fix: revert ObservableStatus to a strict (non-union) type

[tyler-reitz]

Summary

4.2.4 shipped ObservableStatus<T> as a discriminated union (#583), so data became T | undefined unless narrowed on status. That broke the documented pattern of reading .data directly (e.g. const { data } = useFirestoreCollectionData(q); data.map(...)) across every data hook, including the suspense pattern, and it went out as a patch.

This reverts ObservableStatus to its previous strict shape (data: T) so the fix ships as a patch, and adds a type-check over the test suite in CI so a regression like this fails at compile time going forward.

Commits

1. test: type-check the test suite in CI adds tsconfig.test.json (type-checks src + test) and runs it in the type-check workflow. With the union still in place this turns the check red with 28 TS18048 "possibly undefined" errors on the existing test assertions. Also fixes pre-existing test-only type issues the check surfaces (unused imports, node globals, a children prop annotation).
2. fix: revert ObservableStatus to a strict (non-union) type reverts the type to data: T. The check goes green (0 errors).
3. docs: regenerate reference docs for the ObservableStatus type change (drops the per-status sub-interface pages, retargets links from type-aliases/ to interfaces/).
4. test: strengthen the type guard with a typed useDatabaseObjectData read (which fails to compile if ObservableStatus regresses to a union) and a concretely-typed useFirestoreDocData read, per review.

The existing tests already read .data off hook results the way consumers do, so once type-checked they catch this class of break with no separate type-regression file.

What stays correctly typed per hook

The genuinely-optional cases keep their undefined / null at the hook level, which is where it belongs:

• useFirestoreDocData / useFirestoreDocDataOnce return ObservableStatus<T | undefined> (fix: update useFirestoreDocData return type to include undefined #733)
• useUser returns ObservableStatus<User | null>
• useDatabaseListData returns ObservableStatus<T[] | null>

Reverting the union cleared all 28 possibly-undefined errors, confirming no other hook needed per-hook undefined.

Removed types (for release notes)

Reverting removes the three interfaces 4.2.4 introduced: ObservableStatusSuccess, ObservableStatusError, ObservableStatusLoading. Anyone who adopted them in 4.2.4 should read data off ObservableStatus<T> directly again. Worth a changelog line on the 4.2.5 release.

Verification

• Red then green: 28 TS18048 at commit 1, 0 at commit 2.
• tsc --noEmit green on both src and src + test.
• Non-emulator tests (useObservable, firebaseApp) pass (21/21); emulator suites green in CI.
• Consumer check: packed this branch and type-checked the documented useFirestoreCollectionData(...).data.map(...) pattern under strict, green here, red on 4.2.4.

Intended to ship as a patch (4.2.5). Tracks #749.

[gemini-code-assist]

Caution

The consumer version of Gemini Code Assist on GitHub has been sunset. All code review activity has officially ceased.

[gemini-code-assist]

Caution

The consumer version of Gemini Code Assist on GitHub has been sunset. All code review activity has officially ceased.

[armando-navarro]

Nice fix, along with the CI type-check. I verified the whole thing on current main: the revert is faithful to the pre-4.2.4 shape, the red-then-green holds, and types, tests, and docs are all green.

What I verified

• The revert restores ObservableStatus<T> to the flat data: T shape (identical to 4.2.3), and the genuinely-optional cases stay where they belong: useFirestoreDocData/DocDataOnce → T | undefined, useUser → User | null, useDatabaseListData → T[] | null.
• Red then green: tsc -p tsconfig.test.json reports exactly 28 TS18048 at the guard commit (union still in place) and 0 after the revert. The 28 are real .data reads, and the test fixes added no as any / @ts-ignore / ! suppressions, so the guard has real teeth.
• tsc is clean on src and src + test; the non-emulator suites are 21/21; the firestore/database/auth emulator suites are green; and the regenerated reference docs match a clean npm run docs, so the docs check will pass.

The one decision that isn't mine: semver

Reverting removes three types that 4.2.4 published (ObservableStatusSuccess, ObservableStatusError, ObservableStatusLoading) and re-narrows data. It restores the 4.2.3 contract, so shipping it as a patch to undo a bad patch reads as reasonable to me, but removing exported types is technically breaking, so I would rather Jeff make that call explicitly.

Either way, a changelog line noting those three types are gone would help anyone who adopted them in 4.2.4.

Smaller notes

• The guard is genuine but not exhaustive: the useFirestoreDocData tests use <any>, so .data is untyped there, and useDatabaseObjectData/useDatabaseListData are not exercised at all, so a future union reintroduction on those would not be caught. One concretely-typed .data read for doc data plus an object/list test would close the gaps. Non-blocking.
• The description says two commits, but there are three (the docs regen is the third, and worth keeping).

Everything code-level checks out, so approving on that, with the semver call left to Jeff.

[jhuleatt]

Thanks!

[tyler-reitz]

Thanks Armando! Got both in a new commit: added a useDatabaseObjectData test with a typed .data read (fails to compile if ObservableStatus goes back to a union, confirmed) plus a concretely-typed docData read instead of the ones, no suppressions. Also fixed the commit count and added a "Removed types" note for ObservableStatusSuccess/Error/Loading. Landing as a patch for 4.2.5.

[tyler-reitz]

Final due-diligence: published .d.ts surface diff

Packed this branch and diffed the emitted type declarations against both the broken release (4.2.4) and the last-good one (4.2.3), the same release-time check tracked in #749.

vs 4.2.4 — surgical. The only .d.ts that changes is useObservable.d.ts (the ObservableStatus revert + removal of the three sub-interfaces). Every other module, firestore/database/auth/storage/etc., is byte-identical to 4.2.4. No collateral changes.

vs 4.2.3 — contract restored. The ObservableStatus interface is identical to 4.2.3. The only difference in the whole file is one additive line:

- preloadObservable<T>(source, id): SuspenseSubject<T>
+ preloadObservable<T>(source, id, suspenseEnabled?): SuspenseSubject<T>

That optional suspenseEnabled? comes from #583's useSyncExternalStore runtime (kept intentionally, we reverted only the type). Optional param = additive/non-breaking.

Net: 4.2.3's ObservableStatus contract is restored, #733's per-hook undefined is preserved, and the only delta from 4.2.3 is a benign additive param.