Fixes #5097. Kitty is wasting the keyboard shortcuts Ctrl+Shift+Alt+A/Z which returns as Ctrl+Alt+A/Z

Terminal.Gui/Drivers/AnsiHandling/KittyKeyboardPattern.cs

@@ -91,9 +91,16 @@ public class KittyKeyboardPattern : AnsiKeyboardParserPattern
             return null;
         }
 
+        string baseKeyCode = "";
+
+        if (key.KeyCode < KeyCode.CharMask && (key.KeyCode & (KeyCode.ShiftMask | KeyCode.AltMask | KeyCode.CtrlMask)) == 0)
+        {
+            baseKeyCode = new Rune ((uint)key.KeyCode).ToString ();
+        }
+
         // Extract alternate key codes (kitty flag 4: report alternate keys)
-        var shiftedKeyCode = KeyCode.Null;
-        var baseLayoutKeyCode = KeyCode.Null;
+        KeyCode shiftedKeyCode = KeyCode.Null;
+        KeyCode baseLayoutKeyCode = KeyCode.Null;
 
         if (match.Groups [2].Success && int.TryParse (match.Groups [2].Value, CultureInfo.InvariantCulture, out int shiftedCode) && shiftedCode > 0)
         {
@@ -105,7 +112,7 @@ public class KittyKeyboardPattern : AnsiKeyboardParserPattern
             baseLayoutKeyCode = (KeyCode)baseCode;
         }
 
-        var associatedText = string.Empty;
+        string associatedText = string.Empty;
 
         if (match.Groups [5].Success)
         {
@@ -117,8 +124,8 @@ public class KittyKeyboardPattern : AnsiKeyboardParserPattern
             key = new Key (key) { ShiftedKeyCode = shiftedKeyCode, BaseLayoutKeyCode = baseLayoutKeyCode, AssociatedText = associatedText };
         }
 
-        string modifierField = match.Groups [4].Value;
-        modifierField = ApplyImplicitModifierState (key, modifierField);
+        string originalModifierField = match.Groups [4].Value;
+        string modifierField = ApplyImplicitModifierState (key, originalModifierField);
 
         if (!string.IsNullOrEmpty (modifierField))
         {
@@ -127,10 +134,10 @@ public class KittyKeyboardPattern : AnsiKeyboardParserPattern
 
         if (!string.IsNullOrEmpty (modifierField))
         {
-            key = ApplyModifiersAndEventType (modifierField, key);
+            key = ApplyModifiersAndEventType (MaxModifierFieldValue (originalModifierField, modifierField), key);
         }
 
-        if ((key.IsAlt || key.IsCtrl) && !string.IsNullOrEmpty (key.AssociatedText))
+        if ((key.IsAlt || key.IsCtrl) && (key.ShiftedKeyCode != KeyCode.Null || baseKeyCode.Equals (key.AssociatedText, StringComparison.OrdinalIgnoreCase)) && !string.IsNullOrEmpty (key.AssociatedText))
         {
             key = new Key (key) { AssociatedText = string.Empty };
         }
@@ -222,6 +229,38 @@ private static string ApplyImplicitModifierState (Key key, string modifierField)
         return string.Join (':', parts);
     }
 
+    private static string MaxModifierFieldValue (string modifierField1, string modifierField2)
+    {
+        if (string.IsNullOrEmpty (modifierField1))
+        {
+            return modifierField2;
+        }
+
+        if (string.IsNullOrEmpty (modifierField2))
+        {
+            return modifierField1;
+        }
+
+        string [] parts1 = modifierField1.Split (':');
+        string [] parts2 = modifierField2.Split (':');
+
+        if (parts1.Length == 0 || parts2.Length == 0)
+        {
+            return modifierField1;
+        }
+
+        if (!int.TryParse (parts1 [0], CultureInfo.InvariantCulture, out int encodedModifiers1)
+            || !int.TryParse (parts2 [0], CultureInfo.InvariantCulture, out int encodedModifiers2))
+        {
+            return modifierField1;
+        }
+
+        int maxEncodedModifiers = Math.Max (encodedModifiers1, encodedModifiers2);
+        parts1 [0] = maxEncodedModifiers.ToString (CultureInfo.InvariantCulture);
+
+        return string.Join (':', parts1);
+    }
+
     private static (Key Key, string ModifierField) NormalizeShiftedPrintableKey (Key key, string modifierField)
     {
         string [] parts = modifierField.Split (':');

Terminal.Gui/Input/Keyboard/Key.cs

@@ -217,7 +217,7 @@ public string AsGrapheme
 
             if (IsShift && ShiftedKeyCode != KeyCode.Null)
             {
-                Rune shiftedRune = ToRune (ShiftedKeyCode);
+                Rune shiftedRune = ToRune (ShiftedKeyCode | KeyCode.ShiftMask);
 
                 if (shiftedRune != default (Rune))
                 {
@@ -278,7 +278,7 @@ public Rune AsRune
 
             if (IsShift && ShiftedKeyCode != KeyCode.Null)
             {
-                Rune shiftedRune = ToRune (ShiftedKeyCode);
+                Rune shiftedRune = ToRune (ShiftedKeyCode | KeyCode.ShiftMask);
 
                 if (shiftedRune != default (Rune))
                 {

Terminal.Gui/Views/TextInput/TextField/TextField.Keyboard.cs

@@ -73,7 +73,10 @@ protected override bool OnKeyDownNotHandled (Key a)
             return false;
         }
 
-        if (a.IsAlt || a.IsCtrl)
+        // Never insert modified keys, except for AltGr combinations with associated text of the unmodified key.
+        // This allows users to input characters that require AltGr (e.g. '@' on a Portuguese keyboard which is AltGr+2 with associated text "@"),
+        // while still preventing most modified keys from being inserted into the TextField.
+        if ((a.IsAlt && string.IsNullOrEmpty (a.AsGrapheme)) || a.IsCtrl)
         {
             // Never insert modified keys
             return false;

Terminal.Gui/Views/TextInput/TextView/TextView.Keyboard.cs

@@ -142,7 +142,10 @@ protected override bool OnKeyDownNotHandled (Key a)
             return Autocomplete.ProcessKey (a);
         }
 
-        if (a.IsAlt || a.IsCtrl)
+        // Never insert modified keys, except for AltGr combinations with associated text of the unmodified key.
+        // This allows users to input characters that require AltGr (e.g. '@' on a Portuguese keyboard which is AltGr+2 with associated text "@"),
+        // while still preventing most modified keys from being inserted into the TextView.
+        if ((a.IsAlt && string.IsNullOrEmpty (a.AsGrapheme)) || a.IsCtrl)
         {
             // Never insert modified keys
             return false;

Tests/UnitTestsParallelizable/Drivers/AnsiHandling/KittyAlternateKeyTests.cs

@@ -108,7 +108,7 @@ public void ViewKeyDown_ShiftedAndBase_Preserved ()
 
         // View level — same alternate key fields must arrive
         Assert.Single (viewDown);
-        Assert.Equal (new Key ('@'), viewDown [0]);
+        Assert.Equal (new Key ('@').WithShift, viewDown [0]);
         Assert.Equal ((KeyCode)64, viewDown [0].ShiftedKeyCode);
         Assert.Equal (KeyCode.Null, viewDown [0].BaseLayoutKeyCode);
         Assert.Equal ("@", viewDown [0].AssociatedText);
@@ -125,7 +125,7 @@ public void ViewKeyDown_AssociatedText_Preserved ()
         Assert.Equal ("!", appDown [0].GetPrintableText ());
 
         Assert.Single (viewDown);
-        Assert.Equal (new Key ('!'), viewDown [0]);
+        Assert.Equal (new Key ('!').WithShift, viewDown [0]);
         Assert.Equal ("!", viewDown [0].AssociatedText);
         Assert.Equal ("!", viewDown [0].GetPrintableText ());
     }
@@ -178,7 +178,7 @@ public void ViewKeyDown_WithModifiersAndEventType_Preserved ()
         (_, List<Key> viewDown, _) = InjectRawSequenceToView ("\x1b[50:64;6:1u");
 
         Assert.Single (viewDown);
-        Assert.Equal (new Key ('@').WithCtrl, viewDown [0]);
+        Assert.Equal (new Key ('@').WithCtrl.WithShift, viewDown [0]);
         Assert.Equal ((KeyCode)64, viewDown [0].ShiftedKeyCode);
         Assert.Equal (KeyCode.Null, viewDown [0].BaseLayoutKeyCode);
         Assert.Equal (KeyEventType.Press, viewDown [0].EventType);
@@ -194,7 +194,7 @@ public void ViewKeyUp_AlternateKeys_Preserved ()
         // Release events go to KeyUp, not KeyDown
         Assert.Empty (viewDown);
         Assert.Single (viewUp);
-        Assert.Equal (new Key ('@'), viewUp [0]);
+        Assert.Equal (new Key ('@').WithShift, viewUp [0]);
         Assert.Equal ((KeyCode)64, viewUp [0].ShiftedKeyCode);
         Assert.Equal (KeyCode.Null, viewUp [0].BaseLayoutKeyCode);
         Assert.Equal (KeyEventType.Release, viewUp [0].EventType);