QSignalBlocker: (new) RAII class for QObject::blockSignals()

I don't think I ever worked on a project of non-trivial
size that didn't at some point add a QSignalBlocker.

This commit adds code, tests and documentation. Later
commits will convert naked blockSignals() calls to use
QSignalBlocker.

The implementation is purely inline to avoid the heavy
overhead of cross-dll function calls for this miniscule
task. This should not be a problem because QSignalBlocker
only uses public API and a pattern that we anyway need
to keep working until Qt 6, at least, so even changing
the implementation later will be no problem as the old
implementation lurking in non-recompiled code will be
acceptable, too.

This implementation is an evolution from KDTools'
KDSignalBlocker, with the following changes:
- Implements unblock() and reblock()
- Uses the return value of blockSignals() instead of a
  separate signalsBlocked() call.

Change-Id: I1933dfd72a0f5190324be377cfca3c54cf3d6828
Reviewed-by: Olivier Goffart <ogoffart@woboq.com>

1 files changed, 49 insertions, 0 deletions

diff --git a/tests/auto/corelib/kernel/qobject/tst_qobject.cpp b/tests/auto/corelib/kernel/qobject/tst_qobject.cpp
index 05d81c2bd1..f429500077 100644
--- a/tests/auto/corelib/kernel/qobject/tst_qobject.cpp
+++ b/tests/auto/corelib/kernel/qobject/tst_qobject.cpp
@@ -102,6 +102,7 @@ private slots:
 #ifndef QT_NO_PROCESS
     void recursiveSignalEmission();
 #endif
+    void signalBlocking();
     void blockingQueuedConnection();
     void childEvents();
     void installEventFilter();
@@ -2979,6 +2980,54 @@ void tst_QObject::recursiveSignalEmission()
 }
 #endif
 
+void tst_QObject::signalBlocking()
+{
+    SenderObject sender;
+    ReceiverObject receiver;
+
+    receiver.connect(&sender, SIGNAL(signal1()), SLOT(slot1()));
+
+    sender.emitSignal1();
+    QVERIFY(receiver.called(1));
+    receiver.reset();
+
+    {
+        QSignalBlocker blocker(&sender);
+
+        sender.emitSignal1();
+        QVERIFY(!receiver.called(1));
+        receiver.reset();
+
+        sender.blockSignals(false);
+
+        sender.emitSignal1();
+        QVERIFY(receiver.called(1));
+        receiver.reset();
+
+        sender.blockSignals(true);
+
+        sender.emitSignal1();
+        QVERIFY(!receiver.called(1));
+        receiver.reset();
+
+        blocker.unblock();
+
+        sender.emitSignal1();
+        QVERIFY(receiver.called(1));
+        receiver.reset();
+
+        blocker.reblock();
+
+        sender.emitSignal1();
+        QVERIFY(!receiver.called(1));
+        receiver.reset();
+    }
+
+    sender.emitSignal1();
+    QVERIFY(receiver.called(1));
+    receiver.reset();
+}
+
 void tst_QObject::blockingQueuedConnection()
 {
     {