Change "A non-empty glob must import something with the glob's visibility" to be a lint?

[fpoli]

Consider the following three examples: A and C are accepted and B has a compilation error. However, the message reported in B looks more like a lint than a compilation error.

A consequence of this error is that adding a non-public function to a module (e.g. the bar in B) may break code that imports from that module. This causes surprises when refactoring.

Shouldn't "A non-empty glob must import something with the glob's visibility" be a lint?

The original discussion is here: https://users.rust-lang.org/t/a-non-empty-glob-must-import-something-with-the-globs-visibility-uhhh-okay-but-why

A

pub use self::a::*;
mod a {
    fn foo() {}
}

B

// ERROR: A non-empty glob must import something with the glob's visibility
pub use self::b::*;
mod b {
    fn foo() {}
    pub(super) fn bar() {}
}

C

// okay: there's a pub item
pub use self::c::*;
mod c {
    fn foo() {}
    pub(super) fn bar() {}
    pub fn baz() {}
}

[petrochenkov]

The error was introduced in #35894 as a part of import modularization, and discussed in one of the related issues, but I can't find where exactly.

The error was introduced by analogy with errors for single imports (and just to be conservative):

mod m {
    fn f() {}
}

use m::f; // Doesn't import anything and therefore reports an error.
use m::g; // Doesn't import anything and therefore reports an error.
use m::*; // Doesn't import anything and therefore reports an error.

The error is not technically necessary, and we should be able to report it as a lint for glob imports while keeping it an error for single imports.

[fpoli]

Would this be a "good first issue" or is it complex to fix?

[petrochenkov]

No, not complex.

• Find where "non-empty glob must import something" is reported.
• Replace span_err with buffer_lint(UNUSED_IMPORTS, ...).

[traxys]

I want to do this issue but the problem I have is with a test (ui/imports/reexports) that checks for this error, I don't know the compiler structure so I don't know when compiling this file the lint will not be reported because of the other errors or not. Else I changed the span_err to buffer_lint