meta not indicated as reserved crate name when shadowing module

[yodaldevoid]

Taken from this internals thread: https://internals.rust-lang.org/t/is-the-module-name-meta-forbidden/9587

A module named meta is shadowed leading to misleading error messages. meta was reserved as a built-in crate name in 2018 edition, but the error message does not indicate this.

I tried this code:

mod meta {
    pub struct Thing;
}

use meta::Thing;

fn main() {}

Above code compiled with rustc --edition 2018 {file}

This is expected to indicated that meta is a reserved crate name.

Instead, the following error is reported:

error[E0463]: can't find crate for `meta`
 --> testy.rs:5:5
  |
5 | use meta::Thing;
  |     ^^^^ can't find crate

error: aborting due to previous error

For more information about this error, try `rustc --explain E0463`.

Meta

rustc --version --verbose:

rustc 1.44.1 (c7087fe00 2020-06-17)
binary: rustc
commit-hash: c7087fe00d2ba919df1d813c040a5d47e43b0fe7
commit-date: 2020-06-17
host: x86_64-unknown-linux-gnu
release: 1.44.1
LLVM version: 9.0

This issue has been assigned to @Chocol4te via this comment.

[fmckeogh]

@rustbot claim

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[fmckeogh]

@rustbot claim

[eddyb]

It's not forbidden as a module name, this obviously works:

mod meta {
    pub struct Thing;
}

use crate::meta::Thing;

I think the confusion arises from that fact that this works without crate:::

mod foo {
    pub struct Thing;
}

use foo::Thing;

But those are uniform imports (or at least I think that's what they're called), and only resolve to the surrounding scope if unambiguous (which it is for meta due to the.

I'm guessing the right fix here is to add more information to the error suggesting that if the intention wasn't to refer to a crate, crate:: or self:: etc. should/can be used explicitly.

(EDIT: I went to the internals thread to reply, and it's from March 2019 apparently, and also crate:: was mentioned there, but I guess the fact that the name meta is perfectly fine outside of use meta::...; wasn't brought up)

cc @petrochenkov

[yodaldevoid]

@eddyb

I believe the crate:: "fix" was mentioned in a reddit thread linking to the internals thread, but I forgot to mention it. I will reword the issue as it is misworded, as you pointed out. Lastly, what you suggested for a fix lines up with what I was expecting.

Also, now you know how deep my backlog of todo items is.