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docker-stacks/docs/contributing/lint.md
2024-06-11 11:59:32 +01:00

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# Lint
To enforce some rules, **linters** are used in this project.
Linters can be run either during the **development phase** (by the developer) or the **integration phase** (by GitHub Actions).
To integrate and enforce this process in the project lifecycle, we are using **git hooks** through [pre-commit](https://pre-commit.com/).
## Using pre-commit hooks
### Pre-commit hook installation
_pre-commit_ is a Python package that needs to be installed.
To achieve this, use the generic task to install all Python development dependencies.
```sh
# Install all development dependencies for the project
pip install --upgrade -r requirements-dev.txt
# It can also be installed directly
pip install pre-commit
```
Then the git hooks scripts configured for the project in `.pre-commit-config.yaml` need to be installed in the local git repository.
```sh
pre-commit install
```
### Run
Now, _pre-commit_ (and so configured hooks) will run automatically on `git commit` on each changed file.
However, it is also possible to trigger it against all files.
```{note}
Hadolint pre-commit uses Docker to run, so `docker` should be running while running this command.
```
```sh
pre-commit run --all-files --hook-stage manual
```
```{note}
We're running `pre-commit` with `--hook-stage manual`, because works with changed files, which doesn't work well for mypy.
More information can be found in [`.pre-commit-config.yaml` file](https://github.com/jupyter/docker-stacks/blob/main/.pre-commit-config.yaml)
```
## Image Lint
To comply with [Docker best practices](https://docs.docker.com/build/building/best-practices/),
we are using the [Hadolint](https://github.com/hadolint/hadolint) tool to analyze each `Dockerfile`.
### Ignoring Rules
Sometimes it is necessary to ignore [some rules](https://github.com/hadolint/hadolint#rules).
The following rules are ignored by default for all images in the `.hadolint.yaml` file.
- [`DL3006`][dl3006]: We use a specific policy to manage image tags.
- The `docker-stacks-foundation` `FROM` clause is fixed but based on an argument (`ARG`).
- Building downstream images from (`FROM`) the latest is done on purpose.
- [`DL3008`][dl3008]: System packages are always updated (`apt-get`) to the latest version.
- [`DL3013`][dl3013]: We always install the latest packages using `pip`
The preferred way to do it for other rules is to flag ignored ones in the `Dockerfile`.
> It is also possible to ignore rules by using a special comment directly above the Dockerfile instruction you want to make an exception for.
> Ignore rule comments look like `# hadolint ignore=DL3001,SC1081`.
> For example:
```dockerfile
FROM ubuntu
# hadolint ignore=DL3003,SC1035
RUN cd /tmp && echo "hello!"
```
[dl3006]: https://github.com/hadolint/hadolint/wiki/DL3006
[dl3008]: https://github.com/hadolint/hadolint/wiki/DL3008
[dl3013]: https://github.com/hadolint/hadolint/wiki/DL3013