Fix pygments language to Ace mode translation

lib/gollum/frontend/public/gollum/livepreview/js/livepreview.js

@@ -244,6 +244,27 @@ function highlight( element, language ) {
   element.parentNode.parentNode.replaceChild( newDiv, element.parentNode );
 }
 
+// Pygments and Ace have different names for languages.
+function pygmentsLanguageToAceMode( declaredLanguage ) {
+  switch ( declaredLanguage ) {
+    case 'c':
+    case 'c++':
+    case 'cpp':
+    case 'objective-c':
+      return 'c_cpp';
+    case 'c#':
+      return 'csharp';
+    case 'coffeescript':
+      return 'coffee';
+    case 'html+erb':
+      return 'html'
+  }
+
+  // Assume language name is the same
+  // if it's not handled above.
+  return declaredLanguage;
+}
+
 var makePreviewHtml = function () {
   var text = editorSession.getValue();
 
@@ -294,21 +315,7 @@ var makePreviewHtml = function () {
       // the syntax for code highlighting means all code, even one line, contains newlines.
       if ( txt.length > 1 && codeHTML.match( /\n/ ) ) {
         var declaredLanguage = element.className.toLowerCase();
-        var aceMode = declaredLanguage;
+        var aceMode = pygmentsLanguageToAceMode( declaredLanguage );
-
-        // GitHub supports 'c', 'c++', 'cpp'
-        // which must trigger the 'c_cpp' mode in Ace.
-        if ( declaredLanguage === 'c'   ||
-             declaredLanguage === 'c++' ||
-             declaredLanguage === 'cpp' ) {
-          aceMode = 'c_cpp';
-        }
-
-        // Pygments's name for CoffeeScript is 'coffeescript', but Ace
-        // calls it 'coffee'.
-        if ( declaredLanguage === 'coffeescript' ) {
-          aceMode = 'coffee';
-        }
 
         if ( $.inArray( declaredLanguage, languages ) === -1 ) {
           // Unsupported language.