Add applying option in protoc

Author: Pouya Yarandi

Sources/protoc-gen-swift/GeneratorOptions.swift

@@ -53,6 +53,7 @@ class GeneratorOptions {
   let protoToModuleMappings: ProtoFileToModuleMappings
   let visibility: Visibility
   let implementationOnlyImports: Bool
+  let generateApplyingMethods: Bool
 
   /// A string snippet to insert for the visibility
   let visibilitySourceSnippet: String
@@ -63,6 +64,7 @@ class GeneratorOptions {
     var visibility: Visibility = .internal
     var swiftProtobufModuleName: String? = nil
     var implementationOnlyImports: Bool = false
+    var generateApplyingMethods: Bool = false
 
     for pair in parameter.parsedPairs {
       switch pair.key {
@@ -100,6 +102,13 @@ class GeneratorOptions {
           throw GenerationError.invalidParameterValue(name: pair.key,
                                                       value: pair.value)
         }
+      case "Applying":
+        if let value = Bool(pair.value) {
+          generateApplyingMethods = value
+        } else {
+          throw GenerationError.invalidParameterValue(name: pair.key,
+                                                      value: pair.value)
+        }
       default:
         throw GenerationError.unknownParameter(name: pair.key)
       }
@@ -119,6 +128,7 @@ class GeneratorOptions {
 
     self.outputNaming = outputNaming
     self.visibility = visibility
+    self.generateApplyingMethods = generateApplyingMethods
 
     switch visibility {
     case .internal:

Sources/protoc-gen-swift/MessageGenerator.swift

@@ -194,9 +194,10 @@ class MessageGenerator {
   }
 
   func generateRuntimeSupport(printer p: inout CodePrinter, file: FileGenerator, parent: MessageGenerator?) {
+    let protoApplyingExtension = generatorOptions.generateApplyingMethods ? ", \(namer.swiftProtobufModulePrefix)_ProtoApplying" : ""
     p.print(
         "",
-        "extension \(swiftFullName): \(namer.swiftProtobufModulePrefix)Message, \(namer.swiftProtobufModulePrefix)_MessageImplementationBase, \(namer.swiftProtobufModulePrefix)_ProtoNameProviding, \(namer.swiftProtobufModulePrefix)_ProtoApplying {")
+        "extension \(swiftFullName): \(namer.swiftProtobufModulePrefix)Message, \(namer.swiftProtobufModulePrefix)_MessageImplementationBase, \(namer.swiftProtobufModulePrefix)_ProtoNameProviding\(protoApplyingExtension) {")
     p.withIndentation { p in
       if let parent = parent {
         p.print("\(visibility)static let protoMessageName: String = \(parent.swiftFullName).protoMessageName + \".\(descriptor.name)\"")
@@ -220,8 +221,10 @@ class MessageGenerator {
       generateTraverse(printer: &p)
       p.print()
       generateMessageEquality(printer: &p)
-      p.print()
-      generateMessageApplying(printer: &p)
+      if generatorOptions.generateApplyingMethods {
+        p.print()
+        generateMessageApplying(printer: &p)
+      }
     }
     p.print("}")
 
@@ -408,7 +411,7 @@ class MessageGenerator {
     p.print("\(visibility)func applying(_ value: Any, for fieldNumber: Int) throws -> \(swiftFullName) {")
     if fields.isEmpty {
       p.withIndentation { p in
-        p.print("throw \(namer.swiftProtobufModulePrefix)MessageModificationError.invalidFieldNumber")
+        p.print("throw \(namer.swiftProtobufModulePrefix)ProtoApplyingError.invalidFieldNumber")
       }
       p.print("}")
       return