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Fix just_from submit exception specification #2212

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Merged
ericniebler merged 2 commits into from
Aug 18, 2026
Merged

Fix just_from submit exception specification #2212

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9ec59c6
Make just_from submit conditionally noexcept
fallintoplace Aug 16, 2026
5742a1f
Address just_from submit review
fallintoplace Aug 16, 2026
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38 changes: 19 additions & 19 deletions include/exec/just_from.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -30,17 +30,17 @@ namespace experimental::execution

namespace detail
{
auto _just_from(just_from_t*) -> STDEXEC::set_value_t;
auto _just_from(just_error_from_t*) -> STDEXEC::set_error_t;
auto _just_from(just_stopped_from_t*) -> STDEXEC::set_stopped_t;
auto _just_from(just_from_t *) -> STDEXEC::set_value_t;
auto _just_from(just_error_from_t *) -> STDEXEC::set_error_t;
auto _just_from(just_stopped_from_t *) -> STDEXEC::set_stopped_t;
} // namespace detail

template <class JustTag>
struct _just_from
{ // NOLINT(bugprone-crtp-constructor-accessibility)
private:
friend JustTag;
using _set_tag_t = decltype(detail::_just_from(static_cast<JustTag*>(nullptr)));
using _set_tag_t = decltype(detail::_just_from(static_cast<JustTag *>(nullptr)));

using _diag_t = STDEXEC::__if_c<STDEXEC_IS_SAME(_set_tag_t, STDEXEC::set_error_t),
AN_ERROR_COMPLETION_MUST_HAVE_EXACTLY_ONE_ERROR_ARGUMENT,
Expand All @@ -54,11 +54,11 @@ namespace experimental::execution
struct _probe_fn
{
template <class... Ts>
auto operator()(Ts&&... ts) const noexcept -> _error_t<Ts...>;
auto operator()(Ts &&...ts) const noexcept -> _error_t<Ts...>;

template <class... Ts>
requires STDEXEC::__cmplsigs::__is_compl_sig<_set_tag_t(Ts...)>
auto operator()(Ts&&...) const noexcept -> STDEXEC::completion_signatures<_set_tag_t(Ts...)>
auto operator()(Ts &&...) const noexcept -> STDEXEC::completion_signatures<_set_tag_t(Ts...)>
{
return {};
}
Expand All @@ -67,13 +67,13 @@ namespace experimental::execution
template <class Rcvr>
struct _complete_fn
{
Rcvr& _rcvr;
Rcvr &_rcvr;

template <class... Ts>
STDEXEC_ATTRIBUTE(always_inline, host, device)
void operator()(Ts&&... ts) const noexcept
void operator()(Ts &&...ts) const noexcept
{
_set_tag_t()(static_cast<Rcvr&&>(_rcvr), static_cast<Ts&&>(ts)...);
_set_tag_t()(static_cast<Rcvr &&>(_rcvr), static_cast<Ts &&>(ts)...);
}
};

Expand All @@ -89,17 +89,17 @@ namespace experimental::execution
{
if constexpr (STDEXEC::__nothrow_callable<Fn, _complete_fn<Rcvr>>)
{
static_cast<Fn&&>(_fn)(_complete_fn<Rcvr>{_rcvr});
static_cast<Fn &&>(_fn)(_complete_fn<Rcvr>{_rcvr});
}
else
{
STDEXEC_TRY
{
static_cast<Fn&&>(_fn)(_complete_fn<Rcvr>{_rcvr});
static_cast<Fn &&>(_fn)(_complete_fn<Rcvr>{_rcvr});
}
STDEXEC_CATCH_ALL
{
STDEXEC::set_error(static_cast<Rcvr&&>(_rcvr), std::current_exception());
STDEXEC::set_error(static_cast<Rcvr &&>(_rcvr), std::current_exception());
}
}
}
Expand Down Expand Up @@ -149,15 +149,15 @@ namespace experimental::execution
auto connect(Rcvr rcvr) && noexcept(STDEXEC::__nothrow_decay_copyable<Rcvr, Fn>)
-> _opstate<Rcvr, Fn>
{
return _opstate<Rcvr, Fn>{static_cast<Rcvr&&>(rcvr), static_cast<Fn&&>(_fn)};
return _opstate<Rcvr, Fn>{static_cast<Rcvr &&>(rcvr), static_cast<Fn &&>(_fn)};
}

template <class Rcvr>
STDEXEC_ATTRIBUTE(host, device)
auto connect(Rcvr rcvr) const & noexcept(STDEXEC::__nothrow_decay_copyable<Rcvr, Fn const &>)
-> _opstate<Rcvr, Fn>
{
return _opstate<Rcvr, Fn>{static_cast<Rcvr&&>(rcvr), _fn};
return _opstate<Rcvr, Fn>{static_cast<Rcvr &&>(rcvr), _fn};
}

[[nodiscard]]
Expand All @@ -172,17 +172,17 @@ namespace experimental::execution

template <class Rcvr>
STDEXEC_ATTRIBUTE(host, device)
auto submit(Rcvr rcvr) && noexcept -> void
auto submit(Rcvr rcvr) && noexcept(STDEXEC::__nothrow_decay_copyable<Fn>) -> void
{
auto op = static_cast<_sndr_base&&>(*this).connect(static_cast<Rcvr&&>(rcvr));
auto op = static_cast<_sndr_base &&>(*this).connect(static_cast<Rcvr &&>(rcvr));
STDEXEC::start(op);
}

template <class Rcvr>
STDEXEC_ATTRIBUTE(host, device)
auto submit(Rcvr rcvr) const & noexcept -> void
auto submit(Rcvr rcvr) const & noexcept(STDEXEC::__nothrow_decay_copyable<Fn const &>) -> void
{
auto op = this->connect(static_cast<Rcvr&&>(rcvr));
auto op = this->connect(static_cast<Rcvr &&>(rcvr));
STDEXEC::start(op);
}
};
Expand All @@ -203,7 +203,7 @@ namespace experimental::execution
"must return an instance of a specialization of " STDEXEC_PP_STRINGIZE(
STDEXEC) "::completion_signatures<>.");
return _sndr<Fn>{
{{}, static_cast<Fn&&>(fn)}
{{}, static_cast<Fn &&>(fn)}
};
}
else
Expand Down
38 changes: 30 additions & 8 deletions test/exec/test_just_from.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -15,6 +15,7 @@
*/

#include "exec/just_from.hpp"
#include "test_common/receivers.hpp"
#include "test_common/tuple.hpp"
#include "test_common/type_helpers.hpp"

Expand All @@ -26,13 +27,19 @@ namespace

struct throwing_move_callable
{
throwing_move_callable() = default;
throwing_move_callable(throwing_move_callable const &) noexcept = default;
throwing_move_callable(throwing_move_callable &&other) noexcept(false)
explicit throwing_move_callable(bool& should_throw) noexcept
: should_throw_(&should_throw)
{}

throwing_move_callable(throwing_move_callable const & other) noexcept
: should_throw_(other.should_throw_)
{}

throwing_move_callable(throwing_move_callable&& other) noexcept(false)
: should_throw_(other.should_throw_)
{
#if !STDEXEC_NO_STDCPP_EXCEPTIONS()
if (should_throw_)
if (*should_throw_)
{
throw 42;
}
Expand All @@ -45,7 +52,7 @@ namespace
return sink();
}

bool should_throw_{false};
bool* should_throw_;
};

TEST_CASE("just_from is a sender", "[just_from]")
Expand Down Expand Up @@ -94,15 +101,30 @@ namespace
};
STATIC_REQUIRE(noexcept(exec::just_from(nothrow_fn)));

throwing_move_callable fn;
bool should_throw = false;
throwing_move_callable fn{should_throw};
STATIC_REQUIRE_FALSE(noexcept(exec::just_from(fn)));

#if !STDEXEC_NO_STDCPP_EXCEPTIONS()
fn.should_throw_ = true;
should_throw = true;
CHECK_THROWS_AS(exec::just_from(fn), int);
#endif
}

TEST_CASE("just_from submit is conditionally noexcept", "[just_from]")
{
bool should_throw = false;
auto s = exec::just_from(throwing_move_callable{should_throw});

STATIC_REQUIRE_FALSE(noexcept(static_cast<decltype(s)&&>(s).submit(empty_recv::recv0{})));
STATIC_REQUIRE(noexcept(s.submit(empty_recv::recv0{})));

#if !STDEXEC_NO_STDCPP_EXCEPTIONS()
should_throw = true;
CHECK_THROWS_AS(static_cast<decltype(s)&&>(s).submit(empty_recv::recv0{}), int);
#endif
}

TEST_CASE("just_from with multiple completions", "[just_from]")
{
auto fn = [](auto sink) noexcept
Expand Down Expand Up @@ -141,7 +163,7 @@ namespace
global_int = 42;
auto s = exec::just_from([](auto sink) noexcept { return sink(global_int); })
| ex::then(
[](int &i) noexcept
[](int& i) noexcept
{
CHECK(&i == &global_int);
return std::ref(i);
Expand Down
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