formik: validateField does not validate nested field

Bug report

Current Behavior

As stated in the title, validateField does not validate nested fields like user.name.

Expected behavior

It should set the correct error.

Reproducible example

You can switch between the commented lines. This shows the difference between usage of validateField with a not nested field and a nested one.

https://codesandbox.io/s/naughty-frost-013fk?file=/src/App.js

Suggested solution(s)

It took me soooo many hours when I encountered it till I realized that the bug might actually be in the Formik itself. I found that when the field error is set, it should use getIn(error, name) instead of error[name]. I’m gonna create a PR with a fix and a test.

diff --git a/packages/formik/src/Formik.tsx b/packages/formik/src/Formik.tsx
index d952a90..8b2d1b7 100755
--- a/packages/formik/src/Formik.tsx
+++ b/packages/formik/src/Formik.tsx
@@ -513,7 +513,7 @@ export function useFormik<Values extends FormikValues = FormikValues>({
         .then((error: any) => {
           dispatch({
             type: 'SET_FIELD_ERROR',
-            payload: { field: name, value: error[name] },
+            payload: { field: name, value: getIn(error, name) },
           });
           dispatch({ type: 'SET_ISVALIDATING', payload: false });
         });

Your environment

Software	Version(s)
Formik	2.2.6
React	17.0.1
TypeScript	4.2.4
Browser	Any
npm/Yarn	npm 7.16.0
Operating System	MacOS 11 Big Sur