TypeScript does not infer equivalence of generic type arguments, TS2322 for equivalent types

[thomaslaich]

TypeScript Version: 3.7.2 or nightly

Search Terms: generic constrained type parameter error, error TS2322

Code: Consider the following example:

function myFunc<TProps extends { foo: any }>(props: TProps) {
    type NewType = Omit<TProps & { state: any }, "state">;
    /* declare */ const nt: NewType = 0 as any;
    const test: TProps = props;
    const test2: TProps = nt; // error
}

Actual behaviour: This yields the following error message on the line where I try to assign nt to test2:

Type 'Pick<TProps & { state: any; }, Exclude<keyof TProps, "state">>' is not assignable to type 'TProps'.
  'Pick<TProps & { state: any; }, Exclude<keyof TProps, "state">>' is assignable to the constraint of type 'TProps', but 'TProps' could be instantiated with a different subtype of constraint '{ foo: any; }'.(2322)

Expected behaviour: Should have no error.

Background: This error message is correctly shown on something like this:

function fn1<T extends string>(x: T): T {
  return "hello world!";
}

However, in the above example NewType should be the same as TProps no matter how TProps is instantiated.

Playground Link: TS Playground

Related issues:
#29049

[fatcerberus]

TProps might have a state property. NewType definitely doesn’t (because you’ve Omitted it).

[RyanCavanaugh]

Some day we will write an error message that convinces people these errors are correct 😢