DifferentialChangesetParser.php
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DifferentialChangesetParser.php
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	<?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 $highlightingDisabled;
	private $showEditAndReplyLinks = true;
	private $canMarkDone;
	private $objectOwnerPHID;
	private $offsetMode;

	private $rangeStart;
	private $rangeEnd;
	private $mask;
	private $linesOfContext = 8;

	private $highlightEngine;
	private $viewer;

	private $viewState;
	private $availableDocumentEngines;

	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 setViewState(PhabricatorChangesetViewState $view_state) {
	$this->viewState = $view_state;
	return $this;
	}

	public function getViewState() {
	return $this->viewState;
	}

	public function setRenderer(DifferentialChangesetRenderer $renderer) {
	$this->renderer = $renderer;
	return $this;
	}

	public function getRenderer() {
	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 function setViewer(PhabricatorUser $viewer) {
	$this->viewer = $viewer;
	return $this;
	}

	public function getViewer() {
	return $this->viewer;
	}

	private function newRenderer() {
	$viewer = $this->getViewer();
	$viewstate = $this->getViewstate();

	$renderer_key = $viewstate->getRendererKey();

	if ($renderer_key === null) {
	$is_unified = $viewer->compareUserSetting(
	PhabricatorUnifiedDiffsSetting::SETTINGKEY,
	PhabricatorUnifiedDiffsSetting::VALUE_ALWAYS_UNIFIED);

	if ($is_unified) {
	$renderer_key = '1up';
	} else {
	$renderer_key = $viewstate->getDefaultDeviceRendererKey();
	}
	}

	switch ($renderer_key) {
	case '1up':
	$renderer = new DifferentialChangesetOneUpRenderer();
	break;
	default:
	$renderer = new DifferentialChangesetTwoUpRenderer();
	break;
	}

	return $renderer;
	}

	const CACHE_VERSION = 14;
	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 setVisibleLinesMask(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 $id The Differential Changeset ID that comments added to the
	* right side of the visible diff should be attached to.
	* @param bool $is_new 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.
	*
	* @param string $key 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 setCoverage($coverage) {
	$this->coverage = $coverage;
	return $this;
	}
	private function getCoverage() {
	return $this->coverage;
	}

	public function parseInlineComment(
	PhabricatorInlineComment $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(
	$conn_r,
	'SELECT * FROM %T WHERE cacheIndex = %s',
	DifferentialChangeset::TABLE_CACHE,
	PhabricatorHash::digestForIndex($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(
	$conn_w,
	'INSERT INTO %T (cacheIndex, cache, dateCreated) VALUES (%s, %B, %d)
	ON DUPLICATE KEY UPDATE cache = VALUES(cache)',
	DifferentialChangeset::TABLE_CACHE,
	PhabricatorHash::digestForIndex($render_cache_key),
	$cache,
	PhabricatorTime::getNow());
	} 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) {
	$result = $text;

	if (isset($intra[$key])) {
	$result = PhabricatorDifferenceEngine::applyIntralineDiff(
	$result,
	$intra[$key]);
	}

	$result = $this->adjustRenderedLineForDisplay($result);

	$render[$key] = $result;
	}
	}

	private function getHighlightFuture($corpus) {
	$language = $this->getViewState()->getHighlightLanguage();

	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() {
	$changeset = $this->getChangeset();
	if (!$changeset->hasSourceTextBody()) {

	// TODO: This isn't really correct (the change is not "generated"), the
	// intent is just to not render a text body for Subversion directory
	// changes, etc.
	$this->markGenerated();

	return;
	}

	$viewstate = $this->getViewState();

	$skip_cache = false;

	if ($this->disableCache) {
	$skip_cache = true;
	}

	$character_encoding = $viewstate->getCharacterEncoding();
	if ($character_encoding !== null) {
	$skip_cache = true;
	}

	$highlight_language = $viewstate->getHighlightLanguage();
	if ($highlight_language !== null) {
	$skip_cache = true;
	}

	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();
	$hunk_parser->generateVisibleLinesMask($lines_context);

	$this->setOldLines($hunk_parser->getOldLines());
	$this->setNewLines($hunk_parser->getNewLines());
	$this->setIntraLineDiffs($hunk_parser->getIntraLineDiffs());
	$this->setDepthOnlyLines($hunk_parser->getDepthOnlyLines());
	$this->setVisibleLinesMask($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()) {

	$viewer = $this->getViewer();

	$renderer = $this->getRenderer();
	if (!$renderer) {
	$renderer = $this->newRenderer();
	$this->setRenderer($renderer);
	}

	// "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();

	$viewstate = $this->getViewState();

	$encoding = null;

	$character_encoding = $viewstate->getCharacterEncoding();
	if ($character_encoding) {
	// 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 = $character_encoding;
	foreach ($this->changeset->getHunks() as $hunk) {
	$hunk->forceEncoding($character_encoding);
	}
	} 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->getViewer())
	->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())
	->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());

	if ($this->markupEngine) {
	$renderer->setMarkupEngine($this->markupEngine);
	}

	list($engine, $old_ref, $new_ref) = $this->newDocumentEngine();
	if ($engine) {
	$engine_blocks = $engine->newEngineBlocks(
	$old_ref,
	$new_ref);
	} else {
	$engine_blocks = null;
	}

	$has_document_engine = ($engine_blocks !== null);

	// Remove empty comments that don't have any unsaved draft data.
	PhabricatorInlineComment::loadAndAttachVersionedDrafts(
	$viewer,
	$this->comments);
	foreach ($this->comments as $key => $comment) {
	if ($comment->isVoidComment($viewer)) {
	unset($this->comments[$key]);
	}
	}

	// See T13515. Sometimes, we collapse file content by default: for
	// example, if the file is marked as containing generated code.

	// If a file has inline comments, that normally means we never collapse
	// it. However, if the viewer has already collapsed all of the inlines,
	// it's fine to collapse the file.

	$expanded_comments = array();
	foreach ($this->comments as $comment) {
	if ($comment->isHidden()) {
	continue;
	}
	$expanded_comments[] = $comment;
	}

	$collapsed_count = (count($this->comments) - count($expanded_comments));

	$shield_raw = null;
	$shield_text = null;
	$shield_type = null;
	if ($this->isTopLevel && !$expanded_comments && !$has_document_engine) {
	if ($this->isGenerated()) {
	$shield_text = pht(
	'This file contains generated code, which does not normally '.
	'need to be reviewed.');
	} else if ($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.
	$shield_raw = '';
	} else if ($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';
	}

	$shield_type = $type;

	$type_add = DifferentialChangeType::TYPE_ADD;
	if ($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_text = pht('This is an empty file.');
	} else {
	$shield_text = pht('The contents of this file were not changed.');
	}
	} else if ($this->isDeleted()) {
	$shield_text = pht('This file was completely deleted.');
	} else if ($this->changeset->getAffectedLineCount() > 2500) {
	$shield_text = pht(
	'This file has a very large number of changes (%s lines).',
	new PhutilNumber($this->changeset->getAffectedLineCount()));
	}
	}

	$shield = null;
	if ($shield_raw !== null) {
	$shield = $shield_raw;
	} else if ($shield_text !== null) {
	if ($shield_type === null) {
	$shield_type = 'default';
	}

	// If we have inlines and the shield would normally show the whole file,
	// downgrade it to show only text around the inlines.
	if ($collapsed_count) {
	if ($shield_type === 'text') {
	$shield_type = 'default';
	}

	$shield_text = array(
	$shield_text,
	' ',
	pht(
	'This file has %d collapsed inline comment(s).',
	new PhutilNumber($collapsed_count)),
	);
	}

	$shield = $renderer->renderShield($shield_text, $shield_type);
	}

	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();

	// See T13524. Lint inlines from Harbormaster may not have a line
	// number.
	if ($line === null) {
	$back_line = null;
	} else if ($new_side) {
	$back_line = idx($new_backmap, $line);
	} else {
	$back_line = idx($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);

	$old_max_display = 1;
	foreach ($this->old as $old) {
	if (isset($old['line'])) {
	$old_max_display = $old['line'];
	}
	}

	$new_max_display = 1;
	foreach ($this->new as $new) {
	if (isset($new['line'])) {
	$new_max_display = $new['line'];
	}
	}

	foreach ($this->comments as $comment) {
	$display_line = $comment->getLineNumber() + $comment->getLineLength();
	$display_line = max(1, $display_line);

	if ($this->isCommentOnRightSideWhenDisplayed($comment)) {
	$display_line = min($new_max_display, $display_line);
	$new_comments[$display_line][] = $comment;
	} else {
	$display_line = min($old_max_display, $display_line);
	$old_comments[$display_line][] = $comment;
	}
	}
	}

	$renderer
	->setOldComments($old_comments)
	->setNewComments($new_comments);

	if ($engine_blocks !== null) {
	$reference = $this->getRenderingReference();
	$parts = explode('/', $reference);
	if (count($parts) == 2) {
	list($id, $vs) = $parts;
	} else {
	$id = $parts[0];
	$vs = 0;
	}

	// If we don't have an explicit "vs" changeset, it's the left side of
	// the "id" changeset.
	if (!$vs) {
	$vs = $id;
	}

	if ($mask_force) {
	$engine_blocks->setRevealedIndexes(array_keys($mask_force));
	}

	if ($range_start !== null \|\| $range_len !== null) {
	$range_min = $range_start;

	if ($range_len === null) {
	$range_max = null;
	} else {
	$range_max = (int)$range_start + (int)$range_len;
	}

	$engine_blocks->setRange($range_min, $range_max);
	}

	$renderer
	->setDocumentEngine($engine)
	->setDocumentEngineBlocks($engine_blocks);

	return $renderer->renderDocumentEngineBlocks(
	$engine_blocks,
	(string)$id,
	(string)$vs);
	}

	// If we've made it here with a type of file we don't know how to render,
	// bail out with a default empty rendering. Normally, we'd expect a
	// document engine to catch these changes before we make it this far.
	switch ($this->changeset->getFileType()) {
	case DifferentialChangeType::FILE_DIRECTORY:
	case DifferentialChangeType::FILE_BINARY:
	case DifferentialChangeType::FILE_IMAGE:
	$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 PhabricatorInlineComment $comment Comment to test for visibility.
	* @return bool True if the comment is visible on the rendered diff.
	*/
	private function isCommentVisibleOnRenderedDiff(
	PhabricatorInlineComment $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 PhabricatorInlineComment $comment Comment to test for display
	* location.
	* @return bool True for right, false for left.
	*/
	private function isCommentOnRightSideWhenDisplayed(
	PhabricatorInlineComment $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 $spec Range specification, indicating the range of the diff
	* that should be rendered.
	* @return tuple List of <start, end, mask> suitable for passing to
	* @{method:render}.
	*/
	public static function parseRangeSpecification($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 === null) {
	continue;
	}

	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 => $old) {
	if ($old === null) {
	continue;
	}
	$old_back[$old['line']] = $old['line'];
	}
	foreach ($this->new as $ii => $new) {
	if ($new === null) {
	continue;
	}
	$new_back[$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());
	}

	private function adjustRenderedLineForDisplay($line) {
	// IMPORTANT: We're using "str_replace()" against raw HTML here, which can
	// easily become unsafe. The input HTML has already had syntax highlighting
	// and intraline diff highlighting applied, so it's full of "<span />" tags.

	static $search;
	static $replace;
	if ($search === null) {
	$rules = $this->newSuspiciousCharacterRules();

	$map = array();
	foreach ($rules as $key => $spec) {
	$tag = phutil_tag(
	'span',
	array(
	'data-copy-text' => $key,
	'class' => $spec['class'],
	'title' => $spec['title'],
	),
	$spec['replacement']);
	$map[$key] = phutil_string_cast($tag);
	}

	$search = array_keys($map);
	$replace = array_values($map);
	}

	$is_html = false;
	if ($line instanceof PhutilSafeHTML) {
	$is_html = true;
	$line = hsprintf('%s', $line);
	}

	$line = phutil_string_cast($line);

	// TODO: This should be flexible, eventually.
	$tab_width = 2;

	$line = self::replaceTabsWithSpaces($line, $tab_width);
	$line = str_replace($search, $replace, $line);

	if ($is_html) {
	$line = phutil_safe_html($line);
	}

	return $line;
	}

	private function newSuspiciousCharacterRules() {
	// The "title" attributes are cached in the database, so they're
	// intentionally not wrapped in "pht(...)".

	$rules = array(
	"\xE2\x80\x8B" => array(
	'title' => 'ZWS',
	'class' => 'suspicious-character',
	'replacement' => '!',
	),
	"\xC2\xA0" => array(
	'title' => 'NBSP',
	'class' => 'suspicious-character',
	'replacement' => '!',
	),
	"\x7F" => array(
	'title' => 'DEL (0x7F)',
	'class' => 'suspicious-character',
	'replacement' => "\xE2\x90\xA1",
	),
	);

	// Unicode defines special pictures for the control characters in the
	// range between "0x00" and "0x1F".

	$control = array(
	'NULL',
	'SOH',
	'STX',
	'ETX',
	'EOT',
	'ENQ',
	'ACK',
	'BEL',
	'BS',
	null, // "\t" Tab
	null, // "\n" New Line
	'VT',
	'FF',
	null, // "\r" Carriage Return,
	'SO',
	'SI',
	'DLE',
	'DC1',
	'DC2',
	'DC3',
	'DC4',
	'NAK',
	'SYN',
	'ETB',
	'CAN',
	'EM',
	'SUB',
	'ESC',
	'FS',
	'GS',
	'RS',
	'US',
	);

	foreach ($control as $idx => $label) {
	if ($label === null) {
	continue;
	}

	$rules[chr($idx)] = array(
	'title' => sprintf('%s (0x%02X)', $label, $idx),
	'class' => 'suspicious-character',
	'replacement' => "\xE2\x90".chr(0x80 + $idx),
	);
	}

	return $rules;
	}

	public static function replaceTabsWithSpaces($line, $tab_width) {
	static $tags = array();
	if (empty($tags[$tab_width])) {
	for ($ii = 1; $ii <= $tab_width; $ii++) {
	$tag = phutil_tag(
	'span',
	array(
	'data-copy-text' => "\t",
	),
	str_repeat(' ', $ii));
	$tag = phutil_string_cast($tag);
	$tags[$ii] = $tag;
	}
	}

	// Expand all prefix tabs until we encounter any non-tab character. This
	// is cheap and often immediately produces the correct result with no
	// further work (and, particularly, no need to handle any unicode cases).

	$len = strlen($line);

	$head = 0;
	for ($head = 0; $head < $len; $head++) {
	$char = $line[$head];
	if ($char !== "\t") {
	break;
	}
	}

	if ($head) {
	if (empty($tags[$tab_width * $head])) {
	$tags[$tab_width * $head] = str_repeat($tags[$tab_width], $head);
	}
	$prefix = $tags[$tab_width * $head];
	$line = substr($line, $head);
	} else {
	$prefix = '';
	}

	// If we have no remaining tabs elsewhere in the string after taking care
	// of all the prefix tabs, we're done.
	if (strpos($line, "\t") === false) {
	return $prefix.$line;
	}

	$len = strlen($line);

	// If the line is particularly long, don't try to do anything special with
	// it. Use a faster approximation of the correct tabstop expansion instead.
	// This usually still arrives at the right result.
	if ($len > 256) {
	return $prefix.str_replace("\t", $tags[$tab_width], $line);
	}

	$in_tag = false;
	$pos = 0;

	// See PHI1210. If the line only has single-byte characters, we don't need
	// to vectorize it and can avoid an expensive UTF8 call.

	$fast_path = preg_match('/^[\x01-\x7F]*\z/', $line);
	if ($fast_path) {
	$replace = array();
	for ($ii = 0; $ii < $len; $ii++) {
	$char = $line[$ii];
	if ($char === '>') {
	$in_tag = false;
	continue;
	}

	if ($in_tag) {
	continue;
	}

	if ($char === '<') {
	$in_tag = true;
	continue;
	}

	if ($char === "\t") {
	$count = $tab_width - ($pos % $tab_width);
	$pos += $count;
	$replace[$ii] = $tags[$count];
	continue;
	}

	$pos++;
	}

	if ($replace) {
	// Apply replacements starting at the end of the string so they
	// don't mess up the offsets for following replacements.
	$replace = array_reverse($replace, true);

	foreach ($replace as $replace_pos => $replacement) {
	$line = substr_replace($line, $replacement, $replace_pos, 1);
	}
	}
	} else {
	$line = phutil_utf8v_combined($line);
	foreach ($line as $key => $char) {
	if ($char === '>') {
	$in_tag = false;
	continue;
	}

	if ($in_tag) {
	continue;
	}

	if ($char === '<') {
	$in_tag = true;
	continue;
	}

	if ($char === "\t") {
	$count = $tab_width - ($pos % $tab_width);
	$pos += $count;
	$line[$key] = $tags[$count];
	continue;
	}

	$pos++;
	}

	$line = implode('', $line);
	}

	return $prefix.$line;
	}

	private function newDocumentEngine() {
	$changeset = $this->changeset;
	$viewer = $this->getViewer();

	list($old_file, $new_file) = $this->loadFileObjectsForChangeset();

	$no_old = !$changeset->hasOldState();
	$no_new = !$changeset->hasNewState();

	if ($no_old) {
	$old_ref = null;
	} else {
	$old_ref = id(new PhabricatorDocumentRef())
	->setName($changeset->getOldFile());
	if ($old_file) {
	$old_ref->setFile($old_file);
	} else {
	$old_data = $this->getRawDocumentEngineData($this->old);
	$old_ref->setData($old_data);
	}
	}

	if ($no_new) {
	$new_ref = null;
	} else {
	$new_ref = id(new PhabricatorDocumentRef())
	->setName($changeset->getFilename());
	if ($new_file) {
	$new_ref->setFile($new_file);
	} else {
	$new_data = $this->getRawDocumentEngineData($this->new);
	$new_ref->setData($new_data);
	}
	}

	$old_engines = null;
	if ($old_ref) {
	$old_engines = PhabricatorDocumentEngine::getEnginesForRef(
	$viewer,
	$old_ref);
	}

	$new_engines = null;
	if ($new_ref) {
	$new_engines = PhabricatorDocumentEngine::getEnginesForRef(
	$viewer,
	$new_ref);
	}

	if ($new_engines !== null && $old_engines !== null) {
	$shared_engines = array_intersect_key($new_engines, $old_engines);
	$default_engine = head_key($new_engines);
	} else if ($new_engines !== null) {
	$shared_engines = $new_engines;
	$default_engine = head_key($shared_engines);
	} else if ($old_engines !== null) {
	$shared_engines = $old_engines;
	$default_engine = head_key($shared_engines);
	} else {
	return null;
	}

	foreach ($shared_engines as $key => $shared_engine) {
	if (!$shared_engine->canDiffDocuments($old_ref, $new_ref)) {
	unset($shared_engines[$key]);
	}
	}

	$this->availableDocumentEngines = $shared_engines;

	$viewstate = $this->getViewState();

	$engine_key = $viewstate->getDocumentEngineKey();
	if (phutil_nonempty_string($engine_key)) {
	if (isset($shared_engines[$engine_key])) {
	$document_engine = $shared_engines[$engine_key];
	} else {
	$document_engine = null;
	}
	} else {
	// If we aren't rendering with a specific engine, only use a default
	// engine if the best engine for the new file is a shared engine which
	// can diff files. If we're less picky (for example, by accepting any
	// shared engine) we can end up with silly behavior (like ".json" files
	// rendering as Jupyter documents).

	if (isset($shared_engines[$default_engine])) {
	$document_engine = $shared_engines[$default_engine];
	} else {
	$document_engine = null;
	}
	}

	if ($document_engine) {
	return array(
	$document_engine,
	$old_ref,
	$new_ref);
	}

	return null;
	}

	private function loadFileObjectsForChangeset() {
	$changeset = $this->changeset;
	$viewer = $this->getViewer();

	$old_phid = $changeset->getOldFileObjectPHID();
	$new_phid = $changeset->getNewFileObjectPHID();

	$old_file = null;
	$new_file = null;

	if ($old_phid \|\| $new_phid) {
	$file_phids = array();
	if ($old_phid) {
	$file_phids[] = $old_phid;
	}
	if ($new_phid) {
	$file_phids[] = $new_phid;
	}

	$files = id(new PhabricatorFileQuery())
	->setViewer($viewer)
	->withPHIDs($file_phids)
	->execute();
	$files = mpull($files, null, 'getPHID');

	if ($old_phid) {
	$old_file = idx($files, $old_phid);
	if (!$old_file) {
	throw new Exception(
	pht(
	'Failed to load file data for changeset ("%s").',
	$old_phid));
	}
	$changeset->attachOldFileObject($old_file);
	}

	if ($new_phid) {
	$new_file = idx($files, $new_phid);
	if (!$new_file) {
	throw new Exception(
	pht(
	'Failed to load file data for changeset ("%s").',
	$new_phid));
	}
	$changeset->attachNewFileObject($new_file);
	}
	}

	return array($old_file, $new_file);
	}

	public function newChangesetResponse() {
	// NOTE: This has to happen first because it has side effects. Yuck.
	$rendered_changeset = $this->renderChangeset();

	$renderer = $this->getRenderer();
	$renderer_key = $renderer->getRendererKey();

	$viewstate = $this->getViewState();

	$undo_templates = $renderer->renderUndoTemplates();
	foreach ($undo_templates as $key => $undo_template) {
	$undo_templates[$key] = hsprintf('%s', $undo_template);
	}

	$document_engine = $renderer->getDocumentEngine();
	if ($document_engine) {
	$document_engine_key = $document_engine->getDocumentEngineKey();
	} else {
	$document_engine_key = null;
	}

	$available_keys = array();
	$engines = $this->availableDocumentEngines;
	if (!$engines) {
	$engines = array();
	}

	$available_keys = mpull($engines, 'getDocumentEngineKey');

	// TODO: Always include "source" as a usable engine to default to
	// the buitin rendering. This is kind of a hack and does not actually
	// use the source engine. The source engine isn't a diff engine, so
	// selecting it causes us to fall through and render with builtin
	// behavior. For now, overall behavir is reasonable.

	$available_keys[] = PhabricatorSourceDocumentEngine::ENGINEKEY;
	$available_keys = array_fuse($available_keys);
	$available_keys = array_values($available_keys);

	$state = array(
	'undoTemplates' => $undo_templates,
	'rendererKey' => $renderer_key,
	'highlight' => $viewstate->getHighlightLanguage(),
	'characterEncoding' => $viewstate->getCharacterEncoding(),
	'requestDocumentEngineKey' => $viewstate->getDocumentEngineKey(),
	'responseDocumentEngineKey' => $document_engine_key,
	'availableDocumentEngineKeys' => $available_keys,
	'isHidden' => $viewstate->getHidden(),
	);

	return id(new PhabricatorChangesetResponse())
	->setRenderedChangeset($rendered_changeset)
	->setChangesetState($state);
	}

	private function getRawDocumentEngineData(array $lines) {
	$text = array();

	foreach ($lines as $line) {
	if ($line === null) {
	continue;
	}

	// If this is a "No newline at end of file." annotation, don't hand it
	// off to the DocumentEngine.
	if ($line['type'] === '\\') {
	continue;
	}

	$text[] = $line['text'];
	}

	return implode('', $text);
	}

	}

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