A better fix for C++23 P2266R1

After 6d6a143913603b040c10a5db83c2103557899011 "Address some of the sprintf in
vcl/source/fontsubset/cff.cxx", --with-latest-c++ builds that pick up a C++23
compiler that implements
<http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2021/p2266r1.html> "P2266R1:
Simpler implicit move" started to fail with something like

> vcl/source/fontsubset/cff.cxx:2061:16: error: no viable conversion from returned value of type 'char[64]' to function return type 'OString'
>         return aDefaultGlyphName;
>                ^~~~~~~~~~~~~~~~~
[...]
> include/rtl/string.hxx:313:5: note: candidate constructor [with T = char[64]] not viable: expects an lvalue for 1st argument
>     OString( T& value, typename libreoffice_internal::NonConstCharArrayDetector< T, libreoffice_internal::Dummy >::Type = libreoffice_internal::Dummy() )
>     ^

etc.  So I figured there should be something better than
433ab39b2175bdadb4916373cd2dc8e1aabc08a5 "Adapt implicit OString return value
construction to C++23 P2266R1" (which this commit reverts, modulo its conflicts
in comphelper/source/xml/xmltools.cxx and
sc/source/filter/xcl97/XclExpChangeTrack.cxx) to address the underlying issue in
a way that keeps code that works up to C++20 also working in C++23.

(The fix is only relevant for non-explicit constructors that involve
NonConstCharArrayDetector and non-const lvalue references, not for other
functions involving those.  OUString has a similar constructor but which is
explicit, and OUStringBuffer doesn't have any similar constructors at all, so
this only affects OString and OStringBuffer constructors.)

Change-Id: I31cf16b9507899f5999243f8467dfa24bc94c5ac
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/142455
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

9 files changed, 47 insertions, 7 deletions

diff --git a/include/rtl/strbuf.hxx b/include/rtl/strbuf.hxx
index dbdcd7fea39a..97368ce3ca4d 100644
--- a/include/rtl/strbuf.hxx
+++ b/include/rtl/strbuf.hxx
@@ -180,6 +180,17 @@ public:
         rtl_stringbuffer_newFromStr_WithLength( &pData, value, length );
     }
 
+#if __cplusplus > 202002L // C++23 P2266R3 "Simpler implicit move"
+    template< typename T >
+    OStringBuffer( T&& value, typename libreoffice_internal::NonConstCharArrayDetector< T, libreoffice_internal::Dummy >::Type = libreoffice_internal::Dummy())
+        : pData(NULL)
+    {
+        sal_Int32 length = rtl_str_getLength( value );
+        nCapacity = length + 16;
+        rtl_stringbuffer_newFromStr_WithLength( &pData, value, length );
+    }
+#endif
+
     /**
       Constructs a string buffer so that it represents the same
         sequence of characters as the string literal.
diff --git a/include/rtl/string.hxx b/include/rtl/string.hxx
index 472d3074bd1b..24c6a64008cf 100644
--- a/include/rtl/string.hxx
+++ b/include/rtl/string.hxx
@@ -316,6 +316,15 @@ public:
         rtl_string_newFromStr( &pData, value );
     }
 
+#if __cplusplus > 202002L // C++23 P2266R3 "Simpler implicit move"
+    template< typename T >
+    OString( T&& value, typename libreoffice_internal::NonConstCharArrayDetector< T, libreoffice_internal::Dummy >::Type = libreoffice_internal::Dummy() )
+    {
+        pData = NULL;
+        rtl_string_newFromStr( &pData, value );
+    }
+#endif
+
     /**
       New string from a string literal.
 
diff --git a/l10ntools/source/po.cxx b/l10ntools/source/po.cxx
index b053067ea163..e075d52b0bd5 100644
--- a/l10ntools/source/po.cxx
+++ b/l10ntools/source/po.cxx
@@ -425,7 +425,7 @@ OString PoEntry::genKeyId(const OString& rGenerator)
         nCRC >>= 6;
     }
     sKeyId[5] = '\0';
-    return OString(sKeyId);
+    return sKeyId;
 }
 
 namespace
@@ -437,7 +437,7 @@ namespace
         struct tm* pNow = localtime(&aNow);
         char pBuff[50];
         strftime( pBuff, sizeof pBuff, "%Y-%m-%d %H:%M%z", pNow );
-        return OString(pBuff);
+        return pBuff;
     }
 }
 
diff --git a/sal/osl/unx/uunxapi.cxx b/sal/osl/unx/uunxapi.cxx
index 5311bc71917f..d1fc6c4f9d3f 100644
--- a/sal/osl/unx/uunxapi.cxx
+++ b/sal/osl/unx/uunxapi.cxx
@@ -154,7 +154,7 @@ static OString macxp_resolveAliasAndConvert(OString const & p)
     {
         strcpy(path, p.getStr());
         macxp_resolveAlias(path, PATH_MAX);
-        return OString(path);
+        return path;
     }
     return p;
 }
diff --git a/sal/qa/rtl/strings/nonconstarray.cxx b/sal/qa/rtl/strings/nonconstarray.cxx
index 4b66e4e311c3..d759049582d0 100644
--- a/sal/qa/rtl/strings/nonconstarray.cxx
+++ b/sal/qa/rtl/strings/nonconstarray.cxx
@@ -12,11 +12,24 @@
 #include <cppunit/TestAssert.h>
 #include <cppunit/TestFixture.h>
 #include <cppunit/extensions/HelperMacros.h>
+#include <rtl/strbuf.hxx>
 #include <rtl/string.hxx>
 #include <rtl/ustring.hxx>
 
 namespace
 {
+OString returnOString()
+{
+    char buf[] = "foo\0bar";
+    return buf;
+}
+
+OStringBuffer returnOStringBuffer()
+{
+    char buf[] = "foo\0bar";
+    return buf;
+}
+
 class Test : public CppUnit::TestFixture
 {
 private:
@@ -81,10 +94,17 @@ private:
         }
     }
 
+    void testP2266R3()
+    {
+        CPPUNIT_ASSERT_EQUAL(OString("foo"), returnOString());
+        CPPUNIT_ASSERT_EQUAL(OString("foo"), returnOStringBuffer().makeStringAndClear());
+    }
+
     CPPUNIT_TEST_SUITE(Test);
     CPPUNIT_TEST(testOString);
     CPPUNIT_TEST(testOUStringChar);
     CPPUNIT_TEST(testOUStringChar16t);
+    CPPUNIT_TEST(testP2266R3);
     CPPUNIT_TEST_SUITE_END();
 };
 
diff --git a/sc/source/filter/excel/xestream.cxx b/sc/source/filter/excel/xestream.cxx
index ee75b188b0f7..0ee697dfeba8 100644
--- a/sc/source/filter/excel/xestream.cxx
+++ b/sc/source/filter/excel/xestream.cxx
@@ -712,7 +712,7 @@ OString XclXmlUtils::ToOString( const Color& rColor )
     char buf[9];
     o3tl::sprintf( buf, "%.2X%.2X%.2X%.2X", rColor.GetAlpha(), rColor.GetRed(), rColor.GetGreen(), rColor.GetBlue() );
     buf[8] = '\0';
-    return OString(buf);
+    return buf;
 }
 
 OStringBuffer& XclXmlUtils::ToOString( OStringBuffer& s, const ScAddress& rAddress )
diff --git a/sc/source/filter/html/htmlexp.cxx b/sc/source/filter/html/htmlexp.cxx
index 4cc01d868603..16db15316121 100644
--- a/sc/source/filter/html/htmlexp.cxx
+++ b/sc/source/filter/html/htmlexp.cxx
@@ -191,7 +191,7 @@ static OString lcl_makeHTMLColorTriplet(const Color& rColor)
     // <font COLOR="#00FF40">hello</font>
     snprintf( buf, 24, "\"#%02X%02X%02X\"", rColor.GetRed(), rColor.GetGreen(), rColor.GetBlue() );
 
-    return OString(buf);
+    return buf;
 }
 
 ScHTMLExport::ScHTMLExport( SvStream& rStrmP, OUString _aBaseURL, ScDocument* pDocP,
diff --git a/sc/source/filter/xcl97/XclExpChangeTrack.cxx b/sc/source/filter/xcl97/XclExpChangeTrack.cxx
index bbee834806c3..57fd143bf659 100644
--- a/sc/source/filter/xcl97/XclExpChangeTrack.cxx
+++ b/sc/source/filter/xcl97/XclExpChangeTrack.cxx
@@ -48,7 +48,7 @@ static OString lcl_DateTimeToOString( const DateTime& rDateTime )
             rDateTime.GetYear(), rDateTime.GetMonth(), rDateTime.GetDay(),
             rDateTime.GetHour(), rDateTime.GetMin(), rDateTime.GetSec(),
             rDateTime.GetNanoSec() );
-    return OString(sBuf);
+    return sBuf;
 }
 
 // local functions
diff --git a/unotools/source/i18n/resmgr.cxx b/unotools/source/i18n/resmgr.cxx
index 641fa61be6dc..ddedf5b9e8a2 100644
--- a/unotools/source/i18n/resmgr.cxx
+++ b/unotools/source/i18n/resmgr.cxx
@@ -92,7 +92,7 @@ namespace
             nCRC >>= 6;
         }
         sKeyId[5] = '\0';
-        return OString(sKeyId);
+        return sKeyId;
     }
 }