08_static_code_checks.rst

Static code checks

The static code checks in Airflow are used to verify that the code meets certain quality standards. All the static code checks can be run through prek hooks.

The prek hooks perform all the necessary installation when you run them for the first time.

You can also run the checks via Breeze environment.

Table of Contents

• Prek hooks
• Installing prek hooks
• Enabling prek hooks
• Available prek hooks
• Using prek
• Disabling particular checks
• Disabling goproxy for firewall issues
• Manual prek hooks
• Mypy checks
  • Adding a new shared library

Prek hooks

Prek hooks help speed up your local development cycle and place less burden on the CI infrastructure. Consider installing the prek hooks as a necessary prerequisite.

The hooks by default only check the files you are currently working on (and are staged) which makes the checks rather fast. Yet, these checks use exactly the same environment as the CI tests use. So, you can be sure your modifications will also work for CI if they pass prek hooks.

We have integrated the prek framework in our development workflow. It can be installed in various ways and does not even need pip or

python to be installed. It is a drop-in replacement for the legacy pre-commit tool, but it is much faster and more feature-rich. It is written in Rust and it is designed to install environments in parallel, so it is much faster than the pre-commit tool.

Installing prek hooks

It is the best to use prek hooks when you have your local virtualenv for Airflow activated since then prek hooks and other dependencies are automatically installed. You can also install the prek hooks manually using uv or pipx.

uv tool install prek

pipx install prek

Since we have a lot of hooks and sometimes you want to run them individually, it's advised to install auto-completion for the prek command. You can do it by adding the following line to your .bashrc or .zshrc file:

For bash:

eval "$(COMPLETE=bash prek)"  # for bash

For zsh:

eval "$(COMPLETE=zsh prek)"

Similarly for other shells like fish, powershell, etc.

After installation, prek hooks are run automatically when you commit the code and they will only run on the files that you change during your commit, so they are usually pretty fast and do not slow down your iteration speed on your changes. There are also ways to disable the prek hooks temporarily when you commit your code with --no-verify switch or skip certain checks that you find to much disturbing your local workflow. See Using prek

The prek hooks use several external linters that need to be installed before prek is run. Each of the checks installs its own environment, so you do not need to install those, but there are some checks that require locally installed binaries. On Linux, you typically install them with sudo apt install, on macOS - with brew install.

The current list of prerequisites is limited to xmllint and golang if you want to modify the Golang code.:

• on Linux, install via sudo apt install libxml2-utils golang
• on macOS, install via brew install libxml2 golang

Some prek hooks also require the Docker Engine to be configured as the static checks are executed in the Docker environment. You should build the images locally before installing prek checks as described in Breeze docs.

Sometimes your image is outdated and needs to be rebuilt because some dependencies have been changed. In such cases, the Docker-based prek will inform you that you should rebuild the image.

Enabling prek hooks

To turn on prek checks for commit operations in git, enter:

prek install

To install the checks also for pre-push operations, enter:

prek install --hook-type pre-push

For details on advanced usage of the install method, use:

prek install --help

Note

The prek tool is a drop-in replacement for the legacy pre-commit tool - much faster and more feature-rich, If you have already installed pre-commit to handle your hooks, you can run prek install -f to replace the existing pre-commit hooks with the prek hooks.

Available prek hooks

You can see the list of available hooks by running:

prek list

You can also see more details about the hooks by running:

prek list --verbose

And if you want to see the details of a particular hook, you can run:

prek list --verbose <hook-id>

When you install auto-completion, you can also use the tab-completion to see the available hooks.

Using prek

After installation, prek hooks are run automatically when you commit the code or push it to the repository (depending on stages configured for the hooks). Some of the hooks are configured to run on "manual" stage only and are not run automatically.

By default when you run prek, the pre-commit stage hooks are run.

But you can run prek hooks manually as needed.

• Run all checks on your staged files by using:

prek

• Run only mypy check on your staged airflow and dev files by specifying the mypy-airflow-core and mypy-dev prek hooks (more hooks can be specified). For non-provider projects, mypy runs locally via uv (no breeze image needed):

prek mypy-airflow-core mypy-dev

• Run only mypy airflow checks on all "airflow-core" files by using:

prek mypy-airflow-core --all-files

• Run all pre-commit stage hooks on all files by using:

prek --all-files

• Run all pre-commit stage hooks only on files modified in the last locally available commit in your checked out branch:

prek --last-commit

• Run all pre-commit stage hooks only on files modified in your last branch that is targeted to be merged into the main branch:

prek --from-ref main

• Show files modified automatically by prek when prek automatically fixes errors (after running all pre-commit stage hooks on locally modified files):

prek --show-diff-on-failure

• Skip one or more of the checks by specifying a comma-separated list of checks to skip in the SKIP variable:

SKIP=ruff,rst-backticks prek --all-files

You can always skip running the tests by providing --no-verify flag to the git commit command.

To check other usage types of the pre-commit framework, see Pre-commit website.

Disabling particular checks

In case you have a problem with running particular prek check you can still continue using the benefits of having prek installed, with some of the checks disabled. In order to disable checks you might need to set SKIP environment variable to coma-separated list of checks to skip. For example, when you want to skip some checks (ruff/mypy for example), you should be able to do it by setting export SKIP=ruff,mypy-airflow-core,. You can also add this to your .bashrc or .zshrc if you do not want to set it manually every time you enter the terminal.

In case you do not have breeze image configured locally, you can also disable all checks that require breeze the image by setting SKIP_BREEZE_PREK_HOOKS to "true". This will mark the tests as "green" automatically when run locally (note that those checks will anyway run in CI).

Disabling goproxy for firewall issues

Sometimes your environment might not allow to connect to the goproxy server, which is used to proxy/cache Go modules. When your firewall blocks go proxy it usually ends with message similar to:

lookup proxy.golang.org: i/o timeout

In such case, you can disable the goproxy by setting the GOPROXY environment variable to "direct". You can do it by running:

export GOPROXY=direct

Alternatively if your company has its own Go proxy, you can set the GOPROXY to your company Go proxy URL. For example:

export GOPROXY=https://mycompanygoproxy.com

See Go Proxy lesson) for more details on how to configure Go proxy - including setting multiple proxies.

You can add the variable to your .bashrc or .zshrc if you do not want to set it manually every time you enter the terminal.

Manual prek hooks

Most of the checks we run are configured to run automatically when you commit the code or push PR. However, there are some checks that are not run automatically and you need to run them manually. You can run them manually by running prek --stage manual <hook-id>.

Mypy checks

When we run mypy checks locally, the mypy-* checks run depending on the files you are changing: mypy-airflow-core, mypy-dev, mypy-providers, mypy-scripts, mypy-task-sdk, mypy-airflow-ctl, mypy-devel-common, mypy-airflow-ctl-tests, mypy-helm-tests, mypy-airflow-e2e-tests, mypy-task-sdk-integration-tests, mypy-docker-tests, mypy-kubernetes-tests, and one mypy-shared-<dist> hook per shared/<dist> workspace distribution (e.g. mypy-shared-configuration, mypy-shared-logging).

For non-provider projects, mypy runs locally using uv — no breeze CI image is needed. These checks run as regular prek hooks in the pre-commit stage, checking whole directories at once. This means they run both as part of local commits and as part of regular static checks in CI (not as separate mypy CI jobs).

Each non-provider mypy-* hook uses a dedicated virtualenv and mypy cache under .build/ so running mypy never mutates your regular project .venv and each hook keeps a stable, CI-aligned dependency set:

• virtualenvs: .build/mypy-venvs/<hook-name>/
• mypy caches: .build/mypy-caches/<hook-name>/

The hook prefers uv from your project's main .venv/bin/uv — so the uv version used to sync and run mypy is pinned by the project rather than whatever uv is on your PATH. If that binary is missing, the hook falls back to uv on PATH and prints a warning. uv is part of the dev dependency group via the all extras, so a plain sync installs it:

uv sync

Prek hooks that invoke uv (directly or via breeze) also verify that the uv they are about to run is at least the version pinned in [tool.uv] required-version in the root pyproject.toml. If your uv is older, the hook fails fast with an instruction to run uv self update (or uv sync to refresh the project-pinned uv).

Adding a new shared library

Every shared/<dist> workspace member has its own mypy-shared-<dist> prek hook so it is type-checked in isolation against its own dependency set. When you add a new shared library under shared/<new-dist>/, you also need to:

1. Add a [dependency-groups] section with mypy = ["apache-airflow-devel-common[mypy]"] in shared/<new-dist>/pyproject.toml (so uv sync --group mypy installs mypy into the hook's dedicated virtualenv).
2. Create shared/<new-dist>/.pre-commit-config.yaml with a mypy-shared-<new-dist> hook entry that calls ../../scripts/ci/prek/run_mypy_full_dist_local_venv_or_breeze_in_ci.py shared/<new-dist>.

The check-shared-mypy-hooks prek hook enforces step 2 — it fails and prints the exact config contents to add when any shared/<dist> is missing its dedicated mypy hook.

To run the prek hook for a specific project (example for airflow-core files):

prek mypy-airflow-core --all-files

To show unused mypy ignores, run:

export SHOW_UNUSED_MYPY_WARNINGS=true
prek mypy-airflow-core --all-files

For providers, mypy still runs via breeze (breeze run mypy) as a separate CI job and requires breeze ci-image build --python 3.10 to be built locally. Providers use a separate docker-volume (called mypy-cache-volume) that keeps the cache of last MyPy execution.

To clear all mypy caches (the Docker volume used by providers, any legacy repo-root .mypy_cache, and the per-hook venvs + caches under .build/mypy-venvs/ and .build/mypy-caches/), run breeze down --cleanup-mypy-cache.

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Once your code passes all the static code checks, you should take a look at Testing documentation to learn about various ways to test the code.