tree af7e2aba7d43722e8eecba97f025aeb0596eb97c
parent 0eed98875a69baa6d0cdabb17ed2840d2a494ad2
author Emilio Cobos Álvarez <emilio@crisal.io> 1688761931 +0000
committer moz-wptsync-bot <wptsync@mozilla.com> 1688769011 +0100

Simplify first-line reparenting a bit.

The TLDR is that our first-line implementation is complete madness, but
I'm not fixing bug 1465474 yet.

The guarantee that first-line style reparenting relies on is that
reparenting shouldn't change reset properties (that's why we had all
this "style to inherit ignoring first-line" to inherit reset
properties). Bug 1839223 broke this guarantee in the case the mapped
attribute declarations are reused / mutated (which is something we want
to do for performance).

What's going on in the test-case is that the old style's rule-node
declarations are mutated by the mapped attributes code. Re-cascading the
old styles yields a different `float` property value.

When a style change that causes a reframe like this one happens, we
don't update the frame tree styles with the new styles: it'd be wrong
and also useless work.

First-line reparenting happens after we've recomputed the styles, but
before we've reframed as needed. In this intermediate state, the frame
remains with the old (floated) style, but the ::first-line reparenting
code isn't aware that this frame is going away, so it happily
re-cascades and updates the style anyways, creating a floated
frame that has float: none in its computed style information.

This causes the frame destruction code to crash.

This patch restores that guarantee that ::first-line doesn't change
reset properties by re-using the "reset properties cache" code-path.
This is also simpler since it avoids us having to compute the "parent
ignoring ::first-line" style.

The code is also more explicit with the new enum rather than just an
Option.

Differential Revision: https://phabricator.services.mozilla.com/D182769

bugzilla-url: https://bugzilla.mozilla.org/show_bug.cgi?id=1841128
gecko-commit: 43977d30a10af8e193044a9aa578f2bc8b33edf7
gecko-reviewers: TYLin