[gcc r17-816] libstdc++: Revert making ref_view<R> statically sized.

[Tomasz Kaminski]

https://gcc.gnu.org/g:bd02a048e92a778c2d3fcc011b8a88e1ac6f8183

commit r17-816-gbd02a048e92a778c2d3fcc011b8a88e1ac6f8183
Author: Tomasz Kamiński <tkaminsk@redhat.com>
Date:   Tue May 26 18:01:40 2026 +0200

    libstdc++: Revert making ref_view<R> statically sized.
    
    This patch reverts all changes except introduction of
    ranges::__static_size from r17-810-g7239744d25dadf.
    
    In addition to expected errors from breaking inplace_vector
    preconditions, this lead to change in the return type of
    define_static_array, when applied on (adapted) ref_view:
      int x[10];
      auto x = define_static_array(x | views::transform(...));
    Type of x changed from span<const ...> to span<const ..., 10>,
    due size being statically know.
    
    This was considered beyond the scope of implementation freedom,
    and we should wait for acceptance of P3928R0 instead.
    
    libstdc++-v3/ChangeLog:
    
            * include/std/ranges (ref_view::size()): Only call ranges::size(*_M_r).
            (ref_view::empty): Only call ranges::empty(*_M_r).
            * testsuite/23_containers/inplace_vector/cons/from_iota_neg.cc:
            Except no errors from ref_view uses.
            * testsuite/23_containers/inplace_vector/cons/from_range_neg.cc:
            Likewise.

Diff:
---
 libstdc++-v3/include/std/ranges                        | 18 ++----------------
 .../23_containers/inplace_vector/cons/from_iota_neg.cc |  6 ++++--
 .../inplace_vector/cons/from_range_neg.cc              | 10 ++++++----
 3 files changed, 12 insertions(+), 22 deletions(-)

diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges
index 2f11cc2336f7..7d8b37f8c5cf 100644
--- a/libstdc++-v3/include/std/ranges
+++ b/libstdc++-v3/include/std/ranges
@@ -1382,25 +1382,11 @@ namespace views::__adaptor
 
       constexpr bool
       empty() const requires requires { ranges::empty(*_M_r); }
-      {
-#if __cplusplus > 202302L
-	if constexpr (__static_sized_range<_Range>)
-	  return ranges::__static_size<_Range>() == 0;
-	else
-#endif
-	  return ranges::empty(*_M_r);
-      }
+      { return ranges::empty(*_M_r); }
 
       constexpr auto
       size() const requires sized_range<_Range>
-      {
-#if __cplusplus > 202302L
-	if constexpr (__static_sized_range<_Range>)
-	  return ranges::__static_size<_Range>();
-	else
-#endif
-	  return ranges::size(*_M_r);
-      }
+      { return ranges::size(*_M_r); }
 
       constexpr auto
       data() const requires contiguous_range<_Range>
diff --git a/libstdc++-v3/testsuite/23_containers/inplace_vector/cons/from_iota_neg.cc b/libstdc++-v3/testsuite/23_containers/inplace_vector/cons/from_iota_neg.cc
index 6b66b5d97ed9..ae0b96175b7d 100644
--- a/libstdc++-v3/testsuite/23_containers/inplace_vector/cons/from_iota_neg.cc
+++ b/libstdc++-v3/testsuite/23_containers/inplace_vector/cons/from_iota_neg.cc
@@ -33,12 +33,14 @@ test_all()
   std::inplace_vector<int, 15> tr1(std::from_range, ref_view(m12));
 
   std::inplace_vector<int, 10> tm2(std::from_range, m12); // { dg-error "(from here|expansion of)" }
-  std::inplace_vector<int, 10> tr2(std::from_range, ref_view(m12)); // { dg-error "(from here|expansion of)" }
+  // ref_view is not statically sized due pointer dereference
+  std::inplace_vector<int, 10> tr2(std::from_range, ref_view(m12));
 
   StaticIota<__int128, 0> mm;
 
   std::inplace_vector<int, 10> tm3(std::from_range, mm); // { dg-error "(from here|expansion of)" }
-  std::inplace_vector<int, 10> tr3(std::from_range, ref_view(mm)); // { dg-error "(from here|expansion of)" }
+  // ref_view is not statically sized due pointer dereference
+  std::inplace_vector<int, 10> tr3(std::from_range, ref_view(mm));
 }
 
 // { dg-error "static assertion failed" "" { target *-*-* } 0 }
diff --git a/libstdc++-v3/testsuite/23_containers/inplace_vector/cons/from_range_neg.cc b/libstdc++-v3/testsuite/23_containers/inplace_vector/cons/from_range_neg.cc
index ea187761e5e7..48d5b4c56f59 100644
--- a/libstdc++-v3/testsuite/23_containers/inplace_vector/cons/from_range_neg.cc
+++ b/libstdc++-v3/testsuite/23_containers/inplace_vector/cons/from_range_neg.cc
@@ -62,14 +62,16 @@ test_all()
 
   test_one(a1); // { dg-error "from here" }
   test_one(s1); // { dg-error "from here" }
-  test_one(ref_view(a1)); // { dg-error "from here" }
-  test_one(a5 | std::views::adjacent<5> | std::views::elements<0>); // { dg-error "from here" }
+  // ref_view is not statically sized due pointer dereference
+  test_one(ref_view(a1));
+  test_one(a5 | std::views::adjacent<7> | std::views::elements<0>);
   test_one(s5 | std::views::adjacent<5> | std::views::elements<0>); // { dg-error "from here" }
 
   test_five(a5); // { dg-error "from here" }
   test_five(s5); // { dg-error "from here" }
-  test_five(ref_view(a5)); // { dg-error "from here" }
-  test_five(a7 | std::views::adjacent<3> | std::views::elements<0>); // { dg-error "from here" }
+  // ref_view is not statically sized due pointer dereference
+  test_five(ref_view(a5));
+  test_five(a7 | std::views::adjacent<3> | std::views::elements<0>);
   test_five(s7 | std::views::adjacent<3> | std::views::elements<0>); // { dg-error "from here" }
 }