Merge branch 'main' into receiver-proxy-start-sched-query

Author: yulin25

include/stdexec/__detail/__let.hpp

@@ -565,6 +565,24 @@ namespace STDEXEC
               using __what_t = __bad_result_sender_t<__sndr2_t, _LetTag, __env2_t<_Child, _Env>...>;
               return STDEXEC::__throw_compile_time_error(__what_t());
             }
+            else if constexpr (__nothrow_decay_copyable<_Args...>
+                               && __nothrow_invocable<_Fun, __decay_t<_Args>&...>
+                               && sizeof...(_Env) == 0)
+            {
+              auto __completions =
+                STDEXEC::get_completion_signatures<__sndr2_t, __env2_t<_Child, _Env>...>();
+              STDEXEC_IF_OK(__completions)
+              {
+                if constexpr (__completions.template __contains<__eptr_sig_t>())
+                {
+                  return __completions;
+                }
+                else
+                {
+                  return STDEXEC::__throw_dependent_sender_error<__sndr2_t>();
+                }
+              }
+            }
             else if constexpr (__nothrow_decay_copyable<_Args...>
                                && __nothrow_invocable<_Fun, __decay_t<_Args>&...>
                                && (__nothrow_connectable<__sndr2_t, __rcvr2_t<_Child, _Env>>

test/stdexec/algos/adaptors/test_let_error.cpp

@@ -100,6 +100,16 @@ namespace
     STDEXEC::sync_wait(std::move(snd));
   }
 
+  TEST_CASE("let_error can be followed by upon_error", "[adaptors][let_error]")
+  {
+    auto snd = ex::just_error(2)
+             | ex::let_error([](int n) noexcept { return ex::just_error(n * 10); })
+             | ex::upon_error([](int n) noexcept { return n + 3; });
+    auto opt = ex::sync_wait(std::move(snd));
+    REQUIRE(opt.has_value());
+    CHECK(std::get<0>(*opt) == 23);
+  }
+
 #if !STDEXEC_NO_STDCPP_EXCEPTIONS()
   TEST_CASE("let_error can be used to produce values (error to value)", "[adaptors][let_error]")
   {