Fix read_with_default connect noexcept (#2208)

* Fix read_with_default connect noexcept

* Format Clang sources

* Format read_with_default changes

* Guard read_with_default exception test

---------

Co-authored-by: Eric Niebler <eniebler@nvidia.com>

Author: fallintoplace

include/exec/env.hpp

@@ -180,8 +180,10 @@ namespace experimental::execution
 
       template <__decays_to<__sender> _Self, class _Receiver>
       constexpr STDEXEC_EXPLICIT_THIS_BEGIN(auto connect)(this _Self&& __self, _Receiver __rcvr)
-        noexcept(std::is_nothrow_move_constructible_v<_Receiver>)
-          -> __opstate<_Query, __default_t<env_of_t<_Receiver>>, _Receiver>
+        noexcept(__nothrow_constructible_from<
+                 __opstate<_Query, __default_t<env_of_t<_Receiver>>, _Receiver>,
+                 __default_t<env_of_t<_Receiver>>,
+                 _Receiver>) -> __opstate<_Query, __default_t<env_of_t<_Receiver>>, _Receiver>
       {
         using __opstate_t = __opstate<_Query, __default_t<env_of_t<_Receiver>>, _Receiver>;
         return __opstate_t{static_cast<_Self&&>(__self).__default_,

test/exec/test_env.cpp

@@ -23,6 +23,53 @@
 
 namespace
 {
+#if !STDEXEC_NO_STDCPP_EXCEPTIONS()
+  struct missing_query : STDEXEC::__query<missing_query>
+  {
+    using STDEXEC::__query<missing_query>::operator();
+  };
+
+  struct default_move_error
+  {};
+
+  struct throwing_default
+  {
+    explicit throwing_default(bool* throw_on_move) noexcept
+      : throw_on_move_{throw_on_move}
+    {}
+
+    throwing_default(throwing_default const &) noexcept = default;
+
+    throwing_default(throwing_default&& other)
+      : throw_on_move_{other.throw_on_move_}
+    {
+      if (*throw_on_move_)
+      {
+        throw default_move_error{};
+      }
+    }
+
+    bool* throw_on_move_;
+  };
+
+  struct read_with_default_receiver
+  {
+    using receiver_concept = STDEXEC::receiver_tag;
+
+    template <class _Value>
+    void set_value(_Value&&) noexcept
+    {}
+
+    void set_error(std::exception_ptr) noexcept {}
+    void set_stopped() noexcept {}
+
+    auto get_env() const noexcept -> STDEXEC::env<>
+    {
+      return {};
+    }
+  };
+#endif  // !STDEXEC_NO_STDCPP_EXCEPTIONS()
+
   // Two dummy properties:
   constexpr struct Foo
     : STDEXEC::__query<Foo>
@@ -57,6 +104,18 @@ namespace
     CHECK(bar(e4) == 43);
   }
 
+#if !STDEXEC_NO_STDCPP_EXCEPTIONS()
+  TEST_CASE("read_with_default connect propagates default move exceptions", "[env]")
+  {
+    bool throw_on_move = false;
+    auto sndr          = exec::read_with_default(missing_query{}, throwing_default{&throw_on_move});
+    throw_on_move      = true;
+
+    STATIC_REQUIRE_FALSE(noexcept(std::move(sndr).connect(read_with_default_receiver{})));
+    CHECK_THROWS_AS(std::move(sndr).connect(read_with_default_receiver{}), default_move_error);
+  }
+#endif  // !STDEXEC_NO_STDCPP_EXCEPTIONS()
+
   TEST_CASE("without propagates environment move exceptions", "[env]")
   {
     struct missing_query : STDEXEC::__query<missing_query>