Test warning -- explicitly defaulted default constructor is implicitly deleted

[vddvss]

When compiling with Clang trunk, I get a defaulted-function-deleted warning for the test.tuple.cnstr.trap test (compiler output below).

The constructor for struct Foo is defaulted:

https://github.com/boostorg/hana/blob/9ffeb079fed195849d384fa7ed2f8dbcf9c04c88/test/tuple/cnstr.trap.cpp#L113

struct Foo has a member hana::tuple<Trap4> t;, but the default constructor for struct Trap4

https://github.com/boostorg/hana/blob/9ffeb079fed195849d384fa7ed2f8dbcf9c04c88/test/tuple/cnstr.trap.cpp#L59

is implicitly deleted, since the explicitly defaulted copy constructors and the templated rvalue constructor of struct Trap4 implicitly delete the default constructor.

If you'd like, I can do a PR to either remove or mark as deleted struct Foos's default constructor or to explicitly define a default constructor for struct Trap4.

Compiler output:

$ ninja test.tuple.cnstr.trap
[1/2] Building CXX object test/CMakeFiles/test.tuple.cnstr.trap.dir/tuple/cnstr.trap.cpp.o
FAILED: test/CMakeFiles/test.tuple.cnstr.trap.dir/tuple/cnstr.trap.cpp.o
/home/colin/.local/lib64/llvm-installs/nightly/bin/clang++  -DBOOST_HANA_CONFIG_ENABLE_STRING_UDL -I../test/_include -I../include -fdiagnostics-color -ftemplate-backtrace-limit=0 -pedantic -Wall -Werror -Wextra -Wno-self-assign-overloaded -Wno-unused-local-typedefs -Wwrite-strings -Wno-gnu-string-literal-operator-template -std=c++14 -MD -MT test/CMakeFiles/test.tuple.cnstr.trap.dir/tuple/cnstr.trap.cpp.o -MF test/CMakeFiles/test.tuple.cnstr.trap.dir/tuple/cnstr.trap.cpp.o.d -o test/CMakeFiles/test.tuple.cnstr.trap.dir/tuple/cnstr.trap.cpp.o -c ../test/tuple/cnstr.trap.cpp
../test/tuple/cnstr.trap.cpp:113:13: error: explicitly defaulted default constructor is implicitly deleted [-Werror,-Wdefaulted-function-deleted]
            Foo() = default;
            ^
../test/tuple/cnstr.trap.cpp:116:32: note: default constructor of 'Foo' is implicitly deleted because field 't' has no default constructor
            hana::tuple<Trap4> t;
                               ^
1 error generated.
ninja: build stopped: subcommand failed.

[ldionne]

Thanks for the report. I'm hitting the same problem.