2061083 - [css-typed-arithmetic] Fix infinities escaping a calculation when typed arithmetic is involved

Status: RESOLVED FIXED

(Core :: CSS Parsing and Computation, defect)

Description

[Sajid Anwar [:sajidanwar]]

In the typed arithmetic patch in Bug 1827404, there was a failing case in typed_arithmetic.html related to escaping infinities. From my comment:

One test (margin-left: calc(1px * 10em / -0em)) which is resolving to a value of -Infinity but which isn't being clamped to a finite value like it should.

Comment 1

[Sajid Anwar [:sajidanwar]]

Discovered that this isn't actually the result of typed arithmetic, but rather a longstanding bug where infinity can escape when a length calc expression simplifies to an infinite value at computed-value-time. I downloaded Firefox 131 to be sure that this was present before my other calc changes, and I can reproduce the issue:

document.body.style = 'margin-left: calc(10em / sign(1em - 16px))';
getComputedStyle(document.body).getPropertyValue('margin-left') 
// "Infinitypx"

This doesn't happen for something like margin-left: calc(10em / 0), which simplifies to a single length leaf node with an infinite em value. That gets clamped away to a finite value when the em is replaced with the computed font size.

Fix here is to perform the finite clamping here.

Comment 2

[Sajid Anwar [:sajidanwar]]

Attachment: Bug 2061083 - Clamp infinite length-percentage calc expressions. r=#style

Comment 3

[Pulsebot]

Pushed by [e-mail]:
https://github.com/mozilla-firefox/firefox/commit/9165316d6b72
https://hg.mozilla.org/integration/autoland/rev/f67df042f451
Clamp infinite length-percentage calc expressions. r=firefox-style-system-reviewers,emilio

Comment 4

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

Created web-platform-tests PR https://github.com/web-platform-tests/wpt/pull/61812 for changes under testing/web-platform/tests

Comment 5

[Sandor Molnar[:smolnar]]

https://hg.mozilla.org/mozilla-central/rev/f67df042f451

Comment 6

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

Upstream PR merged by moz-wptsync-bot