Report func-returns-value for decorated methods

mypy/checkexpr.py

@@ -731,6 +731,18 @@ def always_returns_none(self, node: Expression) -> bool:
 
     def defn_returns_none(self, defn: SymbolNode | None) -> bool:
         """Check if `defn` can _only_ return None."""
+        if isinstance(defn, Decorator):
+            # Decorated functions (e.g. @staticmethod, @classmethod) are wrapped
+            # in a Decorator node; the resulting callable type is stored on the
+            # synthetic Var. We use that callable's return type so that
+            # `func-returns-value` is reported for decorated methods the same
+            # way it is for plain functions
+            # (https://github.com/python/mypy/issues/14179). The Var is marked
+            # is_inferred=True so we cannot reuse the Var branch below.
+            typ = get_proper_type(defn.var.type)
+            return isinstance(typ, CallableType) and isinstance(
+                get_proper_type(typ.ret_type), NoneType
+            )
         if isinstance(defn, FuncDef):
             return isinstance(defn.type, CallableType) and isinstance(
                 get_proper_type(defn.type.ret_type), NoneType

test-data/unit/check-errorcodes.test

@@ -682,6 +682,31 @@ def main() -> None:
     y = A().g()  # E: "g" of "A" does not return a value (it only ever returns None)  [func-returns-value]
     z = c()  # E: Function does not return a value (it only ever returns None)  [func-returns-value]
 
+[case testErrorCodeFuncReturnsValueStaticAndClassMethod]
+# Regression test for https://github.com/python/mypy/issues/14179
+# Decorated methods (staticmethod, classmethod) should report
+# func-returns-value just like instance methods do.
+class Example:
+    def instance_op(self) -> None:
+        return None
+
+    @staticmethod
+    def static_op() -> None:
+        return None
+
+    @classmethod
+    def class_op(cls) -> None:
+        return None
+
+def main() -> None:
+    ex = Example()
+    a = ex.instance_op()  # E: "instance_op" of "Example" does not return a value (it only ever returns None)  [func-returns-value]
+    b = ex.static_op()    # E: "static_op" of "Example" does not return a value (it only ever returns None)  [func-returns-value]
+    c = ex.class_op()     # E: "class_op" of "Example" does not return a value (it only ever returns None)  [func-returns-value]
+    d = Example.static_op()  # E: "static_op" of "Example" does not return a value (it only ever returns None)  [func-returns-value]
+    e = Example.class_op()   # E: "class_op" of "Example" does not return a value (it only ever returns None)  [func-returns-value]
+[builtins fixtures/classmethod.pyi]
+
 [case testErrorCodeInstantiateAbstract]
 from abc import abstractmethod