Tracking issue for `inaccessible_extern_crate` compatibility lint

[petrochenkov]

What is this lint about

Private items cannot be used outside of their module

mod m {
    struct S;
}

use m::S; // <- attempt to access a private item, privacy error is reported

, however, older versions of the compiler erroneously ignored privacy on extern crate items and accepted code like this without errors:

mod m {
    extern crate c;
}

use m::c; // <- attempt to access a private item, privacy error was not reported in earlier compiler versions

#31362 fixed this oversight.

How to fix this warning/error

Mark the extern crate as pub if it's intended to be used from outside of the module it's defined in.

Current status

• resolve: fix the visibility of extern crates #31362 introduces the inaccessible_extern_crate lint as warn-by-default
• Make sufficiently old or low-impact compatibility lints deny-by-default #36894 makes the inaccessible_extern_crate lint deny-by-default
• Turn sufficiently old compatibility lints into hard errors #42136 makes the inaccessible_extern_crate lint a hard error