Add mypy infrastructure for type annotation migration

This commit adds the tooling necessary to support gradual type
annotation of the codebase:
- Add mypy to test-requirements.txt
- Add mypy configuration to pyproject.toml with a list of
  type-checked modules (initially empty, to be populated as
  modules are migrated)
- Add tox mypy environment for running type checks
- Add mypy pre-commit hook

This follows the same pattern established in `ironic-prometheus-exporter`.

Change-Id: Ie9e4b5ebccff4ce29b4e014c62f09594d968d721
Signed-off-by: Karan Anand <anandkarancompsci@gmail.com>

.pre-commit-config.yaml

@@ -0,0 +1,6 @@
+repos:
+  - repo: https://github.com/pre-commit/mirrors-mypy
+    rev: v1.14.1
+    hooks:
+      - id: mypy
+        args: [--config-file=pyproject.toml]

pyproject.toml

@@ -1,3 +1,12 @@
 [build-system]
 requires = ["pbr>=6.0.0", "setuptools>=64.0.0"]
 build-backend = "pbr.build"
+
+[tool.mypy]
+python_version = "3.10"
+warn_return_any = true
+warn_unused_configs = true
+ignore_missing_imports = true
+# Modules that have been fully type-annotated. Add modules here as they are
+# migrated to enable strict type checking for them.
+files = []

test-requirements.txt

@@ -7,3 +7,6 @@ tempest>=17.1.0 # Apache-2.0
 stestr>=1.0.0 # Apache-2.0
 ddt>=1.0.1 # MIT
 python-openstackclient>=3.12.0 # Apache-2.0
+
+# Type checking
+mypy>=1.0.0 # MIT

tox.ini

@@ -91,4 +91,13 @@ deps = codespell
 # note(JayF): {posargs} lets us run `tox -ecodespell -- -w` to get codespell
 #             to correct spelling issues in our code it's aware of.
 commands =
-  codespell {posargs}
+  codespell {posargs}
+
+[testenv:mypy]
+description =
+  Run type checks using mypy
+deps =
+  -c{env:TOX_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
+  -r{toxinidir}/requirements.txt
+  -r{toxinidir}/test-requirements.txt
+commands = mypy {posargs}