fix(form-core): handle string array indices in prefixSchemaToErrors

packages/form-core/src/standardSchemaValidator.ts

@@ -27,9 +27,12 @@ function prefixSchemaToErrors(issues: readonly StandardSchemaV1Issue[]) {
       .map((segment) => {
         const normalizedSegment =
           typeof segment === 'object' ? segment.key : segment
-        return typeof normalizedSegment === 'number'
-          ? `[${normalizedSegment}]`
-          : normalizedSegment
+        const isArrayIndex =
+          typeof normalizedSegment === 'number' ||
+          (typeof normalizedSegment === 'string' &&
+            /^\d+$/.test(normalizedSegment))
+
+        return isArrayIndex ? `[${normalizedSegment}]` : normalizedSegment
       })
       .join('.')
       .replace(/\.\[/g, '[')

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

@@ -398,4 +398,161 @@ describe('standard schema validator', () => {
   it.todo(
     'Should allow for `disableErrorFlat` to disable flattening `errors` array',
   )
+
+  describe('array path handling', () => {
+    it('should handle numeric array indices correctly', async () => {
+      const form = new FormApi({
+        defaultValues: {
+          people: [{ name: '' }],
+        },
+        validators: {
+          onChange: z.object({
+            people: z.array(
+              z.object({
+                name: z.string().min(1, 'Name is required'),
+              }),
+            ),
+          }),
+        },
+      })
+
+      const field = new FieldApi({
+        form,
+        name: 'people[0].name',
+      })
+
+      field.mount()
+
+      field.setValue('')
+      expect(form.state.errors).toMatchObject([
+        {
+          'people[0].name': [{ message: 'Name is required' }],
+        },
+      ])
+    })
+
+    it('should handle string array indices correctly (Yup compatibility)', async () => {
+      // Mock a Standard Schema validator that returns string indices like Yup
+      const mockYupLikeValidator = {
+        '~standard': {
+          version: 1 as const,
+          vendor: 'mock-yup',
+          validate: (value: unknown) => {
+            const typedValue = value as { people?: { name?: string }[] }
+            if (!typedValue.people?.[0]?.name) {
+              return {
+                issues: [
+                  {
+                    message: 'Name is required',
+                    path: ['people', '0', 'name'], // String index like Yup
+                  },
+                ],
+              }
+            }
+            return { value: typedValue }
+          },
+        },
+      }
+
+      const form = new FormApi({
+        defaultValues: {
+          people: [{ name: '' }],
+        },
+        validators: {
+          onChange: mockYupLikeValidator,
+        },
+      })
+
+      const field = new FieldApi({
+        form,
+        name: 'people[0].name',
+      })
+
+      field.mount()
+
+      field.setValue('')
+      expect(form.state.errors).toMatchObject([
+        {
+          'people[0].name': [{ message: 'Name is required' }],
+        },
+      ])
+    })
+
+    it('should handle nested arrays with mixed numeric and string indices', async () => {
+      const form = new FormApi({
+        defaultValues: {
+          users: [
+            {
+              addresses: [
+                { street: 'Main St' },
+                { street: '' }, // This will fail validation
+              ],
+            },
+          ],
+        },
+        validators: {
+          onChange: z.object({
+            users: z.array(
+              z.object({
+                addresses: z.array(
+                  z.object({
+                    street: z.string().min(1, 'Street is required'),
+                  }),
+                ),
+              }),
+            ),
+          }),
+        },
+      })
+
+      const field = new FieldApi({
+        form,
+        name: 'users[0].addresses[1].street',
+      })
+
+      field.mount()
+      field.setValue('')
+
+      expect(form.state.errors).toMatchObject([
+        {
+          'users[0].addresses[1].street': [{ message: 'Street is required' }],
+        },
+      ])
+    })
+
+    it('should handle regular object paths without array indices', async () => {
+      const form = new FormApi({
+        defaultValues: {
+          user: {
+            profile: {
+              name: '',
+            },
+          },
+        },
+        validators: {
+          onChange: z.object({
+            user: z.object({
+              profile: z.object({
+                name: z.string().min(1, 'Name is required'),
+              }),
+            }),
+          }),
+        },
+      })
+
+      const field = new FieldApi({
+        form,
+        name: 'user.profile.name',
+      })
+
+      field.mount()
+
+      field.setValue('')
+      expect(form.state.errors).toMatchObject([
+        {
+          'user.profile.name': [{ message: 'Name is required' }],
+        },
+      ])
+    })
+  })
 })