Run mypy in CI

.github/workflows/ci.yml

@@ -13,8 +13,6 @@ jobs:
     runs-on: ubuntu-22.04
     steps:
       - uses: actions/checkout@v3
-        with:
-          submodules: true
       - uses: actions/setup-python@v4
       - run: python -m pip install --upgrade pip
       - run: python -m pip install -r requirements/ci.txt
@@ -23,6 +21,19 @@ jobs:
         with:
           commit_message: Apply automatic formatting
 
+  type-checking:
+    name: Type checking
+    needs: formatting
+    runs-on: ubuntu-22.04
+    steps:
+      - uses: actions/checkout@v3
+      - uses: actions/setup-python@v4
+        with:
+          python-version: 3.11
+      - run: python -m pip install --upgrade pip
+      - run: python -m pip install -r requirements/ci.txt
+      - run: tox -e mypy
+
   tests:
     name: Tests ${{ matrix.os }} ${{ matrix.tox }}
     needs: formatting
@@ -41,8 +52,6 @@ jobs:
       - run: sudo apt install --yes docker-compose
         if: ${{ contains(matrix.variant.os, 'ubuntu') }}
       - uses: actions/checkout@v3
-        with:
-          submodules: true
       - uses: actions/setup-python@v4
         with:
           python-version: ${{ matrix.python }}

docs/release-notes.rst

@@ -68,6 +68,8 @@ Deprecations
 Stability, Maintainability, and Testing
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
+* The codebase now gets type-checked in CI.
+
 v23.08.0 (2023-08-28)
 ---------------------
 

tox.ini

@@ -35,6 +35,11 @@ allowlist_externals = sh
 # either the different formatters can't agree on a format or that static analysis failed.
 commands = sh -c 'pre-commit run -a || (echo "" && pre-commit run -a)'
 
+[testenv:mypy]
+description = Type checking (mypy)
+deps = -r requirements/mypy.txt
+commands = python -m mypy .
+
 [testenv:deps]
 description = Update dependencies by running pip-compile-multi
 deps = pip-compile-multi