Unable to build in C++20 on Mac

[FellowTraveler]

• Compiler Used: clang 14.0.3
• Operating System: MacOS 13.3.1
• Architecture (ARM/x86/32bit/64bit/etc): x86_64-apple-darwin22.4.0

Expected Behavior

It should compile with C++20 but fails. (It does successfully compile in C++17).

Actual Behavior

Fails to compile using C++20; errors all apparently due to incomplete type: AST_Node_Trace

Minimal Example to Reproduce Behavior

Change C++ version from 17 to 20 in CMakeLists.txt and then see lots of errors like this:

In file included from /Users/au/src/ChaiScript/unittests/boxed_cast_test.cpp:1:
In file included from /Users/au/src/ChaiScript/include/chaiscript/utility/utility.hpp:13:
In file included from /Users/au/src/ChaiScript/include/chaiscript/utility/../language/chaiscript_common.hpp:15:
In file included from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX13.3.sdk/usr/include/c++/v1/sstream:186:
In file included from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX13.3.sdk/usr/include/c++/v1/istream:165:
In file included from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX13.3.sdk/usr/include/c++/v1/ostream:168:
In file included from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX13.3.sdk/usr/include/c++/v1/bitset:128:
In file included from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX13.3.sdk/usr/include/c++/v1/string:551:
In file included from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX13.3.sdk/usr/include/c++/v1/string_view:223:
In file included from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX13.3.sdk/usr/include/c++/v1/functional:515:
In file included from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX13.3.sdk/usr/include/c++/v1/__functional/boyer_moore_searcher.h:26:
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX13.3.sdk/usr/include/c++/v1/vector:540:52: error: arithmetic on a pointer to an incomplete type 'chaiscript::AST_Node_Trace'
{return static_cast<size_type>(__end_cap() - this->_begin);}
~~~~~~~~~~~ ^
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX13.3.sdk/usr/include/c++/v1/vector:760:56: note: in instantiation of member function 'std::vectorchaiscript::AST_Node_Trace::capacity' requested here
__annotate_contiguous_container(data(), data() + capacity(),
^
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX13.3.sdk/usr/include/c++/v1/vector:431:7: note: in instantiation of member function 'std::vectorchaiscript::AST_Node_Trace::__annotate_delete' requested here
__annotate_delete();
^
/Users/au/src/ChaiScript/include/chaiscript/utility/../language/chaiscript_common.hpp:211:7: note: in instantiation of member function 'std::vectorchaiscript::AST_Node_Trace::~vector' requested here
eval_error(const std::string &t_why,
^
/Users/au/src/ChaiScript/include/chaiscript/utility/../language/chaiscript_common.hpp:173:10: note: forward declaration of 'chaiscript::AST_Node_Trace'
struct AST_Node_Trace;
^

[larkwiot]

Having this issue as well on Linux x64.

[zethon]

@FellowTraveler Just a guess, did you try a new build folder? I've gotten errors before when I switched CMAKE_CXX_STANDARD from 17 to 20 and then tried to re-use the build folder.