Proposed resolution:

This wording is relative to N5001.

1. Change [exec.snd.expos] as indicated:

   -2- For a queryable object `env`, FWD-ENV(env) is an expression whose type satisfies `queryable` such that for a query object `q` and a pack of subexpressions `as`, the expression FWD-ENV(env).query(q, as...) is ill-formed if `forwarding_query(q)` is `false`; otherwise, it is expression-equivalent to `env.query(q, as...)`. The type FWD-ENV-T(Env) is decltype(FWD-ENV(declval<Env>())).

2. Change [exec.schedule.from] as indicated:

   -6- The member impls-for<schedule_from_t>::get-state is initialized with a callable object equivalent to the following lambda:

     []<class Sndr, class Rcvr>(Sndr&& sndr, Rcvr& rcvr) noexcept(see below)
      requires sender_in<child-type<Sndr>, FWD-ENV-T(env_of_t<Rcvr>)> {
   

   …

   -8- Let `Sigs` be a pack of the arguments to the `completion_signatures` specialization named by completion_signatures_of_t<child-type<Sndr>, FWD-ENV-T(env_of_t<Rcvr>)>. Let as-tuple be an alias template that transforms a completion signature Tag(Args...) into the tuple specialization decayed-tuple<Tag, Args...>. Then variant_t denotes the type variant<monostate, as-tuple<Sigs>...>, except with duplicate types removed.

3. Change [exec.let] as indicated:

   -6- Let `receiver2` denote the following exposition-only class template:

     namespace std::execution {
       …
     }
   

   Invocation of the function receiver2::get_env returns an object `e` such that

   1. (6.1) — `decltype(e)` models `queryable` and
   2. (6.2) — given a query object `q`, the expression `e.query(q)` is expression-equivalent to env.query(q) if that expression is valid,; otherwise, if the type of `q` satisfies `forwarding-query`, `e.query(q)` is expression-equivalent to get_env(rcvr).query(q) ; otherwise, `e.query(q)` is ill-formed.

   -7- impls-for<decayed-typeof<let-cpo>>::get-state is initialized with a callable object […]

   -8- Let `Sigs` be a pack of the arguments to the `completion_signatures` specialization named by completion_signatures_of_t<child-type<Sndr>, FWD-ENV-T(env_of_t<Rcvr>)>. Let `LetSigs` be a pack of those types in `Sigs` with a return type of decayed-typeof<set-cpo>. Let `as-tuple` be an alias template such that as-tuple<Tag(Args...)> denotes the type decayed-tuple<Args...>. Then `args_variant_t` denotes the type variant<monostate, as-tuple<LetSigs>...> except with duplicate types removed.

4. Change [exec.when.all] as indicated:

   -6- The member impls-for<when_all_t>::get-env is initialized with a callable object equivalent to the following lambda expression:

     []<class State, class Rcvr>(auto&&, State& state, const Receiver& rcvr) noexcept {
       return see below;
     }
   

   Returns an object `e` such that

   1. (6.1) — `decltype(e)` models `queryable`, and
   2. (6.2) — `e.query(get_stop_token)` is expression-equivalent to state.stop-src.get_token(), and
   3. (6.3) — given a query object `q` with type other than cv `stop_token_t` and whose type satisfies `forwarding-query`, `e.query(q)` is expression-equivalent to `get_env(rcvr).query(q)`.

   -7- The member impls-for<when_all_t>::get-state is initialized with a callable object equivalent to the following lambda expression:

     []<class Sndr, class Rcvr>(Sndr&& sndr, Rcvr& rcvr) noexcept(e) -> decltype(e) {
       return e;
     }
   

   where e is the expression

     std::forward<Sndr>(sndr).apply(make-state<Rcvr>())
   

   and `make-state` is the following exposition-only class template:

     template<class Sndr, class Env>
     concept max-1-sender-in = sender_in<Sndr, Env> && // exposition only
       (tuple_size_v<value_types_of_t<Sndr, Env, tuple, tuple>> <= 1);
   
     enum class disposition { started, error, stopped }; // exposition only
   
     template<class Rcvr>
     struct make-state {
      template<max-1-sender-in<FWD-ENV-T(env_of_t<Rcvr>)>... Sndrs>
   

   …

   -8- Let `copy_fail` be `exception_ptr` if […]

   -9- The alias `values_tuple` denotes the type

     tuple<value_types_of_t<Sndrs, FWD-ENV-T(env_of_t<Rcvr>), decayed-tuple, optional>...>
   

   if that type is well-formed; otherwise, tuple<>.

5. Change [exec.into.variant] as indicated:

   -5- The member impls-for<into_variant_t>::get-state is initialized with a callable object equivalent to the following lambda:

     []<class Sndr, class Rcvr>(Sndr&& sndr, Rcvr& rcvr) noexcept
       -> type_identity<value_types_of_t<child-type<Sndr>, FWD-ENV-T(env_of_t<Rcvr>)>> {
       return {};
     }
   

6. Change [exec.stopped.opt] as indicated:

   -3- Let `sndr` and `env` be subexpressions such that `Sndr` is `decltype((sndr))` and `Env` is `decltype((env))`. If sender-for<Sndr, stopped_as_optional_t> is `false`, or if the type single-sender-value-type<child-type<Sndr>, FWD-ENV-T(Env)> is ill-formed or `void`, then the expression `stopped_as_optional.transform_sender(sndr, env)` is ill-formed; otherwise, it is equivalent to:

     auto&& [_, _, child] = sndr;
     using V = single-sender-value-type<child-type<Sndr>, FWD-ENV-T(Env)>;
   

   …

[ 2025-02-07; Reflector poll ]

Set priority to 1 after reflector poll.

[ The resolution touches some of the same text as LWG 4198, but without conflicting. ]

Imported from: cplusplus/sender-receiver #315.

[exec.when.all] p6 reads:

The member impls-for<when_all_t>::get-env is initialized with a callable object equivalent to the following lambda expression:

  []<class State, class Rcvr>(auto&&, State& state, const Receiver& rcvr) noexcept {
    return see below;
  }

Returns an object `e` such that

1. (6.1) — `decltype(e)` models `queryable`, and
2. (6.2) — `e.query(get_stop_token)` is expression-equivalent to state.stop-src.get_token(), and
3. (6.3) — given a query object `q` with type other than cv `stop_token_t`, `e.query(q)` is expression-equivalent to `get_env(rcvr).query(q)`.

Imported from: cplusplus/sender-receiver #316.

The child senders should only see the parent's queries if they are forwarding queries.

Imported from: cplusplus/sender-receiver #311.

[exec.stopped.opt]/para 3 reads:

Let `sndr` and `env` be subexpressions such that `Sndr` is `decltype((sndr))` and `Env` is `decltype((env))`. If sender-for<Sndr, stopped_as_optional_t> is `false`, or if the type single-sender-value-type<Sndr, Env> is ill-formed or `void`, then the expression `stopped_as_optional.transform_sender(sndr, env)` is ill-formed; otherwise, it is equivalent to:

In addition, it should be applying `FWD-ENV-T` to `Env` so that only forwarding queries are forwarded.

Imported from: cplusplus/sender-receiver #313 and cplusplus/sender-receiver #314.

[exec.schedule.from] p6 reads:

The member impls-for<schedule_from_t>::get-state is initialized with a callable object equivalent to the following lambda:

  []<class Sndr, class Rcvr>(Sndr&& sndr, Rcvr& rcvr) noexcept(see below)
     requires sender_in<child-type<Sndr>, env_of_t<Rcvr>> {