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Named capture group syntax: (?<name>exp)
#955
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To get this out of the way: this would be a backwards compatible change because currently all forms of I think the original reason why I didn't do this was to 1) match RE2 syntax and 2) I didn't want two ways of doing the same thing. But I do think my stance has softened somewhat over time on this. Another related example is that I plan to relax the escaping rules in order to make the differences between at least the surface level syntax smaller between other regex engines. (For example, right now I'll also say though that what you're facing here is a surface level problem. There are assuredly many other differences between this regex engine and Oniguruma. How will you deal with those? If compatibility is your ultimate goal, then you probably just need to use Oniguruma itself. Or do you see this more as a "let's get some compatibility, but not all of it" sort of situation? The problem there is that there may be many incompatibilities that are totally silent. (I don't have an Oniguruma environment that I can easily test with at the moment.) I'll note that RE2 specifically only implements
I am quite sympathetic to this line of reasoning personally. And chasing this sort of "let's just keep adding alternative forms of everything until we capture all the different ways other regex engines do things" will lead us into undesirable territory. I also wonder whether you could easily work around this by looking for a I'm undecided on this personally. @junyer do you have any thoughts here? |
It sounds like you and I (and @rsc) are aligned here at least philosophically. And now speaking pragmatically, adding support for |
I still basically agree with what I wrote in the RE2 comment long ago. I could change my mind given evidence of (1) significant usage of .NET forms or (2) significant environments that only support the .NET forms. It sounds like jq might be one such environment. Reading the other link, maybe Java or Boost has (?...) without (?P...)? It's unclear to me. On the surface syntax issue and
|
Thanks for your very detailed answers.
Yes, I see the situation as "let's get some compatibility, but not all of it". (Using Oniguruma from Rust is not really an option for me, all the more because I already have an implementation of regexes using the
I agree in principle; however, when searching for "regex named capture group", among the first four matches,
There might be a lot of tricky cases to handle. Consider:
Given that I am not a regex expert, I would not trust myself to get this right.
Why is there such a need for synchronisation? Is there some kind of agreement between the Rust Would it perhaps be possible to have some opt-in option, for example in |
Regarding Java, I read at least three sites, all of which exclusively mentioned the For Boost, the documentation says that the Perl syntax is the default behaviour, and details that this supports |
To clarify here, @junyer and @rsc are RE2 maintainers, and RE2, RE2/J and Go's There is no synchronization promise with those three and the regex crate though. The regex crate does actually have some substantial differences (like the escaping strategy, although I expect that to change in the direction of RE2's) and also support for character class set operations and nested classes and probably a few other minor things. Still though, I value their input and "consistent with RE2" is, overall, something I value. But not over everything else. |
I see. Thanks for clarifying your synchronisation policy. Just on the side: I believe that implementing the If I can do anything else to convince you about the utility of supporting |
I found an interesting bit of history from the Python project that explains among others how the syntax
So the |
@01mf02 The history and original reason for the
I think (1) and (2) are where I am at the moment. Unfortunately, there's no real objective criteria to evaluate here. I am overall leaning towards doing this.
I agree that the patch here is likely quite simple, but it is probably not this simple. Whether |
Have we identified any regexp implementations other than onigurama that don't implement Also, is the suggestion to allow both |
Not sure about
I think that's all I could find at the moment. I think the closest thing to a consensus among non-RE2 engines is "support both |
I think the suggestion on the table is just first, as that's what is used by Oniguruma in the context of The |
I hope this comment doesn't distract too much but I really appreciate how @BurntSushi addresses issues raised, explaining his reasoning and so on. I learn so much from just following along and it usually causes me to think about considerations I might have otherwise missed. I just want to say thank you, I really appreciate the time you put into your responses. |
I second @c-git in that I also value your very detailed responses, @BurntSushi. And of course I'm happy to read that you are leaning towards implementing my suggestion.
The documentation of the boost regex module mentions named capture groups only in the Perl syntax flavour, which says that
Ah, I see. I suppose it is for round-tripping? If you wish, I could tackle this. I understand that the ast::Group::CaptureName variant would either need to be extended by some bit that indicates the presence of |
Yes, round-tripping. The point of the AST is that it exhaustively describes the syntax as it is. Lowering it into something simpler and easier to analyze happens in a second pass. (You'll need to make what is likely a trivial change to the AST->HIR translator, also inside of I think a new variant for |
Talked to @junyer a bit, and I think this change make sense to do in RE2 and Go as well. I filed golang/go#58458, and assuming it goes through we'll update RE2 and Go in about a month. |
@rsc SGTM! If y'all add support for it then I definitely will as well. We might not line up timing wise, but I think that's okay! |
Great! I'm very happy that we seem to have reached a consensus on this issue. :) I have opened a PR with my proposed changes. Have a good weekend! |
It turns out that both '(?P<name>...)' and '(?<name>...)' are rather common among regex engines. There are several that support just one or the other. Until this commit, the regex crate only supported the former, along with both RE2, RE2/J and Go's regexp package. There are also several regex engines that only supported the latter, such as Onigmo, Onuguruma, Java, Ruby, Boost, .NET and Javascript. To decrease friction, and because there is somewhat little cost to doing so, we elect to support both. It looks like perhaps RE2 and Go's regexp package will go the same route, but it isn't fully decided yet: golang/go#58458 Closes #955
It turns out that both '(?P<name>...)' and '(?<name>...)' are rather common among regex engines. There are several that support just one or the other. Until this commit, the regex crate only supported the former, along with both RE2, RE2/J and Go's regexp package. There are also several regex engines that only supported the latter, such as Onigmo, Onuguruma, Java, Ruby, Boost, .NET and Javascript. To decrease friction, and because there is somewhat little cost to doing so, we elect to support both. It looks like perhaps RE2 and Go's regexp package will go the same route, but it isn't fully decided yet: golang/go#58458 Closes #955, Closes #956
It turns out that both '(?P<name>...)' and '(?<name>...)' are rather common among regex engines. There are several that support just one or the other. Until this commit, the regex crate only supported the former, along with both RE2, RE2/J and Go's regexp package. There are also several regex engines that only supported the latter, such as Onigmo, Onuguruma, Java, Ruby, Boost, .NET and Javascript. To decrease friction, and because there is somewhat little cost to doing so, we elect to support both. It looks like perhaps RE2 and Go's regexp package will go the same route, but it isn't fully decided yet: golang/go#58458 Closes #955, Closes #956
It turns out that both '(?P<name>...)' and '(?<name>...)' are rather common among regex engines. There are several that support just one or the other. Until this commit, the regex crate only supported the former, along with both RE2, RE2/J and Go's regexp package. There are also several regex engines that only supported the latter, such as Onigmo, Onuguruma, Java, Ruby, Boost, .NET and Javascript. To decrease friction, and because there is somewhat little cost to doing so, we elect to support both. It looks like perhaps RE2 and Go's regexp package will go the same route, but it isn't fully decided yet: golang/go#58458 Closes #955, Closes #956
It turns out that both '(?P<name>...)' and '(?<name>...)' are rather common among regex engines. There are several that support just one or the other. Until this commit, the regex crate only supported the former, along with both RE2, RE2/J and Go's regexp package. There are also several regex engines that only supported the latter, such as Onigmo, Onuguruma, Java, Ruby, Boost, .NET and Javascript. To decrease friction, and because there is somewhat little cost to doing so, we elect to support both. It looks like perhaps RE2 and Go's regexp package will go the same route, but it isn't fully decided yet: golang/go#58458 Closes #955, Closes #956
It turns out that both '(?P<name>...)' and '(?<name>...)' are rather common among regex engines. There are several that support just one or the other. Until this commit, the regex crate only supported the former, along with both RE2, RE2/J and Go's regexp package. There are also several regex engines that only supported the latter, such as Onigmo, Onuguruma, Java, Ruby, Boost, .NET and Javascript. To decrease friction, and because there is somewhat little cost to doing so, we elect to support both. It looks like perhaps RE2 and Go's regexp package will go the same route, but it isn't fully decided yet: golang/go#58458 Closes #955, Closes #956
It turns out that both '(?P<name>...)' and '(?<name>...)' are rather common among regex engines. There are several that support just one or the other. Until this commit, the regex crate only supported the former, along with both RE2, RE2/J and Go's regexp package. There are also several regex engines that only supported the latter, such as Onigmo, Onuguruma, Java, Ruby, Boost, .NET and Javascript. To decrease friction, and because there is somewhat little cost to doing so, we elect to support both. It looks like perhaps RE2 and Go's regexp package will go the same route, but it isn't fully decided yet: golang/go#58458 Closes #955, Closes #956
It turns out that both '(?P<name>...)' and '(?<name>...)' are rather common among regex engines. There are several that support just one or the other. Until this commit, the regex crate only supported the former, along with both RE2, RE2/J and Go's regexp package. There are also several regex engines that only supported the latter, such as Onigmo, Onuguruma, Java, Ruby, Boost, .NET and Javascript. To decrease friction, and because there is somewhat little cost to doing so, we elect to support both. It looks like perhaps RE2 and Go's regexp package will go the same route, but it isn't fully decided yet: golang/go#58458 Closes #955, Closes #956
It turns out that both '(?P<name>...)' and '(?<name>...)' are rather common among regex engines. There are several that support just one or the other. Until this commit, the regex crate only supported the former, along with both RE2, RE2/J and Go's regexp package. There are also several regex engines that only supported the latter, such as Onigmo, Onuguruma, Java, Ruby, Boost, .NET and Javascript. To decrease friction, and because there is somewhat little cost to doing so, we elect to support both. It looks like perhaps RE2 and Go's regexp package will go the same route, but it isn't fully decided yet: golang/go#58458 Closes #955, Closes #956
It turns out that both '(?P<name>...)' and '(?<name>...)' are rather common among regex engines. There are several that support just one or the other. Until this commit, the regex crate only supported the former, along with both RE2, RE2/J and Go's regexp package. There are also several regex engines that only supported the latter, such as Onigmo, Onuguruma, Java, Ruby, Boost, .NET and Javascript. To decrease friction, and because there is somewhat little cost to doing so, we elect to support both. It looks like perhaps RE2 and Go's regexp package will go the same route, but it isn't fully decided yet: golang/go#58458 Closes #955, Closes #956
It turns out that both '(?P<name>...)' and '(?<name>...)' are rather common among regex engines. There are several that support just one or the other. Until this commit, the regex crate only supported the former, along with both RE2, RE2/J and Go's regexp package. There are also several regex engines that only supported the latter, such as Onigmo, Onuguruma, Java, Ruby, Boost, .NET and Javascript. To decrease friction, and because there is somewhat little cost to doing so, we elect to support both. It looks like perhaps RE2 and Go's regexp package will go the same route, but it isn't fully decided yet: golang/go#58458 Closes #955, Closes #956
It turns out that both '(?P<name>...)' and '(?<name>...)' are rather common among regex engines. There are several that support just one or the other. Until this commit, the regex crate only supported the former, along with both RE2, RE2/J and Go's regexp package. There are also several regex engines that only supported the latter, such as Onigmo, Onuguruma, Java, Ruby, Boost, .NET and Javascript. To decrease friction, and because there is somewhat little cost to doing so, we elect to support both. It looks like perhaps RE2 and Go's regexp package will go the same route, but it isn't fully decided yet: golang/go#58458 Closes #955, Closes #956
It turns out that both '(?P<name>...)' and '(?<name>...)' are rather common among regex engines. There are several that support just one or the other. Until this commit, the regex crate only supported the former, along with both RE2, RE2/J and Go's regexp package. There are also several regex engines that only supported the latter, such as Onigmo, Onuguruma, Java, Ruby, Boost, .NET and Javascript. To decrease friction, and because there is somewhat little cost to doing so, we elect to support both. It looks like perhaps RE2 and Go's regexp package will go the same route, but it isn't fully decided yet: golang/go#58458 Closes #955, Closes #956
It turns out that both '(?P<name>...)' and '(?<name>...)' are rather common among regex engines. There are several that support just one or the other. Until this commit, the regex crate only supported the former, along with both RE2, RE2/J and Go's regexp package. There are also several regex engines that only supported the latter, such as Onigmo, Onuguruma, Java, Ruby, Boost, .NET and Javascript. To decrease friction, and because there is somewhat little cost to doing so, we elect to support both. It looks like perhaps RE2 and Go's regexp package will go the same route, but it isn't fully decided yet: golang/go#58458 Closes #955, Closes #956
It turns out that both '(?P<name>...)' and '(?<name>...)' are rather common among regex engines. There are several that support just one or the other. Until this commit, the regex crate only supported the former, along with both RE2, RE2/J and Go's regexp package. There are also several regex engines that only supported the latter, such as Onigmo, Onuguruma, Java, Ruby, Boost, .NET and Javascript. To decrease friction, and because there is somewhat little cost to doing so, we elect to support both. It looks like perhaps RE2 and Go's regexp package will go the same route, but it isn't fully decided yet: golang/go#58458 Closes #955, Closes #956
1.8.0 (2023-04-20) ================== This is a sizeable release that will be soon followed by another sizeable release. Both of them will combined close over 40 existing issues and PRs. This first release, despite its size, essentially represent preparatory work for the second release, which will be even bigger. Namely, this release: * Increases the MSRV to Rust 1.60.0, which was released about 1 year ago. * Upgrades its dependency on `aho-corasick` to the recently release 1.0 version. * Upgrades its dependency on `regex-syntax` to the simultaneously released `0.7` version. The changes to `regex-syntax` principally revolve around a rewrite of its literal extraction code and a number of simplifications and optimizations to its high-level intermediate representation (HIR). The second release, which will follow ~shortly after the release above, will contain a soup-to-nuts rewrite of every regex engine. This will be done by bringing [`regex-automata`](https://github.com/BurntSushi/regex-automata) into this repository, and then changing the `regex` crate to be nothing but an API shim layer on top of `regex-automata`'s API. These tandem releases are the culmination of about 3 years of on-and-off work that [began in earnest in March 2020](#656). Because of the scale of changes involved in these releases, I would love to hear about your experience. Especially if you notice undocumented changes in behavior or performance changes (positive *or* negative). Most changes in the first release are listed below. For more details, please see the commit log, which reflects a linear and decently documented history of all changes. New features: * [FEATURE #501](#501): Permit many more characters to be escaped, even if they have no significance. More specifically, any ASCII character except for `[0-9A-Za-z<>]` can now be escaped. Also, a new routine, `is_escapeable_character`, has been added to `regex-syntax` to query whether a character is escapeable or not. * [FEATURE #547](#547): Add `Regex::captures_at`. This filles a hole in the API, but doesn't otherwise introduce any new expressive power. * [FEATURE #595](#595): Capture group names are now Unicode-aware. They can now begin with either a `_` or any "alphabetic" codepoint. After the first codepoint, subsequent codepoints can be any sequence of alpha-numeric codepoints, along with `_`, `.`, `[` and `]`. Note that replacement syntax has not changed. * [FEATURE #810](#810): Add `Match::is_empty` and `Match::len` APIs. * [FEATURE #905](#905): Add an `impl Default for RegexSet`, with the default being the empty set. * [FEATURE #908](#908): A new method, `Regex::static_captures_len`, has been added which returns the number of capture groups in the pattern if and only if every possible match always contains the same number of matching groups. * [FEATURE #955](#955): Named captures can now be written as `(?<name>re)` in addition to `(?P<name>re)`. * FEATURE: `regex-syntax` now supports empty character classes. * FEATURE: `regex-syntax` now has an optional `std` feature. (This will come to `regex` in the second release.) * FEATURE: The `Hir` type in `regex-syntax` has had a number of simplifications made to it. * FEATURE: `regex-syntax` has support for a new `R` flag for enabling CRLF mode. This will be supported in `regex` proper in the second release. * FEATURE: `regex-syntax` now has proper support for "regex that never matches" via `Hir::fail()`. * FEATURE: The `hir::literal` module of `regex-syntax` has been completely re-worked. It now has more documentation, examples and advice. * FEATURE: The `allow_invalid_utf8` option in `regex-syntax` has been renamed to `utf8`, and the meaning of the boolean has been flipped. Performance improvements: * PERF: The upgrade to `aho-corasick 1.0` may improve performance in some cases. It's difficult to characterize exactly which patterns this might impact, but if there are a small number of longish (>= 4 bytes) prefix literals, then it might be faster than before. Bug fixes: * [BUG #514](#514): Improve `Debug` impl for `Match` so that it doesn't show the entire haystack. * BUGS [#516](#516), [#731](#731): Fix a number of issues with printing `Hir` values as regex patterns. * [BUG #610](#610): Add explicit example of `foo|bar` in the regex syntax docs. * [BUG #625](#625): Clarify that `SetMatches::len` does not (regretably) refer to the number of matches in the set. * [BUG #660](#660): Clarify "verbose mode" in regex syntax documentation. * BUG [#738](#738), [#950](#950): Fix `CaptureLocations::get` so that it never panics. * [BUG #747](#747): Clarify documentation for `Regex::shortest_match`. * [BUG #835](#835): Fix `\p{Sc}` so that it is equivalent to `\p{Currency_Symbol}`. * [BUG #846](#846): Add more clarifying documentation to the `CompiledTooBig` error variant. * [BUG #854](#854): Clarify that `regex::Regex` searches as if the haystack is a sequence of Unicode scalar values. * [BUG #884](#884): Replace `__Nonexhaustive` variants with `#[non_exhaustive]` attribute. * [BUG #893](#893): Optimize case folding since it can get quite slow in some pathological cases. * [BUG #895](#895): Reject `(?-u:\W)` in `regex::Regex` APIs. * [BUG #942](#942): Add a missing `void` keyword to indicate "no parameters" in C API. * [BUG #965](#965): Fix `\p{Lc}` so that it is equivalent to `\p{Cased_Letter}`. * [BUG #975](#975): Clarify documentation for `\pX` syntax.
1.8.0 (2023-04-20) ================== This is a sizeable release that will be soon followed by another sizeable release. Both of them will combined close over 40 existing issues and PRs. This first release, despite its size, essentially represent preparatory work for the second release, which will be even bigger. Namely, this release: * Increases the MSRV to Rust 1.60.0, which was released about 1 year ago. * Upgrades its dependency on `aho-corasick` to the recently release 1.0 version. * Upgrades its dependency on `regex-syntax` to the simultaneously released `0.7` version. The changes to `regex-syntax` principally revolve around a rewrite of its literal extraction code and a number of simplifications and optimizations to its high-level intermediate representation (HIR). The second release, which will follow ~shortly after the release above, will contain a soup-to-nuts rewrite of every regex engine. This will be done by bringing [`regex-automata`](https://github.com/BurntSushi/regex-automata) into this repository, and then changing the `regex` crate to be nothing but an API shim layer on top of `regex-automata`'s API. These tandem releases are the culmination of about 3 years of on-and-off work that [began in earnest in March 2020](#656). Because of the scale of changes involved in these releases, I would love to hear about your experience. Especially if you notice undocumented changes in behavior or performance changes (positive *or* negative). Most changes in the first release are listed below. For more details, please see the commit log, which reflects a linear and decently documented history of all changes. New features: * [FEATURE #501](#501): Permit many more characters to be escaped, even if they have no significance. More specifically, any ASCII character except for `[0-9A-Za-z<>]` can now be escaped. Also, a new routine, `is_escapeable_character`, has been added to `regex-syntax` to query whether a character is escapeable or not. * [FEATURE #547](#547): Add `Regex::captures_at`. This filles a hole in the API, but doesn't otherwise introduce any new expressive power. * [FEATURE #595](#595): Capture group names are now Unicode-aware. They can now begin with either a `_` or any "alphabetic" codepoint. After the first codepoint, subsequent codepoints can be any sequence of alpha-numeric codepoints, along with `_`, `.`, `[` and `]`. Note that replacement syntax has not changed. * [FEATURE #810](#810): Add `Match::is_empty` and `Match::len` APIs. * [FEATURE #905](#905): Add an `impl Default for RegexSet`, with the default being the empty set. * [FEATURE #908](#908): A new method, `Regex::static_captures_len`, has been added which returns the number of capture groups in the pattern if and only if every possible match always contains the same number of matching groups. * [FEATURE #955](#955): Named captures can now be written as `(?<name>re)` in addition to `(?P<name>re)`. * FEATURE: `regex-syntax` now supports empty character classes. * FEATURE: `regex-syntax` now has an optional `std` feature. (This will come to `regex` in the second release.) * FEATURE: The `Hir` type in `regex-syntax` has had a number of simplifications made to it. * FEATURE: `regex-syntax` has support for a new `R` flag for enabling CRLF mode. This will be supported in `regex` proper in the second release. * FEATURE: `regex-syntax` now has proper support for "regex that never matches" via `Hir::fail()`. * FEATURE: The `hir::literal` module of `regex-syntax` has been completely re-worked. It now has more documentation, examples and advice. * FEATURE: The `allow_invalid_utf8` option in `regex-syntax` has been renamed to `utf8`, and the meaning of the boolean has been flipped. Performance improvements: * PERF: The upgrade to `aho-corasick 1.0` may improve performance in some cases. It's difficult to characterize exactly which patterns this might impact, but if there are a small number of longish (>= 4 bytes) prefix literals, then it might be faster than before. Bug fixes: * [BUG #514](#514): Improve `Debug` impl for `Match` so that it doesn't show the entire haystack. * BUGS [#516](#516), [#731](#731): Fix a number of issues with printing `Hir` values as regex patterns. * [BUG #610](#610): Add explicit example of `foo|bar` in the regex syntax docs. * [BUG #625](#625): Clarify that `SetMatches::len` does not (regretably) refer to the number of matches in the set. * [BUG #660](#660): Clarify "verbose mode" in regex syntax documentation. * BUG [#738](#738), [#950](#950): Fix `CaptureLocations::get` so that it never panics. * [BUG #747](#747): Clarify documentation for `Regex::shortest_match`. * [BUG #835](#835): Fix `\p{Sc}` so that it is equivalent to `\p{Currency_Symbol}`. * [BUG #846](#846): Add more clarifying documentation to the `CompiledTooBig` error variant. * [BUG #854](#854): Clarify that `regex::Regex` searches as if the haystack is a sequence of Unicode scalar values. * [BUG #884](#884): Replace `__Nonexhaustive` variants with `#[non_exhaustive]` attribute. * [BUG #893](#893): Optimize case folding since it can get quite slow in some pathological cases. * [BUG #895](#895): Reject `(?-u:\W)` in `regex::Regex` APIs. * [BUG #942](#942): Add a missing `void` keyword to indicate "no parameters" in C API. * [BUG #965](#965): Fix `\p{Lc}` so that it is equivalent to `\p{Cased_Letter}`. * [BUG #975](#975): Clarify documentation for `\pX` syntax.
This PR contains the following updates: | Package | Type | Update | Change | |---|---|---|---| | [regex](https://github.com/rust-lang/regex) | dependencies | minor | `1.7.3` -> `1.8.1` | --- ### Release Notes <details> <summary>rust-lang/regex</summary> ### [`v1.8.1`](https://github.com/rust-lang/regex/blob/HEAD/CHANGELOG.md#​181-2023-04-21) \================== This is a patch release that fixes a bug where a regex match could be reported where none was found. Specifically, the bug occurs when a pattern contains some literal prefixes that could be extracted *and* an optional word boundary in the prefix. Bug fixes: - [BUG #​981](rust-lang/regex#981): Fix a bug where a word boundary could interact with prefix literal optimizations and lead to a false positive match. ### [`v1.8.0`](https://github.com/rust-lang/regex/blob/HEAD/CHANGELOG.md#​180-2023-04-20) \================== This is a sizeable release that will be soon followed by another sizeable release. Both of them will combined close over 40 existing issues and PRs. This first release, despite its size, essentially represents preparatory work for the second release, which will be even bigger. Namely, this release: - Increases the MSRV to Rust 1.60.0, which was released about 1 year ago. - Upgrades its dependency on `aho-corasick` to the recently released 1.0 version. - Upgrades its dependency on `regex-syntax` to the simultaneously released `0.7` version. The changes to `regex-syntax` principally revolve around a rewrite of its literal extraction code and a number of simplifications and optimizations to its high-level intermediate representation (HIR). The second release, which will follow ~shortly after the release above, will contain a soup-to-nuts rewrite of every regex engine. This will be done by bringing [`regex-automata`](https://github.com/BurntSushi/regex-automata) into this repository, and then changing the `regex` crate to be nothing but an API shim layer on top of `regex-automata`'s API. These tandem releases are the culmination of about 3 years of on-and-off work that [began in earnest in March 2020](rust-lang/regex#656). Because of the scale of changes involved in these releases, I would love to hear about your experience. Especially if you notice undocumented changes in behavior or performance changes (positive *or* negative). Most changes in the first release are listed below. For more details, please see the commit log, which reflects a linear and decently documented history of all changes. New features: - [FEATURE #​501](rust-lang/regex#501): Permit many more characters to be escaped, even if they have no significance. More specifically, any ASCII character except for `[0-9A-Za-z<>]` can now be escaped. Also, a new routine, `is_escapeable_character`, has been added to `regex-syntax` to query whether a character is escapeable or not. - [FEATURE #​547](rust-lang/regex#547): Add `Regex::captures_at`. This filles a hole in the API, but doesn't otherwise introduce any new expressive power. - [FEATURE #​595](rust-lang/regex#595): Capture group names are now Unicode-aware. They can now begin with either a `_` or any "alphabetic" codepoint. After the first codepoint, subsequent codepoints can be any sequence of alpha-numeric codepoints, along with `_`, `.`, `[` and `]`. Note that replacement syntax has not changed. - [FEATURE #​810](rust-lang/regex#810): Add `Match::is_empty` and `Match::len` APIs. - [FEATURE #​905](rust-lang/regex#905): Add an `impl Default for RegexSet`, with the default being the empty set. - [FEATURE #​908](rust-lang/regex#908): A new method, `Regex::static_captures_len`, has been added which returns the number of capture groups in the pattern if and only if every possible match always contains the same number of matching groups. - [FEATURE #​955](rust-lang/regex#955): Named captures can now be written as `(?<name>re)` in addition to `(?P<name>re)`. - FEATURE: `regex-syntax` now supports empty character classes. - FEATURE: `regex-syntax` now has an optional `std` feature. (This will come to `regex` in the second release.) - FEATURE: The `Hir` type in `regex-syntax` has had a number of simplifications made to it. - FEATURE: `regex-syntax` has support for a new `R` flag for enabling CRLF mode. This will be supported in `regex` proper in the second release. - FEATURE: `regex-syntax` now has proper support for "regex that never matches" via `Hir::fail()`. - FEATURE: The `hir::literal` module of `regex-syntax` has been completely re-worked. It now has more documentation, examples and advice. - FEATURE: The `allow_invalid_utf8` option in `regex-syntax` has been renamed to `utf8`, and the meaning of the boolean has been flipped. Performance improvements: - PERF: The upgrade to `aho-corasick 1.0` may improve performance in some cases. It's difficult to characterize exactly which patterns this might impact, but if there are a small number of longish (>= 4 bytes) prefix literals, then it might be faster than before. Bug fixes: - [BUG #​514](rust-lang/regex#514): Improve `Debug` impl for `Match` so that it doesn't show the entire haystack. - BUGS [#​516](rust-lang/regex#516), [#​731](rust-lang/regex#731): Fix a number of issues with printing `Hir` values as regex patterns. - [BUG #​610](rust-lang/regex#610): Add explicit example of `foo|bar` in the regex syntax docs. - [BUG #​625](rust-lang/regex#625): Clarify that `SetMatches::len` does not (regretably) refer to the number of matches in the set. - [BUG #​660](rust-lang/regex#660): Clarify "verbose mode" in regex syntax documentation. - BUG [#​738](rust-lang/regex#738), [#​950](rust-lang/regex#950): Fix `CaptureLocations::get` so that it never panics. - [BUG #​747](rust-lang/regex#747): Clarify documentation for `Regex::shortest_match`. - [BUG #​835](rust-lang/regex#835): Fix `\p{Sc}` so that it is equivalent to `\p{Currency_Symbol}`. - [BUG #​846](rust-lang/regex#846): Add more clarifying documentation to the `CompiledTooBig` error variant. - [BUG #​854](rust-lang/regex#854): Clarify that `regex::Regex` searches as if the haystack is a sequence of Unicode scalar values. - [BUG #​884](rust-lang/regex#884): Replace `__Nonexhaustive` variants with `#[non_exhaustive]` attribute. - [BUG #​893](rust-lang/regex#893): Optimize case folding since it can get quite slow in some pathological cases. - [BUG #​895](rust-lang/regex#895): Reject `(?-u:\W)` in `regex::Regex` APIs. - [BUG #​942](rust-lang/regex#942): Add a missing `void` keyword to indicate "no parameters" in C API. - [BUG #​965](rust-lang/regex#965): Fix `\p{Lc}` so that it is equivalent to `\p{Cased_Letter}`. - [BUG #​975](rust-lang/regex#975): Clarify documentation for `\pX` syntax. </details> --- ### Configuration 📅 **Schedule**: Branch creation - At any time (no schedule defined), Automerge - At any time (no schedule defined). 🚦 **Automerge**: Disabled by config. 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This ended up being a very effective feature request. It caused RE2, Go's regexp package and this crate to all start supporting |
Thanks, @BurntSushi! |
Would it be possible to support in addition to the existing syntax
(?P<name>exp)
for named capture groups also the syntax(?<name>exp)
?My use case for this is that I am currently writing a jq clone called jaq. Recently, I have added support for regular expressions to jaq using the
regex
crate, which works very well. However, because jq supports only the(?<name>exp)
syntax (because of theoniguruma
library) and jaq only the(?P<name>exp)
syntax (because of theregex
crate), it is currently impossible to write regexes with named capture groups that are valid in both jaq and jq.Apart from this, the
(?<name>exp)
syntax seems reasonably popular, so apart from my special use case, it might make sense to add support for this syntax. :)The text was updated successfully, but these errors were encountered: