1072106 - "ASSERTION: After-spacing inside a ligature" with justified text

Status: RESOLVED FIXED

(Core :: Layout: Text and Fonts, defect)

Description

[Jesse Ruderman]

Attachment: testcase

###!!! ASSERTION: After-spacing inside a ligature!: 'i - 1 <= aStart || aSpacing[i - 1 - aStart].mAfter == 0', file gfx/thebes/gfxTextRun.cpp, line 355

Comment 1

[Jesse Ruderman]

Attachment: stack+

Comment 2

[Jonathan Kew [:jfkthame]]

Although the comment in IsJustifiableCharacter() claims that we "Don't justify spaces that are combined with diacriticals"[1], the helper it uses (nsTextFrameUtils::IsSpaceCombiningSequenceTail) does not actually check that; it checks ONLY for a following zero-width joiner character[2].

As a result, we will apply justification to space (or no-break space) characters that are being used as the base for a combining mark. So besides hitting the assertion here in a debug build, it's also possible to construct examples that will render incorrectly because of this bug.

[1] http://mxr.mozilla.org/mozilla-central/source/layout/generic/nsTextFrame.cpp#2693
[2] http://mxr.mozilla.org/mozilla-central/source/layout/generic/nsTextFrameUtils.h#78

Comment 3

[Jonathan Kew [:jfkthame]]

Attachment: Be more careful about checking for spaces that should not have justification applied.

Comment 4

[Jonathan Kew [:jfkthame]]

Attachment: Reftest for justification of accented space characters.

Reftest for the justification behavior affected by this. These examples fail on current trunk, but pass once the patch is applied.

Comment 5

[Jonathan Kew [:jfkthame]]

Note that this similarly affects the behavior of CSS word-spacing; on trunk, an example like

  data:text/html,<div style="word-spacing:10px">abc &%23x308;def

will apply the word-spacing, resulting in a rendering like

  abc¨   def

while the patch will make it render as

  abc¨def

which I believe is correct: when the <space> is being used as the base for a combining mark, it should no longer be treated as a space for word-separation purposes.

Comment 6

[Jonathan Kew [:jfkthame]]

https://hg.mozilla.org/integration/mozilla-inbound/rev/cc4e54e76940
https://hg.mozilla.org/integration/mozilla-inbound/rev/b5556bdf4c15

Comment 7

[Ryan VanderMeulen [:RyanVM]]

https://hg.mozilla.org/mozilla-central/rev/cc4e54e76940
https://hg.mozilla.org/mozilla-central/rev/b5556bdf4c15