Add `defmt::file!()`

[darkwater]

I'm writing a parser and would like to have an error type containing filename + line where a parser failed. I believe right now my only options are:

• defmt::error!() at the place where parsing fails (but that might not be a real error because I'd want to try multiple parsers)
• Use core Location::caller() or file!() which embed &str into the binary

So a file!() macro returning an interned Str containing the filename would cover my use case, analogous to std::file!(). A module_path!() would be cool too but I'm not sure if there's a way to do that.

[jonathanpallant]

You can log at INFO level, and only turn on the logging at that level for that specific module. See https://defmt.ferrous-systems.com/filtering#modules.

It's not immediately clear to me where you'd be able to use the interned string returned by a defmt::file!() call? Would you just log it later on with {=istr}?

[darkwater]

Would you just log it later on with {=istr}?

Yeah, if an actual unexpected parsing error occurs, I'd print it and show the location. Putting a log at the point where it fails would mean I couldn't use patterns like:

fn option_a(input) -> ParseResult { ... }
fn option_b(input) -> ParseResult { ... }

fn parse_message(input) -> ParseResult {
  if let Ok(value) = option_a(input) { return value };
  if let Ok(value) = option_b(input) { return value };
}

[jonathanpallant]

Sounds reasonable then.