include_str!(file!()) does not work on godbolt

[CohenArthur]

as found by @liamnaddell in #1085

#![feature(rustc_attrs)]

#[rustc_builtin_macro]
macro_rules! include_str {
    () => {{}};
}

#[rustc_builtin_macro]
macro_rules! file {
    () => {{}};
}

fn main() {
    let _ = include_str!(file!());
}

I expected to see this happen: no error

Instead, this happened: gccrs complains that it is not able to open the file at /app/<source> even though printing the result of the file!() macro shows /app/example.rs

[liamnaddell]

How do we know this is a gccrs bug instead of a godbolt bug?

[liamnaddell]

I tried this code in godbolt and got the following interesting result: https://godbolt.org/z/hMb9bso3j

<source>:14:4: error: assignment of read-only location '{.data=(unsigned char * const *) "<source>", .len=15}'
   14 |    file!() = "bob";
      |    ^~~~
Compiler returned: 1

However, for gccrs on my laptop, I get

main2.rs:14:4: error: assignment of read-only location ‘{.data=(unsigned char * const *) "main2.rs", .len=8}’
   14 |    file!() = "bob";
      |    ^~~~

If you use rustc, and try the valid version of this code, you get /app/example.rs. I wonder if they handle rustc and gccrs differently in this case?