Fix focus handling when leaving locator

Pressing escape or triggering an item should get your focus back to
where you were, also in external editor and help windows.
Fixes triggering editor related menu items like "Close" from locator.

Task-number: QTCREATORBUG-20071
Change-Id: I0111b846e9476697a7bba7856bb2cc4b5bef7979
Reviewed-by: David Schulz <david.schulz@qt.io>

src/plugins/coreplugin/locator/locatorwidget.cpp

@@ -592,6 +592,8 @@ LocatorWidget::LocatorWidget(Locator *locator) :
         updatePlaceholderText(locateCmd);
     }
 
+    connect(qApp, &QApplication::focusChanged, this, &LocatorWidget::updatePreviousFocusWidget);
+
     connect(locator, &Locator::filtersChanged, this, &LocatorWidget::updateFilterList);
     updateFilterList();
 }
@@ -620,6 +622,28 @@ void LocatorWidget::updateFilterList()
     m_filterMenu->addAction(m_configureAction);
 }
 
+bool LocatorWidget::isInMainWindow() const
+{
+    return window() == ICore::mainWindow();
+}
+
+void LocatorWidget::updatePreviousFocusWidget(QWidget *previous, QWidget *current)
+{
+    const auto isInLocator = [this](QWidget *w) { return w == this || isAncestorOf(w); };
+    if (isInLocator(current) && !isInLocator(previous))
+        m_previousFocusWidget = previous;
+}
+
+static void resetFocus(QPointer<QWidget> previousFocus, bool isInMainWindow)
+{
+    if (previousFocus) {
+        previousFocus->setFocus();
+        ICore::raiseWindow(previousFocus);
+    } else if (isInMainWindow) {
+        ModeManager::setFocusToCurrentMode();
+    }
+}
+
 bool LocatorWidget::eventFilter(QObject *obj, QEvent *event)
 {
     if (obj == m_fileLineEdit && event->type() == QEvent::ShortcutOverride) {
@@ -706,7 +730,12 @@ bool LocatorWidget::eventFilter(QObject *obj, QEvent *event)
         case Qt::Key_Escape:
             if (!ke->modifiers()) {
                 event->accept();
-                QTimer::singleShot(0, this, &LocatorWidget::setFocusToCurrentMode);
+                QTimer::singleShot(0,
+                                   this,
+                                   [focus = m_previousFocusWidget,
+                                    isInMainWindow = isInMainWindow()] {
+                                       resetFocus(focus, isInMainWindow);
+                                   });
                 return true;
             }
             break;
@@ -723,11 +752,6 @@ bool LocatorWidget::eventFilter(QObject *obj, QEvent *event)
     return QWidget::eventFilter(obj, event);
 }
 
-void LocatorWidget::setFocusToCurrentMode()
-{
-    ModeManager::setFocusToCurrentMode();
-}
-
 void LocatorWidget::showPopupDelayed()
 {
     m_updateRequested = true;
@@ -858,7 +882,7 @@ void LocatorWidget::acceptEntry(int row)
     entry.filter->accept(entry, &newText, &selectionStart, &selectionLength);
     if (newText.isEmpty()) {
         emit hidePopup();
-        m_fileLineEdit->clearFocus();
+        resetFocus(m_previousFocusWidget, isInMainWindow());
     } else {
         showText(newText, selectionStart, selectionLength);
     }

src/plugins/coreplugin/locator/locatorwidget.h

@@ -79,9 +79,10 @@ private:
     void showConfigureDialog();
     void addSearchResults(int firstIndex, int endIndex);
     void handleSearchFinished();
-    void setFocusToCurrentMode();
     void updateFilterList();
+    bool isInMainWindow() const;
 
+    void updatePreviousFocusWidget(QWidget *previous, QWidget *current);
     bool eventFilter(QObject *obj, QEvent *event) override;
 
     void updateCompletionList(const QString &text);
@@ -103,6 +104,7 @@ private:
     QWidget *m_progressIndicator = nullptr;
     QTimer m_showProgressTimer;
     Utils::optional<int> m_rowRequestedForAccept;
+    QPointer<QWidget> m_previousFocusWidget;
 };
 
 class LocatorPopup : public QWidget