Do not discover properties when iterating fixtures (#12781) (#12788)

Resolves #12446

(cherry picked from commit c6a5290)

Co-authored-by: Anthony Sottile <asottile@umich.edu>

changelog/12446.bugfix.rst

@@ -0,0 +1 @@
+Avoid calling ``@property`` (and other instance descriptors) during fixture discovery -- by :user:`asottile`

src/_pytest/fixtures.py

@@ -53,6 +53,7 @@
 from _pytest.compat import NOTSET
 from _pytest.compat import NotSetType
 from _pytest.compat import safe_getattr
+from _pytest.compat import safe_isclass
 from _pytest.config import _PluggyPlugin
 from _pytest.config import Config
 from _pytest.config import ExitCode
@@ -1724,17 +1725,26 @@ def parsefactories(
         if holderobj in self._holderobjseen:
             return
 
+        # Avoid accessing `@property` (and other descriptors) when iterating fixtures.
+        if not safe_isclass(holderobj) and not isinstance(holderobj, types.ModuleType):
+            holderobj_tp: object = type(holderobj)
+        else:
+            holderobj_tp = holderobj
+
         self._holderobjseen.add(holderobj)
         for name in dir(holderobj):
             # The attribute can be an arbitrary descriptor, so the attribute
-            # access below can raise. safe_getatt() ignores such exceptions.
-            obj = safe_getattr(holderobj, name, None)
-            marker = getfixturemarker(obj)
+            # access below can raise. safe_getattr() ignores such exceptions.
+            obj_ub = safe_getattr(holderobj_tp, name, None)
+            marker = getfixturemarker(obj_ub)
             if not isinstance(marker, FixtureFunctionMarker):
                 # Magic globals  with __getattr__ might have got us a wrong
                 # fixture attribute.
                 continue
 
+            # OK we know it is a fixture -- now safe to look up on the _instance_.
+            obj = getattr(holderobj, name)
+
             if marker.name:
                 name = marker.name
 

testing/python/collect.py

@@ -263,6 +263,43 @@ def prop(self):
         result = pytester.runpytest()
         assert result.ret == ExitCode.NO_TESTS_COLLECTED
 
+    def test_does_not_discover_properties(self, pytester: Pytester) -> None:
+        """Regression test for #12446."""
+        pytester.makepyfile(
+            """\
+            class TestCase:
+                @property
+                def oops(self):
+                    raise SystemExit('do not call me!')
+            """
+        )
+        result = pytester.runpytest()
+        assert result.ret == ExitCode.NO_TESTS_COLLECTED
+
+    def test_does_not_discover_instance_descriptors(self, pytester: Pytester) -> None:
+        """Regression test for #12446."""
+        pytester.makepyfile(
+            """\
+            # not `@property`, but it acts like one
+            # this should cover the case of things like `@cached_property` / etc.
+            class MyProperty:
+                def __init__(self, func):
+                    self._func = func
+                def __get__(self, inst, owner):
+                    if inst is None:
+                        return self
+                    else:
+                        return self._func.__get__(inst, owner)()
+
+            class TestCase:
+                @MyProperty
+                def oops(self):
+                    raise SystemExit('do not call me!')
+            """
+        )
+        result = pytester.runpytest()
+        assert result.ret == ExitCode.NO_TESTS_COLLECTED
+
     def test_abstract_class_is_not_collected(self, pytester: Pytester) -> None:
         """Regression test for #12275 (non-unittest version)."""
         pytester.makepyfile(