[ASTGen] Update PluginMessage for conformance macro

Author: rintaro

lib/ASTGen/Sources/ASTGen/Macros.swift

@@ -554,12 +554,15 @@ func expandAttachedMacroIPC(
 
   // Map the macro role.
   let macroRole: PluginMessage.MacroRole
-  switch MacroRole(rawValue: rawMacroRole) {
+  switch MacroRole(rawValue: rawMacroRole)! {
   case .Accessor: macroRole = .accessor
   case .Member: macroRole = .member
   case .MemberAttribute: macroRole = .memberAttribute
   case .Peer: macroRole = .peer
-  default:
+  case .Conformance: macroRole = .conformance
+  case
+      .Expression,
+      .FreestandingDeclaration:
     preconditionFailure("unhandled macro role for attached macro")
   }
 

lib/ASTGen/Sources/ASTGen/PluginMessages.swift

@@ -40,7 +40,7 @@ internal enum PluginToHostMessage: Codable {
 }
 
 /*namespace*/ internal enum PluginMessage {
-  static var PROTOCOL_VERSION_NUMBER: Int { 1 }
+  static var PROTOCOL_VERSION_NUMBER: Int { 2 } // Added 'MacroRole.conformance'
 
   struct PluginCapability: Codable {
     var protocolVersion: Int
@@ -65,6 +65,7 @@ internal enum PluginToHostMessage: Codable {
     case memberAttribute
     case member
     case peer
+    case conformance
   }
 
   struct SourceLocation: Codable {