QVarLengthArray: fix size update on failed append()

If the in-place constructor throws, the old code had already updated
the container's size(). Fix by delaying the update to after the
in-place construction.

[ChangeLog][QtCore][QVarLengthArray] Fixed a bug whereby a failed
append() would leave the container with an inconsistent size().

Pick-to: 6.2 5.15
Change-Id: Ief1e668d945149bd8ba96c8af1398baaa7876880
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>

1 files changed, 5 insertions, 6 deletions

diff --git a/src/corelib/tools/qvarlengtharray.h b/src/corelib/tools/qvarlengtharray.h
index 2a86a1dd7f..c412f96110 100644
--- a/src/corelib/tools/qvarlengtharray.h
+++ b/src/corelib/tools/qvarlengtharray.h
@@ -228,20 +228,19 @@ public:
         if (size() == capacity()) { // i.e. size() != 0
             T copy(t);
             reallocate(size(), size() << 1);
-            const qsizetype idx = s++;
-            new (data() + idx) T(std::move(copy));
+            new (end()) T(std::move(copy));
         } else {
-            const qsizetype idx = s++;
-            new (data() + idx) T(t);
+            new (end()) T(t);
         }
+        ++s;
     }
 
     void append(T &&t)
     {
         if (size() == capacity())
             reallocate(size(), size() << 1);
-        const qsizetype idx = s++;
-        new (data() + idx) T(std::move(t));
+        new (end()) T(std::move(t));
+        ++s;
     }
 
     void append(const T *buf, qsizetype size);