Fwd: [Libreoffice-commits] core.git: Add --with-latest-c++ to explicitly opt in for -std=c++20/-std:c++latest

FYI:


-------- Forwarded Message --------
Subject: [Libreoffice-commits] core.git: configure.ac
Date: Mon, 20 Apr 2020 13:41:29 +0000 (UTC)
From: Stephan Bergmann (via logerrit) <logerrit@kemper.freedesktop.org>
Reply-To: libreoffice@lists.freedesktop.org
To: libreoffice-commits@lists.freedesktop.org

 configure.ac |   18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

New commits:
commit 42f29b7f3f1bedac3fc057edfab985ffb03fd53b
Author:     Stephan Bergmann <sbergman@redhat.com>
AuthorDate: Mon Apr 20 11:40:24 2020 +0200
Commit:     Stephan Bergmann <sbergman@redhat.com>
CommitDate: Mon Apr 20 15:40:55 2020 +0200

    Add --with-latest-c++ to explicitly opt in for 
-std=c++20/-std:c++latest
        cd472d1d8489f30797f47d3f6dafede28c1feb90 "Compile as C++2a, 
where available" had
    started to unconditionally check for support of -std=c++2a (and 
later also
    -std=c++20) for Clang and GCC, but that can cause occasional issues 
especially
    for Linux distros, see e.g. 
55c724b93dfd4c9a1afb10d60fbc2d7a9a66cf61 "replace
    boost::bimap in sdext pdfimport" or
    <https://bugzilla.redhat.com/show_bug.cgi?id=1818723>
    "/usr/include/boost/format/alt_sstream_impl.hpp incompatible with 
-std=c++20
    (std::allocator::allocate hint argument)" (where
    677c8de4fa79cd9b278b142013ba7f1c9e4e41c3 "external/boost: Adapt to
    std::allocator parts removed in C++20" is not picked up due to
    --with-system-boost).
        So better require an explicit opt-in via a new 
--with-latest-c++.  And while at
    it, also make that enable -std:c++latest for MSVC.
        Change-Id: I2d1f03144fad9a7884562e56b1b76cab5eb8f080
    Reviewed-on: https://gerrit.libreoffice.org/c/core/+/92555
    Tested-by: Jenkins
    Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

diff --git a/configure.ac b/configure.ac
index 2c4a018b0dd8..376bdf4816da 100644
--- a/configure.ac
+++ b/configure.ac
@@ -2178,6 +2178,12 @@ libo_FUZZ_ARG_WITH(lxml,
          report widget classes and ids.]),
 ,)
 +libo_FUZZ_ARG_WITH(latest-c++,
+    AS_HELP_STRING([--with-latest-c++],
+        [Try to enable the latest features of the C++ compiler, even if 
they are not yet part of a
+         published standard.]),,
+        [$with_latest_c__=no])
+
 dnl ===================================================================
 dnl Branding
 dnl ===================================================================
@@ -6517,9 +6523,17 @@ dnl 
===================================================================
 AC_MSG_CHECKING([whether $CXX_BASE supports C++17])
 CXXFLAGS_CXX11=
 if test "$COM" = MSC -a "$COM_IS_CLANG" != TRUE; then
-    CXXFLAGS_CXX11='-std:c++17 -Zc:__cplusplus'
+    if test "$with_latest_c__" = yes; then
+        CXXFLAGS_CXX11=-std:c++latest
+    else
+        CXXFLAGS_CXX11=-std:c++17
+    fi
+    CXXFLAGS_CXX11="$CXXFLAGS_CXX11 -Zc:__cplusplus"
 elif test "$GCC" = "yes" -o "$COM_IS_CLANG" = TRUE; then
-    my_flags='-std=c++20 -std=c++2a -std=c++17 -std=c++1z'
+    my_flags='-std=c++17 -std=c++1z'
+    if test "$with_latest_c__" = yes; then
+        my_flags='-std=c++20 -std=c++2a $my_flags'
+    fi
     for flag in $my_flags; do
         if test "$COM" = MSC; then
             flag="-Xclang $flag"