Add qHash() overload for QSet

...using qHashRangeCommutative(). Also add a test.

[ChangeLog][QtCore][QSet] Can now be used as the key in QSet, QHash.

Change-Id: Ie7c81d257a3b324fc03d394fa7c9fcf0c6fb062a
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/tools/qset.h

@@ -237,6 +237,15 @@ private:
     }
 };
 
+template <typename T>
+uint qHash(const QSet<T> &key, uint seed = 0)
+Q_DECL_NOEXCEPT_EXPR(noexcept(qHashRangeCommutative(key.begin(), key.end(), seed)))
+{
+    return qHashRangeCommutative(key.begin(), key.end(), seed);
+}
+
+// inline function implementations
+
 template <class T>
 Q_INLINE_TEMPLATE void QSet<T>::reserve(int asize) { q_hash.reserve(asize); }
 

src/corelib/tools/qset.qdoc

@@ -968,3 +968,14 @@
 
     \sa{Serializing Qt Data Types}{Format of the QDataStream operators}
 */
+
+/*!
+    \fn uint qHash(const QSet<T> &key, uint seed = 0)
+    \relates QHash
+    \since 5.5
+
+    Returns the hash value for the \a key, using \a seed to seed the calculation.
+
+    The hash value is independent of the order of elements in \a key, that is, sets
+    that contain the same elements hash to the same value.
+*/

tests/auto/corelib/tools/qset/tst_qset.cpp

@@ -72,6 +72,7 @@ private slots:
     void javaMutableIterator();
     void makeSureTheComfortFunctionsCompile();
     void initializerList();
+    void qhash();
 };
 
 struct IdentityTracker {
@@ -968,6 +969,50 @@ void tst_QSet::initializerList()
 #endif
 }
 
+QT_BEGIN_NAMESPACE
+extern Q_CORE_EXPORT QBasicAtomicInt qt_qhash_seed; // from qhash.cpp
+QT_END_NAMESPACE
+
+void tst_QSet::qhash()
+{
+    //
+    // check that sets containing the same elements hash to the same value
+    //
+    {
+        QSet<int> s1;
+        s1.reserve(4);
+        s1 << 400 << 300 << 200 << 100;
+
+        // also change the seed:
+        qt_qhash_seed = qt_qhash_seed + 0x9e3779b9;
+
+        QSet<int> s2;
+        s2.reserve(100); // provoke different bucket counts
+        s2 << 100 << 200 << 300 << 400; // and insert elements in different order, too
+
+        QVERIFY(s1.capacity() != s2.capacity());
+        QCOMPARE(s1, s2);
+        QVERIFY(!std::equal(s1.cbegin(), s1.cend(), s2.cbegin())); // verify that the order _is_ different
+        QCOMPARE(qHash(s1), qHash(s2));
+    }
+
+    //
+    // check that sets of sets work:
+    //
+    {
+#ifdef Q_COMPILER_INITIALIZER_LISTS
+        QSet<QSet<int> > intSetSet = { { 0, 1, 2 }, { 0, 1 }, { 1, 2 } };
+#else
+        QSet<QSet<int> > intSetSet;
+        QSet<int> intSet01, intSet12;
+        intSet01 << 0 << 1;
+        intSet12 << 1 << 2;
+        intSetSet << intSet01 << intSet12 << (intSet01|intSet12);
+#endif
+        QCOMPARE(intSetSet.size(), 3);
+    }
+}
+
 QTEST_APPLESS_MAIN(tst_QSet)
 
 #include "tst_qset.moc"