[wook10]

Fixes #1595

Summary

With a prefix (e.g. @import "tailwindcss" prefix(tw)), the theme variables Tailwind emits are prefixed: --tw-color-red-500, --tw-font-sans, etc. Completions inside var(…) still suggested the unprefixed names, which don't exist in the output CSS.

var(…), theme(…) and --theme(…) all get their items from themeKeyCompletions(), which uses resolveKnownThemeKeys(). That function strips the prefix, which is right for theme(…) / --theme(…) but not for var(…).

This passes the helper name to themeKeyCompletions() and, for var(…) only, adds the prefix back to the label. Values and color previews are still resolved from the unprefixed key. Without a prefix the labels are unchanged.

Test plan

Added two tests to tests/completions/completions.test.js:

• var(…) with prefix(tw) suggests --tw-font-sans and --tw-color-custom (still shown as a color), and nothing unprefixed. Fails without this change (--font-sans is suggested instead).
• --theme(…) with prefix(tw) still suggests unprefixed keys. Passes before and after.

cd packages/tailwindcss-language-server
pnpm exec vitest run tests/completions/completions.test.js -t "Theme key"

The whole tests/completions/completions.test.js file passes (48 tests). I also ran vitest run in packages/tailwindcss-language-service (734 tests pass) and tsc --noEmit there (no errors).

[greptile-apps]

Confidence Score: 5/5

[Medium impact] The PR appears safe to merge.

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