Difference in typechecking results for a TSX file in 7.0.0-dev.20260218.1 and later

[connorshea]

Steps to reproduce

Repo link: https://github.com/connorshea/tsgo-repro/blob/main/repro.tsx

I had Claude create a reproduction case out of the actual codebase I ran into this with, and confirmed myself that it recreates the exact same issue, and is as minimal as I can make it.

Steps:

• git clone https://github.com/connorshea/tsgo-repro
• cd tsgo-repro
• npm install
• npx tsc, see there's no typecheck failure
• npx tsgo, see there's a typecheck failure

I should also note that the regression was only in the last few days, it works fine in tsgo on 7.0.0-dev.20260217.1:

• Passes: tsc 5.9.3, tsc 6.0.0-beta, tsgo <= 7.0.0-dev.20260217.1
• Fails: tsgo >= 7.0.0-dev.20260218.1

The problematic code is a tsx file:

import { Formik } from 'formik';
import { type SWRMutationResponse } from 'swr/mutation';

interface FormData {
  name: string;
  email: string;
}

type TriggerType = SWRMutationResponse<
  { result: string },
  Error,
  string,
  FormData
>['trigger'];

const trigger = null as unknown as TriggerType;

const initialValues: FormData = {
  name: '',
  email: '',
};

// ERROR in tsgo >= 7.0.0-dev.20260218.1:
//   Type 'TriggerWithArgs<...>' is not assignable to type
//     '(values: FormData, formikHelpers: FormikHelpers<FormData>) => void | Promise<any>'.
//   Types of parameters 'options' and 'formikHelpers' are incompatible.
//     Type 'FormikHelpers<FormData>' has no properties in common with
//       type 'SWRMutationConfiguration<...>'.
const element = (
  <Formik initialValues={initialValues} onSubmit={trigger}>
    {({ dirty }) => {
      return <div />;
    }}
  </Formik>
);

Behavior with typescript@6.0

No error when typechecking.

Behavior with tsgo

% npx tsgo
repro.tsx:49:41 - error TS2322: Type 'TriggerWithArgs<{ result: string; }, Error, string, FormData>' is not assignable to type '(values: FormData, formikHelpers: FormikHelpers<FormData>) => void | Promise<any>'.
  Types of parameters 'options' and 'formikHelpers' are incompatible.
    Type 'FormikHelpers<FormData>' has no properties in common with type 'SWRMutationConfiguration<{ result: string; }, Error, string, FormData, any>'.

49   <Formik initialValues={initialValues} onSubmit={trigger}>
                                           ~~~~~~~~

  node_modules/formik/dist/types.d.ts:164:5 - The expected type comes from property 'onSubmit' which is declared here on type 'IntrinsicAttributes & FormikConfig<FormData>'
    164     onSubmit: (values: Values, formikHelpers: FormikHelpers<Values>) => void | Promise<any>;
            ~~~~~~~~

[ahejlsberg]

I believe the tsgo error is correct. Consider:

const element = Formik({ initialValues: initialValues, onSubmit: trigger, children: ( dirty ) => {
    return <div />;
}});

This is the regular code equivalent of the JSX in the repro and it generates exactly the same error, both with tsc and tsgo. We merged #2803 a couple of days ago that fixes type inference and aligns the JSX with the regular code behavior in tsgo. We'll likely back-port that to TS 6.0 such that tsc will consistently error on both forms.

[DanielRosenwasser]

We're looking to bring this behavior back to 6.0 microsoft/TypeScript#63163

[connorshea]

Fair, as long as it's backported to 6.0 that's fine by me :) Thanks!