nodes: deprecate fspath arguments to node constructors

This is unfortunately a dependency on `py.path` which cannot be moved to
an external plugins or eased in any way, so has to be deprecated in
order for pytest to be able to eventually remove the dependency on `py`.

src/_pytest/nodes.py

@@ -28,6 +28,7 @@ from _pytest.compat import legacy_path
 from _pytest.config import Config
 from _pytest.config import ConftestImportFailure
 from _pytest.deprecated import FSCOLLECTOR_GETHOOKPROXY_ISINITPATH
+from _pytest.deprecated import NODE_CTOR_FSPATH_ARG
 from _pytest.mark.structures import Mark
 from _pytest.mark.structures import MarkDecorator
 from _pytest.mark.structures import NodeKeywords
@@ -101,7 +102,18 @@ def _check_path(path: Path, fspath: LEGACY_PATH) -> None:
         )
 
 
-def _imply_path(path: Optional[Path], fspath: Optional[LEGACY_PATH]) -> Path:
+def _imply_path(
+    node_type: Type["Node"],
+    path: Optional[Path],
+    fspath: Optional[LEGACY_PATH],
+) -> Path:
+    if fspath is not None:
+        warnings.warn(
+            NODE_CTOR_FSPATH_ARG.format(
+                node_type_name=node_type.__name__,
+            ),
+            stacklevel=3,
+        )
     if path is not None:
         if fspath is not None:
             _check_path(path, fspath)
@@ -196,7 +208,7 @@ class Node(metaclass=NodeMeta):
         #: Filesystem path where this node was collected from (can be None).
         if path is None and fspath is None:
             path = getattr(parent, "path", None)
-        self.path = _imply_path(path, fspath=fspath)
+        self.path = _imply_path(type(self), path, fspath=fspath)
 
         # The explicit annotation is to avoid publicly exposing NodeKeywords.
         #: Keywords/markers collected from all scopes.
@@ -573,7 +585,7 @@ class FSCollector(Collector):
                 assert path is None
                 path = path_or_parent
 
-        path = _imply_path(path, fspath=fspath)
+        path = _imply_path(type(self), path, fspath=fspath)
         if name is None:
             name = path.name
             if parent is not None and parent.path != path: