misc: Add initial support for Mypy checks (#469)

This is the initial change to start adding typing hints to the project.
It includes:

* Adding `mypy` checks to GitHub actions, and Tox.
* Adding `mypy` command to `run.sh` script.
* Initial `mypy` configuration options in `setup.cfg`.
* Small fixes for existing typing issues.

.github/workflows/python-package.yml

@@ -63,6 +63,27 @@ jobs:
           # exit-zero treats all errors as warnings. The GitHub editor is 127 chars wide
           flake8 . --count --exit-zero --max-complexity=10 --max-line-length=127 --statistics
 
+  typecheck:
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v3
+      - uses: actions/setup-python@v4
+      - uses: actions/cache@v3
+        with:
+          path: ~/.cache/pip
+          key: ${{ matrix.python-version }}-pip-${{ hashFiles('**/requirements.txt') }}
+          restore-keys: |
+            ${{ matrix.python-version }}-pip-
+      - name: Install dependencies
+        run: |
+          python -m pip install --upgrade pip
+          python -m pip install tox-gh-actions
+          if [ -f requirements.txt ]; then pip install -r requirements.txt; fi
+      - name: Type-check
+        run: |
+          tox -e typecheck
+
   i18n:
     runs-on: ubuntu-latest
 

CONTRIBUTING.rst

@@ -61,15 +61,17 @@ To be mergable, patches must:
 - add tests for new code (bug fixes should include regression tests, new
   features should have relevant tests),
 - not introduce any new flake8_ errors (run ``./run.sh lint``),
+- not introduce any new mypy_ errors (run ``./run.sh typecheck``),
 - include updated source translations (run ``./run.sh makemessages`` and ``./run.sh compilemessages``),
 - document any new features, and
 - have a `good commit message`_.
 
 Regressions tests should fail without the rest of the patch and pass
-with it. 
+with it.
 
 
 .. _open a new issue: https://github.com/django-waffle/django-waffle/issues/new
 .. _Fork: https://github.com/django-waffle/django-waffle/fork
 .. _flake8: https://pypi.python.org/pypi/flake8
+.. _mypy: https://www.mypy-lang.org/
 .. _good commit message: http://tbaggery.com/2008/04/19/a-note-about-git-commit-messages.html

requirements.txt

@@ -4,4 +4,5 @@ transifex-client
 
 flake8
 mock==1.3.0
+mypy
 tox

run.sh

@@ -7,6 +7,7 @@ usage() {
     echo "USAGE: $0 [command]"
     echo "  test - run the waffle tests"
     echo "  lint - run flake8"
+    echo "  typecheck - run mypy"
     echo "  shell - open the Django shell"
     echo "  makemigrations - create a schema migration"
     exit 1
@@ -20,6 +21,8 @@ case "$CMD" in
         DJANGO_SETTINGS_MODULE=test_settings django-admin test waffle $@ ;;
     "lint" )
         flake8 waffle $@ ;;
+    "typecheck" )
+        mypy waffle $@ ;;
     "shell" )
         django-admin shell $@ ;;
     "makemigrations" )

setup.cfg

@@ -6,3 +6,11 @@ max-line-length = 120
 #  - docs: contains autogenerated code that doesn't need a check
 exclude = */migrations/*,docs
 ignore = E731
+
+[mypy]
+python_version = 3.7
+disallow_incomplete_defs = True
+disallow_untyped_decorators = True
+strict_equality = True
+[mypy-django.*]
+ignore_missing_imports = True

tox.ini

@@ -28,3 +28,10 @@ commands =
     ./run.sh makemessages
     ./run.sh compilemessages
     ./run.sh find_uncommitted_translations
+
+[testenv:typecheck]
+deps =
+	Django>=3.2,<4.2
+	-r{toxinidir}/requirements.txt
+commands =
+    ./run.sh typecheck

waffle/jinja.py

@@ -8,7 +8,7 @@
     from jinja2 import pass_context
 except ImportError:
     # NOTE: We can get rid of this when we stop supporting Jinja2 < 3.
-    from jinja2 import contextfunction as pass_context
+    from jinja2 import contextfunction as pass_context  # type: ignore
 
 
 @pass_context

waffle/mixins.py

@@ -1,4 +1,5 @@
 from functools import partial
+from typing import Optional
 
 from django.http import Http404
 
@@ -24,7 +25,7 @@ class WaffleFlagMixin(BaseWaffleMixin):
     waffle_flag
     """
 
-    waffle_flag = None
+    waffle_flag: Optional[str] = None
 
     def dispatch(self, request, *args, **kwargs):
         func = partial(flag_is_active, request)
@@ -42,7 +43,7 @@ class WaffleSampleMixin(BaseWaffleMixin):
     waffle_sample.
     """
 
-    waffle_sample = None
+    waffle_sample: Optional[str] = None
 
     def dispatch(self, request, *args, **kwargs):
         active = self.validate_waffle(self.waffle_sample, sample_is_active)
@@ -59,7 +60,7 @@ class WaffleSwitchMixin(BaseWaffleMixin):
     waffle_switch.
     """
 
-    waffle_switch = None
+    waffle_switch: Optional[str] = None
 
     def dispatch(self, request, *args, **kwargs):
         active = self.validate_waffle(self.waffle_switch, switch_is_active)