QHash/QSet: fix squeeze() for default-constructed container

QHash::squeeze() was unconditionally calling reserve(0), which is
always allocating memory (even for 0 size).
This was leading to a confusing situation when calling squeeze() on
a default-constructed container with 0 capacity() actually allocated
memory. This is very misleading, as squeeze() is supposed to free
unneeded memory, not to allocate more.

This patch adds a check for non-zero capacity. As a result, nothing
is done for default-constructed container.

Note that this patch also affects the QSet::squeeze() behavior, because
QSet uses QHash as its underlying data type.

Task-number: QTBUG-91736
Pick-to: 6.2 6.1
Change-Id: Ib1c3c8b7b3de6ddeefea0e70b1ec71803e8fd3b3
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>
Reviewed-by: Andreas Buhr <andreas.buhr@qt.io>

1 files changed, 5 insertions, 1 deletions

diff --git a/src/corelib/tools/qhash.h b/src/corelib/tools/qhash.h
index b030fd2a93..38f23d822f 100644
--- a/src/corelib/tools/qhash.h
+++ b/src/corelib/tools/qhash.h
@@ -850,7 +850,11 @@ public:
         else
             d = Data::detached(d, size_t(size));
     }
-    inline void squeeze() { reserve(0); }
+    inline void squeeze()
+    {
+        if (capacity())
+            reserve(0);
+    }
 
     inline void detach() { if (!d || d->ref.isShared()) d = Data::detached(d); }
     inline bool isDetached() const noexcept { return d && !d->ref.isShared(); }