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repeat_* noexcept fixes #1797

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justend29 wants to merge 4 commits into from
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repeat_* noexcept fixes #1797

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88883af
Clean repeat_ states
justend29 Jan 26, 2026
2d1467e
Merge remote-tracking branch 'origin' into repeat-noexcept-fixes
justend29 Jan 27, 2026
5fe222b
repeat_* conditionally add set_error_t(std::exception_ptr)
justend29 Jan 28, 2026
a32754c
Merge branch 'main' of github.com:NVIDIA/stdexec into repeat-noexcept…
justend29 Jan 28, 2026
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41 changes: 30 additions & 11 deletions include/exec/repeat_n.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -39,14 +39,20 @@ namespace exec {
constexpr explicit __opstate_base(_Receiver &&__rcvr, std::size_t __count) noexcept
: __rcvr_{static_cast<_Receiver &&>(__rcvr)}
, __count_{__count} {
static_assert(
std::is_nothrow_default_constructible_v<trampoline_scheduler>,
"trampoline_scheduler c'tor is always expected to be noexcept");
}

virtual constexpr void __cleanup() noexcept = 0;
virtual constexpr void __repeat() noexcept = 0;

_Receiver __rcvr_;
std::size_t __count_;
trampoline_scheduler __sched_;
trampoline_scheduler __sched_{};

protected:
~__opstate_base() noexcept = default;
};

template <class _ReceiverId>
Expand Down Expand Up @@ -90,16 +96,14 @@ namespace exec {
};

template <class _Child, class _Receiver>
struct __opstate : __opstate_base<_Receiver> {
struct __opstate final : __opstate_base<_Receiver> {
using __receiver_t = STDEXEC::__t<__receiver<__id<_Receiver>>>;
using __bouncy_sndr_t =
__result_of<exec::sequence, schedule_result_t<trampoline_scheduler>, _Child &>;
using __child_op_t = STDEXEC::connect_result_t<__bouncy_sndr_t, __receiver_t>;
static constexpr bool __nothrow_connect =
STDEXEC::__nothrow_connectable<__bouncy_sndr_t, __receiver_t>;

constexpr explicit __opstate(std::size_t __count, _Child __child, _Receiver __rcvr)
noexcept(__nothrow_connect)
noexcept(std::is_nothrow_move_constructible_v<_Child> && noexcept(__connect()))
: __opstate_base<_Receiver>{static_cast<_Receiver &&>(__rcvr), __count}
, __child_(std::move(__child)) {
if (this->__count_ != 0) {
Expand All @@ -115,18 +119,19 @@ namespace exec {
}
}

constexpr auto __connect() noexcept(__nothrow_connect) -> __child_op_t & {
constexpr __child_op_t &
__connect() noexcept(STDEXEC::__nothrow_connectable<__bouncy_sndr_t, __receiver_t>) {
return __child_op_.__emplace_from(
STDEXEC::connect,
exec::sequence(STDEXEC::schedule(this->__sched_), __child_),
__receiver_t{this});
}

constexpr void __cleanup() noexcept final {
constexpr void __cleanup() noexcept override {
__child_op_.reset();
}

constexpr void __repeat() noexcept final {
constexpr void __repeat() noexcept override {
STDEXEC_ASSERT(this->__count_ > 0);
STDEXEC_TRY {
if (--this->__count_ == 0) {
Expand All @@ -137,7 +142,9 @@ namespace exec {
}
}
STDEXEC_CATCH_ALL {
STDEXEC::set_error(std::move(this->__rcvr_), std::current_exception());
if constexpr (!noexcept(__connect())) {
STDEXEC::set_error(std::move(this->__rcvr_), std::current_exception());
}
}
}

Expand All @@ -164,12 +171,24 @@ namespace exec {
template <class _Error>
using __error_t = completion_signatures<set_error_t(__decay_t<_Error>)>;

template <class _Sender, class... _Env>
using __errors_nothrow_copyable = STDEXEC::__error_types_t<
STDEXEC::__completion_signatures_of_t<_Sender, _Env...>, // sigs
STDEXEC::__q<STDEXEC::__nothrow_decay_copyable_t> // variant
>;

template <class _Sender, class... _Env>
using __with_eptr_completion = STDEXEC::__eptr_completion_unless_t<STDEXEC::__mand<
__errors_nothrow_copyable<_Sender, _Env...>,
__mbool<STDEXEC::__nothrow_connectable<_Sender, STDEXEC::__receiver_archetype<_Env>>>...
>>;

template <class _Child, class... _Env>
using __completions_t = STDEXEC::transform_completion_signatures<
__completion_signatures_of_t<_Child &, _Env...>,
STDEXEC::transform_completion_signatures<
__completion_signatures_of_t<STDEXEC::schedule_result_t<exec::trampoline_scheduler>, _Env...>,
__eptr_completion,
__completion_signatures_of_t<STDEXEC::schedule_result_t<trampoline_scheduler>, _Env...>,
__with_eptr_completion<_Child, _Env...>,
__cmplsigs::__default_set_value,
__error_t
>,
Expand Down
58 changes: 45 additions & 13 deletions include/exec/repeat_until.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -36,15 +36,21 @@ namespace exec {

template <class _Receiver>
struct __opstate_base {
constexpr explicit __opstate_base(_Receiver &&__rcvr)
: __rcvr_{static_cast<_Receiver &&>(__rcvr)} {
constexpr explicit __opstate_base(_Receiver &&__rcvr) noexcept
: __rcvr_{std::move(__rcvr)} {
static_assert(
std::is_nothrow_default_constructible_v<trampoline_scheduler>,
"trampoline_scheduler c'tor is always expected to be noexcept");
}

virtual constexpr void __cleanup() noexcept = 0;
virtual constexpr void __repeat() noexcept = 0;

_Receiver __rcvr_;
trampoline_scheduler __sched_;
trampoline_scheduler __sched_{};

protected:
~__opstate_base() noexcept = default;
};

template <class _Boolean, bool _Expected>
Expand Down Expand Up @@ -123,15 +129,13 @@ namespace exec {
STDEXEC_PRAGMA_IGNORE_GNU("-Wtsan")

template <class _Child, class _Receiver>
struct __opstate : __opstate_base<_Receiver> {
struct __opstate final : __opstate_base<_Receiver> {
using __receiver_t = STDEXEC::__t<__receiver<__id<_Receiver>>>;
using __bouncy_sndr_t =
__result_of<exec::sequence, schedule_result_t<trampoline_scheduler>, _Child &>;
using __child_op_t = STDEXEC::connect_result_t<__bouncy_sndr_t, __receiver_t>;
static constexpr bool __nothrow_connect =
STDEXEC::__nothrow_connectable<__bouncy_sndr_t, __receiver_t>;

constexpr explicit __opstate(_Child __child, _Receiver __rcvr) noexcept(__nothrow_connect)
constexpr explicit __opstate(_Child __child, _Receiver __rcvr) noexcept(noexcept(__connect()))
: __opstate_base<_Receiver>(static_cast<_Receiver &&>(__rcvr))
, __child_(static_cast<_Child &&>(__child)) {
__connect();
Expand All @@ -141,23 +145,25 @@ namespace exec {
STDEXEC::start(*__child_op_);
}

constexpr auto __connect() noexcept(__nothrow_connect) -> __child_op_t & {
constexpr __child_op_t& __connect() noexcept(STDEXEC::__nothrow_connectable<__bouncy_sndr_t, __receiver_t>) {
return __child_op_.__emplace_from(
STDEXEC::connect,
exec::sequence(STDEXEC::schedule(this->__sched_), __child_),
__receiver_t{this});
}

constexpr void __cleanup() noexcept final {
constexpr void __cleanup() noexcept override {
__child_op_.reset();
}

constexpr void __repeat() noexcept final {
constexpr void __repeat() noexcept override {
STDEXEC_TRY {
STDEXEC::start(__connect());
}
STDEXEC_CATCH_ALL {
STDEXEC::set_error(static_cast<_Receiver &&>(this->__rcvr_), std::current_exception());
if constexpr (!noexcept(__connect())) {
STDEXEC::set_error(static_cast<_Receiver &&>(this->__rcvr_), std::current_exception());
}
}
}

Expand Down Expand Up @@ -189,20 +195,46 @@ namespace exec {
>
>;

template <class... _Booleans>
using __values_overload_nothrow_bool_convertible =
STDEXEC::__mand<std::is_nothrow_convertible<_Booleans &&, bool>...>;

template <class _Sender, class... _Env>
using __values_nothrow_bool_convertible = STDEXEC::__value_types_t<
STDEXEC::__completion_signatures_of_t<_Sender, _Env...>, // sigs
STDEXEC::__qq<__values_overload_nothrow_bool_convertible>, // tuple
STDEXEC::__q<STDEXEC::__mand> // variant
>;

template <class _Sender, class... _Env>
using __errors_nothrow_copyable = STDEXEC::__error_types_t<
STDEXEC::__completion_signatures_of_t<_Sender, _Env...>, // sigs
STDEXEC::__q<STDEXEC::__nothrow_decay_copyable_t> // variant
>;

template <typename _Sender, typename... _Env>
using __with_eptr_completion = STDEXEC::__eptr_completion_unless_t<STDEXEC::__mand<
__values_nothrow_bool_convertible<_Sender, _Env...>,
__errors_nothrow_copyable<_Sender, _Env...>,
__mbool<STDEXEC::__nothrow_connectable<_Sender, STDEXEC::__receiver_archetype<_Env>>>...
>>;

template <class...>
using __delete_set_value_t = completion_signatures<>;

template <class _Child, class... _Env>
using __completions_t = STDEXEC::transform_completion_signatures<
__completion_signatures_of_t<__decay_t<_Child> &, _Env...>,
STDEXEC::transform_completion_signatures<
__completion_signatures_of_t<STDEXEC::schedule_result_t<exec::trampoline_scheduler>, _Env...>,
__eptr_completion,
__completion_signatures_of_t<STDEXEC::schedule_result_t<trampoline_scheduler>, _Env...>,
__with_eptr_completion<_Child, _Env...>,
__delete_set_value_t
>,
__mbind_front_q<__values_t, _Child>::template __f
>;

struct __repeat_until_tag { };

struct __repeat_until_impl : __sexpr_defaults {
template <class _Sender, class... _Env>
static consteval auto get_completion_signatures() {
Expand Down
43 changes: 43 additions & 0 deletions test/exec/test_repeat_n.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -141,4 +141,47 @@ namespace {
REQUIRE(called);
REQUIRE(!failed.load());
}

TEST_CASE("repeat_n conditionally adds set_error_t(exception)", "[adaptors][repeat_n]") {
// 0. ensure exception isn't always added
{
ex::sender auto snd = ex::just() | exec::repeat_n(1);
static_assert(
std::same_as<ex::error_types_of_t<decltype(snd)>, ex::__detail::__not_a_variant>,
"Expected no errors ");
}

// There are two main cases that will contribute set_error_t(std::exception_ptr)
// 1. error's copy constructor could throw
// 2. connect() could throw
{
// 1.
struct Error_with_throw_copy {
Error_with_throw_copy() noexcept = default;
Error_with_throw_copy(const Error_with_throw_copy&) noexcept(false) = default;
};
ex::sender auto snd = ex::just_error(Error_with_throw_copy{}) | exec::repeat_n(1);
static_assert(
std::same_as<
ex::error_types_of_t<decltype(snd)>,
std::variant<Error_with_throw_copy, std::exception_ptr>
>,
"Missing added set_error_t(std::exception_ptr)");
}
{
// 2.
using Sender_connect_throws = just_with_env<ex::env<>>;
static_assert(
!ex::__error_types_t<
ex::completion_signatures_of_t<Sender_connect_throws>,
ex::__mcontains<ex::set_error_t(std::exception_ptr)>
>::value,
"Sender can't already emit exception to test if repeat_until() adds it");
ex::sender auto snd = Sender_connect_throws{} | exec::repeat_n(1);
static_assert(
std::same_as<ex::error_types_of_t<decltype(snd)>, std::variant<std::exception_ptr>>,
"Missing added set_error_t(std::exception_ptr)");
}
}

} // namespace
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