TypeScript Version: 3.5.1, 3.8.3

Search Terms:
conditional types, generics, equality

Code

strictNullChecks and strictFunctionTypes enabled

export type Equals<A1 extends any, A2 extends any> =
    (<A>() => A extends A1 ? 1 : 0) extends (<A>() => A extends A2 ? 1 : 0)
    ? 1
    : 0

interface Foo<T> {
    x : () => T
}

declare const a: Foo<Date>;
declare const b: Foo<Date | null>;

//Expected 0, Actual 1
type ShouldBe0 = Equals<typeof a, typeof b>;

Expected behavior:

Evaluates to 0

Actual behavior:

Evaluates to 1

Playground Link: http://www.typescriptlang.org/play/?ssl=1&ssc=1&pln=16&pc=1#code/FAUwHgDg9gTgLgAjgTwiBBRAjgVwIYA2AzgDwCCAjAuHCAHYAmRCedyANAmQEzVi2NmrZAD4EAXmAJpCABTkRsgJQSxZPgKZcqAfgRUAXAgAMKmvS3yyileLUaLzHgj2GTSqTNefpR48GAASzpaGAAzPABjdAAxKCgSABUxAG8fBDAEI2VVBETgAF8AhhBIgjwYdEioOiJEPCM4hIARPFoRAG5gErKKqpq6hAAjRviSVtoEAB8EOhwCAk6AgHpljEhS2gYTTjJIuHwCfWAUNAQAZQALKHmGACEQYwlMXEJSU5AoMJZOD6-hpZAA

Related Issues: Not that I know of

I filed this issue over here as well, millsp/ts-toolbelt#97

Looking at the type, it should work. But it doesn't. I think it might indicate something is broken with TS