[PyROOT] False positive in cppyy proxy cache

[guitargeek]

Reproducer:

import ROOT

ROOT.gInterpreter.Declare("""
struct A {
   int a;
   A(int _a) : a(_a) {}
};

std::unique_ptr<A> create() { return std::make_unique<A>(42); }

struct Consumer {
public:
   Consumer(std::unique_ptr<A> & ptr) : fPtr{std::move(ptr)}
     { ptr.reset(); }

   const A &get() const { return *fPtr; }

private:
   std::unique_ptr<A> fPtr;
};

""")


x = ROOT.create()
print(x)
print(x.a)
c = ROOT.Consumer(x)
print(x)
x = c.get()
print(x)
print(x.a)

Output:

<cppyy.gbl.A object at 0x5d77cc252e40 held by std::unique_ptr<A,default_delete<A> > at 0x5d77cc2432e0>
42
<cppyy.gbl.A object at 0x(nil) held by std::unique_ptr<A,default_delete<A> > at 0x5d77cc2432e0>
<cppyy.gbl.A object at 0x(nil) held by std::unique_ptr<A,default_delete<A> > at 0x5d77cc2432e0>
Traceback (most recent call last):
  File "/home/rembserj/spaces/master/root/src/root/jonas.py", line 32, in <module>
    print(x.a)
          ^^^
ReferenceError: attempt to access a null-pointer

The new x should not be a nullptr anymore, but a reference to the object that the Consumer points to internally.

Thanks to @hahnjo for finding this problem!