WIP Add type checking with mypy

.github/workflows/core.yml

@@ -64,6 +64,8 @@ concurrency:
 
 jobs:
   test_linux:
+    # UNDO ME, don't need this for this PR
+    if: false
     name: Build and test Firedrake (Linux)
     strategy:
       # We want to know all of the tests which fail, so don't kill real if
@@ -481,11 +483,15 @@ jobs:
       - name: Setup flake8 annotations
         uses: rbialon/flake8-annotations@v1
       - name: Install linting packages
-        run: pip install flake8 pylint
+        run: pip install flake8 mypy pylint
       - name: Lint codebase
         run: make lint GITHUB_ACTIONS_FORMATTING=1
+      - name: Run type checks
+        run: mypy -p firedrake -p pyop2 -p tsfc
 
   build_docs:
+    # UNDO ME
+    if: false
     name: Build documentation
     runs-on: [self-hosted, Linux]
     container:

firedrake/external_operators/abstract_external_operators.py

@@ -91,6 +91,7 @@ def __init__(self, *operands, function_space, derivatives=None, argument_slots=(
     def function_space(self):
         return self._function_space
 
+    @staticmethod
     def assemble_method(derivs, args):
         """Decorator helper function to specify the type of external operator type associated with each assembly methods.
 

pyproject.toml

@@ -169,3 +169,24 @@ pyop2 = [
   "*.pyx",
   "codegen/c/*.c",
 ]
+
+[tool.mypy]
+# from https://quantlane.com/blog/type-checking-large-codebase/
+
+# TODO: enable at some point
+# disallow_untyped_calls = true
+# disallow_untyped_defs = true
+# disallow_incomplete_defs = true
+# disallow_untyped_decorators = true
+# check_untyped_defs = true
+
+# warn_redundant_casts = true
+# warn_unused_ignores = true
+# warn_unused_configs = true
+# show_error_codes = true
+
+ignore_missing_imports = true
+follow_imports = "silent"
+disable_error_code = ["attr-defined", "import-untyped"]
+
+exclude = ["firedrake/_check"]