start properly testing attributes in positions

[mejrs]

See the readme for the motivation. Just doing three attributes for now to get feedback on the overall implementation and direction.

Please let me know if there are additional positions that need testing!

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[jieyouxu]

r? jieyouxu

[ehuss]

Oh, this is great! I was just recently working on this, but happy to have someone actually make it happen.

I look forward to this being accepted. Let me know if you want any help.

I think there are a few tests that could eventually get deleted once everything gets covered. For example:

• ui/feature-gates/issue-43106-gating-of-builtin-attrs.rs -- This is a bit of a mess
• ui/issues/issue-54044.rs
• ui/issues/issue-78957.rs
• ui/lint/unused/unused_attributes-must_use.rs
• Probably others...

Some suggestions:

• Inner attributes on outline modules sometimes go through a different code path. I'm wondering if it would be helpful to include that? Unfortunately that could double the number of files.
• Some others that seem to be missing:
  • Inner attributes:
    • Trait definition
    • Const blocks (which are handled differently than regular blocks)
    • match block
    • Unstable things:
      • gen block
      • try block
  • Outer attributes:
    • Closure arguments (seems to be included in allow.rs though?)
    • Struct pattern fields
    • type: bare function parameter
    • type: bare function ...

[jieyouxu]

cc @jdonszelmann (as you may want to co-review)

[jdonszelmann]

Yes, I'd like that. might take a little because of rust week @rustbot claim

[mejrs]

I think we also ought to test combinations of attributes. Such as

#[ATTRIBUTE]
#[naked]
extern "C" fn naked(){}

Are there more like that?

Closure arguments (seems to be included in allow.rs though?)

Just added another commit with these. I originally had them..not sure where they went...

[mejrs]

Just these couple of edits have already been quite annoying and error prone. Doing this for dozens of attributes is going to be untenable in the long run.

This needs to be automatically generated, and I have some ideas about how to do that.