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Implement LWG-4399 enable_nonlocking_formatter_optimization for pair and tuple needs remove_cvref_t #5897

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Merged
Stephan T. Lavavej (StephanTLavavej) merged 4 commits into from
Nov 27, 2025
Merged

Implement LWG-4399 enable_nonlocking_formatter_optimization for pair and tuple needs remove_cvref_t #5897

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9a95027
Add tests
vmichal Nov 21, 2025
c288f74
Apply remove_cv_ref_t in specialization of enable_nonlocking_formatte…
vmichal Nov 21, 2025
68b801e
Mention LWG-4399 in the test suite
vmichal Nov 21, 2025
e3a0891
Extract helpers to also test `const T` and `const T&`.
StephanTLavavej Nov 23, 2025
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5 changes: 3 additions & 2 deletions stl/inc/__msvc_formatter.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -401,11 +401,12 @@ constexpr bool enable_nonlocking_formatter_optimization<basic_string_view<_CharT

template <class _Ty1, class _Ty2>
constexpr bool enable_nonlocking_formatter_optimization<pair<_Ty1, _Ty2>> =
enable_nonlocking_formatter_optimization<_Ty1> && enable_nonlocking_formatter_optimization<_Ty2>;
enable_nonlocking_formatter_optimization<remove_cvref_t<_Ty1>>
&& enable_nonlocking_formatter_optimization<remove_cvref_t<_Ty2>>;

template <class... _Ts>
constexpr bool enable_nonlocking_formatter_optimization<tuple<_Ts...>> =
(enable_nonlocking_formatter_optimization<_Ts> && ...);
(enable_nonlocking_formatter_optimization<remove_cvref_t<_Ts>> && ...);

template <class _CharT>
struct _Fill_align_and_width_specs {
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29 changes: 23 additions & 6 deletions tests/std/tests/P3107R5_enabled_specializations/test.compile.pass.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -121,12 +121,29 @@ static_assert(enable_nonlocking_formatter_optimization<long double>);
static_assert(enable_nonlocking_formatter_optimization<nullptr_t>);
static_assert(enable_nonlocking_formatter_optimization<void*>);
static_assert(enable_nonlocking_formatter_optimization<const void*>);
static_assert(enable_nonlocking_formatter_optimization<pair<int, int>>);
static_assert(!enable_nonlocking_formatter_optimization<pair<unoptimized, int>>);
static_assert(!enable_nonlocking_formatter_optimization<pair<int, unoptimized>>);
static_assert(enable_nonlocking_formatter_optimization<tuple<int, int>>);
static_assert(!enable_nonlocking_formatter_optimization<tuple<unoptimized, int>>);
static_assert(!enable_nonlocking_formatter_optimization<tuple<int, unoptimized>>);

// Extended to test LWG-4399 "enable_nonlocking_formatter_optimization for pair and tuple needs remove_cvref_t"
template <template <class, class> class PairOrTuple, class T, class U, bool Expected>
constexpr void test_lwg_4399_impl() {
static_assert(enable_nonlocking_formatter_optimization<PairOrTuple<T, U>> == Expected);
static_assert(enable_nonlocking_formatter_optimization<PairOrTuple<T&, U>> == Expected);
static_assert(enable_nonlocking_formatter_optimization<PairOrTuple<T, U&>> == Expected);
static_assert(enable_nonlocking_formatter_optimization<PairOrTuple<const T, U>> == Expected);
static_assert(enable_nonlocking_formatter_optimization<PairOrTuple<T, const U>> == Expected);
static_assert(enable_nonlocking_formatter_optimization<PairOrTuple<const T&, U>> == Expected);
static_assert(enable_nonlocking_formatter_optimization<PairOrTuple<T, const U&>> == Expected);
}

template <class T, class U, bool Expected>
constexpr bool test_lwg_4399() {
test_lwg_4399_impl<pair, T, U, Expected>();
test_lwg_4399_impl<tuple, T, U, Expected>();
return true;
}

static_assert(test_lwg_4399<int, int, true>());
static_assert(test_lwg_4399<unoptimized, int, false>());
static_assert(test_lwg_4399<int, unoptimized, false>());

// Validate that various ranges are unoptimized
static_assert(!enable_nonlocking_formatter_optimization<list<int>>);
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