flip sides source and target when we check signature relations

[vladima]

and report errors during contravariant check. This is partial rollback of 5e69332 that introduced perf regressions #7293, #7082.

Note: errors in baselines has changed but personally I like new errors more since they more accurately reflect runtime behavior. I.e.

let a: (s: string) => void;
let b: (s: number) => void;
a = b;
// a("42");

used to be

t.ts(3,1): error TS2322: Type '(s: number) => void' is not assignable to type '(s: string) => void'.
  Types of parameters 's' and 's' are incompatible.
    Type 'number' is not assignable to type 'string'.

now

t.ts(3,1): error TS2322: Type '(s: number) => void' is not assignable to type '(s: string) => void'.
  Types of parameters 's' and 's' are incompatible.
    Type 'string' is not assignable to type 'number'.

In runtime a will have argument of type string that is not assignable to type number that is expected by b and this is exactly what is said in new error message.

[mhegazy]

👍

[DanielRosenwasser]

👍

[RyanCavanaugh]

👍