contributing-docs/08_static_code_checks.rst

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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 <../dev/breeze/doc/README.rst>`_ environment.

.. contents:: Table of Contents
   :depth: 2
   :local:

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 <https://github.com/j178/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``.

.. code-block:: bash

    uv tool install prek

.. code-block:: bash

    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:

.. code-block:: bash

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

For zsh:

.. code-block:: 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 <#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 <../dev/breeze/doc/README.rst>`__.

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:

.. code-block:: bash

    prek install

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

.. code-block:: bash

    prek install --hook-type pre-push

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

.. code-block:: bash

   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:

.. code-block:: bash

    prek list

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

.. code-block:: bash

    prek list --verbose

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

.. code-block:: bash

    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:

.. code-block:: bash

    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):

.. code-block:: bash

    prek mypy-airflow-core mypy-dev

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

.. code-block:: bash

    prek mypy-airflow-core --all-files

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

.. code-block:: bash

    prek --all-files

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

.. code-block:: bash

    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:

.. code-block:: bash

    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):

.. code-block:: bash

    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:

.. code-block:: bash

    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 <https://pre-commit.com/>`__.

.. AGENT-SKILL-START
   type: agents-md-commands
   order: 30
   lines:
     - "- **Type-check (non-providers):** run the prek hook \u2014 `prek run mypy-<project> --all-files` (e.g. `mypy-airflow-core`, `mypy-task-sdk`, `mypy-shared-logging`; each `shared/<dist>` workspace member has its own `mypy-shared-<dist>` hook). The hook uses a dedicated virtualenv and mypy cache under `.build/mypy-venvs/<hook>/` and `.build/mypy-caches/<hook>/`; mypy itself is installed from `uv.lock` via the `mypy` dependency group (`uv sync --group mypy`), so it never mutates your project `.venv`. The hook prefers `uv` from the project's main `.venv/bin/uv` (installed by `uv sync` \u2014 `uv` is part of the `dev` dependency group via the `all` extras) for a project-pinned uv version; it falls back to `uv` on `$PATH` with a warning if that binary is missing. Clear with `breeze down --cleanup-mypy-cache`."
     - "- **Type-check (providers):** `breeze run mypy path/to/code`"
     - "- **Lint with ruff only:** `prek run ruff --from-ref <target_branch>`"
     - "- **Format with ruff only:** `prek run ruff-format --from-ref <target_branch>`"
     - "- **Run regular (fast) static checks:** `prek run --from-ref <target_branch> --stage pre-commit`"
     - "- **Run manual (slower) checks:** `prek run --from-ref <target_branch> --stage manual`"
     - "- **Build docs:** `breeze build-docs`"
     - "- **Determine which tests to run based on changed files:** `breeze selective-checks --commit-ref <commit_with_squashed_changes>`"
.. AGENT-SKILL-END

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:

.. code-block:: text

  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:

.. code-block:: bash

    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:

.. code-block:: bash

    export GOPROXY=https://mycompanygoproxy.com

See `Go Proxy lesson <https://www.practical-go-lessons.com/chap-18-go-module-proxies#configuration-of-the-go-module-proxy>`__)
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:

.. code-block:: bash

  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):

.. code-block:: bash

  prek mypy-airflow-core --all-files

To show unused mypy ignores, run:

.. code-block:: bash

  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``.

-----------

Once your code passes all the static code checks, you should take a look at `Testing documentation <09_testing.rst>`__
to learn about various ways to test the code.