p8-pcre

PCRE2's regular expressions in safe Rust: no C, no unsafe, no JIT.

p8 (p8runtime/runtime) uses it for PHP's preg_* functions (APS 6), and it is published on crates.io as p8-pcre for anyone who needs PCRE semantics without linking C.

Status: planned, not started. The runtime comes first.

Plan

• Port PCRE2 10.44's compiler and backtracking matcher. That's about 22k lines of C, or roughly 15–20k lines of Rust. 10.44 is the version php-src 8.4 bundles.
• Generate the Unicode tables from Unicode's data rather than porting them.
• Leave out:
  • the JIT (it emits machine code, so it would need unsafe);
  • the DFA matcher, pattern conversion and the debug printer, which PHP doesn't use.
• Make it fast without a JIT: patterns that don't need backtracking (no backreferences, lookaround, recursion or backtracking verbs) run on the regex crate's automata. Only the rest use the backtracking matcher.
• Match PCRE2 exactly: match results, capture groups, (*MARK), error messages and their offsets, and match and depth limits.

Gates

• PCRE2's own test suite (testdata/testinput*, about 1.8 MB of expected output), driven by a pcre2test-compatible runner.
• php-src's ext/pcre tests, through p8.
• #![forbid(unsafe_code)] and no C in the dependency tree.

Why not wrap PCRE2

Every PCRE crate on crates.io wraps the C library. p8 builds no C (p8 APS 2).

The regex crate deliberately leaves out backtracking features, and fancy-regex covers only part of them. This crate fills that gap.