Introduction

A faithful Rust port of rez's phase-based package solver, callable from Python via PyO3.

What rer is

r.e.r stands for "Rez En Rust" — a pun on the Parisian suburban train (réseau express régional d'Île-de-France).

rer is a Rust reimplementation of the solver hotpath of rez, the VFX / animation package manager. The end goal is a hybrid integration: a Rust library callable from Python via PyO3 that accelerates rez resolves while leaving the rest of rez untouched.

What "faithful port" means

The solver in rer-resolver's rez_solver module is a port of rez/src/rez/solver.py — not a different algorithm dressed up to look similar. It reproduces rez's mechanics exactly:

• weak (~) and conflict (!) requirement semantics
• variant selection order
• the extract / intersect / reduce / split cycle
• implicit backtracking
• the same phase stack the Python solver uses

The goal is output that matches rez 1:1, not merely "a valid resolve". The earlier pubgrub-based solver was removed once the port matched rez bit-for-bit on rez's bundled 188-case benchmark.

Status

• ✅ Solver — complete and rez-faithful.
• ✅ Validated 1:1 against rez's bundled 188-case benchmark dataset — every resolve matches rez's own recorded result (same status, same package set).
• ✅ Fast — on that benchmark, on one machine, rer resolves all 188 requests in ~44s versus ~206s for rez 3.3.0 (rez benchmark). Correctness is version-independent; the timing is same-machine context, not a lab claim.
• ✅ Python bridge — pip install pyrer, then pyrer.solve(...) runs the ported solver.

How rer fits into a rez workflow

rer works on an in-memory package repository: a mapping from family → version → {requires, variants}. It does not read the filesystem itself — the host (rez) hands the loaded data in.

That means rer is a drop-in accelerator for rez's resolve step, not a replacement for rez. rez still discovers packages, parses package.py, builds the environment, and manages contexts. rer just does the solving.

Next steps

• Quick Start → — install rer and run your first resolve from Python or Rust.
• Wiring pyrer into rez → — how to plug pyrer in behind a normal rez env / ResolvedContext flow, with a minimal shim and the caveats.
• Stability commitments → — what 1.0 commits us to (supported Pythons, supported rez range, semver scope, what's modelled and what's not).
• Engineering notes → — design decisions and measurements behind the port (e.g. why some rez optimisations are intentionally absent).
• Contributing → — how to help.
• FAQ → — common questions.