regex

This is a release that fixes a bug where incorrect regex match offsets could be reported. Note that this doesn't impact whether a match occurs or not, just where it occurs. The match offsets are still valid for slicing, they just may not refer to the correct leftmost-first match. See #1364 for (many) more details.

Bug fixes:

• #1354: Fixes previously unsound reverse suffix and inner optimizations.

This release includes a new API, a regex! macro, for lazy compilation of a regex from a string literal. If you use regexes a lot, it's likely you've already written one exactly like it. The new macro can be used like this:

use regex::regex;

fn is_match(line: &str) -> bool {
    // The regex will be compiled approximately once and reused automatically.
    // This avoids the footgun of using `Regex::new` here, which would
    // guarantee that it would be compiled every time this routine is called.
    // This would likely make this routine much slower than it needs to be.
    regex!(r"bar|baz").is_match(line)
}

let hay = "\
path/to/foo:54:Blue Harvest
path/to/bar:90:Something, Something, Something, Dark Side
path/to/baz:3:It's a Trap!
";

let matches = hay.lines().filter(|line| is_match(line)).count();
assert_eq!(matches, 2);

Improvements:

• #709: Add a new regex! macro for efficient and automatic reuse of a compiled regex.

This release includes a performance optimization for compilation of regexes with very large character classes.

Improvements:

• #1308: Avoid re-canonicalizing the entire interval set when pushing new class ranges.

This release excludes some unnecessary things from the archive published to crates.io. Specifically, fuzzing data and various shell scripts are now excluded. If you run into problems, please file an issue.

Improvements:

• #1319: Switch from a Cargo exclude list to an include list, and exclude some unnecessary stuff.

This release fixes a cargo doc breakage on nightly when --cfg docsrs is enabled. This caused documentation to fail to build on docs.rs.

Bug fixes:

• BUG #1305: Switches the doc_auto_cfg feature to doc_cfg on nightly for docs.rs builds.

This release makes a bug fix in the new regex::Captures::get_match API introduced in 1.12.0. There was an oversight with the lifetime parameter for the Match returned. This is technically a breaking change, but given that it was caught almost immediately and I've yanked the 1.12.0 release, I think this is fine.

This release contains a smattering of bug fixes, a fix for excessive memory consumption in some cases and a new regex::Captures::get_match API.

Improvements:

• FEATURE #1146: Add Capture::get_match for returning the overall match without unwrap().

Bug fixes:

• BUG #1083: Fixes a panic in the lazy DFA (can only occur for especially large regexes).
• BUG #1116: Fixes a memory usage regression for large regexes (introduced in regex 1.9).
• BUG #1195: Fix universal start states in sparse DFA.
• BUG #1295: Fixes a panic when deserializing a corrupted dense DFA.
• BUG 8f5d9479: Make regex_automata::meta::Regex::find consistently return None when WhichCaptures::None is used.

This is a small patch release with an improvement in memory usage in some cases.

Improvements:

• BUG #1297: Improve memory usage by trimming excess memory capacity in some spots.

This is a new patch release of regex with some minor fixes. A larger number of typo or lint fix patches were merged. Also, we now finally recommend using std::sync::LazyLock.

Improvements:

• BUG #1217: Switch recommendation from once_cell to std::sync::LazyLock.
• BUG #1225: Add DFA::set_prefilter to regex-automata.

Bug fixes:

• BUG #1165: Remove std dependency from perf-literal-multisubstring crate feature.
• BUG #1165: Clarify the meaning of (?R)$ in the documentation.
• BUG #1281: Remove fuzz/ and record/ directories from published crate on crates.io.

This is a new patch release of regex that fixes compilation on nightly Rust when the unstable pattern crate feature is enabled. Users on nightly Rust without this feature enabled are unaffected.

Bug fixes:

• BUG #1231: Fix the Pattern trait implementation as a result of nightly API breakage.

This is a new minor release of regex that brings in an update to the Unicode Character Database. Specifically, this updates the Unicode data used by regex internally to the version 16 release.

New features:

• FEATURE #1228: Add new regex::SetMatches::matched_all method.
• FEATURE #1229: Update to Unicode Character Database (UCD) version 16.

This is a new patch release with a fix for the unstable crate feature that enables std::str::Pattern trait integration.

Bug fixes:

• BUG #1219: Fix the Pattern trait implementation as a result of nightly API breakage.

This is a new patch release with some minor fixes.

Bug fixes:

• BUG #1203: Escape invalid UTF-8 when in the Debug impl of regex::bytes::Match.

This is a new patch release with some minor fixes.

• BUG #1169: Fixes a bug with compiling a reverse NFA automaton in regex-automata.
• BUG #1178: Clarifies that when Cow::Borrowed is returned from replace APIs, it is equivalent to the input.

This is a new patch release that fixes the feature configuration of optional dependencies, and fixes an unsound use of bounds check elision.

Bug fixes:

• BUG #1147: Set default-features=false for the memchr and aho-corasick dependencies.
• BUG #1154: Fix unsound bounds check elision.

This is a new patch release that fixes a search regression where incorrect matches could be reported.

Bug fixes:

• BUG #1110: Revert broadening of reverse suffix literal optimization introduced in 1.10.1.

This is a new patch release with a minor increase in the number of valid patterns and a broadening of some literal optimizations.

New features:

• FEATURE 04f5d7be: Loosen ASCII-compatible rules such that regexes like (?-u:☃) are now allowed.

Performance improvements:

• PERF 8a8d599f: Broader the reverse suffix optimization to apply in more cases.

This is a new minor release of regex that adds support for start and end word boundary assertions. That is, \< and \>. The minimum supported Rust version has also been raised to 1.65, which was released about one year ago.

The new word boundary assertions are:

• \< or \b{start}: a Unicode start-of-word boundary (\W|\A on the left, \w on the right).
• \> or \b{end}: a Unicode end-of-word boundary (\w on the left, \W|\z on the right).
• \b{start-half}: half of a Unicode start-of-word boundary (\W|\A on the left).
• \b{end-half}: half of a Unicode end-of-word boundary (\W|\z on the right).

The \< and \> are GNU extensions to POSIX regexes. They have been added to the regex crate because they enjoy somewhat broad support in other regex engines as well (for example, vim). The \b{start} and \b{end} assertions are aliases for \< and \>, respectively.

The \b{start-half} and \b{end-half} assertions are not found in any other regex engine (although regex engines with general look-around support can certainly express them). They were added principally to support the implementation of word matching in grep programs, where one generally wants to be a bit more flexible in what is considered a word boundary.

New features:

• FEATURE #469: Add support for \< and \> word boundary assertions.
• FEATURE(regex-automata) #1031: DFAs now have a start_state method that doesn't use an Input.

Performance improvements:

• PERF #1051: Unicode character class operations have been optimized in regex-syntax.
• PERF #1090: Make patterns containing lots of literal characters use less memory.

Bug fixes:

• BUG #1046: Fix a bug that could result in incorrect match spans when using a Unicode word boundary and searching non-ASCII strings.
• BUG(regex-syntax) #1047: Fix panics that can occur in Ast->Hir translation (not reachable from regex crate).
• BUG(regex-syntax) #1088: Remove guarantees in the API that connect the u flag with a specific HIR representation.

regex-automata breaking change release:

This release includes a regex-automata 0.4.0 breaking change release, which was necessary in order to support the new word boundary assertions. For example, the Look enum has new variants and the LookSet type now uses u32 instead of u16 to represent a bitset of look-around assertions. These are overall very minor changes, and most users of regex-automata should be able to move to 0.4 from 0.3 without any changes at all.

regex-syntax breaking change release:

This release also includes a regex-syntax 0.8.0 breaking change release, which, like regex-automata, was necessary in order to support the new word boundary assertions. This release also includes some changes to the Ast type to reduce heap usage in some cases. If you are using the Ast type directly, your code may require some minor modifications. Otherwise, users of regex-syntax 0.7 should be able to migrate to 0.8 without any code changes.

regex-lite release:

The regex-lite 0.1.1 release contains support for the new word boundary assertions. There are no breaking changes.

This is a patch release that fixes a panic that can occur when the default regex size limit is increased to a large number.

• BUG aa4e4c71: Fix a bug where computing the maximum haystack length for the bounded backtracker could result underflow and thus provoke a panic later in a search due to a broken invariant.

This is a patch release that hopefully mostly fixes a performance bug that occurs when sharing a regex across multiple threads.

Issue #934 explains this in more detail. It is also noted in the crate documentation. The bug can appear when sharing a regex across multiple threads simultaneously, as might be the case when using a regex from a OnceLock, lazy_static or similar primitive. Usually high contention only results when using many threads to execute searches on small haystacks.

One can avoid the contention problem entirely through one of two methods. The first is to use lower level APIs from regex-automata that require passing state explicitly, such as meta::Regex::search_with. The second is to clone a regex and send it to other threads explicitly. This will not use any additional memory usage compared to sharing the regex. The only downside of this approach is that it may be less convenient, for example, it won't work with things like OnceLock or lazy_static or once_cell.

With that said, as of this release, the contention performance problems have been greatly reduced. This was achieved by changing the free-list so that it was sharded across threads, and that ensuring each sharded mutex occupies a single cache line to mitigate false sharing. So while contention may still impact performance in some cases, it should be a lot better now.

Because of the changes to how the free-list works, please report any issues you find with this release. That not only includes search time regressions but also significant regressions in memory usage. Reporting improvements is also welcome as well! If possible, provide a reproduction.

Bug fixes:

• BUG #934: Fix a performance bug where high contention on a single regex led to massive slow-downs.

This is a patch release that fixes a bug where RegexSet::is_match(..) could incorrectly return false (even when RegexSet::matches(..).matched_any() returns true).

Bug fixes:

• BUG #1070: Fix a bug where a prefilter was incorrectly configured for a RegexSet.

This is a patch release that fixes a bug where some searches could result in incorrect match offsets being reported. It is difficult to characterize the types of regexes susceptible to this bug. They generally involve patterns that contain no prefix or suffix literals, but have an inner literal along with a regex prefix that can conditionally match.

Bug fixes:

• BUG #1060: Fix a bug with the reverse inner literal optimization reporting incorrect match offsets.

This is a patch release that fixes another memory usage regression. This particular regression occurred only when using a RegexSet. In some cases, much more heap memory (by one or two orders of magnitude) was allocated than in versions prior to 1.9.0.

Bug fixes:

• BUG #1059: Fix a memory usage regression when using a RegexSet.

This is a patch release which fixes a memory usage regression. In the regex 1.9 release, one of the internal engines used a more aggressive allocation strategy than what was done previously. This patch release reverts to the prior on-demand strategy.

Bug fixes:

• BUG #1027: Change the allocation strategy for the backtracker to be less aggressive.

This release marks the end of a years long rewrite of the regex crate internals. Since this is such a big release, please report any issues or regressions you find. We would also love to hear about improvements as well.

In addition to many internal improvements that should hopefully result in "my regex searches are faster," there have also been a few API additions:

• A new Captures::extract method for quickly accessing the substrings that match each capture group in a regex.
• A new inline flag, R, which enables CRLF mode. This makes . match any Unicode scalar value except for \r and \n, and also makes (?m:^) and (?m:$) match after and before both \r and \n, respectively, but never between a \r and \n.
• RegexBuilder::line_terminator was added to further customize the line terminator used by (?m:^) and (?m:$) to be any arbitrary byte.
• The std Cargo feature is now actually optional. That is, the regex crate can be used without the standard library.
• Because regex 1.9 may make binary size and compile times even worse, a new experimental crate called regex-lite has been published. It prioritizes binary size and compile times over functionality (like Unicode) and performance. It shares no code with the regex crate.

New features:

• FEATURE #244: One can opt into CRLF mode via the R flag. e.g., (?mR:$) matches just before \r\n.
• FEATURE #259: Multi-pattern searches with offsets can be done with regex-automata 0.3.
• FEATURE #476: std is now an optional feature. regex may be used with only alloc.
• FEATURE #644: RegexBuilder::line_terminator configures how (?m:^) and (?m:$) behave.
• FEATURE #675: Anchored search APIs are now available in regex-automata 0.3.
• FEATURE #824: Add new Captures::extract method for easier capture group access.
• FEATURE #961: Add regex-lite crate with smaller binary sizes and faster compile times.
• FEATURE #1022: Add TryFrom implementations for the Regex type.

Performance improvements:

• PERF #68: Added a one-pass DFA engine for faster capture group matching.
• PERF #510: Inner literals are now used to accelerate searches, e.g., \w+@\w+ will scan for @.
• PERF #787, PERF #891: Makes literal optimizations apply to regexes of the form \b(foo|bar|quux)\b.

(There are many more performance improvements as well, but not all of them have specific issues devoted to them.)

Bug fixes:

• BUG #429: Fix matching bugs related to \B and inconsistencies across internal engines.
• BUG #517: Fix matching bug with capture groups.
• BUG #579: Fix matching bug with word boundaries.
• BUG #779: Fix bug where some regexes like (re)+ were not equivalent to (re)(re)*.
• BUG #850: Fix matching bug inconsistency between NFA and DFA engines.
• BUG #921: Fix matching bug where literal extraction got confused by $.
• BUG #976: Add documentation to replacement routines about dealing with fallibility.
• BUG #1002: Use corpus rejection in fuzz testing.

This is a patch release that fixes a bug where (?-u:\B) was allowed in Unicode regexes, despite the fact that the current matching engines can report match offsets between the code units of a single UTF-8 encoded codepoint. That in turn means that match offsets that split a codepoint could be reported, which in turn results in panicking when one uses them to slice a &str.

This bug occurred in the transition to regex 1.8 because the underlying syntactical error that prevented this regex from compiling was intentionally removed. That's because (?-u:\B) will be permitted in Unicode regexes in regex 1.9, but the matching engines will guarantee to never report match offsets that split a codepoint. When the underlying syntactical error was removed, no code was added to ensure that (?-u:\B) didn't compile in the regex 1.8 transition release. This release, regex 1.8.4, adds that code such that Regex::new(r"(?-u:\B)") returns to the regex <1.8 behavior of not compiling. (A bytes::Regex can still of course compile it.)

Bug fixes:

• BUG #1006: Fix a bug where (?-u:\B) was allowed in Unicode regexes, and in turn could lead to match offsets that split a codepoint in &str.

This is a patch release that fixes a bug where the regex would report a match at every position even when it shouldn't. This could occur in a very small subset of regexes, usually an alternation of simple literals that have particular properties. (See the issue linked below for a more precise description.)

Bug fixes:

• BUG #999: Fix a bug where a match at every position is erroneously reported.

This is a patch release that fixes a bug where regex compilation could panic in debug mode for regexes with large counted repetitions. For example, a{2147483516}{2147483416}{5} resulted in an integer overflow that wrapped in release mode but panicking in debug mode. Despite the unintended wrapping arithmetic in release mode, it didn't cause any other logical bugs since the errant code was for new analysis that wasn't used yet.

Bug fixes:

• BUG #995: Fix a bug where regex compilation with large counted repetitions could panic.

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: Fix a bug where a word boundary could interact with prefix literal optimizations and lead to a false positive match.

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 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.

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: 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 escapable or not.
• FEATURE #547: Add Regex::captures_at. This fills a hole in the API, but doesn't otherwise introduce any new expressive power.
• FEATURE #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 alphanumeric codepoints, along with _, ., [ and ]. Note that replacement syntax has not changed.
• FEATURE #810: Add Match::is_empty and Match::len APIs.
• FEATURE #905: Add an impl Default for RegexSet, with the default being the empty set.
• FEATURE #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: 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: Improve Debug impl for Match so that it doesn't show the entire haystack.
• BUGS #516, #731: Fix a number of issues with printing Hir values as regex patterns.
• BUG #610: Add explicit example of foo|bar in the regex syntax docs.
• BUG #625: Clarify that SetMatches::len does not (regrettably) refer to the number of matches in the set.
• BUG #660: Clarify "verbose mode" in regex syntax documentation.
• BUG #738, #950: Fix CaptureLocations::get so that it never panics.
• BUG #747: Clarify documentation for Regex::shortest_match.
• BUG #835: Fix \p{Sc} so that it is equivalent to \p{Currency_Symbol}.
• BUG #846: Add more clarifying documentation to the CompiledTooBig error variant.
• BUG #854: Clarify that regex::Regex searches as if the haystack is a sequence of Unicode scalar values.
• BUG #884: Replace __Nonexhaustive variants with #[non_exhaustive] attribute.
• BUG #893: Optimize case folding since it can get quite slow in some pathological cases.
• BUG #895: Reject (?-u:\W) in regex::Regex APIs.
• BUG #942: Add a missing void keyword to indicate "no parameters" in C API.
• BUG #965: Fix \p{Lc} so that it is equivalent to \p{Cased_Letter}.
• BUG #975: Clarify documentation for \pX syntax.

This is a small release that fixes a bug in Regex::shortest_match_at that could cause it to panic, even when the offset given is valid.

Bug fixes:

• BUG #969: Fix a bug in how the reverse DFA was called for Regex::shortest_match_at.

This is a small release that fixes a failing test on FreeBSD.

Bug fixes:

• BUG #967: Fix "no stack overflow" test which can fail due to the small stack size.

This release was done principally to try and fix the doc.rs rendering for the regex crate.

Performance improvements:

• PERF #930: Optimize replacen. This also applies to replace, but not replace_all.

Bug fixes:

• BUG #945: Maybe fix rustdoc rendering by just bumping a new release?

This release principally includes an upgrade to Unicode 15.

New features:

• FEATURE #832: Upgrade to Unicode 15.

This release principally includes an upgrade to Unicode 14.

New features:

• FEATURE #832: Clarify that Captures::len includes all groups, not just matching groups.
• FEATURE #857: Add an ExactSizeIterator impl for SubCaptureMatches.
• FEATURE #861: Improve RegexSet documentation examples.
• FEATURE #877: Upgrade to Unicode 14.

Bug fixes:

• BUG #792: Fix error message rendering bug.

This release includes a few bug fixes, including a bug that produced incorrect matches when a non-greedy ? operator was used.

• BUG #680: Fixes a bug where [[:alnum:][:^ascii:]] dropped [:alnum:] from the class.
• BUG #859: Fixes a bug where Hir::is_match_empty returned false for \b.
• BUG #862: Fixes a bug where 'ab??' matches 'ab' instead of 'a' in 'ab'.

This releases fixes a security bug in the regex compiler. This bug permits a vector for a denial-of-service attack in cases where the regex being compiled is untrusted. There are no known problems where the regex is itself trusted, including in cases of untrusted haystacks.

• SECURITY #GHSA-m5pq-gvj9-9vr8: Fixes a bug in the regex compiler where empty sub-expressions subverted the existing mitigations in place to enforce a size limit on compiled regexes. The Rust Security Response WG published an advisory about this: https://groups.google.com/g/rustlang-security-announcements/c/NcNNL1Jq7Yw

This release fixes another compilation failure when building regex. This time, the fix is for when the pattern feature is enabled, which only works on nightly Rust. CI has been updated to test this case.

• BUG #772: Fix build when pattern feature is enabled.

This releases fixes a bug when building regex with only the unicode-perl feature. It turns out that while CI was building this configuration, it wasn't actually failing the overall build on a failed compilation.

• BUG #769: Fix build in regex-syntax when only the unicode-perl feature is enabled.

This release fixes a performance bug when Unicode word boundaries are used. Namely, for certain regexes on certain inputs, it's possible for the lazy DFA to stop searching (causing a fallback to a slower engine) when it doesn't actually need to.

PR #768 fixes the bug, which was originally reported in ripgrep#1860.

This is a patch release that fixes a compilation error when the perf-literal feature is not enabled.

This release primarily updates to Rust 2018 (finally) and bumps the MSRV to Rust 1.41 (from Rust 1.28). Rust 1.41 was chosen because it's still reasonably old, and is what's in Debian stable at the time of writing.

This release also drops this crate's own bespoke substring search algorithms in favor of a new memmem implementation provided by the memchr crate. This will change the performance profile of some regexes, sometimes getting a little worse, and hopefully more frequently, getting a lot better. Please report any serious performance regressions if you find them.

This is a small patch release that fixes the compiler's size check on how much heap memory a regex uses. Previously, the compiler did not account for the heap usage of Unicode character classes. Now it does. It's possible that this may make some regexes fail to compile that previously did compile. If that happens, please file an issue.

• BUG OSS-fuzz#33579: Some regexes can use more heap memory than one would expect.

This is a small patch release that fixes a regression in the size of a Regex in the 1.4.4 release. Prior to 1.4.4, a Regex was 552 bytes. In the 1.4.4 release, it was 856 bytes due to internal changes. In this release, a Regex is now 16 bytes. In general, the size of a Regex was never something that was on my radar, but this increased size in the 1.4.4 release seems to have crossed a threshold and resulted in stack overflows in some programs.

• BUG #750: Fixes stack overflows seemingly caused by a large Regex size by decreasing its size.

This is a small patch release that contains some bug fixes. Notably, it also drops the thread_local (and lazy_static, via transitivity) dependencies.

Bug fixes:

• BUG #362: Memory leaks caused by an internal caching strategy should now be fixed.
• BUG #576: All regex types now implement UnwindSafe and RefUnwindSafe.
• BUG #728: Add missing Replacer impls for Vec<u8>, String, Cow, etc.

This is a small patch release that adds some missing standard trait implementations for some types in the public API.

Bug fixes:

• BUG #734: Add FusedIterator and ExactSizeIterator impls to iterator types.
• BUG #735: Add missing Debug impls to public API types.

This is a small bug fix release that bans \P{any}. We previously banned empty classes like [^\w\W], but missed the \P{any} case. In the future, we hope to permit empty classes.

• BUG #722: Ban \P{any} to avoid a panic in the regex compiler. Found by OSS-Fuzz.

This is a small bug fix release that makes \p{cf} work. Previously, it would report "property not found" even though cf is a valid abbreviation for the Format general category.

• BUG #719: Fixes bug that prevented \p{cf} from working.

This releases has a few minor documentation fixes as well as some very minor API additions. The MSRV remains at Rust 1.28 for now, but this is intended to increase to at least Rust 1.41.1 soon.

This release also adds support for OSS-Fuzz. Kudos to @DavidKorczynski for doing the heavy lifting for that!

New features:

• FEATURE #649: Support [, ] and . in capture group names.
• FEATURE #687: Add is_empty predicate to RegexSet.
• FEATURE #689: Implement Clone for SubCaptureMatches.
• FEATURE #715: Add empty constructor to RegexSet for convenience.

Bug fixes:

• BUG #694: Fix doc example for Replacer::replace_append.
• BUG #698: Clarify docs for s flag when using a bytes::Regex.
• BUG #711: Clarify is_match docs to indicate that it can match anywhere in string.

This release fixes a MSRV (Minimum Support Rust Version) regression in the 1.3.8 release. Namely, while 1.3.8 compiles on Rust 1.28, it actually does not compile on other Rust versions, such as Rust 1.39.

Bug fixes:

• BUG #685: Remove use of doc_comment crate, which cannot be used before Rust 1.43.

This release contains a couple of important bug fixes driven by better support for empty-subexpressions in regexes. For example, regexes like b| are now allowed. Major thanks to @sliquister for implementing support for this in #677.

Bug fixes:

• BUG #523: Add note to documentation that spaces can be escaped in x mode.
• BUG #524: Add support for empty sub-expressions, including empty alternations.
• BUG #659: Fix match bug caused by an empty sub-expression miscompilation.

This release contains a small bug fix that fixes how regex forwards crate features to regex-syntax. In particular, this will reduce recompilations in some cases.

Bug fixes:

• BUG #665: Fix feature forwarding to regex-syntax.

This release contains a sizable (~30%) performance improvement when compiling some kinds of large regular expressions.

Performance improvements:

• PERF #657: Improvement performance of compiling large regular expressions.

This release updates this crate to Unicode 13.

New features:

• FEATURE #653: Update regex-syntax to Unicode 13.

This is a small bug fix release that fixes a bug related to the scoping of flags in a regex. Namely, before this fix, a regex like ((?i)a)b) would match aB despite the fact that b should not be matched case insensitively.

Bug fixes:

• BUG #640: Fix bug related to the scoping of flags in a regex.

This is a small maintenance release that upgrades the dependency on thread_local from 0.3 to 1.0. The minimum supported Rust version remains at Rust 1.28.

This is a small maintenance release with some house cleaning and bug fixes.

New features:

• FEATURE #631: Add a Match::range method an a From<Match> for Range impl.

Bug fixes:

• BUG #521: Corrects /-/.splitn("a", 2) to return ["a"] instead of ["a", ""].
• BUG #594: Improve error reporting when writing \p\.
• BUG #627: Corrects /-/.split("a-") to return ["a", ""] instead of ["a"].
• BUG #633: Squash deprecation warnings for the std::error::Error::description method.

This is a maintenance release with no changes in order to try to work around a docs.rs/Cargo issue.

This release adds a plethora of new crate features that permit users of regex to shrink its size considerably, in exchange for giving up either functionality (such as Unicode support) or runtime performance. When all such features are disabled, the dependency tree for regex shrinks to exactly 1 crate (regex-syntax). More information about the new crate features can be found in the docs.

Note that while this is a new minor version release, the minimum supported Rust version for this crate remains at 1.28.0.

New features:

• FEATURE #474: The use_std feature has been deprecated in favor of the std feature. The use_std feature will be removed in regex 2. Until then, use_std will remain as an alias for the std feature.
• FEATURE #583: Add a substantial number of crate features shrinking regex.

This release does a bit of house cleaning. Namely:

• This repository is now using rustfmt.
• License headers have been removed from all files, in following suit with the Rust project.
• Teddy has been removed from the regex crate, and is now part of the aho-corasick crate. See aho-corasick's new packed submodule for details.
• The utf8-ranges crate has been deprecated, with its functionality moving into the utf8 sub-module of regex-syntax.
• The ucd-util dependency has been dropped, in favor of implementing what little we need inside of regex-syntax itself.

In general, this is part of an ongoing (long term) effort to make optimizations in the regex engine easier to reason about. The current code is too convoluted, and thus it is very easy to introduce new bugs. This simplification effort is the primary motivation behind re-working the aho-corasick crate to not only bundle algorithms like Teddy, but to also provide regex-like match semantics automatically.

Moving forward, the plan is to join up with the bstr and regex-automata crates, with the former providing more sophisticated substring search algorithms (thereby deleting existing code in regex) and the latter providing ahead-of-time compiled DFAs for cases where they are inexpensive to compute.