1559276 - Retiring support for 3-valued <position> (excluding background)

Status: RESOLVED FIXED

(Core :: CSS Parsing and Computation, enhancement, P3)

Description

[Boris Chiou [:boris]]

Based on spec issue 2140, the 3-valued positions shouldn't be accepted, except for background. Blink retires the support in Chrome 68, and they added some tests into wpt [1][2][3]. Perhaps we should update the parser of these properties (or values::generics::position::Position type).

Besides, the spec, https://drafts.csswg.org/css-values-4/#position, mention:

Note: The background-position property also accepts a three-value syntax. This has been disallowed generically because it creates parsing ambiguities when combined with other length or percentage components in a property value.

[1] <object-position>
[2] <perspective-origin>
[3] <offset-anchor>

Comment 1

[Emilio Cobos Álvarez (:emilio)]

Perhaps we should update the parser of these properties (or values::generics::position::Position type).

Sounds good, moving the current parse implementation to something like parse_three_value or parse_legacy, then implementing a simpler parse seems reasonable.

Comment 2

[Boris Chiou [:boris]]

Cool. Thanks for the suggestion. This should be easy to fix.

Comment 3

[Boris Chiou [:boris]]

Attachment: Bug 1559276 - Part 1: Avoid using 3 valued syntax for position.

Update the existing reftests to not use 3 valued syntax.

I run the script to update the syntax in
layout/reftests/w3c-css/submitted/images3/*,
layout/reftests/xul/*, and
layout/reftests/webm-video/*:

function rename() {
    find layout/reftests/\
         -type f\
         ! -path "./obj*"\
         ! -path "./.git"\
         ! -path "./.hg"\
         \( -name "*.html" -or\
            -name "*.xul" \)\
            -exec sed -i -e "s/$1/$2/g" "{}" \;
}

rename "object-position: top 3px center" "object-position: top 3px left 50%"
rename "object-position: center right 25%" "object-position: top 50% right 25%"

For others, I just manually update them.

Comment 4

[Boris Chiou [:boris]]

Attachment: Bug 1559276 - Part 2: Retire the support for 3-valued syntax for position.

According to this resolved spec issue:
https://github.com/w3c/csswg-drafts/issues/2140,
we retire the 3-valued <position> on

1. object-position
2. perspective-origin,
3. mask-position
4. circle() and ellipse()
   , but still keep the support for background-position.

Comment 5

[Boris Chiou [:boris]]

try: https://treeherder.mozilla.org/#/jobs?repo=try&revision=c0f041570d145ae268e4b681274279d724ff3640

Comment 6

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/7018488ca120
Part 1: Avoid using 3 valued syntax for position. r=emilio
https://hg.mozilla.org/integration/autoland/rev/6ec2809da4e3
Part 2: Retire the support for 3-valued syntax for position. r=emilio

Comment 7

[Web Platform Test Sync Bot [:wpt-sync] (Matrix: #interop:mozilla.org)]

Created web-platform-tests PR https://github.com/web-platform-tests/wpt/pull/17777 for changes under testing/web-platform/tests

Comment 8

[Cosmin Sabou [:CosminS]]

https://hg.mozilla.org/mozilla-central/rev/7018488ca120
https://hg.mozilla.org/mozilla-central/rev/6ec2809da4e3

Comment 9

[David Baron :dbaron: (⌚️UTC-4, no longer working on Mozilla)]

CSS WPT import at https://github.com/web-platform-tests/wpt/pull/17784

Comment 10

[Web Platform Test Sync Bot [:wpt-sync] (Matrix: #interop:mozilla.org)]

Upstream PR merged

Comment 11

[Kohei Yoshino]

Posted site compatibility note: https://www.fxsitecompat.dev/en-CA/docs/2019/3-valued-css-position-is-no-longer-supported-except-for-background-position/

Comment 12

[Boris Chiou [:boris]]

(In reply to Kohei Yoshino [:kohei] (Bugzilla UX) (FxSiteCompat) from comment #11)

Posted site compatibility note: https://www.fxsitecompat.dev/en-CA/docs/2019/3-valued-css-position-is-no-longer-supported-except-for-background-position/

Looks great. Thanks for this.

Comment 14

[Chris Mills [:cmills]]

Documented as per https://github.com/mdn/sprints/issues/2084

Comment 15

[Boris Chiou [:boris]]

Attachment: Bug 1559276 - Drop stale WPT annotation .ini files after vendor-imports was synced.

Comment 16

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/5f78ce29be79
Drop stale WPT annotation .ini files after vendor-imports was synced. r=dholbert

Comment 17

[Stefan Hindli [:stefan_hindli]]

https://hg.mozilla.org/mozilla-central/rev/5f78ce29be79