[BUG] `llvm-cov` warning `mismatched data` when double slash comment above `use`

bug

llvm-cov warning: 1 functions have mismatched data caused by comment line

background

Found llvm-cov warning: N functions have mismatched data.

After debug, very suprisingly find out this may all caused by comment line.

actual

llvm-cov warning: 1 functions have mismatched data caused by comment line // foo

crate A

#![feature(str_from_raw_parts)]

// foo
use core::str::from_raw_parts;

/// # Safety
///
/// TODO
#[inline]
#[must_use]
pub const unsafe fn str_from_raw_parts<'a>(ptr: *const u8, len: usize) -> &'a str {
    from_raw_parts(ptr, len)
}

crate B

    use feature_str_from_raw_parts_util::str_from_raw_parts;

    #[test]
    fn should_ok() {
        let x = unsafe { str_from_raw_parts("foobar".as_ptr(), 3) };
        let _ = x;

$ yarn cleanup:everything && yarn test:coverage
...
+ /path/to/llvm-cov report ...
warning: 1 functions have mismatched data
...

expected

comment line // foo should not lead to llvm-cov warning: 1 functions have mismatched data

crate A remove comment line

#![feature(str_from_raw_parts)]

use core::str::from_raw_parts;

/// # Safety
///
/// TODO
#[inline]
#[must_use]
pub const unsafe fn str_from_raw_parts<'a>(ptr: *const u8, len: usize) -> &'a str {
    from_raw_parts(ptr, len)
}

$ yarn cleanup:everything && yarn test:coverage
...
(llvm-cov no warning)
...

version

rustc 1.82.0-nightly (1f12b9b0f 2024-08-27)
binary: rustc
commit-hash: 1f12b9b0fdbe735968ac002792a720f0ba4faca6
commit-date: 2024-08-27
host: x86_64-unknown-linux-gnu
release: 1.82.0-nightly
LLVM version: 19.1.0

Reproduce the report using the two Rust crates shown in the issue and the yarn cleanup:everything && yarn test:coverage command. Compare coverage output with and without the // foo line above the use statement, then trace the relevant Rust coverage and LLVM integration from the failing behavior. Done means the comment no longer produces the mismatched data warning.