Hi @0lione,

Thanks a lot for this PR. At first glance it looks good. I need a bit of time for a more in-depth review.

@0lione Can you run pre-commit on your changes? That should help you resolve the linting errors.

This looks good.

Just a few comments regarding naming.

Maybe it's possible to create a separate Gtk.EventControllerKey in the item_tool() function (it should return a tuple of controllers then), so they can share a single state object (as is done here). Then there's no need to maintain that state on the presentation objects themselves.

But if you feel that complicates things, that's also fine.

Could you elaborate on that? I'm not understanding what you want me to do.

Sorry for the late reply.

What I meant was that it may be possible to keep the whole cancel logic in itemtool.py.

# gaphor/diagram/tools/itemtool.py

class DragState:
    def __init__(self):
        self.dragging = False


def item_tool(event_manager) -> tuple[Gtk.GestureDrag, Gtk.EventControllerKey]:
    state = DragState()
    gesture = _item_tool()
    gesture.connect_after("drag-begin", on_drag_begin, event_manager, state)
    gesture.connect_after("drag-update", on_drag_update)
    gesture.connect_after("drag-end", on_drag_end, state)

    key_ctrl = Gtk.EventControllerKey.new()
    key_ctrl.connect("key-pressed", key_pressed, event_manager, state)
    return gesture, key_ctrl

...

def key_pressed(ctrl, keyval, keycode, _state, event_manager, state):
    if state.dragging and keyval == Gdk.KEY_Escape:
        Transaction.mark_rollback()

(may need to make gaphor.transaction.Transaction.mark_rollback() a class method)

I think what it should do, is roll back the transaction. Then the handle should be nicely be reverted to its old position and everything should be as before the drag operation started.

Okay I got it working using the transaction rollback but I had to do some changes to the transactional_tool function so the rollback could work. I also had to change the PlacementState because whenever we pressed any key while placing a connection the "drag-end" event was never called. Hope the modifications are satisfactory, if not feel free to provide feedback on what changes you'd like to see

I've been playing with your PR a bit. This problem is a lot harder than I expected.
The problem is indeed, that when you press any key during a drag operation, the drag is cancelled and we end up with an inconsistent state, because our transactions are not properly closed. This causes errors during undo, for example.

I think you're on the right track, by adding a key-pressed handler to transactional_tool.

I've been fiddling a bit around with that. I found that if we cancel (reset) all transactions as soon as a key press is recorded, we can roll back the transaction and let the tools do their cleanup.

Due to limitations in the GitHub interface (I was not able to create a PR from this repo to yours), I created a PR here. I did not need the key-pressed handlers for item and placement tools anymore. I think we should give this some thorough testing, though.

@0lione can you review the changes I did in #3254, please?