Provide the CloseWindow warning experience for the 'X' button

src/cascadia/TerminalApp/App.cpp

@@ -582,6 +582,22 @@ namespace winrt::TerminalApp::implementation
         }
     }
 
+    // Method Description:
+    // - Used to tell the app that the 'X' button has been clicked and
+    //   the user wants to close the app. We kick off the close warning
+    //   experience.
+    // Arguments:
+    // - <none>
+    // Return Value:
+    // - <none>
+    void App::WindowCloseButtonClicked()
+    {
+        if (_root)
+        {
+            _root->CloseWindow();
+        }
+    }
+
     // Methods that proxy typed event handlers through TerminalPage
     winrt::event_token App::SetTitleBarContent(Windows::Foundation::TypedEventHandler<winrt::Windows::Foundation::IInspectable, winrt::Windows::UI::Xaml::UIElement> const& handler)
     {

src/cascadia/TerminalApp/App.h

@@ -38,6 +38,8 @@ namespace winrt::TerminalApp::implementation
         hstring Title();
         void TitlebarClicked();
 
+        void WindowCloseButtonClicked();
+
         // -------------------------------- WinRT Events ---------------------------------
         DECLARE_EVENT_WITH_TYPED_EVENT_HANDLER(TitleChanged, _titleChangeHandlers, winrt::Windows::Foundation::IInspectable, winrt::hstring);
         DECLARE_EVENT_WITH_TYPED_EVENT_HANDLER(LastTabClosed, _lastTabClosedHandlers, winrt::Windows::Foundation::IInspectable, winrt::TerminalApp::LastTabClosedEventArgs);

src/cascadia/TerminalApp/App.idl

@@ -26,6 +26,7 @@ namespace TerminalApp
         Windows.Foundation.Point GetLaunchDimensions(UInt32 dpi);
         Boolean GetShowTabsInTitlebar();
         void TitlebarClicked();
+        void WindowCloseButtonClicked();
 
         event Windows.Foundation.TypedEventHandler<Object, Windows.UI.Xaml.UIElement> SetTitleBarContent;
         event Windows.Foundation.TypedEventHandler<Object, String> TitleChanged;

src/cascadia/TerminalApp/AppActionHandlers.cpp

@@ -63,7 +63,7 @@ namespace winrt::TerminalApp::implementation
     void TerminalPage::_HandleCloseWindow(const IInspectable& /*sender*/,
                                           const TerminalApp::ActionEventArgs& args)
     {
-        _CloseWindow();
+        CloseWindow();
         args.Handled(true);
     }
 

src/cascadia/TerminalApp/TerminalPage.cpp

@@ -823,9 +823,9 @@ namespace winrt::TerminalApp::implementation
     }
 
     // Method Description:
-    // - Close the terminal app with keys. If there is more
+    // - Close the terminal app. If there is more
     //   than one tab opened, show a warning dialog.
-    void TerminalPage::_CloseWindow()
+    void TerminalPage::CloseWindow()
     {
         if (_tabs.size() > 1)
         {

src/cascadia/TerminalApp/TerminalPage.h

@@ -36,6 +36,8 @@ namespace winrt::TerminalApp::implementation
 
         void TitlebarClicked();
 
+        void CloseWindow();
+
         // -------------------------------- WinRT Events ---------------------------------
         DECLARE_EVENT_WITH_TYPED_EVENT_HANDLER(TitleChanged, _titleChangeHandlers, winrt::Windows::Foundation::IInspectable, winrt::hstring);
         DECLARE_EVENT_WITH_TYPED_EVENT_HANDLER(LastTabClosed, _lastTabClosedHandlers, winrt::Windows::Foundation::IInspectable, winrt::TerminalApp::LastTabClosedEventArgs);
@@ -94,7 +96,6 @@ namespace winrt::TerminalApp::implementation
         void _SetFocusedTabIndex(int tabIndex);
         void _CloseFocusedTab();
         void _CloseFocusedPane();
-        void _CloseWindow();
         void _CloseAllTabs();
 
         // Todo: add more event implementations here

src/cascadia/TerminalApp/TitlebarControl.cpp

@@ -87,7 +87,7 @@ namespace winrt::TerminalApp::implementation
 
     void TitlebarControl::Close_Click(winrt::Windows::Foundation::IInspectable const& sender, winrt::Windows::UI::Xaml::RoutedEventArgs const& e)
     {
-        ::PostQuitMessage(0);
+        ::PostMessage(_window, WM_SYSCOMMAND, SC_CLOSE, 0);
     }
 
     void TitlebarControl::SetWindowVisualState(WindowVisualState visualState)

src/cascadia/WindowsTerminal/AppHost.cpp

@@ -70,6 +70,10 @@ void AppHost::Initialize()
         _app.SetTitleBarContent({ this, &AppHost::_UpdateTitleBarContent });
     }
 
+    // Register the 'X' button of the window for a warning experience of multiple
+    // tabs opened, this is consistent with Alt+F4 closing
+    _window->WindowCloseButtonClicked([this]() { _app.WindowCloseButtonClicked(); });
+
     // Add an event handler to plumb clicks in the titlebar area down to the
     // application layer.
     _window->DragRegionClicked([this]() { _app.TitlebarClicked(); });

src/cascadia/WindowsTerminal/IslandWindow.cpp

@@ -198,6 +198,14 @@ void IslandWindow::OnSize(const UINT width, const UINT height)
         // key that does not correspond to any mnemonic or accelerator key,
         return MAKELRESULT(0, MNC_CLOSE);
     }
+    case WM_CLOSE:
+    {
+        // If the user wants to close the app by clicking 'X' button,
+        // we hand off the close experience to the app layer. If all the tabs
+        // are closed, the window will be closed as well.
+        _windowCloseButtonClickedHandler();
+        return 0;
+    }
     }
 
     // TODO: handle messages here...
@@ -285,3 +293,4 @@ void IslandWindow::UpdateTheme(const winrt::Windows::UI::Xaml::ElementTheme& req
 }
 
 DEFINE_EVENT(IslandWindow, DragRegionClicked, _DragRegionClickedHandlers, winrt::delegate<>);
+DEFINE_EVENT(IslandWindow, WindowCloseButtonClicked, _windowCloseButtonClickedHandler, winrt::delegate<>);

src/cascadia/WindowsTerminal/IslandWindow.h

@@ -68,6 +68,7 @@ class IslandWindow :
 #pragma endregion
 
     DECLARE_EVENT(DragRegionClicked, _DragRegionClickedHandlers, winrt::delegate<>);
+    DECLARE_EVENT(WindowCloseButtonClicked, _windowCloseButtonClickedHandler, winrt::delegate<>);
 
 protected:
     void ForceResize()