fix(form-core): prevent double re-render when no async validators (#1929)

* fix(form-core): prevent double re-render when no async validators

Fields were re-rendering twice on each keystroke because `isValidating`
was being toggled (true -> false) even when there were no async validators.

This fix checks if there are actual async validators before setting
`isValidating` state, preventing unnecessary re-renders.

Fixes #1130

* ci: apply automated fixes and generate docs

---------

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

Author: tt-a1i

.changeset/fix-double-render-keystroke.md

@@ -0,0 +1,9 @@
+---
+'@tanstack/form-core': patch
+---
+
+fix: prevent unnecessary re-renders when there are no async validators
+
+Fields were re-rendering twice on each keystroke because `isValidating` was being set to `true` then `false` even when there were no async validators to run. This fix checks if there are actual async validators before toggling the `isValidating` state.
+
+Fixes #1130

packages/form-core/src/FieldApi.ts

@@ -1728,21 +1728,30 @@ export class FieldApi<
       >,
     )
 
-    if (!this.state.meta.isValidating) {
-      this.setMeta((prev) => ({ ...prev, isValidating: true }))
-    }
-
-    for (const linkedField of linkedFields) {
-      linkedField.setMeta((prev) => ({ ...prev, isValidating: true }))
-    }
-
     /**
      * We have to use a for loop and generate our promises this way, otherwise it won't be sync
      * when there are no validators needed to be run
      */
     const validatesPromises: Promise<ValidationError | undefined>[] = []
     const linkedPromises: Promise<ValidationError | undefined>[] = []
 
+    // Check if there are actual async validators to run before setting isValidating
+    // This prevents unnecessary re-renders when there are no async validators
+    // See: https://github.com/TanStack/form/issues/1130
+    const hasAsyncValidators =
+      validates.some((v) => v.validate) ||
+      linkedFieldValidates.some((v) => v.validate)
+
+    if (hasAsyncValidators) {
+      if (!this.state.meta.isValidating) {
+        this.setMeta((prev) => ({ ...prev, isValidating: true }))
+      }
+
+      for (const linkedField of linkedFields) {
+        linkedField.setMeta((prev) => ({ ...prev, isValidating: true }))
+      }
+    }
+
     const validateFieldAsyncFn = (
       field: AnyFieldApi,
       validateObj: AsyncValidator<any>,
@@ -1845,10 +1854,13 @@ export class FieldApi<
       await Promise.all(linkedPromises)
     }
 
-    this.setMeta((prev) => ({ ...prev, isValidating: false }))
+    // Only reset isValidating if we set it to true earlier
+    if (hasAsyncValidators) {
+      this.setMeta((prev) => ({ ...prev, isValidating: false }))
 
-    for (const linkedField of linkedFields) {
-      linkedField.setMeta((prev) => ({ ...prev, isValidating: false }))
+      for (const linkedField of linkedFields) {
+        linkedField.setMeta((prev) => ({ ...prev, isValidating: false }))
+      }
     }
 
     return results.filter(Boolean)

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

@@ -797,6 +797,47 @@ describe('field api', () => {
     expect(field.getMeta().errors.length).toBe(0)
   })
 
+  it('should not toggle isValidating when there are no async validators', async () => {
+    // Test for https://github.com/TanStack/form/issues/1130
+    // Fields were re-rendering twice on each keystroke because isValidating
+    // was being set to true then false even when there were no async validators
+    vi.useFakeTimers()
+
+    const form = new FormApi({
+      defaultValues: {
+        name: 'test',
+      },
+    })
+
+    form.mount()
+
+    const field = new FieldApi({
+      form,
+      name: 'name',
+      // No async validators defined - only sync or none
+    })
+
+    field.mount()
+
+    // Track isValidating changes
+    const isValidatingStates: boolean[] = []
+    field.store.subscribe(() => {
+      isValidatingStates.push(field.getMeta().isValidating)
+    })
+
+    // Initial state
+    expect(field.getMeta().isValidating).toBe(false)
+
+    // Trigger validation by changing value
+    field.setValue('new value')
+    await vi.runAllTimersAsync()
+
+    // isValidating should never have been set to true since there are no async validators
+    // This prevents unnecessary re-renders
+    expect(isValidatingStates.every((state) => state === false)).toBe(true)
+    expect(field.getMeta().isValidating).toBe(false)
+  })
+
   it('should run async validation onChange', async () => {
     vi.useFakeTimers()