Intent to Deprecate and Remove: Unitless Zero Angles in offset-rotate

[Eric Willigers]

Primary eng email

ericwi...@chromium.org

 

Summary

The offset-rotate property, with syntax '[ auto | reverse ] || <angle>', will no longer accept unitless '0' literals as angle values.

 

Offset shorthand values 'path(...) 0' and 'path(...) auto 0' will no longer be ambiguous.

 

Motivation

Allowing unitless 0 for both lengths and angles led to an ambiguity in the offset shorthand. This has been resolved by CSS forbidding unitless 0 angles in general, with two exceptions due to legacy content (transform, linear-gradient).

 

Interoperability and Compatibility Risk

 

Edge: offset-rotate not supported

Firefox: offset-rotate not supported

Safari: offset-rotate not supported

 

The offset properties currently have low usage, so risk is minimal.

 

Note that Blink currently also supports unitless 0 angles in the hue-rotate function for the CSS filter property.  A use counter has recently been added; when M60 reaches stable we will receive data for either a new deprecation and removal discussion, or for a proposal to the CSS Working Group to support unitless zero angles in filter's hue-rotate as a third exception.

 

 

Alternative implementation suggestion for web developers

Web developers can use '0deg' instead of '0' when specifying angles in CSS.

 

Usage information from UseCounter

 

The offset properties are only having an effect when offset-path is not 'auto' 0.000%

 

offset-rotate has low usage. offset-rotate 0.017%

 

Many of these pages may be explicitly setting all properties to their initial values.

 

Use counters for unitless zero angles were added in M60:

offset-rotate (no data yet)

filter  hue-rotate (no data yet)

 

OWP launch tracking bug

https://bugs.chromium.org/p/chromium/issues/detail?id=728027

 

Entry on the feature dashboard

No entry, this is a small change.

 

Requesting approval to remove too?

Intend to show a deprecation warning, with support to be removed in M62.

 

With M62 we will pass the web platform test

/css/motion-1/parsing/offset-rotate-parsing-invalid.html

 

[Rick Byers]

I checked the internal UseCounter data for M60 (dev channel)

CSSOffsetInEffect:  <0.00001% (similar for past milestones)

UnitlessZeroAngleOffsetRotate: 0 (except for one day where there was exactly one hit - probably you testing?) But this has only be shipping in dev channel since yesterday (60.0.3112.7).

Anyway, given this isn't supported elsewhere, is a new API, and is at most 0.00001% of page views I'd say this is completely safe and doesn't even need a deprecation period.  LGTM1 to just remove now if you like (or if you prefer to deprecate and remove in M62 that's OK with me too - just seems like overkill).

Rick

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[Eric Willigers]

Sounds good to me. I can remove now.

[Philip Jägenstedt]

LGTM2 to remove immediately.

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[Chris Harrelson]

LGTM3

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