add file!() and line!() macros

[tgolsson]

Hello!

From discussion on Discord - this adds the file!() and line!() macros, which transform into string and number literals representing the current filename and line number (1-indexed). I tried to follow the pattern from format!(), but it seems a bit awkward being unable to implement these in runestick, instead feature-gating it in rune-modules.

➜ cat test.rn
pub fn main() {
   println(`Hello from ${file!()}:${line!()}`);
}

➜ target/release/rune test.rn
Hello from test.rn:2
== () (25.346µs)

[udoprog]

Great job. Only the comment about using self.source.path() needs to be addressed for now. Especially nice touch re-using the assembly impl for LitStr and LitNumber!

[udoprog]

hah, not that it matters (line count should be the same), but it would be nice with an utf8 version of this as well.

[tgolsson]

How'd that work - I can't see any information about the actual encoding of the incoming source? This should probably use the unicode variant though, not utf16.

[udoprog]

utf16cu stands for UTF-16 code units, the position function does some work to re-encode each character to utf-16 in order to find the column. An equivalent version for UTF-8 would simply rely on the emitted chars instead.

See: https://github.com/rune-rs/rune/blob/master/crates/runestick/src/source.rs#L135

Not a blocker though, since the line will be the same.

[udoprog]

All blockers are resolved. 🚀