[css-variables-1] Short-circuiting var(), attr(), env()

[andruud]

WebKittens

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Title of the proposal

[css-variables-1] Short-circuiting var(), attr(), env()

URL to the spec

https://drafts.csswg.org/css-variables/#replace-a-var-function

URL to the spec's repository

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Issue Tracker URL

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Explainer URL

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TAG Design Review URL

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Mozilla standards-positions issue URL

https://github.com/mozilla/standards-positions/issues/1224

WebKit Bugzilla URL

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Radar URL

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Description

In https://github.com/w3c/csswg-drafts/issues/11500, the CSSWG resolved to make all substitution functions short-circuiting, meaning that we don't evaluate branches we don't care about (not even to look for cycles). In the issue, we were not sure if we could actually apply this resolution to var() due to certain tricks that rely on the existing behavior. However, my compat investigation did not find any evidence of this trick being in widespread use, and I consider this a safe change to make.