Adapt o3tl::span to P1872R0

..."span should have size_type, not index_type"
(<http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p1872r0.pdf>), as
implemented by libc++ since <https://github.com/llvm/llvm-project/commit/
1466335cf4b2854a0be1defcf279fe50772bad6f> "[libc++][P1872] span should have
size_type, not index_type."

All uses of index_type had been added to mitigate the previous std::span change
from signed (ptrdiff_t) to unsigned (size_t) index_type, see
6ef8420fdbf8dff16de13147c5ab833bc5e01121 "Adapt o3tl::span to updated C++2a
std::span".  There is no easy solution to transparently support all three
std::span variants currently out there (signed index_type, unsigned index_type,
unsigned size_type), without causing compilation failures due to
CPPUNIT_ASSERT_EQUAL with arguments of different types, or compiler warnings
about mixed signed/unsigned comparisons.  So rule out the oldest std::span
variant (signed index_type) in configure.ac (so that o3tl::span will use its
own hand-rolled code in that case) and simplify the uses of index_type to
std::size_t (as had already been mentioned in
6ef8420fdbf8dff16de13147c5ab833bc5e01121).

Change-Id: I6ddf424ffb7941da3f69ad66fd29ecd35f09afae
Reviewed-on: https://gerrit.libreoffice.org/84652
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

1 files changed, 8 insertions, 6 deletions

diff --git a/include/o3tl/span.hxx b/include/o3tl/span.hxx
index 1618b86df897..b19d2d847ac7 100644
--- a/include/o3tl/span.hxx
+++ b/include/o3tl/span.hxx
@@ -12,7 +12,9 @@
 
 #include <sal/config.h>
 
-#if __has_include(<span>)
+#include <config_global.h>
+
+#if HAVE_CPP_SPAN
 
 #include <span>
 
@@ -40,7 +42,7 @@ public:
     using iterator = pointer;
     using const_reverse_iterator = std::reverse_iterator<const_iterator>;
     using reverse_iterator = std::reverse_iterator<iterator>;
-    using index_type = std::size_t;
+    using size_type = std::size_t;
     using difference_type = std::ptrdiff_t;
 
     constexpr span() noexcept : data_(nullptr), size_(0) {}
@@ -48,7 +50,7 @@ public:
     template<std::size_t N>
     constexpr span (T (&a)[N]) noexcept : data_(a), size_(N) {}
 
-    constexpr span (T *a, index_type len) noexcept
+    constexpr span (T *a, size_type len) noexcept
         : data_(a), size_(len)
     {
         // not terribly sure about this, might need to strengthen it
@@ -72,9 +74,9 @@ public:
     { return rbegin(); }
     constexpr const_reverse_iterator crend() const noexcept { return rend(); }
 
-    constexpr index_type size() const noexcept { return size_; }
+    constexpr size_type size() const noexcept { return size_; }
 
-    constexpr reference operator [](index_type pos) const {
+    constexpr reference operator [](size_type pos) const {
         assert(pos < size());
         return data_[pos];
     }
@@ -83,7 +85,7 @@ public:
 
 private:
     pointer    data_;
-    index_type size_;
+    size_type size_;
 };
 
 } // namespace o3tl