ahriman/CONTRIBUTING.md

# Contributing to ahriman

Welcome to ahriman! The goal of the project is to provide the best user experience to manage Arch linux repositories. In order to follow this we set some limitations for the issue creations and heavily restricted code contribution.

## Create an issue

Basically just follow the suggested templates:

* Bug report requires at least the way to reproduce the issue and behaviour description (expected and actual ones). In order to resolve the bug, the additional questions may be asked, please consider them as lesser evil.
* Feature requests basically just require feature description and the purpose why do you want this feature to be implemented. It is required to make sure that the feature you want is going to be implemented in the way you really want it (and to make sure that this feature is not already implemented).
* Questions and discussions have free templates, and you are free to ask your question in the way you want.

## Code contribution

There are some strict limitation for suggested pull requests:

* `autopep8`, `bandit`, `pylint`, `mypy` must pass.
* Test coverage must remain 100%.

### Code formatting

In order to resolve all difficult cases the `autopep8` is used. You can perform formatting at any time by running `make check` or running `autopep8` command directly.

### Code style

Again, the most checks can be performed by `make check` command, though some additional guidelines must be applied:

* Every class, every function (including private and protected), every attribute must be documented. The project follows [Google style documentation](https://google.github.io/styleguide/pyguide.html). The only exception is local functions.
* Correct way to document function, if section is empty, e.g. no notes or there are no args, it should be omitted:

    ```python
    def foo(argument: str, *, flag: bool = False) -> int:
        """
        do foo
  
        Note:
            Very important note about this function
  
        Args:
            argument(str): an argument
            flag(bool, optional): a flag (Default value = False)
  
        Returns:
            int: result
  
        Raises:
            RuntimeException: a local function error occurs
  
        Examples:
            Very informative example how to use this function, e.g.::
  
                >>> foo("argument", flag=False)
  
            Note that function documentation is in rST.
        """
    ```
  
  `Returns` should be replaced with `Yields` for generators.

  Class attributes should be documented in the following way:

    ```python
    class Clazz(BaseClazz):
        """
        brand-new implementation of ``BaseClazz``
  
        Attributes:
            CLAZZ_ATTRIBUTE(int): (class attribute) a brand-new class attribute
            instance_attribute(str): an instance attribute
  
        Examples:
            Very informative class usage example, e.g.::
  
                >>> from module import Clazz
                >>> clazz = Clazz()
        """
  
        CLAZZ_ATTRIBUTE = 42
  
        def __init__(self) -> None:
            """
            default constructor
            """
            self.instance_attribute = ""
    ```

* Type annotations are the must, even for local functions.
* Recommended order of function definitions in class:

    ```python
    class Clazz:
  
        def __init__(self) -> None: ...  # replace with `__post_init__` for dataclasses

        @property
        def property(self) -> Any: ...

        @classmethod
        def class_method(cls: Type[Clazz]) -> Clazz: ...

        @staticmethod
        def static_method() -> Any: ...

        def __private_method(self) -> Any: ...

        def _protected_method(self) -> Any: ...

        def usual_method(self) -> Any: ...

        def __hash__(self) -> int: ...  # basically any magic (or look-alike) method
    ```
  
  Methods inside one group should be ordered alphabetically, the only exception is `__init__` method (`__post__init__` for dataclasses) which should be defined first. For test methods it is recommended to follow the order in which functions are defined.

  Though, we would like to highlight abstract methods (i.e. ones which raise `NotImplementedError`), we still keep in global order at the moment.

* Abstract methods must raise `NotImplementedError` instead of using `abc.abstractmethod`. The reason behind this restriction is the fact that we have class/static abstract methods for those we need to define their attribute first making the code harder to read.
* For any path interactions `pathlib.Path` must be used.
* Configuration interactions must go through `ahriman.core.configuration.Configuration` class instance.
* In case if class load requires some actions, it is recommended to create class method which can be used for class instantiating.
* The code must follow the exception safety, unless it is explicitly asked by end user. It means that most exceptions must be handled and printed to log, no other actions must be done (e.g. raising another exception).
* For the external command `ahriman.core.util.check_output` function must be used.
* Every temporary file/directory must be removed at the end of processing, no matter what. The `tempfile` module provides good ways to do it.
* Import order must be the following:

    ```python
    # optional imports from future module
    from __future__ import annotations

    # Module import for those which are installed into environment (no matter standard library or not)...
    import os
    # ...one per line...
    import pyalpm
    # ...in alphabetical order
    import sys

    # Blank line between
    # ``from module import submodule`` import
    from pathlib import Path
    # ...again in alphabet order. It is possible to do several imports, but make sure that they are also in alphabetical order.
    from pyalpm import Handle, Package

    # Blank line again and package imports
    from ahriman.core.configuration import Configuration
    ```

* One file should define only one class, exception is class satellites in case if file length remains less than 400 lines.
* It is possible to create file which contains some functions (e.g. `ahriman.core.util`), but in this case you would need to define `__all__` attribute.
* The file size mentioned above must be applicable in general. In case of big classes consider splitting them into traits. Note, however, that `pylint` includes comments and docstrings into counter, thus you need to check file size by other tools.
* No global variable is allowed outside of `ahriman.version` module. `ahriman.core.context` is also special case.
* Single quotes are not allowed. The reason behind this restriction is the fact that docstrings must be written by using double quotes only, and we would like to make style consistent.
* If your class writes anything to log, the `ahriman.core.log.LazyLogging` trait must be used.

### Other checks

The projects also uses typing checks (provided by `mypy`) and some linter checks provided by `pylint` and `bandit`. Those checks must be passed successfully for any open pull requests.