Allow escaping < and >

[mqudsi]

What version of ripgrep are you using?

ripgrep 0.10.0
-SIMD -AVX (compiled)
+SIMD +AVX (runtime)

How did you install ripgrep?

cargo

What operating system are you using ripgrep on?

FreeBSD 12

Describe your question, feature request, or bug.

Depending on the particular variant of regex used, it is sometimes needed to escape a literal < and > in a regex and sometimes not. rg does not use named captures and thus > and < are not considered special characters that need to be escaped in its regex syntax.

If you write pcre2-ish regexes by default, you may be accustomed to escaping these literals. If you do so, ripgrep errors out:

mqudsi@ZBOOK /m/c/U/m/r/a/t/debug> rg '\<'
regex parse error:
    \<
    ^^
error: unrecognized escape sequence

May I humbly request that \> and \< be treated as legal escapes evaluating to > and < for compatibility purposes?

[BurntSushi]

rg does not use named captures and thus > and < are not considered special characters that need to be escaped in its regex syntax.

ripgrep does support named captures:

$ echo foo123bar | rg '(?P<number>[0-9]+)' -or 'the number: $number'
the number: 123

However, neither < nor > need to be escapeable because they can only appear after a specific sequence of characters (namely, (?P), where both ( and ? are escapeable.

With that said, I'm going to pass on this for two reasons:

1. This is a property of the underlying regex engine, not ripgrep, and I have generally remained quite conservative with respect to escape sequences in order to make it possible to expand the syntax in a backwards compatible manner.
2. Incidentally, \< and \> do actually have special meaning in some regex engines that correspond to zero width assertions for left and right word boundaries, respectively. There is even a tracking ticket on the regex engine to consider supporting them. If the regex engine added support for nominal escapes of < and >, then the left/right word boundary feature couldn't be added without a backwards incompatible change.

for compatibility purposes?

In the future, please include specific concrete use cases. "compatibility purposes" is not particularly compelling to me in isolation.

[mqudsi]

Thank you.