752459 - word-wrap:break-word should not break up base+diacritic clusters or surrogate pairs

Status: RESOLVED FIXED

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

Description

[Jonathan Kew [:jfkthame]]

The word-wrap:break-word property (being renamed to overflow-wrap in CSS3 Text) inappropriately causes breaks between a base character and its applied diacritics, and (even worse) breaks between the two code units of a surrogate pair.

Testcase:
data:text/html;charset=utf-8,
  <div style="width:0px;word-wrap:break-word">abc d̥e̕f̣  

Comment 1

[Jonathan Kew [:jfkthame]]

Argh, I forgot bugzilla would truncate my text as soon as it encountered a surrogate codepoint.

Trying again....

data:text/html;charset=utf-8,
  <div style="width:0px;word-wrap:break-word">abc d̥e̕f̣ %F0%90%90%80%F0%90%90%81%F0%90%90%82

Note the "blank" lines between the Deseret letters, because internally we split the low surrogate onto a separate line. (The fact that they're split across lines can be demonstrated by drag-selecting one of the Deseret glyphs (or hexboxes), *or* one of the invisible blanks in between them, and copy-pasting it into the search box - you get just the single, unpaired surrogate codepoint.)

Comment 2

[Jonathan Kew [:jfkthame]]

Attachment: patch, respect clusters when doing word-wrap:break-word

It looks like this can be trivially fixed, actually - we just need to check whether the current character is a cluster start when considering a possible breakpoint for word-wrap:break-word.

Comment 3

[Jonathan Kew [:jfkthame]]

Attachment: add a reftest for word-wrap cluster support

Comment 4

[Jonathan Kew [:jfkthame]]

https://hg.mozilla.org/integration/mozilla-inbound/rev/9b57d5c5a713
https://hg.mozilla.org/integration/mozilla-inbound/rev/88c5fc8ffd6c

Comment 5

[Ryan VanderMeulen [:RyanVM]]

https://hg.mozilla.org/mozilla-central/rev/9b57d5c5a713
https://hg.mozilla.org/mozilla-central/rev/88c5fc8ffd6c