feat(css): add support for SCSS binary expressions in lexer and parser by denbezrukov · Pull Request #9343 · biomejs/biome

denbezrukov · 2026-03-05T13:17:19Z

Summary

SCSS expressions with tight signed numeric tokens were parsed inconsistently in binary contexts
(for example 1+2, 10+10px, 10+10%).

This PR updates SCSS expression parsing so signed numeric-like tokens are handled as binary
operators where appropriate, and adds targeted parser/formatter coverage for these cases,
including unary/binary combinations like 1 - -2, 1 + -3, and 1 + +5.

Test Plan

Ran and passed:

cargo test -p biome_css_parser
cargo test -p biome_css_formatter

changeset-bot · 2026-03-05T13:17:24Z

⚠️ No Changeset found

Latest commit: 1699f0c

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coderabbitai · 2026-03-05T13:24:09Z

No actionable comments were generated in the recent review. 🎉

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📥 Commits

Reviewing files that changed from the base of the PR and between 32e1c51 and 1699f0c.

📒 Files selected for processing (2)

crates/biome_css_parser/src/syntax/property/mod.rs
crates/biome_css_parser/src/syntax/scss/expression/mod.rs

Walkthrough

Adds SCSS-specific re-lexing and parser changes to treat leading +/- in expressions as standalone SCSS operators and to re-lex signed numeric literals. A ScssExpression variant was added to CssReLexContext and CssLexer::consume_scss_expression_token was introduced; the parser gains re_lex_signed_numeric_as_scss_operator, report_and_bump_scss_ellipsis, and uses parse_generic_component_value for generic delimiters. A new SCSS test/spec exercising many signed numeric/operator spacing variants was added, and is_at_generic_delimiter visibility was widened.

Possibly related PRs

feat(css): add unary expression parsing #9093: Implements generic unary/signed +/- expression parsing/formatting—overlaps operator/token handling in the expression pipeline.
feat(css): add SCSS unary and binary expression #9222: Modifies SCSS expression parsing and lexer re-lexing for signed numeric/unary/binary operator behaviour—closely related at lexer/parser code paths.

Suggested labels

L-SCSS

Suggested reviewers

ematipico

🚥 Pre-merge checks | ✅ 2

✅ Passed checks (2 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately summarizes the main change: adding SCSS binary expression support in lexer and parser for handling tight signed numeric tokens.
Description check	✅ Passed	The description clearly relates to the changeset, explaining the problem (inconsistent parsing of signed numeric tokens in SCSS), the solution, and test coverage.

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✨ Finishing Touches

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🧪 Generate unit tests (beta)

Create PR with unit tests
Post copyable unit tests in a comment
Commit unit tests in branch db/binary-expr-fix

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codspeed-hq · 2026-03-05T13:26:23Z

Merging this PR will degrade performance by 7.56%

❌ 1 regressed benchmark
✅ 28 untouched benchmarks
⏩ 187 skipped benchmarks¹

⚠️ Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Benchmark	`BASE`	`HEAD`	Efficiency
❌	`pure_9395922602181450299.css[uncached]`	4 ms	4.3 ms	-7.56%

_{Comparing db/binary-expr-fix (1699f0c) with main (20a64c4)}

187 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. ↩

coderabbitai

🧹 Nitpick comments (1)

crates/biome_css_parser/src/syntax/scss/expression/mod.rs (1)

271-281: Consider adding a brief doc comment.

The function works correctly, but a short rustdoc comment would clarify its purpose and side-effect nature for future maintainers.

📝 Suggested doc comment

+/// Re-lexes signed numeric tokens (e.g., `+5`, `-10px`) as separate operator
+/// and value tokens when in a binary expression context.
 #[inline]
 fn re_lex_signed_numeric_as_scss_operator(p: &mut CssParser) {

Based on learnings: "Use inline rustdoc documentation for rules, assists, and their options".

🤖 Prompt for AI Agents

Verify each finding against the current code and only fix it if needed.

In `@crates/biome_css_parser/src/syntax/scss/expression/mod.rs` around lines 271 -
281, Add a short rustdoc comment above the function
re_lex_signed_numeric_as_scss_operator explaining that it checks the current
token for a numeric literal or dimension that begins with '+' or '-' and, if so,
calls p.re_lex with CssReLexContext::ScssExpression to treat the sign as a SCSS
operator (note the side effect of mutating the parser state via
CssParser::re_lex). Keep it concise (one or two sentences), mention the
conditions checked (CSS_NUMBER_LITERAL or is_at_any_dimension) and the mutation
side effect.

🤖 Prompt for all review comments with AI agents

Verify each finding against the current code and only fix it if needed.

Nitpick comments:
In `@crates/biome_css_parser/src/syntax/scss/expression/mod.rs`:
- Around line 271-281: Add a short rustdoc comment above the function
re_lex_signed_numeric_as_scss_operator explaining that it checks the current
token for a numeric literal or dimension that begins with '+' or '-' and, if so,
calls p.re_lex with CssReLexContext::ScssExpression to treat the sign as a SCSS
operator (note the side effect of mutating the parser state via
CssParser::re_lex). Keep it concise (one or two sentences), mention the
conditions checked (CSS_NUMBER_LITERAL or is_at_any_dimension) and the mutation
side effect.

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📥 Commits

Reviewing files that changed from the base of the PR and between 74f7836 and b3fac2f.

📒 Files selected for processing (1)

crates/biome_css_parser/src/syntax/scss/expression/mod.rs

…delimiter function

#9343) Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>

feat(css): add support for SCSS binary expressions in lexer and parser

74f7836

github-actions Bot added A-Parser Area: parser A-Formatter Area: formatter L-CSS Language: CSS and super languages labels Mar 5, 2026

[autofix.ci] apply automated fixes

b3fac2f

coderabbitai Bot reviewed Mar 5, 2026

View reviewed changes

denbezrukov added 2 commits March 5, 2026 16:10

feat(css): add generic delimiter handling in SCSS parser

32e1c51

refactor(css): replace SCSS_GENERIC_DELIMITER_SET with is_at_generic_…

1699f0c

…delimiter function

denbezrukov merged commit 4509fc6 into main Mar 5, 2026
15 of 16 checks passed

denbezrukov deleted the db/binary-expr-fix branch March 5, 2026 17:51

ematipico pushed a commit that referenced this pull request Mar 6, 2026

feat(css): add support for SCSS binary expressions in lexer and parser (

e8c9f81

#9343) Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>

coderabbitai Bot mentioned this pull request Mar 9, 2026

feat(css): add support for sass() in SCSS conditional expressions #9414

Merged

Netail added the L-SCSS label Mar 9, 2026

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feat(css): add support for SCSS binary expressions in lexer and parser#9343

feat(css): add support for SCSS binary expressions in lexer and parser#9343
denbezrukov merged 4 commits into
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denbezrukov commented Mar 5, 2026

Summary

Test Plan

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Walkthrough

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Merging this PR will degrade performance by 7.56%

Performance Changes

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