Add more sender-receiver issues to 4203

Author: jwakely

xml/issue4203.xml

@@ -2,24 +2,26 @@
 <!DOCTYPE issue SYSTEM "lwg-issue.dtd">
 
 <issue num="4203" status="New">
-<title>constraints on `schedule_from`'s <i>`get-state`</i> function are incorrect</title>
+<title>Constraints on <i>`get-state`</i> functions are incorrect</title>
 <section><sref ref="[exec.schedule.from]"/></section>
 <submitter>Eric Niebler</submitter>
 <date>03 Feb 2025</date>
 <priority>99</priority>
 
 <discussion>
 <p>
-Imported from <a href="https://github.com/cplusplus/sender-receiver/issues/313">cplusplus/sender-receiver #313</a>.
+Imported from:
+<a href="https://github.com/cplusplus/sender-receiver/issues/313">cplusplus/sender-receiver #313</a>
+and
+<a href="https://github.com/cplusplus/sender-receiver/issues/314">cplusplus/sender-receiver #314</a>.
 </p>
 <p>
 <sref ref="[exec.schedule.from]"/> p6 reads:
 
 <blockquote>
 The member <code><i>impls-for</i>&lt;schedule_from_t&gt;::get-state</code>
 is initialized with a callable object equivalent to the following lambda:
-<pre><code>
-  []&lt;class Sndr, class Rcvr&gt;(Sndr&amp;&amp; sndr, Rcvr&amp; rcvr) noexcept(<i>see below</i>)
+<pre><code>  []&lt;class Sndr, class Rcvr&gt;(Sndr&amp;&amp; sndr, Rcvr&amp; rcvr) noexcept(<i>see below</i>)
      requires sender_in&lt;<i>child-type</i>&lt;Sndr&gt;, env_of_t&lt;Rcvr&gt;&gt; {
 </code></pre>
 </blockquote>
@@ -28,7 +30,74 @@ The constraint should account for the fact that the child sender will
 be connected with <code><i>FWD-ENV</i>(get_env(rcvr))</code>.
 </p>
 
-<note>The resolution touches the same text as LWG <iref ref="4198"/>.</note>
+<note>
+The resolution touches some of the same text as LWG <iref ref="4198"/>,
+but without conflicting.
+</note>
+
+<p>
+Imported from:
+<a href="https://github.com/cplusplus/sender-receiver/issues/315">cplusplus/sender-receiver #315</a>.
+</p>
+<p>
+<sref ref="[exec.when.all]"/> p6 reads:
+
+<blockquote>
+The member <code>impls-for&lt;when_all_t&gt;::<i>get-env</i></code>
+is initialized with a callable object equivalent to the following lambda
+expression:
+<pre><code>  []&lt;class State, class Rcvr&gt;(auto&amp;&amp;, State&amp; state, const Receiver&amp; rcvr) noexcept {
+    return <i>see below</i>;
+  }
+</code></pre>
+Returns an object `e` such that
+<ol style="list-style-type:none">
+<li>(6.1) &mdash; `decltype(e)` models <i>`queryable`</i>, and</li>
+<li>(6.2) &mdash; `e.query(get_stop_token)` is expression-equivalent to
+<code>state.<i>stop-src</i>.get_token()</code>, and</li>
+<li>(6.3) &mdash;
+given a query object `q` with type other than <i>cv</i> `stop_token_t`,
+`e.query(q)` is expression-equivalent to `get_env(rcvr).query(q)`.
+</li>
+</ol>
+</blockquote>
+
+The problem is in (6.3). It should be forwarding on <i>`forwarding-query`</i>'s
+to `get_env(rcvr)` but is is instead forwarding all queries.
+</p>
+
+<p>
+Imported from:
+<a href="https://github.com/cplusplus/sender-receiver/issues/316">cplusplus/sender-receiver #316</a>.
+</p>
+<p>
+The child senders should only see the parent's queries if they are forwarding queries.
+</p>
+
+<p>
+Imported from:
+<a href="https://github.com/cplusplus/sender-receiver/issues/311">cplusplus/sender-receiver #311</a>.
+</p>
+
+<p>
+<sref ref="[exec.stopped.opt]"/>/para 3 reads:
+
+<blockquote>
+Let `sndr` and `env` be subexpressions such that `Sndr` is `decltype((sndr))`
+and `Env` is `decltype((env))`.
+If <code><i>sender-for</i>&lt;Sndr, stopped_as_optional_t&gt;</code> is `false`,
+or if the type <code><i>single-sender-value-type</i>&lt;Sndr, Env&gt;</code>
+is ill-formed or `void`,
+then the expression `stopped_as_optional.transform_sender(sndr, env)`
+is ill-formed; otherwise, it is equivalent to:
+</blockquote>
+the test for <code>single-sender-value-type&lt;Sndr, Env&gt;</code> is incorrect.
+It should be testing its child for single-sender-ness.
+</p>
+<p>
+In addition, it should be applying <i>`FWD-ENV-T`</i> to `Env`
+so that only forwarding queries are forwarded.
+</p>
 
 </discussion>
 
@@ -65,8 +134,7 @@ Change <sref ref="[exec.schedule.from]"/> as indicated:
 The member
 <code><i>impls-for</i>&lt;schedule_from_t&gt;::<i>get-state</i></code>
 is initialized with a callable object equivalent to the following lambda:
-<pre><code>
-  []&lt;class Sndr, class Rcvr&gt;(Sndr&amp;&amp; sndr, Rcvr&amp; rcvr) noexcept(<i>see below</i>)
+<pre><code>  []&lt;class Sndr, class Rcvr&gt;(Sndr&amp;&amp; sndr, Rcvr&amp; rcvr) noexcept(<i>see below</i>)
    requires sender_in&lt;child-type&lt;Sndr&gt;, <ins><i>FWD-ENV-T</i>(</ins>env_of_t&lt;Rcvr&gt;<ins>)</ins>&gt; {
 </code></pre>
 <p>&hellip;</p>
@@ -86,6 +154,157 @@ except with duplicate types removed.
 </p>
 </blockquote>
 </li>
+
+<li>
+Change <sref ref="[exec.let]"/> as indicated:
+
+<blockquote>
+<p>
+-6-
+Let <i>`receiver2`</i> denote the following exposition-only class template:
+<pre><code>  namespace std::execution {
+    &hello;
+  }
+</code></pre>
+Invocation of the function <code><i>receiver2</i>::get_env</code>
+returns an object `e` such that
+<ol style="list-style-type:none">
+<li>(6.1) &mdash;
+`decltype(e)` models <i>`queryable`</i> and
+</li>
+<li>(6.2) &mdash;
+given a query object `q`, the expression `e.query(q)` is expression-equivalent
+to
+<code><i>env</i>.query(q)</code>
+if that expression is valid<del>,</del><ins>;</ins>
+otherwise,
+<ins>if the type of `q` satisfies <i>`forwarding-query`</i>,</ins>
+`e.query(q)` is expression-equivalent to
+<code>get_env(<i>rcvr</i>).query(q)</code>
+<ins>; otherwise, `e.query(q)` is ill-formed</ins>.
+</li>
+</ol>
+</p>
+<p>
+-7-
+<code><i>impls-for</i>&lt;<i>decayed-typeof</i>&lt;<i>let-cpo</i>&gt;&gt;::<i>get-state</i></code>
+is initialized with a callable object [&hellip;]
+</p>
+<p>
+-8-
+Let `Sigs` be a pack of the arguments to the `completion_signatures`
+specialization named by
+<code>completion_signatures_of_t&lt;<i>child-type</i>&lt;Sndr&gt;,
+<ins><i>FWD-ENV-T</i>(</ins>env_of_t&lt;Rcvr&gt;<ins>)</ins>&gt;</code>.
+Let `LetSigs` be a pack of those types in `Sigs` with a return type of
+<code><i>decayed-typeof</i>&lt;<i>set-cpo</i>&gt;</code>.
+Let `as-tuple` be an alias template such that
+<code><i>as-tuple</i>&lt;Tag(Args...)&gt;</code>
+denotes the type <code><i>decayed-tuple</i>&lt;Args...&gt;</code>.
+Then `args_variant_t` denotes the type
+<code>variant&lt;monostate, <i>as-tuple</i>&lt;LetSigs&gt;...&gt;</code>
+except with duplicate types removed.
+</p>
+</blockquote>
+</li>
+
+<li>
+Change <sref ref="[exec.when.all]"/> as indicated:
+
+<blockquote>
+<p>
+-6-
+The member <code>impls-for&lt;when_all_t&gt;::<i>get-env</i></code>
+is initialized with a callable object equivalent to the following lambda
+expression:
+<pre><code>  []&lt;class State, class Rcvr&gt;(auto&amp;&amp;, State&amp; state, const Receiver&amp; rcvr) noexcept {
+    return <i>see below</i>;
+  }
+</code></pre>
+Returns an object `e` such that
+<ol style="list-style-type:none">
+<li>(6.1) &mdash; `decltype(e)` models <i>`queryable`</i>, and</li>
+<li>(6.2) &mdash; `e.query(get_stop_token)` is expression-equivalent to
+<code>state.<i>stop-src</i>.get_token()</code>, and</li>
+<li>(6.3) &mdash;
+given a query object `q` with type other than <i>cv</i> `stop_token_t`
+<ins>and whose type satisfies <i>`forwarding-query`</i></ins>,
+`e.query(q)` is expression-equivalent to `get_env(rcvr).query(q)`.
+</li>
+</ol>
+</p>
+<p>
+-7-
+The member <code><i>impls-for</i>&lt;when_all_t&gt;::<i>get-state</i></code>
+is initialized with a callable object equivalent to the following
+lambda expression:
+<pre><code>  []&lt;class Sndr, class Rcvr&gt;(Sndr&amp;&amp; sndr, Rcvr&amp; rcvr) noexcept(e) -&gt; decltype(e) {
+    return <i>e</i>;
+  }
+</code></pre>
+where <i>e</i> is the expression
+<pre><code>  std::forward&lt;Sndr&gt;(sndr).apply(<i>make-state</i>&lt;Rcvr&gt;())
+</code></pre>
+and <i>`make-state`</i> is the following exposition-only class template:
+<pre><code>  template&lt;class Sndr, class Env&gt;
+  concept max-1-sender-in = sender_in&lt;Sndr, Env&gt; &amp;&amp; <i>// exposition only</i>
+    (tuple_size_v&lt;value_types_of_t&lt;Sndr, Env, tuple, tuple&gt;&gt; &lt;= 1);
+
+  enum class <i>disposition</i> { <i>started</i>, <i>error</i>, <i>stopped</i> }; <i>// exposition only</i>
+
+  template&lt;class Rcvr&gt;
+  struct make-state {
+   template&lt;max-1-sender-in&lt;<ins><i>FWD-ENV-T</i>(</ins>env_of_t&lt;Rcvr&gt;<ins>)</ins>&gt;... Sndrs&gt;
+</code></pre>
+&hellip;
+</p>
+<p>
+-8- Let <i>`copy_fail`</i> be `exception_ptr` if [&hellip;]
+</p>
+<p>
+-9-
+The alias `values_tuple` denotes the type
+<pre><code>  tuple&lt;value_types_of_t&lt;Sndrs, <ins><i>FWD-ENV-T</i>(</ins>env_of_t&lt;Rcvr&gt;<ins>)</ins>, <i>decayed-tuple</i>, optional&gt;...&gt;
+</code></pre>
+if that type is well-formed; otherwise, <code>tuple&lt;&gt;</code>.
+</p>
+</blockquote>
+</li>
+
+<li>
+Change <sref ref="[exec.into.variant]"/> as indicated:
+
+<blockquote>
+-5-
+The member <code>impls-for&lt;into_variant_t&gt;::<i>get-state</i></code>
+is initialized with a callable object equivalent to the following lambda:
+<pre><code>  []&lt;class Sndr, class Rcvr&gt;(Sndr&amp;&amp; sndr, Rcvr&amp; rcvr) noexcept
+    -&gt; type_identity&lt;value_types_of_t&lt;<i>child-type</i>&lt;Sndr&gt;, <ins><i>FWD-ENV-T</i>(</ins>env_of_t&lt;Rcvr&gt;<ins>)</ins>&gt;&gt; {
+    return {};
+  }
+</code></pre>
+</blockquote>
+</li>
+
+<li>
+Change <sref ref="[exec.stopped.opt]"/> as indicated:
+
+<blockquote>
+-3-
+Let `sndr` and `env` be subexpressions such that `Sndr` is `decltype((sndr))`
+and `Env` is `decltype((env))`.
+If <code><i>sender-for</i>&lt;Sndr, stopped_as_optional_t&gt;</code> is `false`,
+or if the type <code><i>single-sender-value-type</i>&lt;<ins><i>child-type</i>&lt;</ins>Sndr<ins>&gt;</ins>, <ins><i>FWD-ENV-T</i>(</ins>Env<ins>)</ins>&gt;</code>
+is ill-formed or `void`,
+then the expression `stopped_as_optional.transform_sender(sndr, env)`
+is ill-formed; otherwise, it is equivalent to:
+<pre><code>  auto&amp;&amp; [_, _, child] = sndr;
+  using V = <i>single-sender-value-type</i>&lt;<ins><i>child-type</i>&lt;</ins>Sndr<ins>&gt;</ins>, <ins><i>FWD-ENV-T</i>(</ins>Env<ins>)</ins>&gt;;
+</code></pre>
+&hellip;
+</blockquote>
+</li>
+
 </ol>
 
 </resolution>