[cppyy] Allow implicit conversion on templated constructor call

bindings/pyroot/cppyy/CPyCppyy/src/TemplateProxy.cxx

@@ -663,8 +663,8 @@ static PyObject* tpp_call(TemplateProxy* pytmpl, PyObject* args, PyObject* kwds)
         int pcnt = 0;
         pymeth = pytmpl->Instantiate(pytmpl->fTI->fCppName, args, nargsf, pref, &pcnt);
         if (pymeth) {
-        // attempt actual call; argument based, so do not allow implicit conversions
-            result = CallMethodImp(pytmpl, pymeth, args, nargsf, kwds, false, sighash);
+        // attempt actual call; even if argument based, allow implicit conversions, for example for non-template arguments
+            result = CallMethodImp(pytmpl, pymeth, args, nargsf, kwds, true, sighash);
             if (result) TPPCALL_RETURN;
         }
         Utility::FetchError(errors);

bindings/pyroot/cppyy/cppyy/test/test_templates.py

@@ -1,4 +1,4 @@
 import pytest, os
 from pytest import mark, raises
 from support import setup_make, pylong, IS_WINDOWS
 
@@ -23,8 +23,8 @@
     def test01_template_member_functions(self):
         """Template member functions lookup and calls"""
 
         import cppyy
         import sys
 
         m = cppyy.gbl.MyTemplatedMethodClass()
 
@@ -40,7 +40,7 @@
         if sys.hexversion >= 0x3000000:
             targ = 'long'
         else:
             targ = long
         assert m.get_size[targ]()     == m.get_long_size()
 
         import ctypes
@@ -104,15 +104,15 @@
         from cppyy.gbl.std import vector
         # float in, float out
         ggsr = cppyy.gbl.global_get_some_result['std::vector<float>']
         assert type(ggsr(vector['float']([0.5])).m_retval) == float
         assert ggsr(vector['float']([0.5])).m_retval == 0.5
         # int in, float out
         ggsr = cppyy.gbl.global_get_some_result['std::vector<int>']
         assert type(ggsr(vector['int']([5])).m_retval) == float
         assert ggsr(vector['int']([5])).m_retval == 5.
         # float in, int out
         ggsr = cppyy.gbl.global_get_some_result['std::vector<float>, int']
         assert type(ggsr(vector['float']([0.3])).m_retval) == int
         assert ggsr(vector['float']([0.3])).m_retval == 0
         # int in, int out
         ggsr = cppyy.gbl.global_get_some_result['std::vector<int>, int']
@@ -1184,6 +1184,29 @@
         with pytest.raises(TypeError, match=r"could not construct C\+\+ name"):
             cppyy.gbl.test35_func[set(), list()]()
 
+    def test36_constructor_implicit_conversion(self):
+        """Implicit conversion to call a templated constructor"""
+
+        import cppyy
+
+        cppyy.cppdef("""\
+        namespace ConstructorImplicitConversion {
+        struct IntWrapper {
+            IntWrapper(int i) : m_i(i) {}
+            int m_i;
+        };
+        struct S {
+            template <typename T>
+            S(IntWrapper a, T b) : m_a(a.m_i) {}
+
+            int m_a = 0;
+        }; }""")
+
+        ns = cppyy.gbl.ConstructorImplicitConversion
+
+        a = ns.S(1, 2)
+        assert a.m_a == 1
+
 
 class TestTEMPLATED_TYPEDEFS:
     def setup_class(cls):