QCache: Adapt to upcoming QHash changes

QHash changes some of its preconditions, so we must not call
findNode without verifying !isEmpty()

Task-number: QTBUG-91739
Task-number: QTBUG-98436
Change-Id: I2701b9a01187530f541a7c9a12db56c92f856d87
Reviewed-by: Lars Knoll <lars.knoll@qt.io>

2 files changed, 23 insertions, 1 deletions

diff --git a/src/corelib/tools/qcache.h b/src/corelib/tools/qcache.h
index 8a341c8555..32d822e892 100644
--- a/src/corelib/tools/qcache.h
+++ b/src/corelib/tools/qcache.h
@@ -160,6 +160,8 @@ class QCache
     }
     T *relink(const Key &key) const noexcept
     {
+        if (isEmpty())
+            return nullptr;
         Node *n = d.findNode(key);
         if (!n)
             return nullptr;
@@ -269,11 +271,13 @@ public:
     }
     inline bool contains(const Key &key) const noexcept
     {
-        return d.findNode(key) != nullptr;
+        return !isEmpty() && d.findNode(key) != nullptr;
     }
 
     bool remove(const Key &key) noexcept(std::is_nothrow_destructible_v<Node>)
     {
+        if (isEmpty())
+            return false;
         Node *n = d.findNode(key);
         if (!n) {
             return false;
@@ -285,6 +289,8 @@ public:
 
     T *take(const Key &key) noexcept(std::is_nothrow_destructible_v<Key>)
     {
+        if (isEmpty())
+            return nullptr;
         Node *n = d.findNode(key);
         if (!n)
             return nullptr;
diff --git a/tests/auto/corelib/tools/qcache/tst_qcache.cpp b/tests/auto/corelib/tools/qcache/tst_qcache.cpp
index eb024e8f9e..58b8d6e4c6 100644
--- a/tests/auto/corelib/tools/qcache/tst_qcache.cpp
+++ b/tests/auto/corelib/tools/qcache/tst_qcache.cpp
@@ -37,6 +37,7 @@ public slots:
     void initTestCase();
     void cleanupTestCase();
 private slots:
+    void empty();
     void maxCost();
     void setMaxCost();
     void totalCost();
@@ -75,6 +76,21 @@ void tst_QCache::cleanupTestCase()
     QCOMPARE(Foo::count, 0);
 }
 
+void tst_QCache::empty()
+{
+    QCache<int, int> cache;
+    QCOMPARE(cache.size(), 0);
+    QCOMPARE(cache.count(), 0);
+    QVERIFY(cache.isEmpty());
+    QVERIFY(!cache.contains(1));
+    QCOMPARE(cache.keys().size(), 0);
+    QCOMPARE(cache.take(1), nullptr);
+    QVERIFY(!cache.remove(1));
+    QCOMPARE(cache.object(1), nullptr);
+    QCOMPARE(cache[1], nullptr);
+    QCOMPARE(cache.totalCost(), 0);
+}
+
 void tst_QCache::maxCost()
 {
     QCache<QString, int> cache1, cache2(100), cache3(200), cache4(-50);