[utils] Move getFilter, serializeValue, and stringifyAsLabel to @base-ui/utils

[flaviendelangle]

I need to access those utils on the Tree component in the new repo.

Summary

• Moves serializeValue, stringifyAsLabel, and the Filter/getFilter utilities from @base-ui/react internal utils to @base-ui/utils so they can be shared across packages.
• Updates all imports in @base-ui/react to use @base-ui/utils/filter, @base-ui/utils/serializeValue, and @base-ui/utils/stringifyAsLabel directly.
• Deletes the now-unused packages/react/src/utils/serializeValue.ts file.

Test plan

• TypeScript type-checking passes
• ESLint passes on all changed files
• Combobox tests pass (649 tests)

🤖 Generated with Claude Code

[pkg-pr-new]

• base-ui-tanstack-start

• vite-css-base-ui-example

  pnpm add https://pkg.pr.new/mui/base-ui/@base-ui/react@4449
  

  pnpm add https://pkg.pr.new/mui/base-ui/@base-ui/utils@4449
  

commit: 7cc43d8

[mui-bot]

Bundle size report

Bundle	Parsed size	Gzip size
@base-ui/react	0B(0.00%)	🔺+7B(0.00%)

Details of bundle changes

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[flaviendelangle]

Claude Code review

Summary

This PR extracts three utilities from @base-ui/react internal code into the shared @base-ui/utils package so they can be reused by the Tree component in another package.

Moved utilities:

• getFilter + Filter / GetFilterParameters types → packages/utils/src/filter.ts
• serializeValue → packages/utils/src/serializeValue.ts (renamed from packages/react/src/utils/serializeValue.ts)
• stringifyAsLabel → packages/utils/src/stringifyAsLabel.ts (extracted from resolveValueLabel.tsx)

Review Verdict: Looks good ✓

The PR is a clean mechanical extraction with no logic changes. All imports are correctly updated and no stale references remain.

What's done well

1. Exact code preservation — stringifyAsLabel and the getFilter/Filter/cache logic are byte-for-byte identical to the originals. serializeValue is a pure rename (100% similarity).

2. Backward compatibility in useFilter.ts — Re-exports UseFilterOptions as an alias for GetFilterParameters and keeps useCoreFilter as a typed wrapper around getFilter, so internal consumers don't break.

3. No stale imports left — Verified: no file in packages/react/ still imports stringifyAsLabel from resolveValueLabel, serializeValue from the old local path, or Filter from the old useFilter location.

4. Package exports work — packages/utils/package.json uses a "./*": "./src/*.ts" wildcard, so @base-ui/utils/filter, @base-ui/utils/serializeValue, and @base-ui/utils/stringifyAsLabel all resolve correctly without any config changes.

5. Second commit cleans up — The follow-up commit removes an unnecessary stringifyAsLabel re-export from resolveValueLabel.tsx while keeping the import (which is still used by resolveSelectedLabel at line 77).

Minor observations (non-blocking)

1. No dedicated unit tests for the extracted utils — stringifyAsLabel, serializeValue, and getFilter are now standalone public utilities in @base-ui/utils but don't have their own test files. They're exercised indirectly through the Combobox tests. Consider adding targeted unit tests if these will be consumed by multiple packages going forward.

2. useCoreFilter naming — This is pre-existing, but useCoreFilter follows React hook naming convention (use prefix) while it's just getFilter (a plain function, not a hook). Not introduced by this PR, so not actionable here.

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[romgrk]

What do you think of depending on @base-ui/react in other packages instead of placing some of these in @base-ui/utils? Reason is, the utils package is meant to be low-level stuff that could be used in any repository (core, X), whereas @base-ui/react is Base UI proper. The utils package is only in the @base-ui org because we needed to put it somewhere.

[flaviendelangle]

I know that we don't want to expose stuff from @base-ui/react as stable everytime we want to use it in other package within the company. The package is stable and we care a lot about its DX so anything made public there should be made public because we want people to use it, not because of internal needs.

With that being said, we have two alternatives to this:

• expose stuff from @base-ui/react as unstable_
• create a new @base-ui/internals package

I just don't want us to loose time figuring out how to share some code everytime we need a new util.
Because this will happen more and more as we create new packages.

We have a broader ongoing discussing on Slack and Notion