fix(form-core): keep reset(values) baseline on update() with unchanged props defaultValues

packages/form-core/src/FormApi.ts

@@ -1067,6 +1067,15 @@ export class FormApi<
    */
   private _devtoolsSubmissionOverride: boolean
 
+  /**
+   * The `defaultValues` carried by the options on the previous `update()` call
+   * (i.e. the last values that came from the framework adapter / props). Used
+   * to detect a genuine props change without being fooled by `reset(values)`,
+   * which legitimately mutates `this.options.defaultValues`.
+   * See https://github.com/TanStack/form/issues/1681
+   */
+  private _prevUpdateDefaultValues: TFormData | undefined = undefined
+
   /**
    * Constructs a new `FormApi` instance with the given form options.
    */
@@ -1748,13 +1757,29 @@ export class FormApi<
 
     const oldOptions = this.options
 
-    // Options need to be updated first so that when the store is updated, the state is correct for the derived state
-    this.options = options
-
-    const shouldUpdateValues =
-      options.defaultValues &&
-      !evaluate(options.defaultValues, oldOptions.defaultValues) &&
-      !this.state.isTouched
+    // `reset(values)` moves the baseline by writing `this.options.defaultValues`.
+    // Compare the incoming `defaultValues` against the ones seen on the previous
+    // `update()` (the previous props), NOT against `this.options.defaultValues`,
+    // so a reset isn't misread as a props change and doesn't get clobbered.
+    // See https://github.com/TanStack/form/issues/1681
+    const prevUpdateDefaultValues = this._prevUpdateDefaultValues
+    this._prevUpdateDefaultValues = options.defaultValues
+
+    const defaultValuesChanged =
+      !!options.defaultValues &&
+      !evaluate(options.defaultValues, prevUpdateDefaultValues)
+
+    // Options need to be updated first so that when the store is updated, the state is correct for the derived state.
+    // When the props `defaultValues` did not actually change, preserve the
+    // current baseline (e.g. one set by `reset(values)`) instead of overwriting
+    // it, so `isDirty`/`isDefaultValue` stay correct after a reset.
+    this.options =
+      defaultValuesChanged ||
+      evaluate(options.defaultValues, oldOptions.defaultValues)
+        ? options
+        : { ...options, defaultValues: oldOptions.defaultValues }
+
+    const shouldUpdateValues = defaultValuesChanged && !this.state.isTouched
 
     const shouldUpdateState =
       !evaluate(options.defaultState, oldOptions.defaultState) &&

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

@@ -1232,6 +1232,41 @@ describe('form api', () => {
     expect(form.getFieldValue('name')).toEqual('two')
   })
 
+  it('should keep reset() values when a subsequent update() reuses the original props defaultValues', () => {
+    // Reproduces https://github.com/TanStack/form/issues/1681
+    // In react-form, `formApi.update(opts)` runs in a layout effect on every
+    // render. When `reset(newValues)` is called (e.g. inside onSubmit) it both
+    // changes the store and updates `options.defaultValues`, which triggers a
+    // re-render. The following `update()` still carries the *original* props
+    // `defaultValues`, which previously looked like a real change and clobbered
+    // the freshly reset values.
+    const form = new FormApi({
+      defaultValues: {
+        name: 'original',
+      },
+    })
+    form.mount()
+
+    // user edits the field -> form becomes touched
+    form.setFieldValue('name', 'edited')
+    expect(form.getFieldValue('name')).toEqual('edited')
+
+    // onSubmit calls reset with brand new default values
+    form.reset({ name: 'new-default' })
+    expect(form.getFieldValue('name')).toEqual('new-default')
+    expect(form.state.isTouched).toBe(false)
+
+    // re-render fires the layout effect with the UNCHANGED props defaultValues
+    form.update({
+      defaultValues: {
+        name: 'original',
+      },
+    })
+
+    // the reset values must survive: props defaultValues never actually changed
+    expect(form.getFieldValue('name')).toEqual('new-default')
+  })
+
   it('should delete field from the form', () => {
     const form = new FormApi({
       defaultValues: {

packages/react-form/tests/useForm.test.tsx

@@ -124,6 +124,54 @@ describe('useForm', () => {
     )
   })
 
+  it('should keep reset(values) called inside onSubmit while subscribed to isDirty', async () => {
+    // Reproduces https://github.com/TanStack/form/issues/1681
+    // A component-level `isDirty` subscription re-renders the component after
+    // reset(), which re-runs the `formApi.update(opts)` layout effect with the
+    // unchanged props defaultValues. That update must not clobber the values
+    // just set by reset() back to the original default values.
+    function Comp() {
+      const form = useForm({
+        defaultValues: { firstName: 'FirstName' },
+        onSubmit: () => {
+          form.reset({ firstName: 'ResetName' })
+        },
+      })
+
+      const isDirty = useStore(form.store, (state) => state.isDirty)
+
+      return (
+        <>
+          <form.Field
+            name="firstName"
+            children={(field) => (
+              <input
+                data-testid="firstName"
+                value={field.state.value}
+                onBlur={field.handleBlur}
+                onChange={(e) => field.handleChange(e.target.value)}
+              />
+            )}
+          />
+          <p>isDirty: {String(isDirty)}</p>
+          <button onClick={form.handleSubmit}>Submit</button>
+        </>
+      )
+    }
+
+    const { getByTestId, getByText } = render(<Comp />)
+    const input = getByTestId('firstName') as HTMLInputElement
+
+    // make the form dirty, then submit -> reset({ firstName: 'ResetName' })
+    await user.type(input, 'X')
+    await user.click(getByText('Submit'))
+
+    // the reset values must survive the post-reset update() sync
+    await waitFor(() => expect(input.value).toBe('ResetName'))
+    // and the reset baseline should make the form pristine again
+    await waitFor(() => expect(getByText('isDirty: false')).toBeInTheDocument())
+  })
+
   it('should run on form mount', async () => {
     function Comp() {
       const [formMounted, setFormMounted] = useState(false)