templates: support string patterns in template language

[lf-]

This is a basic implementation of the same string pattern system as in
the revset language. It's currently only used for string.matches, so
you can now do:

"foo".matches(regex:'[a-f]o+')

In the future this could be added to more string functions (and e.g.
the ability to parse things out of strings could be added).

CC: #6893

Checklist

If applicable:

• I have updated CHANGELOG.md
• I have updated the documentation (README.md, docs/, demos/)
• I have updated the config schema (cli/src/config-schema.json)
• I have added/updated tests to cover my changes

[lf-]

cc @yuja

[PhilipMetzger]

just a reminder to adhere to commit guidelines here: https://github.com/jj-vcs/jj/blob/main/docs/contributing.md#commit-guidelines since. a feat: isn't really a topic. My suggestion would be templater:.

[lf-]

The full completion of this feature to be able to pull out the matching text in question probably involves introducing a new type that represents a match result (and match groups in regex), but doing so requires some rework and semantics design of the string pattern system itself.

I think that would probably be .match. Which probably means this boolean one should be called is_match actually as matches might mean "what is the list of matches in this string". Either that or this one should be called match and then we extend the output type to be a more substantive type later and just assume that everyone's using it as truthiness now. Thoughts?

[yuja]

The full completion of this feature to be able to pull out the matching text in question probably involves introducing a new type that represents a match result (and match groups in regex), but doing so requires some rework and semantics design of the string pattern system itself.

For this use case, I think we can add .match/es and .replace. The user might have to write the same regex twice, but that seems okay?

# .match(pat) -> String and/or .matches(path) -> List<String>
# .replace_all(pat, subst) -> String
.match(regex:'#\d+\b").replace_all(regex:'^#(.*)', 'issue-$2')

(match/matches might be a bad name, but I'm not sure.)

Implementation-wise, we'll need StringPattern::to_regex() or something, and use string-based substitution provided by Regex. We could add lambda syntax for subst expression, but that would be more complex, and I don't know if we'll need expressivity provided by arbitrary templates.

https://docs.rs/regex/latest/regex/struct.Regex.html#method.replace

[lf-]

The issue I have is that it seems nontrivial to make a to_regex translator for globs, and that IME it is most ideal to have the ability to match groups with a regex. But that's probably going to require creating a language type to be able to extract groups and matches; a regex feature that only does full matches is quite a bit harder to use.

So I'm partially trying to figure out how to incrementally deliver something useful without simply . inventing good regex support in my first code PR to the project heh. I think the path forward on that is calling the function introduced in this PR is_match.

[yuja]

The issue I have is that it seems nontrivial to make a to_regex translator for globs,

I think we'll need to switch to the globset crate at some point. The current StringPattern API doesn't have a separate .to_matcher() step, so adapting to GlobSet might not be straightforward. Still I think we can leverage globset to implement .to_regex().

https://docs.rs/globset/0.4.16/globset/struct.Glob.html

[lf-]

I've rebased and rewritten this based on #6967. It should be ready to go from my end minus one code question I couldn't figure out and need help with :)

[lf-]

Should be sufficiently rebased and feedback addressed.

[PhilipMetzger]

last minor thing from me.

[lf-]

rebased, I'm going to fix up the feedback now

edit: done!

[yuja]

LG, thanks.

[PhilipMetzger]

LG

[lf-]

okay, i think that's good to go now

[lf-]

Feedback should be fully addressed, PTAL.