Test "option (apple_swift_prefix)", fix it.

There's a bug that extension fields were not correctly handled
in nested submessages (the extension set data was not always
passed down to generated subdecoders).

Author: tbkka

Protos/google/protobuf/map_unittest_proto3.proto

@@ -40,7 +40,8 @@ option cc_enable_arenas = true;
 option csharp_namespace = "Google.Protobuf.TestProtos";
 
 // Disambiguate from map_unittest.proto messages
-option swift_prefix = "Proto3";
+import "swift-options.proto";
+option (apple_swift_prefix) = "Proto3";
 
 import "google/protobuf/unittest_proto3.proto";
 

Protos/swift-options.proto

@@ -0,0 +1,9 @@
+
+syntax="proto2";
+
+import "google/protobuf/descriptor.proto";
+
+extend google.protobuf.FileOptions {
+   optional string apple_swift_prefix = 50138;
+}
+

Sources/Protobuf/ProtobufBinaryDecoding.swift

@@ -134,21 +134,21 @@ private struct ProtobufFieldWireType2: ProtobufBinaryFieldDecoder {
 
     mutating func decodeOptionalMessageField<M: ProtobufMessage>(fieldType: M.Type, value: inout M?) throws -> Bool {
         var v = value ?? M()
-        var subDecoder = ProtobufBinaryDecoder(protobufPointer: buffer)
+        var subDecoder = ProtobufBinaryDecoder(protobufPointer: buffer, extensions: scanner.extensions)
         try subDecoder.decodeFullObject(message: &v)
         value = v
         return true
     }
 
     mutating func decodeRepeatedMessageField<M: ProtobufMessage>(fieldType: M.Type, value: inout [M]) throws -> Bool {
-        value.append(try M(protobufBuffer: buffer))
+        value.append(try M(protobufBuffer: buffer, extensions: scanner.extensions))
         return true
     }
 
     mutating func decodeMapField<KeyType: ProtobufTypeProperties, ValueType: ProtobufMapValueType>(fieldType: ProtobufMap<KeyType, ValueType>.Type, value: inout ProtobufMap<KeyType, ValueType>.BaseType) throws -> Bool where KeyType: ProtobufMapKeyType, KeyType.BaseType: Hashable {
         var k: KeyType.BaseType?
         var v: ValueType.BaseType?
-        var subdecoder = ProtobufBinaryDecoder(protobufPointer: buffer)
+        var subdecoder = ProtobufBinaryDecoder(protobufPointer: buffer, extensions: scanner.extensions)
         try subdecoder.decodeFullObject {(decoder: inout ProtobufFieldDecoder, protoFieldNumber: Int) throws -> Bool in
             switch protoFieldNumber {
             case 1:

Tests/ProtobufTests/swift-options.pb.swift

@@ -0,0 +1,24 @@
+/*
+ * DO NOT EDIT.
+ *
+ * Generated by the protocol buffer compiler.
+ * Source: swift-options.proto
+ *
+ */
+
+import Foundation
+import Protobuf
+
+
+let Google_Protobuf_FileOptions_appleSwiftPrefix = ProtobufGenericMessageExtension<ProtobufOptionalField<ProtobufString>, Google_Protobuf_FileOptions>(protoFieldNumber: 50138, protoFieldName: "apple_swift_prefix", jsonFieldName: "appleSwiftPrefix", swiftFieldName: "appleSwiftPrefix", defaultValue: nil)
+
+extension Google_Protobuf_FileOptions {
+  var appleSwiftPrefix: String? {
+    get {return getExtensionValue(ext: Google_Protobuf_FileOptions_appleSwiftPrefix)}
+    set {setExtensionValue(ext: Google_Protobuf_FileOptions_appleSwiftPrefix, value: newValue)}
+  }
+}
+
+let SwiftOptions_Extensions: ProtobufExtensionSet = [
+  Google_Protobuf_FileOptions_appleSwiftPrefix
+]