Allow specifying custom syntax highlighter

Summary: Related to D2873.

Test Plan: Specified it and verified that highlighting still works.

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D2874

conf/default.conf.php

@@ -1081,12 +1081,16 @@ return array(
   // of classes which extend PhabricatorEventListener here.
   'events.listeners'  => array(),
 
-// -- Pygments -------------------------------------------------------------- //
+// -- Syntax Highlighting --------------------------------------------------- //
 
-  // Phabricator can highlight PHP by default, but if you want syntax
-  // highlighting for other languages you should install the python package
-  // 'Pygments', make sure the 'pygmentize' script is available in the
-  // $PATH of the webserver, and then enable this.
+  // Phabricator can highlight PHP by default and use Pygments for other
+  // languages if enabled. You can provide a custom highlighter engine by
+  // extending class PhutilSyntaxHighlighterEngine.
+  'syntax-highlighter.engine' => 'PhutilDefaultSyntaxHighlighterEngine',
+
+  // If you want syntax highlighting for other languages than PHP then you can
+  // install the python package 'Pygments', make sure the 'pygmentize' script is
+  //  available in the $PATH of the webserver, and then enable this.
   'pygments.enabled'            => false,
 
   // In places that we display a dropdown to syntax-highlight code,

src/applications/markup/PhabricatorMarkupEngine.php

@@ -90,6 +90,8 @@ class PhabricatorMarkupEngine {
       'macros'        => true,
       'uri.allowed-protocols' => PhabricatorEnv::getEnvConfig(
         'uri.allowed-protocols'),
+      'syntax-highlighter.engine' => PhabricatorEnv::getEnvConfig(
+        'syntax-highlighter.engine'),
     );
   }
 
@@ -106,6 +108,9 @@ class PhabricatorMarkupEngine {
       $options['uri.allowed-protocols']);
     $engine->setConfig('differential.diff', $options['differential.diff']);
     $engine->setConfig('header.generate-toc', $options['header.generate-toc']);
+    $engine->setConfig(
+      'syntax-highlighter.engine',
+      $options['syntax-highlighter.engine']);
 
     $rules = array();
     $rules[] = new PhutilRemarkupRuleEscapeRemarkup();

src/applications/markup/PhabricatorSyntaxHighlighter.php

@@ -22,7 +22,7 @@
 final class PhabricatorSyntaxHighlighter {
 
   public static function newEngine() {
-    $engine = new PhutilDefaultSyntaxHighlighterEngine();
+    $engine = PhabricatorEnv::newObjectFromConfig('syntax-highlighter.engine');
 
     $config = array(
       'pygments.enabled' => PhabricatorEnv::getEnvConfig('pygments.enabled'),

src/infrastructure/PhabricatorEnv.php

@@ -316,6 +316,7 @@ final class PhabricatorEnv {
       'mysql.implementation' => 'AphrontMySQLDatabaseConnectionBase',
       'differential.attach-task-class' => 'DifferentialTasksAttacher',
       'mysql.configuration-provider' => 'DatabaseConfigurationProvider',
+      'syntax-highlighter.engine' => 'PhutilSyntaxHighlighterEngine',
     );
   }