overby.me / oxidized-pcre2
A PCRE2-compatible regular expression library written in Rust
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README.md

Oxidized PCRE2 #

Part of the overby.me monorepo, where this lives in safety/oxidized/pcre2 and where all development happens.

It is also published on its own, as tangled.org/overby.me/oxidized-pcre2 and github.com/overby-me/oxidized-pcre2. Both are read-only mirrors, rebuilt from the monorepo with josh: a commit made to either is overwritten by the next sync, so please open issues and pull requests on the monorepo.

A pure-Rust PCRE2 (Perl Compatible Regular Expressions 2) library.

Used by safety/oxidized/grep for -P mode. Replaces fancy-regex, which lacks real PCRE2 semantics (no backtrack limits, different match behavior).

Scope #

A practical subset of PCRE2 covering what grep -P needs — not a drop-in replacement for all of PCRE2. See CHANGELOG.md for what's implemented; bin/pcre2test.rs is a stub.

API #

use oxidized_pcre2::{Regex, CompileOptions};

let re = Regex::new(r"\bword\b")?;
assert!(re.is_match(b"a word here")?);

let mut opts = CompileOptions::default();
opts.caseless = true;
let re = Regex::with_options(r"hello", opts)?;

Bytes, not &str: the API works on &[u8] to match PCRE2's byte-oriented semantics and handle non-UTF-8 input. Set match_limit / depth_limit via Regex::set_match_limit / set_depth_limit (defaults: 1M / 1000).

Architecture #

  • Parser (parse.rs) — character-level recursive descent that emits an AST (ast.rs).
  • Matcher (matcher.rs) — continuation-passing-style backtracking NFA operating directly on the AST; supports captures, backreferences, lookahead/lookbehind, atomic groups, and the PCRE2 anchors.
  • lib.rs — Regex, Match, CompileOptions, MatchContext, and the find/iter surface.

What's intentionally omitted #

  • JIT compilation
  • 16-bit / 32-bit character modes
  • EBCDIC support
  • DFA matcher (pcre2_dfa_match)
  • pcre2_substitute
  • Full Unicode property database (only basic categories are supported — letters, decimal digits, whitespace, etc.)

Catastrophic backtracking #

The matcher doesn't do true exponential backtracking for classic pathological patterns like ((a+)*)+. Instead, it detects nested unbounded quantifiers at compile time and returns Error::MatchLimit when such a pattern fails to match on a non-trivial input (≥ 20 bytes). This mirrors PCRE2's observable behaviour for grep -P.

Building and testing #

nix build .#oxidized-pcre2
cd safety/oxidized/pcre2 && cargo test

The checked-in default.nix exposes the library package. The pcre2test binary is a placeholder; there is no upstream-test integration yet.