Quick info shows method with type any[] at declaration and string[] at use

[ghost]

TypeScript Version: nightly (2.5.0-dev.20170619)

Code

/// <reference path='fourslash.ts'/>

// @noImplicitAny: true

////interface I { m(): string[] }
////
////const i: I = {
////    /*1*/m() { return []; }
////}
////
////i./*2*/m();

verify.quickInfoAt("2", "(method) I.m(): string[]");
verify.quickInfoAt("1", "(method) m(): string[]");

Expected behavior:

Test passes.

Actual behavior:

AssertionError: At 1: quick info text: expected '(method) m(): any[]' to equal '(method) m(): string[]'

[DanielRosenwasser]

Here's what's happening here:

1. The object is contextually typed by I
2. The method m is contextually typed by the type of the property m within I
3. The return expressions of m are contextually typed by the return type of the m within I
4. The array literal is contextually typed, but arrays only change their type when contextually typed by a tuple type. You end up with a regular array whose element type is the widening undefined type.

[JsonFreeman]

Would it be reasonable for an empty array literal with a contextual type to just acquire the element type as its own? Even if the contextual type isn't a tuple

That said, I think the current behavior is reasonable. After all, the method does return an empty array.

[mhegazy]

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