cpsat-rs

Rust bindings for Google OR-Tools CP-SAT solver.

Provides a Rust builder API for constructing CP-SAT models, with solving delegated to OR-Tools via FFI.

How it works

Model construction happens in Rust using prost-generated protobuf types. The model is serialized, passed to OR-Tools' C API (SolveCpModelWithParameters), and the response is deserialized back. There are two unsafe blocks in src/ffi.rs for this boundary.

Rust builder API → CpModelProto (prost) → serialize → C FFI → OR-Tools → deserialize → response

This is not a pure-Rust solver. It requires the OR-Tools C++ library installed on the system.

Quick Start

use cpsat_rs::prelude::*;

let mut model = CpModel::new();
let x = model.new_int_var(0..=10, "x");
let y = model.new_int_var(0..=10, "y");
model.add((x + y).le(15));
model.minimize(x + y);

let response = CpSolver::solve(&model).unwrap();
if response.is_optimal() {
    println!("x={}, y={}", response.value(x), response.value(y));
}

Requirements

OR-Tools C++ library must be installed:

# macOS
brew install or-tools

# Linux: see https://developers.google.com/optimization/install

# If not in a standard location:
export ORTOOLS_PREFIX=/path/to/or-tools

Also requires protoc for proto compilation during build.

What's included

• IntVar, BoolVar, IntervalVar handle types
• LinearExpr with arithmetic operators
• Constraints: linear, all_different, no_overlap, cumulative, circuit, table, automaton, element, boolean
• Scheduling: interval variables, no_overlap, no_overlap_2d, cumulative
• Minimize/maximize objectives
• Solution hints
• Solver parameters (time limit, workers, etc.)

Examples

cargo run --example nqueens      # 8-Queens puzzle
cargo run --example jobshop      # FT06 job shop scheduling (optimal=55)

Limitations

• Requires OR-Tools system library (not pure Rust)
• FFI boundary: two unsafe blocks for serialize/deserialize + free
• No solve cancellation (blocking FFI call)
• Variable handles are plain indices with no model provenance check
• Proto files vendored from OR-Tools v9.15

License

Apache-2.0