perf(tv): memoize slot invocations with simple args

[benjamincanac]

🔗 Linked issue

Relates to #6293

❓ Type of change

• 👌 Enhancement (improving an existing functionality)

📚 Description

Every render re-invokes the tv slot functions (ui.base(), ui.label(), ui.td(), ...), re-running variant resolution and twMerge even when the arguments are identical to the previous call — per table cell, per navigation item, per re-render. tailwind-variants caches nothing across invocations, and CPU profiling showed this as the largest remaining theming cost after the reactivity fixes in #6736.

This memoizes slot invocations in the tv wrapper when the arguments are fully serializable: primitives and arrays of primitives. Anything else, clsx-style object classes and the (defaults) => classes replacer functions from #6562, bails to the existing uncached path, so those semantics are untouched (covered by test/utils/tv.spec.ts). JSON.stringify is used as the cache key, and its dropping of undefined values matches tv's own treatment of undefined variants. The cache lives on the invocation result, so an app.config.ui change or a variant-prop recompute starts fresh, and each slot's cache is capped at 500 entries to guard against pathological dynamic inputs.

Measured with the benchmarks from #6728/#6736: a 100-cell ui.td() loop goes from 5,510 to 73,962 ops/s (13.4x), and a Button re-render from 4,103 to 5,235 ops/s on top of #6736 (2x cumulatively vs v4). Output classes are byte-identical: full suite passes with zero snapshot changes.

📝 Checklist

• I have linked an issue or discussion.
• I have updated the documentation accordingly.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: ab91b1fb-86d5-444b-8e1c-6916af0da6bd

📥 Commits

Reviewing files that changed from the base of the PR and between 05272d7 and 6dfb300.

📒 Files selected for processing (1)

• test/utils/tv.spec.ts

🚧 Files skipped from review as they are similar to previous changes (1)

• test/utils/tv.spec.ts

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📝 Walkthrough

Walkthrough

wrapSlots now memoizes slot results when slot props contain cacheable primitive or nested primitive-array values and no replacer is present. It generates JSON-based keys, handles undefined values consistently, stores results per slot, reuses cached strings, and clears caches above 500 entries. Tests cover cache reuse, argument isolation, key ordering, and non-cacheable class inputs.

Estimated code review effort: 2 (Simple) | ~10 minutes

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly summarizes the main change: memoizing tv slot invocations for simple arguments.
Description check	✅ Passed	The description is directly about the slot memoization change and its behavior, tests, and performance impact.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
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.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch perf/tv-slot-memo

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[pkg-pr-new]

npm i https://pkg.pr.new/@nuxt/ui@6737

commit: 6dfb300

[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@test/utils/tv.spec.ts`:
- Around line 162-165: Rename the test case around build to clarify that it
verifies identical output for reordered keys, not memoization cache reuse; leave
the assertion and implementation unchanged.

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Fix all unresolved CodeRabbit comments on this PR:

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• Create a new PR with the fixes

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 3b50c4c8-f271-457c-b88c-ebc679c4ffdb

📥 Commits

Reviewing files that changed from the base of the PR and between ef66e18 and 05272d7.

📒 Files selected for processing (2)

• src/runtime/utils/tv.ts
• test/utils/tv.spec.ts

🚧 Files skipped from review as they are similar to previous changes (1)

• src/runtime/utils/tv.ts