@rebornix, thanks for your PR! By analyzing the history of the files in this pull request, we identified @alexandrudima and @egamma to be potential reviewers.

Now I already stop adding secondary cursors when drag and move. Instead I put a new widget to simulate the cursor, which is somehow not pixel perfect but not that ugly.

The next step is moving the content cut and paste logic into that widget as well then our code is clean enough.

The dnd now works pretty reasonably in the editor. The target cursor you see while dragging is actually virtual, which looks the same as a secondary cursor but not a real cursor.

The catch here is I'm putting logic into Contrib part as I create content widget to mimic the cursor but in this way I have to listen to drag and drop related events. That's why I emit these two events in view controller but they are not 100% compatible with Browsers native drag/drop events (lack of dataTransfer).

A proper way to make the data transfer work is adding the dataTransfer object to related events in CommonCodeEditor, where we can access the editor and the model. Then we maintain our own implementation of drag events. Look forward to Alex's comment on this @alexandrudima

@alexandrudima I've made some updates to the code

it should sit behind an option and be turned off by default

Add editor.enableDragAndDrop

drop outside the editor or drop on a view zone or drop on a widget, etc. all kind of targets except content or perhaps content_empty should result in a no-op

Right now drop on elements other than content or content_empty of current editor will lead to no-op. When you drag and move the cursor, we still try to draw the target hint in the editor, just like what we did for selection.

the drop target should IMHO be rendered very differently than a regular cursor. I was confused by the drop target looking like a regular cursor.

Now I drop dependency to Cursor and use its own CSS. The reason that I leveraged original cursor style is to make sure it looks reasonable in different third party themes. Right now I used simple dotted line to represent the drop target.

About the comment you put in #20565 (comment) , the reason that I set this._mouseState.lastMouseDownEvent as drop only when users drag and move is because users might just single click on a selection and the outgoing events should only be mouseDown + mouseUp. So basically previous workflow is like

• If user clicks on a selection, monitor MouseDownThenDrag, otherwise monitor MouseDownThenMove handler.
• Emit mouseDown
• When user drags, emit mouseDrag Event
• When user stops dragging or moving or cancel, check whether it's a click or a drag. For the former, update cursor position; For the latter, emit mouseDrop event.

Right now we only update this._mouseState.lastMouseDownEvent in the start phrase. The workflow is like

• User clicks on a selection
• Emit MouseDrag Event, monitor MouseMove
• Emit MouseDown (this is emitted always whether it's a drag or not)
• Emit MouseUp when User releases the mouse
• Emit MouseDrop and update the cursor

In this case, MouseDrag and MouseDrop events are always emitted even if users just click on a selection. But it's not a big deal as we hide these events from external. I don't favor this part so you may want to change it somehow.

Most comments are addressed, feel free to polish it :)

Very very nice!