macOS: Support gestures for going back and forward

in the editor and help viewer, when setting macOS Trackpad preferences
to "Swipe between pages: Swipe with Three Fingers".

Fixes: QTCREATORBUG-7387
Change-Id: I1c2684f846d72bb98ba6626c3a04f01fb57b8e24
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>

src/plugins/coreplugin/editormanager/editorview.cpp

@@ -324,6 +324,23 @@ void EditorView::focusInEvent(QFocusEvent *)
     EditorManagerPrivate::setCurrentView(this);
 }
 
+bool EditorView::event(QEvent *e)
+{
+    if (e->type() == QEvent::NativeGesture) {
+        auto ev = static_cast<QNativeGestureEvent *>(e);
+        if (ev->gestureType() == Qt::SwipeNativeGesture) {
+            if (ev->value() > 0 && canGoBack()) { // swipe from right to left == go back
+                goBackInNavigationHistory();
+                return true;
+            } else if (ev->value() <= 0 && canGoForward()) {
+                goForwardInNavigationHistory();
+                return true;
+            }
+        }
+    }
+    return false;
+}
+
 void EditorView::addEditor(IEditor *editor)
 {
     if (m_editors.contains(editor))

src/plugins/coreplugin/editormanager/editorview.h

@@ -111,6 +111,7 @@ protected:
     void paintEvent(QPaintEvent *) override;
     void mousePressEvent(QMouseEvent *e) override;
     void focusInEvent(QFocusEvent *) override;
+    bool event(QEvent *e) override;
 
 private:
     friend class SplitterOrView; // for setParentSplitterOrView

src/plugins/help/helpviewer.cpp

@@ -15,9 +15,10 @@
 #include <QFileInfo>
 #include <QUrl>
 
-#include <QGuiApplication>
 #include <QDesktopServices>
+#include <QGuiApplication>
 #include <QMouseEvent>
+#include <QNativeGestureEvent>
 
 #include <QHelpEngine>
 
@@ -189,6 +190,23 @@ void HelpViewer::wheelEvent(QWheelEvent *event)
     QWidget::wheelEvent(event);
 }
 
+bool HelpViewer::event(QEvent *e)
+{
+    if (e->type() == QEvent::NativeGesture) {
+        auto ev = static_cast<QNativeGestureEvent *>(e);
+        if (ev->gestureType() == Qt::SwipeNativeGesture) {
+            if (ev->value() > 0 && isBackwardAvailable()) { // swipe from right to left == go back
+                backward();
+                return true;
+            } else if (ev->value() <= 0 && isForwardAvailable()) {
+                forward();
+                return true;
+            }
+        }
+    }
+    return false;
+}
+
 void HelpViewer::incrementZoom(int steps)
 {
     const int incrementPercentage = 10 * steps; // 10 percent increase by single step

src/plugins/help/helpviewer.h

@@ -88,6 +88,7 @@ signals:
 
 protected:
     void wheelEvent(QWheelEvent *event) override;
+    bool event(QEvent *e) override;
 
     void slotLoadStarted();
     void slotLoadFinished();