improve diagnostic for literals in lint attributes

[annieversary]

Improves the diagnostic for literals in lint attributes, like #[allow("meow")].

Before:

error[E0452]: malformed lint attribute input
 --> main.rs:5:9
  |
5 | #[allow("meow")]
  |         ^^^^^^ bad attribute argument

error[E0452]: malformed lint attribute input
 --> main.rs:8:8
  |
8 | #[deny(1.0)]
  |        ^^^ bad attribute argument

After:

error: expected path to a lint, found literal
 --> main.rs:5:9
  |
5 | #[allow("meow")]
  |         ^^^^^^ not a lint
  |
  = help: try using `#[allow(meow)]`

error: expected path to a lint, found literal
 --> main.rs:8:8
  |
8 | #[deny(1.0)]
  |        ^^^ not a lint
  |
  = help: for example, write `#[deny(dead_code)]` for `dead_code`

Probably easier to review with whitespace changes turned off.

r? JonathanBrouwer

[rustbot]

Some changes occurred in compiler/rustc_attr_parsing

cc @jdonszelmann, @JonathanBrouwer

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[jdonszelmann]

Could you add a test for this change?

View changes since this review

[jdonszelmann]

Also grats on your first contrib ^.^

[annieversary]

I added a test (as a commit before the one with my change, as suggested by @N1ark), changed the original commit to update this test and another that failed, and made another commit to rename sub to kind. :3

[JonathanBrouwer]

r=me after that

View changes since this review

[JonathanBrouwer]

"expected a lint, found literal"

[JonathanBrouwer]

lint names are indeed paths, but I think emphasizing this is not needed

[JonathanBrouwer]

Could you also add a case that covers this variant to tests/ui/lint/lint-attribute-literals.rs?

[rustbot]

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