minimal_timed_async_executor_test_exe fails to compile on master (d6f505c)

[zao]

Debian 9.2, Clang 3.8.1, C++14, Boost 1.65.1, RelWithDebInfo.
This failure was observed on a branch earlier, seems to have been merged onto master. There may be additional failures, didn't continue the build. The output below is from master commit d6f505c.

According to @K-ballo on IRC:

with C++14 the algorithm dispatch machinery is not sfinae-friendly (for diagnostics reasons), and something is inadvertently instantiating those with a const deferred_call/one-shot

[1167/1443] Building CXX object tests/unit/parallel/executors/CMakeFiles/minimal_timed_async_executor_test_exe.dir/minimal_timed_async_executor.cpp
.o
FAILED: tests/unit/parallel/executors/CMakeFiles/minimal_timed_async_executor_test_exe.dir/minimal_timed_async_executor.cpp.o
/usr/bin/clang++   -DBOOST_DISABLE_ASSERTS -DHPX_APPLICATION_EXPORTS -DHPX_APPLICATION_NAME=minimal_timed_async_executor_test_exe -DHPX_APPLICATION
_STRING=\"minimal_timed_async_executor_test_exe\" -DHPX_DISABLE_ASSERTS -DHPX_PREFIX=\"/tree/build-rwdi\" -D_GNU_SOURCE -I/tree/hpx -isystem /opt/b
oost-1.65.1-cxx14/include -I. -I/tree/hpx/tests -pthread -Wall -Wextra -Wno-unused-local-typedefs -Wno-strict-aliasing -Wno-sign-promo -Wno-attribu
tes -Wno-cast-align -Wno-unused-parameter -Wformat=2 -Wno-format-nonliteral -Winit-self -Wdouble-promotion -Wcast-qual -Werror=parentheses -Werror=
reorder -Werror=return-type -Werror=sequence-point -Werror=uninitialized -Werror=format -Werror=missing-braces -Werror=sign-compare -fdiagnostics-s
how-option -Werror=vla -Werror=return-type -Wno-cast-align -O2 -g -DNDEBUG   -std=c++14 -MD -MT tests/unit/parallel/executors/CMakeFiles/minimal_ti
med_async_executor_test_exe.dir/minimal_timed_async_executor.cpp.o -MF tests/unit/parallel/executors/CMakeFiles/minimal_timed_async_executor_test_e
xe.dir/minimal_timed_async_executor.cpp.o.d -o tests/unit/parallel/executors/CMakeFiles/minimal_timed_async_executor_test_exe.dir/minimal_timed_asy
nc_executor.cpp.o -c /tree/hpx/tests/unit/parallel/executors/minimal_timed_async_executor.cpp
In file included from /tree/hpx/tests/unit/parallel/executors/minimal_timed_async_executor.cpp:7:
In file included from /tree/hpx/hpx/hpx.hpp:10:
In file included from /tree/hpx/hpx/include/lcos.hpp:11:
In file included from /tree/hpx/hpx/include/actions.hpp:11:
In file included from /tree/hpx/hpx/runtime/actions/action_invoke_no_more_than.hpp:12:
In file included from /tree/hpx/hpx/runtime/actions/continuation.hpp:14:
In file included from /tree/hpx/hpx/runtime/actions/trigger.hpp:11:
In file included from /tree/hpx/hpx/lcos/future.hpp:1646:
In file included from /tree/hpx/hpx/lcos/local/packaged_continuation.hpp:24:
/tree/hpx/hpx/util/deferred_call.hpp:173:16: error: call to deleted constructor of 'typename std::decay<deferred<id (*(int &&))(int)> &>::type' (ak
a 'hpx::util::detail::deferred<hpx::thread::id (*(int &&))(int)>')
        return std::forward<F>(f);
               ^~~~~~~~~~~~~~~~~~
/tree/hpx/hpx/async.hpp:176:23: note: in instantiation of function template specialization 'hpx::util::deferred_call<hpx::util::detail::deferred<hp
x::thread::id (*(int &&))(int)> &>' requested here
                util::deferred_call(std::forward<F>(f), std::forward<Ts>(ts)...));
                      ^
/tree/hpx/hpx/lcos/async.hpp:330:16: note: in instantiation of function template specialization 'hpx::detail::async_launch_policy_dispatch<hpx::uti
l::detail::deferred<hpx::thread::id (*(int &&))(int)>, void>::call<hpx::util::detail::deferred<hpx::thread::id (*(int &&))(int)> &>' requested here
            >::call(std::forward<Policy_>(launch_policy), std::forward<F>(f),
               ^
/tree/hpx/hpx/async.hpp:350:16: note: in instantiation of function template specialization 'hpx::detail::async_dispatch<hpx::detail::async_policy,
void>::call<const hpx::detail::async_policy &, hpx::util::detail::deferred<hpx::thread::id (*(int &&))(int)> &>' requested here
            >::call(std::forward<F>(f), std::forward<Ts>(ts)...);
               ^
/tree/hpx/tests/unit/parallel/executors/minimal_timed_async_executor.cpp:174:21: note: in instantiation of function template specialization 'hpx::a
sync<const hpx::detail::async_policy &, hpx::util::detail::deferred<hpx::thread::id (*(int &&))(int)> &>' requested here
        return hpx::async(hpx::launch::async, std::forward<F>(f),
                    ^
/tree/hpx/hpx/parallel/executors/execution.hpp:270:25: note: in instantiation of function template specialization 'test_async_executor1::async_exec
ute<hpx::util::detail::deferred<hpx::thread::id (*(int &&))(int)> &>' requested here
            return exec.async_execute(std::forward<F>(f),
                        ^
/tree/hpx/hpx/parallel/executors/execution.hpp:288:24: note: (skipping 6 contexts in backtrace; use -ftemplate-backtrace-limit=0 to see all)
                return async_execute_dispatch(0,
                       ^
/tree/hpx/hpx/parallel/executors/execution.hpp:288:24: note: in instantiation of function template specialization 'hpx::parallel::execution::detail
::async_execute_dispatch<hpx::parallel::execution::timed_executor<test_async_executor1> &, hpx::thread::id (*)(int), int>' requested here
/tree/hpx/hpx/parallel/executors/execution_fwd.hpp:222:20: note: in instantiation of function template specialization 'hpx::parallel::execution::de
tail::async_execute_fn_helper<hpx::parallel::execution::timed_executor<test_async_executor1>, void>::call<hpx::parallel::execution::timed_executor<
test_async_executor1> &, hpx::thread::id (*)(int), int>' requested here
                >::call(std::forward<Executor>(exec), std::forward<F>(f),
                   ^
/tree/hpx/hpx/parallel/executors/execution_fwd.hpp:323:20: note: in instantiation of function template specialization 'hpx::parallel::execution::de
tail::async_execute<hpx::parallel::execution::timed_executor<test_async_executor1> &, hpx::thread::id (*)(int), int>' requested here
            return async_execute(std::forward<Executor>(exec),
                   ^
/tree/hpx/tests/unit/parallel/executors/minimal_timed_async_executor.cpp:152:5: note: in instantiation of function template specialization 'test_ti
med_async<test_async_executor1>' requested here
    test_timed_async(exec);
    ^
/tree/hpx/tests/unit/parallel/executors/minimal_timed_async_executor.cpp:285:5: note: in instantiation of function template specialization 'test_ti
med_executor<test_async_executor1>' requested here
    test_timed_executor<test_async_executor1>({{ 0, 0, 6, 0, 0, 0 }});
    ^
/tree/hpx/hpx/util/deferred_call.hpp:97:13: note: 'deferred' has been explicitly marked deleted here
            deferred(deferred const&) = delete;
            ^
1 error generated.

[zao]

Please note that this fails already at compile time, blocking the building of tests in general and as such, prevents me from running the test suite.

[K-ballo]

I'm still looking into it.

@zao As a workaround you could build in C++11 mode, or disable return type deduction.