impl_trait_in_params doesn't work for non-public functions

[CobaltCause]

Summary

The lint only appears for public functions (i.e. public API surface of a library).

Lint Name

impl_trait_in_params

Reproducer

I tried this code:

#![deny(clippy::impl_trait_in_params)]
#![allow(dead_code)]
pub fn true_positive(_: impl Sized) {}
fn false_negative(_: impl Sized) {}

I expected to see this happen:

2 instances of impl_trait_in_params should appear, one for each function.

Instead, this happened:

Only 1 instance appeared for the pub function:

error: `impl Trait` used as a function parameter
 --> src/lib.rs:3:25
  |
3 | pub fn true_positive(_: impl Sized) {}
  |                         ^^^^^^^^^^
  |
  = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#impl_trait_in_params
note: the lint level is defined here
 --> src/lib.rs:1:9
  |
1 | #![deny(clippy::impl_trait_in_params)]
  |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
help: add a type parameter
  |
3 | pub fn true_positive<{ /* Generic name */ }: Sized>(_: impl Sized) {}
  |                     +++++++++++++++++++++++++++++++

Version

rustc 1.78.0 (9b00956e5 2024-04-29)
binary: rustc
commit-hash: 9b00956e56009bab2aa15d7bff10916599e3d6d6
commit-date: 2024-04-29
host: x86_64-unknown-linux-gnu
release: 1.78.0
LLVM version: 18.1.2

[J-ZhengLi]

looks like it was intended by design, but the doc didn't specify that:

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

Line 61 in a4a1a73

&& cx.tcx.visibility(cx.tcx.hir().body_owner_def_id(body.id())).is_public()

[CobaltCause]

Hmm, I just read through the PR in which the lint was added (#10197) and there wasn't any discussion about whether this was desirable or intentional. Maybe it being written this way was accidental. Either way, I personally think this lint should apply to all instances, not just public ones.