fix(css): add missing CSS functions to noUnknownFunction by andre-lmarinho · Pull Request #8926 · biomejs/biome

andre-lmarinho · 2026-01-31T22:08:19Z

Summary

This PR extends the noUnknownFunction CSS linter rule to recognize five additional modern CSS functions that were previously being flagged as unknown:

contrast-color() - Calculates a contrasting color value
dynamic-range-limit-mix() - Mixes dynamic range limits for HDR content
progress() - Progress notation for scroll-driven animations
superellipse() - Defines corner shapes using superellipse curves

Motivation: Similar to PR #8924 which added sibling-count() and sibling-index(), these are valid CSS functions defined in various CSS specification modules (CSS Color Module Level 5, CSS Values and Units Module Level 5, CSS Borders Module Level 4). Currently, Biome incorrectly reports these as unknown functions, causing false positives in projects using modern CSS features.

Related: This extends the work from #8920 to cover additional CSS functions that have emerged in recent specifications.

Browser Compatibility

Function	Status	Chrome	Firefox	Safari	Experimental
`contrast-color()`	Standard Track	❌	✅ 146+	✅ 26+	No
`dynamic-range-limit-mix()`	Standard Track	✅ 136+	❌	❌	Yes
`progress()`	Standard Track	✅ 138+	❌	✅ 26+	No
`superellipse()`	Standard Track	✅ 139+	❌	❌	Yes

Note: While some of these functions are marked as experimental and have limited browser support, they are part of official CSS specifications. Including them in Biome's function list allows developers working with cutting-edge CSS features or progressive enhancement to avoid false positives in linting.

Documentation

contrast-color() - CSS Color Module Level 5
dynamic-range-limit-mix() - CSS Color HDR Module
progress() - CSS Values and Units Module Level 5
superellipse() - CSS Borders Module Level 4

Changeset

A changeset has been created in .changeset/brave-lions-smile.md.

Test Plan

Added test cases for all five functions in valid.css:

a { color: contrast-color(#000); }
a { color: dynamic-range-limit-mix(standard 50%, high 50%); }
a { animation-delay: progress(scroll() from 0% to 100%); }
a { clip-path: superellipse(50% 50%, 80% 80%, 2.5); }

The functions were added to the FUNCTION_KEYWORDS array in keywords.rs in alphabetical order, following the existing pattern.

When tests are run, these functions should no longer trigger the noUnknownFunction diagnostic.

Docs

No additional documentation needed - this is an additive change to the existing noUnknownFunction rule's keyword list. The rule behavior remains unchanged; it simply recognizes additional valid CSS functions.

Disclaimer!

This PR was created with AI assistance (Claude Code). Claude Code was used to explore the repository structure and review existing CSS functions. The results were then manually validated against the official MDN documentation to confirm accuracy and identify gaps.

changeset-bot · 2026-01-31T22:08:24Z

🦋 Changeset detected

Latest commit: 9b6f999

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 13 packages

Name	Type
@biomejs/biome	Patch
@biomejs/cli-win32-x64	Patch
@biomejs/cli-win32-arm64	Patch
@biomejs/cli-darwin-x64	Patch
@biomejs/cli-darwin-arm64	Patch
@biomejs/cli-linux-x64	Patch
@biomejs/cli-linux-arm64	Patch
@biomejs/cli-linux-x64-musl	Patch
@biomejs/cli-linux-arm64-musl	Patch
@biomejs/wasm-web	Patch
@biomejs/wasm-bundler	Patch
@biomejs/wasm-nodejs	Patch
@biomejs/backend-jsonrpc	Patch

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

coderabbitai · 2026-01-31T22:12:33Z

Walkthrough

Adds four CSS function names — contrast-color, dynamic-range-limit-mix, progress, and superellipse — to the FUNCTION_KEYWORDS constant in the Biome CSS analyser. Adds corresponding valid tests to noUnknownFunction and a changeset patch entry for the @biomejs/biome release note documenting recognition of these functions.

Possibly related PRs

biomejs/biome PR 8846: Modifies the same FUNCTION_KEYWORDS constant to recognise additional CSS functions.
biomejs/biome PR 8924: Extends FUNCTION_KEYWORDS and adds noUnknownFunction tests for new function names.

Suggested reviewers

ematipico
siketyan

🚥 Pre-merge checks | ✅ 2

✅ Passed checks (2 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately reflects the main change: adding missing CSS functions to the noUnknownFunction linter rule.
Description check	✅ Passed	The pull request description clearly explains the addition of four CSS functions to the noUnknownFunction rule, with motivation, browser compatibility, documentation links, and test cases.

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coderabbitai

Actionable comments posted: 1

🤖 Fix all issues with AI agents

In `@crates/biome_css_analyze/src/keywords.rs`:
- Around line 681-685: The FUNCTION_KEYWORDS array is out of alphabetical order:
the entry "if" must come before the "image", "image-rect", and "image-set"
entries to satisfy test_function_keywords_sorted; update the FUNCTION_KEYWORDS
definition by moving "if" so the list is alphabetically sorted (ensure the
symbol FUNCTION_KEYWORDS is updated accordingly).

…WORDS

codspeed-hq · 2026-01-31T22:20:58Z

CodSpeed Performance Report

Merging this PR will not alter performance

_{Comparing andre-lmarinho:fix/modern-css-functions (98f5421) with main (871b45e)}

Summary

✅ 29 untouched benchmarks
⏩ 126 skipped benchmarks¹

126 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

andre-lmarinho · 2026-01-31T22:39:08Z

Question for Reviewers

I noticed that adding tests for these five new functions increased the parser diagnostic count from 3 to 5 in the valid.css.snap snapshot:

-Note: The parser emitted 3 diagnostics which are not shown here.
+Note: The parser emitted 5 diagnostics which are not shown here.

This suggests that some of the new CSS functions I added may have syntax that the Biome CSS parser doesn't fully recognize yet. The functions themselves are now recognized by noUnknownFunction (which was the goal), but the parser emits additional diagnostics when parsing them.

Questions:

Is this acceptable, or should we only add functions that the parser can handle without emitting diagnostics?
Should I adjust the test cases to use simpler syntax that doesn't trigger parser diagnostics?
Alternatively, should we skip adding tests for functions that cause parser issues?

I'm happy to modify the PR based on your guidance. Let me know which approach you prefer.

ematipico · 2026-01-31T23:10:03Z

Are you really asking us questions via claude code? Damn, that's so demoralising...

We shouldn't increase the diagnostics, so make sure the parser is correct

ematipico

Blocking, since the issue is in the parser, not the linter only

new info

andre-lmarinho · 2026-01-31T23:57:47Z

I removed the functions both from the tests and from the keyword list, so there’s nothing in the codebase without proper parser support / coverage. Do you want me to document this function as an Issue?

ematipico · 2026-02-01T07:30:02Z

Why was if added?

andre-lmarinho · 2026-02-01T12:08:35Z

It's a valid CSS function. Doc | compatibility

But, tbh I'm not sure that this was the right way to implement it. Rust is not my expertise, just trying to help here.

fix(css): add missing CSS functions to noUnknownFunction

ee94c64

github-actions Bot added A-Linter Area: linter L-CSS Language: CSS and super languages labels Jan 31, 2026

coderabbitai Bot reviewed Jan 31, 2026

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Comment thread crates/biome_css_analyze/src/keywords.rs

fix(css): correct alphabetical order of 'if' function in FUNCTION_KEY…

98f5421

…WORDS

dyc3 previously approved these changes Jan 31, 2026

View reviewed changes

ematipico requested changes Jan 31, 2026

View reviewed changes

fix(css): remove if function due to parser limitations

9b6f999

andre-lmarinho closed this Feb 1, 2026

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fix(css): add missing CSS functions to noUnknownFunction#8926

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