Replace deprecated load_module with exec_module (#498)

* Replace to be deprecated load_module

* Satisfy mypy (sort of)

* Add tests to cover new statements

* Factor out the loader function and test seperately

nox/tasks.py

@@ -13,10 +13,11 @@
 # limitations under the License.
 
 import ast
-import importlib.machinery
+import importlib.util
 import io
 import json
 import os
+import sys
 import types
 from argparse import Namespace
 from typing import List, Union
@@ -31,6 +32,42 @@
 from nox.sessions import Result
 
 
+def _load_and_exec_nox_module(global_config: Namespace) -> types.ModuleType:
+    """
+    Loads, executes, then returns the global_config nox module.
+
+    Args:
+        global_config (Namespace): The global config.
+
+    Raises:
+        IOError: If the nox module cannot be loaded. This
+            exception is chosen such that it will be caught
+            by load_nox_module and logged appropriately.
+
+    Returns:
+        types.ModuleType: The initialised nox module.
+    """
+    spec = importlib.util.spec_from_file_location(
+        "user_nox_module", global_config.noxfile
+    )
+    if not spec:
+        raise IOError(f"Could not get module spec from {global_config.noxfile}")
+
+    module = importlib.util.module_from_spec(spec)
+    if not module:
+        raise IOError(f"Noxfile {global_config.noxfile} is not a valid python module.")
+
+    sys.modules["user_nox_module"] = module
+
+    loader = spec.loader
+    if not loader:  # pragma: no cover
+        raise IOError(f"Could not get module loader for {global_config.noxfile}")
+    # See https://docs.python.org/3/library/importlib.html#importing-a-source-file-directly
+    # unsure why mypy doesn't like this
+    loader.exec_module(module)  # type: ignore
+    return module
+
+
 def load_nox_module(global_config: Namespace) -> Union[types.ModuleType, int]:
     """Load the user's noxfile and return the module object for it.
 
@@ -64,9 +101,8 @@ def load_nox_module(global_config: Namespace) -> Union[types.ModuleType, int]:
         # guess. The original working directory (the directory that Nox was
         # invoked from) gets stored by the .invoke_from "option" in _options.
         os.chdir(noxfile_parent_dir)
-        return importlib.machinery.SourceFileLoader(
-            "user_nox_module", global_config.noxfile
-        ).load_module()
+
+        return _load_and_exec_nox_module(global_config)
 
     except (VersionCheckFailed, InvalidVersionSpecifier) as error:
         logger.error(str(error))

tests/test_tasks.py

@@ -95,9 +95,7 @@ def test_load_nox_module_IOError(caplog):
     our_noxfile = Path(__file__).parent.parent.joinpath("noxfile.py")
     config = _options.options.namespace(noxfile=str(our_noxfile))
 
-    with mock.patch(
-        "nox.tasks.importlib.machinery.SourceFileLoader.load_module"
-    ) as mock_load:
+    with mock.patch("nox.tasks.importlib.util.module_from_spec") as mock_load:
         mock_load.side_effect = IOError
 
         assert tasks.load_nox_module(config) == 2
@@ -112,15 +110,35 @@ def test_load_nox_module_OSError(caplog):
     our_noxfile = Path(__file__).parent.parent.joinpath("noxfile.py")
     config = _options.options.namespace(noxfile=str(our_noxfile))
 
-    with mock.patch(
-        "nox.tasks.importlib.machinery.SourceFileLoader.load_module"
-    ) as mock_load:
+    with mock.patch("nox.tasks.importlib.util.module_from_spec") as mock_load:
         mock_load.side_effect = OSError
 
         assert tasks.load_nox_module(config) == 2
         assert "Failed to load Noxfile" in caplog.text
 
 
+def test_load_nox_module_invalid_spec():
+    our_noxfile = Path(__file__).parent.parent.joinpath("noxfile.py")
+    config = _options.options.namespace(noxfile=str(our_noxfile))
+
+    with mock.patch("nox.tasks.importlib.util.spec_from_file_location") as mock_spec:
+        mock_spec.return_value = None
+
+        with pytest.raises(IOError):
+            tasks._load_and_exec_nox_module(config)
+
+
+def test_load_nox_module_invalid_module():
+    our_noxfile = Path(__file__).parent.parent.joinpath("noxfile.py")
+    config = _options.options.namespace(noxfile=str(our_noxfile))
+
+    with mock.patch("nox.tasks.importlib.util.module_from_spec") as mock_spec:
+        mock_spec.return_value = None
+
+        with pytest.raises(IOError):
+            tasks._load_and_exec_nox_module(config)
+
+
 @pytest.fixture
 def reset_needs_version():
     """Do not leak ``nox.needs_version`` between tests."""