GCC 12.2.0 build warning for uninitialized variable

[christophe-lunarg]

Describe the bug The GCC 12.2.0 compiler warns that a variable may be uninitialized when building JSONCPP, specifically here (v):

  case tokenNull:
    {
    Value v;
    currentValue().swapPayload(v);
    currentValue().setOffsetStart(token.start_ - begin_);
    currentValue().setOffsetLimit(token.end_ - begin_);
    }
    break;

in jsoncpp.cpp

To Reproduce Just building jsoncpp.cpp in a project.

Expected behavior No warning.

I even expect that :

Value v(); 

We resolve the issue.

Desktop (please complete the following information):

• vanilla Arch Linux, GCC 12.2.0

[johnzupin]

I'm seeing this issue as well on Fedora 36.

 [ 29%] Building CXX object via/CMakeFiles/vkvia.dir/__/submodules/jsoncpp/dist/jsoncpp.cpp.o
In file included from /usr/include/c++/12/bits/new_allocator.h:36,
                 from /usr/include/c++/12/x86_64-redhat-linux/bits/c++allocator.h:33,
                 from /usr/include/c++/12/bits/allocator.h:46,
                 from /usr/include/c++/12/string:41,
                 from /root/1.3.224.1/source/VulkanTools/submodules/jsoncpp/dist/json/json.h:127,
                 from /root/1.3.224.1/source/VulkanTools/submodules/jsoncpp/dist/jsoncpp.cpp:76:
In function ‘std::_Require<std::__not_<std::__is_tuple_like<_Tp> >, std::is_move_constructible<_Tp>, std::is_move_assignable<_Tp> > std::swap(_Tp&, _Tp&) [with _Tp = Json::Value::ValueHolder]’,
    inlined from ‘void Json::Value::swapPayload(Json::Value&)’ at /root/1.3.224.1/source/VulkanTools/submodules/jsoncpp/dist/jsoncpp.cpp:2967:12,
    inlined from ‘bool Json::Reader::readValue()’ at /root/1.3.224.1/source/VulkanTools/submodules/jsoncpp/dist/jsoncpp.cpp:433:31:
/usr/include/c++/12/bits/move.h:205:7: error: ‘v.Json::Value::value_’ may be used uninitialized [-Werror=maybe-uninitialized]
  205 |       __a = _GLIBCXX_MOVE(__b);
      |       ^~~
/root/1.3.224.1/source/VulkanTools/submodules/jsoncpp/dist/jsoncpp.cpp: In member function ‘bool Json::Reader::readValue()’:
/root/1.3.224.1/source/VulkanTools/submodules/jsoncpp/dist/jsoncpp.cpp:432:11: note: ‘v’ declared here
  432 |     Value v;
      |           ^
In function ‘std::_Require<std::__not_<std::__is_tuple_like<_Tp> >, std::is_move_constructible<_Tp>, std::is_move_assignable<_Tp> > std::swap(_Tp&, _Tp&) [with _Tp = Json::Value::ValueHolder]’,
    inlined from ‘void Json::Value::swapPayload(Json::Value&)’ at /root/1.3.224.1/source/VulkanTools/submodules/jsoncpp/dist/jsoncpp.cpp:2967:12,
    inlined from ‘bool Json::Reader::readValue()’ at /root/1.3.224.1/source/VulkanTools/submodules/jsoncpp/dist/jsoncpp.cpp:446:33:
/usr/include/c++/12/bits/move.h:205:7: error: ‘v.Json::Value::value_’ may be used uninitialized [-Werror=maybe-uninitialized]
  205 |       __a = _GLIBCXX_MOVE(__b);
      |       ^~~
/root/1.3.224.1/source/VulkanTools/submodules/jsoncpp/dist/jsoncpp.cpp: In member function ‘bool Json::Reader::readValue()’:
/root/1.3.224.1/source/VulkanTools/submodules/jsoncpp/dist/jsoncpp.cpp:445:13: note: ‘v’ declared here
  445 |       Value v;
      |             ^
In function ‘std::_Require<std::__not_<std::__is_tuple_like<_Tp> >, std::is_move_constructible<_Tp>, std::is_move_assignable<_Tp> > std::swap(_Tp&, _Tp&) [with _Tp = Json::Value::ValueHolder]’,
    inlined from ‘void Json::Value::swapPayload(Json::Value&)’ at /root/1.3.224.1/source/VulkanTools/submodules/jsoncpp/dist/jsoncpp.cpp:2967:12,
    inlined from ‘bool Json::OurReader::readValue()’ at /root/1.3.224.1/source/VulkanTools/submodules/jsoncpp/dist/jsoncpp.cpp:1355:31:
/usr/include/c++/12/bits/move.h:205:7: error: ‘v.Json::Value::value_’ may be used uninitialized [-Werror=maybe-uninitialized]
  205 |       __a = _GLIBCXX_MOVE(__b);
      |       ^~~
/root/1.3.224.1/source/VulkanTools/submodules/jsoncpp/dist/jsoncpp.cpp: In member function ‘bool Json::OurReader::readValue()’:
/root/1.3.224.1/source/VulkanTools/submodules/jsoncpp/dist/jsoncpp.cpp:1354:11: note: ‘v’ declared here
 1354 |     Value v;
      |           ^
In function ‘std::_Require<std::__not_<std::__is_tuple_like<_Tp> >, std::is_move_constructible<_Tp>, std::is_move_assignable<_Tp> > std::swap(_Tp&, _Tp&) [with _Tp = Json::Value::ValueHolder]’,
    inlined from ‘void Json::Value::swapPayload(Json::Value&)’ at /root/1.3.224.1/source/VulkanTools/submodules/jsoncpp/dist/jsoncpp.cpp:2967:12,
    inlined from ‘bool Json::OurReader::readValue()’ at /root/1.3.224.1/source/VulkanTools/submodules/jsoncpp/dist/jsoncpp.cpp:1392:33:
/usr/include/c++/12/bits/move.h:205:7: error: ‘v.Json::Value::value_’ may be used uninitialized [-Werror=maybe-uninitialized]
  205 |       __a = _GLIBCXX_MOVE(__b);
      |       ^~~
/root/1.3.224.1/source/VulkanTools/submodules/jsoncpp/dist/jsoncpp.cpp: In member function ‘bool Json::OurReader::readValue()’:
/root/1.3.224.1/source/VulkanTools/submodules/jsoncpp/dist/jsoncpp.cpp:1391:13: note: ‘v’ declared here
 1391 |       Value v;
      |             ^
cc1plus: all warnings being treated as errors
make[2]: *** [via/CMakeFiles/vkvia.dir/build.make:132: via/CMakeFiles/vkvia.dir/__/submodules/jsoncpp/dist/jsoncpp.cpp.o] Error 1
make[1]: *** [CMakeFiles/Makefile2:510: via/CMakeFiles/vkvia.dir/all] Error 2
make: *** [Makefile:146: all] Error 2

[root@7308de54a448 build]# gcc --version
gcc (GCC) 12.2.1 20220819 (Red Hat 12.2.1-2)
Copyright (C) 2022 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.