Almost working draft of basic undo coalescence

lib/ace/edit_session.js

@@ -406,10 +406,11 @@ var EditSession = function(text, mode) {
                 if (self.$deltas.length > 0) {
                     undoManager.execute({
                         action: "aceupdate",
-                        args: [self.$deltas, self]
+                        args: [self.$deltas, self],
+                        merge: self.coalesceDeltas
                     });
                 }
-
+                self.coalesceDeltas = false;
                 self.$deltas = [];
             }
             this.$informUndoManager = lang.delayedCall(this.$syncInformUndoManager);

lib/ace/editor.js

@@ -701,8 +701,14 @@ var Editor = function(renderer, session) {
         if (this.getBehavioursEnabled()) {
             // Get a transform if the current mode wants one.
             var transform = mode.transformAction(session.getState(cursor.row), 'insertion', this, session, text);
-            if (transform)
+            if (transform) {
+                if (text !== transform.text) {
+                    this.session.coalesceDeltas = false;
+                    this.coalesceNextCommand = false;
+                }
                 text = transform.text;
+
+            }
         }
 
         text = text.replace("\t", this.session.getTabString());

lib/ace/keyboard/keybinding.js

@@ -105,6 +105,28 @@ var KeyBinding = function(editor) {
             if (toExecute.command == "null") {
                 success = true;
             } else {
+                var mergeableCommands = ["backspace", "del"];
+                var previousCommand = this.$editor.previousCommand || {};
+                if (
+                    // previous command was the same
+                    toExecute.command.name == previousCommand.name
+                    // the command is mergeable
+                    && mergeableCommands.indexOf(toExecute.command.name) !== -1
+                    // cursor was not moved since last command
+                    && !this.$editor.cursorMoved
+                    // the sequence is not too long
+                    && (new Date()) - this.$editor.sequenceStartTime < 2000
+                    )
+                    this.$editor.session.coalesceDeltas = true
+                else
+                    if (mergeableCommands.indexOf(toExecute.command.name) !== -1)
+                        this.$editor.sequenceStartTime = new Date().getTime();
+
+                this.$editor.previousCommand = {
+                    name: toExecute.command.name,
+                    text: toExecute.command.text
+                }
+                this.$editor.cursorMoved = false;
                 success = commands.exec(toExecute.command, this.$editor, toExecute.args, e);                
             }
             // do not stop input events to not break repeating
@@ -123,8 +145,36 @@ var KeyBinding = function(editor) {
 
     this.onTextInput = function(text) {
         var success = this.$callKeyboardHandlers(-1, text);
-        if (!success)
+        if (!success) {
+            if (this.$editor.coalesceNextCommand === undefined) {
+                this.$editor.coalesceNextCommand = true;
+            }
+            var previousCommand = this.$editor.previousCommand || {};
+            if (
+                // previous command was the same
+                "insertstring" == previousCommand.name
+                // cursor was not moved since last command
+                && !this.$editor.cursorMoved
+                // previous command allows to coalesce with
+                && this.$editor.coalesceNextCommand
+                // previous insertion was not a new line or a whitespace
+                // or this is a sequence of a new line or a whitespace insertions
+                && (!/ |\r\n|\r|\n/.test(text) || / |\r\n|\r|\n/.test(previousCommand.text))
+                // the sequence is not too long
+                && (new Date()) - this.$editor.sequenceStartTime < 2000
+                )
+                this.$editor.session.coalesceDeltas = true;
+            else
+                this.$editor.sequenceStartTime = new Date().getTime();
+
+            this.$editor.previousCommand = {
+                name: "insertstring",
+                text: text
+            }
+            this.$editor.cursorMoved = false;
+            this.$editor.coalesceNextCommand = true;
             this.$editor.commands.exec("insertstring", this.$editor, text);
+        }
     };
 
 }).call(KeyBinding.prototype);

lib/ace/undomanager.js

@@ -63,6 +63,9 @@ var UndoManager = function() {
     this.execute = function(options) {
         var deltas = options.args[0];
         this.$doc  = options.args[1];
+        if (options.merge && this.hasUndo()){
+            deltas = this.$undoStack.pop().concat(deltas);
+        }
         this.$undoStack.push(deltas);
         this.$redoStack = [];