Static AMBIGUOUS_DERIVE_HELPERS 

pub static AMBIGUOUS_DERIVE_HELPERS: &'static Lint

The ambiguous_derive_helpers lint detects cases where a derive macro’s helper attribute is the same name as that of a built-in attribute.

Example

#![crate_type = "proc-macro"]
#![deny(ambiguous_derive_helpers)]

use proc_macro::TokenStream;

#[proc_macro_derive(Trait, attributes(ignore))]
pub fn example(input: TokenStream) -> TokenStream {
    TokenStream::new()
}

Produces:

warning: there exists a built-in attribute with the same name
  --> file.rs:5:39
   |
 5 | #[proc_macro_derive(Trait, attributes(ignore))]
   |                                       ^^^^^^
   |
   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
   = note: for more information, see issue #151152 <https://github.com/rust-lang/rust/issues/151152>
   = note: `#[deny(ambiguous_derive_helpers)]` (part of `#[deny(future_incompatible)]`) on by default

Explanation

Attempting to use this helper attribute will throw an error:

#[derive(Trait)]
struct Example {
    #[ignore]
    fields: ()
}

Produces:

error[E0659]: `ignore` is ambiguous
 --> src/lib.rs:5:7
  |
5 |     #[ignore]
  |       ^^^^^^ ambiguous name
  |
  = note: ambiguous because of a name conflict with a builtin attribute
  = note: `ignore` could refer to a built-in attribute
note: `ignore` could also refer to the derive helper attribute defined here
 --> src/lib.rs:3:10
  |
3 | #[derive(Trait)]
  |          ^^^^^