MSVC: disable [[msvc::no_unique_address]] due to incorrect codegen

include/stdexec/__detail/__config.hpp

@@ -345,11 +345,14 @@ namespace STDEXEC::__std
 #define STDEXEC_ATTRIBUTE_CASE_DEFAULT(...)              [[__VA_ARGS__]]
 
 // [[no_unique_address]]
-#if (STDEXEC_NVHPC() && STDEXEC_NVHPC_VERSION < 2305)                                              \
-  || (STDEXEC_MSVC() && STDEXEC_MSVC_VERSION < 1943)                                               \
+// MSVCBUG https://developercommunity.visualstudio.com/t/Incorrect-codegen-when-using-msvc::no_/10452874
+// [[msvc::no_unique_address]] still miscompiles on current MSVC, overrunning stack objects
+// and corrupting data (see https://github.com/NVIDIA/stdexec/issues/2099), so it is disabled
+// for all MSVC versions until a fixed compiler can be gated on.
+#if (STDEXEC_NVHPC() && STDEXEC_NVHPC_VERSION < 2305) || STDEXEC_MSVC()                            \
   || (STDEXEC_CLANG_CL() && STDEXEC_CLANG_VERSION < 1801)
 #  define STDEXEC_ATTRIBUTE_CASE_NO_UNIQUE_ADDRESS
-#elif STDEXEC_CLANG_CL() || STDEXEC_MSVC()
+#elif STDEXEC_CLANG_CL()
 #  define STDEXEC_ATTRIBUTE_CASE_NO_UNIQUE_ADDRESS       [[msvc::no_unique_address]]
 #else
 #  define STDEXEC_ATTRIBUTE_CASE_NO_UNIQUE_ADDRESS       [[no_unique_address]]

test/exec/test_fork_join.cpp

@@ -224,13 +224,7 @@ namespace
 
     CHECK(counter::copy_constructions == 0);
     CHECK(counter::copy_assignments == 0);
-#if STDEXEC_MSVC()
-    // TODO: MSVC drops the initialization entirely, even though there is an observable side effect (atomic increment).
-    //       See https://github.com/NVIDIA/stdexec/pull/2302#issuecomment-6110273094.
-    CHECK(counter::move_constructions == 0);
-#else
     CHECK(counter::move_constructions == 1);
-#endif
     CHECK(counter::move_assignments == 0);
 
     CHECK(witness == 2);

test/stdexec/algos/adaptors/test_let_value.cpp

@@ -29,6 +29,7 @@
 import std;
 #else
 #  include <chrono>  // IWYU pragma: keep for chrono_literals
+#  include <cstdint>
 #  include <exception>
 #  include <memory>
 #endif
@@ -82,6 +83,24 @@ namespace
     STDEXEC::sync_wait(std::move(snd));
   }
 
+  // Regression test for https://github.com/NVIDIA/stdexec/issues/2099: MSVC miscompiled
+  // the layout of [[msvc::no_unique_address]] members, so constructing this sender wrote
+  // past the end of a stack temporary and corrupted the captured values.
+  TEST_CASE("let_value preserves a function's captures alongside a nested sender",
+            "[adaptors][let_value]")
+  {
+    auto work = ex::just() | ex::let_value([] { return ex::just(); });
+    auto snd  = ex::just(std::uintptr_t{0x1111})
+             | ex::let_value([sentinel = 0x5A5A5A5A, work](std::uintptr_t v)
+                             {
+                               (void) work;
+                               return ex::just(sentinel, v);
+                             });
+    auto [sentinel, v] = STDEXEC::sync_wait(std::move(snd)).value();
+    CHECK(sentinel == 0x5A5A5A5A);
+    CHECK(v == 0x1111);
+  }
+
   TEST_CASE("let_value can be used to produce values", "[adaptors][let_value]")
   {
     ex::sender auto snd = ex::just() | ex::let_value([] { return ex::just(13); });