clippy::missing_const_for_fn triggering for tests is kind of pointless

[tv42]

Summary

I wrote a test to make sure I remembered to keep a type implementing Copy. The real type is defined by a fairly elaborate macro, so that felt like a real risk. It's meant to be a "does this compile" test. Clippy told me I should make my unit test const fn, which seems pointless.

I suggest clippy::missing_const_for_fn should ignore anything #[test].

Lint Name

clippy::missing_const_for_fn

Reproducer

I tried this code:

#[derive(Clone, Copy)]
pub struct Foo {
    pub n: u32,
}

impl Foo {
    #[must_use]
    pub const fn new(n: u32) -> Foo {
        Foo { n }
    }
}

#[test]
fn foo_is_copy() {
    let foo = Foo::new(42);
    let one = foo;
    let two = foo;
    _ = one;
    _ = two;
}

I saw this happen:

cargo clippy --tests -- -W clippy::missing_const_for_fn
+ command cargo clippy --tests -- -W clippy::missing_const_for_fn
    Checking rust-clippy-silly v0.1.0 (/home/tv/src/eagain.net/2024/rust-clippy-silly)
warning: this could be a `const fn`
  --> src/lib.rs:14:1
   |
14 | / fn foo_is_copy() {
15 | |     let foo = Foo::new(42);
16 | |     let one = foo;
17 | |     let two = foo;
18 | |     _ = one;
19 | |     _ = two;
20 | | }
   | |_^
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#missing_const_for_fn
   = note: requested on the command line with `-W clippy::missing-const-for-fn`
help: make the function `const`
   |
14 | const fn foo_is_copy() {
   | +++++

warning: `rust-clippy-silly` (lib test) generated 1 warning (run `cargo clippy --fix --lib -p rust-clippy-silly --tests` to apply 1 suggestion)
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.04s

I expected to see this happen: *blissful silence*

Version

Additional Labels

No response

[alex-semenyuk]

@rustbot claim