Improve/revisit _setup_collect_fakemodule (#279)

Ref: pytest-dev#6803

Author: blueyed

src/_pytest/compat.py

@@ -34,6 +34,7 @@
 
 
 if TYPE_CHECKING:
+    from types import ModuleType  # noqa: F401 (used in type string)
     from typing import Type  # noqa: F401 (used in type string)
 
 
@@ -336,28 +337,28 @@ def safe_isclass(obj: object) -> bool:
         return False
 
 
-COLLECT_FAKEMODULE_ATTRIBUTES = (
-    "Collector",
-    "Module",
-    "Function",
-    "Instance",
-    "Session",
-    "Item",
-    "Class",
-    "File",
-    "_fillfuncargs",
-)
-
-
-def _setup_collect_fakemodule() -> None:
+def _setup_collect_fakemodule() -> "ModuleType":
+    """Setup pytest.collect fake module for backward compatibility."""
     from types import ModuleType
-    import pytest
+    import _pytest.nodes
+
+    collect_fakemodule_attributes = (
+        ("Collector", _pytest.nodes.Collector),
+        ("Module", _pytest.python.Module),
+        ("Function", _pytest.python.Function),
+        ("Instance", _pytest.python.Instance),
+        ("Session", _pytest.main.Session),
+        ("Item", _pytest.nodes.Item),
+        ("Class", _pytest.python.Class),
+        ("File", _pytest.nodes.File),
+        ("_fillfuncargs", _pytest.fixtures.fillfixtures),
+    )
 
-    # Types ignored because the module is created dynamically.
-    pytest.collect = ModuleType("pytest.collect")  # type: ignore
-    pytest.collect.__all__ = []  # type: ignore  # used for setns
-    for attr_name in COLLECT_FAKEMODULE_ATTRIBUTES:
-        setattr(pytest.collect, attr_name, getattr(pytest, attr_name))  # type: ignore
+    mod = ModuleType("pytest.collect")
+    mod.__all__ = []  # type: ignore  # used for setns (obsolete?)
+    for attr_name, value in collect_fakemodule_attributes:
+        setattr(mod, attr_name, value)
+    return mod
 
 
 class CaptureIO(io.TextIOWrapper):

src/pytest/__init__.py

@@ -1,9 +1,10 @@
 """
 pytest: unit and functional testing with Python.
 """
+import sys
+
 from _pytest import __version__
 from _pytest.assertion import register_assert_rewrite
-from _pytest.compat import _setup_collect_fakemodule
 from _pytest.config import cmdline
 from _pytest.config import ExitCode
 from _pytest.config import hookimpl
@@ -45,7 +46,6 @@
 from _pytest.warning_types import PytestUnknownMarkWarning
 from _pytest.warning_types import PytestWarning
 
-
 __all__ = [
     "__version__",
     "_fillfuncargs",
@@ -92,5 +92,18 @@
 ]
 
 
-_setup_collect_fakemodule()
-del _setup_collect_fakemodule
+if sys.version_info >= (3, 7):
+
+    def __getattr__(name):
+        if name == "collect":
+            from _pytest.compat import _setup_collect_fakemodule
+
+            return _setup_collect_fakemodule()
+        raise AttributeError(name)
+
+
+else:
+    from _pytest.compat import _setup_collect_fakemodule
+
+    collect = _setup_collect_fakemodule()
+    del _setup_collect_fakemodule

testing/conftest.py

@@ -165,6 +165,27 @@ def testdir(testdir: Testdir) -> Testdir:
     return testdir
 
 
+@pytest.fixture
+def symlink_or_skip():
+    """Return a function that creates a symlink or raises ``Skip``.
+
+    On Windows `os.symlink` is available, but normal users require special
+    admin privileges to create symlinks.
+    """
+
+    def wrap_os_symlink(src, dst, *args, **kwargs):
+        if os.path.islink(dst):
+            return
+
+        try:
+            os.symlink(src, dst, *args, **kwargs)
+        except OSError as e:
+            pytest.skip("os.symlink({!r}) failed: {!r}".format((src, dst), e))
+        assert os.path.islink(dst)
+
+    return wrap_os_symlink
+
+
 @pytest.fixture(scope="session")
 def color_mapping():
     """Returns a utility class which can replace keys in strings in the form "{NAME}"

testing/test_meta.py

@@ -10,6 +10,7 @@
 
 import _pytest
 import pytest
+from _pytest.pytester import Testdir
 
 pytestmark = [pytest.mark.integration, pytest.mark.slow]
 
@@ -34,3 +35,39 @@ def test_no_warnings(module):
         "-c", "import {}".format(module),
     ))
     # fmt: on
+
+
+def test_pytest_collect_attribute(_sys_snapshot):
+    from types import ModuleType
+
+    del sys.modules["pytest"]
+
+    import pytest
+
+    assert isinstance(pytest.collect, ModuleType)
+    assert pytest.collect.Item is pytest.Item
+
+    with pytest.raises(ImportError):
+        import pytest.collect
+
+    if sys.version_info >= (3, 7):
+        with pytest.raises(AttributeError, match=r"^doesnotexist$"):
+            pytest.doesnotexist
+    else:
+        with pytest.raises(AttributeError, match=r"doesnotexist"):
+            pytest.doesnotexist
+
+
+def test_pytest_circular_import(testdir: Testdir, symlink_or_skip) -> None:
+    """Importing pytest should not import pytest itself."""
+    import pytest
+    import os.path
+
+    symlink_or_skip(os.path.dirname(pytest.__file__), "another")
+
+    del sys.modules["pytest"]
+
+    testdir.syspathinsert()
+    import another  # noqa: F401
+
+    assert "pytest" not in sys.modules

testing/test_own_conftest.py

@@ -0,0 +1,22 @@
+import os
+
+import pytest
+
+
+def test_symlink_or_skip(monkeypatch, tmpdir, symlink_or_skip):
+    symlink_or_skip("src", "dst")
+    assert os.path.islink("dst")
+
+    def oserror(src, dst):
+        raise OSError("foo")
+
+    monkeypatch.setattr("os.symlink", oserror)
+
+    # Works with existing symlinks.
+    symlink_or_skip("src", "dst")
+
+    with pytest.raises(
+        pytest.skip.Exception,
+        match=r"os\.symlink\(\('src', 'dst2'\)\) failed: OSError\('foo',?\)",
+    ):
+        symlink_or_skip("src", "dst2")