Show exact error position in arrays & arrow functions

[cevek]

If it is not assignable error and infered expression type origin comes from inside of ast error boundaries we can show exact position of an error source

interface Foo {
    a: number;
}

function foo1(): () => Foo {
    return () => ({a: ''});
}

function foo2(): Promise<Foo> {
    return Promise.resolve({a: ''});
}

function foo3(): Foo[] {
    return [{a: ''}];
}
var y: Foo[] = [{a: ''}] 
var z: Foo[] = [].map(() => ({a: ''}))

@DanielRosenwasser what do you think?

[DanielRosenwasser]

This can get arbitrarily complex, but I think that for certain arrays and arrow functions, we can definitely do better here.

[DanielRosenwasser]

Specifically I can see us dealing with foo1, foo3, and y pretty easily. I think that foo2 and z will be harder.

[weswigham]

@DanielRosenwasser It should just be a matter of adding more cases to elaborateError to handle diving into more expressions.

[DanielRosenwasser]

I think that the majority of work done has been done here; the Promise.resolve case is a little harder, but if it's compelling enough for your day-to-day coding I encourage you to open up another issue. Thanks @cevek!