Module 02 — The Rust Library

Goal

Create the initial Rust library that will become the Open Engineering Mini Kernel.

The domain implementation must exist independently of any Python binding.

Project layout

kernel/
├── Cargo.toml
├── pyproject.toml      # added later for Maturin
├── src/
│   └── lib.rs
├── tests/              # integration tests (optional)
└── README.md

Cargo.toml essentials

[package]
name = "open_engineering_kernel"
version = "0.1.0"
edition = "2021"

[dependencies]
pyo3 = { version = "0.22", features = ["extension-module"] }

[lib]
name = "open_engineering_kernel"
crate-type = ["cdylib", "rlib"]   # rlib for Rust tests, cdylib for Python

First domain function

/// Normalize an identifier candidate: trim whitespace and lowercase.
pub fn normalize_identifier(value: &str) -> String {
    value.trim().to_lowercase()
}

Rust concepts introduced (only what is needed)

Concept	Why it appears here
Functions	Entry points for domain logic
&str / String	Borrowed vs owned text
Modules	Later split into identifier, manifest, rule
Result	Used when we introduce fallible parsing
Cargo	Build, test, and dependency management

Establish the independence principle

Write the native Rust test before any Python binding exists:

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn normalize_trims_and_lowercases() {
        assert_eq!(
            normalize_identifier("  OE.PICO.LAMP  "),
            "oe.pico.lamp"
        );
    }
}

Run:

cargo test --lib

Why this order matters

Rust domain logic
       ▲
       │  tested here first
       │
   later: PyO3 binding

If the kernel only works when called from Python, the boundary has leaked into the domain.

Exercise

1. Create the crate (or use the provided kernel/ directory).
2. Implement normalize_identifier.
3. Add the unit test above.
4. Confirm cargo test passes with no Python tooling installed.