Allow Ctrl+Alt <> AltGr aliasing to be disabled (#6212)

## Summary of the Pull Request

Some people wish to use Ctrl+Alt combinations without Windows treating those as an alias for AltGr combinations. This PR adds a new `altGrAliasing` setting allowing one to control this behavior.

## PR Checklist
* [x] Closes #6211
* [x] CLA signed. If not, go over [here](https://cla.opensource.microsoft.com/microsoft/Terminal) and sign the CLA
* [x] Manual testing
* [x] Requires documentation to be updated: MicrosoftDocs/terminal#50
* [x] I've discussed this with core contributors already. If not checked, I'm ready to accept this work might be rejected in favor of a different grand plan. Issue number where discussion took place: #xxx

## Validation Steps Performed

* Choose a German keyboard layout
* Using `showkey -a` ensured that both `Ctrl+Alt+Q/E` and `AltGr+Q/E` produce `@/€`
* Added `"altGrAliasing": false` to the WSL profile
* Using `showkey -a` ensured `Ctrl+Alt+Q/E` now produces `^[^Q/E` while `AltGr+Q/E` continues to produce `@/€`

doc/cascadia/SettingsSchema.md

@@ -59,6 +59,7 @@ Properties listed below are specific to each unique profile.
 | `scrollbarState` | Optional | String | `"visible"` | Defines the visibility of the scrollbar. Possible values: `"visible"`, `"hidden"` |
 | `selectionBackground` | Optional | String | | Sets the selection background color of the profile. Overrides `selectionBackground` set in color scheme if `colorscheme` is set. Uses hex color format: `"#rrggbb"`. |
 | `snapOnInput` | Optional | Boolean | `true` | When set to `true`, the window will scroll to the command input line when typing. When set to `false`, the window will not scroll when you start typing. |
+| `altGrAliasing` | Optional | Boolean | `true` | By default Windows treats Ctrl+Alt as an alias for AltGr. When altGrAliasing is set to false, this behavior will be disabled. |
 | `source` | Optional | String | | Stores the name of the profile generator that originated this profile. _There are no discoverable values for this field._ |
 | `startingDirectory` | Optional | String | `%USERPROFILE%` | The directory the shell starts in when it is loaded. |
 | `suppressApplicationTitle` | Optional | Boolean | `false` | When set to `true`, `tabTitle` overrides the default title of the tab and any title change messages from the application will be suppressed. When set to `false`, `tabTitle` behaves as normal. |

doc/cascadia/profiles.schema.json

@@ -615,6 +615,11 @@
           "description": "When set to true, the window will scroll to the command input line when typing. When set to false, the window will not scroll when you start typing.",
           "type": "boolean"
         },
+        "altGrAliasing": {
+          "default": true,
+          "description": "By default Windows treats Ctrl+Alt as an alias for AltGr. When altGrAliasing is set to false, this behavior will be disabled.",
+          "type": "boolean"
+        },
         "source": {
           "description": "Stores the name of the profile generator that originated this profile.",
           "type": ["string", "null"]

src/cascadia/TerminalApp/Profile.cpp

@@ -28,6 +28,7 @@ static constexpr std::string_view TabTitleKey{ "tabTitle" };
 static constexpr std::string_view SuppressApplicationTitleKey{ "suppressApplicationTitle" };
 static constexpr std::string_view HistorySizeKey{ "historySize" };
 static constexpr std::string_view SnapOnInputKey{ "snapOnInput" };
+static constexpr std::string_view AltGrAliasingKey{ "altGrAliasing" };
 static constexpr std::string_view CursorColorKey{ "cursorColor" };
 static constexpr std::string_view CursorShapeKey{ "cursorShape" };
 static constexpr std::string_view CursorHeightKey{ "cursorHeight" };
@@ -121,6 +122,7 @@ Profile::Profile(const std::optional<GUID>& guid) :
     _suppressApplicationTitle{},
     _historySize{ DEFAULT_HISTORY_SIZE },
     _snapOnInput{ true },
+    _altGrAliasing{ true },
     _cursorShape{ CursorStyle::Bar },
     _cursorHeight{ DEFAULT_CURSOR_HEIGHT },
 
@@ -188,6 +190,7 @@ TerminalSettings Profile::CreateTerminalSettings(const std::unordered_map<std::w
     // Fill in the Terminal Setting's CoreSettings from the profile
     terminalSettings.HistorySize(_historySize);
     terminalSettings.SnapOnInput(_snapOnInput);
+    terminalSettings.AltGrAliasing(_altGrAliasing);
     terminalSettings.CursorHeight(_cursorHeight);
     terminalSettings.CursorShape(_cursorShape);
 
@@ -475,6 +478,8 @@ void Profile::LayerJson(const Json::Value& json)
 
     JsonUtils::GetBool(json, SnapOnInputKey, _snapOnInput);
 
+    JsonUtils::GetBool(json, AltGrAliasingKey, _altGrAliasing);
+
     JsonUtils::GetUInt(json, CursorHeightKey, _cursorHeight);
 
     if (json.isMember(JsonKey(CursorShapeKey)))

src/cascadia/TerminalApp/Profile.h

@@ -142,6 +142,7 @@ class TerminalApp::Profile final
     bool _suppressApplicationTitle;
     int32_t _historySize;
     bool _snapOnInput;
+    bool _altGrAliasing;
     uint32_t _cursorHeight;
     winrt::Microsoft::Terminal::Settings::CursorStyle _cursorShape;
 

src/cascadia/TerminalApp/defaults-universal.json

@@ -41,6 +41,7 @@
             "icon": "ms-appx:///ProfileIcons/{550ce7b8-d500-50ad-8a1a-c400c3262db3}.png",
             "padding": "8, 8, 8, 8",
             "snapOnInput": true,
+            "altGrAliasing": true,
             "useAcrylic": false,
             "backgroundImage": "ms-appx:///internal-background.png",
             "backgroundImageAlignment": "bottomRight",

src/cascadia/TerminalApp/defaults.json

@@ -42,6 +42,7 @@
             "historySize": 9001,
             "padding": "8, 8, 8, 8",
             "snapOnInput": true,
+            "altGrAliasing": true,
             "startingDirectory": "%USERPROFILE%",
             "useAcrylic": false
         },
@@ -60,6 +61,7 @@
             "historySize": 9001,
             "padding": "8, 8, 8, 8",
             "snapOnInput": true,
+            "altGrAliasing": true,
             "startingDirectory": "%USERPROFILE%",
             "useAcrylic": false
         }

src/cascadia/TerminalCore/Terminal.cpp

@@ -140,11 +140,9 @@ void Terminal::UpdateSettings(winrt::Microsoft::Terminal::Settings::ICoreSetting
     }
 
     _snapOnInput = settings.SnapOnInput();
-
+    _altGrAliasing = settings.AltGrAliasing();
     _wordDelimiters = settings.WordDelimiters();
-
     _suppressApplicationTitle = settings.SuppressApplicationTitle();
-
     _startingTitle = settings.StartingTitle();
 
     // TODO:MSFT:21327402 - if HistorySize has changed, resize the buffer so we
@@ -419,6 +417,7 @@ bool Terminal::SendKeyEvent(const WORD vkey, const WORD scanCode, const ControlK
     _StoreKeyEvent(vkey, scanCode);
 
     const auto isAltOnlyPressed = states.IsAltPressed() && !states.IsCtrlPressed();
+    const auto isSuppressedAltGrAlias = !_altGrAliasing && states.IsAltPressed() && states.IsCtrlPressed();
 
     // DON'T manually handle Alt+Space - the system will use this to bring up
     // the system menu for restore, min/maximize, size, move, close.
@@ -428,7 +427,17 @@ bool Terminal::SendKeyEvent(const WORD vkey, const WORD scanCode, const ControlK
         return false;
     }
 
-    const auto ch = _CharacterFromKeyEvent(vkey, scanCode, states);
+    // By default Windows treats Ctrl+Alt as an alias for AltGr.
+    // When the altGrAliasing setting is set to false, this behaviour should be disabled.
+    //
+    // Whenever possible _CharacterFromKeyEvent() will return a valid character.
+    // For instance both Ctrl+Alt+Q as well as AltGr+Q return @ on a German keyboard.
+    //
+    // We can achieve the altGrAliasing functionality by skipping the call to _CharacterFromKeyEvent,
+    // as TerminalInput::HandleKey will then fall back to using the vkey which
+    // is the underlying ASCII character (e.g. A-Z) on the keyboard in our case.
+    // See GH#5525/GH#6211 for more details
+    const auto ch = isSuppressedAltGrAlias ? UNICODE_NULL : _CharacterFromKeyEvent(vkey, scanCode, states);
 
     // Delegate it to the character event handler if this key event can be
     // mapped to one (see method description above). For Alt+key combinations

src/cascadia/TerminalCore/Terminal.hpp

@@ -212,6 +212,7 @@ class Microsoft::Terminal::Core::Terminal final :
     COLORREF _defaultBg;
 
     bool _snapOnInput;
+    bool _altGrAliasing;
     bool _suppressApplicationTitle;
 
 #pragma region Text Selection

src/cascadia/TerminalSettings/ICoreSettings.idl

@@ -25,6 +25,7 @@ namespace Microsoft.Terminal.Settings
         Int32 RowsToScroll;
 
         Boolean SnapOnInput;
+        Boolean AltGrAliasing;
 
         UInt32 CursorColor;
         CursorStyle CursorShape;

src/cascadia/TerminalSettings/terminalsettings.h

@@ -52,6 +52,7 @@ namespace winrt::Microsoft::Terminal::Settings::implementation
         GETSET_PROPERTY(int32_t, InitialCols, 80);
 
         GETSET_PROPERTY(bool, SnapOnInput, true);
+        GETSET_PROPERTY(bool, AltGrAliasing, true);
         GETSET_PROPERTY(uint32_t, CursorColor, DEFAULT_CURSOR_COLOR);
         GETSET_PROPERTY(CursorStyle, CursorShape, CursorStyle::Vintage);
         GETSET_PROPERTY(uint32_t, CursorHeight, DEFAULT_CURSOR_HEIGHT);

src/cascadia/UnitTests_TerminalCore/MockTermSettings.h

@@ -29,6 +29,7 @@ namespace TerminalCoreUnitTests
         uint32_t DefaultForeground() { return COLOR_WHITE; }
         uint32_t DefaultBackground() { return COLOR_BLACK; }
         bool SnapOnInput() { return false; }
+        bool AltGrAliasing() { return true; }
         uint32_t CursorColor() { return COLOR_WHITE; }
         CursorStyle CursorShape() const noexcept { return CursorStyle::Vintage; }
         uint32_t CursorHeight() { return 42UL; }
@@ -49,6 +50,7 @@ namespace TerminalCoreUnitTests
         void DefaultForeground(uint32_t) {}
         void DefaultBackground(uint32_t) {}
         void SnapOnInput(bool) {}
+        void AltGrAliasing(bool) {}
         void CursorColor(uint32_t) {}
         void CursorShape(CursorStyle const&) noexcept {}
         void CursorHeight(uint32_t) {}