# Contributing to TFHE-rs

This document provides guidance on how to contribute to **TFHE-rs**.

There are two ways to contribute:

- **Report issues:** Open issues on GitHub to report bugs, suggest improvements, or note typos.
- **Submit code**: To become an official contributor, you must sign our Contributor License Agreement (CLA). Our CLA-bot will guide you through this process when you open your first pull request.

## 1. Setting up the project

Start by [forking](https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/working-with-forks/fork-a-repo) the **TFHE-rs** repository.

{% hint style="info" %}
- **Rust version**:  Ensure that you use a Rust version >= 1.81 to compile **TFHE-rs**.
- **Incompatibility**: AArch64-based machines are not yet supported for Windows as it's currently missing an entropy source to be able to seed the [CSPRNGs](https://en.wikipedia.org/wiki/Cryptographically_secure_pseudorandom_number_generator) used in **TFHE-rs**.
- **Performance**: For optimal performance, it is highly recommended to run **TFHE-rs** code in release mode with cargo's `--release` flag.
{% endhint %}

To get more details about the library, please refer to the [documentation](https://docs.zama.ai/tfhe-rs).

## 2. Creating a new branch

When creating your branch, make sure to use the following format :

```
git checkout -b {feat|fix|docs|chore…}/short_description
```

For example:

```
git checkout -b feat/new_feature_X
```

## 3. Before committing

### 3.1 Linting

Each commit to **TFHE-rs** should conform to the standards of the project. In particular, every source code, docker or workflows files should be linted to prevent programmatic and stylistic errors.

- Rust source code linters: `clippy`
- Typescript/Javascript source code linters: `eslint`, `prettier`

To apply automatic code formatting, run:

```
make fmt
```

You can perform linting of all Cargo targets with:

```
make clippy_all_targets
```

### 3.2 Testing

Your contributions must include comprehensive documentation and tests without breaking existing tests. To run pre-commit checks, execute:

```
make pcc
```

This command ensure that all the targets in the library are building correctly.
For a faster check, use:

```
make fpcc
```

If you're contributing to GPU code, run also:

```
make pcc_gpu
```

Unit testing suites are heavy and can require a lot of computing power and RAM availability.
Whilst tests are run automatically in continuous integration pipeline, you can run tests locally.

All unit tests have a command formatted as:

```
make test_*
```

Run `make help` to display a list of all the commands available.

To quickly test your changes locally, follow these steps:
 1. Locate where the code has changed.
 2. Add (or modify) a Cargo test filter to the corresponding `make` target in Makefile.
 3. Run the target.

{% hint style="success" %}
`make test_<something>` will print the underlying cargo command in STDOUT. You can quickly test your changes by copy/pasting the command and then modify it to suit your needs.
{% endhint %}

For example, if you made changes in `tfhe/src/integer/*`, you can test them with the following steps:
 1. In `test_integer` target, replace the filter `-- integer::` by `-- my_new_test`.
 2. Run `make test_integer`.

## 4. Committing

**TFHE-rs** follows the conventional commit specification to maintain a consistent commit history, essential for Semantic Versioning ([semver.org](https://semver.org/)).
Commit messages are automatically checked in CI and will be rejected if they do not comply, so make sure that you follow the commit conventions detailed on [this page](https://www.conventionalcommits.org/en/v1.0.0/).

## 5. Rebasing

Before creating a pull request, rebase your branch on the repository's `main` branch. Merge commits are not permitted, thus rebasing ensures fewer conflicts and a smoother PR review process.

## 6. Opening a Pull Request

Once your changes are ready, open a pull request.

For instructions on creating a PR from a fork, refer to GitHub's [official documentation](https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/proposing-changes-to-your-work-with-pull-requests/creating-a-pull-request-from-a-fork).

## 7. Continuous integration

Before a pull request can be merged, several test suites run automatically. Below is an overview of the CI process:

```mermaid
---
title: Continuous Integration Process
---
sequenceDiagram
    autonumber

    participant Contributor
    participant GitHub
    participant Reviewer
    participant CI-pipeline

    Contributor ->> GitHub: Open pull-request
    GitHub -->> Contributor: Ask for CLA signing (once)
    loop
        Reviewer ->> GitHub: Review code
        Reviewer ->> CI-pipeline: Approve workflows (short-run)
        CI-pipeline -->> GitHub: Send checks results
        Contributor ->> GitHub: Make changes
    end
    Reviewer ->> GitHub: Pull-request approval
    Reviewer ->> CI-pipeline: Approve workflows (long-run)
    CI-pipeline -->> GitHub: Send checks results
    Reviewer -->> GitHub: Merge if pipeline green
```

{% hint style="info" %}

## Useful details:

- pipeline is triggered by humans
- review team is located in Paris timezone, pipeline launch will most likely happen during office hours
- direct changes to CI related files are not allowed for external contributors
- run `make pcc` to fix any build errors before pushing commits
{% endhint %}

## 8. Data versioning

Data serialized with TFHE-rs must remain backward compatible. This is done using the [tfhe-versionable](https://crates.io/crates/tfhe-versionable) crate.

If you modify a type that derives `Versionize` in a backward-incompatible way, an upgrade implementation must be provided.

For example, these changes are data breaking:
 * Adding a field to a struct.
 * Changing the order of the fields within a struct or the variants within an enum.
 * Renaming a field of a struct or a variant of an enum.
 * Changing the type of field in a struct or a variant in an enum.

On the contrary, these changes are *not* data breaking:
 * Renaming a type (unless it implements the `Named` trait).
 * Adding a variant to the end of an enum.

Historical data from previous TFHE-rs versions are stored inside `utils/tfhe-backward-compat-data`. They are used to check on every PR that backward compatibility has been preserved.

## Example: adding a field

Suppose you want to add an i32 field to a type named `MyType`. The original type is defined as:
```rust
#[derive(Serialize, Deserialize, Versionize)]
#[versionize(MyTypeVersions)]
struct MyType {
  val: u64,
}
```
And you want to change it to:
```rust
#[derive(Serialize, Deserialize, Versionize)]
#[versionize(MyTypeVersions)]
struct MyType {
  val: u64,
  other_val: i32
}
```

Follow these steps:

 1. Navigate to the definition of the dispatch enum of this type. This is the type inside the `#[versionize(MyTypeVersions)]` macro attribute. In general, this type has the same name as the base type with a `Versions` suffix. You should find something like

```rust
#[derive(VersionsDispatch)]
enum MyTypeVersions {
  V0(MyTypeV0),
  V1(MyType)
}
```

 2. Add a new variant to the enum to preserve the previous version of the type. You can simply copy and paste the previous definition of the type and add a version suffix:

```rust
#[derive(Version)]
struct MyTypeV1 {
  val: u64,
}

#[derive(VersionsDispatch)]
enum MyTypeVersions {
  V0(MyTypeV0),
  V1(MyTypeV1),
  V2(MyType) // Here this points to your modified type
}
```

 3. Implement the `Upgrade` trait to define how we should go from the previous version to the current version:
```rust
impl Upgrade<MyType> for MyTypeV1 {
  type Error = Infallible;

   fn upgrade(self) -> Result<MyType, Self::Error> {
       Ok(MyType {
           val: self.val,
           other_val: 0
        })
   }
}
```

 4. Fix the upgrade target of the previous version. In this example, `impl Upgrade<MyType> for MyTypeV0 {` should simply be changed to `impl Upgrade<MyTypeV1> for MyTypeV0 {`
