419100 - 'direction' override for 'auto' margins on absolutely positioned elements happens when only one margin is auto

Status: RESOLVED FIXED

(Core :: Layout: Positioned, defect)

Description

[David Baron :dbaron: (⌚️UTC-5, no longer working on Mozilla)]

In CSS 2.1 sections 10.3.7 and 10.3.8, 'direction' beats 'auto' margins only when both margins are 'auto'.  We implement this behavior when only one margin is 'auto'.  Safari 3 gets it right.  (Opera and IE don't; Opera 9.25 doesn't implement the direction-override at all; IE 7 doesn't implement auto margins.)

Steps to reproduce: load http://dbaron.org/css/test/2008/abs-pos-auto-margin

Expected results:
 1. direction:ltr, wide, margin-left:auto should overflow the yellow box to the right
 2. direction:rtl, wide, margin-right:auto should overflow the yellow box to the left

Actual results:
 1. it overflows to the left
 2. it overflows to the right

This should be a simple fix in nsHTMLReflowState::InitAbsoluteConstraints.

Comment 1

[David Baron :dbaron: (⌚️UTC-5, no longer working on Mozilla)]

I actually hard-coded the buggy behavior described in this bug into the reference renderings in layout/reftests/box-properties/abspos-non-replaced-width-offset-margin-ref.html and layout/reftests/box-properties/abspos-replaced-width-offset-margin-ref.html ; these should be fixed when we fix this bug.

Comment 2

[Anders G. Jørgensen]

Is this still a bug?

Comment 3

[David Baron :dbaron: (⌚️UTC-5, no longer working on Mozilla)]

The behavior described is still present; I haven't checked whether the spec has changed in the last 18 months.

Comment 4

[David Baron :dbaron: (⌚️UTC-5, no longer working on Mozilla)]

Attachment: patch

This fixes the two tests mentioned above (which are also in the CSS 2.1 test suite, with no passing implementations, although every implementation I've checked fails differently).

I still need to (a) write tests for the vertical case (b) figure out whether that FIXME I added in the vertical case should result in a spec change or a code change.

Comment 5

[David Baron :dbaron: (⌚️UTC-5, no longer working on Mozilla)]

https://hg.mozilla.org/projects/birch/rev/52512f6d14c9

Comment 6

[David Baron :dbaron: (⌚️UTC-5, no longer working on Mozilla)]

https://hg.mozilla.org/mozilla-central/rev/52512f6d14c9

Comment 7

[Boris Zbarsky [:bzbarsky]]

> I still need to (a) write tests for the vertical case (b) figure out whether that FIXME I
> added in the vertical case should result in a spec change or a code change.

Given that IE and Blink at least are following the spec, I'd say code change.  That's happening in bug 1100073.

Comment 8

[Gérard Talbot]

(In reply to David Baron [:dbaron] ⌚️UTC-7 (review requests must explain patch) from comment #4)
> This fixes the two tests mentioned above (which are also in the CSS 2.1 test
> suite, with no passing implementations, although every implementation I've
> checked fails differently).

http://test.csswg.org/suites/css2.1/nightly-unstable/html4/abspos-non-replaced-width-margin-000.htm

http://test.csswg.org/suites/css2.1/nightly-unstable/html4/reference/abspos-non-replaced-width-margin-000-ref.htm

Firefox 46 and Chrome 50 pass these 2 tests.