P3887R1 Make when_all a Ronseal Algorithm

Author: eisenwave

source/exec.tex

@@ -4630,9 +4630,15 @@
 \item
 Otherwise, evaluates:
 \begin{codeblock}
-@\exposid{on_stop}@.reset();
-set_stopped(std::move(rcvr));
+if constexpr (@\placeholder{sends-stopped}@) {
+  @\exposid{on_stop}@.reset();
+  set_stopped(std::move(rcvr));
+}
 \end{codeblock}
+where \tcode{\placeholder{sends-stopped}} equals \tcode{true}
+if and only if there exists an element \tcode{S} of \tcode{Sndrs} such that
+\tcode{completion_signatures_of_t<S, \exposid{when-all-env}<Env>>}
+contains \tcode{set_stopped_t()}.
 \end{itemize}
 
 \pnum
@@ -4645,12 +4651,7 @@
   state.@\exposid{on_stop}@.emplace(
     get_stop_token(get_env(rcvr)),
     @\exposid{on-stop-request}@{state.@\exposid{stop_src}@});
-  if (state.@\exposid{stop_src}@.stop_requested()) {
-    state.@\exposid{on_stop.}@reset();
-    set_stopped(std::move(rcvr));
-  } else {
-    (start(ops), ...);
-  }
+  (start(ops), ...);
 }
 \end{codeblock}