Couple apparent bugs with variance checking

Bug Report

🔎 Search Terms

variance, methods, generics

NB: I did not search very exhaustively, but I did minimize the examples, so should be pretty easy to review and close as dupe or "by design" or whatever.

🕗 Version & Regression Information

• This is the behavior in every version I tried, and I reviewed the FAQ for entries about strictFunctionTypes

⏯ Playground Link

Variance checking does not interact correctly with extends:

https://www.typescriptlang.org/play?#code/C4TwDgpgBAYgPAewK7CgQQDRWagQgPigF4o4ANKCAD2AgDsATAZ3WPXwAoA3ALijICUxQrgBQogMYI6TVAEM+8OhC4QATlmWq1hEl2FQuk6bKgAjRXDpIAtmfWaV63VDnGZqNRCZIANsD4tdTYzDgAWACYhAHpoqAB3AAsEBDAmIA

Variance checking does not interact correctly with "records with methods" types:

https://www.typescriptlang.org/play?#code/C4TwDgpgBAGgPAewK7CgZQHxQLxQN4BQUUAHgBQDOAXOgJQ0B2EAbhAE4EC+BBAxggwqoAhjXhNWbLLjykaFHFgXd+g1ACMxcJAwDWDBAHcG0qML4ChUQwAsECMNSgT2OKOoB05ACwAmWgRAA

💻 Code

Variance checking does not interact correctly with extends:

type F<out A, out B> = <X extends A = A>(v: X) => B

const a: F<never, never> = v => v
const b: F<unknown, never> = a
const result: never = b(42) // whoops

Variance checking does not interact correctly with "records with methods" types:

type X<out S> = {
  x(s: S): never
}

const a: X<never> = { x: s => s }
const b: X<unknown> = a
const whoops: never = b.x(42)

🙁 Actual behavior

In both cases the typechecker allows me to inhabit never.

🙂 Expected behavior

The typechecker should reject my incorrect variance annotations (F<out A, ...> and X<out S>) and not allow me to inhabit never.

---

Incidentally this came to light out of some discussion in the "forall for non-functions" issue here: https://github.com/microsoft/TypeScript/issues/17574#issuecomment-1465094919, but these things don't really seem materially related.

Related to #48240.

Beginne mit den beiden TypeScript Playground-Reproduktionen und vergleiche die annotierten Varianzfälle, die extends und record methods betreffen. Verfolge, wie der typechecker Varianzannotationen validiert, und bestätige anschließend, dass beide inkorrekten Annotationen abgelehnt werden und kein Beispiel never inhabiten kann.