From 6572dbc2fa36fb9189bd1ed21748e73a88418e15 Mon Sep 17 00:00:00 2001
From: Stephan Bergmann <sbergman@redhat.com>
Date: Fri, 6 Dec 2019 16:36:01 +0100
Subject: Adapt o3tl::span to P1872R0
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..."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).

Reviewed-on: https://gerrit.libreoffice.org/84652
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>
(cherry picked from commit 8e6865188242bccb3d8aa857ddc990d72a058d3d)
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/87757
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
(cherry picked from commit bb9833594b031c6d0ec91422f85968c4b1f2f8bc)

Change-Id: I6ddf424ffb7941da3f69ad66fd29ecd35f09afae
---
 configure.ac | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

(limited to 'configure.ac')

diff --git a/configure.ac b/configure.ac
index 2b33e5f0bc0a..0e61b295b66f 100644
--- a/configure.ac
+++ b/configure.ac
@@ -6766,6 +6766,22 @@ AC_COMPILE_IFELSE([AC_LANG_SOURCE([
 CXXFLAGS=$save_CXXFLAGS
 AC_LANG_POP([C++])
 
+AC_MSG_CHECKING([whether $CXX supports C++2a <span> with unsigned size_type])
+AC_LANG_PUSH([C++])
+save_CXXFLAGS=$CXXFLAGS
+CXXFLAGS="$CXXFLAGS $CXXFLAGS_CXX11"
+AC_COMPILE_IFELSE([AC_LANG_SOURCE([
+        #include <span>
+        #include <type_traits>
+        // Don't check size_type directly, as it was called index_type before P1872R0:
+        void f(std::span<int> s) { static_assert(std::is_unsigned_v<decltype(s.size())>); };
+    ])], [
+        AC_DEFINE([HAVE_CPP_SPAN],[1])
+        AC_MSG_RESULT([yes])
+    ], [AC_MSG_RESULT([no])])
+CXXFLAGS=$save_CXXFLAGS
+AC_LANG_POP([C++])
+
 AC_MSG_CHECKING([whether $CXX has GCC bug 87150])
 AC_LANG_PUSH([C++])
 save_CXXFLAGS=$CXXFLAGS
-- 
cgit