fix: leave relative-color slash operations for the browser - #4529
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Under --math=always, rgb(from ... r g b / 0.9) parsed the slash as Keyword / Dimension and threw before rgb() could pass the call through. Fixes less#4528
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Included review availability: Your plan provides up to 10 included reviews per hour; 8 remain after this review. 📝 WalkthroughWalkthroughLess now preserves CSS Color Level 5 relative ChangesRelative color support
Priority: ➖ Normal Estimated code review effort: 3 (Moderate) | ~20 minutes Severity of issue fixed: Medium Merge Risk: ⚪ Minimal · up to Relative CSS color expressions now pass through for browser evaluation under math-always while classic Less color construction remains evaluated. The added coverage includes relative colors and invalid non-color keyword operations, leaving no identified merge-blocking risk. 🚥 Pre-merge checks | ✅ 4 | ❌ 1❌ Failed checks (1 warning)
✅ Passed checks (4 passed)
Full details: Docstring CoverageExplanation Docstring coverage is 33.33% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 3 functions across 2 files. (4 skipped: 4 unsupported.)
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 The PR is not yet safe to merge because its global Keyword/Call fallback silently accepts unrelated invalid Less arithmetic. Findings
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| if (isBrowserOperand(a) || isBrowserOperand(b)) { | ||
| return new Operation(this.op, [a, b], this.isSpaced); |
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Under math: always, ordinary arithmetic such as width: (auto + 1px) now reaches this fallback because auto is a Keyword. Less emits the invalid CSS auto + 1px instead of reporting Operation on an invalid type. Because this check applies to every keyword and every operator, it changes unrelated Less arithmetic rather than only deferring the relative-color slash operation.
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(auto + 1px) never reaches Operation.eval. It is a parse error.
The parser only treats [lchrgbs] as colorOperand (from #4346). auto, inherit, and friends are not operations, so this fallback could not emit auto + 1px.
The Keyword check is now limited to relative-color channel names. Call (var()) is unchanged. Added a math-always fixture for auto - 1px / hidden / 2 (not operations) and b / 0.9 outside a color function (is an operation, still pass-through).
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You're right. My original concern does not apply: (auto + 1px) cannot reach Operation.eval() because the parser only creates operations for the relevant color operands, so this fallback cannot silently emit it. The narrowed Keyword check is limited to relative-color channel names, while the Call behavior remains necessary for var(). The added fixtures also cover the ordinary keywords and standalone channel slash cases. I’m withdrawing this finding; no blocking issue remains.
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Inline comments:
In `@packages/less/lib/less/tree/operation.js`:
- Around line 22-25: Update isBrowserOperand so it does not classify every
Keyword as browser-resolved: restrict keyword handling to relative-color channel
keywords or propagate relative-color context into operation evaluation. Preserve
prior invalid-operation validation for expressions such as width: (10px + auto),
and add a regression test outside a color function.
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packages/less/lib/less/functions/color.jspackages/less/lib/less/tree/operation.jspackages/test-data/tests-config/math-always/relative-color-alpha.csspackages/test-data/tests-config/math-always/relative-color-alpha.lesspackages/test-data/tests-unit/color-functions/modern.csspackages/test-data/tests-unit/color-functions/modern.less
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`auto + 1px` is a parse error, not an eval error: the parser only treats [lchrgbs] as colorOperands. Restrict the Keyword fallback to those channel names so unrelated identifiers stay untouched. Fixtures now use var(--surface).
1 participant
What:
rgb(from var(--x) r g b / 0.9)throwsOperation on an invalid typewhen--math=always. The slash is a LessOperationon the channel keywordb.functionCallerevaluates arguments first, sorgb()never seesfrom.This leaves the operation in the tree when an operand is a Keyword (channel names) or a Call (
var()).rgb()andhsl()also return nothing when the first argument isfrom, so the call is printed as CSS.A hex origin has no
var(), so this is not the same as #4480. Classicrgb(17, 34, 51)still compiles to a hex.Why:
Relative color with an alpha slash is valid CSS Color Level 5. Default
parens-divisionalready leaves/alone. Builds that still usemath: 'always'(including less-loader) die on this.Fixes #4528
Checklist:
Summary by CodeRabbit
New Features
rgb(from ...),hsl(from ...), andoklch(from ...).light-dark().Tests