Add mypy CI and config (ref #358) (#518)

Estalish a minimal mypy config that ensures annotations are compatible
with Python 3.8 (the oldest supported Python version).

Add a forgiving CI job that does not affect the status of the GitHub
workflow run.

Co-authored-by: André Colomb <src@andre.colomb.de>

Author: erlend-aasland

.github/workflows/pr-linters.yaml

@@ -0,0 +1,28 @@
+name: Run PR linters
+
+on:
+  pull_request:
+  workflow_dispatch:
+
+permissions:
+  contents: read
+  pull-requests: read
+
+jobs:
+
+  mypy:
+    name: Run mypy static type checker (optional)
+    runs-on: ubuntu-latest
+    continue-on-error: true
+    steps:
+    - uses: actions/checkout@v4
+    - uses: actions/setup-python@v5
+      with:
+        python-version: 3.12
+        cache: pip
+        cache-dependency-path: |
+          'pyproject.toml'
+          'requirements-dev.txt'
+    - run: pip install -r requirements-dev.txt -e .
+    - name: Run mypy and report
+      run: mypy --config-file pyproject.toml .

pyproject.toml

@@ -48,3 +48,11 @@ testpaths = [
 filterwarnings = [
     "ignore::DeprecationWarning",
 ]
+
+[tool.mypy]
+python_version = "3.8"
+exclude = [
+    "^examples*",
+    "^test*",
+    "^setup.py*",
+]

requirements-dev.txt

@@ -1,2 +1,3 @@
+mypy~=1.10
 pytest~=8.3
 pytest-cov~=5.0