Compiler marks import as unnecessary when it isn't (panic_handler)

I tried this code:

lib.rs:

#![no_std]

#[cfg_attr(not(test), panic_handler)]
pub fn panic_handler(_info: &core::panic::PanicInfo<'_>) -> ! {
    loop {}
}

main.rs:

#![no_std]
#![no_main]

use playground;

Cargo.toml:

[package]
name = "playground"
version = "0.0.1"
edition = "2021"

# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html

[dependencies]

[profile.dev]
panic = "abort"

Upon running cargo check it gives this output:

warning: unused import: `playground`
 --> src/main.rs:4:5
  |
4 | use playground;
  |     ^^^^^^^^^^
  |
  = note: `#[warn(unused_imports)]` on by default

warning: `playground` (bin "playground") generated 1 warning (run `cargo fix --bin "playground"` to apply 1 suggestion)
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.00s

This is incorrect, as the import provides panic_handler for main, even though it is not directly imported.

To get a minimal reproduction you can run:
git clone --branch panic_handler_import_bug https://github.com/mysteriouslyseeing/playground.git

Note that cargo build will fail at linkage with that minimal reproduction due to the #![no_main] present. An alternate entry point would have to be specified based on the binaries' target to allow cargo build to work.

Meta

rustc --version --verbose: (stable)

rustc 1.79.0 (129f3b996 2024-06-10)
binary: rustc
commit-hash: 129f3b9964af4d4a709d1383930ade12dfe7c081
commit-date: 2024-06-10
host: x86_64-unknown-linux-gnu
release: 1.79.0
LLVM version: 18.1.7

rustc --version --verbose: (nightly)

rustc 1.81.0-nightly (032be6f7b 2024-07-16)
binary: rustc
commit-hash: 032be6f7bbe091c7dfa29f115e94b9cc9bae1758
commit-date: 2024-07-16
host: x86_64-unknown-linux-gnu
release: 1.81.0-nightly
LLVM version: 18.1.7

cargo fix:

    Checking playground v0.0.1 (/home/wschroeder/Projects/playground)
warning: failed to automatically apply fixes suggested by rustc to crate `playground`
This likely indicates a bug in either rustc or cargo itself,
and we would appreciate a bug report! You're likely to see
a number of compiler warnings after this message which cargo
attempted to fix but failed. If you could open an issue at
https://github.com/rust-lang/rust/issues
quoting the full output of this command we'd be very appreciative!
Note that you may be able to make some more progress in the near-term
fixing code with the `--broken-code` flag

The following errors were reported:
error: `#[panic_handler]` function required, but not found

error: aborting due to 1 previous error

Original diagnostics will follow.

warning: unused import: `playground`
 --> src/main.rs:4:5
  |
4 | use playground;
  |     ^^^^^^^^^^
  |
  = note: `#[warn(unused_imports)]` on by default

warning: `playground` (bin "playground") generated 1 warning (run `cargo fix --bin "playground"` to apply 1 suggestion)
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.06s

Reproduce the warning with the lib.rs, main.rs, and Cargo.toml setup from the issue by running cargo check. Then trace the compiler's unused-import analysis for the panic_handler dependency; done means the import is not marked unnecessary and the panic handler remains available without the warning.