Fix missing move in let value (#187)

* added a missing move in the let_value implementation (issue-186)

* removed some left-over code from identifying the issue

* added a missing newline at the end of the file

Author: dietmarkuehl

include/beman/execution/detail/let.hpp

@@ -167,7 +167,7 @@ struct impls_for<::beman::execution::detail::let_t<Completion>> : ::beman::execu
         auto mkop{[&] {
             return ::beman::execution::connect(
                 ::std::apply(::std::move(state.fun),
-                             state.args.template emplace<args_t>(::std::forward<Args>(args)...)),
+                             ::std::move(state.args.template emplace<args_t>(::std::forward<Args>(args)...))),
                 let_receiver<Receiver, decltype(state.env)>{receiver, state.env});
         }};
         ::beman::execution::start(

tests/beman/execution/CMakeLists.txt

@@ -13,6 +13,7 @@ list(
     APPEND
     execution_tests
     issue-174.test
+    issue-186.test
     exec-scope-counting.test
     exec-spawn.test
     exec-stop-when.test

tests/beman/execution/issue-186.test.cpp

@@ -0,0 +1,34 @@
+#include <beman/execution/execution.hpp>
+#include <cassert>
+
+namespace ex = beman::execution;
+
+namespace {
+struct move_only_type {
+    move_only_type() : val(0) {}
+    explicit move_only_type(int v) : val(v) {}
+    ~move_only_type() = default;
+
+    move_only_type(const move_only_type&)            = delete;
+    move_only_type& operator=(const move_only_type&) = delete;
+
+    move_only_type& operator=(move_only_type&&) = default;
+    move_only_type(move_only_type&&)            = default;
+    int val; // NOLINT
+};
+} // namespace
+
+int main() {
+    auto snd = ex::just(move_only_type(1))                                      //
+               | ex::then([](move_only_type v) noexcept { return v.val * 2; })  //
+               | ex::let_value([](int v) noexcept { return ex::just(v * 3); }); // int
+    auto [ret] = ex::sync_wait(std::move(snd)).value();
+    assert(ret == 6);
+
+    // NOTE: Compile time error with move_only_type
+    auto snd2 = ex::just(move_only_type(1))                                                     //
+                | ex::then([](move_only_type v) noexcept { return move_only_type{v.val * 2}; }) //
+                | ex::let_value([](move_only_type v) noexcept { return ex::just(v.val * 3); }); // move_only_type
+    auto [ret2] = ex::sync_wait(std::move(snd2)).value();
+    assert(ret2 == 6);
+}