Cold start performance improvements

[smnbbrv]

Summary

Hi guys, thanks for you great work!

I work on performance improvements on https://github.com/schoero/eslint-plugin-better-tailwindcss project. Part of issues can be fixed on the tailwind side only.

This is a first fix, I have a bigger one in mind, it would require a small additional public API method - out of scope of this PR.

Please let me know what you think.

Finding

getVariantOrder() re-sorts all parsed variants with the (expensive) variant comparator on every call, and it is called by every compileCandidates() invocation — per build pass, per @apply substitution, and hundreds of times during candidate canonicalization via the variant signature caches. Since parsedVariants is append-only, the computed order only changes when a new variant is parsed, so we can cache the result and invalidate on parsedVariants.size. This makes cold canonicalization (IntelliSense, lint plugins) faster and removes repeated sorting from @apply substitution and incremental rebuilds.

Test plan

Tested at https://github.com/smnbbrv/better-tailwindcss-bench . The relevant part is the epbt-now / tw-patched

plugin cost (ms, cold run net of parse baseline)

codebase	epbt-now / tw-now	epbt-patched / tw-now	epbt-now / tw-patched	epbt-patched / tw-patched
mixed	6292	3965 (-37%)	5395 (-14%)	3595 (-43%)
repetitive	5279	2425 (-54%)	4819 (-9%)	2124 (-60%)
unique	6096	5458 (-10%)	5507 (-10%)	5295 (-13%)

[greptile-apps]

Greptile encountered an error while reviewing this PR. Please reach out to support@greptile.com for assistance and include this reference: e3634fa1-d526-4f12-99d8-395e4850b10b.

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• packages/tailwindcss/src/design-system.ts

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Walkthrough

Added cached state for variant ordering in the design system. getVariantOrder() returns the cached order when the parsed variant count is unchanged. The method recomputes and stores the order when new variants are parsed.

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Title check	✅ Passed	The title clearly identifies the main purpose of the change: improving cold-start performance through variant-order caching.
Description check	✅ Passed	The description explains the repeated variant sorting problem, the caching solution, and benchmarked performance improvements.

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