Allow DocumentEngine to elect into diff construction

Summary:
Ref T13425. Allow DocumentEngines to claim they can produce diffs. If both sides of a change can be diffed by the same document engine and it can produce diffs, have it diff them.

This has no impact on runtime behavior because no upstream engine elects into diff generation yet.

Test Plan: Loaded some revisions, nothing broke.

Maniphest Tasks: T13425

Differential Revision: https://secure.phabricator.com/D20830

src/applications/differential/controller/DifferentialChangesetViewController.php

@@ -166,6 +166,7 @@ final class DifferentialChangesetViewController extends DifferentialController {
       DifferentialChangesetParser::parseRangeSpecification($spec);
 
     $parser = id(new DifferentialChangesetParser())
+      ->setViewer($viewer)
       ->setCoverage($coverage)
       ->setChangeset($changeset)
       ->setRenderingReference($rendering_reference)

src/applications/differential/parser/DifferentialChangesetParser.php

@@ -58,6 +58,7 @@ final class DifferentialChangesetParser extends Phobject {
   private $linesOfContext = 8;
 
   private $highlightEngine;
+  private $viewer;
 
   public function setRange($start, $end) {
     $this->rangeStart = $start;
@@ -149,6 +150,15 @@ final class DifferentialChangesetParser extends Phobject {
     return $this->offsetMode;
   }
 
+  public function setViewer(PhabricatorUser $viewer) {
+    $this->viewer = $viewer;
+    return $this;
+  }
+
+  public function getViewer() {
+    return $this->viewer;
+  }
+
   public static function getDefaultRendererForViewer(PhabricatorUser $viewer) {
     $is_unified = $viewer->compareUserSetting(
       PhabricatorUnifiedDiffsSetting::SETTINGKEY,
@@ -1003,6 +1013,11 @@ final class DifferentialChangesetParser extends Phobject {
       ->setOldComments($old_comments)
       ->setNewComments($new_comments);
 
+    $engine_view = $this->newDocumentEngineChangesetView();
+    if ($engine_view !== null) {
+      return $engine_view;
+    }
+
     switch ($this->changeset->getFileType()) {
       case DifferentialChangeType::FILE_IMAGE:
         $old = null;
@@ -1675,4 +1690,57 @@ final class DifferentialChangesetParser extends Phobject {
     return $prefix.$line;
   }
 
+  private function newDocumentEngineChangesetView() {
+    $changeset = $this->changeset;
+    $viewer = $this->getViewer();
+
+    // TODO: This should probably be made non-optional in the future.
+    if (!$viewer) {
+      return null;
+    }
+
+    $old_data = $this->old;
+    $old_data = ipull($old_data, 'text');
+    $old_data = implode('', $old_data);
+
+    $new_data = $this->new;
+    $new_data = ipull($new_data, 'text');
+    $new_data = implode('', $new_data);
+
+    $old_ref = id(new PhabricatorDocumentRef())
+      ->setName($changeset->getOldFile())
+      ->setData($old_data);
+
+    $new_ref = id(new PhabricatorDocumentRef())
+      ->setName($changeset->getFilename())
+      ->setData($new_data);
+
+    $old_engines = PhabricatorDocumentEngine::getEnginesForRef(
+      $viewer,
+      $old_ref);
+
+    $new_engines = PhabricatorDocumentEngine::getEnginesForRef(
+      $viewer,
+      $new_ref);
+
+    $shared_engines = array_intersect_key($old_engines, $new_engines);
+
+    $document_engine = null;
+    foreach ($shared_engines as $shared_engine) {
+      if ($shared_engine->canDiffDocuments($old_ref, $new_ref)) {
+        $document_engine = $shared_engine;
+        break;
+      }
+    }
+
+
+    if ($document_engine) {
+      return $document_engine->newDiffView(
+        $old_ref,
+        $new_ref);
+    }
+
+    return null;
+  }
+
 }

src/applications/files/document/PhabricatorDocumentEngine.php

@@ -31,6 +31,18 @@ abstract class PhabricatorDocumentEngine
     return $this->canRenderDocumentType($ref);
   }
 
+  public function canDiffDocuments(
+    PhabricatorDocumentRef $uref,
+    PhabricatorDocumentRef $vref) {
+    return false;
+  }
+
+  public function newDiffView(
+    PhabricatorDocumentRef $uref,
+    PhabricatorDocumentRef $vref) {
+    throw new PhutilMethodNotImplementedException();
+  }
+
   public function canConfigureEncoding(PhabricatorDocumentRef $ref) {
     return false;
   }

src/applications/files/document/PhabricatorDocumentRef.php

@@ -11,6 +11,7 @@ final class PhabricatorDocumentRef
   private $symbolMetadata = array();
   private $blameURI;
   private $coverage = array();
+  private $data;
 
   public function setFile(PhabricatorFile $file) {
     $this->file = $file;
@@ -65,6 +66,10 @@ final class PhabricatorDocumentRef
       return $this->byteLength;
     }
 
+    if ($this->data !== null) {
+      return strlen($this->data);
+    }
+
     if ($this->file) {
       return (int)$this->file->getByteSize();
     }
@@ -72,7 +77,26 @@ final class PhabricatorDocumentRef
     return null;
   }
 
+  public function setData($data) {
+    $this->data = $data;
+    return $this;
+  }
+
   public function loadData($begin = null, $end = null) {
+    if ($this->data !== null) {
+      $data = $this->data;
+
+      if ($begin !== null && $end !== null) {
+        $data = substr($data, $begin, $end - $begin);
+      } else if ($begin !== null) {
+        $data = substr($data, $begin);
+      } else if ($end !== null) {
+        $data = substr($data, 0, $end);
+      }
+
+      return $data;
+    }
+
     if ($this->file) {
       $iterator = $this->file->getFileDataIterator($begin, $end);