[RFC] python: remove the Instance collector node

src/_pytest/junitxml.py

@@ -450,10 +450,6 @@ def pytest_unconfigure(config: Config) -> None:
 def mangle_test_address(address: str) -> List[str]:
     path, possible_open_bracket, params = address.partition("[")
     names = path.split("::")
-    try:
-        names.remove("()")
-    except ValueError:
-        pass
     # Convert file path to dotted path.
     names[0] = names[0].replace(nodes.SEP, ".")
     names[0] = re.sub(r"\.py$", "", names[0])

src/_pytest/main.py

@@ -781,9 +781,6 @@ class Session(nodes.FSCollector):
                                     submatchnodes.append(r)
                             if submatchnodes:
                                 work.append((submatchnodes, matchnames[1:]))
-                            # XXX Accept IDs that don't have "()" for class instances.
-                            elif len(rep.result) == 1 and rep.result[0].name == "()":
-                                work.append((rep.result, matchnames))
                         else:
                             # Report collection failures here to avoid failing to run some test
                             # specified in the command line because the module could not be

src/_pytest/mark/__init__.py

@@ -158,7 +158,7 @@ class KeywordMatcher:
         import pytest
 
         for node in item.listchain():
-            if not isinstance(node, (pytest.Instance, pytest.Session)):
+            if not isinstance(node, pytest.Session):
                 mapped_names.add(node.name)
 
         # Add the names added as extra keywords to current or parent items.

src/_pytest/nodes.py

@@ -225,9 +225,7 @@ class Node(metaclass=NodeMeta):
         else:
             if not self.parent:
                 raise TypeError("nodeid or parent must be provided")
-            self._nodeid = self.parent.nodeid
-            if self.name != "()":
-                self._nodeid += "::" + self.name
+            self._nodeid = self.parent.nodeid + "::" + self.name
 
         #: A place where plugins can store information on the node for their
         #: own use.

src/_pytest/python.py

@@ -272,12 +272,6 @@ class PyobjMixin(nodes.Node):
         node = self.getparent(Class)
         return node.obj if node is not None else None
 
-    @property
-    def instance(self):
-        """Python instance object this node was collected from (can be None)."""
-        node = self.getparent(Instance)
-        return node.obj if node is not None else None
-
     @property
     def obj(self):
         """Underlying Python object."""
@@ -285,7 +279,7 @@ class PyobjMixin(nodes.Node):
         if obj is None:
             self._obj = obj = self._getobj()
             # XXX evil hack
-            # used to avoid Instance collector marker duplication
+            # used to avoid Function marker duplication
             if self._ALLOW_MARKERS:
                 self.own_markers.extend(get_unpacked_marks(self.obj))
         return obj
@@ -307,8 +301,6 @@ class PyobjMixin(nodes.Node):
         chain.reverse()
         parts = []
         for node in chain:
-            if isinstance(node, Instance):
-                continue
             name = node.name
             if isinstance(node, Module):
                 name = os.path.splitext(name)[0]
@@ -407,8 +399,9 @@ class PyCollector(PyobjMixin, nodes.Collector):
 
         # Avoid random getattrs and peek in the __dict__ instead.
         dicts = [getattr(self.obj, "__dict__", {})]
-        for basecls in self.obj.__class__.__mro__:
-            dicts.append(basecls.__dict__)
+        if isinstance(self.obj, type):
+            for basecls in self.obj.__mro__:
+                dicts.append(basecls.__dict__)
 
         # In each class, nodes should be definition ordered. Since Python 3.6,
         # __dict__ is definition ordered.
@@ -488,7 +481,6 @@ class PyCollector(PyobjMixin, nodes.Collector):
                     self,
                     name=subname,
                     callspec=callspec,
-                    callobj=funcobj,
                     fixtureinfo=fixtureinfo,
                     keywords={callspec.id: True},
                     originalname=name,
@@ -773,6 +765,9 @@ class Class(PyCollector):
         """The public constructor."""
         return super().from_parent(name=name, parent=parent, **kw)
 
+    def newinstance(self):
+        return self.obj()
+
     def collect(self) -> Iterable[Union[nodes.Item, nodes.Collector]]:
         if not safe_getattr(self.obj, "__test__", True):
             return []
@@ -800,7 +795,9 @@ class Class(PyCollector):
         self._inject_setup_class_fixture()
         self._inject_setup_method_fixture()
 
-        return [Instance.from_parent(self, name="()")]
+        self.session._fixturemanager.parsefactories(self.newinstance(), self.nodeid)
+
+        return super().collect()
 
     def _inject_setup_class_fixture(self) -> None:
         """Inject a hidden autouse, class scoped fixture into the collected class object
@@ -871,25 +868,12 @@ class Class(PyCollector):
         self.obj.__pytest_setup_method = xunit_setup_method_fixture
 
 
-class Instance(PyCollector):
-    _ALLOW_MARKERS = False  # hack, destroy later
-    # Instances share the object with their parents in a way
-    # that duplicates markers instances if not taken out
-    # can be removed at node structure reorganization time.
-
-    def _getobj(self):
-        # TODO: Improve the type of `parent` such that assert/ignore aren't needed.
-        assert self.parent is not None
-        obj = self.parent.obj  # type: ignore[attr-defined]
-        return obj()
-
-    def collect(self) -> Iterable[Union[nodes.Item, nodes.Collector]]:
-        self.session._fixturemanager.parsefactories(self)
-        return super().collect()
-
-    def newinstance(self):
-        self.obj = self._getobj()
-        return self.obj
+# Instance used to be a node type between Class and Function.  It has been
+# removed in pytest 7.0. Some plugins exist which reference `pytest.Instance`
+# only to ignore it; this dummy class keeps them working. This could probably
+# be removed at some point.
+class Instance:
+    pass
 
 
 def hasinit(obj: object) -> bool:
@@ -1674,9 +1658,23 @@ class Function(PyobjMixin, nodes.Item):
         """Underlying python 'function' object."""
         return getimfunc(self.obj)
 
+    @property
+    def instance(self):
+        """Python instance object the function is bound to.
+
+        Returns None if not a test method, e.g. for a standalone test function
+        or a staticmethod.
+        """
+        return getattr(self.obj, "__self__", None)
+
     def _getobj(self):
         assert self.parent is not None
-        return getattr(self.parent.obj, self.originalname)  # type: ignore[attr-defined]
+        if isinstance(self.parent, Class):
+            # Each Function gets a fresh class instance.
+            parent_obj = self.parent.newinstance()
+        else:
+            parent_obj = self.parent.obj  # type: ignore[attr-defined]
+        return getattr(parent_obj, self.originalname)
 
     @property
     def _pyfuncitem(self):
@@ -1688,9 +1686,6 @@ class Function(PyobjMixin, nodes.Item):
         self.ihook.pytest_pyfunc_call(pyfuncitem=self)
 
     def setup(self) -> None:
-        if isinstance(self.parent, Instance):
-            self.parent.newinstance()
-            self.obj = self._getobj()
         self._request._fillfixtures()
 
     def _prunetraceback(self, excinfo: ExceptionInfo[BaseException]) -> None:

src/_pytest/terminal.py

@@ -756,9 +756,6 @@ class TerminalReporter:
                     rep.toterminal(self._tw)
 
     def _printcollecteditems(self, items: Sequence[Item]) -> None:
-        # To print out items and their parent collectors
-        # we take care to leave out Instances aka ()
-        # because later versions are going to get rid of them anyway.
         if self.config.option.verbose < 0:
             if self.config.option.verbose < -1:
                 counts = Counter(item.nodeid.split("::", 1)[0] for item in items)
@@ -778,8 +775,6 @@ class TerminalReporter:
                 stack.pop()
             for col in needed_collectors[len(stack) :]:
                 stack.append(col)
-                if col.name == "()":  # Skip Instances.
-                    continue
                 indent = (len(stack) - 1) * "  "
                 self._tw.line(f"{indent}{col}")
                 if self.config.option.verbose >= 1:

src/pytest/collect.py

@@ -11,7 +11,6 @@ COLLECT_FAKEMODULE_ATTRIBUTES = [
     "Collector",
     "Module",
     "Function",
-    "Instance",
     "Session",
     "Item",
     "Class",

testing/python/collect.py

@@ -12,7 +12,7 @@ from _pytest.monkeypatch import MonkeyPatch
 from _pytest.nodes import Collector
 from _pytest.pytester import Pytester
 from _pytest.python import Class
-from _pytest.python import Instance
+from _pytest.python import Function
 
 
 class TestModule:
@@ -585,7 +585,7 @@ class TestFunction:
                     pass
         """
         )
-        colitems = modcol.collect()[0].collect()[0].collect()
+        colitems = modcol.collect()[0].collect()
         assert colitems[0].name == "test1[a-c]"
         assert colitems[1].name == "test1[b-c]"
         assert colitems[2].name == "test2[a-c]"
@@ -1183,19 +1183,26 @@ class TestReportInfo:
         modcol = pytester.getmodulecol(
             """
             # lineno 0
-            class TestClass(object):
+            class TestClass:
                 def __getattr__(self, name):
                     return "this is not an int"
 
+                def __class_getattr__(cls, name):
+                    return "this is not an int"
+
                 def intest_foo(self):
                     pass
+
+                def test_bar(self):
+                    pass
         """
         )
         classcol = pytester.collect_by_name(modcol, "TestClass")
         assert isinstance(classcol, Class)
-        instance = list(classcol.collect())[0]
-        assert isinstance(instance, Instance)
-        path, lineno, msg = instance.reportinfo()
+        path, lineno, msg = classcol.reportinfo()
+        func = list(classcol.collect())[0]
+        assert isinstance(func, Function)
+        path, lineno, msg = func.reportinfo()
 
 
 def test_customized_python_discovery(pytester: Pytester) -> None:

testing/python/integration.py

@@ -5,6 +5,7 @@ from _pytest import runner
 from _pytest._code import getfslineno
 from _pytest.fixtures import getfixturemarker
 from _pytest.pytester import Pytester
+from _pytest.python import Function
 
 
 class TestOEJSKITSpecials:
@@ -475,3 +476,28 @@ class TestParameterize:
         )
         res = pytester.runpytest("--collect-only")
         res.stdout.fnmatch_lines(["*spam-2*", "*ham-2*"])
+
+
+def test_function_instance(pytester: Pytester) -> None:
+    items = pytester.getitems(
+        """
+        def test_func(): pass
+        class TestIt:
+            def test_method(self): pass
+            @classmethod
+            def test_class(cls): pass
+            @staticmethod
+            def test_static(): pass
+        """
+    )
+    assert len(items) == 3
+    assert isinstance(items[0], Function)
+    assert items[0].name == "test_func"
+    assert items[0].instance is None
+    assert isinstance(items[1], Function)
+    assert items[1].name == "test_method"
+    assert items[1].instance is not None
+    assert items[1].instance.__class__.__name__ == "TestIt"
+    assert isinstance(items[2], Function)
+    assert items[2].name == "test_static"
+    assert items[2].instance is None

testing/test_cacheprovider.py

@@ -979,7 +979,7 @@ class TestLastFailed:
                 "",
                 "<Module pkg1/test_1.py>",
                 "  <Class TestFoo>",
-                "      <Function test_fail>",
+                "    <Function test_fail>",
                 "  <Function test_other>",
                 "",
                 "*= 2/3 tests collected (1 deselected) in *",

testing/test_collection.py

@@ -74,9 +74,7 @@ class TestCollector:
         )
         cls = pytester.collect_by_name(modcol, "TestClass")
         assert isinstance(cls, pytest.Class)
-        instance = pytester.collect_by_name(cls, "()")
-        assert isinstance(instance, pytest.Instance)
-        fn = pytester.collect_by_name(instance, "test_foo")
+        fn = pytester.collect_by_name(cls, "test_foo")
         assert isinstance(fn, pytest.Function)
 
         module_parent = fn.getparent(pytest.Module)

testing/test_junitxml.py

@@ -936,7 +936,7 @@ class TestPython:
 def test_mangle_test_address() -> None:
     from _pytest.junitxml import mangle_test_address
 
-    address = "::".join(["a/my.py.thing.py", "Class", "()", "method", "[a-1-::]"])
+    address = "::".join(["a/my.py.thing.py", "Class", "method", "[a-1-::]"])
     newnames = mangle_test_address(address)
     assert newnames == ["a.my.py.thing", "Class", "method", "[a-1-::]"]
 

testing/test_nose.py

@@ -272,8 +272,10 @@ def test_nose_setup_ordering(pytester: Pytester) -> None:
         class TestClass(object):
             def setup(self):
                 assert visited
+                self.visited_cls = True
             def test_first(self):
-                pass
+                assert visited
+                assert self.visited_cls
         """
     )
     result = pytester.runpytest()

testing/test_session.py

@@ -227,7 +227,7 @@ class TestNewSession(SessionTests):
         started = reprec.getcalls("pytest_collectstart")
         finished = reprec.getreports("pytest_collectreport")
         assert len(started) == len(finished)
-        assert len(started) == 8
+        assert len(started) == 6
         colfail = [x for x in finished if x.failed]
         assert len(colfail) == 1