[Python] Overloads like `foo(bool=true)` not correctly resolved

[guitargeek]

Reproducer:

python
>>> import ROOT
>>> ROOT.RooFit.Minos(1).getSet(0).Print("v")
  1) 0x6535abd27b70 RooConstVar:: 1 = 1  "1"

Should be like in C++:

root [1] RooFit::Minos(1).getSet(0)
(const RooArgSet *) nullptr

The function has overloads like this:

RooCmdArg Minos(bool);
RooCmdArg Minos(RooArgSet const&);

The RooArgSet has a constructor RooArgSet(double) which is accidentally taken by PyROOT here, even though the call to Minos(bool) would be correct.

This caused some bad experience for users who tried to enable Minos for all parameters with Minos(1), resulting in nothing happening (Minos was only attempted for this constant "1" parameter, which of course does nothing).

Not a high priority in this case because the workaround is easy: Minos(True). But it's very possible that users are also bitten in other cases by this faulty overload resolution, so we need to fix it.

[guitargeek]

To make this a bit more actionable, I have created a standalone reproducer that doesn't use RooFit:

import cppyy

cppyy.cppdef("""

struct MyClass {
  explicit MyClass(int arg) {}
};

void foo(MyClass const&) { std::cout << "foo(MyClass const&)" << std::endl; }
void foo(bool) { std::cout << "foo(bool)" << std::endl; }

void bar(MyClass const&) { std::cout << "bar(MyClass const&)" << std::endl; }
void bar(bool = true) { std::cout << "bar(bool = true)" << std::endl; }

foo(1);
bar(1);

""")

cppyy.gbl.foo(1)
cppyy.gbl.bar(1) # the default bool argument confuses the overload resolution!

The output will be (also with the compiler-research cppyy fork):

foo(bool)
bar(bool = true)
foo(bool)
bar(MyClass const&)

The implicit conversion to MyClass should never happen because its constructor is explicit!