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/desktop/inc/app.hxx b/desktop/inc/app.hxx
index 817945c54e47..2fc67ab92c14 100644
--- a/desktop/inc/app.hxx
+++ b/desktop/inc/app.hxx
@@ -20,7 +20,7 @@
 #ifndef INCLUDED_DESKTOP_INC_APP_HXX
 #define INCLUDED_DESKTOP_INC_APP_HXX
 
-#include <boost/optional.hpp>
+#include <o3tl/optional.hxx>
 #include <com/sun/star/lang/XMultiServiceFactory.hpp>
 #include <sal/log.hxx>
 #include <vcl/svapp.hxx>
@@ -175,7 +175,7 @@ class Desktop : public Application
 };
 
 OUString GetURL_Impl(
-    const OUString& rName, boost::optional< OUString > const & cwdUrl );
+    const OUString& rName, o3tl::optional< OUString > const & cwdUrl );
 
 OUString ReplaceStringHookProc(const OUString& rStr);
 
diff --git a/desktop/inc/pch/precompiled_deployment.hxx b/desktop/inc/pch/precompiled_deployment.hxx
index f6fbcba0d6de..667e9e562ece 100644
--- a/desktop/inc/pch/precompiled_deployment.hxx
+++ b/desktop/inc/pch/precompiled_deployment.hxx
@@ -27,7 +27,7 @@
 #include <ostream>
 #include <unordered_map>
 #include <vector>
-#include <boost/optional.hpp>
+#include <o3tl/optional.hxx>
 #endif // PCH_LEVEL >= 1
 #if PCH_LEVEL >= 2
 #include <osl/diagnose.h>
diff --git a/desktop/inc/pch/precompiled_deploymentgui.hxx b/desktop/inc/pch/precompiled_deploymentgui.hxx
index e1ad0a551535..994036573ac1 100644
--- a/desktop/inc/pch/precompiled_deploymentgui.hxx
+++ b/desktop/inc/pch/precompiled_deploymentgui.hxx
@@ -37,7 +37,7 @@
 #include <string>
 #include <utility>
 #include <vector>
-#include <boost/optional.hpp>
+#include <o3tl/optional.hxx>
 #endif // PCH_LEVEL >= 1
 #if PCH_LEVEL >= 2
 #include <osl/conditn.hxx>
diff --git a/desktop/inc/pch/precompiled_deploymentmisc.hxx b/desktop/inc/pch/precompiled_deploymentmisc.hxx
index 3cf05ba57055..703c029f8609 100644
--- a/desktop/inc/pch/precompiled_deploymentmisc.hxx
+++ b/desktop/inc/pch/precompiled_deploymentmisc.hxx
@@ -29,7 +29,7 @@
 #include <string>
 #include <utility>
 #include <vector>
-#include <boost/optional.hpp>
+#include <o3tl/optional.hxx>
 #endif // PCH_LEVEL >= 1
 #if PCH_LEVEL >= 2
 #include <osl/diagnose.h>
diff --git a/desktop/inc/pch/precompiled_sofficeapp.hxx b/desktop/inc/pch/precompiled_sofficeapp.hxx
index 9428ba122b31..87bcfaf98187 100644
--- a/desktop/inc/pch/precompiled_sofficeapp.hxx
+++ b/desktop/inc/pch/precompiled_sofficeapp.hxx
@@ -44,7 +44,7 @@
 #include <type_traits>
 #include <utility>
 #include <vector>
-#include <boost/optional.hpp>
+#include <o3tl/optional.hxx>
 #include <boost/property_tree/ptree.hpp>
 #endif // PCH_LEVEL >= 1
 #if PCH_LEVEL >= 2