Compiler warning with -Wmaybe-uninitialized when using Fedora 36 and gcc 12.1.1

[bryancall]

Describe the bug
Compiler warning with maybe-uninitialized when using Fedora 36 and gcc 12.1.1. Fedora 35 and an older version of gcc works. I am curious if anyone else has run into this issue before.

Expected behavior
I expect it to build without warnings.

Reproduction steps
Build ATS on Fedora 36 and turn on -Werror and build the unit tests with make test

Platform information:

• OS: Fedora 36
• Compiler+version: gcc 12.1.1
• Catch version: 2.13.8 and 2.13.9

Additional context
Here is a link to our issue of the problem: apache/trafficserver#8848

Compiler error

  CXX      unit_tests/freelist_benchmark-freelist_benchmark.o
In file included from /usr/include/c++/12/functional:59,
                 from /home/bcall/dev/apache/trafficserver/build-Linux_gcc/../tests/include/catch.hpp:3483,
                 from ../../../src/tscore/unit_tests/freelist_benchmark.cc:25:
In constructor ‘std::function<_Res(_ArgTypes ...)>::function(std::function<_Res(_ArgTypes ...)>&&) [with _Res = bool; _ArgTypes = {char}]’,
    inlined from ‘std::__detail::_State<_Char_type>::_State(std::__detail::_State<_Char_type>&&) [with _Char_type = char]’ at /usr/include/c++/12/bits/regex_automaton.h:149:4,
    inlined from ‘std::__detail::_State<_Char_type>::_State(std::__detail::_State<_Char_type>&&) [with _Char_type = char]’ at /usr/include/c++/12/bits/regex_automaton.h:146:7,
    inlined from ‘std::__detail::_StateIdT std::__detail::_NFA<_TraitsT>::_M_insert_subexpr_end() [with _TraitsT = std::__cxx11::regex_traits<char>]’ at /usr/include/c++/12/bits/regex_automaton.h:290:24:
/usr/include/c++/12/bits/std_function.h:405:42: error: ‘*(std::function<bool(char)>*)((char*)&__tmp + offsetof(std::__detail::_StateT, std::__detail::_State<char>::<unnamed>.std::__detail::_State_base::<unnamed>)).std::function<bool(char)>::_M_invoker’ may be used uninitialized [-Werror=maybe-uninitialized]
  405 |       : _Function_base(), _M_invoker(__x._M_invoker)
      |                                      ~~~~^~~~~~~~~~
In file included from /usr/include/c++/12/regex:63,
                 from /home/bcall/dev/apache/trafficserver/build-Linux_gcc/../tests/include/catch.hpp:11706:
/usr/include/c++/12/bits/regex_automaton.h: In member function ‘std::__detail::_StateIdT std::__detail::_NFA<_TraitsT>::_M_insert_subexpr_end() [with _TraitsT = std::__cxx11::regex_traits<char>]’:
/usr/include/c++/12/bits/regex_automaton.h:287:17: note: ‘__tmp’ declared here
  287 |         _StateT __tmp(_S_opcode_subexpr_end);
      |                 ^~~~~
In member function ‘bool std::_Function_base::_M_empty() const’,
    inlined from ‘std::function<_Res(_ArgTypes ...)>::operator bool() const [with _Res = bool; _ArgTypes = {char}]’ at /usr/include/c++/12/bits/std_function.h:574:25,
    inlined from ‘std::function<_Res(_ArgTypes ...)>::function(std::function<_Res(_ArgTypes ...)>&&) [with _Res = bool; _ArgTypes = {char}]’ at /usr/include/c++/12/bits/std_function.h:407:6,
    inlined from ‘std::__detail::_State<_Char_type>::_State(std::__detail::_State<_Char_type>&&) [with _Char_type = char]’ at /usr/include/c++/12/bits/regex_automaton.h:149:4,
    inlined from ‘std::__detail::_State<_Char_type>::_State(std::__detail::_State<_Char_type>&&) [with _Char_type = char]’ at /usr/include/c++/12/bits/regex_automaton.h:146:7,
    inlined from ‘std::__detail::_StateIdT std::__detail::_NFA<_TraitsT>::_M_insert_subexpr_end() [with _TraitsT = std::__cxx11::regex_traits<char>]’ at /usr/include/c++/12/bits/regex_automaton.h:290:24:
/usr/include/c++/12/bits/std_function.h:247:37: error: ‘*(const std::_Function_base*)((char*)&__tmp + offsetof(std::__detail::_StateT, std::__detail::_State<char>::<unnamed>.std::__detail::_State_base::<unnamed>)).std::_Function_base::_M_manager’ may be used uninitialized [-Werror=maybe-uninitialized]
  247 |     bool _M_empty() const { return !_M_manager; }
      |                                     ^~~~~~~~~~
/usr/include/c++/12/bits/regex_automaton.h: In member function ‘std::__detail::_StateIdT std::__detail::_NFA<_TraitsT>::_M_insert_subexpr_end() [with _TraitsT = std::__cxx11::regex_traits<char>]’:
/usr/include/c++/12/bits/regex_automaton.h:287:17: note: ‘__tmp’ declared here
  287 |         _StateT __tmp(_S_opcode_subexpr_end);
      |                 ^~~~~
cc1plus: all warnings being treated as errors

Patch to get around this issue

+#pragma GCC diagnostic error "-Wmaybe-uninitialized"
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wmaybe-uninitialized"
 #include <functional>
+#pragma GCC diagnostic pop
+#pragma GCC diagnostic pop

[olbender]

Also got it in Arch Linux with gcc 12.1.0.

[complexoctonion]

This seems to be a bug in gcc 12.1.0, see https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105562

[horenmar]

Yeah I am not suppressing warning in system header caused by overeager compiler.