Created attachment 633446 [details]
Reported from fxinput: http://input.mozilla.org/opinion/3001588
It says that this page layout is broken only on Fx.
The page specifies the width of table as 760px but actual width is wider than it because there is a line which has only IDEOGRAPHIC SPACEs (U+3000).
See the attached testcase. On WebKit and Opera, the line is broken between them. I'm not sure for IE9. IE9 doesn't break the page layout but doesn't break lines on the testcase.
Anyway, we should break lines before IDEOGRAPHIC SPACE after a white space.
Created attachment 633447 [details] [diff] [review]
Comment on attachment 633447 [details] [diff] [review]
Review of attachment 633447 [details] [diff] [review]:
@@ +225,5 @@
> + mBreakHere ||
> + // U+3000 is IDEOGRAPHIC SPACE. Japanese authors may use it instead of
> + // ASCII white space accidentally. Like WebKit and Opera, we should
> + // allow to break lines before it.
> + (mAfterBreakableSpace && (!isBreakableSpace || ch == 0x3000)) ||
This is a bit complicated.
This code is trying not to break inside runs of breakable spaces, only at the end of a run of breakable spaces. For normal spaces that usually can't produce long lines since runs normal spaces are compressed by default. But 0x3000 isn't compressed by nsTextFrameUtils::TransformText (and they're not compressed by any other browser, so we shouldn't start doing that.
Opera and Webkit allow breaking both before and after 0x3000, which your patch doesn't do.
Could we remove 0x3000 from IsSpace and/or NS_IsSpace, and rely on nsILineBreaker to return allowed break positions before and after 0x3000? That might be the cleanest way to fix this.
Created attachment 633794 [details] [diff] [review]
Okay, this doesn't hurt other parts calling the method.
see also https://tbpl.mozilla.org/?tree=Try&usebuildbot=1&rev=a41b43d0bea0