fix(form-core): make fieldMeta values optional to reflect runtime behaviour. (#1787)

* fix(form-core): make fieldMeta values optional to reflect runtime behavior

fieldMeta is typed as Record<DeepKeys<TData>, AnyFieldMeta> but is
initialized as an empty object. This causes TypeScript to incorrectly
assume that accessing any valid field key will return a defined
AnyFieldMeta object, leading to runtime crashes when accessing field
metadata during the first render.

Updated the fieldMeta type to include undefined to accurately reflect
that field metadata is only available after a field has been mounted.

BREAKING CHANGE: fieldMeta values are now typed as potentially undefined.
Code that accesses fieldMeta without null checks will now show TypeScript
errors. Use optional chaining or explicit undefined checks.

Fixes #1774

* chore: add changeset

* ci: apply automated fixes and generate docs

* refactor: address review feedback, change to patch version and clean up tests

* ci: apply automated fixes and generate docs

* fix: sort imports alphabetically

* chore: remove unused eslint directives

* Adjust changeset description

---------

Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>
Co-authored-by: LeCarbonator <18158911+LeCarbonator@users.noreply.github.com>

Author: 3 people

.changeset/bumpy-boats-roll.md

@@ -0,0 +1,5 @@
+---
+'@tanstack/form-core': patch
+---
+
+- Make `fieldMeta` record type `Partial<>` to reflect runtime behaviour

packages/form-core/src/FormApi.ts

@@ -618,7 +618,7 @@ export type BaseFormState<
   /**
    * A record of field metadata for each field in the form, not including the derived properties, like `errors` and such
    */
-  fieldMetaBase: Record<DeepKeys<TFormData>, AnyFieldMetaBase>
+  fieldMetaBase: Partial<Record<DeepKeys<TFormData>, AnyFieldMetaBase>>
   /**
    * A boolean indicating if the form is currently in the process of being submitted after `handleSubmit` is called.
    *
@@ -733,7 +733,7 @@ export type DerivedFormState<
   /**
    * A record of field metadata for each field in the form.
    */
-  fieldMeta: Record<DeepKeys<TFormData>, AnyFieldMeta>
+  fieldMeta: Partial<Record<DeepKeys<TFormData>, AnyFieldMeta>>
 }
 
 export interface FormState<
@@ -924,8 +924,22 @@ export class FormApi<
       TOnServer
     >
   >
-  fieldMetaDerived!: Derived<Record<DeepKeys<TFormData>, AnyFieldMeta>>
-  store!: Derived<
+  fieldMetaDerived: Derived<
+    FormState<
+      TFormData,
+      TOnMount,
+      TOnChange,
+      TOnChangeAsync,
+      TOnBlur,
+      TOnBlurAsync,
+      TOnSubmit,
+      TOnSubmitAsync,
+      TOnDynamic,
+      TOnDynamicAsync,
+      TOnServer
+    >['fieldMeta']
+  >
+  store: Derived<
     FormState<
       TFormData,
       TOnMount,
@@ -1019,7 +1033,7 @@ export class FormApi<
 
         let originalMetaCount = 0
 
-        const fieldMeta = {} as FormState<
+        const fieldMeta: FormState<
           TFormData,
           TOnMount,
           TOnChange,
@@ -1031,7 +1045,7 @@ export class FormApi<
           TOnDynamic,
           TOnDynamicAsync,
           TOnServer
-        >['fieldMeta']
+        >['fieldMeta'] = {}
 
         for (const fieldName of Object.keys(
           currBaseStore.fieldMetaBase,
@@ -1652,7 +1666,6 @@ export class FormApi<
         for (const field of Object.keys(
           this.state.fieldMeta,
         ) as DeepKeys<TFormData>[]) {
-          // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
           if (this.baseStore.state.fieldMetaBase[field] === undefined) {
             continue
           }
@@ -1860,7 +1873,6 @@ export class FormApi<
           for (const field of Object.keys(
             this.state.fieldMeta,
           ) as DeepKeys<TFormData>[]) {
-            // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
             if (this.baseStore.state.fieldMetaBase[field] === undefined) {
               continue
             }
@@ -2215,15 +2227,15 @@ export class FormApi<
    * resets every field's meta
    */
   resetFieldMeta = <TField extends DeepKeys<TFormData>>(
-    fieldMeta: Record<TField, AnyFieldMeta>,
-  ): Record<TField, AnyFieldMeta> => {
+    fieldMeta: Partial<Record<TField, AnyFieldMeta>>,
+  ): Partial<Record<TField, AnyFieldMeta>> => {
     return Object.keys(fieldMeta).reduce(
-      (acc: Record<TField, AnyFieldMeta>, key) => {
+      (acc, key) => {
         const fieldKey = key as TField
         acc[fieldKey] = defaultFieldMeta
         return acc
       },
-      {} as Record<TField, AnyFieldMeta>,
+      {} as Partial<Record<TField, AnyFieldMeta>>,
     )
   }
 

packages/form-core/tests/FormApi.spec.ts

@@ -169,6 +169,35 @@ describe('form api', () => {
     expect(form.state.values).toEqual({ name: 'initial' })
   })
 
+  it('should handle multiple fields with mixed mount states', () => {
+    const form = new FormApi({
+      defaultValues: {
+        firstName: '',
+        lastName: '',
+        email: '',
+      },
+    })
+
+    const firstNameField = new FieldApi({
+      form,
+      name: 'firstName',
+    })
+
+    firstNameField.mount()
+
+    expect(form.state.fieldMeta.firstName).toBeDefined()
+
+    expect(form.state.fieldMeta.email).toBeUndefined()
+
+    const lastNameField = new FieldApi({
+      form,
+      name: 'lastName',
+    })
+    lastNameField.mount()
+
+    expect(form.state.fieldMeta.lastName).toBeDefined()
+  })
+
   it("should get a field's value", () => {
     const form = new FormApi({
       defaultValues: {
@@ -1691,10 +1720,10 @@ describe('form api', () => {
     await form.handleSubmit()
     expect(form.state.isFieldsValid).toEqual(false)
     expect(form.state.canSubmit).toEqual(false)
-    expect(form.state.fieldMeta['firstName'].errors).toEqual([
+    expect(form.state.fieldMeta['firstName']!.errors).toEqual([
       'first name is required',
     ])
-    expect(form.state.fieldMeta['lastName'].errors).toEqual([
+    expect(form.state.fieldMeta['lastName']!.errors).toEqual([
       'last name is required',
     ])
   })
@@ -1730,10 +1759,10 @@ describe('form api', () => {
     await form.handleSubmit()
     expect(form.state.isFieldsValid).toEqual(false)
     expect(form.state.canSubmit).toEqual(false)
-    expect(form.state.fieldMeta['person.firstName'].errors).toEqual([
+    expect(form.state.fieldMeta['person.firstName']!.errors).toEqual([
       'first name is required',
     ])
-    expect(form.state.fieldMeta['person.lastName'].errors).toEqual([
+    expect(form.state.fieldMeta['person.lastName']!.errors).toEqual([
       'last name is required',
     ])
   })
@@ -1764,7 +1793,7 @@ describe('form api', () => {
     await form.handleSubmit()
     expect(form.state.isFieldsValid).toEqual(false)
     expect(form.state.canSubmit).toEqual(false)
-    expect(form.state.fieldMeta['firstName'].errors).toEqual([
+    expect(form.state.fieldMeta['firstName']!.errors).toEqual([
       'first name is required',
       'first name must be longer than 3 characters',
     ])
@@ -1873,7 +1902,7 @@ describe('form api', () => {
     await vi.runAllTimersAsync()
     expect(form.state.isFieldsValid).toEqual(false)
     expect(form.state.canSubmit).toEqual(false)
-    expect(form.state.fieldMeta['firstName'].errorMap).toEqual({
+    expect(form.state.fieldMeta['firstName']!.errorMap).toEqual({
       onChange: 'first name is required',
       onBlur: 'first name must be longer than 3 characters',
     })
@@ -1900,14 +1929,14 @@ describe('form api', () => {
     await form.handleSubmit()
     expect(form.state.isFieldsValid).toEqual(false)
     expect(form.state.canSubmit).toEqual(false)
-    expect(form.state.fieldMeta['firstName'].errorMap['onSubmit']).toEqual(
+    expect(form.state.fieldMeta['firstName']!.errorMap['onSubmit']).toEqual(
       'first name is required',
     )
     field.handleChange('test')
     expect(form.state.isFieldsValid).toEqual(true)
     expect(form.state.canSubmit).toEqual(true)
     expect(
-      form.state.fieldMeta['firstName'].errorMap['onSubmit'],
+      form.state.fieldMeta['firstName']!.errorMap['onSubmit'],
     ).toBeUndefined()
   })
 

packages/form-core/tests/fieldMeta.spec.ts

@@ -0,0 +1,186 @@
+import { describe, expect, it } from 'vitest'
+import { FieldApi, FormApi } from '../src/index'
+
+describe('fieldMeta accessing', () => {
+  it('should return undefined for unmounted fields', () => {
+    const form = new FormApi({
+      defaultValues: {
+        name: '',
+        email: '',
+      },
+    })
+
+    expect(form.state.fieldMeta.name).toBeUndefined()
+    expect(form.state.fieldMeta.email).toBeUndefined()
+  })
+
+  it('should have defined fieldMeta after field is mounted', () => {
+    const form = new FormApi({
+      defaultValues: {
+        name: '',
+      },
+    })
+
+    const field = new FieldApi({
+      form,
+      name: 'name',
+    })
+
+    field.mount()
+
+    expect(form.state.fieldMeta.name).toBeDefined()
+    expect(form.state.fieldMeta.name?.isValid).toBe(true)
+    expect(form.state.fieldMeta.name?.isTouched).toBe(false)
+    expect(form.state.fieldMeta.name?.isDirty).toBe(false)
+  })
+
+  it('should handle nested field paths', () => {
+    const form = new FormApi({
+      defaultValues: {
+        user: {
+          profile: {
+            firstName: '',
+            lastName: '',
+          },
+        },
+      },
+    })
+
+    expect(form.state.fieldMeta['user.profile.firstName']).toBeUndefined()
+    expect(form.state.fieldMeta['user.profile.lastName']).toBeUndefined()
+
+    const firstNameField = new FieldApi({
+      form,
+      name: 'user.profile.firstName',
+    })
+
+    firstNameField.mount()
+
+    expect(form.state.fieldMeta['user.profile.firstName']).toBeDefined()
+
+    expect(form.state.fieldMeta['user.profile.lastName']).toBeUndefined()
+  })
+
+  it('should handle array fields', () => {
+    const form = new FormApi({
+      defaultValues: {
+        items: ['item1', 'item2'],
+      },
+    })
+
+    expect(form.state.fieldMeta['items[0]']).toBeUndefined()
+    expect(form.state.fieldMeta['items[1]']).toBeUndefined()
+
+    const field0 = new FieldApi({
+      form,
+      name: 'items[0]',
+    })
+
+    field0.mount()
+
+    expect(form.state.fieldMeta['items[0]']).toBeDefined()
+    expect(form.state.fieldMeta['items[1]']).toBeUndefined()
+  })
+
+  it('should handle getFieldMeta returning undefined', () => {
+    const form = new FormApi({
+      defaultValues: {
+        name: '',
+      },
+    })
+
+    const fieldMeta = form.getFieldMeta('name')
+    expect(fieldMeta).toBeUndefined()
+
+    const field = new FieldApi({
+      form,
+      name: 'name',
+    })
+
+    field.mount()
+
+    const fieldMetaAfterMount = form.getFieldMeta('name')
+    expect(fieldMetaAfterMount).toBeDefined()
+    expect(fieldMetaAfterMount?.isValid).toBe(true)
+  })
+
+  it('should handle multiple fields with mixed mount states', () => {
+    const form = new FormApi({
+      defaultValues: {
+        firstName: '',
+        lastName: '',
+        email: '',
+      },
+    })
+
+    const firstNameField = new FieldApi({
+      form,
+      name: 'firstName',
+    })
+
+    const lastNameField = new FieldApi({
+      form,
+      name: 'lastName',
+    })
+
+    firstNameField.mount()
+
+    expect(form.state.fieldMeta.firstName).toBeDefined()
+    expect(form.state.fieldMeta.email).toBeUndefined()
+  })
+
+  it('should preserve fieldMeta after unmounting and remounting', () => {
+    const form = new FormApi({
+      defaultValues: {
+        name: '',
+      },
+    })
+
+    const field = new FieldApi({
+      form,
+      name: 'name',
+    })
+
+    const cleanup = field.mount()
+
+    field.setValue('test')
+    expect(form.state.fieldMeta.name?.isTouched).toBe(true)
+    expect(form.state.fieldMeta.name?.isDirty).toBe(true)
+
+    cleanup()
+
+    const metaAfterCleanup = form.state.fieldMeta.name
+
+    expect(metaAfterCleanup).toBeDefined()
+  })
+
+  it('should work with form validation that accesses fieldMeta', () => {
+    const form = new FormApi({
+      defaultValues: {
+        password: '',
+        confirmPassword: '',
+      },
+      validators: {
+        onChange: ({ value }) => {
+          if (value.password !== value.confirmPassword) {
+            return 'Passwords must match'
+          }
+          return undefined
+        },
+      },
+    })
+
+    form.mount()
+
+    const passwordField = new FieldApi({
+      form,
+      name: 'password',
+    })
+
+    passwordField.mount()
+
+    expect(() => {
+      passwordField.setValue('test123')
+    }).not.toThrow()
+  })
+})