Tuple struct associated constants can't be initialized with Self()

[jsgf]

There's an inconsistency when initializing tuple structs as associated constants with Self:

struct Foo(i32);

impl Foo {
const A: Self = Self(1); // Fails with "did you mean `Self { /* fields */ }`?"
const B: Self = Self { 0: 2 }; // succeeds
}

I'd expect Self(1) to work if Self { 0: 2 } works.

[jsgf]

Actually, this looks like a general problem with Self and tuple types. This also doesn't work:

impl Foo {
    fn new(x: i32) -> Self {
        Self(x) // same failure
    }
}

[petrochenkov]

Duplicate of #42601 and maybe a couple of other closed issues.

This is not supposed to work and the fix is kinda on the RFC territory, but given that it's requested regularly, I think it's reasonable to make this change and support Self in value namespace as a constructor alias.

[TimNN]

Closing as duplicate.