`disallowed_names` triggers within external macro generated code

[Nemo157]

Summary

disallowed_names triggers within external macro generated code. I noticed this when trying to remove err from a crate as it is used within syn::parse_macro_input!.

Lint Name

disallowed_names

Reproducer

I tried this code:

#![deny(clippy::disallowed_names)]

#[proc_macro]
pub fn foo(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
    let output = input.clone();
    let _ = syn::parse_macro_input!(input as syn::DeriveInput);
    output
}

with the config:

disallowed-names = ["err"]

I saw this happen:

error: use of a disallowed/placeholder name `err`
 --> src/lib.rs:6:13
  |
6 |     let _ = syn::parse_macro_input!(input as syn::DeriveInput);
  |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |
  = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#disallowed_names
note: the lint level is defined here
 --> src/lib.rs:1:9
  |
1 | #![deny(clippy::disallowed_names)]
  |         ^^^^^^^^^^^^^^^^^^^^^^^^
  = note: this error originates in the macro `syn::parse_macro_input` (in Nightly builds, run with -Z macro-backtrace for more info)

I expected to see this happen:

No error since the identifier is within an external macro.

Version

rustc 1.88.0-nightly (2e6882ac5 2025-05-05)
binary: rustc
commit-hash: 2e6882ac5be27a73293d6f7ae56397fdf32848de
commit-date: 2025-05-05
host: x86_64-unknown-linux-gnu
release: 1.88.0-nightly
LLVM version: 20.1.4

Additional Labels

No response

[donkomura]

@rustbot claim

[Nemo157]

Just happened across a simpler repro:

#[derive(Debug)] pub struct Foo;

with config

disallowed-names = ["f"]

gives

warning: use of a disallowed/placeholder name `f`
 --> src/lib.rs:1:10
  |
1 | #[derive(Debug)] pub struct Foo;
  |          ^^^^^
  |
  = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#disallowed_names
  = note: `#[warn(clippy::disallowed_names)]` on by default