experiment with node metaclass for ctor warning

src/_pytest/main.py

@@ -384,10 +384,9 @@ def __init__(self, config):
 
         self.config.pluginmanager.register(self, name="session")
 
-    @nodes.Node.constructor
     @classmethod
     def from_config(cls, config):
-        return cls(config)
+        return cls._create(config)
 
     def __repr__(self):
         return "<%s %s exitstatus=%r testsfailed=%d testscollected=%d>" % (

src/_pytest/nodes.py

@@ -67,12 +67,32 @@ def ischildnode(baseid, nodeid):
     return node_parts[: len(base_parts)] == base_parts
 
 
-class Node:
+class NodeMeta(type):
+    __in_named_ctor = False
+
+    def __call__(self, *k, **kw):
+        if not self.__in_named_ctor:
+            warnings.warn(
+                NODE_USE_FROM_PARENT.format(name=self.__name__),
+                stacklevel=3,
+            )
+        return self._create(*k, **kw)
+
+    @contextmanager
+    def __ctor_entered(self):
+        self.__in_named_ctor = True
+        yield
+        self.__in_named_ctor = False
+
+    def _create(self, *k, **kw):
+        with self.__ctor_entered():
+            return super().__call__(*k, **kw)
+
+
+class Node(metaclass=NodeMeta):
     """ base class for Collector and Item the test collection tree.
     Collector subclasses have children, Items are terminal nodes."""
 
-    __in_named_ctor = False
-
     def __init__(
         self, name, parent=None, config=None, session=None, fspath=None, nodeid=None
     ):
@@ -111,33 +131,9 @@ def __init__(
             if self.name != "()":
                 self._nodeid += "::" + self.name
 
-        if not type(self).__in_named_ctor:
-            warnings.warn(
-                NODE_USE_FROM_PARENT.format(name=type(self).__name__),
-                stacklevel=3,
-            )
-
-    @classmethod
-    @contextmanager
-    def __ctor_entered(cls):
-        cls.__in_named_ctor = True
-        yield
-        cls.__in_named_ctor = False
-
-    @staticmethod
-    def constructor(ctor):
-        @classmethod
-        @wraps(ctor)
-        def wrapped(cls, *k, **kw):
-            with cls.__ctor_entered():
-                return ctor.__get__(None, cls)(*k, **kw)
-
-        return wrapped
-
     @classmethod
     def from_parent(cls, parent, **kw):
-        with cls.__ctor_entered():
-            return cls(**kw, parent=parent)
+        return cls._create(**kw, parent=parent)
 
     @property
     def ihook(self):

src/_pytest/python.py

@@ -429,11 +429,6 @@ def _genfunctions(self, name, funcobj):
 class Module(nodes.File, PyCollector):
     """ Collector for test classes and functions. """
 
-    @nodes.Node.constructor
-    @classmethod
-    def from_parent(cls, parent, **kw):
-        return cls(parent=parent, **kw)
-
     def _getobj(self):
         return self._importtestmodule()
 
@@ -689,10 +684,9 @@ def _get_first_non_fixture_func(obj, names):
 class Class(PyCollector):
     """ Collector for test methods. """
 
-    @nodes.Node.constructor
     @classmethod
     def from_parent(cls, parent, *, name, obj=None):
-        return cls(name=name, parent=parent)
+        return cls._create(name=name, parent=parent)
 
     def collect(self):
         if not safe_getattr(self.obj, "__test__", True):
@@ -1407,11 +1401,6 @@ def __init__(
         #: .. versionadded:: 3.0
         self.originalname = originalname
 
-    @nodes.Node.constructor
-    @classmethod
-    def from_parent(cls, parent, **kw):
-        return cls(parent=parent, **kw)
-
     def _initrequest(self):
         self.funcargs = {}
         self._request = fixtures.FixtureRequest(self)