Various small fixes

packages/pigeon/lib/swift_generator.dart

@@ -76,13 +76,14 @@ class SwiftGenerator extends StructuredGenerator<SwiftOptions> {
     required String dartPackageName,
   }) {
     indent.writeln('import Foundation');
+    indent.newln();
     indent.format('''
 #if os(iOS)
-import Flutter
+  import Flutter
 #elseif os(macOS)
-import FlutterMacOS
+  import FlutterMacOS
 #else
-#error("Unsupported platform.")
+  #error("Unsupported platform.")
 #endif''');
   }
 
@@ -160,6 +161,9 @@ import FlutterMacOS
     indent.addScoped('{', '}', () {
       indent.write('return ');
       indent.addScoped('[', ']', () {
+        // Follow swift-format style, which is to use a trailing comma unless
+        // there is only one element.
+        final String separator = classDefinition.fields.length > 1 ? ',' : '';
         for (final NamedType field
             in getFieldsInSerializationOrder(classDefinition)) {
           String toWriteValue = '';
@@ -173,7 +177,7 @@ import FlutterMacOS
             toWriteValue = field.name;
           }
 
-          indent.writeln('$toWriteValue,');
+          indent.writeln('$toWriteValue$separator');
         }
       });
     });
@@ -294,7 +298,7 @@ import FlutterMacOS
     indent.write('class ${api.name}: ${api.name}Protocol ');
     indent.addScoped('{', '}', () {
       indent.writeln('private let binaryMessenger: FlutterBinaryMessenger');
-      indent.write('init(binaryMessenger: FlutterBinaryMessenger)');
+      indent.write('init(binaryMessenger: FlutterBinaryMessenger) ');
       indent.addScoped('{', '}', () {
         indent.writeln('self.binaryMessenger = binaryMessenger');
       });
@@ -333,7 +337,7 @@ import FlutterMacOS
                   'completion(.failure(createConnectionError(withChannelName:channelName)))');
               indent.writeln('return');
             });
-            indent.writeScoped('if (listResponse.count > 1) {', '} ', () {
+            indent.writeScoped('if listResponse.count > 1 {', '} ', () {
               indent.writeln('let code: String = listResponse[0] as! String');
               indent.writeln(
                   'let message: String? = nilOrValue(listResponse[1])');
@@ -343,7 +347,7 @@ import FlutterMacOS
                   'completion(.failure(FlutterError(code: code, message: message, details: details)));');
             }, addTrailingNewline: false);
             if (!func.returnType.isNullable && !func.returnType.isVoid) {
-              indent.addScoped('else if (listResponse[0] == nil) {', '} ', () {
+              indent.addScoped('else if listResponse[0] == nil {', '} ', () {
                 indent.writeln(
                     'completion(.failure(FlutterError(code: "null-error", message: "Flutter api returned null value for non-null return value.", details: "")))');
               }, addTrailingNewline: false);
@@ -495,8 +499,14 @@ import FlutterMacOS
                 });
               }
               final String tryStatement = method.isAsynchronous ? '' : 'try ';
+              // Empty parens are not required when calling a method whose only
+              // argument is a trailing closure.
+              final String argumentString =
+                  methodArgument.isEmpty && method.isAsynchronous
+                      ? ''
+                      : '(${methodArgument.join(', ')})';
               final String call =
-                  '${tryStatement}api.${components.name}(${methodArgument.join(', ')})';
+                  '${tryStatement}api.${components.name}$argumentString';
               if (method.isAsynchronous) {
                 final String resultName =
                     method.returnType.isVoid ? 'nil' : 'res';
@@ -506,7 +516,7 @@ import FlutterMacOS
 
                 indent.addScoped('{ result in', '}', () {
                   indent.write('switch result ');
-                  indent.addScoped('{', '}', () {
+                  indent.addScoped('{', '}', nestCount: 0, () {
                     final String nullsafe =
                         method.returnType.isNullable ? '?' : '';
                     final String enumTag =
@@ -573,7 +583,7 @@ import FlutterMacOS
         indent.write('override func readValue(ofType type: UInt8) -> Any? ');
         indent.addScoped('{', '}', () {
           indent.write('switch type ');
-          indent.addScoped('{', '}', () {
+          indent.addScoped('{', '}', nestCount: 0, () {
             for (final EnumeratedClass customClass
                 in getCodecClasses(api, root)) {
               indent.writeln('case ${customClass.enumeration}:');
@@ -764,14 +774,14 @@ import FlutterMacOS
         indent.addScoped('[', ']', () {
           indent.writeln('flutterError.code,');
           indent.writeln('flutterError.message,');
-          indent.writeln('flutterError.details');
+          indent.writeln('flutterError.details,');
         });
       });
       indent.write('return ');
       indent.addScoped('[', ']', () {
         indent.writeln(r'"\(error)",');
         indent.writeln(r'"\(type(of: error))",');
-        indent.writeln(r'"Stacktrace: \(Thread.callStackSymbols)"');
+        indent.writeln(r'"Stacktrace: \(Thread.callStackSymbols)",');
       });
     });
   }

packages/pigeon/test/swift_generator_test.dart

@@ -52,6 +52,7 @@ void main() {
     expect(code, contains('var field1: Int64? = nil'));
     expect(code, contains('static func fromList(_ list: [Any?]) -> Foobar?'));
     expect(code, contains('func toList() -> [Any?]'));
+    expect(code, isNot(contains('if (')));
   });
 
   test('gen one enum', () {
@@ -80,6 +81,7 @@ void main() {
     expect(code, contains('enum Foobar: Int'));
     expect(code, contains('  case one = 0'));
     expect(code, contains('  case two = 1'));
+    expect(code, isNot(contains('if (')));
   });
 
   test('primitive enum host', () {
@@ -116,6 +118,7 @@ void main() {
     final String code = sink.toString();
     expect(code, contains('enum Foo: Int'));
     expect(code, contains('let fooArg = Foo(rawValue: args[0] as! Int)!'));
+    expect(code, isNot(contains('if (')));
   });
 
   test('gen one host api', () {
@@ -170,6 +173,7 @@ void main() {
     expect(code, contains('protocol Api'));
     expect(code, matches('func doSomething.*Input.*Output'));
     expect(code, contains('doSomethingChannel.setMessageHandler'));
+    expect(code, isNot(contains('if (')));
   });
 
   test('all the simple datatypes header', () {
@@ -298,6 +302,7 @@ void main() {
     expect(code, contains('class Api'));
     expect(code, contains('init(binaryMessenger: FlutterBinaryMessenger)'));
     expect(code, matches('func doSomething.*Input.*Output'));
+    expect(code, isNot(contains('if (')));
   });
 
   test('gen host void api', () {
@@ -339,6 +344,7 @@ void main() {
     final String code = sink.toString();
     expect(code, isNot(matches('.*doSomething(.*) ->')));
     expect(code, matches('doSomething(.*)'));
+    expect(code, isNot(contains('if (')));
   });
 
   test('gen flutter void return api', () {
@@ -381,6 +387,7 @@ void main() {
     expect(code,
         contains('completion: @escaping (Result<Void, FlutterError>) -> Void'));
     expect(code, contains('completion(.success(Void()))'));
+    expect(code, isNot(contains('if (')));
   });
 
   test('gen host void argument api', () {
@@ -419,6 +426,7 @@ void main() {
     expect(code, contains('func doSomething() throws -> Output'));
     expect(code, contains('let result = try api.doSomething()'));
     expect(code, contains('reply(wrapResult(result))'));
+    expect(code, isNot(contains('if (')));
   });
 
   test('gen flutter void argument api', () {
@@ -459,6 +467,7 @@ void main() {
         contains(
             'func doSomething(completion: @escaping (Result<Output, FlutterError>) -> Void)'));
     expect(code, contains('channel.sendMessage(nil'));
+    expect(code, isNot(contains('if (')));
   });
 
   test('gen list', () {
@@ -484,6 +493,7 @@ void main() {
     final String code = sink.toString();
     expect(code, contains('struct Foobar'));
     expect(code, contains('var field1: [Any?]? = nil'));
+    expect(code, isNot(contains('if (')));
   });
 
   test('gen map', () {
@@ -509,6 +519,7 @@ void main() {
     final String code = sink.toString();
     expect(code, contains('struct Foobar'));
     expect(code, contains('var field1: [AnyHashable: Any?]? = nil'));
+    expect(code, isNot(contains('if (')));
   });
 
   test('gen nested', () {
@@ -556,6 +567,9 @@ void main() {
     expect(code, contains('static func fromList(_ list: [Any?]) -> Outer?'));
     expect(code, contains('nested = Nested.fromList(nestedList)'));
     expect(code, contains('func toList() -> [Any?]'));
+    expect(code, isNot(contains('if (')));
+    // Single-element list serializations should not have a trailing comma.
+    expect(code, matches(RegExp(r'return \[\s*data\s*]')));
   });
 
   test('gen one async Host Api', () {
@@ -611,6 +625,7 @@ void main() {
     expect(code, contains('protocol Api'));
     expect(code, contains('api.doSomething(arg: argArg) { result in'));
     expect(code, contains('reply(wrapResult(res))'));
+    expect(code, isNot(contains('if (')));
   });
 
   test('gen one async Flutter Api', () {
@@ -665,6 +680,7 @@ void main() {
     final String code = sink.toString();
     expect(code, contains('class Api'));
     expect(code, matches('func doSomething.*Input.*completion.*Output.*Void'));
+    expect(code, isNot(contains('if (')));
   });
 
   test('gen one enum class', () {
@@ -705,6 +721,7 @@ void main() {
     expect(code, contains('enum Enum1: Int'));
     expect(code, contains('case one = 0'));
     expect(code, contains('case two = 1'));
+    expect(code, isNot(contains('if (')));
   });
 
   Iterable<String> makeIterable(String string) sync* {