Add static type checker mypy to the tests and pre-commit hooks

.github/workflows/code-format.yml

@@ -38,3 +38,18 @@ jobs:
       - name: isort
         run: |
           isort . --check --diff
+
+  typing-check-mypy:
+    runs-on: ubuntu-20.04
+    steps:
+      - uses: actions/checkout@master
+      - uses: actions/setup-python@v2
+        with:
+          python-version: 3.8
+      - name: Install mypy
+        run: |
+          pip install mypy
+          pip --version
+      - name: mypy
+        run: |
+          mypy

.pre-commit-config.yaml

@@ -2,4 +2,8 @@ repos:
   - repo: https://github.com/pycqa/isort
     rev: 5.5.2
     hooks:
-      - id: isort
+      - id: isort
+
+  - repo: https://github.com/pre-commit/mirrors-mypy
+    hooks:
+      - id: mypy

setup.cfg

@@ -61,3 +61,65 @@ license_file = LICENSE
 description-file = README.md
 # long_description = file:README.md
 # long_description_content_type = text/markdown
+
+[mypy]
+# Typing tests is low priority, but enabling type checking on the
+# untyped test functions (using `--check-untyped-defs`) is still
+# high-value because it helps test the typing.
+files = pl_bolts, tests
+disallow_untyped_defs = True
+ignore_missing_imports = True
+
+[mypy-pl_bolts.*]
+ignore_errors = True
+
+[mypy-pl_bolts.callbacks.*]
+ignore_errors = True
+
+[mypy-pl_bolts.datamodules.*]
+ignore_errors = True
+
+[mypy-pl_bolts.datasets.*]
+ignore_errors = True
+
+[mypy-pl_bolts.losses.*]
+ignore_errors = True
+
+[mypy-pl_bolts.metrics.*]
+ignore_errors = True
+
+[mypy-pl_bolts.models.*]
+ignore_errors = True
+
+[mypy-pl_bolts.models.autoencoders.*]
+ignore_errors = True
+
+[mypy-pl_bolts.models.detection.*]
+ignore_errors = True
+
+[mypy-pl_bolts.models.gans.*]
+ignore_errors = True
+
+[mypy-pl_bolts.models.regression.*]
+ignore_errors = True
+
+[mypy-pl_bolts.models.rl.*]
+ignore_errors = True
+
+[mypy-pl_bolts.models.self_supervised.*]
+ignore_errors = True
+
+[mypy-pl_bolts.models.vision.*]
+ignore_errors = True
+
+[mypy-pl_bolts.optimizers.*]
+ignore_errors = True
+
+[mypy-pl_bolts.transforms.*]
+ignore_errors = True
+
+[mypy-pl_bolts.utils.*]
+ignore_errors = True
+
+[mypy-tests.*]
+ignore_errors = True