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Suggestions are often invalid for proc-macro produced code #85932

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m-ou-se opened this issue Jun 2, 2021 · 3 comments · Fixed by #85937
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Suggestions are often invalid for proc-macro produced code #85932

m-ou-se opened this issue Jun 2, 2021 · 3 comments · Fixed by #85937
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@m-ou-se
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A-suggestion-diagnostics Area: Suggestions generated by the compiler applied by `cargo fix` D-confusing Diagnostics: Confusing error or lint that should be reworked. D-invalid-suggestion Diagnostics: A structured suggestion resulting in incorrect code. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue.

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@m-ou-se
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m-ou-se commented Jun 2, 2021

The tokens generated by proc_macro (e.g. from quote!()) use Span::call_site(), which makes some suggestions produce invalid output:

error[E0308]: mismatched types
 --> src/main.rs:3:1
  |
3 | #[hello]
  | ^^^^^^^^
  | |
  | expected `&mut i32`, found integer
  | help: consider mutably borrowing here: `&mut #[hello]`

It's a bit tricky, because this call_site span does point into the current crate (to #[hello]), so this situaiton isn't detected in the same way as external macro_rules.
@m-ou-se m-ou-se added T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. A-suggestion-diagnostics Area: Suggestions generated by the compiler applied by `cargo fix` D-confusing Diagnostics: Confusing error or lint that should be reworked. D-invalid-suggestion Diagnostics: A structured suggestion resulting in incorrect code. labels Jun 2, 2021
@m-ou-se m-ou-se self-assigned this Jun 2, 2021
@m-ou-se
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m-ou-se commented Jun 2, 2021

Looks like rustc_middle::lint::in_external_macro should be used in more places. That one detects this call_site span by checking if def_site is a dummy or imported.

@m-ou-se
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m-ou-se commented Jun 2, 2021

I'm working on a fix specifically for these typeck/borrowing suggestions. Not sure how many other suggestions have the same problem.

@m-ou-se m-ou-se mentioned this issue Jun 2, 2021
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@estebank
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estebank commented Jun 3, 2021

@m-ou-se this is a prevalent problem. We need to add metadata to spans to distinguish call sites explicitly in an easy way and always ignore suggestions in them.

JohnTitor added a commit to JohnTitor/rust that referenced this issue Jun 3, 2021
@JohnTitor
Rollup merge of rust-lang#85937 - m-ou-se:macro-ref-suggestions, r=es…
2bd3237 
…tebank

Fix bad suggestions for code from proc_macro

Fixes rust-lang#85932

This disables these suggestions for spans from external macros, while keeping them for macros defined locally:

Before:
```
3 | #[hello]
  | ^^^^^^^^
  | |
  | expected `&mut i32`, found integer
  | help: consider mutably borrowing here: `&mut #[hello]`
```

After:
```
3 | #[hello]
  | ^^^^^^^^ expected `&mut i32`, found integer
```

Unchanged:
```
26 | macro_rules! bla { () => { x(123); } }
   |                              ^^^
   |                              |
   |                              expected `&mut i32`, found integer
   |                              help: consider mutably borrowing here: `&mut 123`
...
29 |     bla!();
   |     ------- in this macro invocation
```
@bors bors closed this as completed in 99fc56b Jun 4, 2021
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A-suggestion-diagnostics Area: Suggestions generated by the compiler applied by `cargo fix` D-confusing Diagnostics: Confusing error or lint that should be reworked. D-invalid-suggestion Diagnostics: A structured suggestion resulting in incorrect code. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue.
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Fix bad suggestions for code from proc_macro m-ou-se/rust
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@m-ou-se @estebank