Avoid rendering dead keys (2nd attempt) (#945)

Author: daxian-dbw

PSReadLine/Keys.cs

@@ -182,7 +182,8 @@ void AppendPart(string str)
                 sb.Append(str);
             }
 
-            switch (key.Key)
+            var consoleKey = key.Key;
+            switch (consoleKey)
             {
                 // Keys we definitely bind or might bind.
                 case ConsoleKey.PageUp: case ConsoleKey.PageDown:
@@ -221,22 +222,36 @@ void AppendPart(string str)
                     if (isShift) { AppendPart("Shift"); }
                     if (isCtrl) { AppendPart("Ctrl"); }
                     if (isAlt) { AppendPart("Alt"); }
-                    AppendPart(key.Key.ToString());
+                    AppendPart(consoleKey.ToString());
                     return sb.ToString();
             }
 
             var c = key.KeyChar;
             var isDeadKey = false;
-            if (char.IsControl(c) )
+            if (char.IsControl(c))
             {
                 // We have the virtual key code and Windows has a handy api to map that to the non-control
                 // character that use for a friendly UI.
                 //
                 // If this fails, we rely on some hard coded control characters below.
                 if (RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
                 {
-                    var keySansControl = new ConsoleKeyInfo(key.KeyChar, key.Key, isShift, isAlt, control: false);
-                    TryGetCharFromConsoleKey(keySansControl, ref c, ref isDeadKey);
+                    // A heuristic to check for dead keys --
+                    //   We got an 'OemXXX' ConsoleKey, '\0' key char, and no 'Ctrl' modifier. It's very likely generated by a dead key.
+                    //   We check for 'Ctrl' modifier because it's easy to generate '\0' KeyChar and 'OemXXX' by combinding 'Ctrl' with
+                    //   another special key, such as 'Ctrl+?' and 'Ctrl+;'.
+                    isDeadKey = (c == '\0') && (consoleKey >= ConsoleKey.Oem1 && consoleKey <= ConsoleKey.Oem102) && !isCtrl;
+
+                    if (!isDeadKey)
+                    {
+                        // A dead key could pass the above heuristic check, such as 'Shift+6' in US-INTL keyboard, which represents the
+                        // diacritic '^' and generates 'D6' ConsoleKey, '\0' key char and 'Shift' modifier.
+                        // For those dead keys we try again to identify them by calling the Win32 API 'ToUnicode'. This API doesn't work
+                        // well with keyboards that are not natively supported by Windows, such as the Neo keyboard layout. Hopefully,
+                        // dead keys of the non-natively-supported keyboard layouts are captured by our heuristic check above.
+                        var keySansControl = new ConsoleKeyInfo(key.KeyChar, consoleKey, isShift, isAlt, control: false);
+                        TryGetCharFromConsoleKey(keySansControl, ref c, ref isDeadKey);
+                    }
                 }
             }
             else if (isAlt && isCtrl)
@@ -281,10 +296,9 @@ void AppendPart(string str)
                     // This could be a dead key for a particular keyboard layout in Windows console.
                     // The dead key is not an issue when there is tty involved, so on non-Windows, `isDeadKey` is always false.
                     //
-                    // When we believe it's a dead key, we use the text form of the virtual key so the resulted PSKeyInfo can be
-                    // converted back to ConsoleKeyInfo correctly later on, and be properly ignored during rendering.
+                    // When we believe it's a dead key, we use '\0' so it can be properly ignored during rendering.
                     // Otherwise, we use `@` in case `key.KeyChar = '\0'`. This is ugly but familiar.
-                    s = isDeadKey ? key.Key.ToString() : "@";
+                    s = isDeadKey ? c.ToString() : "@";
                     break;
 
                 case char _ when (c >= 1 && c <= 26):