`clippy::op_ref` on `CString` triggers even when MSRV does not support the required trait impls

[lopopolo]

Summary

Clippy does not respect MSRV when suggesting to remove an & when comparing a CString and a &CStr on Rust 1.76.0.

Lint Name

clippy::op_ref

Reproducer

I tried this code:

fn intern_get_roundtrip(cstring: CString) -> bool {
    let mut table = SymbolTable::new();
    let sym = table.intern(cstring.clone()).unwrap();
    let retrieved_c_string = table.get(sym).unwrap();
    &*cstring == retrieved_c_string
}

I saw this happen:

warning: needlessly taken reference of left operand
    --> src/cstr.rs:1027:13
     |
1027 |             &*cstring == retrieved_c_string
     |             ---------^^^^^^^^^^^^^^^^^^^^^^
     |             |
     |             help: use the left value directly: `*cstring`
     |
     = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#op_ref
note: the lint level is defined here
    --> src/lib.rs:1:9
     |
   1 | #![warn(clippy::all)]
     |         ^^^^^^^^^^^
     = note: `#[warn(clippy::op_ref)]` implied by `#[warn(clippy::all)]`

I expected to see this happen: the lint should not fire because the crate has rust-version = "1.76.0" declared in Cargo.toml.

Applying this diff:

diff --git a/src/cstr.rs b/src/cstr.rs
index 75d702b..e2d3fa3 100644
--- a/src/cstr.rs
+++ b/src/cstr.rs
@@ -1024,7 +1024,7 @@ mod tests {
             let mut table = SymbolTable::new();
             let sym = table.intern(cstring.clone()).unwrap();
             let retrieved_c_string = table.get(sym).unwrap();
-            &*cstring == retrieved_c_string
+            *cstring == retrieved_c_string
         }

         fn table_contains_sym(cstring: CString) -> bool {

yields this error

   Compiling intaglio v1.10.0 (/home/runner/work/intaglio/intaglio)
error[E0308]: mismatched types
    --> src/cstr.rs:1027:25
     |
1027 |             *cstring == retrieved_c_string
     |             --------    ^^^^^^^^^^^^^^^^^^ expected `CStr`, found `&CStr`
     |             |
     |             expected because this is `CStr`
     |
help: consider dereferencing the borrow
     |
1027 |             *cstring == *retrieved_c_string
     |                         +

For more information about this error, try `rustc --explain E0308`.
error: could not compile `intaglio` (lib test) due to 1 previous error
warning: build failed, waiting for other jobs to finish...

when building with Rust 1.76.0, which does not have the required trait impls.

Failing GitHub Actions run is here: https://github.com/artichoke/intaglio/actions/runs/18436896685/job/52531604213?pr=324

Version

rustc 1.76.0 (07dca489a 2024-02-04)
binary: rustc
commit-hash: 07dca489ac2d933c78d3c5158e3f43beefeb02ce
commit-date: 2024-02-04
host: x86_64-unknown-linux-gnu
release: 1.76.0
LLVM version: 17.0.6

Additional Labels

No response

[lopopolo]

@rustbot label -I-false-positive +I-suggestion-causes-error

[samueltardieu]

Self-contained reproducer:

use std::ffi::{CStr, CString};

#[clippy::msrv = "1.76"]
fn main() {
    let (a, b): (CString, &CStr) = (todo!(), todo!());
    _ = &*a == b;   // Should not get the suggestion `*a == b` from `clippy::op_ref`
}

It happens with the current nightly version of Clippy (the one given by OP doesn't implement this lint):

rustc 1.92.0-nightly (be0ade2b6 2025-10-11)
binary: rustc
commit-hash: be0ade2b602bdfe37a3cc259fcc79e8624dcba94
commit-date: 2025-10-11
host: x86_64-unknown-linux-gnu
release: 1.92.0-nightly
LLVM version: 21.1.2