[WIP] Converters not created for templated method arguments

[aaronj0]

Fails the vectorcall from TemplateProxies when calling the corresponding Executor (in CPyCppyy/Executors.cxx).
Reproducible example:

cppyy.cppdef('''class MyTemplatedMethodClass {
public:
template<class A>
long get_size(A) {
    return sizeof(A)+1;
}
''')

m = cppyy.gbl.MyTemplatedMethodClass()
m.get_size(1)

there are two issues here:
1 is not a priority which is the GetSmartPtrInfo interface which is missing but when we create converters for normal C++ classes it returns false anyway so most tests/usecases it will still work.

the second is the interesting bug. The converter creation for args relies on a loop over args that sets up the dispatch cache.
where we do fullType = GetMethodArgType(fMethod, iarg)
The cling implementation does

TFunction* f = m2f(method);
TMethodArg* arg = (TMethodArg*)f->GetListOfMethodArgs()->At((int)iarg);
std::string ft = arg->GetFullTypeName();

which will always return the C++ type of the arg with which we call the function.

For example if we do

m = cppyy.gbl.MyTemplatedMethodClass()
m.get_size(1)

it will be

arg->GetTypeNormalizedName()
$22 = "int"

but with m.get_size('A')

p fullType
$2 = "std::string"

But with clang this returns theParmVarDeclwhich for a templated parameter is ‘A’ in the case of

template<class A>
long get_size(A) {
	
    return sizeof(A)+1;
}

And we cannot create a converter passing a string type 'A'
I did think of one way to approach this. We look for the Clang::DeclStmt that should be created when the python side cppyy.obj.function(arg) is called.
Then we traverse the AST which should contain the CXXMemberCallExpr for the MemberExpr which is our bound member function get_size and the nodes would contain the types of the literals passed.
We get the normalised type and go from there. This should even work for multiple template parameters:

template<class A, class B>
long get_size(A, B) {
    return sizeof(A)+sizeof(B);
}|
long res = a.get_size(1.5, 'A');

CallExpr node will contain:

|-FloatingLiteral <col:27> 'double' 1.500000e+00
`-CharacterLiteral <col:32> 'char' 65 (edited) 

[aaronj0]

Closing as this is fixed with:

• Enable template features #215