`drag-payload` was documented as "called when a drag starts, so it
always reflects the selection as it is at that moment". Neither half is
true, and the comment is the only reason anyone would believe the drop
reads it.
`DragArea` tests `data.is_empty()` in its event filter — on every
pointer event, the first one included, which arrives long before there
is a drag. And a Slint binding that calls a callback has no dependency
to be invalidated on, so it is evaluated once, when a finger first lands
on that cell, and cached for the life of the cell. What it answers is
therefore always an empty selection.
None of the drop handlers read it; every one of them reads `dragging`,
which `drag-started` fills in at the moment that matters. What this
callback does is keep the `DragArea` armed, and it manages that only
because `set_user_data` is called unconditionally — an empty `Vec` is
still user data. Guarding that call, which reads as an obvious tidy-up,
would silently stop the grid dragging at all.
Comments only.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
dtourolleandClaude Opus 5
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