Seek most-overlapping types when relating object types in unions

[DanielRosenwasser]

From @rkirov at DefinitelyTyped/DefinitelyTyped#28044 (comment)

interface A {
    a: string;
    b: number
};

interface Other {
    o: number;
}

declare function f(x: A | Other): any;

export let x = { a: '', b: '' };
export let y = f(x);

Expected

Argument of type '{ a: string; b: string; }' is not assignable to parameter of type 'Other | A'.
  Type '{ a: string; b: string; }' is not assignable to type 'A'.
    Types of property 'b' are incompatible.
      Type 'string' is not assignable to type 'number'.

Actual

Argument of type '{ a: string; b: string; }' is not assignable to parameter of type 'A | Other'.
  Type '{ a: string; b: string; }' is not assignable to type 'Other'.
    Property 'o' is missing in type '{ a: string; b: string; }'.

[bowenni]

I'm not sure if this is a valid ask. Would it be possible to use the most-overlapping declaration in error message for overloads too?

declare function f(a: string, b: string, c: string): void;
declare function f(a: () => string, b: () => string, c: () => string): void;
f('1', '1', {});

Actual
ERROR(3,3): : Argument of type '"1"' is not assignable to parameter of type '() => string'.
Expected
ERROR(3,13): : Argument of type '{}' is not assignable to parameter of type 'string'.

[DanielRosenwasser]

@bowenni I think that is a UX improvement we want to see, but I'd rather we file a different issue there. Overload resolution is pretty complicated and would warrant its own work item.

[CyrusNajmabadi]

A vote on this over from Pulumi land. We have extensive use of union types, and errors here can be painful :)

[KaelWD]

Similar problem with Vue.

Code:

Vue.extend({
  props: {
    value: null
  }
})

3.0.1:

Argument of type '{ props: { value: null; }; }' is not assignable to parameter of type 'ComponentOptions<Vue, DefaultData<Vue>, DefaultMethods<Vue>, DefaultComputed, PropsDefinition<Record<string, any>>, Record<string, any>>'.
  Types of property 'props' are incompatible.
    Type '{ value: null; }' is not assignable to type 'string[] | RecordPropsDefinition<Record<string, any>> | undefined'.
      Type '{ value: null; }' is not assignable to type 'undefined'.

2.9.2:

Argument of type '{ props: { value: null; }; }' is not assignable to parameter of type 'ComponentOptions<Vue, DefaultData<Vue>, DefaultMethods<Vue>, DefaultComputed, PropsDefinition<Rec...'.
  Type '{ props: { value: null; }; }' is not assignable to type 'ComponentOptions<Vue, DefaultData<Vue>, DefaultMethods<Vue>, DefaultComputed, PropsDefinition<Rec...'.
    Types of property 'props' are incompatible.
      Type '{ value: null; }' is not assignable to type 'string[] | RecordPropsDefinition<Record<string, any>> | undefined'.
        Type '{ value: null; }' is not assignable to type 'RecordPropsDefinition<Record<string, any>>'.
          Property 'value' is incompatible with index signature.
            Type 'null' is not assignable to type 'PropValidator<any>'.

[DanielRosenwasser]

Doesn't "dive in" to the objects like @joeduffy and @CyrusNajmabadi were hoping for, but a fix is up on #27087. Maybe @weswigham has some ideas here.