Merge pull request #1711 from RobertLeahy/let_value_use_after_move_20251213

let_value, _error, & _stopped: Use After Move On Exception From Connect

Author: ericniebler

include/stdexec/__detail/__let.hpp

@@ -111,7 +111,7 @@ namespace stdexec {
           return __env::__join(__env_, stdexec::get_env(__rcvr_));
         }
 
-        _Receiver __rcvr_;
+        _Receiver& __rcvr_;
         const _Env2& __env_;
       };
     };
@@ -296,7 +296,7 @@ namespace stdexec {
 
       template <class _ResultSender, class _OpState>
       auto __get_result_receiver(const _ResultSender&, _OpState& __op_state) -> decltype(auto) {
-        return __rcvr_t{static_cast<_Receiver&&>(__op_state.__rcvr_), __env2_};
+        return __rcvr_t{__op_state.__rcvr_, __env2_};
       }
 
       STDEXEC_IMMOVABLE_NO_UNIQUE_ADDRESS

test/stdexec/algos/adaptors/test_let_value.cpp

@@ -24,6 +24,8 @@
 #include <exec/env.hpp>
 
 #include <chrono> // IWYU pragma: keep for chrono_literals
+#include <exception>
+#include <memory>
 
 namespace ex = stdexec;
 
@@ -347,4 +349,41 @@ namespace {
     ex::start(op);
     CHECK(completed);
   }
+
+  struct throws_on_connect {
+    using sender_concept = ::stdexec::sender_t;
+    template <typename... Args>
+    static consteval ::stdexec::completion_signatures<::stdexec::set_value_t()>
+      get_completion_signatures(const Args&...) noexcept {
+      return {};
+    }
+    template <typename Receiver>
+    auto connect(Receiver) const
+      -> ::stdexec::connect_result_t<decltype(::stdexec::just()), Receiver> {
+      throw std::logic_error("TEST");
+    }
+  };
+
+  TEST_CASE(
+    "When connecting the successor throws an exception let_value delivers an error completion "
+    "signal to a valid receiver",
+    "[adaptors][let_value]") {
+    struct receiver {
+      using receiver_concept = ::stdexec::receiver_t;
+      std::shared_ptr<int> ptr;
+      void set_value() noexcept {
+        FAIL_CHECK("Operation should end in error");
+      }
+      void set_error(std::exception_ptr ex) noexcept {
+        CHECK(ex);
+        REQUIRE(ptr);
+        *ptr = 5;
+      }
+    };
+    const auto ptr = std::make_shared<int>(0);
+    auto sender = ex::let_value(::stdexec::just(), []() noexcept { return throws_on_connect{}; });
+    auto op = ex::connect(std::move(sender), receiver{ptr});
+    ex::start(op);
+    CHECK(*ptr == 5);
+  }
 } // namespace