fix bug in domain handling that permits when_all(a,b) when a and b have different completion domains

Author: ericniebler

include/nvexec/stream/common.cuh

@@ -142,7 +142,7 @@ namespace nv::execution
 {
   // The stream_domain is how the stream scheduler customizes the sender algorithms. All of the
   // algorithms use the current scheduler's domain to transform senders before starting them.
-  struct stream_domain : STDEXEC::default_domain
+  struct stream_domain
   {
     template <::exec::sender_for Sender, class Tag = STDEXEC::tag_of_t<Sender>, class Env>
       requires _strm::has_stream_transform<Sender, Env>

include/stdexec/__detail/__domain.hpp

@@ -96,16 +96,10 @@ namespace STDEXEC
   //! @c default_domain when passed the same arguments. The concept is modeled when either
   //! of the following is
   template <class _Domain, class _OpTag, class _Sndr, class _Env>
-  concept __default_domain_like = __same_as<
-    __decay_t<__detail::__transform_sender_result_t<default_domain, _OpTag, _Sndr, _Env>>,
-    __decay_t<__mcall<
-      __mtry_catch_q<
-        __detail::__transform_sender_result_t,
-        __mconst<__detail::__transform_sender_result_t<default_domain, _OpTag, _Sndr, _Env>>>,
-      _Domain,
-      _OpTag,
-      _Sndr,
-      _Env>>>;
+  concept __default_domain_like =
+    (!__detail::__has_transform_sender<_Domain, _OpTag, _Sndr, _Env>)
+    || __same_as<__detail::__transform_sender_result_t<_Domain, _OpTag, _Sndr, _Env>,
+                 __detail::__transform_sender_result_t<default_domain, _OpTag, _Sndr, _Env>>;
 
   template <class... _Domains>
   struct indeterminate_domain
@@ -127,15 +121,14 @@ namespace STDEXEC
     //! same arguments. If this check fails, the @c static_assert triggers with: "ERROR:
     //! indeterminate domains: cannot pick an algorithm customization"
     template <class _OpTag, class _Sndr, class _Env>
-      requires __detail::__has_transform_sender<tag_of_t<_Sndr>, _OpTag, _Sndr, _Env>
     [[nodiscard]]
     static constexpr auto transform_sender(_OpTag, _Sndr &&__sndr, _Env const &__env)
-      noexcept(__detail::__has_nothrow_transform_sender<tag_of_t<_Sndr>, _OpTag, _Sndr, _Env>)
-        -> __detail::__transform_sender_result_t<tag_of_t<_Sndr>, _OpTag, _Sndr, _Env>
+      noexcept(__detail::__has_nothrow_transform_sender<default_domain, _OpTag, _Sndr, _Env>)
+        -> __detail::__transform_sender_result_t<default_domain, _OpTag, _Sndr, _Env>
     {
       static_assert((__default_domain_like<_Domains, _OpTag, _Sndr, _Env> && ...),
                     "ERROR: indeterminate domains: cannot pick an algorithm customization");
-      return tag_of_t<_Sndr>{}.transform_sender(_OpTag{}, static_cast<_Sndr &&>(__sndr), __env);
+      return default_domain().transform_sender(_OpTag{}, static_cast<_Sndr &&>(__sndr), __env);
     }
   };
 

test/nvexec/CMakeLists.txt

@@ -62,3 +62,11 @@ target_link_libraries(test.nvexec
 # endif()
 
 catch_discover_tests(test.nvexec PROPERTIES TIMEOUT 30)
+
+icm_add_build_failure_test(
+    NAME when_all_fail
+    TARGET when_all_fail
+    SOURCES PARSE when_all_fail.cu
+    LIBRARIES stdexec nvexec
+    FOLDER test
+)

test/nvexec/when_all_fail.cu

@@ -0,0 +1,35 @@
+/*
+ * Copyright (c) 2021-2024 NVIDIA Corporation
+ *
+ * Licensed under the Apache License Version 2.0 with LLVM Exceptions
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ *   https://llvm.org/LICENSE.txt
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <stdexec/execution.hpp>
+
+#include <exec/single_thread_context.hpp>
+#include <nvexec/stream_context.cuh>
+
+namespace ex = STDEXEC;
+
+auto main() -> int
+{
+  nvexec::stream_context      stream_ctx{};
+  exec::single_thread_context thread_ctx{};
+
+  auto sndr = ex::when_all(ex::schedule(stream_ctx.get_scheduler()),
+                           ex::schedule(thread_ctx.get_scheduler()))
+            | ex::continues_on(thread_ctx.get_scheduler());
+
+  // build error: ERROR: indeterminate domains: cannot pick an algorithm customization
+  ex::sync_wait(std::move(sndr));
+}