warning: used import from `std` instead of `core` in external macros

Summary

When enabling std_instead_of_core, the warning is emitted for code derived using derive macros.

This is likely not the desired behavior since there is a check using in_external_macro in the implementation.

Lint Name

std_instead_of_core

Reproducer

I tried this code:

#![warn(clippy::std_instead_of_core)]

use arbitrary::Arbitrary;

#[derive(Arbitrary)]
pub struct SomeStruct;

I saw this happen:

warning: used import from `std` instead of `core`
  --> crates/ironvnc-core/src/pixel_format.rs:10:42
   |
10 | #[cfg_attr(feature = "arbitrary", derive(arbitrary::Arbitrary))]
   |                                          ^^^^^^^^^^^^^^^^^^^^
   |
   = help: consider importing the item from `core`
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#std_instead_of_core
   = note: this warning originates in the derive macro `arbitrary::Arbitrary` (in Nightly builds, run with -Z macro-backtrace for more info)

I expected to see this happen: no warning

Version

rustc 1.74.0 (79e9716c9 2023-11-13)
binary: rustc
commit-hash: 79e9716c980570bfd1f666e3b16ac583f0168962
commit-date: 2023-11-13
host: x86_64-unknown-linux-gnu
release: 1.74.0
LLVM version: 17.0.4

Additional Labels

No response

Start by locating the std_instead_of_core lint implementation and its in_external_macro check. Reproduce the derive-macro example from the issue, then verify that code generated by the external macro no longer produces the warning while direct std imports remain checked.