[pigeon] Reduce reply-handling duplication in generated Dart code.

packages/pigeon/CHANGELOG.md

@@ -1,3 +1,7 @@
+## 26.1.9
+
+* [dart] Reduces much duplication in reply-handling code.
+
 ## 26.1.8
 
 * Makes some internal class constructors constant.

packages/pigeon/example/app/lib/src/messages.g.dart

@@ -11,11 +11,29 @@ import 'dart:typed_data' show Float64List, Int32List, Int64List, Uint8List;
 import 'package:flutter/foundation.dart' show ReadBuffer, WriteBuffer;
 import 'package:flutter/services.dart';
 
-PlatformException _createConnectionError(String channelName) {
-  return PlatformException(
-    code: 'channel-error',
-    message: 'Unable to establish connection on channel: "$channelName".',
-  );
+Object? _extractReplyValueOrThrow(
+  List<Object?>? replyList,
+  String channelName, {
+  required bool isNullValid,
+}) {
+  if (replyList == null) {
+    throw PlatformException(
+      code: 'channel-error',
+      message: 'Unable to establish connection on channel: "$channelName".',
+    );
+  } else if (replyList.length > 1) {
+    throw PlatformException(
+      code: replyList[0]! as String,
+      message: replyList[1] as String?,
+      details: replyList[2],
+    );
+  } else if (!isNullValid && (replyList.isNotEmpty && replyList[0] == null)) {
+    throw PlatformException(
+      code: 'null-error',
+      message: 'Host platform returned null value for non-null return value.',
+    );
+  }
+  return replyList.firstOrNull;
 }
 
 List<Object?> wrapResponse({
@@ -162,22 +180,13 @@ class ExampleHostApi {
     );
     final Future<Object?> pigeonVar_sendFuture = pigeonVar_channel.send(null);
     final pigeonVar_replyList = await pigeonVar_sendFuture as List<Object?>?;
-    if (pigeonVar_replyList == null) {
-      throw _createConnectionError(pigeonVar_channelName);
-    } else if (pigeonVar_replyList.length > 1) {
-      throw PlatformException(
-        code: pigeonVar_replyList[0]! as String,
-        message: pigeonVar_replyList[1] as String?,
-        details: pigeonVar_replyList[2],
-      );
-    } else if (pigeonVar_replyList[0] == null) {
-      throw PlatformException(
-        code: 'null-error',
-        message: 'Host platform returned null value for non-null return value.',
-      );
-    } else {
-      return (pigeonVar_replyList[0] as String?)!;
-    }
+
+    final Object pigeonVar_replyValue = _extractReplyValueOrThrow(
+      pigeonVar_replyList,
+      pigeonVar_channelName,
+      isNullValid: false,
+    )!;
+    return pigeonVar_replyValue as String;
   }
 
   Future<int> add(int a, int b) async {
@@ -192,22 +201,13 @@ class ExampleHostApi {
       <Object?>[a, b],
     );
     final pigeonVar_replyList = await pigeonVar_sendFuture as List<Object?>?;
-    if (pigeonVar_replyList == null) {
-      throw _createConnectionError(pigeonVar_channelName);
-    } else if (pigeonVar_replyList.length > 1) {
-      throw PlatformException(
-        code: pigeonVar_replyList[0]! as String,
-        message: pigeonVar_replyList[1] as String?,
-        details: pigeonVar_replyList[2],
-      );
-    } else if (pigeonVar_replyList[0] == null) {
-      throw PlatformException(
-        code: 'null-error',
-        message: 'Host platform returned null value for non-null return value.',
-      );
-    } else {
-      return (pigeonVar_replyList[0] as int?)!;
-    }
+
+    final Object pigeonVar_replyValue = _extractReplyValueOrThrow(
+      pigeonVar_replyList,
+      pigeonVar_channelName,
+      isNullValid: false,
+    )!;
+    return pigeonVar_replyValue as int;
   }
 
   Future<bool> sendMessage(MessageData message) async {
@@ -222,22 +222,13 @@ class ExampleHostApi {
       <Object?>[message],
     );
     final pigeonVar_replyList = await pigeonVar_sendFuture as List<Object?>?;
-    if (pigeonVar_replyList == null) {
-      throw _createConnectionError(pigeonVar_channelName);
-    } else if (pigeonVar_replyList.length > 1) {
-      throw PlatformException(
-        code: pigeonVar_replyList[0]! as String,
-        message: pigeonVar_replyList[1] as String?,
-        details: pigeonVar_replyList[2],
-      );
-    } else if (pigeonVar_replyList[0] == null) {
-      throw PlatformException(
-        code: 'null-error',
-        message: 'Host platform returned null value for non-null return value.',
-      );
-    } else {
-      return (pigeonVar_replyList[0] as bool?)!;
-    }
+
+    final Object pigeonVar_replyValue = _extractReplyValueOrThrow(
+      pigeonVar_replyList,
+      pigeonVar_channelName,
+      isNullValid: false,
+    )!;
+    return pigeonVar_replyValue as bool;
   }
 }
 

packages/pigeon/lib/src/dart/dart_generator.dart

@@ -417,7 +417,7 @@ class DartGenerator extends StructuredGenerator<InternalDartOptions> {
       EnumeratedType customType,
       int nonSerializedClassCount,
     ) {
-      indent.writeln('case ${customType.offset(nonSerializedClassCount)}: ');
+      indent.writeln('case ${customType.offset(nonSerializedClassCount)}:');
       indent.nest(1, () {
         if (customType.type == CustomTypes.customClass) {
           if (customType.offset(nonSerializedClassCount) ==
@@ -1116,7 +1116,7 @@ final BinaryMessenger? ${varNamePrefix}binaryMessenger;
     required String dartPackageName,
   }) {
     if (root.containsHostApi || root.containsProxyApi) {
-      _writeCreateConnectionError(indent);
+      _writeExtractReplyValueOrThrow(indent);
     }
     if (root.containsFlutterApi ||
         root.containsProxyApi ||
@@ -1173,15 +1173,38 @@ bool _deepEquals(Object? a, Object? b) {
 ''');
   }
 
-  void _writeCreateConnectionError(Indent indent) {
+  static void _writeExtractReplyValueOrThrow(Indent indent) {
     indent.newln();
     indent.format('''
-PlatformException _createConnectionError(String channelName) {
-\treturn PlatformException(
-\t\tcode: 'channel-error',
-\t\tmessage: 'Unable to establish connection on channel: "\$channelName".',
-\t);
-}''');
+Object? _extractReplyValueOrThrow(
+\t\tList<Object?>? replyList,
+\t\tString channelName, {
+\t\trequired bool isNullValid,
+}) {
+\tif (replyList == null) {
+\t\tthrow PlatformException(
+\t\t\tcode: 'channel-error',
+\t\t\tmessage: 'Unable to establish connection on channel: "\$channelName".',
+\t\t);
+\t} else if (replyList.length > 1) {
+\t\tthrow PlatformException(
+\t\t\tcode: replyList[0]! as String,
+\t\t\tmessage: replyList[1] as String?,
+\t\t\tdetails: replyList[2],
+\t\t);''');
+    // On iOS we can return nil from functions to accommodate error
+    // handling.  Returning a nil value and not returning an error is an
+    // exception.
+    indent.format('''
+\t} else if (!isNullValid && (replyList.isNotEmpty && replyList[0] == null)) {
+\t\tthrow PlatformException(
+\t\t\tcode: 'null-error',
+\t\t\tmessage: 'Host platform returned null value for non-null return value.',
+\t\t);
+\t}
+\treturn replyList.firstOrNull;
+}
+''');
   }
 
   void _writeCodecOverflowUtilities(Indent indent, List<EnumeratedType> types) {
@@ -1298,22 +1321,6 @@ if (wrapped == null) {
         indent.writeln('binaryMessenger: ${varNamePrefix}binaryMessenger,');
       },
     );
-    final String returnTypeName = _makeGenericTypeArguments(returnType);
-    final String genericCastCall = _makeGenericCastCall(returnType);
-    const accessor = '${varNamePrefix}replyList[0]';
-    // Avoid warnings from pointlessly casting to `Object?`.
-    final nullablyTypedAccessor = returnTypeName == 'Object'
-        ? accessor
-        : '($accessor as $returnTypeName?)';
-    final nullHandler = returnType.isNullable
-        ? (genericCastCall.isEmpty ? '' : '?')
-        : '!';
-    var returnStatement = 'return';
-    if (!returnType.isVoid) {
-      returnStatement =
-          '$returnStatement $nullablyTypedAccessor$nullHandler$genericCastCall';
-    }
-    returnStatement = '$returnStatement;';
 
     const sendFutureVar = '${varNamePrefix}sendFuture';
     indent.writeln(
@@ -1329,29 +1336,45 @@ if (wrapped == null) {
 
     indent.format('''
 final ${varNamePrefix}replyList = await $sendFutureVar as List<Object?>?;
-if (${varNamePrefix}replyList == null) {
-\tthrow _createConnectionError(${varNamePrefix}channelName);
-} else if (${varNamePrefix}replyList.length > 1) {
-\tthrow PlatformException(
-\t\tcode: ${varNamePrefix}replyList[0]! as String,
-\t\tmessage: ${varNamePrefix}replyList[1] as String?,
-\t\tdetails: ${varNamePrefix}replyList[2],
-\t);''');
-    // On iOS we can return nil from functions to accommodate error
-    // handling.  Returning a nil value and not returning an error is an
-    // exception.
-    if (!returnType.isNullable && !returnType.isVoid) {
-      indent.format('''
-} else if (${varNamePrefix}replyList[0] == null) {
-\tthrow PlatformException(
-\t\tcode: 'null-error',
-\t\tmessage: 'Host platform returned null value for non-null return value.',
-\t);''');
+''');
+    final validateCall =
+        '''
+_extractReplyValueOrThrow(
+\t\t${varNamePrefix}replyList,
+\t\t${varNamePrefix}channelName,
+\t\tisNullValid: ${returnType.isNullable || returnType.isVoid},
+)
+''';
+    if (returnType.isVoid) {
+      indent.format('$validateCall;');
+    } else {
+      const accessor = '${varNamePrefix}replyValue';
+      if (returnType.isNullable) {
+        indent.format('final Object? $accessor = $validateCall;');
+      } else {
+        indent.format('final Object $accessor = $validateCall!;');
+      }
+      String returnTypeName = _makeGenericTypeArguments(returnType);
+      if (returnType.isNullable) {
+        returnTypeName = '$returnTypeName?';
+      }
+      final String genericCastCall = _makeGenericCastCall(returnType);
+
+      if (genericCastCall.isEmpty) {
+        final castedAccessor = returnType.baseName == 'Object'
+            ? accessor
+            : '$accessor as $returnTypeName';
+        indent.format('return $castedAccessor;');
+      } else {
+        final nullablyTypedAccessor = returnType.baseName == 'Object'
+            ? accessor
+            : '($accessor as $returnTypeName)';
+        final nullHandler = returnType.isNullable ? '?' : '';
+        indent.format(
+          'return $nullablyTypedAccessor$nullHandler$genericCastCall;',
+        );
+      }
     }
-    indent.format('''
-} else {
-\t$returnStatement
-}''');
 
     if (!insideAsyncMethod) {
       indent.dec();

packages/pigeon/lib/src/generator_tools.dart

@@ -15,7 +15,7 @@ import 'generator.dart';
 /// The current version of pigeon.
 ///
 /// This must match the version in pubspec.yaml.
-const String pigeonVersion = '26.1.8';
+const String pigeonVersion = '26.1.9';
 
 /// Read all the content from [stdin] to a String.
 String readStdin() {