fix(form-core): keep optional schema properties optional in looseSchema by roux-lon · Pull Request #2477 · TanStack/form

roux-lon · 2026-11-11T05:35:29Z

🎯 Changes

With formOptions.looseSchema, a schema containing an optional property was accepted as the loose schema but rejected when the same schema was passed to validators[].run:

const schema = z.object({ myProp: z.string().optional() })

formOptions.looseSchema(schema, {
  defaultValues: {},
  validators: [{ triggers: ['change'], run: schema }], // type error
})

InferUnionObject mapped over keyof TBase | keyof TIncoming. A mapped type over a union of keys is not homomorphic, so it drops the ? modifier. myProp?: string became the required myProp: string | undefined, and the schema's own input type was no longer assignable to it.

The keys now come from a homomorphic helper (InferUnionProps), so keys the schema declares take the schema's optionality, and keys only in defaultValues keep their own. A key missing from defaultValues keeps the schema's optionality. Required keys still come out as T | undefined, so existing behavior and tests are unchanged.

A type test covers the case from the issue, an optional property inside a nested object, and a required property that stays required. It fails without the fix with the error from the issue.

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Summary by CodeRabbit

Bug Fixes
- Fixed loose-schema handling so optional properties remain optional in inferred form defaults, including nested properties and when defaults are explicitly provided.
- Improved type inference for properties that are optional across combined schemas, preventing them from being incorrectly treated as required.
- Fixed an issue when using the same schema for form configuration and validation, ensuring schema validation works as expected.

InferUnionObject mapped over a union of keys, which drops the `?` modifier. An optional schema property such as `myProp?: string` became a required key in the merged form type, so the same schema was rejected in `validators[].run`. Take the key modifiers from a homomorphic helper so optionality is preserved. Closes TanStack#2475 Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

changeset-bot · 2026-11-11T05:35:39Z

🦋 Changeset detected

Latest commit: 09ab321

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 13 packages

Name	Type
@tanstack/form-core	Patch
@tanstack/angular-form	Patch
@tanstack/form-devtools	Patch
@tanstack/lit-form	Patch
@tanstack/preact-form	Patch
@tanstack/react-form-nextjs	Patch
@tanstack/react-form-start	Patch
@tanstack/react-form	Patch
@tanstack/solid-form	Patch
@tanstack/svelte-form	Patch
@tanstack/vue-form	Patch
@tanstack/react-form-devtools	Patch
@tanstack/solid-form-devtools	Patch

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coderabbitai · 2026-11-11T05:35:53Z

No actionable comments were generated in the recent review.

Walkthrough

InferUnionObject now preserves optional property modifiers when combining object types. Type tests cover top-level and nested looseSchema properties. A changeset records a patch release for @tanstack/form-core.

Changes: Loose-schema optional properties

Layer / File(s)	Summary
Optional-property inference and validation `packages/form-core/src/utils.public.ts`, `packages/form-core/tests/validation.test-d.ts`, `.changeset/quiet-keys-stay.md`	`InferUnionObject` delegates property mapping to a helper that preserves optional modifiers. Type tests cover omitted and supplied defaults, including nested optional properties. The changeset documents the patch.

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

Change: Bug fix · Severity of issue fixed: Low

Possibly related PRs

TanStack/form#2448: Introduces the formOptions.looseSchema typing and schema-based option contract updated by this change.

Suggested reviewers: lecarbonator

Merge Risk: Minimal · up to 09ab3

Optional loose-schema properties retain their modifiers. No merge-blocking risk was established.

Pre-merge checks: 5

Check name	Status	Explanation
Title check		The title clearly and concisely describes the main change: preserving optional schema properties in form-core looseSchema.
Linked Issues check		Issue [`#2475`] requires optional schema properties to remain omittable and the same schema to be accepted by `validators[].run`. `InferUnionObject` now uses homomorphic `InferUnionProps`, which preserv…
Out of Scope Changes check		The changes are limited to the `InferUnionObject` type fix, related type tests, and a patch changeset. These changes support issue [`#2475`]. No unrelated changes are shown.
Docstring Coverage		No eligible functions found in the changed files. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff with cyclomatic complexity of at least 2. Documentat…
Description check		The pull request description follows the required template. It explains the change and motivation, completes all checklist items, documents test execution, and includes the required changeset for publ…

Full details: Linked Issues check

Explanation

Issue [#2475] requires optional schema properties to remain omittable and the same schema to be accepted by validators[].run. InferUnionObject now uses homomorphic InferUnionProps, which preserves the ? modifier from schema-declared keys. The supplied change summary reports type tests for the reported case, a nested optional property, and a required property. The changeset documents the fix.

Full details: Docstring Coverage

Explanation

No eligible functions found in the changed files. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff with cyclomatic complexity of at least 2. Documentation-only edits and deletions within surviving functions are included; unchanged diff context and fully deleted functions are excluded. Analyzed 0 functions across 2 files.

Full details: Description check

Explanation

The pull request description follows the required template. It explains the change and motivation, completes all checklist items, documents test execution, and includes the required changeset for published code.

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Inline comments:
Review comments at @packages/form-core/src/utils.public.ts:
- Around line 38-49: Update InferUnionProps so a schema-optional property
remains optional when defaultValues supplies it; do not let the default make the
property required in the inferred form-value type. Preserve the existing
required-property behavior for properties required by the schema, and ensure the
resulting type remains assignable to validators[].run input.

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…s set them A property supplied by `defaultValues` was required in the merged form type even when the schema marks it optional, so the same schema was rejected in `validators[].run`. Keys declared by the schema now take its optional modifier; keys only in `defaultValues` keep theirs. Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

LeCarbonator · 2026-11-11T09:52:16Z

+> = InferUnionProps<
+  TBase,
+  TIncoming,
+  {
+    [K in keyof TBase as K extends keyof TIncoming ? never : K]: unknown
+  } & { [K in keyof TIncoming]: unknown }
+>
+
+// Mapping over `keyof TKeys` (a type parameter) is homomorphic, so each key
+// keeps the `?` modifier it has in `TKeys`. Keys that `TIncoming` declares take
+// its modifier, so a schema input that omits a property stays assignable.
+// Keys only in `TBase` keep theirs. Mapping over
+// `keyof TBase | keyof TIncoming` directly would drop every modifier.
+type InferUnionProps<TBase, TIncoming, TKeys> = {
+  [K in keyof TKeys]: K extends keyof TBase


What's the type instantiations like with this change? Seems to potentially add a ton of intersection work.

I tested on the existing form-core type tests, this adds about 0.8% instantiations and check time is unchanged. But this only covers the existing tests with small schemas, so I have not checked the deeply nested ones or the large ones.

I'll test this out with larger schemas later. Shouldn't change the percentage all that much, especially if it's not copying zod types around.

coderabbitai Bot reviewed Nov 11, 2026

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Comment thread packages/form-core/src/utils.public.ts Resolved

LeCarbonator reviewed Nov 11, 2026

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fix(form-core): keep optional schema properties optional in looseSchema - #2477

fix(form-core): keep optional schema properties optional in looseSchema#2477
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roux-lon:fix-form-core-loose-schema-optional-props

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