Don't allow mixed static/non-static overloads

We currently fail at runtime when trying to call a method that is
overloaded with both static and non-static methods.  This is something
python won't allow: the object is either a function or an instance, and
can't be both.

include/pybind11/pybind11.h

@@ -318,6 +318,15 @@ protected:
             m_ptr = rec->sibling.ptr();
             inc_ref();
             chain_start = chain;
+            if (chain->is_method != rec->is_method)
+                pybind11_fail("overloading a method with both static and instance methods is not supported; "
+                    #if defined(NDEBUG)
+                        "compile in debug mode for more details"
+                    #else
+                        "error while attempting to bind " + std::string(rec->is_method ? "instance" : "static") + " method " +
+                        std::string(pybind11::str(rec->scope.attr("__name__"))) + "." + std::string(rec->name) + signature
+                    #endif
+                );
             while (chain->next)
                 chain = chain->next;
             chain->next = rec;

tests/test_methods_and_attributes.cpp

@@ -59,6 +59,8 @@ public:
     py::str overloaded(int, int)     const { return "(int, int) const"; }
     py::str overloaded(float, float) const { return "(float, float) const"; }
 
+    static py::str overloaded() { return "static"; }
+
     int value = 0;
 };
 
@@ -206,6 +208,17 @@ test_initializer methods_and_attributes([](py::module &m) {
         .def("overloaded_const", static_cast<py::str (ExampleMandA::*)(int,     int) const>(&ExampleMandA::overloaded))
         .def("overloaded_const", static_cast<py::str (ExampleMandA::*)(float, float) const>(&ExampleMandA::overloaded))
 #endif
+        // Raise error if trying to mix static/non-static overloads on the same name:
+        .def_static("add_mixed_overloads1", []() {
+            auto emna = py::reinterpret_borrow<py::class_<ExampleMandA>>(py::module::import("pybind11_tests").attr("ExampleMandA"));
+            emna.def       ("overload_mixed1", static_cast<py::str (ExampleMandA::*)(int, int)>(&ExampleMandA::overloaded))
+                .def_static("overload_mixed1", static_cast<py::str (              *)(        )>(&ExampleMandA::overloaded));
+        })
+        .def_static("add_mixed_overloads2", []() {
+            auto emna = py::reinterpret_borrow<py::class_<ExampleMandA>>(py::module::import("pybind11_tests").attr("ExampleMandA"));
+            emna.def_static("overload_mixed2", static_cast<py::str (              *)(        )>(&ExampleMandA::overloaded))
+                .def       ("overload_mixed2", static_cast<py::str (ExampleMandA::*)(int, int)>(&ExampleMandA::overloaded));
+        })
         .def("__str__", &ExampleMandA::toString)
         .def_readwrite("value", &ExampleMandA::value);
 

tests/test_methods_and_attributes.py

@@ -148,6 +148,28 @@ def test_metaclass_override():
     assert isinstance(MetaclassOverride.__dict__["readonly"], int)
 
 
+def test_no_mixed_overloads():
+    from pybind11_tests import debug_enabled
+
+    with pytest.raises(RuntimeError) as excinfo:
+        ExampleMandA.add_mixed_overloads1()
+    assert (str(excinfo.value) ==
+            "overloading a method with both static and instance methods is not supported; " +
+            ("compile in debug mode for more details" if not debug_enabled else
+             "error while attempting to bind static method ExampleMandA.overload_mixed1"
+             "() -> str")
+            )
+
+    with pytest.raises(RuntimeError) as excinfo:
+        ExampleMandA.add_mixed_overloads2()
+    assert (str(excinfo.value) ==
+            "overloading a method with both static and instance methods is not supported; " +
+            ("compile in debug mode for more details" if not debug_enabled else
+             "error while attempting to bind instance method ExampleMandA.overload_mixed2"
+             "(self: pybind11_tests.ExampleMandA, arg0: int, arg1: int) -> str")
+            )
+
+
 @pytest.mark.parametrize("access", ["ro", "rw", "static_ro", "static_rw"])
 def test_property_return_value_policies(access):
     from pybind11_tests import TestPropRVP