fix(form-core): prevent duplicate dots when concatenating withFieldGroup paths (#1639)

stefan-huck · autofix-ci[bot] · LeCarbonator · web-flow · commit 051e87bdc85f · 2025-07-30T21:43:14.000+02:00
* fix(form-core): Fix handle nested withFieldGroup properly

* ci: apply automated fixes and generate docs

* chore: add unit test for concatenatePath

* chore: add FieldGroupApi unit test

---------

Co-authored-by: autofix-ci[bot] &lt;114827586+autofix-ci[bot]@users.noreply.github.com&gt;
Co-authored-by: LeCarbonator &lt;18158911+LeCarbonator@users.noreply.github.com&gt;
diff --git a/packages/form-core/src/utils.ts b/packages/form-core/src/utils.ts
@@ -196,6 +196,11 @@ export function concatenatePaths(path1: string, path2: string): string {
     return path1 + path2
   }
 
+  // In cases where parent and child withFieldGroup forms are both nested
+  if (path2.startsWith('.')) {
+    return path1 + path2
+  }
+
   return `${path1}.${path2}`
 }
 
diff --git a/packages/form-core/tests/FieldGroupApi.spec.ts b/packages/form-core/tests/FieldGroupApi.spec.ts
@@ -888,4 +888,35 @@ describe('field group api', () => {
       'Error',
     ])
   })
+
+  it('should generate form field names properly with nested objects', () => {
+    // https://github.com/TanStack/form/issues/1645
+    const form = new FormApi({
+      defaultValues: {
+        complexValue: {
+          prop1: 0,
+          prop2: 0,
+        },
+      },
+    })
+    form.mount()
+
+    const group = new FieldGroupApi({
+      defaultValues: {
+        complexValue: {
+          prop1: 0,
+          prop2: 0,
+        },
+      },
+      form,
+      fields: {
+        complexValue: 'complexValue',
+      },
+    })
+    group.mount()
+
+    expect(group.getFormFieldName('complexValue.prop1')).toBe(
+      'complexValue.prop1',
+    )
+  })
 })
diff --git a/packages/form-core/tests/utils.spec.ts b/packages/form-core/tests/utils.spec.ts
@@ -688,6 +688,10 @@ describe('concatenatePaths', () => {
     )
     expect(concatenatePaths('data', '[1].value')).toBe('data[1].value')
   })
+
+  it('should not duplicate dots if the second path starts with one', () => {
+    expect(concatenatePaths('foo', '.bar')).toBe('foo.bar')
+  })
 })
 
 describe('createFieldMap', () => {

Original file line number	Diff line number	Diff line change
`@@ -196,6 +196,11 @@ export function concatenatePaths(path1: string, path2: string): string {`
`196`	`196`	`return path1 + path2`
`197`	`197`	`}`
`198`	`198`
	`199`	`+ // In cases where parent and child withFieldGroup forms are both nested`
	`200`	`+ if (path2.startsWith('.')) {`
	`201`	`+ return path1 + path2`
	`202`	`+ }`
	`203`	`+`
`199`	`204`	return `${path1}.${path2}`
`200`	`205`	`}`
`201`	`206`