Suggestion for a typoed crate or module results in compile error

[TaKO8Ki]

This issue is

I implemented a suggestion for typoed crate or module in #89347. However there are still some edge cases.

Given the following code:

https://play.rust-lang.org/?version=nightly&mode=debug&edition=2018&gist=36133bfa20fc000bce25b7b1ea075df9

The current output is:

error[E0433]: failed to resolve: use of undeclared crate or module `my_cor`
  --> $DIR/extern-prelude-from-opaque-fail.rs:10:5
   |
LL |     my_cor::mem::drop(0);
   |     ^^^^^^ use of undeclared crate or module `my_cor`
   |
help: there is a crate or module with a similar name
   |
LL |     my_core::mem::drop(0);
   |     ~~~~~~~

error: aborting due to previous error

For more information about this error, try `rustc --explain E0433`.

However if you apply this suggestion, you get a compiler error like the following.

error[E0433]: failed to resolve: use of undeclared crate or module `my_core`
  --> $DIR/extern-prelude-from-opaque-fail.rs:10:5
   |
LL |     my_core::mem::drop(0);
   |     ^^^^^^^ use of undeclared crate or module `my_core`

error: aborting due to previous error

For more information about this error, try `rustc --explain E0433`.

Ideally the output should look like:

The compiler shouldn't suggest a crate or module name which you can't use.

error[E0433]: failed to resolve: use of undeclared crate or module `my_cor`
  --> $DIR/extern-prelude-from-opaque-fail.rs:10:5
   |
LL |     my_cor::mem::drop(0);
   |     ^^^^^^ use of undeclared crate or module `my_cor`
   |

error: aborting due to previous error

For more information about this error, try `rustc --explain E0433`.

#89347 (comment) might help you.

Other things to do: #89347 (comment)

[PatchMixolydic]

If you can get the span of the module, you might be able to filter candidates by Span::from_expansion. ModuleData::span seems like it could work, but I'm not sure if it'd point to the macro expansion or to the core crate in this case. If ModuleData::span points into the macro expansion, the fix might be as simple as making the following change in compiler/rustc_resolve/src/diagnostic.rs:

self.module_map
    .iter()
    .filter(|(_, module)| {
        current_module.is_ancestor_of(module) && !ptr::eq(current_module, *module)
    })
+   .filter(|(_, module)| {
+       module
+           .span
+           .map(|span| span.from_expansion())
+           .unwrap_or(false) // alternatively `.unwrap_or_default()`
+   })
    .map(|(_, module)| module.kind.name())
    .flatten(),

[estebank]

We should still not show the typo suggestion given it's not accessible, but the suggestions have gotten better.

error[[E0433]](https://doc.rust-lang.org/nightly/error_codes/E0433.html): failed to resolve: use of undeclared crate or module `my_cor`
  --> src/main.rs:10:5
   |
10 |     my_cor::mem::drop(0);
   |     ^^^^^^ use of undeclared crate or module `my_cor`
   |
help: there is a crate or module with a similar name
   |
10 |     my_core::mem::drop(0);
   |     ~~~~~~~
help: consider importing one of these items
   |
3  + [use core::mem;](https://play.rust-lang.org/?version=nightly&mode=debug&edition=2018&gist=36133bfa20fc000bce25b7b1ea075df9#)
   |
3  + [use memoffset::__priv::mem;](https://play.rust-lang.org/?version=nightly&mode=debug&edition=2018&gist=36133bfa20fc000bce25b7b1ea075df9#)
   |
3  + [use nom::lib::std::mem;](https://play.rust-lang.org/?version=nightly&mode=debug&edition=2018&gist=36133bfa20fc000bce25b7b1ea075df9#)
   |
3  + [use pin_utils::core_reexport::mem;](https://play.rust-lang.org/?version=nightly&mode=debug&edition=2018&gist=36133bfa20fc000bce25b7b1ea075df9#)
   |
     and 1 other candidate
help: if you import `mem`, refer to it directly
   |
10 -     my_cor::mem::drop(0);
10 +     mem::drop(0);
   |