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Rename/adjust "Rulesets cannot be evaluated on a property" error message #4558
Description
The error added in #4478 for when a mixin call is used as a property value (e.g. mixin called without specifying which variable to pull out as the value) has a confusingly worded "Rulesets cannot be evaluated on a property" error message. I noted this on the day the pull request was merged back in September.
... the error "Rulesets cannot be evaluated on a property" is still a pretty unsatisfyingly vague error message- I don't know what that even means. I would hope for a more explicit error message instead of reusing the existing one in that branch, like "Assigning mixin result to property requires a return value lookup" etc.
Activity
ThiagoMirandaLiotto commentedon Oct 23, 2026
Hi! I'm Thiago, a student at the technical school of Instituto Politécnico Modelo (Argentina), and I'd like to work on this issue as part of a school open-source contribution assignment.
In
packages/less/lib/less/tree/declaration.jsthe same check covers two cases: a detached ruleset used as a property value (a: @a;) and a mixin call used as a property value (color: #rgbify(#fff);), so both get the same message.My proposal is to split it: keep the current message for detached rulesets, and for mixin calls throw a more explicit one, something like "A mixin call cannot be used as a property value without a lookup, e.g.
#rgbify(#fff)[@rgb]", and update themixin-as-valueerror test. Does that sound good? I'm happy to change the wording if you prefer something else.