[pigeon][swift] Removes FlutterError in favor of PigeonError

packages/pigeon/README.md

@@ -53,8 +53,7 @@ should be returned via the provided callback.
 To pass custom details into `PlatformException` for error handling, 
 use `FlutterError` in your Host API. [Example](./example/README.md#HostApi_Example).
 
-To use `FlutterError` in Swift you must first extend a standard error.
-[Example](./example/README.md#AppDelegate.swift).
+For swift, use `PigeonError` instead of `FlutterError`.
 
 #### Objective-C and C++
 

packages/pigeon/example/README.md

@@ -118,8 +118,6 @@ This is the code that will use the generated Swift code to receive calls from Fl
 packages/pigeon/example/app/ios/Runner/AppDelegate.swift
 <?code-excerpt "ios/Runner/AppDelegate.swift (swift-class)"?>
 ```swift
-// This extension of Error is required to do use FlutterError in any Swift code.
-extension FlutterError: Error {}
 
 private class PigeonApiImplementation: ExampleHostApi {
   func getHostLanguage() throws -> String {
@@ -128,14 +126,14 @@ private class PigeonApiImplementation: ExampleHostApi {
 
   func add(_ a: Int64, to b: Int64) throws -> Int64 {
     if a < 0 || b < 0 {
-      throw FlutterError(code: "code", message: "message", details: "details")
+      throw PigeonError(code: "code", message: "message", details: "details")
     }
     return a + b
   }
 
   func sendMessage(message: MessageData, completion: @escaping (Result<Bool, Error>) -> Void) {
     if message.code == Code.one {
-      completion(.failure(FlutterError(code: "code", message: "message", details: "details")))
+      completion(.failure(PigeonError(code: "code", message: "message", details: "details")))
       return
     }
     completion(.success(true))

packages/pigeon/example/app/ios/Runner/AppDelegate.swift

@@ -5,10 +5,6 @@
 import Flutter
 import UIKit
 
-// #docregion swift-class
-// This extension of Error is required to do use FlutterError in any Swift code.
-extension FlutterError: Error {}
-
 private class PigeonApiImplementation: ExampleHostApi {
   func getHostLanguage() throws -> String {
     return "Swift"

packages/pigeon/example/app/ios/Runner/Messages.g.swift

@@ -14,6 +14,32 @@ import Foundation
   #error("Unsupported platform.")
 #endif
 
+/// Error thrown by Pigeon. Encapsulates a code, message, and details.
+class PigeonError: Swift.Error {
+  let code: String
+  let message: String?
+  let details: Any?
+
+  init(code: String, message: String?, details: Any?) {
+    self.code = code
+    self.message = message
+    self.details = details
+  }
+
+  var localizedDescription: String {
+    let detailsDescription: String
+    if let convertibleObject = details as? CustomStringConvertible {
+      detailsDescription = convertibleObject.description
+    } else if let _ = details {
+      detailsDescription = "<non-convertible object>"
+    } else {
+      detailsDescription = "<nil>"
+    }
+    return
+      "PigeonError(code: \(code), message: \(message ?? "<nil>"), details: \(detailsDescription)"
+  }
+}
+
 private func wrapResult(_ result: Any?) -> [Any?] {
   return [result]
 }
@@ -33,8 +59,8 @@ private func wrapError(_ error: Any) -> [Any?] {
   ]
 }
 
-private func createConnectionError(withChannelName channelName: String) -> FlutterError {
-  return FlutterError(
+private func createConnectionError(withChannelName channelName: String) -> PigeonError {
+  return PigeonError(
     code: "channel-error", message: "Unable to establish connection on channel: '\(channelName)'.",
     details: "")
 }
@@ -193,7 +219,7 @@ class ExampleHostApiSetup {
 /// Generated protocol from Pigeon that represents Flutter messages that can be called from Swift.
 protocol MessageFlutterApiProtocol {
   func flutterMethod(
-    aString aStringArg: String?, completion: @escaping (Result<String, FlutterError>) -> Void)
+    aString aStringArg: String?, completion: @escaping (Result<String, PigeonError>) -> Void)
 }
 class MessageFlutterApi: MessageFlutterApiProtocol {
   private let binaryMessenger: FlutterBinaryMessenger
@@ -203,7 +229,7 @@ class MessageFlutterApi: MessageFlutterApiProtocol {
     self.messageChannelSuffix = messageChannelSuffix.count > 0 ? ".\(messageChannelSuffix)" : ""
   }
   func flutterMethod(
-    aString aStringArg: String?, completion: @escaping (Result<String, FlutterError>) -> Void
+    aString aStringArg: String?, completion: @escaping (Result<String, PigeonError>) -> Void
   ) {
     let channelName: String =
       "dev.flutter.pigeon.pigeon_example_package.MessageFlutterApi.flutterMethod\(messageChannelSuffix)"
@@ -217,11 +243,11 @@ class MessageFlutterApi: MessageFlutterApiProtocol {
         let code: String = listResponse[0] as! String
         let message: String? = nilOrValue(listResponse[1])
         let details: String? = nilOrValue(listResponse[2])
-        completion(.failure(FlutterError(code: code, message: message, details: details)))
+        completion(.failure(PigeonError(code: code, message: message, details: details)))
       } else if listResponse[0] == nil {
         completion(
           .failure(
-            FlutterError(
+            PigeonError(
               code: "null-error",
               message: "Flutter api returned null value for non-null return value.", details: "")))
       } else {

packages/pigeon/lib/pigeon_lib.dart

@@ -2084,6 +2084,8 @@ ${_argParser.usage}''';
         help: 'Path to generated Objective-C header file (.h).')
     ..addOption('objc_prefix',
         help: 'Prefix for generated Objective-C classes and protocols.')
+    ..addOption('swift_emit_error_class',
+        help: 'Adds an error class to the generated Swift code.')
     ..addOption('copyright_header',
         help:
             'Path to file with copyright header to be prepended to generated code.')
@@ -2125,6 +2127,9 @@ ${_argParser.usage}''';
             results['java_use_generated_annotation'] as bool?,
       ),
       swiftOut: results['swift_out'] as String?,
+      swiftOptions: SwiftOptions(
+        swiftEmitErrorClass: results['swift_emit_error_class'] as bool?,
+      ),
       kotlinOut: results['kotlin_out'] as String?,
       kotlinOptions: KotlinOptions(
         package: results['kotlin_package'] as String?,

packages/pigeon/lib/swift_generator.dart

@@ -19,16 +19,22 @@ class SwiftOptions {
   /// Creates a [SwiftOptions] object
   const SwiftOptions({
     this.copyrightHeader,
+    this.swiftEmitErrorClass,
   });
 
   /// A copyright header that will get prepended to generated code.
   final Iterable<String>? copyrightHeader;
 
+  /// Whether to emit the PigeonError class in the generated code.
+  /// Defaults to true.
+  final bool? swiftEmitErrorClass;
+
   /// Creates a [SwiftOptions] from a Map representation where:
   /// `x = SwiftOptions.fromList(x.toMap())`.
   static SwiftOptions fromList(Map<String, Object> map) {
     return SwiftOptions(
       copyrightHeader: map['copyrightHeader'] as Iterable<String>?,
+      swiftEmitErrorClass: map['swiftEmitErrorClass'] as bool?,
     );
   }
 
@@ -37,6 +43,8 @@ class SwiftOptions {
   Map<String, Object> toMap() {
     final Map<String, Object> result = <String, Object>{
       if (copyrightHeader != null) 'copyrightHeader': copyrightHeader!,
+      if (swiftEmitErrorClass != null)
+        'swiftEmitErrorClass': swiftEmitErrorClass!,
     };
     return result;
   }
@@ -316,7 +324,7 @@ class SwiftGenerator extends StructuredGenerator<SwiftOptions> {
           name: func.name,
           parameters: func.parameters,
           returnType: func.returnType,
-          errorTypeName: 'FlutterError',
+          errorTypeName: 'PigeonError',
           isAsynchronous: true,
           swiftFunction: func.swiftFunction,
           getParameterName: _getSafeArgumentName,
@@ -673,10 +681,10 @@ private func nilOrValue<T>(_ value: Any?) -> T? {
   void _writeCreateConnectionError(Indent indent) {
     indent.newln();
     indent.writeScoped(
-        'private func createConnectionError(withChannelName channelName: String) -> FlutterError {',
+        'private func createConnectionError(withChannelName channelName: String) -> PigeonError {',
         '}', () {
       indent.writeln(
-          'return FlutterError(code: "channel-error", message: "Unable to establish connection on channel: \'\\(channelName)\'.", details: "")');
+          'return PigeonError(code: "channel-error", message: "Unable to establish connection on channel: \'\\(channelName)\'.", details: "")');
     });
   }
 
@@ -694,6 +702,10 @@ private func nilOrValue<T>(_ value: Any?) -> T? {
         .whereType<AstFlutterApi>()
         .any((Api api) => api.methods.isNotEmpty);
 
+    if (generatorOptions.swiftEmitErrorClass ?? true) {
+      _writePigeonError(indent);
+    }
+
     if (hasHostApi) {
       _writeWrapResult(indent);
       _writeWrapError(indent);
@@ -718,7 +730,7 @@ private func nilOrValue<T>(_ value: Any?) -> T? {
       name: name,
       parameters: parameters,
       returnType: returnType,
-      errorTypeName: 'FlutterError',
+      errorTypeName: 'PigeonError',
       isAsynchronous: true,
       swiftFunction: swiftFunction,
       getParameterName: _getSafeArgumentName,
@@ -760,12 +772,12 @@ private func nilOrValue<T>(_ value: Any?) -> T? {
           indent.writeln('let message: String? = nilOrValue(listResponse[1])');
           indent.writeln('let details: String? = nilOrValue(listResponse[2])');
           indent.writeln(
-              'completion(.failure(FlutterError(code: code, message: message, details: details)))');
+              'completion(.failure(PigeonError(code: code, message: message, details: details)))');
         }, addTrailingNewline: false);
         if (!returnType.isNullable && !returnType.isVoid) {
           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: "")))');
+                'completion(.failure(PigeonError(code: "null-error", message: "Flutter api returned null value for non-null return value.", details: "")))');
           }, addTrailingNewline: false);
         }
         indent.addScoped('else {', '}', () {
@@ -895,6 +907,51 @@ private func nilOrValue<T>(_ value: Any?) -> T? {
       indent.writeln('$varChannelName.setMessageHandler(nil)');
     });
   }
+
+  void _writePigeonError(Indent indent) {
+    indent.newln();
+    indent.writeln(
+        '/// Error thrown by Pigeon. Encapsulates a code, message, and details.');
+    indent.writeln('class PigeonError: Swift.Error {');
+    indent.nest(1, () {
+      indent.writeln('let code: String');
+      indent.writeln('let message: String?');
+      indent.writeln('let details: Any?');
+      indent.newln();
+      indent.writeln('init(code: String, message: String?, details: Any?) {');
+      indent.nest(1, () {
+        indent.writeln('self.code = code');
+        indent.writeln('self.message = message');
+        indent.writeln('self.details = details');
+      });
+      indent.writeln('}');
+      indent.newln();
+      indent.writeln('var localizedDescription: String {');
+      indent.nest(1, () {
+        indent.writeln('let detailsDescription: String');
+        indent.writeln(
+            'if let convertibleObject = details as? CustomStringConvertible {');
+        indent.nest(1, () {
+          indent.writeln('detailsDescription = convertibleObject.description');
+        });
+        indent.writeln('} else if let _ = details {');
+        indent.nest(1, () {
+          indent.writeln('detailsDescription = "<non-convertible object>"');
+        });
+        indent.writeln('} else {');
+        indent.nest(1, () {
+          indent.writeln('detailsDescription = "<nil>"');
+        });
+        indent.writeln('}');
+        indent.writeln(
+            r'return "PigeonError(code: \(code), message: \(message ?? "<nil>"), details: \(detailsDescription)"');
+      });
+      indent.write('}');
+    });
+    indent.newln();
+    indent.write('}');
+    indent.newln();
+  }
 }
 
 /// Calculates the name of the codec that will be generated for [api].