Part of Ferramenta, a family of Rust tools.

Ferroni — Oniguruma regex in pure Rust

Bring your Oniguruma patterns to Rust. Keep the look-behind, backreferences and recursion your patterns rely on, with a familiar Regex API and a TextMate scanner built for syntax highlighters. Cargo handles the build, including WebAssembly. No C compiler, no bindgen, just Rust.

Quick start

cargo add ferroni

use ferroni::prelude::*;

fn main() -> Result<(), RegexError> {
    // A look-behind and named groups: Oniguruma syntax, a familiar API.
    let re = Regex::new(r"(?<=Date: )(?<year>\d{4})-(?<month>\d{2})-(?<day>\d{2})")?;

    let caps = re.captures("Date: 2026-02-12").unwrap();
    assert_eq!(caps.get(0).unwrap().as_str(), "2026-02-12");
    assert_eq!(caps.name("year").unwrap().as_str(), "2026");
    Ok(())
}

That's a look-behind and three named captures, ready to use in your Rust project. Compile once, then reuse the pattern across your searches.

What are you building?	Start here
Matching, extraction or replacement	Getting started
A tokenizer or TextMate highlighter	Scanner guide
A highlighter that loads the same patterns on every start	Prepared Eager archives
An application moving from regex or onig	API mapping and default differences

Why Ferroni

Give your patterns room to work. Look-around, backreferences, recursive subexpressions and all twelve Oniguruma syntax modes are included. Ferroni is the only Rust engine among those checked with every feature in the feature matrix. When you need linear-time matching for user-supplied patterns, Rust's regex crate is a great fit.

Serious speed for patterns you reuse. In the published regex workloads, Ferroni matches 2.5–3.3× faster than C Oniguruma in the family-weighted aggregate after compilation, without generating machine code at runtime. The tasks come from Django, Rails, WordPress and other projects. Results vary by task. C still compiles patterns faster in the aggregate, so check first-use costs when you rarely reuse a pattern. See the benchmark summary and full results for the measured workloads, platforms and tradeoffs.

Build the highlighter you have in mind. Ferroni's Scanner follows vscode-oniguruma's scanning model, including UTF-16 offsets for editor integrations. It finds the next match across a set of patterns; your TextMate runtime handles grammar rules and scopes. Ferriki builds a Shiki-compatible highlighter on it.

Prepare scanner groups once. Reuse them across starts. With the optional precompiled-eager feature, export compiled programs and prepared Eager group instructions as a portable pair. Ship them with your application, embed them, or serve them as assets for compatible native and WebAssembly builds. Requested records decode on demand; missing or incompatible groups use normal Eager preparation. See the prepared Eager guide for generation, loading and the work that remains local.

An established engine, a Rust future. Oniguruma's C project closed in April 2025. Ferroni continues it, ported function by function, and passes all 2,974 upstream UTF-8 tests. Buffer and string processing use safe Rust. The 10 unsafe sites are confined to links between parse-tree nodes.

Scope

Ferroni covers ASCII and UTF-8, two of Oniguruma's 29 encodings, and leaves out the POSIX and GNU APIs. It backtracks like C Oniguruma, so give searches over untrusted input a time or retry limit. On wasm32-unknown-unknown, the browser target, use a retry limit; that target has no clock for a time limit. See compatibility and untrusted input.

Documentation

• Getting started — your first match, captures, replacement, options and errors.
• Scanner guide — tokenization loops, UTF-16 positions and shared compiled patterns.
• Prepared Eager archives — move reusable scanner preparation into your build step and share it across starts.
• API reference — every public type and function.
• Regex benchmarks — the speed summary, source projects, method and feature matrix.
• Benchmark results — per-platform aggregates, with every case and timing in publication.json and tiktoken pre-tokenization in additional_results.
• Migrating to 2.0 — breaking changes with before and after code.

Project status and contributing

Ferroni's Oniguruma compatibility scope is complete and maintained. Bug fixes, Unicode updates, toolchain upkeep and security fixes remain in scope. Rust-only scanner optimizations and startup reuse extend the port without expanding its syntax or encoding scope. See the project status for the maintenance scope.

CONTRIBUTING.md covers builds, tests and benchmarks; pull requests keep the structural parity with C Oniguruma that the port is built on. Report vulnerabilities privately as described in SECURITY.md.

Acknowledgments and license

Built on K. Kosako's Oniguruma and Microsoft's vscode-oniguruma Scanner API and tests. Ferroni is an independent continuation and is not affiliated with or endorsed by Oniguruma's original author.

BSD-2-Clause, inherited from the Oniguruma source this port is based on.

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