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, 2 insertions, 0 deletions

diff --git a/dist/changes-5.3.0 b/dist/changes-5.3.0
index 87d9c771e7..035d0656ed 100644
--- a/dist/changes-5.3.0
+++ b/dist/changes-5.3.0
@@ -25,5 +25,7 @@ QtWidgets
 QtCore
 ------
 
+- QSignalBlocker: (new) RAII wrapper around QObject::blockSignals()
+
 QtGui
 -----