Stability is not checked for glob imports

[aturon]

Just what it says on the tin: this is especially a problem when importing an unstable trait with stable methods.

[steveklabnik]

Without staged_api anymore, I am not even sure of an easy way to reproduce this outside of the standard library itself...

[petrochenkov]

Maybe I'm missing something, but what is the problem here?

Assume we imported something unstable with a glob import. We still have to name it to use it and the moment we name it it's caught by a stability checker (modulo bugs like #30209).

[alexcrichton]

This is pretty orthogonal to staged_api (this is still very relevant for libstd), but I believe this is still relevant for trait imports. We have to be careful to not have unstable traits with stable methods that aren't in the prelude because otherwise via this bug you can use std::foo::* and then call the methods.

[petrochenkov]

We have to be careful to not have unstable traits with stable methods that aren't in the prelude because otherwise via this bug you can use std::foo::* and then call the methods.

But.. if a method is explicitly marked as stable then we certainly can call it. I don't think it's a bug, it's just something library maintainers have to be aware of - "don't make methods stable if you don't want people to call them on stable".

[alexcrichton]

Perhaps, yeah, although I vaguely remember there being other reasons why this bug was opened that I can't quite recall now.

[bluss]

This code compiles in the stable channel and it's not intentional:

fn main() {
    let s = SliceConcatExt::concat(&[""][..]);
}

The trait itself is supposed to be unstable, not usable by name like this.

[petrochenkov]

@bluss
This is covered by #30209

[petrochenkov]

Closing as per #23049 (comment)