fix(form-core): Validate fields without instances

.changeset/happy-pillows-hear.md

@@ -0,0 +1,5 @@
+---
+'@tanstack/form-core': patch
+---
+
+run validation for fields without instances

packages/form-core/src/FormApi.ts

@@ -1599,7 +1599,18 @@ export class FormApi<
   ) => {
     // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
     const fieldInstance = this.fieldInfo[field]?.instance
-    if (!fieldInstance) return []
+
+    if (!fieldInstance) {
+      const { hasErrored } = this.validateSync(cause)
+
+      if (hasErrored && !this.options.asyncAlways) {
+        return this.getFieldMeta(field)?.errors ?? []
+      }
+
+      return this.validateAsync(cause).then(() => {
+        return this.getFieldMeta(field)?.errors ?? []
+      })
+    }
 
     // If the field is not touched (same logic as in validateAllFields)
     if (!fieldInstance.state.meta.isTouched) {

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

@@ -108,6 +108,31 @@ describe('standard schema validator', () => {
       ])
     })
 
+    it('should handle form-level field errors for fields without a mounted FieldApi instance', () => {
+      const form = new FormApi({
+        defaultValues: {
+          email: '',
+        },
+        validators: {
+          onChange: z.object({
+            email: z.string().email('email must be an email address'),
+          }),
+        },
+      })
+
+      form.mount()
+
+      form.setFieldValue('email', 'not-an-email')
+
+      expect(form.state.errors).toMatchObject([
+        { email: [{ message: 'email must be an email address' }] },
+      ])
+
+      form.setFieldValue('email', 'test@example.com')
+
+      expect(form.state.errors).toEqual([])
+    })
+
     it('should support standard schema async validation with zod', async () => {
       vi.useFakeTimers()