commit 4a776e15c47a7a577e4d0d3b8f4b510258d5da03
author Andreu Botella <abotella@igalia.com> Wed Feb 07 13:29:59 2024
committer Chromium LUCI CQ <chromium-scoped@luci-project-accounts.iam.gserviceaccount.com> Wed Feb 07 13:29:59 2024
tree b535f4a01a0f2ecda216978c70c9c38f9c898520
parent e7029a9df2904a198a4c06989705428eea251ade

Fully implement bidi for a line's trailing spaces (UAX#9 L1)

Per UAX#9 L1, any spaces that after line breaking would fall logically
at the end of a line must be reset to the paragraph's initial
embedding level, regardless of the embedding level of those spaces in
the paragraph. Until now, Blink only had partial support for this.

The reason this was hard to implement in Blink is because the
direction of text is computed in a per-paragraph level, splitting the
text into items with a given direction and embedding level. Those
items are then split into item results when line breaking, but item
results must have the same direction as the item.

As part of line breaking, some item results are produced which only
have trailing spaces. The partial support, implemented in
crrev.com/c/2505486, consisted of marking these results with the
`has_only_trailing_spaces` flag, and using this flag to distinguish
them when reordering the item results.

This patch builds on top of that partial fix by adding a final
processing step to line breaking, which splits item results so that
trailing spaces (with a different embedding level as the paragraph)
are split into its own item result, and by marking all trailing spaces
item results as `has_only_trailing_spaces`.

This also fixes bug 1514753, where having a item result with non-base
direction which had logically trailing spaces was causing the text
(rather than the spaces) to hang, because
`LineInfo::ComputeTrailingSpaceWidth` assumed that UAX#9 L1 held.

This patch also modifies some existing WPT tests to make them use a
monospace Arabic webfont (since it's not guaranteed that all OS's have
one), and by changing the widths slightly to work around bug 1409445.

Bug: 316409, 1514753
Change-Id: I1eb751b457d413b5099dad8f95badba9a1b3e5fb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5199988
Reviewed-by: Koji Ishii <kojii@chromium.org>
Commit-Queue: Andreu Botella <abotella@igalia.com>
Cr-Commit-Position: refs/heads/main@{#1257309}