Confusing error with doc comments in parameter list

[lzybkr]

The following code:

pub fn f(
    /// Comment
    id: u8)
{}

Results in the following error:

error: expected pattern, found `/// Comment`
 --> src/lib.rs:2:5
  |
2 |     /// Comment
  |     ^^^^^^^^^^^ expected pattern

At best, the error is confusing. Ideally it should not be an error, but if doc comments are not allowed in a parameter list, the error should be clearer.

[Havvy]

Attributes, including doc comments, are not allowed on function parameters. Two more test cases:

fn foo(#[allow(dead_code)] id: i32) {}

fn bar(id: #[allow(dead_code)] i32) {}

with current output of

error: expected pattern, found `#`
 --> src/lib.rs:3:8
  |
L | fn foo(#[allow(dead_code)] id: i32) {}
  |        ^ expected pattern

error: expected type, found `#`
 --> src/lib.rs:5:12
  |
L | fn bar(id: #[allow(dead_code)] i32) {}
  |            ^

Ideally it should instead say:

error: expected pattern, found `#`
 --> src/lib.rs:3:8
  |
3 | fn foo(#[allow(dead_code)] id: i32) {}
  |        ^ attributes are not allowed on function parameters.

error: expected type, found `#`
 --> src/lib.rs:5:12
  |
5 | fn bar(id: #[allow(dead_code)] i32) {}
  |            ^ attributes are not allowed on function parameter types.

And then s/attributes/doc comments/ if it's a doc comment.