can't log the same string twice

[japaric]

STR

fn foo() {
    info!(LOGGER, "Hello");
}

fn bar() {
    warn!(LOGGER, "Hello");
}

$ xargo build
error: symbol `Hello` is already defined
 --> src/main.rs:4:1
  |
4 | static BAR: u8 = 0;
  | ^^^^^^^^^^^^^^^^^^^

error: Could not compile `hello`.

[japaric]

My idea to fix this was to prepend the filename and the line number to the message so the previous program would actually log:

$ cat /dev/ttyUSB0 | stcat -e file
INFO(src/main.rs:7) Hello
WARN(src/main.rs:8) Hello

but it's not possible to write #[export_name = concat!(..)] in a macro rules. Trying to work around this problem by concatenating strings outside the macro and then passing the concatenated string to the macro results in rust-lang/rust#42164.

[japaric]

Triage: we can do this using procedural macros that expand into expressions but those are not available so fixing this is blocked on that being stabilized.

[jonas-schievink]

Triage: procedural macros are now stable 🎉

[japaric]

This has been implemented behind the spanned feature in master but requires the unstable proc_macro_span feature in the library and the proc_macro_hygiene at call site.