From 4c40dc41513ee8be7dce441f0d70ca355ef14d9f Mon Sep 17 00:00:00 2001
From: romintomasetti <romin.tomasetti@gmail.com>
Date: Tue, 6 Oct 2026 06:49:40 +0000
Subject: [PATCH 1/2] stdexec(then): noexcept-ness

Signed-off-by: romintomasetti <romin.tomasetti@gmail.com>
---
 include/stdexec/__detail/__then.hpp       |  1 +
 test/stdexec/algos/adaptors/test_then.cpp | 11 +++++++++++
 2 files changed, 12 insertions(+)

diff --git a/include/stdexec/__detail/__then.hpp b/include/stdexec/__detail/__then.hpp
index 1a86eece8..bbf6a3ddc 100644
--- a/include/stdexec/__detail/__then.hpp
+++ b/include/stdexec/__detail/__then.hpp
@@ -240,6 +240,7 @@ namespace STDEXEC
     template <__movable_value _Fun>
     STDEXEC_ATTRIBUTE(always_inline, host, device)
     constexpr auto operator()(_Fun __fun) const
+      noexcept(__nothrow_decay_copyable<_Fun>)
     {
       return __closure(*this, static_cast<_Fun&&>(__fun));
     }
diff --git a/test/stdexec/algos/adaptors/test_then.cpp b/test/stdexec/algos/adaptors/test_then.cpp
index 88e85e0c3..1292d522d 100644
--- a/test/stdexec/algos/adaptors/test_then.cpp
+++ b/test/stdexec/algos/adaptors/test_then.cpp
@@ -179,6 +179,17 @@ namespace
                                                    | ex::then([] { return std::string{"hello"}; }));
   }
 
+  TEST_CASE("then noexceptness", "[adaptors][then]")
+  {
+    auto func = [](){};
+
+    STATIC_REQUIRE(noexcept(ex::then(func)));
+
+    STATIC_REQUIRE(noexcept(STDEXEC::just() | STDEXEC::then(func)));
+
+    STATIC_REQUIRE(noexcept(STDEXEC::then(STDEXEC::just(), func)));
+  }
+
   TEST_CASE("then keeps error_types from input sender", "[adaptors][then]")
   {
     inline_scheduler     sched1{};

From 7d3ea15a3b120e381946cdb34287d73c721891f0 Mon Sep 17 00:00:00 2001
From: romintomasetti <romin.tomasetti@gmail.com>
Date: Mon, 5 Oct 2026 17:45:28 +0000
Subject: [PATCH 2/2] exec(fork_join): coalesce empty and unary calls

Similar to https://github.com/NVIDIA/stdexec/pull/2124. See  P4269R1.

Signed-off-by: romintomasetti <romin.tomasetti@gmail.com>
---
 include/exec/fork_join.hpp   | 24 ++++++++++++++++++++++--
 test/exec/test_fork_join.cpp | 24 ++++++++++++++++++++++++
 2 files changed, 46 insertions(+), 2 deletions(-)

diff --git a/include/exec/fork_join.hpp b/include/exec/fork_join.hpp
index 921c84d86..c306dbd66 100644
--- a/include/exec/fork_join.hpp
+++ b/include/exec/fork_join.hpp
@@ -281,9 +281,28 @@ namespace experimental::execution
 
   struct fork_join_t
   {
-    template <STDEXEC::sender Sndr, class... Closures>
+    /// No closure given.
+    template <STDEXEC::sender Sndr>
     STDEXEC_ATTRIBUTE(host, device)
-    constexpr auto operator()(Sndr&& sndr, Closures&&... closures) const  //
+    constexpr auto operator()(Sndr&& sndr) const noexcept(STDEXEC::__nothrow_decay_copyable<Sndr>)
+    {
+      return static_cast<Sndr&&>(sndr);
+    }
+
+    /// Unary closure.
+    template <STDEXEC::sender Sndr, class Closure> requires (!STDEXEC::sender<Closure>)
+    STDEXEC_ATTRIBUTE(host, device)
+    constexpr auto operator()(Sndr&& sndr, Closure&& clsr) const
+      noexcept(STDEXEC::__nothrow_callable<Closure, Sndr>)
+    {
+      return static_cast<Closure&&>(clsr)(static_cast<Sndr&&>(sndr));
+    }
+
+    /// One sender and multiple closures.
+    template <STDEXEC::sender Sndr, class... Closures> requires (sizeof...(Closures) > 1)
+    STDEXEC_ATTRIBUTE(host, device)
+    constexpr auto operator()(Sndr&& sndr, Closures&&... closures) const
+      noexcept(STDEXEC::__nothrow_decay_copyable<Sndr, Closures...>)
       -> STDEXEC::__well_formed_sender auto
     {
       return STDEXEC::__sexpr{fork_join_t(),
@@ -291,6 +310,7 @@ namespace experimental::execution
                               static_cast<Sndr&&>(sndr)};
     }
 
+    /// One or more closures.
     template <class... Closures>
       requires((!STDEXEC::sender<Closures>) && ...)
     STDEXEC_ATTRIBUTE(host, device)
diff --git a/test/exec/test_fork_join.cpp b/test/exec/test_fork_join.cpp
index a2d6d41b7..05006230d 100644
--- a/test/exec/test_fork_join.cpp
+++ b/test/exec/test_fork_join.cpp
@@ -43,6 +43,30 @@ namespace
                      completion_signatures<set_value_t(), set_error_t(std::exception_ptr)>>);
   }
 
+  TEST_CASE("fork_join coalesces empty and unary calls", "[adaptors][fork_join]")
+  {
+    /// Empty (no closure given).
+    STDEXEC::sender auto empty = exec::fork_join(STDEXEC::just());
+    using empty_t = decltype(empty);
+    STATIC_REQUIRE(std::same_as<empty_t, decltype(STDEXEC::just())>);
+    STATIC_REQUIRE(!exec::sender_for<empty_t, exec::fork_join_t>);
+    STATIC_REQUIRE(noexcept(exec::fork_join(STDEXEC::just())));
+
+    auto then = STDEXEC::then([]() noexcept {});
+
+    /// Unary closure.
+    STDEXEC::sender auto unary = exec::fork_join(STDEXEC::just(), then);
+    using unary_t = decltype(unary);
+    STATIC_REQUIRE(std::same_as<unary_t, decltype(STDEXEC::just() | then)>);
+    STATIC_REQUIRE(!exec::sender_for<unary_t, exec::fork_join_t>);
+    STATIC_REQUIRE(noexcept(exec::fork_join(STDEXEC::just(), then)));
+
+    /// Multiple closures.
+    STDEXEC::sender auto multiple = STDEXEC::just() | exec::fork_join(then, then);
+    STATIC_REQUIRE(exec::sender_for<decltype(multiple), exec::fork_join_t>);
+    STATIC_REQUIRE(noexcept(exec::fork_join(STDEXEC::just(), then, then)));
+  }
+
   struct ForwardingThen
   {
     template <typename Value>