release: 1.8.0

[BurntSushi]

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 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 escapeable or not.
• FEATURE #547: Add Regex::captures_at. This filles 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 alpha-numeric 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 (regretably) 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.