesToNewFile($this->leftSideAttachesToNewFile)
       ->setNewAttachesToNewFile($this->rightSideAttachesToNewFile)
       ->setCodeCoverage($this->getCoverage())
       ->setRenderingReference($this->getRenderingReference())
       ->setMarkupEngine($this->markupEngine)
       ->setHandles($this->handles)
       ->setOldLines($this->old)
       ->setNewLines($this->new)
       ->setOriginalCharacterEncoding($encoding)
       ->setShowEditAndReplyLinks($this->getShowEditAndReplyLinks())
       ->setCanMarkDone($this->getCanMarkDone())
       ->setObjectOwnerPHID($this->getObjectOwnerPHID())
       ->setHighlightingDisabled($this->highlightingDisabled)
       ->setDepthOnlyLines($this->getDepthOnlyLines());
 
     $shield = null;
     if ($this->isTopLevel && !$this->comments) {
       if ($this->isGenerated()) {
         $shield = $renderer->renderShield(
           pht(
             'This file contains generated code, which does not normally '.
             'need to be reviewed.'));
       } else if ($this->isMoveAway()) {
         // We put an empty shield on these files. Normally, they do not have
         // any diff content anyway. However, if they come through `arc`, they
         // may have content. We don't want to show it (it's not useful) and
         // we bailed out of fully processing it earlier anyway.
 
         // We could show a message like "this file was moved", but we show
         // that as a change header anyway, so it would be redundant. Instead,
         // just render an empty shield to skip rendering the diff body.
         $shield = '';
       } else if ($this->isUnchanged()) {
         $type = 'text';
         if (!$rows) {
           // NOTE: Normally, diffs which don't change files do not include
           // file content (for example, if you "chmod +x" a file and then
           // run "git show", the file content is not available). Similarly,
           // if you move a file from A to B without changing it, diffs normally
           // do not show the file content. In some cases `arc` is able to
           // synthetically generate content for these diffs, but for raw diffs
           // we'll never have it so we need to be prepared to not render a link.
           $type = 'none';
         }
 
         $type_add = DifferentialChangeType::TYPE_ADD;
         if ($this->changeset->getChangeType() == $type_add) {
           // Although the generic message is sort of accurate in a technical
           // sense, this more-tailored message is less confusing.
           $shield = $renderer->renderShield(
             pht('This is an empty file.'),
             $type);
         } else {
           $shield = $renderer->renderShield(
             pht('The contents of this file were not changed.'),
             $type);
         }
       } else if ($this->isDeleted()) {
         $shield = $renderer->renderShield(
           pht('This file was completely deleted.'));
       } else if ($this->changeset->getAffectedLineCount() > 2500) {
         $shield = $renderer->renderShield(
           pht(
             'This file has a very large number of changes (%s lines).',
             new PhutilNumber($this->changeset->getAffectedLineCount())));
       }
     }
 
     if ($shield !== null) {
       return $renderer->renderChangesetTable($shield);
     }
 
     // This request should render the "undershield" headers if it's a top-level
     // request which made it this far (indicating the changeset has no shield)
     // or it's a request with no mask information (indicating it's the request
     // that removes the rendering shield). Possibly, this second class of
     // request might need to be made more explicit.
     $is_undershield = (empty($mask_force) || $this->isTopLevel);
     $renderer->setIsUndershield($is_undershield);
 
     $old_comments = array();
     $new_comments = array();
     $old_mask = array();
     $new_mask = array();
     $feedback_mask = array();
     $lines_context = $this->getLinesOfContext();
 
     if ($this->comments) {
       // If there are any comments which appear in sections of the file which
       // we don't have, we're going to move them backwards to the closest
       // earlier line. Two cases where this may happen are:
       //
       //   - Porting ghost comments forward into a file which was mostly
       //     deleted.
       //   - Porting ghost comments forward from a full-context diff to a
       //     partial-context diff.
 
       list($old_backmap, $new_backmap) = $this->buildLineBackmaps();
 
       foreach ($this->comments as $comment) {
         $new_side = $this->isCommentOnRightSideWhenDisplayed($comment);
 
         $line = $comment->getLineNumber();
         if ($new_side) {
           $back_line = $new_backmap[$line];
         } else {
           $back_line = $old_backmap[$line];
         }
 
         if ($back_line != $line) {
           // TODO: This should probably be cleaner, but just be simple and
           // obvious for now.
           $ghost = $comment->getIsGhost();
           if ($ghost) {
             $moved = pht(
               'This comment originally appeared on line %s, but that line '.
               'does not exist in this version of the diff. It has been '.
               'moved backward to the nearest line.',
               new PhutilNumber($line));
             $ghost['reason'] = $ghost['reason']."\n\n".$moved;
             $comment->setIsGhost($ghost);
           }
 
           $comment->setLineNumber($back_line);
           $comment->setLineLength(0);
 
         }
 
         $start = max($comment->getLineNumber() - $lines_context, 0);
         $end = $comment->getLineNumber() +
           $comment->getLineLength() +
           $lines_context;
         for ($ii = $start; $ii <= $end; $ii++) {
           if ($new_side) {
             $new_mask[$ii] = true;
           } else {
             $old_mask[$ii] = true;
           }
         }
       }
 
       foreach ($this->old as $ii => $old) {
         if (isset($old['line']) && isset($old_mask[$old['line']])) {
           $feedback_mask[$ii] = true;
         }
       }
 
       foreach ($this->new as $ii => $new) {
         if (isset($new['line']) && isset($new_mask[$new['line']])) {
           $feedback_mask[$ii] = true;
         }
       }
 
       $this->comments = id(new PHUIDiffInlineThreader())
         ->reorderAndThreadCommments($this->comments);
 
       foreach ($this->comments as $comment) {
         $final = $comment->getLineNumber() +
           $comment->getLineLength();
         $final = max(1, $final);
         if ($this->isCommentOnRightSideWhenDisplayed($comment)) {
           $new_comments[$final][] = $comment;
         } else {
           $old_comments[$final][] = $comment;
         }
       }
     }
     $renderer
       ->setOldComments($old_comments)
       ->setNewComments($new_comments);
 
     switch ($this->changeset->getFileType()) {
       case DifferentialChangeType::FILE_IMAGE:
         $old = null;
         $new = null;
         // TODO: Improve the architectural issue as discussed in D955
         // https://secure.phabricator.com/D955
         $reference = $this->getRenderingReference();
         $parts = explode('/', $reference);
         if (count($parts) == 2) {
           list($id, $vs) = $parts;
         } else {
           $id = $parts[0];
           $vs = 0;
         }
         $id = (int)$id;
         $vs = (int)$vs;
 
         if (!$vs) {
           $metadata = $this->changeset->getMetadata();
           $data = idx($metadata, 'attachment-data');
 
           $old_phid = idx($metadata, 'old:binary-phid');
           $new_phid = idx($metadata, 'new:binary-phid');
         } else {
           $vs_changeset = id(new DifferentialChangeset())->load($vs);
           $old_phid = null;
           $new_phid = null;
 
           // TODO: This is spooky, see D6851
           if ($vs_changeset) {
             $vs_metadata = $vs_changeset->getMetadata();
             $old_phid = idx($vs_metadata, 'new:binary-phid');
           }
 
           $changeset = id(new DifferentialChangeset())->load($id);
           if ($changeset) {
             $metadata = $changeset->getMetadata();
             $new_phid = idx($metadata, 'new:binary-phid');
           }
         }
 
         if ($old_phid || $new_phid) {
           // grab the files, (micro) optimization for 1 query not 2
           $file_phids = array();
           if ($old_phid) {
             $file_phids[] = $old_phid;
           }
           if ($new_phid) {
             $file_phids[] = $new_phid;
           }
 
           $files = id(new PhabricatorFileQuery())
             ->setViewer($this->getUser())
             ->withPHIDs($file_phids)
             ->execute();
           foreach ($files as $file) {
             if (empty($file)) {
               continue;
             }
             if ($file->getPHID() == $old_phid) {
               $old = $file;
             } else if ($file->getPHID() == $new_phid) {
               $new = $file;
             }
           }
         }
 
         $renderer->attachOldFile($old);
         $renderer->attachNewFile($new);
 
         return $renderer->renderFileChange($old, $new, $id, $vs);
       case DifferentialChangeType::FILE_DIRECTORY:
       case DifferentialChangeType::FILE_BINARY:
         $output = $renderer->renderChangesetTable(null);
         return $output;
     }
 
     if ($this->originalLeft && $this->originalRight) {
       list($highlight_old, $highlight_new) = $this->diffOriginals();
       $highlight_old = array_flip($highlight_old);
       $highlight_new = array_flip($highlight_new);
       $renderer
         ->setHighlightOld($highlight_old)
         ->setHighlightNew($highlight_new);
     }
     $renderer
       ->setOriginalOld($this->originalLeft)
       ->setOriginalNew($this->originalRight);
 
     if ($range_start === null) {
       $range_start = 0;
     }
     if ($range_len === null) {
       $range_len = $rows;
     }
     $range_len = min($range_len, $rows - $range_start);
 
     list($gaps, $mask) = $this->calculateGapsAndMask(
       $mask_force,
       $feedback_mask,
       $range_start,
       $range_len);
 
     $renderer
       ->setGaps($gaps)
       ->setMask($mask);
 
     $html = $renderer->renderTextChange(
       $range_start,
       $range_len,
       $rows);
 
     return $renderer->renderChangesetTable($html);
   }
 
   /**
    * This function calculates a lot of stuff we need to know to display
    * the diff:
    *
    * Gaps - compute gaps in the visible display diff, where we will render
    * "Show more context" spacers. If a gap is smaller than the context size,
    * we just display it. Otherwise, we record it into $gaps and will render a
    * "show more context" element instead of diff text below. A given $gap
    * is a tuple of $gap_line_number_start and $gap_length.
    *
    * Mask - compute the actual lines that need to be shown (because they
    * are near changes lines, near inline comments, or the request has
    * explicitly asked for them, i.e. resulting from the user clicking
    * "show more"). The $mask returned is a sparsely populated dictionary
    * of $visible_line_number => true.
    *
    * @return array($gaps, $mask)
    */
   private function calculateGapsAndMask(
     $mask_force,
     $feedback_mask,
     $range_start,
     $range_len) {
 
     $lines_context = $this->getLinesOfContext();
 
     $gaps = array();
     $gap_start = 0;
     $in_gap = false;
     $base_mask = $this->visible + $mask_force + $feedback_mask;
     $base_mask[$range_start + $range_len] = true;
     for ($ii = $range_start; $ii <= $range_start + $range_len; $ii++) {
       if (isset($base_mask[$ii])) {
         if ($in_gap) {
           $gap_length = $ii - $gap_start;
           if ($gap_length <= $lines_context) {
             for ($jj = $gap_start; $jj <= $gap_start + $gap_length; $jj++) {
               $base_mask[$jj] = true;
             }
           } else {
             $gaps[] = array($gap_start, $gap_length);
           }
           $in_gap = false;
         }
       } else {
         if (!$in_gap) {
           $gap_start = $ii;
           $in_gap = true;
         }
       }
     }
     $gaps = array_reverse($gaps);
     $mask = $base_mask;
 
     return array($gaps, $mask);
   }
 
   /**
    * Determine if an inline comment will appear on the rendered diff,
    * taking into consideration which halves of which changesets will actually
    * be shown.
    *
    * @param PhabricatorInlineCommentInterface Comment to test for visibility.
    * @return bool True if the comment is visible on the rendered diff.
    */
   private function isCommentVisibleOnRenderedDiff(
     PhabricatorInlineCommentInterface $comment) {
 
     $changeset_id = $comment->getChangesetID();
     $is_new = $comment->getIsNewFile();
 
     if ($changeset_id == $this->rightSideChangesetID &&
         $is_new == $this->rightSideAttachesToNewFile) {
         return true;
     }
 
     if ($changeset_id == $this->leftSideChangesetID &&
         $is_new == $this->leftSideAttachesToNewFile) {
         return true;
     }
 
     return false;
   }
 
 
   /**
    * Determine if a comment will appear on the right side of the display diff.
    * Note that the comment must appear somewhere on the rendered changeset, as
    * per isCommentVisibleOnRenderedDiff().
    *
    * @param PhabricatorInlineCommentInterface Comment to test for display
    *              location.
    * @return bool True for right, false for left.
    */
   private function isCommentOnRightSideWhenDisplayed(
     PhabricatorInlineCommentInterface $comment) {
 
     if (!$this->isCommentVisibleOnRenderedDiff($comment)) {
       throw new Exception(pht('Comment is not visible on changeset!'));
     }
 
     $changeset_id = $comment->getChangesetID();
     $is_new = $comment->getIsNewFile();
 
     if ($changeset_id == $this->rightSideChangesetID &&
         $is_new == $this->rightSideAttachesToNewFile) {
       return true;
     }
 
     return false;
   }
 
   /**
    * Parse the 'range' specification that this class and the client-side JS
    * emit to indicate that a user clicked "Show more..." on a diff. Generally,
    * use is something like this:
    *
    *   $spec = $request->getStr('range');
    *   $parsed = DifferentialChangesetParser::parseRangeSpecification($spec);
    *   list($start, $end, $mask) = $parsed;
    *   $parser->render($start, $end, $mask);
    *
    * @param string Range specification, indicating the range of the diff that
    *               should be rendered.
    * @return tuple List of <start, end, mask> suitable for passing to
    *               @{method:render}.
    */
   public static function parseRangeSpecification($spec) {
     $range_s = null;
     $range_e = null;
     $mask = array();
 
     if ($spec) {
       $match = null;
       if (preg_match('@^(\d+)-(\d+)(?:/(\d+)-(\d+))?$@', $spec, $match)) {
         $range_s = (int)$match[1];
         $range_e = (int)$match[2];
         if (count($match) > 3) {
           $start = (int)$match[3];
           $len = (int)$match[4];
           for ($ii = $start; $ii < $start + $len; $ii++) {
             $mask[$ii] = true;
           }
         }
       }
     }
 
     return array($range_s, $range_e, $mask);
   }
 
   /**
    * Render "modified coverage" information; test coverage on modified lines.
    * This synthesizes diff information with unit test information into a useful
    * indicator of how well tested a change is.
    */
   public function renderModifiedCoverage() {
     $na = phutil_tag('em', array(), '-');
 
     $coverage = $this->getCoverage();
     if (!$coverage) {
       return $na;
     }
 
     $covered = 0;
     $not_covered = 0;
 
     foreach ($this->new as $k => $new) {
       if (!$new['line']) {
         continue;
       }
 
       if (!$new['type']) {
         continue;
       }
 
       if (empty($coverage[$new['line'] - 1])) {
         continue;
       }
 
       switch ($coverage[$new['line'] - 1]) {
         case 'C':
           $covered++;
           break;
         case 'U':
           $not_covered++;
           break;
       }
     }
 
     if (!$covered && !$not_covered) {
       return $na;
     }
 
     return sprintf('%d%%', 100 * ($covered / ($covered + $not_covered)));
   }
 
   /**
    * Build maps from lines comments appear on to actual lines.
    */
   private function buildLineBackmaps() {
     $old_back = array();
     $new_back = array();
     foreach ($this->old as $ii => $old) {
       $old_back[$old['line']] = $old['line'];
     }
     foreach ($this->new as $ii => $new) {
       $new_back[$new['line']] = $new['line'];
     }
 
     $max_old_line = 0;
     $max_new_line = 0;
     foreach ($this->comments as $comment) {
       if ($this->isCommentOnRightSideWhenDisplayed($comment)) {
         $max_new_line = max($max_new_line, $comment->getLineNumber());
       } else {
         $max_old_line = max($max_old_line, $comment->getLineNumber());
       }
     }
 
     $cursor = 1;
     for ($ii = 1; $ii <= $max_old_line; $ii++) {
       if (empty($old_back[$ii])) {
         $old_back[$ii] = $cursor;
       } else {
         $cursor = $old_back[$ii];
       }
     }
 
     $cursor = 1;
     for ($ii = 1; $ii <= $max_new_line; $ii++) {
       if (empty($new_back[$ii])) {
         $new_back[$ii] = $cursor;
       } else {
         $cursor = $new_back[$ii];
       }
     }
 
     return array($old_back, $new_back);
   }
 
   private function getOffset(array $map, $line) {
     if (!$map) {
       return null;
     }
 
     $line = (int)$line;
     foreach ($map as $key => $spec) {
       if ($spec && isset($spec['line'])) {
         if ((int)$spec['line'] >= $line) {
           return $key;
         }
       }
     }
 
     return $key;
   }
 
+  private function realignDiff(
+    DifferentialChangeset $changeset,
+    DifferentialHunkParser $hunk_parser) {
+    // Normalizing and realigning the diff depends on rediffing the files, and
+    // we currently need complete representations of both files to do anything
+    // reasonable. If we only have parts of the files, skip realignment.
+
+    // We have more than one hunk, so we're definitely missing part of the file.
+    $hunks = $changeset->getHunks();
+    if (count($hunks) !== 1) {
+      return null;
+    }
+
+    // The first hunk doesn't start at the beginning of the file, so we're
+    // missing some context.
+    $first_hunk = head($hunks);
+    if ($first_hunk->getOldOffset() != 1 || $first_hunk->getNewOffset() != 1) {
+      return null;
+    }
+
+    $old_file = $changeset->makeOldFile();
+    $new_file = $changeset->makeNewFile();
+    if ($old_file === $new_file) {
+      // If the old and new files are exactly identical, the synthetic
+      // diff below will give us nonsense and whitespace modes are
+      // irrelevant anyway. This occurs when you, e.g., copy a file onto
+      // itself in Subversion (see T271).
+      return null;
+    }
+
+
+    $engine = id(new PhabricatorDifferenceEngine())
+      ->setNormalize(true);
+
+    $normalized_changeset = $engine->generateChangesetFromFileContent(
+      $old_file,
+      $new_file);
+
+    $type_parser = new DifferentialHunkParser();
+    $type_parser->parseHunksForLineData($normalized_changeset->getHunks());
+
+    $hunk_parser->setNormalized(true);
+    $hunk_parser->setOldLineTypeMap($type_parser->getOldLineTypeMap());
+    $hunk_parser->setNewLineTypeMap($type_parser->getNewLineTypeMap());
+  }
+
+
 }
diff --git a/src/applications/differential/parser/DifferentialHunkParser.php b/src/applications/differential/parser/DifferentialHunkParser.php
index d89089a7e7..d59358bc82 100644
--- a/src/applications/differential/parser/DifferentialHunkParser.php
+++ b/src/applications/differential/parser/DifferentialHunkParser.php
@@ -1,756 +1,819 @@
 <?php
 
 final class DifferentialHunkParser extends Phobject {
 
   private $oldLines;
   private $newLines;
   private $intraLineDiffs;
   private $depthOnlyLines;
   private $visibleLinesMask;
+  private $normalized;
 
   /**
    * Get a map of lines on which hunks start, other than line 1. This
    * datastructure is used to determine when to render "Context not available."
    * in diffs with multiple hunks.
    *
    * @return dict<int, bool>  Map of lines where hunks start, other than line 1.
    */
   public function getHunkStartLines(array $hunks) {
     assert_instances_of($hunks, 'DifferentialHunk');
 
     $map = array();
     foreach ($hunks as $hunk) {
       $line = $hunk->getOldOffset();
       if ($line > 1) {
         $map[$line] = true;
       }
     }
 
     return $map;
   }
 
   private function setVisibleLinesMask($mask) {
     $this->visibleLinesMask = $mask;
     return $this;
   }
   public function getVisibleLinesMask() {
     if ($this->visibleLinesMask === null) {
       throw new PhutilInvalidStateException('generateVisibileLinesMask');
     }
     return $this->visibleLinesMask;
   }
 
   private function setIntraLineDiffs($intra_line_diffs) {
     $this->intraLineDiffs = $intra_line_diffs;
     return $this;
   }
   public function getIntraLineDiffs() {
     if ($this->intraLineDiffs === null) {
       throw new PhutilInvalidStateException('generateIntraLineDiffs');
     }
     return $this->intraLineDiffs;
   }
 
   private function setNewLines($new_lines) {
     $this->newLines = $new_lines;
     return $this;
   }
   public function getNewLines() {
     if ($this->newLines === null) {
       throw new PhutilInvalidStateException('parseHunksForLineData');
     }
     return $this->newLines;
   }
 
   private function setOldLines($old_lines) {
     $this->oldLines = $old_lines;
     return $this;
   }
   public function getOldLines() {
     if ($this->oldLines === null) {
       throw new PhutilInvalidStateException('parseHunksForLineData');
     }
     return $this->oldLines;
   }
 
   public function getOldLineTypeMap() {
     $map = array();
     $old = $this->getOldLines();
     foreach ($old as $o) {
       if (!$o) {
         continue;
       }
       $map[$o['line']] = $o['type'];
     }
     return $map;
   }
 
   public function setOldLineTypeMap(array $map) {
     $lines = $this->getOldLines();
     foreach ($lines as $key => $data) {
       $lines[$key]['type'] = idx($map, $data['line']);
     }
     $this->oldLines = $lines;
     return $this;
   }
 
   public function getNewLineTypeMap() {
     $map = array();
     $new = $this->getNewLines();
     foreach ($new as $n) {
       if (!$n) {
         continue;
       }
       $map[$n['line']] = $n['type'];
     }
     return $map;
   }
 
   public function setNewLineTypeMap(array $map) {
     $lines = $this->getNewLines();
     foreach ($lines as $key => $data) {
       $lines[$key]['type'] = idx($map, $data['line']);
     }
     $this->newLines = $lines;
     return $this;
   }
 
   public function setDepthOnlyLines(array $map) {
     $this->depthOnlyLines = $map;
     return $this;
   }
 
   public function getDepthOnlyLines() {
     return $this->depthOnlyLines;
   }
 
+  public function setNormalized($normalized) {
+    $this->normalized = $normalized;
+    return $this;
+  }
+
+  public function getNormalized() {
+    return $this->normalized;
+  }
+
   public function getIsDeleted() {
     foreach ($this->getNewLines() as $line) {
       if ($line) {
         // At least one new line, so the entire file wasn't deleted.
         return false;
       }
     }
 
     foreach ($this->getOldLines() as $line) {
       if ($line) {
         // No new lines, at least one old line; the entire file was deleted.
         return true;
       }
     }
 
     // This is an empty file.
     return false;
   }
 
   /**
    * Returns true if the hunks change anything, including whitespace.
    */
   public function getHasAnyChanges() {
     return $this->getHasChanges('any');
   }
 
   private function getHasChanges($filter) {
     if ($filter !== 'any' && $filter !== 'text') {
       throw new Exception(pht("Unknown change filter '%s'.", $filter));
     }
 
     $old = $this->getOldLines();
     $new = $this->getNewLines();
 
     $is_any = ($filter === 'any');
 
     foreach ($old as $key => $o) {
       $n = $new[$key];
       if ($o === null || $n === null) {
         // One side is missing, and it's impossible for both sides to be null,
         // so the other side must have something, and thus the two sides are
         // different and the file has been changed under any type of filter.
         return true;
       }
 
       if ($o['type'] !== $n['type']) {
         return true;
       }
 
       if ($o['text'] !== $n['text']) {
         if ($is_any) {
           // The text is different, so there's a change.
           return true;
         } else if (trim($o['text']) !== trim($n['text'])) {
           return true;
         }
       }
     }
 
     // No changes anywhere in the file.
     return false;
   }
 
 
   /**
    * This function takes advantage of the parsing work done in
    * @{method:parseHunksForLineData} and continues the struggle to hammer this
    * data into something we can display to a user.
    *
    * In particular, this function re-parses the hunks to make them equivalent
    * in length for easy rendering, adding `null` as necessary to pad the
    * length.
    *
    * Anyhoo, this function is not particularly well-named but I try.
    *
    * NOTE: this function must be called after
    * @{method:parseHunksForLineData}.
    */
   public function reparseHunksForSpecialAttributes() {
     $rebuild_old = array();
     $rebuild_new = array();
 
     $old_lines = array_reverse($this->getOldLines());
     $new_lines = array_reverse($this->getNewLines());
 
     while (count($old_lines) || count($new_lines)) {
       $old_line_data = array_pop($old_lines);
       $new_line_data = array_pop($new_lines);
 
       if ($old_line_data) {
         $o_type = $old_line_data['type'];
       } else {
         $o_type = null;
       }
 
       if ($new_line_data) {
         $n_type = $new_line_data['type'];
       } else {
         $n_type = null;
       }
 
       // This line does not exist in the new file.
       if (($o_type != null) && ($n_type == null)) {
         $rebuild_old[] = $old_line_data;
         $rebuild_new[] = null;
         if ($new_line_data) {
           array_push($new_lines, $new_line_data);
         }
         continue;
       }
 
       // This line does not exist in the old file.
       if (($n_type != null) && ($o_type == null)) {
         $rebuild_old[] = null;
         $rebuild_new[] = $new_line_data;
         if ($old_line_data) {
           array_push($old_lines, $old_line_data);
         }
         continue;
       }
 
       $rebuild_old[] = $old_line_data;
       $rebuild_new[] = $new_line_data;
     }
 
     $this->setOldLines($rebuild_old);
     $this->setNewLines($rebuild_new);
 
+    $this->updateChangeTypesForNormalization();
+
     return $this;
   }
 
   public function generateIntraLineDiffs() {
     $old = $this->getOldLines();
     $new = $this->getNewLines();
 
     $diffs = array();
     $depth_only = array();
     foreach ($old as $key => $o) {
       $n = $new[$key];
 
       if (!$o || !$n) {
         continue;
       }
 
       if ($o['type'] != $n['type']) {
         $o_segments = array();
         $n_segments = array();
         $tab_width = 2;
 
         $o_text = $o['text'];
         $n_text = $n['text'];
 
         if ($o_text !== $n_text) {
           $o_depth = $this->getIndentDepth($o_text, $tab_width);
           $n_depth = $this->getIndentDepth($n_text, $tab_width);
 
           if ($o_depth < $n_depth) {
             $segment_type = '>';
             $segment_width = $this->getCharacterCountForVisualWhitespace(
               $n_text,
               ($n_depth - $o_depth),
               $tab_width);
             if ($segment_width) {
               $n_text = substr($n_text, $segment_width);
               $n_segments[] = array(
                 $segment_type,
                 $segment_width,
               );
             }
           } else if ($o_depth > $n_depth) {
             $segment_type = '<';
             $segment_width = $this->getCharacterCountForVisualWhitespace(
               $o_text,
               ($o_depth - $n_depth),
               $tab_width);
             if ($segment_width) {
               $o_text = substr($o_text, $segment_width);
               $o_segments[] = array(
                 $segment_type,
                 $segment_width,
               );
             }
           }
 
           // If there are no remaining changes to this line after we've marked
           // off the indent depth changes, this line was only modified by
           // changing the indent depth. Mark it for later so we can change how
           // it is displayed.
           if ($o_text === $n_text) {
             $depth_only[$key] = $segment_type;
           }
         }
 
         $intraline_segments = ArcanistDiffUtils::generateIntralineDiff(
           $o_text,
           $n_text);
 
         foreach ($intraline_segments[0] as $o_segment) {
           $o_segments[] = $o_segment;
         }
 
         foreach ($intraline_segments[1] as $n_segment) {
           $n_segments[] = $n_segment;
         }
 
         $diffs[$key] = array(
           $o_segments,
           $n_segments,
         );
       }
     }
 
     $this->setIntraLineDiffs($diffs);
     $this->setDepthOnlyLines($depth_only);
 
     return $this;
   }
 
   public function generateVisibileLinesMask($lines_context) {
     $old = $this->getOldLines();
     $new = $this->getNewLines();
     $max_length = max(count($old), count($new));
     $visible = false;
     $last = 0;
     $mask = array();
     for ($cursor = -$lines_context; $cursor < $max_length; $cursor++) {
       $offset = $cursor + $lines_context;
       if ((isset($old[$offset]) && $old[$offset]['type']) ||
           (isset($new[$offset]) && $new[$offset]['type'])) {
         $visible = true;
         $last = $offset;
       } else if ($cursor > $last + $lines_context) {
         $visible = false;
       }
       if ($visible && $cursor > 0) {
         $mask[$cursor] = 1;
       }
     }
 
     $this->setVisibleLinesMask($mask);
 
     return $this;
   }
 
   public function getOldCorpus() {
     return $this->getCorpus($this->getOldLines());
   }
 
   public function getNewCorpus() {
     return $this->getCorpus($this->getNewLines());
   }
 
   private function getCorpus(array $lines) {
 
     $corpus = array();
     foreach ($lines as $l) {
       if ($l['type'] != '\\') {
         if ($l['text'] === null) {
           // There's no text on this side of the diff, but insert a placeholder
           // newline so the highlighted line numbers match up.
           $corpus[] = "\n";
         } else {
           $corpus[] = $l['text'];
         }
       }
     }
     return $corpus;
   }
 
   public function parseHunksForLineData(array $hunks) {
     assert_instances_of($hunks, 'DifferentialHunk');
 
     $old_lines = array();
     $new_lines = array();
     foreach ($hunks as $hunk) {
       $lines = $hunk->getSplitLines();
 
       $line_type_map = array();
       $line_text = array();
       foreach ($lines as $line_index => $line) {
         if (isset($line[0])) {
           $char = $line[0];
           switch ($char) {
             case ' ':
               $line_type_map[$line_index] = null;
               $line_text[$line_index] = substr($line, 1);
               break;
             case "\r":
             case "\n":
               // NOTE: Normally, the first character is a space, plus, minus or
               // backslash, but it may be a newline if it used to be a space and
               // trailing whitespace has been stripped via email transmission or
               // some similar mechanism. In these cases, we essentially pretend
               // the missing space is still there.
               $line_type_map[$line_index] = null;
               $line_text[$line_index] = $line;
               break;
             case '+':
             case '-':
             case '\\':
               $line_type_map[$line_index] = $char;
               $line_text[$line_index] = substr($line, 1);
               break;
             default:
               throw new Exception(
                 pht(
                   'Unexpected leading character "%s" at line index %s!',
                   $char,
                   $line_index));
           }
         } else {
           $line_type_map[$line_index] = null;
           $line_text[$line_index] = '';
         }
       }
 
       $old_line = $hunk->getOldOffset();
       $new_line = $hunk->getNewOffset();
 
       $num_lines = count($lines);
       for ($cursor = 0; $cursor < $num_lines; $cursor++) {
         $type = $line_type_map[$cursor];
         $data = array(
           'type'  => $type,
           'text'  => $line_text[$cursor],
           'line'  => $new_line,
         );
         if ($type == '\\') {
           $type = $line_type_map[$cursor - 1];
           $data['text'] = ltrim($data['text']);
         }
         switch ($type) {
           case '+':
             $new_lines[] = $data;
             ++$new_line;
             break;
           case '-':
             $data['line'] = $old_line;
             $old_lines[] = $data;
             ++$old_line;
             break;
           default:
             $new_lines[] = $data;
             $data['line'] = $old_line;
             $old_lines[] = $data;
             ++$new_line;
             ++$old_line;
             break;
         }
       }
     }
 
     $this->setOldLines($old_lines);
     $this->setNewLines($new_lines);
 
     return $this;
   }
 
   public function parseHunksForHighlightMasks(
     array $changeset_hunks,
     array $old_hunks,
     array $new_hunks) {
     assert_instances_of($changeset_hunks, 'DifferentialHunk');
     assert_instances_of($old_hunks,       'DifferentialHunk');
     assert_instances_of($new_hunks,       'DifferentialHunk');
 
     // Put changes side by side.
     $olds = array();
     $news = array();
     $olds_cursor = -1;
     $news_cursor = -1;
     foreach ($changeset_hunks as $hunk) {
       $n_old = $hunk->getOldOffset();
       $n_new = $hunk->getNewOffset();
       $changes = $hunk->getSplitLines();
       foreach ($changes as $line) {
         $diff_type = $line[0]; // Change type in diff of diffs.
         $orig_type = $line[1]; // Change type in the original diff.
         if ($diff_type == ' ') {
           // Use the same key for lines that are next to each other.
           if ($olds_cursor > $news_cursor) {
             $key = $olds_cursor + 1;
           } else {
             $key = $news_cursor + 1;
           }
           $olds[$key] = null;
           $news[$key] = null;
           $olds_cursor = $key;
           $news_cursor = $key;
         } else if ($diff_type == '-') {
           $olds[] = array($n_old, $orig_type);
           $olds_cursor++;
         } else if ($diff_type == '+') {
           $news[] = array($n_new, $orig_type);
           $news_cursor++;
         }
         if (($diff_type == '-' || $diff_type == ' ') && $orig_type != '-') {
           $n_old++;
         }
         if (($diff_type == '+' || $diff_type == ' ') && $orig_type != '-') {
           $n_new++;
         }
       }
     }
 
     $offsets_old = $this->computeOffsets($old_hunks);
     $offsets_new = $this->computeOffsets($new_hunks);
 
     // Highlight lines that were added on each side or removed on the other
     // side.
     $highlight_old = array();
     $highlight_new = array();
     $last = max(last_key($olds), last_key($news));
     for ($i = 0; $i <= $last; $i++) {
       if (isset($olds[$i])) {
         list($n, $type) = $olds[$i];
         if ($type == '+' ||
             ($type == ' ' && isset($news[$i]) && $news[$i][1] != ' ')) {
           $highlight_old[] = $offsets_old[$n];
         }
       }
       if (isset($news[$i])) {
         list($n, $type) = $news[$i];
         if ($type == '+' ||
             ($type == ' ' && isset($olds[$i]) && $olds[$i][1] != ' ')) {
           $highlight_new[] = $offsets_new[$n];
         }
       }
     }
 
     return array($highlight_old, $highlight_new);
   }
 
   public function makeContextDiff(
     array $hunks,
     $is_new,
     $line_number,
     $line_length,
     $add_context) {
 
     assert_instances_of($hunks, 'DifferentialHunk');
 
     $context = array();
 
     if ($is_new) {
       $prefix = '+';
     } else {
       $prefix = '-';
     }
 
     foreach ($hunks as $hunk) {
       if ($is_new) {
         $offset = $hunk->getNewOffset();
         $length = $hunk->getNewLen();
       } else {
         $offset = $hunk->getOldOffset();
         $length = $hunk->getOldLen();
       }
       $start = $line_number - $offset;
       $end = $start + $line_length;
       // We need to go in if $start == $length, because the last line
       // might be a "\No newline at end of file" marker, which we want
       // to show if the additional context is > 0.
       if ($start <= $length && $end >= 0) {
         $start = $start - $add_context;
         $end = $end + $add_context;
         $hunk_content = array();
         $hunk_pos = array('-' => 0, '+' => 0);
         $hunk_offset = array('-' => null, '+' => null);
         $hunk_last = array('-' => null, '+' => null);
         foreach (explode("\n", $hunk->getChanges()) as $line) {
           $in_common = strncmp($line, ' ', 1) === 0;
           $in_old = strncmp($line, '-', 1) === 0 || $in_common;
           $in_new = strncmp($line, '+', 1) === 0 || $in_common;
           $in_selected = strncmp($line, $prefix, 1) === 0;
           $skip = !$in_selected && !$in_common;
           if ($hunk_pos[$prefix] <= $end) {
             if ($start <= $hunk_pos[$prefix]) {
               if (!$skip || ($hunk_pos[$prefix] != $start &&
                 $hunk_pos[$prefix] != $end)) {
                   if ($in_old) {
                     if ($hunk_offset['-'] === null) {
                       $hunk_offset['-'] = $hunk_pos['-'];
                     }
                     $hunk_last['-'] = $hunk_pos['-'];
                   }
                   if ($in_new) {
                     if ($hunk_offset['+'] === null) {
                       $hunk_offset['+'] = $hunk_pos['+'];
                     }
                     $hunk_last['+'] = $hunk_pos['+'];
                   }
 
                   $hunk_content[] = $line;
                 }
             }
             if ($in_old) { ++$hunk_pos['-']; }
             if ($in_new) { ++$hunk_pos['+']; }
           }
         }
         if ($hunk_offset['-'] !== null || $hunk_offset['+'] !== null) {
           $header = '@@';
           if ($hunk_offset['-'] !== null) {
             $header .= ' -'.($hunk->getOldOffset() + $hunk_offset['-']).
               ','.($hunk_last['-'] - $hunk_offset['-'] + 1);
           }
           if ($hunk_offset['+'] !== null) {
             $header .= ' +'.($hunk->getNewOffset() + $hunk_offset['+']).
               ','.($hunk_last['+'] - $hunk_offset['+'] + 1);
           }
           $header .= ' @@';
           $context[] = $header;
           $context[] = implode("\n", $hunk_content);
         }
       }
     }
     return implode("\n", $context);
   }
 
   private function computeOffsets(array $hunks) {
     assert_instances_of($hunks, 'DifferentialHunk');
 
     $offsets = array();
     $n = 1;
     foreach ($hunks as $hunk) {
       $new_length = $hunk->getNewLen();
       $new_offset = $hunk->getNewOffset();
 
       for ($i = 0; $i < $new_length; $i++) {
         $offsets[$n] = $new_offset + $i;
         $n++;
       }
     }
 
     return $offsets;
   }
 
   private function getIndentDepth($text, $tab_width) {
     $len = strlen($text);
 
     $depth = 0;
     for ($ii = 0; $ii < $len; $ii++) {
       $c = $text[$ii];
 
       // If this is a space, increase the indent depth by 1.
       if ($c == ' ') {
         $depth++;
         continue;
       }
 
       // If this is a tab, increase the indent depth to the next tabstop.
 
       // For example, if the tab width is 4, these sequences both lead us to
       // a visual width of 8, i.e. the cursor will be in the 8th column:
       //
       //   <tab><tab>
       //   <space><tab><space><space><space><tab>
 
       if ($c == "\t") {
         $depth = ($depth + $tab_width);
         $depth = $depth - ($depth % $tab_width);
         continue;
       }
 
       break;
     }
 
     return $depth;
   }
 
   private function getCharacterCountForVisualWhitespace(
     $text,
     $depth,
     $tab_width) {
 
     // Here, we know the visual indent depth of a line has been increased by
     // some amount (for example, 6 characters).
 
     // We want to find the largest whitespace prefix of the string we can
     // which still fits into that amount of visual space.
 
     // In most cases, this is very easy. For example, if the string has been
     // indented by two characters and the string begins with two spaces, that's
     // a perfect match.
 
     // However, if the string has been indented by 7 characters, the tab width
     // is 8, and the string begins with "<space><space><tab>", we can only
     // mark the two spaces as an indent change. These cases are unusual.
 
     $character_depth = 0;
     $visual_depth = 0;
 
     $len = strlen($text);
     for ($ii = 0; $ii < $len; $ii++) {
       if ($visual_depth >= $depth) {
         break;
       }
 
       $c = $text[$ii];
 
       if ($c == ' ') {
         $character_depth++;
         $visual_depth++;
         continue;
       }
 
       if ($c == "\t") {
         // Figure out how many visual spaces we have until the next tabstop.
         $tab_visual = ($visual_depth + $tab_width);
         $tab_visual = $tab_visual - ($tab_visual % $tab_width);
         $tab_visual = ($tab_visual - $visual_depth);
 
         // If this tab would take us over the limit, we're all done.
         $remaining_depth = ($depth - $visual_depth);
         if ($remaining_depth < $tab_visual) {
           break;
         }
 
         $character_depth++;
         $visual_depth += $tab_visual;
         continue;
       }
 
       break;
     }
 
     return $character_depth;
   }
 
+  private function updateChangeTypesForNormalization() {
+    if (!$this->getNormalized()) {
+      return;
+    }
+
+    // If we've parsed based on a normalized diff alignment, we may currently
+    // believe some lines are unchanged when they have actually changed. This
+    // happens when:
+    //
+    //   - a line changes;
+    //   - the change is a kind of change we normalize away when aligning the
+    //     diff, like an indentation change;
+    //   - we normalize the change away to align the diff; and so
+    //   - the old and new copies of the line are now aligned in the new
+    //     normalized diff.
+    //
+    // Then we end up with an alignment where the two lines that differ only
+    // in some some trivial way are aligned. This is great, and exactly what
+    // we're trying to accomplish by doing all this alignment stuff in the
+    // first place.
+    //
+    // However, in this case the correctly-aligned lines will be incorrectly
+    // marked as unchanged because the diff alorithm was fed normalized copies
+    // of the lines, and these copies truly weren't any different.
+    //
+    // When lines are aligned and marked identical, but they're not actually
+    // identcal, we now mark them as changed. The rest of the processing will
+    // figure out how to render them appropritely.
+
+    $new = $this->getNewLines();
+    $old = $this->getOldLines();
+    foreach ($old as $key => $o) {
+      $n = $new[$key];
+
+      if (!$o || !$n) {
+        continue;
+      }
+
+      if ($o['type'] === null && $n['type'] === null) {
+        if ($o['text'] !== $n['text']) {
+          $old[$key]['type'] = '-';
+          $new[$key]['type'] = '+';
+        }
+      }
+    }
+
+    $this->setOldLines($old);
+    $this->setNewLines($new);
+  }
+
+
 }
diff --git a/src/infrastructure/diff/PhabricatorDifferenceEngine.php b/src/infrastructure/diff/PhabricatorDifferenceEngine.php
index 90f1d9b10e..84e88ceaaa 100644
--- a/src/infrastructure/diff/PhabricatorDifferenceEngine.php
+++ b/src/infrastructure/diff/PhabricatorDifferenceEngine.php
@@ -1,132 +1,172 @@
 <?php
 
 /**
  * Utility class which encapsulates some shared behavior between different
  * applications which render diffs.
  *
  * @task config Configuring the Engine
  * @task diff Generating Diffs
  */
 final class PhabricatorDifferenceEngine extends Phobject {
 
 
   private $oldName;
   private $newName;
+  private $normalize;
 
 
 /* -(  Configuring the Engine  )--------------------------------------------- */
 
 
   /**
    * Set the name to identify the old file with. Primarily cosmetic.
    *
    * @param  string Old file name.
    * @return this
    * @task config
    */
   public function setOldName($old_name) {
     $this->oldName = $old_name;
     return $this;
   }
 
 
   /**
    * Set the name to identify the new file with. Primarily cosmetic.
    *
    * @param  string New file name.
    * @return this
    * @task config
    */
   public function setNewName($new_name) {
     $this->newName = $new_name;
     return $this;
   }
 
 
+  public function setNormalize($normalize) {
+    $this->normalize = $normalize;
+    return $this;
+  }
+
+  public function getNormalize() {
+    return $this->normalize;
+  }
+
+
 /* -(  Generating Diffs  )--------------------------------------------------- */
 
 
   /**
    * Generate a raw diff from two raw files. This is a lower-level API than
    * @{method:generateChangesetFromFileContent}, but may be useful if you need
    * to use a custom parser configuration, as with Diffusion.
    *
    * @param string Entire previous file content.
    * @param string Entire current file content.
    * @return string Raw diff between the two files.
    * @task diff
    */
   public function generateRawDiffFromFileContent($old, $new) {
 
     $options = array();
 
     // Generate diffs with full context.
     $options[] = '-U65535';
 
     $old_name = nonempty($this->oldName, '/dev/universe').' 9999-99-99';
     $new_name = nonempty($this->newName, '/dev/universe').' 9999-99-99';
 
     $options[] = '-L';
     $options[] = $old_name;
     $options[] = '-L';
     $options[] = $new_name;
 
+    $normalize = $this->getNormalize();
+    if ($normalize) {
+      $old = $this->normalizeFile($old);
+      $new = $this->normalizeFile($new);
+    }
+
     $old_tmp = new TempFile();
     $new_tmp = new TempFile();
 
     Filesystem::writeFile($old_tmp, $old);
     Filesystem::writeFile($new_tmp, $new);
     list($err, $diff) = exec_manual(
       'diff %Ls %s %s',
       $options,
       $old_tmp,
       $new_tmp);
 
     if (!$err) {
       // This indicates that the two files are the same. Build a synthetic,
       // changeless diff so that we can still render the raw, unchanged file
       // instead of being forced to just say "this file didn't change" since we
       // don't have the content.
 
       $entire_file = explode("\n", $old);
       foreach ($entire_file as $k => $line) {
         $entire_file[$k] = ' '.$line;
       }
 
       $len = count($entire_file);
       $entire_file = implode("\n", $entire_file);
 
       // TODO: If both files were identical but missing newlines, we probably
       // get this wrong. Unclear if it ever matters.
 
       // This is a bit hacky but the diff parser can handle it.
       $diff = "--- {$old_name}\n".
               "+++ {$new_name}\n".
               "@@ -1,{$len} +1,{$len} @@\n".
               $entire_file."\n";
     }
 
     return $diff;
   }
 
 
   /**
    * Generate an @{class:DifferentialChangeset} from two raw files. This is
    * principally useful because you can feed the output to
    * @{class:DifferentialChangesetParser} in order to render it.
    *
    * @param string Entire previous file content.
    * @param string Entire current file content.
    * @return @{class:DifferentialChangeset} Synthetic changeset.
    * @task diff
    */
   public function generateChangesetFromFileContent($old, $new) {
     $diff = $this->generateRawDiffFromFileContent($old, $new);
 
     $changes = id(new ArcanistDiffParser())->parseDiff($diff);
     $diff = DifferentialDiff::newEphemeralFromRawChanges(
       $changes);
     return head($diff->getChangesets());
   }
 
+  private function normalizeFile($corpus) {
+    // We can freely apply any other transformations we want to here: we have
+    // no constraints on what we need to preserve. If we normalize every line
+    // to "cat", the diff will still work, the alignment of the "-" / "+"
+    // lines will just be very hard to read.
+
+    // In general, we'll make the diff better if we normalize two lines that
+    // humans think are the same.
+
+    // We'll make the diff worse if we normalize two lines that humans think
+    // are different.
+
+
+    // Strip all whitespace present anywhere in the diff, since humans never
+    // consider whitespace changes to alter the line into a "different line"
+    // even when they're semantic (e.g., in a string constant). This covers
+    // indentation changes, trailing whitepspace, and formatting changes
+    // like "+/-".
+    $corpus = preg_replace('/[ \t]/', '', $corpus);
+
+    return $corpus;
+  }
+
 }