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libstdc++: Avoid hard error in ranges::unique_copy [PR100770]

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Here, in the constexpr if condition within ranges::unique_copy, when
input_iterator<_Out> isn't satisfied we must avoid substituting into
iter_value_t<_Out> because the latter isn't necessarily well-formed
then.  To that end, this patch factors out the condition into a concept
and uses it throughout.

This patch also makes the definition of our testsuite
output_iterator_wrapper more minimal by setting its value_type, pointer
and reference member types to void.  This means our existing tests for
unique_copy already exercise the fix for this bug, so we don't need
to add another test.  The only other fallout of this testsuite iterator
change appears in std/ranges/range.cc, where the use of range_value_t
on a test_output_range is now ill-formed.

libstdc++-v3/ChangeLog:

	* include/bits/ranges_algo.h (__detail::__can_reread_output):
	Factor out this concept from ...
	(__unique_copy_fn::operator()): ... here.  Use the concept
	throughout.
	* testsuite/std/ranges/range.cc: Remove now ill-formed use
	of range_value_t on an output_range.
	* testsuite/util/testsuite_iterators.h (output_iterator_wrapper):
	Define value_type, pointer and reference member types to void.
This commit is contained in:
Patrick Palka 2021-06-03 12:30:29 -04:00
parent cd4dd47265
commit 0614bbbe59
3 changed files with 11 additions and 10 deletions
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16
libstdc++-v3/include/bits/ranges_algo.h
View file

@ -1396,6 +1396,13 @@ namespace ranges
inline constexpr __unique_fn unique{};
namespace __detail
{
template<typename _Out, typename _Tp>
concept __can_reread_output = input_iterator<_Out>
&& same_as<_Tp, iter_value_t<_Out>>;
}
template<typename _Iter, typename _Out>
using unique_copy_result = in_out_result<_Iter, _Out>;
@ -1407,8 +1414,7 @@ namespace ranges
projected<_Iter, _Proj>> _Comp = ranges::equal_to>
requires indirectly_copyable<_Iter, _Out>
&& (forward_iterator<_Iter>
|| (input_iterator<_Out>
&& same_as<iter_value_t<_Iter>, iter_value_t<_Out>>)
|| __detail::__can_reread_output<_Out, iter_value_t<_Iter>>
|| indirectly_copyable_storable<_Iter, _Out>)
constexpr unique_copy_result<_Iter, _Out>
operator()(_Iter __first, _Sent __last, _Out __result,
@ -1432,8 +1438,7 @@ namespace ranges
}
return {__next, std::move(++__result)};
}
else if constexpr (input_iterator<_Out>
&& same_as<iter_value_t<_Iter>, iter_value_t<_Out>>)
else if constexpr (__detail::__can_reread_output<_Out, iter_value_t<_Iter>>)
{
*__result = *__first;
while (++__first != __last)
@ -1467,8 +1472,7 @@ namespace ranges
projected<iterator_t<_Range>, _Proj>> _Comp = ranges::equal_to>
requires indirectly_copyable<iterator_t<_Range>, _Out>
&& (forward_iterator<iterator_t<_Range>>
|| (input_iterator<_Out>
&& same_as<range_value_t<_Range>, iter_value_t<_Out>>)
|| __detail::__can_reread_output<_Out, range_value_t<_Range>>
|| indirectly_copyable_storable<iterator_t<_Range>, _Out>)
constexpr unique_copy_result<borrowed_iterator_t<_Range>, _Out>
operator()(_Range&& __r, _Out __result,

3
libstdc++-v3/testsuite/std/ranges/range.cc
View file

@ -75,9 +75,6 @@ static_assert( same_as<std::ranges::range_difference_t<C>,
static_assert( same_as<std::ranges::range_difference_t<O>,
std::ptrdiff_t> );
static_assert( same_as<std::ranges::range_value_t<O>,
char> );
static_assert( same_as<std::ranges::range_reference_t<I>,
char&> );
static_assert( same_as<std::ranges::range_reference_t<O>,

2
libstdc++-v3/testsuite/util/testsuite_iterators.h
View file

@ -122,7 +122,7 @@ namespace __gnu_test
*/
template<class T>
struct output_iterator_wrapper
: public std::iterator<std::output_iterator_tag, T, std::ptrdiff_t, T*, T&>
: public std::iterator<std::output_iterator_tag, void, std::ptrdiff_t, void, void>
{
protected:
output_iterator_wrapper() : ptr(0), SharedInfo(0)