[Gecko Bug 1665447] Fix BoxToRect when the "relative to" frame is not an ancestor. #25861
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Right now the BoxToRect callback assumes that when it gets a RECTS_ACCOUNT_FOR_TRANSFORMS flag, the "relative to" is an ancestor. This holds for all the callers of GetAllInFlowRectsUnion except for [1], which was introduced in bug 1581876, because they pass GetContainingBlockForClientRect (that is, the root frame) as the root. But that caller passes target, so IB split continuations or such would get two siblings as the from/to frames, messing up the bounds. An alternative would be to not pass the RECTS_ACCOUNT_FOR_TRANSFORMS flag for that call (as it's computing a rect relative to self, but I don't think that'd be quite correct in the presence of fragmentation with transformed containers (if that's possible at all? would need to think harder...)), but it seems like the API should just behave more generally, or assert otherwise. To that effect, this patch adds an assertion to TransformRectToAncestor that would've caught this bug (though there are some pre-existing violations, so we'll fix them in another bug). [1]: https://searchfox.org/mozilla-central/rev/dfd9c0f72f9765bd4a187444e0c1e19e8834a506/dom/base/DOMIntersectionObserver.cpp#340-341 Differential Revision: https://phabricator.services.mozilla.com/D91883 bugzilla-url: https://bugzilla.mozilla.org/show_bug.cgi?id=1665447 gecko-commit: 92f24022a62c77f83ec94de85aeb9e1a520251de gecko-reviewers: dholbert, mstange
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Right now the BoxToRect callback assumes that when it gets a
RECTS_ACCOUNT_FOR_TRANSFORMS flag, the "relative to" is an ancestor.
This holds for all the callers of GetAllInFlowRectsUnion except for 1,
which was introduced in bug 1581876, because they pass
GetContainingBlockForClientRect (that is, the root frame) as the root.
But that caller passes target, so IB split continuations or such would
get two siblings as the from/to frames, messing up the bounds.
An alternative would be to not pass the RECTS_ACCOUNT_FOR_TRANSFORMS
flag for that call (as it's computing a rect relative to self, but I
don't think that'd be quite correct in the presence of fragmentation
with transformed containers (if that's possible at all? would need to
think harder...)), but it seems like the API should just behave more
generally, or assert otherwise.
To that effect, this patch adds an assertion to TransformRectToAncestor
that would've caught this bug (though there are some pre-existing
violations, so we'll fix them in another bug).
Differential Revision: https://phabricator.services.mozilla.com/D91883
bugzilla-url: https://bugzilla.mozilla.org/show_bug.cgi?id=1665447
gecko-commit: 92f24022a62c77f83ec94de85aeb9e1a520251de
gecko-reviewers: dholbert, mstange