Weak typings for Array.prototype.map

[kujon]

TypeScript Version: 2.4.0

Code

The following blows up nicely as expected:

type A = {
    foo: string;
};

/** 'baz' does not exist in type 'A' */
const test1: A[] = [{ foo: 'foo', baz: 42 }];

Put it through the map method though, and any extra fields will be silently accepted:

/** no error */
const test2: A[] = ['foo'].map(val => ({ foo: val, baz: 42 }));

Expected behavior:
Both examples blow up w/ 'baz' does not exist in type 'A'

Actual behavior:
Only the compilation of the first example fails.

Duplicate of #11152 / #3423.
Currently we can't determine a contextual type for the returned expression, so extra properties aren't checked.

[mhegazy]

Automatically closing this issue for housekeeping purposes. The issue labels indicate that it is unactionable at the moment or has already been addressed.