Introduce o3tl::optional as an alias for std::optional

...with a boost::optional fallback for Xcode < 10 (as std::optional is only
available starting with Xcode 10 according to
<https://en.cppreference.com/w/cpp/compiler_support>, and our baseline for iOS
and macOS is still Xcode 9.3 according to README.md).  And mechanically rewrite
all code to use o3tl::optional instead of boost::optional.

One immediate benefit is that disabling -Wmaybe-uninitialized for GCC as per
fed7c3deb3f4ec81f78967c2d7f3c4554398cb9d "Slience bogus
-Werror=maybe-uninitialized" should no longer be necessary (and whose check
happened to no longer trigger for GCC 10 trunk, even though that compiler would
still emit bogus -Wmaybe-uninitialized for uses of boost::optional under
--enable-optimized, which made me ponder whether this switch from
boost::optional to std::optional would be a useful thing to do; I keep that
configure.ac check for now, though, and will only remove it in a follow up
commit).

Another longer-term benefit is that the code is now already in good shape for an
eventual switch to std::optional (a switch we would have done anyway once we no
longer need to support Xcode < 10).

Only desktop/qa/desktop_lib/test_desktop_lib.cxx heavily uses
boost::property_tree::ptree::get_child_optional returning boost::optional, so
let it keep using boost::optional for now.

After a number of preceding commits have paved the way for this change, this
commit is completely mechanical, done with

> git ls-files -z | grep -vz -e '^bin/find-unneeded-includes$' -e '^configure.ac$' -e '^desktop/qa/desktop_lib/test_desktop_lib.cxx$' -e '^dictionaries$' -e '^external/' -e '^helpcontent2$' -e '^include/IwyuFilter_include.yaml$' -e '^sc/IwyuFilter_sc.yaml$' -e '^solenv/gdb/boost/optional.py$' -e '^solenv/vs/LibreOffice.natvis$' -e '^translations$' -e '\.svg$' | xargs -0 sed -i -E -e 's|\<boost(/optional)?/optional\.hpp\>|o3tl/optional.hxx|g' -e 's/\<boost(\s*)::(\s*)(make_)?optional\>/o3tl\1::\2\3optional/g' -e 's/\<boost(\s*)::(\s*)none\>/o3tl\1::\2nullopt/g'

(before committing include/o3tl/optional.hxx, and relying on some GNU features).
It excludes some files where mention of boost::optional et al should apparently
not be changed (and the sub-repo directory stubs).  It turned out that all uses
of boost::none across the code base were in combination with boost::optional, so
had all to be rewritten as o3tl::nullopt.

Change-Id: Ibfd9f4b3d5a8aee6e6eed310b988c4e5ffd8b11b
Reviewed-on: https://gerrit.libreoffice.org/84128
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

2 files changed, 6 insertions, 6 deletions

diff --git a/sw/source/core/txtnode/swfont.cxx b/sw/source/core/txtnode/swfont.cxx
index 9816212aa690..55284ce3d275 100644
--- a/sw/source/core/txtnode/swfont.cxx
+++ b/sw/source/core/txtnode/swfont.cxx
@@ -124,7 +124,7 @@ void SwFont::SetLeftBorder( const editeng::SvxBorderLine* pLeftBorder )
     m_aSub[SwFontScript::Latin].m_nFontCacheId = m_aSub[SwFontScript::CJK].m_nFontCacheId = m_aSub[SwFontScript::CTL].m_nFontCacheId = nullptr;
 }
 
-const boost::optional<editeng::SvxBorderLine>&
+const o3tl::optional<editeng::SvxBorderLine>&
 SwFont::GetAbsTopBorder(const bool bVertLayout, const bool bVertLayoutLRBT) const
 {
     switch (GetOrientation(bVertLayout, bVertLayoutLRBT))
@@ -148,7 +148,7 @@ SwFont::GetAbsTopBorder(const bool bVertLayout, const bool bVertLayoutLRBT) cons
     }
 }
 
-const boost::optional<editeng::SvxBorderLine>&
+const o3tl::optional<editeng::SvxBorderLine>&
 SwFont::GetAbsBottomBorder(const bool bVertLayout, const bool bVertLayoutLRBT) const
 {
     switch (GetOrientation(bVertLayout, bVertLayoutLRBT))
@@ -172,7 +172,7 @@ SwFont::GetAbsBottomBorder(const bool bVertLayout, const bool bVertLayoutLRBT) c
     }
 }
 
-const boost::optional<editeng::SvxBorderLine>&
+const o3tl::optional<editeng::SvxBorderLine>&
 SwFont::GetAbsLeftBorder(const bool bVertLayout, const bool bVertLayoutLRBT) const
 {
     switch (GetOrientation(bVertLayout, bVertLayoutLRBT))
@@ -196,7 +196,7 @@ SwFont::GetAbsLeftBorder(const bool bVertLayout, const bool bVertLayoutLRBT) con
     }
 }
 
-const boost::optional<editeng::SvxBorderLine>&
+const o3tl::optional<editeng::SvxBorderLine>&
 SwFont::GetAbsRightBorder(const bool bVertLayout, const bool bVertLayoutLRBT) const
 {
     switch (GetOrientation(bVertLayout, bVertLayoutLRBT))
diff --git a/sw/source/core/txtnode/txatbase.cxx b/sw/source/core/txtnode/txatbase.cxx
index 188ec6f9a663..e0293d61d881 100644
--- a/sw/source/core/txtnode/txatbase.cxx
+++ b/sw/source/core/txtnode/txatbase.cxx
@@ -17,7 +17,7 @@
  *   the License at http://www.apache.org/licenses/LICENSE-2.0 .
  */
 
-#include <boost/optional.hpp>
+#include <o3tl/optional.hxx>
 #include <libxml/xmlwriter.h>
 #include <svl/itempool.hxx>
 #include <txatbase.hxx>
@@ -96,7 +96,7 @@ void SwTextAttr::dumpAsXml(xmlTextWriterPtr pWriter) const
         xmlTextWriterWriteAttribute(pWriter, BAD_CAST("end"), BAD_CAST(OString::number(*End()).getStr()));
     xmlTextWriterWriteAttribute(pWriter, BAD_CAST("whichId"), BAD_CAST(OString::number(Which()).getStr()));
     const char* pWhich = nullptr;
-    boost::optional<OString> oValue;
+    o3tl::optional<OString> oValue;
     switch (Which())
     {
     case RES_TXTATR_AUTOFMT: