Change isSubmitting behaviour to mimic v1

In version 2 the behaviour of isSubmitting was changed from having the
user handle its state after submitting to always resetting it to false
after the onSubmit handler had returned (or it's promise). This reverts
it back to the version 1 behaviour of not touching the isSubmitting
state after the onSubmit handler has been called.

Solves: #1957

src/Formik.tsx

@@ -31,7 +31,6 @@ import { LowPriority, unstable_runWithPriority } from 'scheduler';
 type FormikMessage<Values> =
   | { type: 'SUBMIT_ATTEMPT' }
   | { type: 'SUBMIT_FAILURE' }
-  | { type: 'SUBMIT_SUCCESS' }
   | { type: 'SET_ISVALIDATING'; payload: boolean }
   | { type: 'SET_ISSUBMITTING'; payload: boolean }
   | { type: 'SET_VALUES'; payload: Values }
@@ -102,11 +101,6 @@ function formikReducer<Values>(
         ...state,
         isSubmitting: false,
       };
-    case 'SUBMIT_SUCCESS':
-      return {
-        ...state,
-        isSubmitting: false,
-      };
     default:
       return state;
   }
@@ -710,18 +704,7 @@ export function useFormik<Values extends FormikValues = FormikValues>({
       (combinedErrors: FormikErrors<Values>) => {
         const isActuallyValid = Object.keys(combinedErrors).length === 0;
         if (isActuallyValid) {
-          return Promise.resolve(executeSubmit())
-            .then(() => {
-              if (!!isMounted.current) {
-                dispatch({ type: 'SUBMIT_SUCCESS' });
-              }
-            })
-            .catch(_errors => {
-              if (!!isMounted.current) {
-                dispatch({ type: 'SUBMIT_FAILURE' });
-                throw _errors;
-              }
-            });
+          return executeSubmit();
         } else if (!!isMounted.current) {
           // ^^^ Make sure Formik is still mounted before calling setState
           dispatch({ type: 'SUBMIT_FAILURE' });

test/Formik.test.tsx

@@ -489,19 +489,6 @@ describe('<Formik>', () => {
           );
         });
       });
-
-      describe('submitForm helper should not break promise chain if handleSubmit has returned rejected Promise', () => {
-        it('submitForm helper should not break promise chain if handleSubmit has returned rejected Promise', async () => {
-          const error = new Error('This Error is typeof Error');
-          const handleSubmit = () => {
-            return Promise.reject(error);
-          };
-          const { getProps } = renderFormik({ onSubmit: handleSubmit });
-
-          const { submitForm } = getProps();
-          await expect(submitForm()).rejects.toEqual(error);
-        });
-      });
     });
 
     describe('with validate (ASYNC)', () => {
@@ -1136,6 +1123,7 @@ describe('<Formik>', () => {
     // do it again async
     await validatePromise;
     // done validating and submitting
+    expect(getProps().isSubmitting).toBe(true);
     expect(getProps().isValidating).toBe(false);
     expect(validate).toHaveBeenCalled();
     expect(onSubmit).toHaveBeenCalled();