add duplicateSelection command

lib/ace/commands/default_commands.js

@@ -319,6 +319,11 @@ exports.commands = [{
     bindKey: bindKey("Ctrl-D", "Command-D"),
     exec: function(editor) { editor.removeLines(); },
     multiSelectAction: "forEach"
+}, {
+    name: "duplicateSelection",
+    bindKey: bindKey("Ctrl-Shift-D", "Command-Shift-D"),
+    exec: function(editor) { editor.duplicateSelection(); },
+    multiSelectAction: "forEach"
 }, {
     name: "togglecomment",
     bindKey: bindKey("Ctrl-/", "Command-/"),

lib/ace/editor.js

@@ -1348,6 +1348,24 @@ var Editor = function(renderer, session) {
         this.clearSelection();
     };
 
+    this.duplicateSelection = function() {
+        var sel = this.selection;
+        var doc = this.session;
+        var range = sel.getRange();
+        if (range.isEmpty()) {
+            var row = range.start.row;
+            doc.duplicateLines(row, row);
+        } else {
+            var reverse = sel.isBackwards()
+            var point = sel.isBackwards() ? range.start : range.end;
+            var endPoint = doc.insert(point, doc.getTextRange(range), false);
+            range.start = point;
+            range.end = endPoint;
+
+            sel.setSelectionRange(range, reverse)
+        }
+    };
+
     /** related to: EditSession.moveLinesDown
      * Editor.moveLinesDown() -> Number
      * + (Number): On success, it returns -1.