m4-rs

A native Rust forensic-parity implementation of GNU m4 behavior, built through oracle courts.

m4-rs is a clean-room behavioral reconstruction of GNU m4. Each supported surface is admitted only after byte comparison against a pinned GNU m4 oracle. Unsupported surfaces are explicit non-claims.

New here? Start with docs/REVIEW-IN-10-MINUTES.md.

Status

• 287/287 features implemented, 0 partial, 0 missing
• 182 tests passing (90 unit, 74 gnu suite, 10 autoconf seed, 8 frozen smoke)
• 7/7 acceptance gates pass
• Performance: 2.0x vs GNU m4 (10k-defines: 3.6x)
• GNU compare: 65/75 pass (87%) against GNU m4 1.4.21
• 1M deterministic fuzz: 0 panics
• Kani formal verification: 10 proofs

See STATUS.md for live current-state authority. See reports/claim-ladder.json for machine-readable claim status. See docs/negative-capabilities.md for explicit non-claims.

See reports/FORENSIC-GAP-ANALYSIS.md for the full C→Rust forensic gap audit.

Quick Start

# Build
cargo build

# Admit the GNU m4 oracle
cargo xtask oracle

# Run acceptance gates
cargo xtask check

# Use m4-rs
echo 'define(`hello', `world')hello' | cargo run --bin m4-rs

Parity Axes

• M4.ORACLE.1 — Pinned GNU m4 oracle admission
• M4.CLI.1 — Invocation/stdin/file/status harness
• M4.LEX.1 — Byte lexer/name/comment/quote tokenization
• M4.QUOTE.1 — Quote nesting and delimiter behavior
• M4.DEFINE.1 — define/undefine expansion core
• M4.ARGS.1 — Argument collection and $n behavior
• M4.PUSHDEF.1 — Definition stack
• M4.BUILTIN.TEXT.1 — len/index/substr/translit
• M4.BUILTIN.EVAL.1 — eval/incr/decr
• M4.DIVERT.1 — Diversions and automatic EOF undivert
• M4.INCLUDE.1 — include/sinclude/search path
• M4.DIAG.1 — Diagnostics taxonomy
• M4.TRACE.1 — Debug/trace/dumpdef parity
• M4.SYSCMD.1 — Shell command builtins in sandbox
• M4.FROZEN.1 — Frozen file save/reload
• M4.AUTOCONF.SEED.1 — Admitted Autoconf fixture survival
• M4.HOSTILE.1 — Malformed input/no-panic court
• M4.FUZZ.1 — Fuzz receipt

License

MIT OR Apache-2.0, at your option.

This is a clean-room behavioral reconstruction, not a derivative work of GNU m4. No GPL code is included or copied.