generic type inference for boolean literals fails

[patsissons]

TypeScript Version: 2.6.1
Code

function test<T>(x: T, f: (y: T) => void) { return x; }
let z: false = false;
test(z, x => { z = x; });
// ------------^
// [ts]
// Type 'boolean | undefined' is not assignable to type 'false | undefined'.
// Type 'true' is not assignable to type 'false | undefined'.

Expected behavior:

z and x should be of the same type

Actual behavior:

x is being inferred as boolean instead of false

[patsissons]

I'll try and test this in @next when i get a chance, just trying to get this issue posted for now.

confirmed on 2.7.0-dev.20171109:

tsc "test.ts"

test.ts(3,16): error TS2322: Type 'boolean' is not assignable to type 'false'.

[Proculopsis]

// let z: false = false;
let z: boolean = false;

Isn't this a compiler bug, letting you use 'false' as a type rather than 'boolean'?

[patsissons]

typescript permits boolean literals as type declarators. this is particularly relevant in React development, since false means do not render anything, but true cannot be rendered.

[RyanCavanaugh]

Mohamed Hegazy (@mhegazy) what is the inferred suggestion here?

[Qwertiy]

Seems working fine on 3.9.2.

[jakebailey]

Just looking at old issues; this was fixed back by #27042.