Restore pre-Qt6 QList::fill() behavior

Somehow QList::fill(t, newSize) introduced a regression in Qt6:
when newSize < QList::size() we should resize to the newSize.
This is aligned with QVector::fill() in 5.15 and std::vector::assign()

While 6.0 is already out, picking it to 6.0.x could save someone who
haven't migrated yet as well as fix some accidental bugs in Qt's code

[ChangeLog][QtCore][QList] Fixed QList::fill() regression introduced in
6.0: calling fill() with size < current list size wouldn't truncate the
list

Fixes: QTBUG-91042
Pick-to: 6.0 6.1
Change-Id: Ic166e2c5e42390b61df1030f7c705e344433f7f2
Reviewed-by: Lars Knoll <lars.knoll@qt.io>

1 files changed, 4 insertions, 1 deletions

diff --git a/src/corelib/tools/qlist.h b/src/corelib/tools/qlist.h
index 662fede6f7..b50cd9090f 100644
--- a/src/corelib/tools/qlist.h
+++ b/src/corelib/tools/qlist.h
@@ -834,8 +834,11 @@ inline QList<T> &QList<T>::fill(parameter_type t, qsizetype newSize)
         // we're detached
         const T copy(t);
         d->assign(d.begin(), d.begin() + qMin(size(), newSize), t);
-        if (newSize > size())
+        if (newSize > size()) {
             d->copyAppend(newSize - size(), copy);
+        } else if (newSize < size()) {
+            d->truncate(newSize);
+        }
     }
     return *this;
 }