On Wed, 26 May 2021, Tim Song wrote:
> On Wed, May 26, 2021 at 1:43 PM Patrick Palka <ppa...@redhat.com> wrote:
> >
> > On Wed, 26 May 2021, Tim Song wrote:
> > >
> > > On Wed, May 26, 2021 at 12:00 PM Patrick Palka via Libstdc++
> > > <libstd...@gcc.gnu.org> wrote:
> > > >
> > > > - else if constexpr (input_iterator<_Out>
> > > > - && same_as<iter_value_t<_Iter>,
> > > > iter_value_t<_Out>>)
> > > > + else if constexpr (requires { requires (input_iterator<_Out>
> > > > + &&
> > > > same_as<iter_value_t<_Iter>,
> > > > +
> > > > iter_value_t<_Out>>); })
> > >
> > > It's arguably cleaner to extract this into a concept which can then
> > > also be used in the constraint.
> >
> > Sounds good, though I'm not sure what name to give to this relatively
> > ad-hoc set of requirements. Any suggestions? :)
> >
>
> Something along the lines of "__can_reread_output", perhaps?
Works for me. Here's v2, which factors out the condition into a concept
and defines the value_type, pointer and reference of output_iterator_wrapper
to void but leaves alone its difference_type. Tested on x86_64-pc-linux-gnu.
-- >8 --
Subject: [PATCH] libstdc++: Avoid hard error in ranges::unique_copy [PR100770]
Here, in the constexpr if condition within 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 in
this case. 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 defining 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.
---
libstdc++-v3/include/bits/ranges_algo.h | 16 ++++++++++------
libstdc++-v3/testsuite/std/ranges/range.cc | 3 ---
.../testsuite/util/testsuite_iterators.h | 2 +-
3 files changed, 11 insertions(+), 10 deletions(-)
diff --git a/libstdc++-v3/include/bits/ranges_algo.h
b/libstdc++-v3/include/bits/ranges_algo.h
index cda3042c11f..ecf1378742d 100644
--- a/libstdc++-v3/include/bits/ranges_algo.h
+++ b/libstdc++-v3/include/bits/ranges_algo.h
@@ -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,
diff --git a/libstdc++-v3/testsuite/std/ranges/range.cc
b/libstdc++-v3/testsuite/std/ranges/range.cc
index 795aca472e5..aa29af471a4 100644
--- a/libstdc++-v3/testsuite/std/ranges/range.cc
+++ b/libstdc++-v3/testsuite/std/ranges/range.cc
@@ -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>,
diff --git a/libstdc++-v3/testsuite/util/testsuite_iterators.h
b/libstdc++-v3/testsuite/util/testsuite_iterators.h
index 67da06b8482..4e668d648f2 100644
--- a/libstdc++-v3/testsuite/util/testsuite_iterators.h
+++ b/libstdc++-v3/testsuite/util/testsuite_iterators.h
@@ -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)
--
2.32.0.rc0
