too_many_lines not triggered on functions with #[tracing::instrument]

[letkemann]

Summary

'too_many_lines' is not trigfgered on functions with #[tracing::instrument].
Other lints seem to work insude the affected functions.

Lint Name

too_many_lines

Reproducer

I tried this code: (with too-many-lines-threshold = 2)

#![warn(clippy::too_many_lines)]
#[allow(unused)]

fn long_function_1() {
    do_something("fn 1.1");
    do_something("fn 1.2");
    do_something("fn 1.3");
}

#[tracing::instrument]
fn long_function_2() {
    do_something("fn 2.1");
    do_something("fn 2.2");
    do_something("fn 2.3");
}

fn do_something(_msg:&str){
    todo!()
}

I expected to see this happen:
Expected warnings on both functions, long_function_1() and long_function_2()

Instead, this happened:
Received only a single warning on long_function_1()

cargo clippy -v
       Fresh unicode-ident v1.0.14
       Fresh proc-macro2 v1.0.92
       Fresh quote v1.0.37
       Fresh syn v2.0.89
       Fresh once_cell v1.20.2
       Fresh tracing-core v0.1.33
       Fresh tracing-attributes v0.1.28
       Fresh pin-project-lite v0.2.15
       Fresh tracing v0.1.41
       Fresh clippy-too-may-lines v0.1.0 (/home/alex/devel/clippy-too-may-lines)
warning: this function has too many lines (3/2)
 --> src/lib.rs:4:1
  |
4 | / fn long_function_1() {
5 | |     do_something("fn 1.1");
6 | |     do_something("fn 1.2");
7 | |     do_something("fn 1.3");
8 | | }
  | |_^
  |
  = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#too_many_lines
note: the lint level is defined here
 --> src/lib.rs:1:9
  |
1 | #![warn(clippy::too_many_lines)]
  |         ^^^^^^^^^^^^^^^^^^^^^^

warning: `clippy-too-may-lines` (lib) generated 1 warning
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.01s

Version

rustc 1.82.0 (f6e511eec 2024-10-15)
binary: rustc
commit-hash: f6e511eec7342f59a25f7c0534f1dbea00d01b14
commit-date: 2024-10-15
host: x86_64-unknown-linux-gnu
release: 1.82.0
LLVM version: 19.1.1

[DylanBulfin]

This lint runs after macro expansion, and so code associated with an external macro is ignored. The clippy book has a section all about this but the basic idea is that by the time this function is linted it is filled with potentially hundreds of lines of auto-generated code the user has no control over. To avoid users having to manually disable lints like this for methods with external attributes, there's an explicit check here:

rust-clippy/clippy_lints/src/functions/too_many_lines.rs

Line 20 in 0a1ba2c

if matches!(kind, FnKind::Closure) || in_external_macro(cx.sess(), span) {