QFlags::testFlag(): handle the zero case appropriately.

Brought up by Andy. See perforce change 314809,
17b07e3ab6192b31f77fd2f126705b9ab53b3937. Related to task 221708.

Reviewed-By: Andy Shaw
(cherry picked from commit cc24c46c117248ecb98200416e7f25375e6bb476)

2 files changed, 25 insertions, 1 deletions

diff --git a/src/corelib/global/qglobal.h b/src/corelib/global/qglobal.h
index 63f6c31..f650bd2 100644
--- a/src/corelib/global/qglobal.h
+++ b/src/corelib/global/qglobal.h
@@ -2017,7 +2017,7 @@ public:
 
     inline bool operator!() const { return !i; }
 
-    inline bool testFlag(Enum f) const { return (i & f) == f; }
+    inline bool testFlag(Enum f) const { return (i & f) == f && (f != 0 || i == f ); }
 };
 
 #define Q_DECLARE_FLAGS(Flags, Enum)\
diff --git a/tests/auto/qflags/tst_qflags.cpp b/tests/auto/qflags/tst_qflags.cpp
index a5f68dc..87d8258 100644
--- a/tests/auto/qflags/tst_qflags.cpp
+++ b/tests/auto/qflags/tst_qflags.cpp
@@ -45,6 +45,7 @@ class tst_QFlags: public QObject
     Q_OBJECT
 private slots:
     void testFlag() const;
+    void testFlagZeroFlag() const;
     void testFlagMultiBits() const;
 };
 
@@ -59,8 +60,31 @@ void tst_QFlags::testFlag() const
     QVERIFY(!btn.testFlag(Qt::LeftButton));
 }
 
+void tst_QFlags::testFlagZeroFlag() const
+{
+    {
+        Qt::MouseButtons btn = Qt::LeftButton | Qt::RightButton;
+        /* Qt::NoButton has the value 0. */
+
+        QVERIFY(!btn.testFlag(Qt::NoButton));
+    }
+
+    {
+        /* A zero enum set should test true with zero. */
+        QVERIFY(Qt::MouseButtons().testFlag(Qt::NoButton));
+    }
+
+    {
+        Qt::MouseButtons btn = Qt::NoButton;
+        QVERIFY(btn.testFlag(Qt::NoButton));
+    }
+}
+
 void tst_QFlags::testFlagMultiBits() const
 {
+    /* Qt::Window is 0x00000001
+     * Qt::Dialog is 0x00000002 | Window
+     */
     {
         const Qt::WindowFlags onlyWindow(Qt::Window);
         QVERIFY(!onlyWindow.testFlag(Qt::Dialog));