More precisely type pipe methods

.github/workflows/ci.yaml

@@ -49,6 +49,7 @@ jobs:
         # Bookend python versions
         python-version: ["3.10", "3.13"]
         env: [""]
+        numprocesses: [4]
         include:
           # Minimum python version:
           - env: "bare-minimum"
@@ -67,6 +68,16 @@ jobs:
           - env: "flaky"
             python-version: "3.13"
             os: ubuntu-latest
+          # The mypy tests must be executed using only 1 process in order to guarantee
+          # predictable mypy output messages for comparison to expectations.
+          - env: "mypy"
+            python-version: "3.10"
+            numprocesses: 1
+            os: ubuntu-latest
+          - env: "mypy"
+            python-version: "3.13"
+            numprocesses: 1
+            os: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
         with:
@@ -88,6 +99,10 @@ jobs:
             then
               echo "CONDA_ENV_FILE=ci/requirements/environment.yml" >> $GITHUB_ENV
               echo "PYTEST_ADDOPTS=-m 'flaky or network' --run-flaky --run-network-tests -W default" >> $GITHUB_ENV
+            elif [[ "${{ matrix.env }}" == "mypy" ]] ;
+            then
+              echo "CONDA_ENV_FILE=ci/requirements/environment.yml" >> $GITHUB_ENV
+              echo "PYTEST_ADDOPTS=-n 1 -m 'mypy' --run-mypy -W default" >> $GITHUB_ENV
             else
               echo "CONDA_ENV_FILE=ci/requirements/${{ matrix.env }}.yml" >> $GITHUB_ENV
             fi
@@ -143,25 +158,12 @@ jobs:
           enableCrossOsArchive: true
           save-always: true
 
-      # Run all tests in *.py files, which excludes tests in *.yml files that test type
-      # annotations via the pytest-mypy-plugins plugin, because the type annotations
-      # tests fail when using multiple processes (the -n option to pytest).
       - name: Run tests
-        run: python -m pytest -n 4
+        run: python -m pytest -n ${{ matrix.numprocesses }}
           --timeout 180
           --cov=xarray
           --cov-report=xml
           --junitxml=pytest.xml
-          xarray/tests/test_*.py
-
-      # As noted in the comment on the previous step, we must run type annotation tests
-      # separately, and we will run them even if the preceding tests failed.  Further,
-      # we must restrict these tests to run only when matrix.env is empty, as this is
-      # the only case when all of the necessary dependencies are included such that
-      # spurious mypy errors due to missing packages are eliminated.
-      - name: Run mypy tests
-        if: ${{ always() && matrix.env == '' }}
-        run: python -m pytest xarray/tests/test_*.yml
 
       - name: Upload test results
         if: always()

.pre-commit-config.yaml

@@ -42,37 +42,23 @@ repos:
       - id: prettier
         args: [--cache-location=.prettier_cache/cache]
   - repo: https://github.com/pre-commit/mirrors-mypy
-    rev: v1.15.0
+    rev: v1.14.1
     hooks:
       - id: mypy
-        files: "^xarray"
-        exclude: "^xarray/util/generate_.*\\.py$"
+        # Copied from setup.cfg
+        exclude: "properties|asv_bench"
         # This is slow and so we take it out of the fast-path; requires passing
         # `--hook-stage manual` to pre-commit
         stages: [manual]
-        additional_dependencies:
-          # Type stubs plus additional dependencies from ci/requirements/environment.yml
-          # required in order to satisfy most (ideally all) type checks.  This is rather
-          # brittle, so it is difficult (if not impossible) to get mypy to succeed in
-          # this context, even when it succeeds in CI.
-          - dask
-          - distributed
-          - hypothesis
-          - matplotlib
-          - numpy==2.1.3
-          - pandas-stubs
-          - pytest
-          - types-colorama
-          - types-defusedxml
-          - types-docutils
-          - types-pexpect
-          - types-psutil
-          - types-Pygments
-          - types-python-dateutil
-          - types-pytz
-          - types-PyYAML
-          - types-setuptools
-          - typing-extensions>=4.1.0
+        additional_dependencies: [
+            # Type stubs
+            types-python-dateutil,
+            types-setuptools,
+            types-PyYAML,
+            types-pytz,
+            typing-extensions>=4.1.0,
+            numpy,
+          ]
   - repo: https://github.com/citation-file-format/cff-converter-python
     rev: ebf0b5e44d67f8beaa1cd13a0d0393ea04c6058d
     hooks:

conftest.py

@@ -3,14 +3,15 @@
 import pytest
 
 
-def pytest_addoption(parser):
+def pytest_addoption(parser: pytest.Parser):
     """Add command-line flags for pytest."""
     parser.addoption("--run-flaky", action="store_true", help="runs flaky tests")
     parser.addoption(
         "--run-network-tests",
         action="store_true",
         help="runs tests requiring a network connection",
     )
+    parser.addoption("--run-mypy", action="store_true", help="runs mypy tests")
 
 
 def pytest_runtest_setup(item):
@@ -21,6 +22,21 @@ def pytest_runtest_setup(item):
         pytest.skip(
             "set --run-network-tests to run test requiring an internet connection"
         )
+    if "mypy" in item.keywords and not item.config.getoption("--run-mypy"):
+        pytest.skip("set --run-mypy option to run mypy tests")
+
+
+# See https://docs.pytest.org/en/stable/example/markers.html#automatically-adding-markers-based-on-test-names
+def pytest_collection_modifyitems(items):
+    for item in items:
+        if "mypy" in item.nodeid:
+            # IMPORTANT: mypy type annotation tests leverage the pytest-mypy-plugins
+            # plugin, and are thus written in test_*.yml files.  As such, there are
+            # no explicit test functions on which we can apply a pytest.mark.mypy
+            # decorator.  Therefore, we mark them via this name-based, automatic
+            # marking approach, meaning that each test case must contain "mypy" in the
+            # name.
+            item.add_marker(pytest.mark.mypy)
 
 
 @pytest.fixture(autouse=True)

pyproject.toml

@@ -367,6 +367,7 @@ filterwarnings = [
 log_cli_level = "INFO"
 markers = [
   "flaky: flaky tests",
+  "mypy: type annotation tests",
   "network: tests requiring a network connection",
   "slow: slow tests",
   "slow_hypothesis: slow hypothesis tests",

xarray/tests/test_dataarray_typing.yml

@@ -1,28 +1,28 @@
-- case: test_pipe_lambda_noarg_return_type
+- case: test_mypy_pipe_lambda_noarg_return_type
   main: |
     from xarray import DataArray
 
     da = DataArray().pipe(lambda data: data)
 
     reveal_type(da)  # N: Revealed type is "xarray.core.dataarray.DataArray"
 
-- case: test_pipe_lambda_posarg_return_type
+- case: test_mypy_pipe_lambda_posarg_return_type
   main: |
     from xarray import DataArray
 
     da = DataArray().pipe(lambda data, arg: arg, "foo")
 
     reveal_type(da)  # N: Revealed type is "builtins.str"
 
-- case: test_pipe_lambda_chaining_return_type
+- case: test_mypy_pipe_lambda_chaining_return_type
   main: |
     from xarray import DataArray
 
     answer = DataArray().pipe(lambda data, arg: arg, "foo").count("o")
 
     reveal_type(answer)  # N: Revealed type is "builtins.int"
 
-- case: test_pipe_lambda_missing_arg
+- case: test_mypy_pipe_lambda_missing_arg
   main: |
     from xarray import DataArray
 
@@ -34,7 +34,7 @@
     main:4: note:     def [P`2, T] pipe(self, func: Callable[[DataArray, **P], T], *args: P.args, **kwargs: P.kwargs) -> T
     main:4: note:     def [T] pipe(self, func: tuple[Callable[..., T], str], *args: Any, **kwargs: Any) -> T
 
-- case: test_pipe_lambda_extra_arg
+- case: test_mypy_pipe_lambda_extra_arg
   main: |
     from xarray import DataArray
 
@@ -46,7 +46,7 @@
     main:4: note:     def [P`2, T] pipe(self, func: Callable[[DataArray, **P], T], *args: P.args, **kwargs: P.kwargs) -> T
     main:4: note:     def [T] pipe(self, func: tuple[Callable[..., T], str], *args: Any, **kwargs: Any) -> T
 
-- case: test_pipe_function_missing_posarg
+- case: test_mypy_pipe_function_missing_posarg
   main: |
     from xarray import DataArray
 
@@ -61,7 +61,7 @@
     main:7: note:     def [P`2, T] pipe(self, func: Callable[[DataArray, **P], T], *args: P.args, **kwargs: P.kwargs) -> T
     main:7: note:     def [T] pipe(self, func: tuple[Callable[..., T], str], *args: Any, **kwargs: Any) -> T
 
-- case: test_pipe_function_extra_posarg
+- case: test_mypy_pipe_function_extra_posarg
   main: |
     from xarray import DataArray
 
@@ -76,7 +76,7 @@
     main:7: note:     def [P`2, T] pipe(self, func: Callable[[DataArray, **P], T], *args: P.args, **kwargs: P.kwargs) -> T
     main:7: note:     def [T] pipe(self, func: tuple[Callable[..., T], str], *args: Any, **kwargs: Any) -> T
 
-- case: test_pipe_function_missing_kwarg
+- case: test_mypy_pipe_function_missing_kwarg
   main: |
     from xarray import DataArray
 
@@ -91,7 +91,7 @@
     main:7: note:     def [P`2, T] pipe(self, func: Callable[[DataArray, **P], T], *args: P.args, **kwargs: P.kwargs) -> T
     main:7: note:     def [T] pipe(self, func: tuple[Callable[..., T], str], *args: Any, **kwargs: Any) -> T
 
-- case: test_pipe_function_missing_keyword
+- case: test_mypy_pipe_function_missing_keyword
   main: |
     from xarray import DataArray
 
@@ -106,7 +106,7 @@
     main:7: note:     def [P`2, T] pipe(self, func: Callable[[DataArray, **P], T], *args: P.args, **kwargs: P.kwargs) -> T
     main:7: note:     def [T] pipe(self, func: tuple[Callable[..., T], str], *args: Any, **kwargs: Any) -> T
 
-- case: test_pipe_function_unexpected_keyword
+- case: test_mypy_pipe_function_unexpected_keyword
   main: |
     from xarray import DataArray
 
@@ -118,7 +118,7 @@
   out: |
     main:7: error: Unexpected keyword argument "kw" for "pipe" of "DataWithCoords"  [call-arg]
 
-- case: test_pipe_tuple_return_type_dataarray
+- case: test_mypy_pipe_tuple_return_type_dataarray
   main: |
     from xarray import DataArray
 
@@ -128,7 +128,7 @@
     da = DataArray().pipe((f, "da"), 42)
     reveal_type(da)  # N: Revealed type is "xarray.core.dataarray.DataArray"
 
-- case: test_pipe_tuple_return_type_other
+- case: test_mypy_pipe_tuple_return_type_other
   main: |
     from xarray import DataArray
 
@@ -139,7 +139,7 @@
 
     reveal_type(answer)  # N: Revealed type is "builtins.int"
 
-- case: test_pipe_tuple_missing_arg
+- case: test_mypy_pipe_tuple_missing_arg
   main: |
     from xarray import DataArray
 
@@ -164,7 +164,7 @@
     main:17: note:     def [P`9, T] pipe(self, func: Callable[[DataArray, **P], T], *args: P.args, **kwargs: P.kwargs) -> T
     main:17: note:     def [T] pipe(self, func: tuple[Callable[..., T], str], *args: Any, **kwargs: Any) -> T
 
-- case: test_pipe_tuple_extra_arg
+- case: test_mypy_pipe_tuple_extra_arg
   main: |
     from xarray import DataArray