fix(form-core): preserve FieldWithValue name string type

.changeset/dark-suits-itch.md

@@ -0,0 +1,5 @@
+---
+'@tanstack/form-core': patch
+---
+
+Fix FieldWithValue name type to preserve string typing

packages/form-core/src/types.public.ts

@@ -50,7 +50,7 @@ export type OneOrMany<TValue> = TValue | Array<TValue>
  * @typeParam TFieldValue - The value type preserved across field reads and update methods.
  */
 export type FieldWithValue<TFieldValue> = FieldApi<
-  any,
+  string,
   TFieldValue,
   any,
   any,

packages/form-core/tests/FieldWithValue.test-d.ts

@@ -0,0 +1,27 @@
+import { describe, expectTypeOf, it } from 'vitest'
+import type { FieldWithValue } from '../src'
+
+describe('FieldWithValue', () => {
+  it('should preserve string typing for field name', () => {
+    const field = null as unknown as FieldWithValue<boolean>
+
+    expectTypeOf<typeof field.name>().toEqualTypeOf<string>()
+    expectTypeOf<typeof field.value>().toEqualTypeOf<boolean>()
+
+    const validName: string = field.name
+
+    // @ts-expect-error Field name must not be a number
+    const invalidName: number = field.name
+
+    // @ts-expect-error Field name does not have Number methods
+    field.name.toFixed()
+
+    // @ts-expect-error Boolean field must not accept a string
+    field.handleChange('not a boolean')
+
+    field.handleChange(true)
+
+    void validName
+    void invalidName
+  })
+})