修复远程桌面软件按 modifier key 时产生幽灵 'a' 按键的问题

sources/MacOSKeyCodes.swift

@@ -65,6 +65,30 @@ struct SquirrelKeycode {
     return UInt32(XK_VoidSymbol)
   }
 
+  static let modifierKeycodes: Set<UInt16> = [
+    UInt16(kVK_Shift), UInt16(kVK_RightShift),
+    UInt16(kVK_CapsLock),
+    UInt16(kVK_Control), UInt16(kVK_RightControl),
+    UInt16(kVK_Option), UInt16(kVK_RightOption),
+    UInt16(kVK_Command), UInt16(kVK_RightCommand),
+    UInt16(kVK_Function)
+  ]
+
+  static func inferModifierKeycode(from changes: NSEvent.ModifierFlags) -> UInt16? {
+    if changes.contains(.capsLock) {
+      return UInt16(kVK_CapsLock)
+    } else if changes.contains(.shift) {
+      return UInt16(kVK_Shift)
+    } else if changes.contains(.control) {
+      return UInt16(kVK_Control)
+    } else if changes.contains(.option) {
+      return UInt16(kVK_Option)
+    } else if changes.contains(.command) {
+      return UInt16(kVK_Command)
+    }
+    return nil
+  }
+
   private static let keycodeMappings: [Int: Int32] = [
     // modifiers
     kVK_CapsLock: XK_Caps_Lock,

sources/SquirrelInputController.swift

@@ -62,9 +62,22 @@ final class SquirrelInputController: IMKInputController {
       }
       // print("[DEBUG] FLAGSCHANGED client: \(sender ?? "nil"), modifiers: \(modifiers)")
       var rimeModifiers: UInt32 = SquirrelKeycode.osxModifiersToRime(modifiers: modifiers)
-      // For flags-changed event, keyCode is available since macOS 10.15
-      // (#715)
-      let rimeKeycode: UInt32 = SquirrelKeycode.osxKeycodeToRime(keycode: event.keyCode, keychar: nil, shift: false, caps: false)
+      // For flags-changed event, keyCode is available since macOS 10.15 (#715)
+      // Some remote desktop software (e.g. Parsec) sends flagsChanged events with
+      // keyCode defaulting to 0 (kVK_ANSI_A) instead of the actual modifier keycode,
+      // causing a ghost 'a' keypress. Validate and infer the correct keycode from
+      // the changed modifier flags when necessary. (#825)
+      var keyCode = event.keyCode
+      if !SquirrelKeycode.modifierKeycodes.contains(keyCode) {
+        guard let inferred = SquirrelKeycode.inferModifierKeycode(from: changes) else {
+          lastModifiers = modifiers
+          rimeUpdate()
+          handled = true
+          break
+        }
+        keyCode = inferred
+      }
+      let rimeKeycode: UInt32 = SquirrelKeycode.osxKeycodeToRime(keycode: keyCode, keychar: nil, shift: false, caps: false)
 
       if changes.contains(.capsLock) {
         // NOTE: rime assumes XK_Caps_Lock to be sent before modifier changes,