[pigeon] make swift enum CaseIterable (#11702)

instead of generating
```swift
enum FooEnum: Int {
  case foo = 0
  ...
```
we will now generate
```swift
enum FooEnum: Int, CaseIterable {
  case foo = 0
  ...
```
allowing consumers to use `FooEnum.allCases` to iterate over all possible enum values in swift platform code

fixes flutter/flutter#186447

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Author: HannesGitH

packages/pigeon/CHANGELOG.md

@@ -1,3 +1,7 @@
+## 27.1.0
+
+* [swift] Adds `CaseIterable` conformance to generated enums.
+
 ## 27.0.0
 
 * **Breaking Change** Overrides `toString` (or equivalent) methods on generated data classes

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

@@ -192,7 +192,7 @@ private func nilOrValue<T>(_ value: Any?) -> T? {
   return value as! T?
 }
 
-enum Code: Int {
+enum Code: Int, CaseIterable {
   case one = 0
   case two = 1
 }

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 = '27.0.0';
+const String pigeonVersion = '27.1.0';
 
 /// Default plugin package name.
 const String defaultPluginPackageName = 'dev.flutter.pigeon';

packages/pigeon/lib/src/swift/swift_generator.dart

@@ -234,7 +234,7 @@ class SwiftGenerator extends StructuredGenerator<InternalSwiftOptions> {
     indent.newln();
     addDocumentationComments(indent, anEnum.documentationComments, _docCommentSpec);
 
-    indent.write('enum ${anEnum.name}: Int ');
+    indent.write('enum ${anEnum.name}: Int, CaseIterable ');
     indent.addScoped('{', '}', () {
       enumerate(anEnum.members, (int index, EnumMember member) {
         addDocumentationComments(indent, member.documentationComments, _docCommentSpec);

packages/pigeon/platform_tests/test_plugin/darwin/test_plugin/Sources/test_plugin/CoreTests.gen.swift

@@ -193,15 +193,15 @@ private func nilOrValue<T>(_ value: Any?) -> T? {
   return value as! T?
 }
 
-enum AnEnum: Int {
+enum AnEnum: Int, CaseIterable {
   case one = 0
   case two = 1
   case three = 2
   case fortyTwo = 3
   case fourHundredTwentyTwo = 4
 }
 
-enum AnotherEnum: Int {
+enum AnotherEnum: Int, CaseIterable {
   case justInCase = 0
 }
 

packages/pigeon/platform_tests/test_plugin/darwin/test_plugin/Sources/test_plugin/EventChannelTests.gen.swift

@@ -161,15 +161,15 @@ private func nilOrValue<T>(_ value: Any?) -> T? {
   return value as! T?
 }
 
-enum EventEnum: Int {
+enum EventEnum: Int, CaseIterable {
   case one = 0
   case two = 1
   case three = 2
   case fortyTwo = 3
   case fourHundredTwentyTwo = 4
 }
 
-enum AnotherEventEnum: Int {
+enum AnotherEventEnum: Int, CaseIterable {
   case justInCase = 0
 }
 

packages/pigeon/platform_tests/test_plugin/darwin/test_plugin/Sources/test_plugin/ProxyApiTests.gen.swift

@@ -590,7 +590,7 @@ private class ProxyApiTestsPigeonInternalProxyApiCodecReaderWriter: FlutterStand
   }
 }
 
-enum ProxyApiTestEnum: Int {
+enum ProxyApiTestEnum: Int, CaseIterable {
   case one = 0
   case two = 1
   case three = 2

packages/pigeon/platform_tests/test_plugin/example/ios/RunnerTests/EnumTests.swift

@@ -57,4 +57,18 @@ struct EnumTests {
     }
   }
 
+  // Verifies that generated enums conform to `CaseIterable` and that
+  // `allCases` returns every member in declaration order with the
+  // expected raw values.
+  @Test
+  func enumIsCaseIterable() {
+    let allCases = AnEnum.allCases
+    #expect(allCases == [.one, .two, .three, .fortyTwo, .fourHundredTwentyTwo])
+    #expect(allCases.count == 5)
+    #expect(allCases.map { $0.rawValue } == [0, 1, 2, 3, 4])
+
+    // Single-member enums should also conform and report a single case.
+    #expect(AnotherEnum.allCases == [.justInCase])
+  }
+
 }

packages/pigeon/pubspec.yaml

@@ -2,7 +2,7 @@ name: pigeon
 description: Code generator tool to make communication between Flutter and the host platform type-safe and easier.
 repository: https://github.com/flutter/packages/tree/main/packages/pigeon
 issue_tracker: https://github.com/flutter/flutter/issues?q=is%3Aissue+is%3Aopen+label%3A%22p%3A+pigeon%22
-version: 27.0.0 # This must match the version in lib/src/generator_tools.dart
+version: 27.1.0 # This must match the version in lib/src/generator_tools.dart
 
 environment:
   sdk: ^3.10.0

packages/pigeon/test/swift_generator_test.dart

@@ -61,7 +61,7 @@ void main() {
     const generator = SwiftGenerator();
     generator.generate(swiftOptions, root, sink, dartPackageName: DEFAULT_PACKAGE_NAME);
     final code = sink.toString();
-    expect(code, contains('enum Foobar: Int'));
+    expect(code, contains('enum Foobar: Int, CaseIterable'));
     expect(code, contains('  case one = 0'));
     expect(code, contains('  case two = 1'));
     expect(code, isNot(contains('if (')));