[DerivedConformance] Correctly set access of derived 'hash(into:)'

[rintaro]

If the access level of the target type is private, derived hash(into:) used to be created with private access. But it should be as accessible as the enclosing type.

rdar://problem/71005827

[rintaro]

Even without this change, the following example is successfully type checked despite the fact E.hash(into:) is synthesized with private.

private enum E {
  case foo, bar
}
private func foo(val: E, hasher: inout Hasher) {
  val.hash(into: &hasher)
}

@xedin Any idea why type checking is not affected by this?

[rintaro]

@swift-ci Please smoke test

[xedin]

I wonder if that's because first lookup for hash(into:) returns just a stub for a method which would be generated later?

[xedin]

Looks like type-checker finds a method on a Hashable protocol which has public access:

(func_decl "hash(into:)" interface type='<Self where Self : Hashable> (Self) -> (inout Hasher) -> ()' access=public
  (parameter "self")
  (parameter_list
    (parameter "hasher" apiName=into type='Hasher' interface type='Hasher' inout)))

and uses it with Self of E although the witness would have private access. Why doesn't this create problems down the line, @CodaFi?

[xedin]

Makes sense to me!

[rintaro]

Apparently the mandatory SIL optimizer correctly(?) resolves and rewrites it to a direct call to E.hash(into:).

-emit-silgen

  %7 = witness_method $E, #Hashable.hash : <Self where Self : Hashable> (Self) -> (inout Hasher) -> () : $@convention(witness_method: Hashable) <τ_0_0 where τ_0_0 : Hashable> (@inout Hasher, @in_guaranteed τ_0_0) -> () // user: %8
  %8 = apply %7<E>(%6, %4) : $@convention(witness_method: Hashable) <τ_0_0 where τ_0_0 : Hashable> (@inout Hasher, @in_guaranteed τ_0_0) -> ()

-emit-sil

  %5 = function_ref @$s4test1E33_83378C430F65473055F1BD53F3ADCDB7LLO4hash4intoys6HasherVz_tF : $@convention(method) (@inout Hasher, E) -> () // user: %6
  %6 = apply %5(%4, %0) : $@convention(method) (@inout Hasher, E) -> ()

Anyway 🚢