From 90f7bbfe2219770ac8b25d0f99320ed3a4fd7736 Mon Sep 17 00:00:00 2001
From: =?utf8?q?Tomasz=20Kami=C5=84ski?= <tkaminsk@redhat.com>
Date: Thu, 5 Jun 2025 10:40:10 +0200
Subject: [PATCH] libstdc++: Uglify __mapping_alike template parameter and fix
 test and typo in comment.
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When the static assert was generated from instantiations of default member
initializer of class B, the error was not generated for B<1, std::layout_left,
std::layout_left> case, only when -D_GLIBCXX_DEBUG was set. Changing B calls to
functions fixes that.

We also replace class with typename in template head of layout_right::mapping
constructors.

libstdc++-v3/ChangeLog:

	* include/std/mdspan (__mdspan::__mapping_alike): Rename template
	parameter from M to _M_p.
	(layout_right::mapping): Replace class with typename in template
	head.
	(layout_stride::mapping): Fix typo in comment.
	* testsuite/23_containers/mdspan/layouts/class_mandate_neg.cc:
	Changed B to function.

Reviewed-by: Jonathan Wakely <jwakely@redhat.com>
Signed-off-by: Tomasz Kamiński <tkaminsk@redhat.com>
---
 libstdc++-v3/include/std/mdspan               | 22 +++++++++----------
 .../mdspan/layouts/class_mandate_neg.cc       | 18 ++++++++-------
 2 files changed, 21 insertions(+), 19 deletions(-)

diff --git a/libstdc++-v3/include/std/mdspan b/libstdc++-v3/include/std/mdspan
index 4a3e863bed5..6dc2441f80b 100644
--- a/libstdc++-v3/include/std/mdspan
+++ b/libstdc++-v3/include/std/mdspan
@@ -691,7 +691,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	: mapping(__other.extents(), __mdspan::__internal_ctor{})
 	{ }
 
-      template<class _OExtents>
+      template<typename _OExtents>
 	requires (extents_type::rank() <= 1)
 	    && is_constructible_v<extents_type, _OExtents>
 	constexpr explicit(!is_convertible_v<_OExtents, extents_type>)
@@ -699,7 +699,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	: mapping(__other.extents(), __mdspan::__internal_ctor{})
 	{ }
 
-      template<class _OExtents>
+      template<typename _OExtents>
 	requires is_constructible_v<extents_type, _OExtents>
 	constexpr explicit(extents_type::rank() > 0)
 	mapping(const layout_stride::mapping<_OExtents>& __other) noexcept
@@ -780,16 +780,16 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
   namespace __mdspan
   {
-    template<typename M>
+    template<typename _Mp>
       concept __mapping_alike = requires
       {
-	requires __is_extents<typename M::extents_type>;
-	{ M::is_always_strided() } -> same_as<bool>;
-	{ M::is_always_exhaustive() } -> same_as<bool>;
-	{ M::is_always_unique() } -> same_as<bool>;
-	bool_constant<M::is_always_strided()>::value;
-	bool_constant<M::is_always_exhaustive()>::value;
-	bool_constant<M::is_always_unique()>::value;
+	requires __is_extents<typename _Mp::extents_type>;
+	{ _Mp::is_always_strided() } -> same_as<bool>;
+	{ _Mp::is_always_exhaustive() } -> same_as<bool>;
+	{ _Mp::is_always_unique() } -> same_as<bool>;
+	bool_constant<_Mp::is_always_strided()>::value;
+	bool_constant<_Mp::is_always_exhaustive()>::value;
+	bool_constant<_Mp::is_always_unique()>::value;
       };
 
     template<typename _Mapping>
@@ -847,7 +847,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       mapping() noexcept
       {
 	// The precondition is either statically asserted, or automatically
-	// satisfied because dynamic extents are zero-initialzied.
+	// satisfied because dynamic extents are zero-initialized.
 	size_t __stride = 1;
 	for (size_t __i = extents_type::rank(); __i > 0; --__i)
 	  {
diff --git a/libstdc++-v3/testsuite/23_containers/mdspan/layouts/class_mandate_neg.cc b/libstdc++-v3/testsuite/23_containers/mdspan/layouts/class_mandate_neg.cc
index 70a25707cb2..7091153daba 100644
--- a/libstdc++-v3/testsuite/23_containers/mdspan/layouts/class_mandate_neg.cc
+++ b/libstdc++-v3/testsuite/23_containers/mdspan/layouts/class_mandate_neg.cc
@@ -18,7 +18,8 @@ template<typename Layout>
   };
 
 template<size_t Count, typename Layout, typename OLayout>
-  struct B
+  bool
+  B()
   {
     using Extents = std::extents<uint8_t, dyn, dyn, Count>;
     using OExtents = std::extents<uint16_t, n, 4, Count>;
@@ -27,20 +28,21 @@ template<size_t Count, typename Layout, typename OLayout>
     using OMapping = typename OLayout::mapping<OExtents>;
 
     Mapping m{OMapping{}};
+    return true;
   };
 
 A<std::layout_left> a_left;                      // { dg-error "required from" }
 A<std::layout_right> a_right;                    // { dg-error "required from" }
 A<std::layout_stride> a_stride;                  // { dg-error "required from" }
 
-B<1, std::layout_left, std::layout_left> b0;     // { dg-error "required here" }
-B<2, std::layout_left, std::layout_stride> b1;   // { dg-error "required here" }
+auto b1 = B<1, std::layout_left, std::layout_left>();     // { dg-error "required from" }
+auto b2 = B<2, std::layout_left, std::layout_stride>();   // { dg-error "required from" }
 
-B<3, std::layout_right, std::layout_right> b2;   // { dg-error "required here" }
-B<4, std::layout_right, std::layout_stride> b3;  // { dg-error "required here" }
+auto b3 = B<3, std::layout_right, std::layout_right>();   // { dg-error "required from" }
+auto b4 = B<4, std::layout_right, std::layout_stride>();  // { dg-error "required from" }
 
-B<5, std::layout_stride, std::layout_right> b4;  // { dg-error "required here" }
-B<6, std::layout_stride, std::layout_left> b5;   // { dg-error "required here" }
-B<7, std::layout_stride, std::layout_stride> b6; // { dg-error "required here" }
+auto b5 = B<5, std::layout_stride, std::layout_right>();  // { dg-error "required from" }
+auto b6 = B<6, std::layout_stride, std::layout_left>();   // { dg-error "required from" }
+auto b7 = B<7, std::layout_stride, std::layout_stride>(); // { dg-error "required from" }
 
 // { dg-prune-output "must be representable as index_type" }
-- 
2.47.2