[PATCH v2 2/2] libstdc++: Make ref_view<R> statically sized if R is statically sized

[Tomasz Kamiński]

If the referenced range is statically sized, instead of referencing a
pointer whose value is not know at compile time, we return
integral_constant<range_difference_t<_Rg>, ranges::size(__rg)>::value.

libstdc++-v3/ChangeLog:

	* include/std/ranges (ref_view::size()): Return constant for statically
	sized ranges, even if pointed object is unknown.
	* testsuite/23_containers/inplace_vector/cons/from_range_neg.cc:
	Expect errors from ref_view of array examples.
---
v2 uses integral_constant to produce a value of ranges size.

 libstdc++-v3/include/std/ranges                | 18 +++++++++++++++++-
 .../inplace_vector/cons/from_range_neg.cc      |  6 ++----
 2 files changed, 19 insertions(+), 5 deletions(-)

diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges
index 95e0109a10c..71ab0d674c9 100644
--- a/libstdc++-v3/include/std/ranges
+++ b/libstdc++-v3/include/std/ranges
@@ -1395,7 +1395,23 @@ namespace views::__adaptor
 
       constexpr auto
       size() const requires sized_range<_Range>
-      { return ranges::size(*_M_r); }
+      {
+#if __cplusplus > 202302L
+	if constexpr (__static_sized_range<_Range>)
+	  {
+	    auto __conjure_size_constant
+	      = [](_Range& __rg)
+	        {
+		  return integral_constant<
+			   range_difference_t<_Range>,
+		  	   ranges::size(__rg)>();
+		};
+	     return decltype(__conjure_size_constant(*_M_r))::value;
+	  }
+        else
+#endif
+	  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_range_neg.cc b/libstdc++-v3/testsuite/23_containers/inplace_vector/cons/from_range_neg.cc
index cf87129da51..15fd7b5c285 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
@@ -57,14 +57,12 @@ test_all()
   test_one(a1); // { dg-error "from here" }
   test_one(s1); // { dg-error "from here" }
   test_one(s5 | std::views::adjacent<5> | std::views::elements<0>); // { dg-error "from here" }
-  // ref_view is not statically sized due pointer dereference
-  test_one(a5 | std::views::adjacent<7> | std::views::elements<0>);
+  test_one(a5 | 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(s7 | std::views::adjacent<3> | std::views::elements<0>); // { dg-error "from here" }
-  // ref_view is not statically sized due pointer dereference
-  test_five(a7 | std::views::adjacent<3> | std::views::elements<0>);
+  test_five(a7 | std::views::adjacent<3> | std::views::elements<0>); // { dg-error "from here" }
 }
 
 // { dg-error "static assertion failed" "" { target *-*-* } 0 }
-- 
2.53.0