Look at proc-macro attributes when encountering unknown attribute

[estebank]

error: cannot find attribute `sede` in this scope
  --> src/main.rs:18:7
   |
18 |     #[sede(untagged)]
   |       ^^^^
   |
help: the derive macros `Serialize` and `Deserialize` accept the similarly named `serde` attribute
   |
18 |     #[serde(untagged)]
   |       ~~~~~

error: cannot find attribute `serde` in this scope
  --> src/main.rs:12:7
   |
12 |     #[serde(untagged)]
   |       ^^^^^
   |
   = note: `serde` is in scope, but it is a crate, not an attribute
help: `serde` is an attribute that can be used by the derive macros `Serialize` and `Deserialize`, you might be missing a `derive` attribute
   |
10 + #[derive(Serialize, Deserialize)]
11 | struct Foo {
   |

Mitigate #47608. Split off of #109278 as requested.

[rustbot]

r? @WaffleLapkin

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[petrochenkov]

r? @petrochenkov

[estebank]

@petrochenkov let me know if this was the split you desired. I guess I could have removed the additional span tracking as well and forego the structured suggestion, but that seemed to significantly reduce the utility of landing the PR in the first place.

[petrochenkov]

let me know if this was the split you desired

No, visit_scopes and add_derive_for_attribute should not be used separately.

Derive helper attributes should be added to suggestion candidates inside fn lookup_import_candidates and fn early_lookup_typo_candidate.
When we encounter a derive macro during the lookup we "open" it and add its helper attributes to the list of candidates too, if they fit.

I guess I could have removed the additional span tracking as well and forego the structured suggestion, but that seemed to significantly reduce the utility of landing the PR in the first place.

Yeah, let's drop all that, I want to land the core change cleanly.
Then we can add more detailed data to TypoSuggestion/ImportSuggestion structures to beautify the output.

@rustbot author

[bors]

☔ The latest upstream changes (presumably #110579) made this pull request unmergeable. Please resolve the merge conflicts.