[PATCH v2] libstdc++: Enable asserts in repeat_view::_Iterator uncoditionally.

[Jonathan Wakely]

On Mon, 21 Sep 2026 at 13:54 +0200, Tomasz Kamiński wrote:
>This implements LWG4624, "Inconsistent preconditions in repeat_view::iterator".
>
>The checks against _M_current being negive were disabled for cases where
>_Bound denotes unreachable_sentinel_t. However, _M_current has ptrdiff_t
>type in that case, and this check are as meaningfull are for integer bound.
>
>The assert in private _Iterator(const _Tp*, __index_type) constructor are
>removed entirelly, as the constructor can only be called internally.
>
>libstdc++-v3/ChangeLog:
>
>	* include/std/ranges (repeat_view::_Iterator::_Iterator):
>	Remove assert, as constructor is used only iternally.
>	(repeat_view::_Iterator::operator--)
>	(repeat_view::_Iterator::operator+=)
>	(repeat_view::_Iterator::operator-=): Unconditionally assert
>	on _M_current having non-negative value.
>---
>v2:
>* links to LWG4624 that I have created to address the wording
>* (as part of above) removes the assert in the private constructor
>
>Tested on x86_64-linux. *random* also tested in all standard modes,
>assertion debug. OK for trunk? Do we want to wait for issue votes?

OK for trunk

>
> libstdc++-v3/include/std/ranges | 16 ++++++----------
> 1 file changed, 6 insertions(+), 10 deletions(-)
>
>diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges
>index 1c0991cae13..fe7c87b8f6e 100644
>--- a/libstdc++-v3/include/std/ranges
>+++ b/libstdc++-v3/include/std/ranges
>@@ -8075,10 +8075,7 @@ namespace views::__adaptor
>     constexpr explicit
>     _Iterator(const _Tp* __value, __index_type __bound = __index_type())
>     : _M_value(__value), _M_current(__bound)
>-    {
>-      if constexpr (!same_as<_Bound, unreachable_sentinel_t>)
>-	__glibcxx_assert(__bound >= 0);
>-    }
>+    { }
>
>     friend repeat_view;
>
>@@ -8112,8 +8109,9 @@ namespace views::__adaptor
>     constexpr _Iterator&
>     operator--()
>     {
>-      if constexpr (!same_as<_Bound, unreachable_sentinel_t>)
>-	__glibcxx_assert(_M_current > 0);
>+      // _GLIBCXX_RESOLVE_LIB_DEFECTS
>+      // 4624. Inconsistent preconditions in repeat_view::iterator
>+      __glibcxx_assert(_M_current > 0);
>       --_M_current;
>       return *this;
>     }
>@@ -8129,8 +8127,7 @@ namespace views::__adaptor
>     constexpr _Iterator&
>     operator+=(difference_type __n)
>     {
>-      if constexpr (!same_as<_Bound, unreachable_sentinel_t>)
>-	__glibcxx_assert(_M_current + __n >= 0);
>+      __glibcxx_assert(_M_current + __n >= 0);
>       _M_current += __n;
>       return *this;
>     }
>@@ -8138,8 +8135,7 @@ namespace views::__adaptor
>     constexpr _Iterator&
>     operator-=(difference_type __n)
>     {
>-      if constexpr (!same_as<_Bound, unreachable_sentinel_t>)
>-	__glibcxx_assert(_M_current - __n >= 0);
>+      __glibcxx_assert(_M_current - __n >= 0);
>       _M_current -= __n;
>       return *this;
>     }
>-- 
>2.55.0
>
>