Coding practices
Please refer to Contribute to debusine for general contributing guidelines. Once you are setup to contribute and know what you want to work on, you should read this document to learn our expectations on the code that you will submit as well as on the process leading to integrate your contribution.
Introduction to Test Driven Development
We expect you to follow this methodology when developing new code so if you are not familiar with it, have a look at Test-Driven Web Development with Python.
The suggested workflow looks like this:
Add a functional test that covers the new feature from the point of view of the user. This test will fail since the feature doesn’t exist yet.
Think about what’s the next step to let the functional test go further (i.e. fail later).
Write a failing unit test for the new code that you want to write.
Write the minimal code to make your unit test pass. You will typically run this very often:
$ ./manage.py test path-to-the-testing-folderRefactor (if needed). You might have introduced some duplication in your code or in your tests. Clean that up now before it’s too late.
Commit (optional). Commit together the (working) unit tests and the new code.
If you made progress from the functional tests point of view, go back to point 2, otherwise go back to point 3. If the functional test passes, continue.
Commit. The functional tests are committed at this point to ensure that they are committed in a working state:
$ git add . $ git commit
When you don’t develop a new feature, your workflow is restricted to steps 3 to 6.
Git commit messages
Please invest some time to write good commit messages. Just like your code, you write it once but it will be read many times by different persons looking to understand why you made the change. So make it pleasant to read.
The first line is the “summary” (or title) and describes briefly what the commit changes. It’s followed by an empty line and a long description. The long description can be as long as you want and should explain why you implemented the change seen in the commit.
The long description can also be used to close GitLab issues by putting
some Fixes: #XXX
pseudo-fields at the end of the description.
Pre-commit hooks
The setup instructions for developers recommend
setting up pre-commit. This runs a variety of
linters on the files changed by the commit to catch some problems that can
be found by static analysis. These are defined as a collection of “hooks”
in .pre-commit-config.yaml
.
To run linters over all files rather than just changed files, run
pre-commit run -a
. This is particularly useful after a rebase, since
the git hooks that pre-commit
uses by default don’t run on rebase (and
the ones that do run on rebase don’t operate on specific files anyway).
pre-commit run -a
is also useful if you want to check unstaged files,
since pre-commit
normally only checks committed and staged files, and
temporarily stashes unstaged changes. Things will normally work better if
you git add
your changes first.
To skip a particular pre-commit hook, you can set the SKIP
environment
variable to a comma-separated list of hook IDs: for example, SKIP=mypy
.
To bypass pre-commit hooks temporarily for a single commit, use git commit
-n
.
To upgrade hooks, run pre-commit autoupdate
, and then pre-commit run
-a
to check for new errors. Note that some hooks may be deliberately
pinned to older versions, in which case you will need to revert changes to
their versions afterwards.
About merge requests
Size of merge requests
Submitted merge requests should have a reasonable size: that is no more than 1000 lines of changes (total of added and removed lines, excluding test data and other auto-generated files) for large changes. We expect the majority of merge requests to be smaller than that.
If you are working on a large feature, we expect you to submit it progressively in multiple independent steps. If the separate merge of those individual steps would break debusine, then ask us to create a staging branch for your new feature and target that separate branch in your merge requests.
If you figure out that some refactoring is needed before you can reasonably implement your feature, consider doing that refactoring in a separate merge request.
A merge request can have multiple independent commits to make it easier to review.
Updates to merge requests
When a merge request has multiple independent commits, we want to preserve that split and not squash all the commits together. This means that fixes and improvements done following the review have to be incorporated in their respective commit.
With regular rebase -i
Assuming that the merge request targets the devel
branch, you can do
that locally with:
$ git commit --fixup=$COMMIT
$ git rebase -i --autosquash $(git merge-base HEAD devel)
$ git push --force-with-lease origin $BRANCH
The rebase command above ensures that the merge request is not rebased
against newer version of the devel
branch: this is important for big
merge requests that have already been reviewed, so that the diff
associated to the push does not include changes coming from the devel
branch.
Note
If you need to rebase such a branch against the latest version of the
devel
branch, please do that in a push where that is the only
change. You can do that with:
$ git fetch origin
$ git rebase origin/devel
$ git push --force-with-lease origin $BRANCH
For small merge requests, this is not so important and you can rebase
against devel
or origin/devel
directly:
$ git rebase -i --autosquash origin/devel
With push of fixup commits
Alternatively, you can simply push fixup commits to the remote branch
while review is in progress, and let the final git rebase -i
--autosquash
be done by whoever gets to merge the branch. Note however
that the presence of fixup commits in the history will change the status
of the merge request back to “draft”.
Note
If the merge request has multiple commits, and if you use GitLab’s “Add
suggestion” feature, please input a commit message fixup!
$TARGET_COMMIT_TITLE
so that it can be easily autosquashed by the
person that will perform the final merge.
Finally, if the merge request has a single commit (and is expected to stay that way), you should be free to select “Squash commits when merge request is accepted” so that the final merge automatically squashes any fixup commit.
Discussions in merge requests
Discussions within merge requests should be limited to code reviews: pointing out mistakes and inconsistencies with the associated issue, suggesting improvements, etc. If there are architecture or design issues that need to be addressed, or if there are disagreements between the coder and the reviewer, then those discussions should be moved to a separate issue and be resolved there before getting back to the merge request.
Work in progress merge requests
In order to benefit from the full CI during development, developers can open merge requests early while they are still working on the feature.
Those merge requests should have the draft status and the MR: Work in
progress
label. They can be freely rebased, refactored and can be
subject to large changes. They also don’t have any assignee or reviewer
set.
Such merge requests are not open for detailed review (unless the submitter explicitly asks for early review).
Once the MR: Work in progress
label is dropped, the merge request is
open for review and subsequent changes should follow the rules described
in Updates to merge requests.
Note
We rely on the label rather than only on the “draft” status, because push of fixup commits might bring back the status of a good merge request back to draft. Hence you can’t rely solely on the presence of the draft flag to decide to not review a merge request.
Merge requests labels
To help keep track of the status of the various merge requests, we have a few labels all starting with “MR:” (for easy auto-completion):
MR: Work in progress
: the work is not yet ready to be reviewedMR: Needs work
: a reviewer found issues, they have to be addressed. This label doesn’t need to be immediately set during review, it can be set later if we realize that the submitter is not dealing with comments in a timely fashion. The label can be dropped by the submitter after having handled all the issues that have been identified.MR: UI review needed
: the merge request contains a prototype UI that needs usability feedback (usually via aplayground-vm
machine) before proceeding with further work
Note that any merge request without any “MR” label is thus implicitly in a status where the branch is assumed to be ready and where the submitter is thus seeking reviews.
Usage of ‘Assignee’ and ‘Reviewer’
As a submitter of a merge request, you don’t have to set those fields, by default every contributor is encouraged to review open merge requests. There are two cases where we might set the Reviewer field:
when the submitter would like to ask someone specific to review the MR (due to former experience on the code being modified for example)
when a reviewer wants to notify other team members that he is currently reviewing that merge request
Final merge and approvals
The final merge, if not done by a core developer, should only happen after a core developer has approved the merge request and after all comments left by the core developer (if any) have been addressed.
Prior to merge, one should always ensure that all fixup commits have been properly squashed in their respective commits.
If such an operation is required, you should take the opportunity to
rebase the branch against the latest version of the devel
branch. The
rebase is also recommended if the base of the merge request is far behind
the current tip of the devel
branch: the rebase will trigger a final
pipeline run on a codebase that will be much closer to the result of the
merge, thus limiting the risk of failed pipeline on devel
after the
merge.
Coding style
In regard to coding style, we observe PEP8 with a few exceptions. And we format the code with black by running
make black
(we use a different line length and don’t impose the single type of quote for strings).Functions are documented using docstrings with Sphinx markup.
Imports are sorted in multiple groups separated by one empty line: first a group for
__future__
imports, then a single group for all the Python standard modules, then one group for each third-party module (and groups are sorted between them as well), followed by groups for the project modules, and last, one group for relative imports.Within each group the
import foo
statements are grouped and sorted at the top, while thefrom foo import bar
statements are grouped and sorted at the end.Example:
from __future__ import print_function
import datetime
import os
from datetime import timedelta
from email.utils import getaddresses, parseaddr
from django.conf import settings
from django.db import connection, models
from django.utils.safestring import mark_safe
import requests
from requests.structures import CaseInsensitiveDict
from debusine.artifacts.models import Artifact
Good code, good design
This section documents different decisions about implementation, naming, etc. that happened during merge requests. It is not an exclusive list of all the discussions and is subject to change.
Those rules are meant to help improve consistency and to obtain a cleaner overall design.
Models
Avoid changing fields from outside the model
Avoid changing fields in the models from their users. Do not do:
worker.connected_at = timezone.now()
Instead, create a method in Worker describing the action that you are doing:
worker.mark_connected()
And change the relevant fields from mark_connected()
.
This allows the model’s fields or logic to change without having to change the code which accesses it.
Read more in Push actions to the model layer.
Push filtering to the model layer
In order to encapsulate logic for filter
and other queries, add a ModelManager
to the Model and do the filtering there. Do not do:
worker.objects.filter(connected_at__isnull=False)
Instead create a connected
method in the Worker’s Manager and use it:
worker.objects.connected()
This allows the code base to be consistent in the filtering.
Read more in Push filtering to the model layer.
Push Model.objects.create() to the model layer
Similar to
Push filtering to the model layer:
avoid using Model.objects.create()
(or .get_or_create()
) and add a method
in the ModelManager describing the operation, such as:
Worker.objects.create_with_fqdn(fqdn, token)
Naming fields
Add the suffix _at for the fields of type DateTime:
created_at = models.DateTimeField()
Model method order
Follow the Code Review Doctor model method order:
Field choice tuples
Database fields
Custom manager attributes
class Meta
def __str__()
def save()
def delete
def get_absolute_url()
Any custom methods
The Code Review Doctor method order is compatible with order in the Django documentation making the choice tuples and delete order explicit.
Templates
Naming templates
If a Django template file is used to render a full page (including the HTML
header, footer, etc.) it should follow a similar structure to
work_request-list.html
.
If a template file is meant to be included from another template, add a _
.
For example: _work_request-list.html
is meant to be included from
another template.
Include templates: specify the context explicitly
When including a template, specify the context made available to it:
{% include "web/_workspace-list.html" with workspace_list=workspace_list user=user only %}
It helps the reader to know which context is used by the template and
also avoids using context that might be available from one
{% include ... %}
but not from another {% include ... %}
.
Tests
Private methods
To facilitate Test-Driven Development and localised tests, it is ok to call private methods from the tests.
Assert function: order of the parameters
In the assert methods, put the “expected” value as second parameter, for example:
self.assertEqual(actual, expected)
Reason: some test methods such as assertQuerysetEqual
expect “actual”
to be the first parameter. Always using this order helps the tests to be
more easily read.
Assert functions: assertEqual or specific
When there is a TestCase method with specific semantics, use them:
self.assertQuerysetEqual()
for testing querysets
self.assertTrue()
orself.assertFalse()
for testing boolean expressions
self.assertIn()
orself.assertNotIn()
Using the specific methods such as self.assertIn()
helps to have a better test
output compared with constructions such as self.assertTrue('john' in people)
.
When possible (actual and expected are the same type), use self.assertEqual()
instead of methods such as self.assertDictEqual()
. self.assertEqual()
will
use the correct underlying method.
Populating the database: Playground
If, while writing test code, you end up creating factory methods to create pydantic or database model objects, for example creating source or binary packages, check if suitable code already exists in the various Playground classes.
If you need to create new ones, consider adding them to Playground classes so they can be reused, both in tests and in creating scenarios for testing UI prototypes.
Playground integrates well with Django’s TestCase.setUpTestData
, so if you
are testing a nontrivial scenario you can create it once per test class, and
have it rolled back to its pristine state before every test method. Playground
takes care to ensure this also works for file store changes.
Evaluating UI prototypes
There is a bin/playground-vm
script that will deploy the branch from a
merge request to a newly created VM, explicitly intended to be used to publish
a draft UI prototype for evaluation by other developers.
The script runs examples/playground/populate
during provisioning, so,
to discuss a UI prototype, you can:
Code the prototype views and templates; at this stage your branch doesn’t need to pass CI or have full code coverage.
Make sure
examples/playground/populate
populates the database with enough information to show the features you are coding. Feel free to extend it otherwise.Push your branch to a merge request. You can push without running the CI by using
git push -o ci.skip
Use
bin/playground-vm
to deploy the merge request to a publicly accessible VM.
Naming data keys
Names of data keys in artifact, collection, and task definitions can be
expected to be used in pydantic
models. As such, they must be valid
Python identifiers: in particular, use underscores rather than hyphens as
separators.
General guidelines
Constants
If one of our dependencies provides defined public constants, use them instead of re-defining them or using magic numbers.
# Use:
from rest_framework import status
code = status.HTTP_501_NOT_IMPLEMENTED
# Instead of:
code = 501
This helps readability for readers that might not know all the internal codes, might avoid typos and if the “constants” depended on versions, environment, etc. the library will take care of them.
Type hints
If you want to indicate the type of a variable, type hints are preferable to adding suffixes to the variable.
# Use:
def method(information: dict):
...
# Instead of:
def method(information_dict):
...
This helps (IDEs, mypy) to give hints to the programmer and it keeps the variable names shorter, avoiding the type repetition.
Early exit
To exit early:
# Use:
raise SystemExit(3)
# Instead of:
sys.exit(3)
exit(3)
It says explicitly what it does and there is no need to import the sys module.
- If any utility in Debusine must exit early:
Use exit code 3. Exit code 1 is used by the Python interpreter for unhandled exceptions and exit code 2 by the argparse module for invalid command syntax.
Make sure to log or print (depending on the circumstances) why an early exit has happened so the user or admin can fix the situation.