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>

5 files changed, 6 insertions, 6 deletions

diff --git a/libreofficekit/qa/gtktiledviewer/gtv-application-window.cxx b/libreofficekit/qa/gtktiledviewer/gtv-application-window.cxx
index cac83565abe8..fec03e046dc2 100644
--- a/libreofficekit/qa/gtktiledviewer/gtv-application-window.cxx
+++ b/libreofficekit/qa/gtktiledviewer/gtv-application-window.cxx
@@ -24,7 +24,7 @@
 #include "gtv-lok-dialog.hxx"
 
 #include <boost/property_tree/json_parser.hpp>
-#include <boost/optional.hpp>
+#include <o3tl/optional.hxx>
 
 namespace {
 
diff --git a/libreofficekit/qa/gtktiledviewer/gtv-calc-header-bar.cxx b/libreofficekit/qa/gtktiledviewer/gtv-calc-header-bar.cxx
index c28349046cb6..a332d9608551 100644
--- a/libreofficekit/qa/gtktiledviewer/gtv-calc-header-bar.cxx
+++ b/libreofficekit/qa/gtktiledviewer/gtv-calc-header-bar.cxx
@@ -19,7 +19,7 @@
 
 #include <map>
 #include <boost/property_tree/json_parser.hpp>
-#include <boost/optional.hpp>
+#include <o3tl/optional.hxx>
 
 namespace {
 
diff --git a/libreofficekit/qa/gtktiledviewer/gtv-lokdocview-signal-handlers.cxx b/libreofficekit/qa/gtktiledviewer/gtv-lokdocview-signal-handlers.cxx
index e16491203139..bcee979766f5 100644
--- a/libreofficekit/qa/gtktiledviewer/gtv-lokdocview-signal-handlers.cxx
+++ b/libreofficekit/qa/gtktiledviewer/gtv-lokdocview-signal-handlers.cxx
@@ -18,7 +18,7 @@
 #include "gtv-lok-dialog.hxx"
 
 #include <boost/property_tree/json_parser.hpp>
-#include <boost/optional.hpp>
+#include <o3tl/optional.hxx>
 
 #include <iostream>
 
diff --git a/libreofficekit/qa/gtktiledviewer/gtv-main-toolbar.cxx b/libreofficekit/qa/gtktiledviewer/gtv-main-toolbar.cxx
index cdbb236a600a..25f7d7890fdb 100644
--- a/libreofficekit/qa/gtktiledviewer/gtv-main-toolbar.cxx
+++ b/libreofficekit/qa/gtktiledviewer/gtv-main-toolbar.cxx
@@ -20,7 +20,7 @@
 #include <memory>
 
 #include <boost/property_tree/json_parser.hpp>
-#include <boost/optional.hpp>
+#include <o3tl/optional.hxx>
 
 namespace {
 
diff --git a/libreofficekit/qa/gtktiledviewer/gtv-signal-handlers.cxx b/libreofficekit/qa/gtktiledviewer/gtv-signal-handlers.cxx
index 288d56d1b2b3..1b0233fee66c 100644
--- a/libreofficekit/qa/gtktiledviewer/gtv-signal-handlers.cxx
+++ b/libreofficekit/qa/gtktiledviewer/gtv-signal-handlers.cxx
@@ -20,7 +20,7 @@
 #include <vector>
 
 #include <boost/property_tree/json_parser.hpp>
-#include <boost/optional.hpp>
+#include <o3tl/optional.hxx>
 
 void btn_clicked(GtkWidget* pButton, gpointer)
 {
@@ -89,7 +89,7 @@ void doPaste(GtkWidget* pButton, gpointer /*pItem*/)
         g_free(pTargets);
     }
 
-    boost::optional<GdkAtom> oTarget;
+    o3tl::optional<GdkAtom> oTarget;
     std::string aTargetName;
 
     std::vector<std::string> aPreferredNames =