Nested conditional types and generics, testing type equality evaluating to incorrect branch

[AnyhowStep]

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

[AnyhowStep]

Type from here, #27024 (comment)

So, #27024 is related

[AnyhowStep]

The comment was made on September 2018.

Around that time, TS 3.0 and TS 3.1 were out.

It also breaks for TS 3.0 and TS 3.1

TS 3.0 Playground

TS 3.1 Playground

[weswigham]

Hm, so this is fixed in master, or at least it no longer reproduces. @RyanCavanaugh do we want to track down and backport the fix to 3.8?

[AnyhowStep]

I'm wondering if this should be added to the test suite, just to be safe =x