default implementation of __sexpr::get_env only forwards the forwarding queries

Author: ericniebler

include/stdexec/__detail/__basic_sender.hpp

@@ -100,7 +100,7 @@ namespace stdexec {
     inline constexpr auto __get_attrs = //
       [](__ignore, const auto&... __child) noexcept -> decltype(auto) {
       if constexpr (sizeof...(__child) == 1) {
-        return stdexec::get_env(__child...); // BUGBUG: should be only the forwarding queries
+        return __env::__fwd_fn()(stdexec::get_env(__child...));
       } else {
         return empty_env();
       }

test/stdexec/algos/adaptors/test_then.cpp

@@ -134,15 +134,15 @@ namespace {
 
   TEST_CASE("then forwards env", "[adaptors][then]") {
     SECTION("returns env by value") {
-      auto snd = just_with_env<value_env, int>{value_env{100}, {0}} | ex::then([](int) { });
-      static_assert(std::same_as<decltype(ex::get_env(snd)), value_env>);
-      CHECK(ex::get_env(snd).value == 100);
+      auto snd = just_with_env<value_env, int>{.env_ = value_env{100}, .values_ = {0}}
+               | ex::then([](int) { });
+      CHECK(value_query(ex::get_env(snd)) == 100);
     }
 
     SECTION("returns env by reference") {
-      auto snd = just_with_env<const value_env&, int>{value_env{100}, {0}} | ex::then([](int) { });
-      static_assert(std::same_as<decltype(ex::get_env(snd)), const value_env&>);
-      CHECK(ex::get_env(snd).value == 100);
+      auto snd = just_with_env<const value_env&, int>{.env_ = value_env{100}, .values_ = {0}}
+               | ex::then([](int) { });
+      CHECK(value_query(ex::get_env(snd)) == 100);
     }
   }
 

test/test_common/senders.hpp

@@ -73,8 +73,21 @@ namespace {
   template <class... Values>
   fallible_just(Values...) -> fallible_just<Values...>;
 
+  inline constexpr struct value_query_t : ex::forwarding_query_t {
+    template <class Env>
+    [[nodiscard]]
+    auto operator()(Env const & env) const noexcept -> decltype(env.query(*this)) {
+      return env.query(*this);
+    }
+  } value_query;
+
   struct value_env {
-    int value;
+    int value{};
+
+    [[nodiscard]]
+    auto query(value_query_t) const noexcept -> int {
+      return value;
+    }
   };
 
   template <class Env, class... Values>