Fix return type checkers calls on ellipses functions

ChangeLog

@@ -64,6 +64,10 @@ Release date: TBA
 
 * Improve node information for ``invalid-name`` on function argument.
 
+* Prevent return type checkers being called on functions with ellipses as body
+
+  Closes #4736
+
 
 What's New in Pylint 2.11.1?
 ============================

pylint/checkers/classes.py

@@ -68,6 +68,7 @@
     is_attr_protected,
     is_builtin_object,
     is_comprehension,
+    is_function_body_ellipsis,
     is_iterable,
     is_overload_stub,
     is_property_setter,
@@ -2168,7 +2169,11 @@ def visit_functiondef(self, node: nodes.FunctionDef) -> None:
 
         inferred = _safe_infer_call_result(node, node)
         # Only want to check types that we are able to infer
-        if inferred and node.name in self._protocol_map:
+        if (
+            inferred
+            and node.name in self._protocol_map
+            and not is_function_body_ellipsis(node)
+        ):
             self._protocol_map[node.name](node, inferred)
 
         if node.name in PYMETHODS:

pylint/checkers/utils.py

@@ -1566,3 +1566,13 @@ def is_reassigned_after_current(node: nodes.NodeNG, varname: str) -> bool:
         a.name == varname and a.lineno > node.lineno
         for a in node.scope().nodes_of_class((nodes.AssignName, nodes.FunctionDef))
     )
+
+
+def is_function_body_ellipsis(node: nodes.FunctionDef) -> bool:
+    """Checks whether a function body only consisst of a single Ellipsis"""
+    return (
+        len(node.body) == 1
+        and isinstance(node.body[0], nodes.Expr)
+        and isinstance(node.body[0].value, nodes.Const)
+        and node.body[0].value.value == Ellipsis
+    )

tests/functional/c/class_protocol_ellipsis.py

@@ -0,0 +1,44 @@
+""""Tests for return type checkers for protocol methods with ellipsis function body"""
+# pylint: disable=missing-class-docstring
+from typing import Any, Iterator
+
+
+class MyClass:
+    """The "invalid-*-returned" messages shouldn't be emitted for stub functions
+    Original issue: https://github.com/PyCQA/pylint/issues/4736"""
+
+    def __len__(self) -> int:
+        ...
+
+    def __hash__(self) -> int:
+        ...
+
+    def __index__(self) -> int:
+        ...
+
+    def __iter__(self) -> Iterator[Any]:
+        ...
+
+    def __bool__(self) -> bool:
+        ...
+
+    def __repr__(self) -> object:
+        ...
+
+    def __str__(self) -> str:
+        ...
+
+    def __bytes__(self) -> bytes:
+        ...
+
+    def __length_hint__(self) -> int:
+        ...
+
+    def __format__(self, format_spec: str) -> str:
+        ...
+
+    def __getnewargs__(self) -> tuple:
+        ...
+
+    def __getnewargs_ex__(self) -> tuple:
+        ...