feat(css): improve scss declaration modifier recovery

[denbezrukov]

Summary

This PR improves SCSS variable declaration modifier recovery in the CSS parser. The changes enable better error recovery when parsing malformed SCSS variable modifiers, allowing the parser to continue parsing subsequent valid modifiers even after encountering invalid tokens.

Test Plan

cargo test -p biome_css_parser

Docs

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Latest commit: 43246e5

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[coderabbitai]

Walkthrough

Reworks SCSS variable declaration parsing by introducing a dedicated modifier parsing workflow and recovery logic. Adds token sets and diagnostics for modifier handling, implements ScssVariableModifierList with end-of-list detection, replaces direct list parsing with parse_scss_variable_modifiers, and adds recovery for malformed/trailing modifier sequences (including a specific diagnostic for disallowed !important). Multiple SCSS tests were added to exercise duplicate-modifier recovery, missing-semicolon recovery, missing values, and namespace/selector boundary cases.

Possibly related PRs

• feat(css): support scss nesting declarations in declaration lists #9135: Modifies SCSS variable declaration parsing in the same source module and touches is_at_scss_declaration/parse_scss_declaration.
• chore(scss): cherry-picks #9149: Updates SCSS variable declaration parsing and related trailing-modifier behaviour in the same parser area.
• feat(scss): add basic SCSS declaration support and comments #8721: Earlier changes to SCSS variable-modifier parsing and list types that overlap with the new modifier-list/refactoring.

Suggested labels

L-SCSS

Suggested reviewers

• denbezrukov
• ematipico
• dyc3

🚥 Pre-merge checks | ✅ 2

✅ Passed checks (2 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly summarises the main change—improving SCSS variable declaration modifier recovery in the CSS parser.
Description check	✅ Passed	The description directly relates to the changeset, explaining the improvements to SCSS modifier error recovery and providing a clear test plan.

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[codspeed-hq]

Merging this PR will not alter performance

✅ 29 untouched benchmarks
⏩ 187 skipped benchmarks¹

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_{Comparing db/better-recovery-scss (43246e5) with main (cb4d7d7)}

Footnotes

1. 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 (2)

crates/biome_css_parser/src/syntax/scss/declaration/variable.rs (2)

159-161: Widen the !important error span to cover both tokens.

Right now the range is captured after bumping !, so diagnostics typically underline only important. Including ! as well would make the message match what users see.

Also applies to: 172-177

🤖 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/declaration/variable.rs` around lines
159 - 161, The diagnostic range for the `!important` error is captured after
consuming/bumping tokens, so the span excludes the leading `!`; update both
places where you call p.error(important_modifier_not_allowed(p, p.cur_range()))
followed by p.bump(T![important]) (and the other similar block) to capture the
range before consuming: call let span = p.cur_range() (or otherwise compute the
span that includes the `!` token) and pass that span into
important_modifier_not_allowed when calling p.error, then proceed to bump the
tokens (p.bump(T![bang]) / p.bump(T![important]) as needed) so the error
underline covers both `!` and `important`.

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109-112: Recovered modifiers placed outside the modifier list reduce accessor convenience.

Line 110 finalises SCSS_VARIABLE_MODIFIER_LIST before recover_scss_variable_modifier_tail() runs on line 111. Recovered modifiers parsed in the tail loop become sibling nodes rather than list children, so callers using declaration.modifiers() will miss them. This weakens the API ergonomics for traversing all modifiers in well-formed declarations that recover from malformed tokens.

Consider incorporating recovered modifiers into the list marker's scope during recovery to preserve CST structure coherence.

🤖 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/declaration/variable.rs` around lines
109 - 112, The recovered modifiers are being finalized outside the
SCSS_VARIABLE_MODIFIER_LIST because ScssVariableModifierList.parse_list(p)
completes before recover_scss_variable_modifier_tail(p) runs; change
parse_scss_variable_modifiers so recovery happens while the list marker is still
open — either call recover_scss_variable_modifier_tail from inside
ScssVariableModifierList.parse_list or move the list finalization to after
recovery so recovered nodes become children of SCSS_VARIABLE_MODIFIER_LIST and
remain visible to callers using declaration.modifiers().

🤖 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/declaration/variable.rs`:
- Around line 159-161: The diagnostic range for the `!important` error is
captured after consuming/bumping tokens, so the span excludes the leading `!`;
update both places where you call p.error(important_modifier_not_allowed(p,
p.cur_range())) followed by p.bump(T![important]) (and the other similar block)
to capture the range before consuming: call let span = p.cur_range() (or
otherwise compute the span that includes the `!` token) and pass that span into
important_modifier_not_allowed when calling p.error, then proceed to bump the
tokens (p.bump(T![bang]) / p.bump(T![important]) as needed) so the error
underline covers both `!` and `important`.
- Around line 109-112: The recovered modifiers are being finalized outside the
SCSS_VARIABLE_MODIFIER_LIST because ScssVariableModifierList.parse_list(p)
completes before recover_scss_variable_modifier_tail(p) runs; change
parse_scss_variable_modifiers so recovery happens while the list marker is still
open — either call recover_scss_variable_modifier_tail from inside
ScssVariableModifierList.parse_list or move the list finalization to after
recovery so recovered nodes become children of SCSS_VARIABLE_MODIFIER_LIST and
remain visible to callers using declaration.modifiers().

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📥 Commits

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📒 Files selected for processing (1)

• crates/biome_css_parser/src/syntax/scss/declaration/variable.rs