[libcxx-commits] [PATCH] D71997: [libcxx] span: Fix incorrect return type of span::subspan

[Michael Schellenberger Costa via Phabricator via libcxx-commits]

miscco created this revision.
Herald added a reviewer: EricWF.
Herald added subscribers: libcxx-commits, ldionne, christof.
Herald added a project: libc++.

The extent of the returned span was incorrect


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D71997

Files:
  libcxx/include/span
  libcxx/test/std/containers/views/span.sub/subspan.pass.cpp


Index: libcxx/test/std/containers/views/span.sub/subspan.pass.cpp
===================================================================
--- libcxx/test/std/containers/views/span.sub/subspan.pass.cpp
+++ libcxx/test/std/containers/views/span.sub/subspan.pass.cpp
@@ -37,8 +37,11 @@
     using S2 = decltype(s2);
     ASSERT_SAME_TYPE(typename Span::value_type, typename S1::value_type);
     ASSERT_SAME_TYPE(typename Span::value_type, typename S2::value_type);
-    static_assert(S1::extent == (Span::extent == std::dynamic_extent ? std::dynamic_extent : Count), "");
-    static_assert(S2::extent == std::dynamic_extent, "");
+    static_assert(S1::extent ==
+			((Count != std::dynamic_extent) ? Count
+											: ((Span::extent != std::dynamic_extent) ? Span::extent - Offset
+																					 : std::dynamic_extent)), "");
+	static_assert(S2::extent == std::dynamic_extent, "");
     return
         s1.data() == s2.data()
      && s1.size() == s2.size()
@@ -76,7 +79,10 @@
     using S2 = decltype(s2);
     ASSERT_SAME_TYPE(typename Span::value_type, typename S1::value_type);
     ASSERT_SAME_TYPE(typename Span::value_type, typename S2::value_type);
-    static_assert(S1::extent == (Span::extent == std::dynamic_extent ? std::dynamic_extent : Count), "");
+    static_assert(S1::extent ==
+			((Count != std::dynamic_extent) ? Count
+											: ((Span::extent != std::dynamic_extent) ? Span::extent - Offset
+																					 : std::dynamic_extent)), "");
     static_assert(S2::extent == std::dynamic_extent, "");
     assert(s1.data() == s2.data());
     assert(s1.size() == s2.size());
Index: libcxx/include/span
===================================================================
--- libcxx/include/span
+++ libcxx/include/span
@@ -445,7 +445,7 @@
 
     template <size_t _Offset, size_t _Count = dynamic_extent>
     _LIBCPP_INLINE_VISIBILITY
-    constexpr span<_Tp, dynamic_extent> subspan() const noexcept
+    constexpr span<element_type, _Count> subspan() const noexcept
     {
         _LIBCPP_ASSERT(_Offset <= size(), "Offset out of range in span::subspan()");
         _LIBCPP_ASSERT(_Count == dynamic_extent || _Offset + _Count <= size(), "Count out of range in span::subspan()");


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