New-type return type of Parser::map

[DaniPopes]

Fixes #468. I'm not sure why this works but it probably has something to do with return-position impl Trait in traits having some exponential behavior in rustc.

Compile times for cargo build --bin egglog went from 40s to 8s on my machine, with egglog (library) now taking about 3s.

[codspeed-hq]

CodSpeed Performance Report

Merging #470 will not alter performance

_{Comparing DaniPopes:parser-map (9c1663d) with main (2c8d947)}

Summary

✅ 8 untouched benchmarks

[saulshanabrook]

Wow, that's a huge improvement! Thanks for tracing this down.

Could you add a comment to the code maybe linking the issue and explaining the fix so that people who come across this code know why it exists?

[Alex-Fischman]

My immediate thought is that I would rather simply revert this commit. It was only changed for ergonomics, and I don't think it's worth either the additional PhantomData complexity or the compile time hit.

@ezrosent Do you agree?