Introduction

We welcome and encourage contributions of all kinds, such as:

1. Tickets with issue reports of feature requests
2. Documentation improvements
3. Code (PR or PR Review)

In addition to submitting new PRs, we have a healthy tradition of community members helping review each other's PRs. Doing so is a great way to help the community as well as get more familiar with Rust and the relevant codebases.

Developer's guide to Arrow Rust

Setting Up Your Build Environment

Install the Rust tool chain:

https://www.rust-lang.org/tools/install

Also, make sure your Rust tool chain is up-to-date, because we always use the latest stable version of Rust to test this project.

rustup update stable

How to compile

This is a standard cargo project with workspaces. To build it, you need to have rust and cargo:

cargo build

You can also use rust's official docker image:

docker run --rm -v $(pwd):/arrow-rs -it rust /bin/bash -c "cd /arrow-rs && rustup component add rustfmt && cargo build"

The command above assumes that are in the root directory of the project, not in the same directory as this README.md.

You can also compile specific workspaces:

cd arrow && cargo build

Git Submodules

Before running tests and examples, it is necessary to set up the local development environment.

The tests rely on test data that is contained in git submodules.

To pull down this data run the following:

git submodule update --init

This populates data in two git submodules:

• ../parquet-testing/data (sourced from https://github.com/apache/parquet-testing.git)
• ../testing (sourced from https://github.com/apache/arrow-testing)

By default, cargo test will look for these directories at their standard location. The following environment variables can be used to override the location:

# Optionally specify a different location for test data
export PARQUET_TEST_DATA=$(cd ../parquet-testing/data; pwd)
export ARROW_TEST_DATA=$(cd ../testing/data; pwd)

From here on, this is a pure Rust project and cargo can be used to run tests, benchmarks, docs and examples as usual.

Running the tests

Run tests using the Rust standard cargo test command:

# run all unit and integration tests
cargo test

# run tests for the arrow crate
cargo test -p arrow

For some changes, you may want to run additional tests. You can find up-to-date information on the current CI tests in .github/workflows. Here are some examples of additional tests you may want to run:

# run tests for the parquet crate
cargo test -p parquet

# run arrow tests with all features enabled
cargo test -p arrow --all-features

# run the doc tests
cargo test --doc

Code Formatting

Our CI uses rustfmt to check code formatting. Before submitting a PR be sure to run the following and check for lint issues:

cargo +stable fmt --all -- --check

Clippy Lints

We recommend using clippy for checking lints during development. While we do not yet enforce clippy checks, we recommend not introducing new clippy errors or warnings.

Run the following to check for clippy lints:

# run clippy with default settings
cargo clippy

More comprehensive clippy checks can be run by adding flags:

# run clippy on the arrow crate with all features enabled, targeting all tests, examples, and benchmarks
cargo clippy -p arrow --all-features --all-targets

If you use Visual Studio Code with the rust-analyzer plugin, you can enable clippy to run each time you save a file. See https://users.rust-lang.org/t/how-to-use-clippy-in-vs-code-with-rust-analyzer/41881.

One of the concerns with clippy is that it often produces a lot of false positives, or that some recommendations may hurt readability. We do not have a policy of which lints are ignored, but if you disagree with a clippy lint, you may disable the lint and briefly justify it.

Search for allow(clippy:: in the codebase to identify lints that are ignored/allowed. We currently prefer ignoring lints on the lowest unit possible.

• If you are introducing a line that returns a lint warning or error, you may disable the lint on that line.
• If you have several lints on a function or module, you may disable the lint on the function or module.
• If a lint is pervasive across multiple modules, you may disable it at the crate level.

Running Benchmarks

Running benchmarks are a good way to test the performance of a change. As benchmarks usually take a long time to run, we recommend running targeted tests instead of the full suite.

# run all benchmarks
cargo bench

# run arrow benchmarks
cargo bench -p arrow

# run benchmark for the parse_time function within the arrow-cast crate
cargo bench -p arrow-cast --bench parse_time

To set the baseline for your benchmarks, use the --save-baseline flag:

git checkout master

cargo bench --bench parse_time -- --save-baseline master

git checkout feature

cargo bench --bench parse_time -- --baseline master

Git Pre-Commit Hook

We can use git pre-commit hook to automate various kinds of git pre-commit checking/formatting.

Suppose you are in the root directory of the project.

First check if the file already exists:

ls -l .git/hooks/pre-commit

If the file already exists, to avoid mistakenly overriding, you MAY have to check the link source or file content. Else if not exist, let's safely soft link pre-commit.sh as file .git/hooks/pre-commit:

ln -s  ../../pre-commit.sh .git/hooks/pre-commit

If sometimes you want to commit without checking, just run git commit with --no-verify:

git commit --no-verify -m "... commit message ..."