Compilation error with clang: exception specification of explicitly defaulted copy constructor does not match the calculated one

[ethanhschwartz]

Trying to compile with clang version 8.0.1 I get an error because clang does not agree with the exception specification of the copy constructor on the parameter template class in expression.hpp. It looks like this dates back to 9e61d9f
(apologies I haven't tried newer clang or other compiler flags)

% /opt/rh/llvm-toolset-8.0/root/usr/bin/clang++ \
 -I.../_deps/jsoncons-src/include \
 -I.../_deps/jsoncons-src/tests \
 -I.../_deps/jsoncons-src/third_party \
 -I.../_deps/jsoncons-src/third_party/catch  \
 -o CMakeFiles/unit_tests.dir/jsonpath/src/jsonpath_flatten_tests.cpp.o \
 -c .../_deps/jsoncons-src/tests/jsonpath/src/jsonpath_flatten_tests.cpp


.../_deps/jsoncons-src/include/jsoncons_ext/jsonpath/expression.hpp:262:9: error: exception specification of explicitly defaulted
      copy constructor does not match the calculated one
        parameter(const parameter& other) noexcept = default;
        ^
/opt/rh/devtoolset-8/root/usr/lib/gcc/x86_64-redhat-linux/8/../../../../include/c++/8/bits/stl_vector.h:806:50: note: in instantiation of template class
      'jsoncons::jsonpath::parameter<jsoncons::basic_json<char, jsoncons::sorted_policy, std::allocator<char> > >' requested here
      { return size_type(this->_M_impl._M_finish - this->_M_impl._M_start); }
                                                 ^
.../_deps/jsoncons-src/include/jsoncons/detail/span.hpp:90:40: note: in instantiation of member function
      'std::vector<jsoncons::jsonpath::parameter<jsoncons::basic_json<char, jsoncons::sorted_policy, std::allocator<char> > >,
      std::allocator<jsoncons::jsonpath::parameter<jsoncons::basic_json<char, jsoncons::sorted_policy, std::allocator<char> > > > >::size' requested here
            : data_(c.data()), size_(c.size())
                                       ^
.../_deps/jsoncons-src/include/jsoncons_ext/jsonpath/expression.hpp:1042:9: note: in instantiation of member function
      'jsoncons::jsonpath::detail::decorator_function<jsoncons::basic_json<char, jsoncons::sorted_policy, std::allocator<char> > >::evaluate' requested here
        decorator_function(jsoncons::optional<std::size_t> arity,
        ^
.../_deps/jsoncons-src/include/jsoncons/config/jsoncons_config.hpp:103:39: note: in instantiation of member function
      'jsoncons::jsonpath::detail::decorator_function<jsoncons::basic_json<char, jsoncons::sorted_policy, std::allocator<char> > >::decorator_function' requested here
        return std::unique_ptr<T>(new T(std::forward<Args>(args)...));
                                      ^
.../_deps/jsoncons-src/include/jsoncons_ext/jsonpath/expression.hpp:2340:53: note: in instantiation of function template
      specialization 'jsoncons::make_unique<jsoncons::jsonpath::detail::decorator_function<jsoncons::basic_json<char, jsoncons::sorted_policy, std::allocator<char> > >,
      jsoncons::detail::optional<unsigned long>, const std::function<jsoncons::basic_json<char, jsoncons::sorted_policy, std::allocator<char> >
      (jsoncons::detail::span<const jsoncons::jsonpath::parameter<jsoncons::basic_json<char, jsoncons::sorted_policy, std::allocator<char> > >, 18446744073709551615>,
      std::error_code &)> &>' requested here
                                          jsoncons::make_unique<decorator_function<Json>>(item.arity(),item.function()));
                                                    ^
.../_deps/jsoncons-src/include/jsoncons_ext/jsonpath/jsonpath_expression.hpp:2572:80: note: in instantiation of member function
      'jsoncons::jsonpath::detail::static_resources<jsoncons::basic_json<char, jsoncons::sorted_policy, std::allocator<char> >, const jsoncons::basic_json<char,
      jsoncons::sorted_policy, std::allocator<char> > &>::static_resources' requested here
            jsoncons::jsonpath::detail::static_resources<value_type,reference> resources(functions);
                                                                               ^
.../_deps/jsoncons-src/include/jsoncons_ext/jsonpath/jsonpath_expression.hpp:2594:43: note: in instantiation of member function
      'jsoncons::jsonpath::jsonpath_expression<jsoncons::basic_json<char, jsoncons::sorted_policy, std::allocator<char> >, const jsoncons::basic_json<char,
      jsoncons::sorted_policy, std::allocator<char> > &>::compile' requested here
        return jsonpath_expression<Json>::compile(expr, functions);
                                          ^
.../_deps/jsoncons-src/include/jsoncons_ext/jsonpath/json_query.hpp:22:21: note: in instantiation of function template
      specialization 'jsoncons::jsonpath::make_expression<jsoncons::basic_json<char, jsoncons::sorted_policy, std::allocator<char> > >' requested here
        auto expr = make_expression<Json>(path, functions);
                    ^
.../_deps/jsoncons-src/tests/jsonpath/src/jsonpath_flatten_tests.cpp:114:40: note: in instantiation of function template
      specialization 'jsoncons::jsonpath::json_query<jsoncons::basic_json<char, jsoncons::sorted_policy, std::allocator<char> > >' requested here
        auto result = jsoncons::jsonpath::json_query(doc, path);
                                          ^
In file included from .../_deps/jsoncons-src/tests/jsonpath/src/jsonpath_flatten_tests.cpp:8:
In file included from .../_deps/jsoncons-src/include/jsoncons_ext/jsonpath/flatten.hpp:18:
In file included from .../_deps/jsoncons-src/include/jsoncons_ext/jsonpath/jsonpath.hpp:10:
In file included from .../_deps/jsoncons-src/include/jsoncons_ext/jsonpath/json_query.hpp:11:
In file included from .../_deps/jsoncons-src/include/jsoncons_ext/jsonpath/jsonpath_expression.hpp:20:
.../_deps/jsoncons-src/include/jsoncons_ext/jsonpath/expression.hpp:266:20: error: exception specification of explicitly defaulted
      copy assignment operator does not match the calculated one
        parameter& operator=(const parameter& other) noexcept = default;
                   ^
.../_deps/jsoncons-src/include/jsoncons_ext/jsonpath/expression.hpp:268:20: error: exception specification of explicitly defaulted
      move assignment operator does not match the calculated one
        parameter& operator=(parameter&& other) noexcept = default;
                   ^
3 errors generated.

What compiler, architecture, and operating system?

• Compiler: clang++ 8.0.1
• Architecture (e.g. x86, x64) x86_64
• Operating system: CentOS Linux release 7.9.2009

What jsoncons library version?

• Latest release 0.167.0
• Other release ______
• master

[danielaparker]

Thanks for reporting this. I believe clang 8 doesn't like noexcept in combination with = default. With travis CI no longer a practical option for open source, we've lost some of our test coverage for older versions of clang, and this crept in. We'll address it shortly.

[danielaparker]

Could you check if it compiles with clang 8.1 on master? Thanks.

[ethanhschwartz]

I am able to compile on Clang 8.0.1 now. Thanks for the quick turnaround!