`ply` has been abandoned, should we consider alternatives?

[wihobbs]

I noticed this morning that the Python ply package has recently been abandoned. We use ply for the constraint parser and it is a dependency of #7252. We should look into the recommended alternatives, either:

1. replace our use of ply with a different, maintained package,
2. take up maintenance ourselves by copying ply/lex.py and ply/yacc.py into src/bindings/python/flux/utils/ (provided of course that the LICENSE is respected), or
3. write a new LALR parser from scratch, ourselves, checking off a CS bucket list item in the process.

[garlick]

Groan, not yet another compiler compiler! (overheard in the bell labs cafeteria, circa 1975)

[wihobbs]

yay for Yet Another YACC 🎉

[sam-maloney]

Lark would seem like the most likely candidate for easy replacement. The only caveat might be availability in older distros as it has not been around for as long; e.g. there is no system package in el8-like distros, and only a "pre-release" v0.9.0 in el9 (I haven't checked Ubuntu/Deb versions yet).

That being said, I am currently developing on Rocky9 and my initial porting of the shape parser to use Lark v0.9.0 is working well, so that version might already be sufficient. But I note that el8 distros are currently used in the CI, so Lark would have to be made available there if those distros continue to be supported.