Make command palette ephemeral (microsoft#8377)

So the implementation is somewhat dirty.
The ideas was nice - add lostFocusHandler

However it broke few things:
* In the TabSwitcher the ListItem must be focusable since otherwise 
the SingleSelectionMode behavior breaks. 
To address this I had to put the lostFocusHandler on the items as well
 
* When you click the flyout, the palette loses focus, 
which makes the terminal page to set the focus on the tab, closing the flyout. 
To address this I had to ensure the tab won't get focused once the flyout is open.
In addition, flyout should fix the focus before opening, 
otherwise alt+tab will put a focus on a tab row rather than on tab

* I also had to close the palette if the tab order changes.
To prevent inconsistencies.

Closes microsoft#8355

src/cascadia/TerminalApp/CommandPalette.cpp

@@ -438,6 +438,44 @@ namespace winrt::TerminalApp::implementation
     void CommandPalette::_rootPointerPressed(Windows::Foundation::IInspectable const& /*sender*/,
                                              Windows::UI::Xaml::Input::PointerRoutedEventArgs const& /*e*/)
     {
+        if (Visibility() != Visibility::Collapsed)
+        {
+            _dismissPalette();
+        }
+    }
+
+    // Method Description:
+    // - The purpose of this event handler is to hide the palette if it loses focus.
+    // We say we lost focus if our root element and all its descendants lost focus.
+    // This handler is invoked when our root element or some descendant loses focus.
+    // At this point we need to learn if the newly focused element belongs to this palette.
+    // To achieve this:
+    // - We start with the newly focused element and traverse its visual ancestors up to the Xaml root.
+    // - If one of the ancestors is this CommandPalette, then by our definition the focus is not lost
+    // - If we reach the Xaml root without meeting this CommandPalette,
+    // then the focus is not contained in it anymore and it should be dismissed
+    // Arguments:
+    // - <unused>
+    // Return Value:
+    // - <none>
+    void CommandPalette::_lostFocusHandler(Windows::Foundation::IInspectable const& /*sender*/,
+                                           Windows::UI::Xaml::RoutedEventArgs const& /*args*/)
+    {
+        auto focusedElementOrAncestor = Input::FocusManager::GetFocusedElement(this->XamlRoot()).try_as<DependencyObject>();
+        while (focusedElementOrAncestor)
+        {
+            if (focusedElementOrAncestor == *this)
+            {
+                // This palette is the focused element or an ancestor of the focused element. No need to dismiss.
+                return;
+            }
+
+            // Go up to the next ancestor
+            focusedElementOrAncestor = winrt::Windows::UI::Xaml::Media::VisualTreeHelper::GetParent(focusedElementOrAncestor);
+        }
+
+        // We got to the root (the element with no parent) and didn't meet this palette on the path.
+        // It means that it lost the focus and needs to be dismissed.
         _dismissPalette();
     }
 

src/cascadia/TerminalApp/CommandPalette.h

@@ -85,6 +85,9 @@ namespace winrt::TerminalApp::implementation
         void _updateUIForStackChange();
 
         void _rootPointerPressed(Windows::Foundation::IInspectable const& sender, Windows::UI::Xaml::Input::PointerRoutedEventArgs const& e);
+
+        void _lostFocusHandler(Windows::Foundation::IInspectable const& sender, Windows::UI::Xaml::RoutedEventArgs const& args);
+
         void _backdropPointerPressed(Windows::Foundation::IInspectable const& sender, Windows::UI::Xaml::Input::PointerRoutedEventArgs const& e);
 
         void _listItemClicked(Windows::Foundation::IInspectable const& sender, Windows::UI::Xaml::Controls::ItemClickEventArgs const& e);

src/cascadia/TerminalApp/CommandPalette.xaml

@@ -17,6 +17,7 @@ the MIT License. See LICENSE in the project root for license information. -->
     PreviewKeyDown="_previewKeyDownHandler"
     KeyDown="_keyDownHandler"
     PreviewKeyUp="_keyUpHandler"
+    LostFocus="_lostFocusHandler"
     mc:Ignorable="d"
     AutomationProperties.Name="{x:Bind ControlName, Mode=OneWay}">
 
@@ -245,8 +246,9 @@ the MIT License. See LICENSE in the project root for license information. -->
                         <!-- This HorizontalContentAlignment="Stretch" is important
                         to make sure it takes the entire width of the line -->
                         <ListViewItem HorizontalContentAlignment="Stretch"
-                                  AutomationProperties.Name="{x:Bind Command.Name, Mode=OneWay}"
-                                  AutomationProperties.AcceleratorKey="{x:Bind Command.KeyChordText, Mode=OneWay}">
+                                      IsTabStop="False"
+                                      AutomationProperties.Name="{x:Bind Command.Name, Mode=OneWay}"
+                                      AutomationProperties.AcceleratorKey="{x:Bind Command.KeyChordText, Mode=OneWay}">
 
                             <Grid HorizontalAlignment="Stretch" ColumnSpacing="8" >
                                 <Grid.ColumnDefinitions>

src/cascadia/TerminalApp/TerminalPage.cpp

@@ -585,6 +585,21 @@ namespace winrt::TerminalApp::implementation
             newTabFlyout.Items().Append(aboutFlyout);
         }
 
+        // Before opening the fly-out set focus on the current tab
+        // so no matter how fly-out is closed later on the focus will return to some tab.
+        // We cannot do it on closing because if the window loses focus (alt+tab)
+        // the closing event is not fired.
+        // It is important to set the focus on the tab
+        // Since the previous focus location might be discarded in the background,
+        // e.g., the command palette will be dismissed by the menu,
+        // and then closing the fly-out will move the focus to wrong location.
+        newTabFlyout.Opening([this](auto&&, auto&&) {
+            if (auto index{ _GetFocusedTabIndex() })
+            {
+                _tabs.GetAt(*index).Focus(FocusState::Programmatic);
+                _UpdateMRUTab(index.value());
+            }
+        });
         _newTabButton.Flyout(newTabFlyout);
     }
 
@@ -1072,19 +1087,6 @@ namespace winrt::TerminalApp::implementation
         _tabView.TabItems().RemoveAt(tabIndex);
         _UpdateTabIndices();
 
-        // If the tab switcher is currently open, update it to reflect the
-        // current list of tabs.
-        const auto tabSwitchMode = _settings.GlobalSettings().TabSwitcherMode();
-        const bool commandPaletteIsVisible = CommandPalette().Visibility() == Visibility::Visible;
-        if (tabSwitchMode == TabSwitcherMode::MostRecentlyUsed && commandPaletteIsVisible)
-        {
-            CommandPalette().SetTabActions(_mruTabActions, false);
-        }
-        else if (commandPaletteIsVisible)
-        {
-            _UpdatePaletteWithInOrderTabs();
-        }
-
         // To close the window here, we need to close the hosting window.
         if (_tabs.Size() == 0)
         {
@@ -2107,6 +2109,7 @@ namespace winrt::TerminalApp::implementation
             }
         }
 
+        CommandPalette().Visibility(Visibility::Collapsed);
         _UpdateTabView();
     }
 
@@ -2693,11 +2696,16 @@ namespace winrt::TerminalApp::implementation
     void TerminalPage::_CommandPaletteClosed(const IInspectable& /*sender*/,
                                              const RoutedEventArgs& /*eventArgs*/)
     {
-        // Return focus to the active control
-        if (auto index{ _GetFocusedTabIndex() })
+        // We don't want to set focus on the tab if fly-out is open as it will be closed
+        // TODO GH#5400: consider checking we are not in the opening state, by hooking both Opening and Open events
+        if (!_newTabButton.Flyout().IsOpen())
         {
-            _tabs.GetAt(*index).Focus(FocusState::Programmatic);
-            _UpdateMRUTab(index.value());
+            // Return focus to the active control
+            if (auto index{ _GetFocusedTabIndex() })
+            {
+                _tabs.GetAt(*index).Focus(FocusState::Programmatic);
+                _UpdateMRUTab(index.value());
+            }
         }
     }
 
@@ -2834,15 +2842,6 @@ namespace winrt::TerminalApp::implementation
             {
                 _mruTabActions.RemoveAt(mruIndex);
                 _mruTabActions.InsertAt(0, command);
-
-                // If the tab switcher is currently open, AND we're using it in
-                // MRU mode, then update it to reflect the current list of tabs.
-                const auto tabSwitchMode = _settings.GlobalSettings().TabSwitcherMode();
-                const bool commandPaletteIsVisible = CommandPalette().Visibility() == Visibility::Visible;
-                if (tabSwitchMode == TabSwitcherMode::MostRecentlyUsed && commandPaletteIsVisible)
-                {
-                    CommandPalette().SetTabActions(_mruTabActions, false);
-                }
             }
         }
     }