Linter warning not fired in macro code

[FrancescElies]

ℹThis report has previously been discussed in Why is a warning suppressed when the code is inside of a macro? - help - The Rust Programming Language Forum

I tried this code:

use std::ffi::CString;
use std::os::raw::c_char;

extern "C" {
    fn puts(s: *const c_char);
}

macro_rules! mymacro {
    () => {
        puts(CString::new("A CString").unwrap().as_ptr());
    };
}

fn main() {
    unsafe {
        puts(CString::new("A CString").unwrap().as_ptr());
        mymacro!();
    }
}

When executing, it does evaluate the code twice:

A CString
A CString

I expected to see a warning for each time I wrote CString::new("A CString").unwrap().as_ptr()

Instead, only one warning was fired.

See Warning (click me)

warning: getting the inner pointer of a temporary `CString`
  --> src/main.rs:16:49
   |
16 |         puts(CString::new("A CString").unwrap().as_ptr());
   |              ---------------------------------- ^^^^^^ this pointer will be invalid
   |              |
   |              this `CString` is deallocated at the end of the statement, bind it to a variable to extend its lifetime
   |
   = note: `#[warn(temporary_cstring_as_ptr)]` on by default
   = note: pointers do not have a lifetime; when calling `as_ptr` the `CString` will be deallocated at the end of the statement because nothing is referencing it as far as the type system is concerned
   = help: for more information, see https://doc.rust-lang.org/reference/destructors.html

rustc --version --verbose:

rustc 1.58.1 (db9d1b20b 2022-01-20)
binary: rustc
commit-hash: db9d1b20bba1968c1ec1fc49616d4742c1725b4b
commit-date: 2022-01-20
host: x86_64-pc-windows-msvc
release: 1.58.1
LLVM version: 13.0.0```

[itamarst]

I just hit this, and it's ... kinda a problem that a warning about undefined behavior is suppressed.