Inconsistent behaviour on failed jitting (transaction rollback issue?)

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Description

Following up on an issue which was buried in https://github.com/root-project/root/pull/12449#issuecomment-1464946488

In current nightlies this test case behaves slightly differently, but still not correctly. It fails with sensible error messages on the first attempt, but then "succeeds" on the second attempt. I would expect it to fail with the same errors again if the state were really fully rolled back.

Reproducer

test.h

template <typename T>
class Helper {

public:

  Helper() {}

  std::size_t operator() () const {
    const std::size_t res = 0;
    res = T{0, 0}.size();
    return res;
  }

};

template <typename H>
std::size_t call_helper(const H &helper) {
  return helper();
}

testdeclare.py

import ROOT

ret = ROOT.gInterpreter.Declare('#include "test.h"')
print("header include ret", ret)

print("creating helper")
helper = ROOT.Helper[ROOT.std.vector["double"]]()

bad_template = "template std::size_t call_helper<Helper<std::vector<double>>>(const Helper<std::vector<double>>&);"

for i in range(2):
    print(f"declare attempt {i}")
    ret = ROOT.gInterpreter.Declare(bad_template)
    print("ret", ret)

output:

header include ret True
creating helper
declare attempt 0
In file included from input_line_34:1:
./test.h:10:9: error: cannot assign to variable 'res' with const-qualified type 'const std::size_t' (aka 'const unsigned long')
    res = T{0, 0}.size();
    ~~~ ^
./test.h:18:10: note: in instantiation of member function 'Helper<std::vector<double, std::allocator<double> > >::operator()' requested here
  return helper();
         ^
./test.h:9:23: note: variable 'res' declared const here
    const std::size_t res = 0;
    ~~~~~~~~~~~~~~~~~~^~~~~~~
ret False
declare attempt 1
ret True

ROOT version

   ------------------------------------------------------------------
  | Welcome to ROOT 6.33.01                        https://root.cern |
  | (c) 1995-2024, The ROOT Team; conception: R. Brun, F. Rademakers |
  | Built for linuxx8664gcc on Oct 02 2024, 00:22:18                 |
  | From heads/master@v6-31-01-3406-g2dc2e0f126                      |
  | With g++ (GCC) 14.2.0                                            |
  | Try '.help'/'.?', '.demo', '.license', '.credits', '.quit'/'.q'  |
   ------------------------------------------------------------------

Installation method

lcg nightlies

Operating system

Linux (alma 9)

Additional context

No response

root-project / root

Inconsistent behaviour on failed jitting (transaction rollback issue?) #16577