New AA_DisableWindowContextHelpButton to globally hide ? button

Dialogs and Sheets by default have the WindowsContextHelpButtonHint
set, which adds a question mark button to dialogs on Windows. This
button then triggers the 'What's this' mode by changing the cursor,
and letting the user explore the UI by showing whatsThis tooltips.

Anyhow, the paradigm is little used today and a lot of applications
do not set any whatsThis properties, leaving the mode pretty
non-functional. It's therefore common to explicitly remove the
WindowsContextHelpButtonHint from dialogs. However, this has to
be done for _every_ dialog.

Instead, this patch adds a global application flag to not set the
WindowsContextHelpButtonHint by default. This allows developers to
already buy into the Qt 6 behavior, where the flag will not be set
anymore by default.

[ChangeLog][QtWidgets] Added AA_DisableWindowContextHelpButton
attribute. Setting this attribute globally prevents the automatic
"What's this" button on dialogs on Windows
(WindowsContextHelpButtonHint).

Change-Id: I497a79575f222c78b2d5d051a6de346b231f72d3
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Lars Knoll <lars.knoll@qt.io>

1 files changed, 6 insertions, 3 deletions

diff --git a/src/widgets/kernel/qwidget.cpp b/src/widgets/kernel/qwidget.cpp
index 4dcee2771b..7b9ccf3837 100644
--- a/src/widgets/kernel/qwidget.cpp
+++ b/src/widgets/kernel/qwidget.cpp
@@ -1117,9 +1117,12 @@ void QWidgetPrivate::adjustFlags(Qt::WindowFlags &flags, QWidget *w)
     }
     if (customize)
         ; // don't modify window flags if the user explicitly set them.
-    else if (type == Qt::Dialog || type == Qt::Sheet)
-        flags |= Qt::WindowTitleHint | Qt::WindowSystemMenuHint | Qt::WindowContextHelpButtonHint | Qt::WindowCloseButtonHint;
-    else if (type == Qt::Tool)
+    else if (type == Qt::Dialog || type == Qt::Sheet) {
+        flags |= Qt::WindowTitleHint | Qt::WindowSystemMenuHint | Qt::WindowCloseButtonHint;
+        // ### fixme: Qt 6: Never set Qt::WindowContextHelpButtonHint flag automatically
+        if (!QApplicationPrivate::testAttribute(Qt::AA_DisableWindowContextHelpButton))
+            flags |= Qt::WindowContextHelpButtonHint;
+    } else if (type == Qt::Tool)
         flags |= Qt::WindowTitleHint | Qt::WindowSystemMenuHint | Qt::WindowCloseButtonHint;
     else
         flags |= Qt::WindowTitleHint | Qt::WindowSystemMenuHint | Qt::WindowMinimizeButtonHint |