Abstract from Regex in pattern validator and add support for regex-lite

[jirutka]

The last commit makes regex-lite an equivalent alternative to regex and allows to drop dependency on the regex crate when regex-lite is enabled. However, since Cargo features are awfully limited and clumsy, it’s quite ugly. I don’t suppose you would accept such change (the last commit), so I leave it here only as a demonstration.

I believe it’s quite useful even without the ability to avoid pulling regex into the dependency graph, because if it’s not used (i.e. the user avoids using the pattern validator with string literals), the compiler will remove it when using LTO.

[jprochazk]

Sorry, haven't had time to properly look at this until now.

My immediate reaction is that I'm not sure if I want to support that exact use-case, because it means testing all patterns against both regex and regex-lite, and I don't really want to have introduce any kind of feature combination hell into this library and giving up on the --all-features flag Just Working™️. I know this change doesn't exactly cause that kind of problem, but it's a bit too close to that for comfort in my opinion.

That being said, I would be open to changing the Pattern trait similar to how you've done here, but without the direct support of regex-lite. Users wishing to change the regex engine used would have to resort to a newtype.

Here's my very rough idea of how this could work:

• Remove the feature gate on garde::rules::pattern
• Matcher trait implemented for regex::Regex (gated behind regex feature)

  trait Matcher {
    fn is_match(v: &str) -> bool;
  }

• Change Pattern to accept a Matcher:

  trait Pattern {
    fn validate_pattern<M: Matcher>(&self, m: M) -> bool;
  }

If you wanted to use regex-lite with #[garde(pattern(...))] (specifically the expr variant, not the string literal one), you'd implement Matcher on a newtype over regex_lite::Regex.

[jirutka]

Done, but I’ll recheck it tomorrow.

[jirutka]

I’ve updated the documentation; it should be ready now.

Just note that the new validate_pattern signature is a better solution per se, but unlike adding a generic parameter with a default value to the trait, this change breaks backward compatibility.

[jprochazk]

LGTM, thanks!

[jprochazk]

Published in v0.14.0