`error: expected statement after outer attribute` gone?

[MauriceKayser]

Upgrading from Rust 1.86 to 1.87 causes tests that were supposed to fail not to fail anymore, but I could not find a Compatibility Note about that, so I wonder if that is intentional or a regression.

Reproduction steps

1. Create a new library: cargo new a --lib
2. Modify src/lib.rs:

   //! ```rust
   //! #[derive(Clone)]
   //! ```
   

3. Run cargo test with 1.86 and expect a failure:

   error: expected statement after outer attribute
    --> src/lib.rs:2:1
     |
   3 | #[derive(Clone)]
     |

4. Append ,compile_fail to the first line:

   //! ```rust,compile_fail
   //! #[derive(Clone)]
   //! ```
   

5. Run cargo test with 1.86 and expect success:

   test src/lib.rs - (line 1) - compile fail ... ok

6. Retry steps 1-3 with 1.87+, which does not fail anymore:

   test src/lib.rs - (line 1) ... ok

7. Retry steps 1-5 with 1.87+, which now fails:

   Test compiled successfully, but it's marked `compile_fail`.

Expected result

With 1.87+, step 3 should fail and step 5 should succeed as before, or it should be mentioned in the Compatibility Notes.

[fmease]

Most likely due to #138104. Definitely a bug. We're unintentionally dropping outer attributes in this case, very odd.