| commit | 28bf572ae39115c939e44e5f6203325ef67658ff | [log] [tgz] |
|---|---|---|
| author | Morten Stenshorne <mstensho@chromium.org> | Wed Nov 02 20:11:02 2022 |
| committer | Blink WPT Bot <blink-w3c-test-autoroller@chromium.org> | Wed Nov 02 20:18:16 2022 |
| tree | cfd3c2a7bc6ab0c8bc66112855300f318eab9087 | |
| parent | 7a78a321019d8f4455f75ec539776e3af06622bc [diff] |
Invalidate layout from changed spanner up to containing block. We need to mark all ancestors between the spanner and its containing block for layout, because they may contain references to the spanner. Just like for out-of-flow positioned elements, there may be references to column spanners from such ancestors. More precisely, there may be a descendant break token for the spanner. So if the spanner is removed, they will point to a dead object. Make sure to mark the ancestors for layout, so that we never hit the cache. It's very hard to hit the cache in front of a spanner, since we force column balancing, which very easily makes us miss the cache (and nuke it). So it was tricky to reproduce. However, it was possible if we had a multicol on a fragmentable table caption (or somewhere inside it), because of a cache miss while side-effects were disabled (which prevented the missed entry from being nuked). Grid layout also sometimes disables side-effects, so it might have been possible there as well. The table layout code initially lays out captions with side-effects disabled, so a stale entry in LayoutBox is kept even if the cache is missed, and then hit when laying out for "real" afterwards (via NGTableLayoutAlgorithm::GenerateFragment()). The entry (fragment) would have an outgoing break token tree containing a dead spanner. We always need a balancing pass in front of a spanner. If the parent of a spanner used to fragment, we'll typically miss the cache and nuke it when performing layout after a DOM / style change. However, with side-effects disabled, this doesn't happen. We just miss the cache, but keep the old result lying around (which should be okay to do). When we get to actual layout with a known fragmentainer block-size, there's nothing that prevents us from hitting the cache. There's a TODO in ComputeCaptionFragments() suggesting that we remove the disable-side-effects scope, if we instead stow away enough caption info in a break token. That's a good idea, solving this bug that way would just hide it. There may be other ways of reproducing it, and I think what the table code does is valid. The test case needs to trigger a break in a parallel flow before a spanner, since that's probably the only way of creating a break token for the spanner. This happens in the IsColumnSpanAll() when laying out children in NGBlockLayoutAlgorithm::Layout(). Bug: 1379635 Change-Id: Ic82462876d0c8b5dbf38ae21be88fff428fbb7fb Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3998595 Commit-Queue: Morten Stenshorne <mstensho@chromium.org> Reviewed-by: Ian Kilpatrick <ikilpatrick@chromium.org> Cr-Commit-Position: refs/heads/main@{#1066634}
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