Accept ZWNJ, ZWJ and PUA characters in input widgets

Private Use Area characters are quite valid input characters when used
in combination with a custom font. Joiners also serve an important language
purpose in semitic writing systems.

Note that there is a hack where we disregard any character produced
using CTRL or CTRL+SHIFT specifically because of German keyboards. I have chosen to
keep the hack in this patch to limit the change (though I have made an exception
for ZWJ and ZWNJ since both are produced using Ctrl+Shift on Windows), but it
will probably have to be reverted.

[ChangeLog][QtWidgets][Input] Accept characters in Private Use Area, as well as
zero-width joiners and zero-width non-joiners in input in QLineEdit and QTextEdit.

Task-number: QTBUG-42074
Task-number: QTBUG-57003
Change-Id: I73f3b7d587a8670de24e902dc52a51f7721dba5a
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>

1 files changed, 7 insertions, 11 deletions

diff --git a/src/widgets/widgets/qwidgetlinecontrol.cpp b/src/widgets/widgets/qwidgetlinecontrol.cpp
index 9b65dc43d1..a862274a3d 100644
--- a/src/widgets/widgets/qwidgetlinecontrol.cpp
+++ b/src/widgets/widgets/qwidgetlinecontrol.cpp
@@ -1924,19 +1924,15 @@ void QWidgetLineControl::processKeyEvent(QKeyEvent* event)
         unknown = false;
     }
 
-    // QTBUG-35734: ignore Ctrl/Ctrl+Shift; accept only AltGr (Alt+Ctrl) on German keyboards
-    if (unknown && !isReadOnly()
-        && event->modifiers() != Qt::ControlModifier
-        && event->modifiers() != (Qt::ControlModifier | Qt::ShiftModifier)) {
-        QString t = event->text();
-        if (!t.isEmpty() && t.at(0).isPrint()) {
-            insert(t);
+    if (unknown
+        && !isReadOnly()
+        && isAcceptableInput(event)) {
+        insert(event->text());
 #ifndef QT_NO_COMPLETER
-            complete(event->key());
+        complete(event->key());
 #endif
-            event->accept();
-            return;
-        }
+        event->accept();
+        return;
     }
 
     if (unknown)