I may be misunderstanding what you're saying, but using #[clippy::msrv = "1.80.0"] does mean "Do not suggest rewrites that would not be compatible with Rust 1.80.0". It does mean "Signal code invalid in Rust 1.80.0", as signaling invalid code is the job of the compiler, not the job of Clippy.

I'd expect a compiler version earlier than 1.82.0 to fail to compile the above code. I'd expect one later than 1.82.0 to compile it without any warnings since the function is defined. I would still expect clippy (1.82.0 and later) to warn about the use of repeat_n.

I filed this bug because when I tried the same formula with other recently-defined standard library functions, clippy complained as expected. I'd expect this code to produce 2 warnings:

#![warn(clippy::incompatible_msrv)]

#[clippy::msrv = "1.80"]
pub fn requires_rust_1_82() {
    let _ = std::iter::repeat_n((), 5);
}

#[clippy::msrv = "1.75"]
pub fn requires_rust_1_79() {
    let _ = std::path::absolute("asdf");
}

but running clippy on the playground only produces 1:

warning: current MSRV (Minimum Supported Rust Version) is `1.75.0` but this item is stable since `1.79.0`
  --> src/lib.rs:10:13
   |
10 |     let _ = std::path::absolute("asdf");
   |             ^^^^^^^^^^^^^^^^^^^
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#incompatible_msrv
note: the lint level is defined here
  --> src/lib.rs:1:9
   |
1  | #![warn(clippy::incompatible_msrv)]
   |         ^^^^^^^^^^^^^^^^^^^^^^^^^

warning: `playground` (lib) generated 1 warning

My bad, you are right. I overlooked the incompatible_msrv lint there.

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