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>

1 files changed, 5 insertions, 5 deletions

diff --git a/svgio/inc/svgnode.hxx b/svgio/inc/svgnode.hxx
index 697c8c312a38..9db4f4750a38 100644
--- a/svgio/inc/svgnode.hxx
+++ b/svgio/inc/svgnode.hxx
@@ -27,7 +27,7 @@
 #include <com/sun/star/xml/sax/XAttributeList.hpp>
 #include <memory>
 #include <vector>
-#include <boost/optional.hpp>
+#include <o3tl/optional.hxx>
 
 // predefines
 namespace svgio
@@ -95,10 +95,10 @@ namespace svgio
             std::vector< std::unique_ptr<SvgNode> >  maChildren;
 
             /// Id svan value
-            boost::optional<OUString>   mpId;
+            o3tl::optional<OUString>   mpId;
 
             /// Class svan value
-            boost::optional<OUString>   mpClass;
+            o3tl::optional<OUString>   mpClass;
 
             /// XmlSpace value
             XmlSpace                    maXmlSpace;
@@ -168,11 +168,11 @@ namespace svgio
             double getCurrentXHeight() const;
 
             /// Id access
-            boost::optional<OUString> const & getId() const { return mpId; }
+            o3tl::optional<OUString> const & getId() const { return mpId; }
             void setId(OUString const &);
 
             /// Class access
-            boost::optional<OUString> const & getClass() const { return mpClass; }
+            o3tl::optional<OUString> const & getClass() const { return mpClass; }
             void setClass(OUString const &);
 
             /// XmlSpace access