Derive with strings not quote

[illicitonion]

For large (thousands of variants) enums, this drops the time to generate
from minutes to seconds.

I don't love this, but it's a significant speedup, and the code we're
generating is pretty simple...

I'll file a bug against proc-quote about the perf.

Fixes #13 /cc @anlumo

[danielhenrymantilla]

Oh, that's both interesting and disappointing 😅
Since the performance gain is huge, we'll have to settle for this version. I am still curious though: since you have already done some benchmarks, could you also benchmark using ::quote::quote! rather than ::proc_quote::quote! ? (c.f. #15)

[illicitonion]

I checked - quote took 88 seconds, compared to proc-quote's 94. I'm going to merge #14 (and switch to regular quote), then rebase and merge this on top, so that it will be easy for us to switch back if the perf issues get resolved :)

[dtolnay]

The slowness is a bug in the compiler's libproc_macro: rust-lang/rust#65080.

I opened dtolnay/proc-macro2#199 with a workaround that drops the cargo expand time of https://github.com/illicitonion/num_enum_regression_13 (using quote) from 118 seconds to 2.0 seconds on my machine.

[danielhenrymantilla]

Wow, thanks for stepping in, @dtolnay. The change you have suggested to proc-macro2 is great, it should be faster to get that going than the original fix on proc-macro.

So the best course of action for this PR is to wait for a quote release (or git rev) to depend on this patched version of proc-macro2, right?

[dtolnay]

I published the workaround in proc-macro2 so the performance should already be fixed once you run cargo update.

[illicitonion]

Closing - fix is pushed to transitive dep :)