When element that is being dragged stays under the mouse,
it prevents the hit target check on drop from working,
because drop target is overlayed by the dragged element.
To workaround this, we perform a one-time hit target check
before moving for the drop, as we used to.
This changes previous layout shift attempt (see #9546)
to account for more valid usecases:
- On the first event that is intercepted we enforce the hit target. This
is similar to the current mode that checks hit target before the action,
but is better timed.
- On subsequent events we assume that everything is fine. This covers more
scenarios like react rerender, glass pane on mousedown, detach on mouseup.
This check is enabled by default, with `process.env.PLAYWRIGHT_NO_LAYOUT_SHIFT_CHECK`
to opt out.
This replaces previous `checkHitTarget` heuristic that took place before the action
with a new `setupHitTargetInterceptor` that works during the action:
- Before the action we set up capturing listeners on the window.
- During the action we ensure that event target is the element we expect to interact with.
- After the action we clear the listeners.
This should catch the "layout shift" issues where things move
between action point calculation and the actual action.
Possible issues:
- **Risk:** `{ trial: true }` might dispatch move events like `mousemove` or `pointerout`,
because we do actually move the mouse but prevent all other events.
- **Timing**: The timing of "hit target check" has moved, so this may affect different web pages
in different ways, for example expose more races. In this case, we should retry the click as before.
- **No risk**: There is still a possibility of mis-targeting with iframes shifting around,
because we only intercept in the target frame. This behavior does not change.
There is an opt-out environment variable PLAYWRIGHT_NO_LAYOUT_SHIFT_CHECK that reverts to previous behavior.
