Cannot self-append OUStringBuffer via concatenation

a5084d15e1b72e303e1628fbff84432036b014a9 "loplugin:stringadd in vcl" had dropped
the intermediary sTemp, but which caused JunitTest_forms_unoapi_1 to fail for me
once with

> ==2657124==ERROR: AddressSanitizer: memcpy-param-overlap: memory ranges [0x50c00086ca58,0x50c00086ca6a) and [0x50c00086ca48, 0x50c00086ca5a) overlap
>  #0 in __asan_memcpy at ~/github.com/llvm/llvm-project/compiler-rt/lib/asan/asan_interceptors_memintrinsics.cpp:22:3
>  #1 in char16_t* rtl::addDataHelper<char16_t>(char16_t*, char16_t const*, unsigned long) at include/rtl/stringconcat.hxx:80:9
>  #2 in rtl::ToStringHelper<rtl::OUStringBuffer>::operator()(char16_t*, rtl::OUStringBuffer const&) const at include/rtl/ustrbuf.hxx:1765:14
>  #3 in rtl::StringConcat<char16_t, rtl::StringConcat<char16_t, rtl::StringConcat<char16_t, char const [3], rtl::OUString, 0>, char const [3], 0>, rtl::OUStringBuffer, 0>::addData(char16_t*) const at include/rtl/stringconcat.hxx:195:64
>  #4 in rtl::ToStringHelper<rtl::StringConcat<char16_t, rtl::StringConcat<char16_t, rtl::StringConcat<char16_t, char const [3], rtl::OUString, 0>, char const [3], 0>, rtl::OUStringBuffer, 0>>::operator()(char16_t*, rtl::StringConcat<char16_t, rtl::StringConcat<char16_t, rtl::StringConcat<char16_t, char const [3], rtl::OUString, 0>, char const [3], 0>, rtl::OUStringBuffer, 0> const&) const at include/rtl/stringconcat.hxx:207:101
>  #5 in rtl::StringConcat<char16_t, rtl::StringConcat<char16_t, rtl::StringConcat<char16_t, rtl::StringConcat<char16_t, char const [3], rtl::OUString, 0>, char const [3], 0>, rtl::OUStringBuffer, 0>, char const [4], 0>::addData(char16_t*) const at include/rtl/stringconcat.hxx:195:88
>  #6 in rtl::ToStringHelper<rtl::StringConcat<char16_t, rtl::StringConcat<char16_t, rtl::StringConcat<char16_t, rtl::StringConcat<char16_t, char const [3], rtl::OUString, 0>, char const [3], 0>, rtl::OUStringBuffer, 0>, char const [4], 0>>::operator()(char16_t*, rtl::StringConcat<char16_t, rtl::StringConcat<char16_t, rtl::StringConcat<char16_t, rtl::StringConcat<char16_t, char const [3], rtl::OUString, 0>, char const [3], 0>, rtl::OUStringBuffer, 0>, char const [4], 0> const&) const at include/rtl/stringconcat.hxx:207:101
>  #7 in rtl::StringConcat<char16_t, rtl::StringConcat<char16_t, rtl::StringConcat<char16_t, rtl::StringConcat<char16_t, rtl::StringConcat<char16_t, char const [3], rtl::OUString, 0>, char const [3], 0>, rtl::OUStringBuffer, 0>, char const [4], 0>, rtl::OUString, 0>::addData(char16_t*) const at include/rtl/stringconcat.hxx:195:88
>  #8 in rtl::ToStringHelper<rtl::StringConcat<char16_t, rtl::StringConcat<char16_t, rtl::StringConcat<char16_t, rtl::StringConcat<char16_t, rtl::StringConcat<char16_t, char const [3], rtl::OUString, 0>, char const [3], 0>, rtl::OUStringBuffer, 0>, char const [4], 0>, rtl::OUString, 0>>::operator()(char16_t*, rtl::StringConcat<char16_t, rtl::StringConcat<char16_t, rtl::StringConcat<char16_t, rtl::StringConcat<char16_t, rtl::StringConcat<char16_t, char const [3], rtl::OUString, 0>, char const [3], 0>, rtl::OUStringBuffer, 0>, char const [4], 0>, rtl::OUString, 0> const&) const at include/rtl/stringconcat.hxx:207:101
>  #9 in rtl::StringConcat<char16_t, rtl::StringConcat<char16_t, rtl::StringConcat<char16_t, rtl::StringConcat<char16_t, rtl::StringConcat<char16_t, rtl::StringConcat<char16_t, char const [3], rtl::OUString, 0>, char const [3], 0>, rtl::OUStringBuffer, 0>, char const [4], 0>, rtl::OUString, 0>, char const [4], 0>::addData(char16_t*) const at include/rtl/stringconcat.hxx:195:88
>  #10 in rtl::ToStringHelper<rtl::StringConcat<char16_t, rtl::StringConcat<char16_t, rtl::StringConcat<char16_t, rtl::StringConcat<char16_t, rtl::StringConcat<char16_t, rtl::StringConcat<char16_t, char const [3], rtl::OUString, 0>, char const [3], 0>, rtl::OUStringBuffer, 0>, char const [4], 0>, rtl::OUString, 0>, char const [4], 0>>::operator()(char16_t*, rtl::StringConcat<char16_t, rtl::StringConcat<char16_t, rtl::StringConcat<char16_t, rtl::StringConcat<char16_t, rtl::StringConcat<char16_t, rtl::StringConcat<char16_t, char const [3], rtl::OUString, 0>, char const [3], 0>, rtl::OUStringBuffer, 0>, char const [4], 0>, rtl::OUString, 0>, char const [4], 0> const&) const at include/rtl/stringconcat.hxx:207:101
>  #11 in rtl::StringConcat<char16_t, rtl::StringConcat<char16_t, rtl::StringConcat<char16_t, rtl::StringConcat<char16_t, rtl::StringConcat<char16_t, rtl::StringConcat<char16_t, rtl::StringConcat<char16_t, char const [3], rtl::OUString, 0>, char const [3], 0>, rtl::OUStringBuffer, 0>, char const [4], 0>, rtl::OUString, 0>, char const [4], 0>, rtl::OUStringBuffer, 0>::addData(char16_t*) const at include/rtl/stringconcat.hxx:195:88
>  #12 in rtl::OUStringBuffer& rtl::OUStringBuffer::operator=<rtl::StringConcat<char16_t, rtl::StringConcat<char16_t, rtl::StringConcat<char16_t, rtl::StringConcat<char16_t, rtl::StringConcat<char16_t, rtl::StringConcat<char16_t, char const [3], rtl::OUString, 0>, char const [3], 0>, rtl::OUStringBuffer, 0>, char const [4], 0>, rtl::OUString, 0>, char const [4], 0>, rtl::OUStringBuffer>(rtl::StringConcat<char16_t, rtl::StringConcat<char16_t, rtl::StringConcat<char16_t, rtl::StringConcat<char16_t, rtl::StringConcat<char16_t, rtl::StringConcat<char16_t, rtl::StringConcat<char16_t, char const [3], rtl::OUString, 0>, char const [3], 0>, rtl::OUStringBuffer, 0>, char const [4], 0>, rtl::OUString, 0>, char const [4], 0>, rtl::OUStringBuffer, 0>&&) at include/rtl/ustrbuf.hxx:378:17
>  #13 in DoubleCurrencyField::UpdateCurrencyFormat() at vcl/source/control/fmtfield.cxx:1120:20

and e.g.

>         OUStringBuffer b("a");
>         b = "b" + b;
>         CPPUNIT_ASSERT_EQUAL(OUString("ba"), b.makeStringAndClear());

would indeed easily fail with

> equality assertion failed
> - Expected: ba
> - Actual  : bb

Change-Id: I3108c18b7c941953a73b5731d9973914b7ba1fbe
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/152495
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

1 files changed, 3 insertions, 1 deletions

diff --git a/vcl/source/control/fmtfield.cxx b/vcl/source/control/fmtfield.cxx
index de5713261e83..69497dec2c1b 100644
--- a/vcl/source/control/fmtfield.cxx
+++ b/vcl/source/control/fmtfield.cxx
@@ -1117,7 +1117,7 @@ void DoubleCurrencyField::UpdateCurrencyFormat()
         OUString sSymbol = getCurrencySymbol();
         sSymbol = comphelper::string::strip(sSymbol, ' ');
 
-        sNewFormat =
+        OUString sTemp =
             "[$" + sSymbol + "] "
             + sNewFormat
         // for negative values : $ -0.00, not -$ 0.00...
@@ -1128,6 +1128,8 @@ void DoubleCurrencyField::UpdateCurrencyFormat()
             + sSymbol
             + "] -"
             + sNewFormat;
+
+        sNewFormat = sTemp;
     }
     else
     {