clippy::transmute_float_to_int in const context should not trigger when rust-version is less than 1.83 in Cargo.toml

[tspiteri]

Summary

When rust-version is less than 1.83, the suggested code does not compile.

Lint Name

clippy::transmute_float_to_int

Reproducer

Cargo.toml contains:

rust-version = "1.82"

I tried this code:

pub const fn f32_to_u32(f: f32) -> u32 {
    unsafe { core::mem::transmute(f) }
}

I saw this happen:

warning: transmute from a `f32` to a `u32`
 --> src/lib.rs:2:14
  |
2 |     unsafe { core::mem::transmute(f) }
  |              ^^^^^^^^^^^^^^^^^^^^^^^ help: consider using: `f.to_bits()`
  |
  = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#transmute_float_to_int
  = note: `#[warn(clippy::transmute_float_to_int)]` on by default

I expected to see this happen:
No warning as rust 1.82.0 does not support f32::to_bits in const context.

Version

rustc 1.83.0-nightly (0ee7cb5e3 2024-09-10)
binary: rustc
commit-hash: 0ee7cb5e3633502d9a90a85c3c367eccd59a0aba
commit-date: 2024-09-10
host: x86_64-unknown-linux-gnu
release: 1.83.0-nightly
LLVM version: 19.1.0

Additional Labels

No response

[tspiteri]

@rustbot label +I-suggestion-causes-error

[y21]

transmute_float_to_int already checks if it's in a const context, so it shouldn't fire here regardless of the version:

rust-clippy/clippy_lints/src/transmute/transmute_float_to_int.rs

Line 21 in 5ead90f

(ty::Float(float_ty), ty::Int(_) | ty::Uint(_)) if !const_context => {

The reproducer also doesn't have any warnings: https://play.rust-lang.org/?version=nightly&mode=debug&edition=2021&gist=87b21a87034fd451c9278971fe6971bb

[tspiteri]

In rust 1.83, f32::to_bits will be usable on const context.

And it seems that the playground clippy is an older version than the one I used above.

[tspiteri]

It seems that in the rust-clippy repo it is conditioned on const_context as pointed out above,but in the rust repo it is not:

https://github.com/rust-lang/rust/blob/1f51450c6826cc4c3d1089cd3f57089a14f49190/src/tools/clippy/clippy_lints/src/transmute/transmute_float_to_int.rs#L20

[y21]

I see. Yeah, looks like those checks were removed in rust-lang/rust#129555 which was merged after the last rust->clippy sync, so that makes sense for why the bug isn't present in the clippy repo yet

[tspiteri]

Since this is in the rust repo, I created rust-lang/rust#130305 in the rust repo for it.