[RFC] python: remove the Instance collector node

changelog/9277.breaking.rst

@@ -0,0 +1,3 @@
+The ``pytest.Instance`` collector type has been removed.
+Importing ``pytest.Instance`` or ``_pytest.python.Instance`` returns a dummy type and emits a deprecation warning.
+See :ref:`instance-collector-deprecation` for details.

doc/en/deprecations.rst

@@ -18,6 +18,25 @@ Deprecated Features
 Below is a complete list of all pytest features which are considered deprecated. Using those features will issue
 :class:`PytestWarning` or subclasses, which can be filtered using :ref:`standard warning filters <warnings>`.
 
+.. _instance-collector-deprecation:
+
+The ``pytest.Instance`` collector
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. versionremoved:: 7.0
+
+The ``pytest.Instance`` collector type has been removed.
+
+Previously, Python test methods were collected as :class:`~pytest.Class` -> ``Instance`` -> :class:`~pytest.Function`.
+Now :class:`~pytest.Class` collects the test methods directly.
+
+Most plugins which reference ``Instance`` do so in order to ignore or skip it,
+using a check such as ``if isinstance(node, Instance): return``.
+Such plugins should simply remove consideration of ``Instance`` on pytest>=7.
+However, to keep such uses working, a dummy type has been instanted in ``pytest.Instance`` and ``_pytest.python.Instance``,
+and importing it emits a deprecation warning. This will be removed in pytest 8.
+
+
 .. _node-ctor-fspath-deprecation:
 
 ``fspath`` argument for Node constructors replaced with ``pathlib.Path``

src/_pytest/deprecated.py

@@ -119,6 +119,11 @@
     "pytest.{func}(msg=...) is now deprecated, use pytest.{func}(reason=...) instead",
 )
 
+INSTANCE_COLLECTOR = PytestDeprecationWarning(
+    "The pytest.Instance collector type is deprecated and is no longer used. "
+    "See https://docs.pytest.org/en/latest/deprecations.html#the-pytest-instance-collector",
+)
+
 # You want to make some `__init__` or function "private".
 #
 #   def my_private_function(some, args):

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 @@ def collect(self) -> Iterator[Union[nodes.Item, nodes.Collector]]:
                                     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 @@ def from_item(cls, item: "Item") -> "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 @@ def __init__(
         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

@@ -58,6 +58,7 @@
 from _pytest.config.argparsing import Parser
 from _pytest.deprecated import check_ispytest
 from _pytest.deprecated import FSCOLLECTOR_GETHOOKPROXY_ISINITPATH
+from _pytest.deprecated import INSTANCE_COLLECTOR
 from _pytest.fixtures import FuncFixtureInfo
 from _pytest.main import Session
 from _pytest.mark import MARK_GEN
@@ -272,20 +273,14 @@ def cls(self):
         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."""
         obj = getattr(self, "_obj", None)
         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 +302,6 @@ def getmodpath(self, stopatmodule: bool = True, includemodule: bool = False) ->
         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 +400,9 @@ def collect(self) -> Iterable[Union[nodes.Item, 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 +482,6 @@ def _genfunctions(self, name: str, funcobj) -> Iterator["Function"]:
                     self,
                     name=subname,
                     callspec=callspec,
-                    callobj=funcobj,
                     fixtureinfo=fixtureinfo,
                     keywords={callspec.id: True},
                     originalname=name,
@@ -773,6 +766,9 @@ def from_parent(cls, parent, *, name, obj=None, **kw):
         """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 +796,9 @@ def collect(self) -> Iterable[Union[nodes.Item, nodes.Collector]]:
         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 +869,22 @@ def xunit_setup_method_fixture(self, request) -> Generator[None, None, None]:
         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.
+class InstanceDummy:
+    """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 will be removed
+    in pytest 8."""
 
-    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()
+    pass
 
-    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
+# Note: module __getattr__ only works on Python>=3.7. Unfortunately
+# we can't provide this deprecation warning on Python 3.6.
+def __getattr__(name: str) -> object:
+    if name == "Instance":
+        warnings.warn(INSTANCE_COLLECTOR, 2)
+        return InstanceDummy
+    raise AttributeError(f"module {__name__} has no attribute {name}")
 
 
 def hasinit(obj: object) -> bool:
@@ -1674,9 +1669,23 @@ def function(self):
         """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 +1697,6 @@ def runtest(self) -> None:
         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 @@ def pytest_collection_finish(self, session: "Session") -> None:
                     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 @@ def _printcollecteditems(self, items: Sequence[Item]) -> None:
                 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/__init__.py

@@ -48,7 +48,6 @@
 from _pytest.pytester import RunResult
 from _pytest.python import Class
 from _pytest.python import Function
-from _pytest.python import Instance
 from _pytest.python import Metafunc
 from _pytest.python import Module
 from _pytest.python import Package
@@ -77,6 +76,7 @@
 
 set_trace = __pytestPDB.set_trace
 
+
 __all__ = [
     "__version__",
     "_fillfuncargs",
@@ -106,7 +106,6 @@
     "HookRecorder",
     "hookspec",
     "importorskip",
-    "Instance",
     "Item",
     "LineMatcher",
     "LogCaptureFixture",
@@ -153,3 +152,12 @@
     "xfail",
     "yield_fixture",
 ]
+
+
+def __getattr__(name: str) -> object:
+    if name == "Instance":
+        # The import emits a deprecation warning.
+        from _pytest.python import Instance
+
+        return Instance
+    raise AttributeError(f"module {__name__} has no attribute {name}")

src/pytest/collect.py

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

testing/deprecated_test.py

@@ -286,3 +286,21 @@ def test_node_ctor_fspath_argument_is_deprecated(pytester: Pytester) -> None:
             parent=mod.parent,
             fspath=legacy_path("bla"),
         )
+
+
+@pytest.mark.skipif(
+    sys.version_info < (3, 7),
+    reason="This deprecation can only be emitted on python>=3.7",
+)
+def test_importing_instance_is_deprecated(pytester: Pytester) -> None:
+    with pytest.warns(
+        pytest.PytestDeprecationWarning,
+        match=re.escape("The pytest.Instance collector type is deprecated"),
+    ):
+        pytest.Instance
+
+    with pytest.warns(
+        pytest.PytestDeprecationWarning,
+        match=re.escape("The pytest.Instance collector type is deprecated"),
+    ):
+        from _pytest.python import Instance  # noqa: F401

testing/python/collect.py

@@ -12,7 +12,7 @@
 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 @@ def test2(self, x, y):
                     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 @@ def test_reportinfo_with_nasty_getattr(self, pytester: Pytester) -> None:
         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: