Suggestion: error when immediate function expression which returns a value is assigned to function type with void return type

[NaridaL]

This would be the analog of the error for additional properties in object literals for function return values.

TypeScript Version: 2.5.3 / nightly (2.6.0-dev.20171007)

Code

declare function voidCallback(cb: () => void)

// actual: no error
// expected: error: callback ignores return value 
voidCallback(() => 23)

const f = () => 45

// should still work:
voidCallback(f)

voidCallback(() => {
    // should still be allowed for flow control
    return
})

[mhegazy]

seems like a duplicate of #8240 and #8584

[NaridaL]

Yeah they are similar, but if I'm not mistaken in this case returning a value is definitely useless (like for object literals) while those are describing more general cases of not using return values.

[RyanCavanaugh]

Consider if you had written voidCallback(() => arr.push(10)), which does return a value but is not wrong.

[NaridaL]

True, you'd have to write () => { arr.push(10) }