STATIC_CODE_CHECKS.rst

• Static Code Checks
  • Pre-commit Hooks
    • Prerequisites for Pre-commit Hooks
    • Enabling Pre-commit Hooks
    • Using Pre-commit Hooks
  • Pylint Static Code Checks
  • Running Static Code Checks via Breeze
    • Running Static Code Checks via Scripts from the Host
    • Running Static Code Checks in the Docker Container
    • Running Static Code Checks for Selected Files

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 pre-commit hooks.

Some of the static checks in pre-commits require Breeze Docker images to be installed locally. The pre-commit hooks perform all the necessary installation when you run them for the first time. See the table below to identify which pre-commit checks require the Breeze Docker images.

Sometimes your image is outdated and needs to be rebuilt because some dependencies have been changed.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

You can also run some static code checks via Breeze environment using available bash scripts.

Pre-commit Hooks

Pre-commit hooks help speed up your local development cycle and place less burden on the CI infrastructure. Consider installing the pre-commit hooks as a necessary prerequisite.

This table lists pre-commit hooks used by Airflow and indicates which hooks require Breeze Docker images to be installed locally:

Hooks	Description	Breeze
base-operator	Checks that BaseOperator is imported properly
build	Builds image for check-apache-licence, mypy, pylint, flake8.
check-apache-license	Checks compatibility with Apache License requirements.
check-executables-have-shebangs	Checks that executables have shebang.
check-hooks-apply	Checks which hooks are applicable to the repository.
check-merge-conflict	Checks if a merge conflict is committed.
check-xml	Checks XML files with xmllint.
consistent-pylint	Consistent usage of pylint enable/disable with space.
debug-statements	Detects accidenatally committed debug statements.
detect-private-key	Detects if private key is added to the repository.
doctoc	Refreshes the table of contents for md files.
end-of-file-fixer	Makes sure that there is an empty line at the end.
flake8	Runs flake8.
forbid-tabs	Fails if tabs are used in the project.
insert-license	Adds licenses for most file types.
isort	Sorts imports in python files.
lint-dockerfile	Lints a dockerfile.
mixed-line-ending	Detects if mixed line ending is used (r vs. rn).
mypy	Runs mypy.
pydevd	Check for accidentally commited pydevd statements.
pylint	Runs pylint for main code.
pylint-tests	Runs pylint for tests.
python-no-log-warn	Checks if there are no deprecate log warn.
rst-backticks	Checks if RST files use double backticks for code.
setup-order	Checks for an order of dependencies in setup.py
shellcheck	Checks shell files with shellcheck.
update-breeze-file	Update output of breeze command in BREEZE.rst.
yamllint	Checks yaml files with yamllint.

The pre-commit hooks only check the files you are currently working on and make them 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 pre-commit hooks.

We have integrated the fantastic pre-commit framework in our development workflow. To install and use it, you need Python 3.6 locally.

It is the best to use pre-commit hooks when you have your local virtualenv for Airflow activated since then pre-commit hooks and other dependencies are automatically installed. You can also install the pre-commit hooks manually using pip install.

The pre-commit hooks 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 pre-commit checks as described in BREEZE.rst. In case you do not have your local images built, the pre-commit hooks fail and provide instructions on what needs to be done.

Prerequisites for Pre-commit Hooks

The pre-commit hooks use several external linters that need to be installed before pre-commit 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:

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

Enabling Pre-commit Hooks

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

pre-commit install

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

pre-commit install -t pre-push

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

pre-commit install --help

Using Pre-commit Hooks

After installation, pre-commit hooks are run automatically when you commit the code. But you can run pre-commit hooks manually as needed.

• Run all checks on your staged files by using:

pre-commit run

• Run only mypy check on your staged files by using:

pre-commit run mypy

• Run only mypy checks on all files by using:

pre-commit run mypy --all-files

• Run all checks on all files by using:

pre-commit run --all-files

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

SKIP=pylint,mypy pre-commit run --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.

Pylint Static Code Checks

We are in the process of fixing the code flagged with pylint checks for the whole Airflow project. This is a huge task so we implemented an incremental approach for the process. Currently most of the code is excluded from pylint checks via scripts/ci/pylint_todo.txt. We have an open JIRA issue AIRFLOW-4364 which has a number of sub-tasks for each of the modules that should be made compatible. Fixing problems identified with pylint is one of straightforward and easy tasks to do (but time-consuming), so if you are a first-time contributor to Airflow, you can choose one of the sub-tasks as your first issue to fix.

To fix a pylint issue, do the following:

1. Remove module/modules from the scripts/ci/pylint_todo.txt.
2. Run scripts/ci/ci_pylint_main.sh and scripts/ci/ci_pylint_tests.sh.
3. Fix all the issues reported by pylint.
4. Re-run scripts/ci/ci_pylint_main.sh and scripts/ci/ci_pylint_tests.sh.
5. If you see "success", submit a PR following Pull Request guidelines.

These are guidelines for fixing errors reported by pylint:

• Fix the errors rather than disable pylint checks. Often you can easily refactor the code (IntelliJ/PyCharm might be helpful when extracting methods in complex code or moving methods around).
• If disabling a particular problem, make sure to disable only that error by using the symbolic name of the error as reported by pylint.

import airflow.*  # pylint: disable=wildcard-import

• If there is a single line where you need to disable a particular error, consider adding a comment to the line that causes the problem. For example:

def  MakeSummary(pcoll, metric_fn, metric_keys): # pylint: disable=invalid-name

• For multiple lines/block of code, to disable an error, you can surround the block with pylint:disable/pylint:enable comment lines. For example:

# pylint: disable=too-few-public-methods
class  LoginForm(Form):
    """Form for the user"""
    username = StringField('Username', [InputRequired()])
    password = PasswordField('Password', [InputRequired()])
# pylint: enable=too-few-public-methods

Running Static Code Checks via Breeze

The static code checks can be launched using the Breeze environment.

You run the static code checks via -S, --static-check flags or -F, --static-check-all-files. The former ones run appropriate checks only for files changed and staged locally, the latter ones run checks on all files.

Note that it may take a lot of time to run checks for all files with pylint on macOS due to a slow filesystem for macOS Docker. As a workaround, you can add their arguments after -- as extra arguments. You cannot pass the --files flag if you select the --static-check-all-files option.

You can see the list of available static checks either via --help flag or by using the autocomplete option. Note that the all static check runs all configured static checks. Also since pylint tests take a lot of time, you can run a special all-but-pylint check that skips pylint checks.

Run the mypy check for the currently staged changes:

./breeze  --static-check mypy

Run the mypy check for all files:

./breeze --static-check-all-files mypy

Run the flake8 check for the tests.core.py file with verbose output:

./breeze  --static-check flake8 -- --files tests/core.py --verbose

Run the flake8 check for the tests.core package with verbose output:

./breeze  --static-check mypy -- --files tests/hooks/test_druid_hook.py

Run all tests for the currently staged files:

./breeze  --static-check all

Run all tests for all files:

./breeze  --static-check-all-files all

Run all tests but pylint for all files:

./breeze  --static-check-all-files all-but-pylint

Run pylint checks for all changed files:

./breeze  --static-check pylint

Run pylint checks for selected files:

./breeze  --static-check pylint -- --files airflow/configuration.py

Run pylint checks for all files:

./breeze --static-check-all-files pylint

The license check is run via a separate script and a separate Docker image containing the Apache RAT verification tool that checks for Apache-compatibility of licenses within the codebase. It does not take pre-commit parameters as extra arguments.

./breeze --static-check-all-files licenses

Running Static Code Checks via Scripts from the Host

You can trigger the static checks from the host environment, without entering the Docker container. To do this, run the following scripts (the same is done in Travis CI):

• scripts/ci/ci_check_license.sh - checks the licenses.
• scripts/ci/ci_docs.sh - checks that documentation can be built without warnings.
• scripts/ci/ci_flake8.sh - runs Flake8 source code style enforcement tool.
• scripts/ci/ci_lint_dockerfile.sh - runs lint checker for the Dockerfile.
• scripts/ci/ci_mypy.sh - runs a check for mypy type annotation consistency.
• scripts/ci/ci_pylint_main.sh - runs pylint static code checker for main files.
• scripts/ci/ci_pylint_tests.sh - runs pylint static code checker for tests.

The scripts may ask you to rebuild the images, if needed.

You can force rebuilding the images by deleting the .build directory. This directory keeps cached information about the images already built and you can safely delete it if you want to start from scratch.

After documentation is built, the HTML results are available in the docs/_build/html folder. This folder is mounted from the host so you can access those files on your host as well.

Running Static Code Checks in the Docker Container

If you are already in the Breeze Docker environment (by running the ./breeze command), you can also run the same static checks via run_scripts:

• Mypy: ./scripts/ci/in_container/run_mypy.sh airflow tests
• Pylint for main files: ./scripts/ci/in_container/run_pylint_main.sh
• Pylint for test files: ./scripts/ci/in_container/run_pylint_tests.sh
• Flake8: ./scripts/ci/in_container/run_flake8.sh
• License check: ./scripts/ci/in_container/run_check_licence.sh
• Documentation: ./scripts/ci/in_container/run_docs_build.sh

Running Static Code Checks for Selected Files

In all static check scripts, both in the container and host versions, you can also pass a module/file path as parameters of the scripts to only check selected modules or files. For example:

In the Docker container:

./scripts/ci/in_container/run_pylint.sh ./airflow/example_dags/

or

./scripts/ci/in_container/run_pylint.sh ./airflow/example_dags/test_utils.py

On the host:

./scripts/ci/ci_pylint.sh ./airflow/example_dags/

./scripts/ci/ci_pylint.sh ./airflow/example_dags/test_utils.py