Use the correct size argument for wcsxfrm

The documentation says that the size argument to wcsxfrm should include
the null terminating character. Currently it doesn't, which breaks
collation, as the last character is omitted.

Task-number: QTBUG-109954
Change-Id: Ic0c78a617ed1d50e31e50cae56e21675d2069ead
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

1 files changed, 12 insertions, 6 deletions

diff --git a/src/corelib/text/qcollator_posix.cpp b/src/corelib/text/qcollator_posix.cpp
index 54c700015b..5ed80c1b8e 100644
--- a/src/corelib/text/qcollator_posix.cpp
+++ b/src/corelib/text/qcollator_posix.cpp
@@ -69,13 +69,19 @@ QCollatorSortKey QCollator::sortKey(const QString &string) const
     if (d->isC()) {
         std::copy(original.cbegin(), original.cend(), result.begin());
     } else {
-        size_t size = std::wcsxfrm(result.data(), original.constData(), string.size());
-        if (size > size_t(result.size())) {
-            result.resize(size+1);
-            size = std::wcsxfrm(result.data(), original.constData(), string.size());
+        auto availableSizeIncludingNullTerminator = result.size();
+        size_t neededSizeExcludingNullTerminator = std::wcsxfrm(
+                result.data(), original.constData(), availableSizeIncludingNullTerminator);
+        if (neededSizeExcludingNullTerminator > size_t(availableSizeIncludingNullTerminator - 1)) {
+            result.resize(neededSizeExcludingNullTerminator + 1);
+            availableSizeIncludingNullTerminator = result.size();
+            neededSizeExcludingNullTerminator = std::wcsxfrm(result.data(), original.constData(),
+                                                             availableSizeIncludingNullTerminator);
+            Q_ASSERT(neededSizeExcludingNullTerminator
+                     == size_t(availableSizeIncludingNullTerminator - 1));
         }
-        result.resize(size+1);
-        result[size] = 0;
+        result.resize(neededSizeExcludingNullTerminator + 1);
+        result[neededSizeExcludingNullTerminator] = 0;
     }
     return QCollatorSortKey(new QCollatorSortKeyPrivate(std::move(result)));
 }