Introduce `switchSelectionEndpoint` action (#13370)

## Summary of the Pull Request
Introduces the `switchSelectionEndpoint` action which switches whichever selection endpoint is targeted when a selection is present. For example, if you are targeting "start", `switchSelectionEndpoint` makes it so that now you are targeting "end". This also updates the selection markers appropriately.

## References
Spec - #5804 
#13358
Closes #3663

## Detailed Description of the Pull Request / Additional comments
Most of the code is just standard code of adding a new action. Other than that, we have...
- if there is no selection, the action fails and the keybinding is passed through (similar to `copy()`)
- when we update the selection endpoint, we need to also update the "pivot". This ensures that future calls of `UpdateSelection()` respect this swap.
- [Corner Case] if the cursor is being moved, we make it so that you basically "anchored" an endpoint and you don't have to hold shift anymore.

doc/cascadia/profiles.schema.json

@@ -354,6 +354,7 @@
         "toggleFocusMode",
         "selectAll",
         "setFocusMode",
+        "switchSelectionEndpoint",
         "toggleFullscreen",
         "setFullScreen",
         "setMaximized",

src/cascadia/TerminalApp/AppActionHandlers.cpp

@@ -1112,4 +1112,14 @@ namespace winrt::TerminalApp::implementation
             args.Handled(handled);
         }
     }
+
+    void TerminalPage::_HandleSwitchSelectionEndpoint(const IInspectable& /*sender*/,
+                                                      const ActionEventArgs& args)
+    {
+        if (const auto& control{ _GetActiveControl() })
+        {
+            const auto handled = control.SwitchSelectionEndpoint();
+            args.Handled(handled);
+        }
+    }
 }

src/cascadia/TerminalControl/ControlCore.cpp

@@ -1089,6 +1089,16 @@ namespace winrt::Microsoft::Terminal::Control::implementation
         return static_cast<Control::SelectionInteractionMode>(_terminal->SelectionMode());
     }
 
+    bool ControlCore::SwitchSelectionEndpoint()
+    {
+        if (_terminal->IsSelectionActive())
+        {
+            _terminal->SwitchSelectionEndpoint();
+            return true;
+        }
+        return false;
+    }
+
     // Method Description:
     // - Pre-process text pasted (presumably from the clipboard)
     //   before sending it over the terminal's connection.

src/cascadia/TerminalControl/ControlCore.h

@@ -86,6 +86,7 @@ namespace winrt::Microsoft::Terminal::Control::implementation
         bool ToggleBlockSelection();
         void ToggleMarkMode();
         Control::SelectionInteractionMode SelectionMode() const;
+        bool SwitchSelectionEndpoint();
 
         void GotFocus();
         void LostFocus();

src/cascadia/TerminalControl/ControlCore.idl

@@ -92,6 +92,7 @@ namespace Microsoft.Terminal.Control
         void ClearSelection();
         Boolean ToggleBlockSelection();
         void ToggleMarkMode();
+        Boolean SwitchSelectionEndpoint();
         void ClearBuffer(ClearBufferType clearType);
 
         void SetHoveredCell(Microsoft.Terminal.Core.Point terminalPosition);

src/cascadia/TerminalControl/TermControl.cpp

@@ -1929,6 +1929,11 @@ namespace winrt::Microsoft::Terminal::Control::implementation
         _core.ToggleMarkMode();
     }
 
+    bool TermControl::SwitchSelectionEndpoint()
+    {
+        return _core.SwitchSelectionEndpoint();
+    }
+
     void TermControl::Close()
     {
         if (!_IsClosing())

src/cascadia/TerminalControl/TermControl.h

@@ -40,6 +40,7 @@ namespace winrt::Microsoft::Terminal::Control::implementation
         void SelectAll();
         bool ToggleBlockSelection();
         void ToggleMarkMode();
+        bool SwitchSelectionEndpoint();
         void Close();
         Windows::Foundation::Size CharacterDimensions() const;
         Windows::Foundation::Size MinimumSize();

src/cascadia/TerminalControl/TermControl.idl

@@ -53,6 +53,7 @@ namespace Microsoft.Terminal.Control
         void SelectAll();
         Boolean ToggleBlockSelection();
         void ToggleMarkMode();
+        Boolean SwitchSelectionEndpoint();
         void ClearBuffer(ClearBufferType clearType);
         void Close();
         Windows.Foundation.Size CharacterDimensions { get; };

src/cascadia/TerminalCore/Terminal.cpp

@@ -48,6 +48,7 @@ Terminal::Terminal() :
     _selectionMode{ SelectionInteractionMode::None },
     _selection{ std::nullopt },
     _selectionEndpoint{ static_cast<SelectionEndpoint>(0) },
+    _anchorInactiveSelectionEndpoint{ false },
     _taskbarState{ 0 },
     _taskbarProgress{ 0 },
     _trimBlockSelection{ false },

src/cascadia/TerminalCore/Terminal.hpp

@@ -271,6 +271,7 @@ public:
     void UpdateSelection(SelectionDirection direction, SelectionExpansion mode, ControlKeyStates mods);
     void SelectAll();
     SelectionInteractionMode SelectionMode() const noexcept;
+    void SwitchSelectionEndpoint();
     void ToggleMarkMode();
 
     using UpdateSelectionParams = std::optional<std::pair<SelectionDirection, SelectionExpansion>>;
@@ -349,6 +350,7 @@ private:
     SelectionExpansion _multiClickSelectionMode;
     SelectionInteractionMode _selectionMode;
     SelectionEndpoint _selectionEndpoint;
+    bool _anchorInactiveSelectionEndpoint;
 #pragma endregion
 
     std::unique_ptr<TextBuffer> _mainBuffer;

src/cascadia/TerminalCore/TerminalSelection.cpp

@@ -309,6 +309,33 @@ void Terminal::ToggleMarkMode()
     }
 }
 
+// Method Description:
+// - switch the targeted selection endpoint with the other one (i.e. start <--> end)
+void Terminal::SwitchSelectionEndpoint()
+{
+    if (IsSelectionActive())
+    {
+        if (WI_IsFlagSet(_selectionEndpoint, SelectionEndpoint::Start) && WI_IsFlagSet(_selectionEndpoint, SelectionEndpoint::End))
+        {
+            // moving cursor --> anchor start, move end
+            _selectionEndpoint = SelectionEndpoint::End;
+            _anchorInactiveSelectionEndpoint = true;
+        }
+        else if (WI_IsFlagSet(_selectionEndpoint, SelectionEndpoint::End))
+        {
+            // moving end --> now we're moving start
+            _selectionEndpoint = SelectionEndpoint::Start;
+            _selection->pivot = _selection->end;
+        }
+        else if (WI_IsFlagSet(_selectionEndpoint, SelectionEndpoint::Start))
+        {
+            // moving start --> now we're moving end
+            _selectionEndpoint = SelectionEndpoint::End;
+            _selection->pivot = _selection->start;
+        }
+    }
+}
+
 Terminal::UpdateSelectionParams Terminal::ConvertKeyEventToUpdateSelectionParams(const ControlKeyStates mods, const WORD vkey) const
 {
     if ((_selectionMode == SelectionInteractionMode::Mark || mods.IsShiftPressed()) && !mods.IsAltPressed())
@@ -365,6 +392,12 @@ Terminal::UpdateSelectionParams Terminal::ConvertKeyEventToUpdateSelectionParams
 // - mods: the key modifiers pressed when performing this update
 void Terminal::UpdateSelection(SelectionDirection direction, SelectionExpansion mode, ControlKeyStates mods)
 {
+    // This is a special variable used to track if we should move the cursor when in mark mode.
+    //   We have special functionality where if you use the "switchSelectionEndpoint" action
+    //   when in mark mode (moving the cursor), we anchor an endpoint and you can use the
+    //   plain arrow keys to move the endpoint. This way, you don't have to hold shift anymore!
+    const bool shouldMoveBothEndpoints = _selectionMode == SelectionInteractionMode::Mark && !_anchorInactiveSelectionEndpoint && !mods.IsShiftPressed();
+
     // 1. Figure out which endpoint to update
     // [Mark Mode]
     // - shift pressed --> only move "end" (or "start" if "pivot" == "end")
@@ -372,7 +405,7 @@ void Terminal::UpdateSelection(SelectionDirection direction, SelectionExpansion
     // [Quick Edit]
     // - just move "end" (or "start" if "pivot" == "end")
     _selectionEndpoint = static_cast<SelectionEndpoint>(0);
-    if (_selectionMode == SelectionInteractionMode::Mark && !mods.IsShiftPressed())
+    if (shouldMoveBothEndpoints)
     {
         WI_SetAllFlags(_selectionEndpoint, SelectionEndpoint::Start | SelectionEndpoint::End);
     }
@@ -405,7 +438,7 @@ void Terminal::UpdateSelection(SelectionDirection direction, SelectionExpansion
 
     // 3. Actually modify the selection state
     _selectionMode = std::max(_selectionMode, SelectionInteractionMode::Keyboard);
-    if (_selectionMode == SelectionInteractionMode::Mark && !mods.IsShiftPressed())
+    if (shouldMoveBothEndpoints)
     {
         // [Mark Mode] + shift unpressed --> move all three (i.e. just use arrow keys)
         _selection->start = targetPos;
@@ -598,6 +631,7 @@ void Terminal::ClearSelection()
     _selection = std::nullopt;
     _selectionMode = SelectionInteractionMode::None;
     _selectionEndpoint = static_cast<SelectionEndpoint>(0);
+    _anchorInactiveSelectionEndpoint = false;
 }
 
 // Method Description:

src/cascadia/TerminalSettingsModel/ActionAndArgs.cpp

@@ -82,6 +82,7 @@ static constexpr std::string_view RestoreLastClosedKey{ "restoreLastClosed" };
 static constexpr std::string_view SelectAllKey{ "selectAll" };
 static constexpr std::string_view MarkModeKey{ "markMode" };
 static constexpr std::string_view ToggleBlockSelectionKey{ "toggleBlockSelection" };
+static constexpr std::string_view SwitchSelectionEndpointKey{ "switchSelectionEndpoint" };
 
 static constexpr std::string_view ActionKey{ "action" };
 
@@ -400,6 +401,7 @@ namespace winrt::Microsoft::Terminal::Settings::Model::implementation
                 { ShortcutAction::SelectAll, RS_(L"SelectAllCommandKey") },
                 { ShortcutAction::MarkMode, RS_(L"MarkModeCommandKey") },
                 { ShortcutAction::ToggleBlockSelection, RS_(L"ToggleBlockSelectionCommandKey") },
+                { ShortcutAction::SwitchSelectionEndpoint, RS_(L"SwitchSelectionEndpointCommandKey") },
             };
         }();
 

src/cascadia/TerminalSettingsModel/AllShortcutActions.h

@@ -95,7 +95,8 @@
     ON_ALL_ACTIONS(RestoreLastClosed)      \
     ON_ALL_ACTIONS(SelectAll)              \
     ON_ALL_ACTIONS(MarkMode)               \
-    ON_ALL_ACTIONS(ToggleBlockSelection)
+    ON_ALL_ACTIONS(ToggleBlockSelection)   \
+    ON_ALL_ACTIONS(SwitchSelectionEndpoint)
 
 #define ALL_SHORTCUT_ACTIONS_WITH_ARGS             \
     ON_ALL_ACTIONS_WITH_ARGS(AdjustFontSize)       \

src/cascadia/TerminalSettingsModel/Resources/en-US/Resources.resw

@@ -564,4 +564,7 @@
   <data name="ToggleBlockSelectionCommandKey" xml:space="preserve">
     <value>Toggle block selection</value>
   </data>
+  <data name="SwitchSelectionEndpointCommandKey" xml:space="preserve">
+    <value>Switch selection endpoint</value>
+  </data>
 </root>

src/cascadia/TerminalSettingsModel/defaults.json

@@ -388,6 +388,7 @@
         { "command": "selectAll", "keys": "ctrl+shift+a" },
         { "command": "markMode", "keys": "ctrl+shift+m" },
         { "command": "toggleBlockSelection" },
+        { "command": "switchSelectionEndpoint" },
 
         // Scrollback
         { "command": "scrollDown", "keys": "ctrl+shift+down" },