fix(form-core): clear errorSourceMap.onMount alongside errorMap.onMount

.changeset/olive-forms-clear.md

@@ -0,0 +1,5 @@
+---
+'@tanstack/form-core': patch
+---
+
+Clear a field's `errorSourceMap.onMount` alongside `errorMap.onMount` when its value is set.

packages/form-core/src/FormApi.ts

@@ -2668,6 +2668,11 @@ export class FormApi<
             ...prev?.errorMap,
             onMount: undefined,
           },
+          errorSourceMap: {
+            // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
+            ...prev?.errorSourceMap,
+            onMount: undefined,
+          },
         }))
       }
 

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

@@ -3233,6 +3233,70 @@ describe('form api', () => {
     expect(firstNameField.state.meta.errors).toEqual(['first name is required'])
   })
 
+  it("clears the onMount error source when a field's value is set", () => {
+    const form = new FormApi({
+      defaultValues: {
+        firstName: '',
+      },
+    })
+
+    form.mount()
+
+    const firstNameField = new FieldApi({
+      form,
+      name: 'firstName',
+      validators: {
+        onMount: () => 'first name is required',
+      },
+    })
+
+    firstNameField.mount()
+
+    expect(firstNameField.state.meta.errorMap.onMount).toBe(
+      'first name is required',
+    )
+    expect(firstNameField.state.meta.errorSourceMap.onMount).toBe('field')
+
+    form.setFieldValue('firstName', 'firstName')
+
+    expect(firstNameField.state.meta.errorMap.onMount).toBeUndefined()
+    expect(firstNameField.state.meta.errorSourceMap.onMount).toBeUndefined()
+  })
+
+  it("clears the form-sourced onMount error source when a field's value is set", () => {
+    const form = new FormApi({
+      defaultValues: {
+        firstName: '',
+      },
+      validators: {
+        onMount: () => ({
+          fields: {
+            firstName: 'first name is required',
+          },
+        }),
+      },
+    })
+
+    form.mount()
+
+    const firstNameField = new FieldApi({
+      form,
+      name: 'firstName',
+    })
+
+    firstNameField.mount()
+
+    expect(firstNameField.state.meta.errorMap.onMount).toBe(
+      'first name is required',
+    )
+    expect(firstNameField.state.meta.errorSourceMap.onMount).toBe('form')
+
+    form.setFieldValue('firstName', 'firstName')
+
+    expect(firstNameField.state.meta.errorMap.onMount).toBeUndefined()
+    expect(firstNameField.state.meta.errorSourceMap.onMount).toBeUndefined()
+  })
+
   it('clears errors on all fields affected by form validation when condition resolves', () => {
     const form = new FormApi({
       defaultValues: {