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cling failure when accessing `std::map` elements from Python

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@guitargeek 已经在做这个了。

开始于 2026年1月19日。

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描述

bug in:Cling in:Python Interface
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Description

Consider the following program

import ROOT

ROOT.gInterpreter.Declare(r"""

struct S{};

std::map<std::string, std::vector<std::unique_ptr<S>>> mymap;
mymap["a"] = std::vector<std::unique_ptr<S>>();
""")

# For some reason, uncommenting the following line will prevent the program from crashing
# print(ROOT.mymap)

for key, value in ROOT.mymap:
    print(key, value)

Running this program in master shows no issues:

$: python test_map.py 
a {}

But I suspect there is a real problem hidden in this code. By applying this simple patch https://github.com/root-project/root/pull/20946, the same program crashes

 *** Break *** illegal instruction
[...]
make_dtor_wrapperFailed to compile
==== SOURCE BEGIN ====
__attribute__((used)) extern "C" void __dtor_0(void* obj, unsigned long nary, int withFree)
{
   if (withFree) {
      if (!nary) {
         delete (std::_Rb_tree_iterator<std::pair<const std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::vector<std::unique_ptr<S, std::default_delete<S> >, std::allocator<std::unique_ptr<S, std::default_delete<S> > > > > >*) obj;
      }
      else {
         delete[] (std::_Rb_tree_iterator<std::pair<const std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::vector<std::unique_ptr<S, std::default_delete<S> >, std::allocator<std::unique_ptr<S, std::default_delete<S> > > > > >*) obj;
      }
   }
   else {
      typedef std::_Rb_tree_iterator<std::pair<const std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::vector<std::unique_ptr<S, std::default_delete<S> >, std::allocator<std::unique_ptr<S, std::default_delete<S> > > > > > Nm;
if (!nary) {
         ((Nm*)obj)->~Nm();
      }
      else {
         do {
            (((Nm*)obj)+(--nary))->~Nm();
         } while (nary);
      }
   }
}

I attach the full stacktrace here

full_stacktrace.txt

Something that looks odd is the presence of const std::basic_string in part of the output from above, while the std::map I create uses just std::basic_string, I don't know if it's related to the issue.

Reproducer

See above

ROOT version

Master with patch https://github.com/root-project/root/pull/20946

Installation method

Build from source

Operating system

Linux

Additional context

No response

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