loplugin:stringadd look for unnecessary temporaries

which defeat the *StringConcat optimisation.
Also make StringConcat conversions treat a nullptr as an empty string,
to match the O*String(char*) constructors.

Change-Id: If45f5b4b6a535c97bfeeacd9ec472a7603a52e5b
Reviewed-on: https://gerrit.libreoffice.org/80724
Tested-by: Jenkins
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>

2 files changed, 9 insertions, 5 deletions

diff --git a/include/oox/export/utils.hxx b/include/oox/export/utils.hxx
index e28b01c1d95d..4e9fa9866341 100644
--- a/include/oox/export/utils.hxx
+++ b/include/oox/export/utils.hxx
@@ -27,7 +27,7 @@ inline OString I32SHEX(sal_Int32 x)
 {
     OString aStr = OString::number(x, 16);
     while (aStr.getLength() < 6)
-        aStr = OString("0") + aStr;
+        aStr = "0" + aStr;
     return aStr;
 }
 
diff --git a/include/rtl/stringconcat.hxx b/include/rtl/stringconcat.hxx
index b751c020e75b..3fd8b6720851 100644
--- a/include/rtl/stringconcat.hxx
+++ b/include/rtl/stringconcat.hxx
@@ -113,9 +113,11 @@ template<>
 struct ToStringHelper< const char* >
     {
     static std::size_t length( const char* str ) {
-        return strlen( str );
+        return str ? strlen( str ) : 0;
+    }
+    static char* addData( char* buffer, const char* str ) {
+        return str ? addDataCString( buffer, str ) : buffer;
     }
-    static char* addData( char* buffer, const char* str ) { return addDataCString( buffer, str ); }
     static const bool allowOStringConcat = true;
     static const bool allowOUStringConcat = false;
     };
@@ -148,9 +150,11 @@ template<>
 struct ToStringHelper< const sal_Unicode* >
     {
     static std::size_t length( const sal_Unicode* str ) {
-        return std::char_traits<char16_t>::length( str );
+        return str ? std::char_traits<char16_t>::length( str ) : 0;
+    }
+    static sal_Unicode* addData( sal_Unicode* buffer, const sal_Unicode* str ) {
+        return str ? addDataUString( buffer, str ) : buffer;
     }
-    static sal_Unicode* addData( sal_Unicode* buffer, const sal_Unicode* str ) { return addDataUString( buffer, str ); }
     static const bool allowOStringConcat = false;
     static const bool allowOUStringConcat = true;
     };