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)]
   |

Fix #47608.

[rustbot]

r? @TaKO8Ki

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[rustbot]

Some changes occurred in src/tools/clippy

cc @rust-lang/clippy

[estebank]

r? compiler

[petrochenkov]

The PR is large and does multiple unrelated things.

Could you first move the emitter change ("show one more line") to a separate PR for someone else to review?
I'm not sure that it is useful, and it's orthogonal to other changes.
@rustbot author

[estebank]

Moved last commit to #109786.

[estebank]

This is so that the case in tests/ui/macros/missing-derive-4.rs (use serde;, but no use serde::Serialize;) is handled.

[petrochenkov]

How is this different from lookup_import_candidates_from_module?

Only macros that would be suggested as imports (and their helper attributes) can be suggested here.
So I suggest removing this separate logic and retrieve helper attributes in the lookup_import_candidates_from_module pass if the import candidate happens to be a derive macro and helper attributes satisfy filter_fn.

Same for typo suggestions, in addition for checking any visited item for being typo-suggestable we also need to check its helper attributes for the same thing, as a part of the regular early_lookup_typo_candidate pass.

[petrochenkov]

I suggest landing the core change first - extending the set of regular import and typo suggestions with helper attributes, and leave all the beautifications for later.

[bors]

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