Bug 236378 – Check bidiLevels are valid before reordering

• Status: RESOLVED
• Resolution: FIXED
• Component: Layout and Rendering

[Brandon]

<rdar://88324745>

[Brandon]

Created attachment 451397 [details]
Patch

[alan]

Comment on attachment 451397 [details]
Patch

View in context: https://bugs.webkit.org/attachment.cgi?id=451397&action=review

> Source/WebCore/layout/formattingContexts/inline/InlineLineBuilder.cpp:350
> +
> +            // bidiLevels are required to be less than the MAX + 1, otherwise
> +            // ubidi_reorderVisual will silently fail.
> +            if (lineRuns[i].bidiLevel() > UBIDI_MAX_EXPLICIT_LEVEL + 1)
> +                continue;
> +

Great patch! What happens here is that 
1. an empty DOM text node (length = 0) generates an InlineTextItem with zero length
2. this InlineTextItem gets ignored at InlineItemsBuilder::breakAndComputeBidiLevels() -this is ok, it's hard to assign a bidi level for a 0 length content.
3. this zero length InlineTextItem enters the bidi reordering with the default UBIDI_DEFAULT_LTR value (254, see InlineItem's c'tor) which is greater than UBIDI_MAX_EXPLICIT_LEVEL (125)
I'd slightly change this patch by adding the following asserts 
ASSERT(lineRuns[I].bidiLevel() == UBIDI_DEFAULT_LTR);
ASSERT(!downcast<InlineTextItem>(lineRuns[I]).length());
as we do not expect any other type of content with such bidi level.

[Brandon]

Created attachment 451579 [details]
Patch

[EWS]

Committed r289597 (247110@main): <https://commits.webkit.org/247110@main>

All reviewed patches have been landed. Closing bug and clearing flags on attachment 451579 [details].