Support attribute selectors in stylex.when and conditional styles #1449
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mellyeliu
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Jan 13, 2026
...s/@stylexjs/babel-plugin/src/shared/preprocess-rules/__tests__/flatten-raw-style-obj-test.js
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"Styling-agnostic" react component systems, such as base-ui, expose state based styling hooks through the use of dom element attributes. Actually listening to these in StyleX, while possible through usage of the `:is()` psedudoselector, is overly verbose and uncessary. This diff addresses this by adding support for attribute selectors in stylex.when calls and conditional styles. ### Motivation - Allow `stylex.when` and conditional style objects to accept attribute selectors (including value-matching forms) rather than only attribute-existence markers. - Treat attribute selectors like pseudo-classes in the preprocessing and validation pipeline so downstream CSS generation remains correct. - Surface attribute-selector usage in types and docs so consumers get proper editor/compile-time guidance. ### Description - Accept keys starting with `[` in validation and preprocessing by updating `basic-validation.js`, `flatten-raw-style-obj.js`, and `PreRule.pseudos` to treat attribute selectors like pseudos. - Extend `when` helpers to accept attribute selectors by adding a `WhenSelector` union, updating `validatePseudoSelector` to allow `[`...`]`, and applying the selector when building `:where` / `:has` clauses in `when.js`. - Update Flow/TypeScript definitions in `StyleXTypes.js` and `StyleXTypes.d.ts` to permit attribute selectors for `stylex.when.*` signatures. - Add/update tests and documentation to use value-based attribute selectors (tests and snapshots in `transform-stylex-when-test.js` and `flatten-raw-style-obj-test.js`, and docs in `when.mdx`). ### Testing - Ran `yarn workspace @stylexjs/babel-plugin test -- transform-stylex-when-test --updateSnapshot`, where the test suite passed and snapshots were updated but the overall command returned non-zero due to global coverage thresholds being unmet. - The changed test file `transform-stylex-when-test.js` passed (all tests green) and snapshots were updated successfully. - Ran `npm run lint`, which completed successfully. - Pre-commit formatting/lint hooks ran as part of the commit and completed successfully.
mellyeliu
approved these changes
Jan 14, 2026
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"Styling-agnostic" react component systems, such as base-ui, expose state based styling hooks through the use of dom element attributes. Actually listening to these in StyleX, while possible through usage of the
:is()psedudoselector, is overly verbose and uncessary. This diff addresses this by adding support for attribute selectors in stylex.when calls and conditional styles.Motivation
stylex.whenand conditional style objects to accept attribute selectors (including value-matching forms) rather than only attribute-existence markers.Description
[in validation and preprocessing by updatingbasic-validation.js,flatten-raw-style-obj.js, andPreRule.pseudosto treat attribute selectors like pseudos.whenhelpers to accept attribute selectors by adding aWhenSelectorunion, updatingvalidatePseudoSelectorto allow[...], and applying the selector when building:where/:hasclauses inwhen.js.StyleXTypes.jsandStyleXTypes.d.tsto permit attribute selectors forstylex.when.*signatures.transform-stylex-when-test.jsandflatten-raw-style-obj-test.js, and docs inwhen.mdx).Testing
yarn workspace @stylexjs/babel-plugin test -- transform-stylex-when-test --updateSnapshot, where the test suite passed and snapshots were updated but the overall command returned non-zero due to global coverage thresholds being unmet.transform-stylex-when-test.jspassed (all tests green) and snapshots were updated successfully.npm run lint, which completed successfully.