impl_trait_in_params should warn associated functions

[taiki-e]

Summary

This lint currently seems to warn only for freestanding functions.

It is correct to not warn associated functions of trait impls (since the user has no control over it), but I think it would be reasonable to warn associated functions of normal impls.

It is also probably reasonable to warn associated functions of trait definitions if the avoid-breaking-exported-api config is set to false.

Mentioning @blyxyas, who implemented this lint in #10197.

Lint Name

impl_trait_in_params

Reproducer

I tried this code:

#![warn(clippy::impl_trait_in_params)]

pub fn a(_s: impl AsRef<str>) {}

pub struct B;

impl B {
    pub fn b(_s: impl AsRef<str>) {}
}

I expected to see this happen: warnings for both a and b.

Instead, this happened:

clippy emits warning only for a.

warning: '`impl Trait` used as a function parameter'
 --> src/lib.rs:3:14
  |
3 | pub fn a(_s: impl AsRef<str>) {}
  |              ^^^^^^^^^^^^^^^
  |
  = 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 | #![warn(clippy::impl_trait_in_params)]
  |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
help: add a type parameter
  |
3 | pub fn a<{ /* Generic name */ }: AsRef<str>>(_s: impl AsRef<str>) {}
  |         ++++++++++++++++++++++++++++++++++++

playground

Version

rustc 1.74.0-nightly (3223b0b5e 2023-09-20)
binary: rustc
commit-hash: 3223b0b5e8dadda3f76c3fd1a8d6c5addc09599e
commit-date: 2023-09-20
host: aarch64-apple-darwin
release: 1.74.0-nightly
LLVM version: 17.0.0

[blyxyas]

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