Unnecessary line-wrapping for no apparent reason

• Component: CSS
• Status: RESOLVED FIXED

[Chris Rebert]

Created attachment 253100 [details]
Screenshot showing incorrect rendering of example on Safari

Original Bootstrap bug: https://github.com/twbs/bootstrap/issues/15998
Safari Version: 8.0.6 (10600.6.3)

To reproduce:
1. Open http://jsfiddle.net/3mzzwbw7/ in Safari
2. Look at the "Chelesa EBALE" text

Expected result:
There is ample horizontal room for the text, so it should fit on a single line.

Actual result:
The text is line-wrapped across 2 lines ("Chelesa" on line 1 and "EBALE" on line 2).

Other browsers:
Both Chrome and Firefox render the text on a single line, as expected.

[Chris Rebert]

Created attachment 253101 [details]
Copy of JS Fiddle example

[Myles C. Maxfield]

<rdar://problem/20950962>

[Myles C. Maxfield]

Likely due to a disagreement with the fast and complex text codepaths

[Myles C. Maxfield]

Created attachment 253414 [details]
Reduction

[Myles C. Maxfield]

Reduction attached. The element is a float. My intuition says that RenderText::computePreferredLogicalWidths()'s measurement of the width of the text is somehow ending up smaller than BreakingContext::handleText()'s measurement.

[Myles C. Maxfield]

Simple line layout means that TextFragmentIterator is used instead of BreakingContext

[Myles C. Maxfield]

This is due to float precision. :(

The disagreement is between RenderText::computePreferredLogicalWidths() and BreakingContext::handleText(). The initial layout uses simple line layout, but when you interact with the page, RenderText::positionForPoint() uses the regular line layout (this subsequent layout is the problematic one).

The width of the float is calculated as the sum of the following items:

"Chelsea" => 64.998001
" " => 5.00400019
"EBALE" => 55.9980011
Total: 126.000000

Simple line layout agrees with this calculation.

However, when we get around to using regular line layout, the width of the text inside the float is calculated as the sum of the following items:

"Chelsea" => 64.998001
" EBALE" => 61.0020065
Total: 126.000008

Note that 126.0f + 1 ULP = 126.000008

[Simon Fraser (smfr)]

No longer occurs

[Chris Rebert]

Confirmed that this no longer repros as of r186963.
I've removed this from Bootstrap's Wall of Browser bugs:
https://github.com/twbs/bootstrap/pull/16842