Hacking on BuildStream ====================== Some tips and guidelines for developers hacking on BuildStream Getting Started --------------- After cloning the BuildStream module with git, you will want a development installation. To do this, first install ``pip`` and run the following command in the buildstream checkout directory:: pip install --user -e . The above will install some dependencies and also a symlink to your buildstream checkout in your local user's python environment, so any changes you make to buildstream will be effective for your user. You can later uninstall the local installation by running:: pip uninstall buildstream Coding Style ------------ Coding style details for BuildStream Style Guide ~~~~~~~~~~~ Python coding style for BuildStream is pep8, which is documented here: https://www.python.org/dev/peps/pep-0008/ We have a couple of minor exceptions to this standard, we dont want to compromise code readability by being overly restrictive on line length for instance. The pep8 linter will run automatically when running the test suite. Imports ~~~~~~~ Module imports inside BuildStream are done with . notation Good:: from .context import Context Bad:: from buildstream.context import Context The exception to the above rule is when authoring plugins, plugins do not reside in the same namespace so they must address buildstream in the imports. An element plugin will derive from Element by importing:: from buildstream import Element When importing utilities specifically, dont import function names from there, instead:: from . import utils This makes things clear when reading code that said functions are not defined in the same file but come from utils.py for example. One Class One Module ~~~~~~~~~~~~~~~~~~~~ BuildStream is mostly Object Oriented with a few utility files. * Every object should go into its own file (module) inside the buildstream package * Files should be named after their class in lower case with no underscore. This is to say a class named FooBar will certainly reside in a file named foobar.py. Unless FooBar is private in which case the file is of course _foobar.py. When adding a public class, it should be imported in toplevel __init__.py so that buildstream consumers can import it directly from the buildstream package, without requiring knowledge of the BuildStream package structure, which is allowed to change over time. Private API ~~~~~~~~~~~ BuildStream strives to guarantee a minimal and comprehensive public API surface both for embedders of the BuildStream pipeline and implementors of custom plugin Elements and Sources. Python does not have a real concept of private API, but as a convention anything which is private uses an underscore prefix. * Modules which are private have their file named _module.py * Private classes are named _Class * Private methods, class variables and instance variables have a leading underscore as well Exceptions to the above rules is to follow a principle of least underscores: * If a module is entirely private, there is no need for the classes it contains to have a leading underscore. * If a class is entirely private, there is no need to mark its members as private with leading underscores. Documenting BuildStream ----------------------- BuildStream starts out as a documented project from day one and uses sphinx to document itself. Useful links: * Sphinx documentation: http://www.sphinx-doc.org/en/1.4.8/contents.html * rst primer: http://www.sphinx-doc.org/en/stable/rest.html Building Docs ~~~~~~~~~~~~~ The documentation build is not integrated into the ``setup.py`` and is difficult (or impossible) to do so, so there is a little bit of setup you need to take care of first. Before you can build the BuildStream documentation yourself, you need to first install ``sphinx`` and ``sphinx-click``, using pip or some other mechanism:: pip install --user sphinx pip install --user sphinx-click Furthermore, the documentation build requires that BuildStream itself be installed first, this can be a developer installation as described at the top of this text:: cd buildstream pip install --user -e . Finally, to build the current set of docs, just run the following:: cd doc make This will give you a build/html directory with the html docs. Man Pages ~~~~~~~~~ Unfortunately it is quite difficult to integrate the man pages build into the ``setup.py``, as such, whenever the frontend command line interface changes, the static man pages should be regenerated and committed with that. To do this, first ensure you have ``click_man`` installed, possibly with:: pip install --user click_man Then, in the toplevel directory of buildstream, run the following:: python3 setup.py --command-packages=click_man.commands man_pages And commit the result, ensuring that you have added anything in the ``man/`` subdirectory, which will be automatically included in the buildstream distribution. Documenting Conventions ~~~~~~~~~~~~~~~~~~~~~~~ When adding a new class to the buildstream core, an entry referring to the new module where the new class is defined should be added to the toplevel index manually in doc/source/index.rst. We use the sphinx.ext.napoleon extension for the purpose of having a bit nicer docstrings than the default sphinx docstrings. A docstring for a method, class or function should have the following format:: """Brief description of entity Args: argument1 (type): Description of arg argument2 (type): Description of arg Returns: Description of returned thing indicating its type Raises: SomeError, SomeOtherError A detailed description can go here if one is needed, only after the above part documents the calling conventions. """ Testing BuildStream ------------------- BuildStream uses pytest for regression tests and testing out the behavior of newly added components. The elaborate documentation for pytest can be found here: http://doc.pytest.org/en/latest/contents.html Don't get lost in the docs if you don't need to, follow existing examples instead. Running Tests ~~~~~~~~~~~~~ To run the tests, just type:: ./setup.py test At the toplevel. When debugging a test, it can be desirable to see the stdout and stderr generated by a test, to do this use the --addopts function to feed arguments to pytest as such:: ./setup.py test --addopts -s You can always abort on the first failure by running:: ./setup.py test --addopts -x If you want to run a specific test or a group of tests, you can specify a prefix to match. E.g. if you want to run all of the frontend tests you can do:: ./setup.py test --addopts '-k tests/frontend/' Adding Tests ~~~~~~~~~~~~ Tests are found in the tests subdirectory, inside of which there is a separarate directory for each *domain* of tests. All tests are collected as:: tests/*/*.py If the new test is not appropriate for the existing test domains, then simply create a new directory for it under the tests subdirectory. Various tests may include data files to test on, there are examples of this in the existing tests. When adding data for a test, create a subdirectory beside your test in which to store data. When creating a test that needs data, use the datafiles extension to decorate your test case (again, examples exist in the existing tests for this), documentation on the datafiles extension can be found here: https://pypi.python.org/pypi/pytest-datafiles The MANIFEST.in and setup.py ---------------------------- When adding a dependency to BuildStream, it's important to update the setup.py accordingly. When adding data files which need to be discovered at runtime by BuildStream, it's important update setup.py accordingly. When adding data files for the purpose of docs or tests, or anything that is not covered by setup.py, it's important to update the MANIFEST.in accordingly. At any time, running the following command to create a source distribution should result in creating a tarball which contains everything we want it to include:: ./setup.py sdist