Allow function pointer extraction from overloaded functions (#2944)

* Add a failure test for overloaded functions

* Allow function pointer extraction from overloaded functions

Author: otamachan

include/pybind11/functional.h

@@ -46,11 +46,17 @@ struct type_caster<std::function<Return(Args...)>> {
             auto c = reinterpret_borrow<capsule>(PyCFunction_GET_SELF(cfunc.ptr()));
             auto rec = (function_record *) c;
 
-            if (rec && rec->is_stateless &&
-                    same_type(typeid(function_type), *reinterpret_cast<const std::type_info *>(rec->data[1]))) {
-                struct capture { function_type f; };
-                value = ((capture *) &rec->data)->f;
-                return true;
+            while (rec != nullptr) {
+                if (rec->is_stateless
+                    && same_type(typeid(function_type),
+                                 *reinterpret_cast<const std::type_info *>(rec->data[1]))) {
+                    struct capture {
+                        function_type f;
+                    };
+                    value = ((capture *) &rec->data)->f;
+                    return true;
+                }
+                rec = rec->next;
             }
         }
 

tests/test_callbacks.cpp

@@ -97,6 +97,8 @@ TEST_SUBMODULE(callbacks, m) {
     // test_cpp_function_roundtrip
     /* Test if passing a function pointer from C++ -> Python -> C++ yields the original pointer */
     m.def("dummy_function", &dummy_function);
+    m.def("dummy_function_overloaded", [](int i, int j) { return i + j; });
+    m.def("dummy_function_overloaded", &dummy_function);
     m.def("dummy_function2", [](int i, int j) { return i + j; });
     m.def("roundtrip", [](std::function<int(int)> f, bool expect_none = false) {
         if (expect_none && f)

tests/test_callbacks.py

@@ -93,6 +93,10 @@ def test_cpp_function_roundtrip():
         m.test_dummy_function(m.roundtrip(m.dummy_function))
         == "matches dummy_function: eval(1) = 2"
     )
+    assert (
+        m.test_dummy_function(m.dummy_function_overloaded)
+        == "matches dummy_function: eval(1) = 2"
+    )
     assert m.roundtrip(None, expect_none=True) is None
     assert (
         m.test_dummy_function(lambda x: x + 2)