Error message for duplicate names suggests invalid Rust

Consider the following library (with hello and aleph externs provided):

extern crate hello;
extern crate aleph as hello;

rustc will reasonably identify a problem:

error[E0259]: the name `hello` is defined multiple times
 --> lib.rs:2:1
  |
1 | extern crate hello;
  | ------------------- previous import of the extern crate `hello` here
2 | extern crate aleph as hello;
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `hello` reimported here
  |
  = note: `hello` must be defined only once in the type namespace of this module

but will then go on to suggest a rather unhelpful solution that isn't even valid Rust code:

help: You can use `as` to change the binding name of the import
  |
2 | extern crate aleph as hello; as Otherhello
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Related to #45799.

#45660 should verify wether the crate has already been renamed before providing the help. I believe this can be done by checking wether the NameBinding.kind::<Import> fields target and source are the same.

@Twey

@Twey, thanks for noticing that and filing an issue 😄

And @estebank, thanks for the instructions. I'll add a commit that fixes this as a part of #45820 when I get the chance.

EDIT: Looks like you've got it handled 👍

Rollup merge of rust-lang#45856 - estebank:issue-45829, r=nikomatsakis

This also happens with uses:

#![allow(unused_imports)]

mod foo {
    pub struct A;
    pub struct B;
}

use foo::{A, B as A};

fn main() {}

error[E0252]: the name `A` is defined multiple times
 --> src/main.rs:8:14
  |
8 | use foo::{A, B as A};
  |           -  ^^^^^^ `A` reimported here
  |           |
  |           previous import of the type `A` here
  |
  = note: `A` must be defined only once in the type namespace of this module
help: You can use `as` to change the binding name of the import
  |
8 | use foo::{A, B as A as OtherA};
  |              ^^^^^^^^^^^^^^^^

@pietroalbini thanks for fishing this out! The fix for use will likely be very similar to #45856.

Hello ! I took a shot at this.

I noticed that rust no longer suggests a new name for an extern crate import that has already been renamed.
This is because the suggestion is behind this check (https://github.com/rust-lang/rust/blob/master/src/librustc_resolve/lib.rs#L4788):

           if let (Ok(snippet), false) = (cm.span_to_snippet(binding.span),
                                           binding.is_renamed_extern_crate()) {

I didn't change that in #55113 in case it was done willingly, but that should be easy to change.

@mockersf

@mockersf commented on the PR. If you can apply the fix to extern statements as well, go ahead :)

Auto merge of #55113 - mockersf:master, r=estebank

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Error message for duplicate names suggests invalid Rust #45829

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Error message for duplicate names suggests invalid Rust #45829

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estebank commented on Nov 7, 2017

Cldfire commented on Nov 8, 2017

emilyalbini commented on Sep 17, 2018

estebank commented on Sep 17, 2018

mockersf commented on Oct 16, 2018

estebank commented on Oct 16, 2018

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