Follow Protobuf Enum style through a new cli option "protobuf-enum-style"

protoc_plugin/lib/names.dart

@@ -669,3 +669,75 @@ int countRealOneofs(DescriptorProto descriptor) {
 
 String lowerCaseFirstLetter(String input) =>
     input[0].toLowerCase() + input.substring(1);
+
+/// Converts a TitleCase or camelCase enum name to UPPER_SNAKE_CASE.
+/// Examples: 'PhoneType' -> 'PHONE_TYPE', 'HTTPStatus' -> 'HTTP_STATUS'
+String titleCaseToUpperSnakeCase(String input) {
+  if (input.isEmpty) return input;
+
+  final buffer = StringBuffer();
+  bool previousWasLower = false;
+
+  for (var i = 0; i < input.length; i++) {
+    final char = input[i];
+    final isUpper = char == char.toUpperCase();
+    final isLower = char == char.toLowerCase();
+
+    if (i > 0 &&
+        isUpper &&
+        (previousWasLower ||
+            (i + 1 < input.length &&
+                input[i + 1] == input[i + 1].toLowerCase()))) {
+      buffer.write('_');
+    }
+
+    buffer.write(char.toUpperCase());
+    previousWasLower = isLower;
+  }
+
+  return buffer.toString();
+}
+
+/// Strips the enum name prefix from a protobuf-style enum value name and converts
+/// the result to camelCase following Dart enum naming conventions.
+/// Examples:
+/// - enumName='PhoneType', valueName='PHONE_TYPE_MOBILE' -> 'mobile'
+/// - enumName='PhoneType', valueName='PHONE_TYPE_UNSPECIFIED' -> 'unspecified'
+/// - enumName='HTTPStatus', valueName='HTTP_STATUS_NOT_FOUND' -> 'notFound'
+/// - enumName='HTTPStatus', valueName='HTTP_STATUS_OK' -> 'ok'
+String stripEnumPrefix(String enumName, String valueName) {
+  final enumPrefix = titleCaseToUpperSnakeCase(enumName);
+  final prefixWithUnderscore = '${enumPrefix}_';
+
+  String strippedName;
+  if (valueName.startsWith(prefixWithUnderscore)) {
+    strippedName = valueName.substring(prefixWithUnderscore.length);
+  } else {
+    // If the value name doesn't start with the expected prefix, use as-is
+    strippedName = valueName;
+  }
+
+  // Convert UPPER_SNAKE_CASE to camelCase
+  return upperSnakeCaseToCamelCase(strippedName);
+}
+
+/// Converts UPPER_SNAKE_CASE to camelCase.
+/// Examples:
+/// - 'MOBILE' -> 'mobile'
+/// - 'NOT_FOUND' -> 'notFound'
+/// - 'UNSPECIFIED' -> 'unspecified'
+String upperSnakeCaseToCamelCase(String input) {
+  if (input.isEmpty) return input;
+
+  final parts = input.toLowerCase().split('_');
+  if (parts.isEmpty) return input.toLowerCase();
+
+  final buffer = StringBuffer(parts[0]);
+  for (var i = 1; i < parts.length; i++) {
+    if (parts[i].isNotEmpty) {
+      buffer.write(parts[i][0].toUpperCase() + parts[i].substring(1));
+    }
+  }
+
+  return buffer.toString();
+}

protoc_plugin/lib/src/enum_generator.dart

@@ -64,8 +64,21 @@ class EnumGenerator extends ProtobufContainer {
         _aliases.add(EnumAlias(value, canonicalValue));
         _originalAliasIndices.add(i);
       }
+      // Generate Dart name for the enum value
+      String dartName;
+      final isProtobufEnumStyle =
+          parent.fileGen?.options.protobufEnumStyle ?? false;
+      if (isProtobufEnumStyle) {
+        // Strip enum prefix from protobuf-style enum values
+        final strippedName = stripEnumPrefix(descriptor.name, value.name);
+        dartName = avoidInitialUnderscore(strippedName);
+      } else {
+        // Use original style
+        dartName = avoidInitialUnderscore(value.name);
+      }
+
       dartNames[value.name] = disambiguateName(
-        avoidInitialUnderscore(value.name),
+        dartName,
         usedNames,
         enumSuffixes(),
       );

protoc_plugin/lib/src/options.dart

@@ -54,11 +54,13 @@ class GenerationOptions {
   final bool useGrpc;
   final bool generateMetadata;
   final bool disableConstructorArgs;
+  final bool protobufEnumStyle;
 
   GenerationOptions({
     this.useGrpc = false,
     this.generateMetadata = false,
     this.disableConstructorArgs = false,
+    this.protobufEnumStyle = false,
   });
 }
 
@@ -112,6 +114,19 @@ class DisableConstructorArgsParser implements SingleOptionParser {
   }
 }
 
+class ProtobufEnumStyleParser implements SingleOptionParser {
+  bool protobufEnumStyleEnabled = false;
+
+  @override
+  void parse(String name, String? value, OnError onError) {
+    if (value != null) {
+      onError('Invalid protobuf-enum-style option. No value expected.');
+      return;
+    }
+    protobufEnumStyleEnabled = true;
+  }
+}
+
 /// Parser used by the compiler, which supports the `rpc` option (see
 /// [GrpcOptionParser]) and any additional option added in [parsers]. If
 /// [parsers] has a key for `rpc`, it will be ignored.
@@ -132,11 +147,15 @@ GenerationOptions? parseGenerationOptions(
   final disableConstructorArgsParser = DisableConstructorArgsParser();
   newParsers['disable_constructor_args'] = disableConstructorArgsParser;
 
+  final protobufEnumStyleParser = ProtobufEnumStyleParser();
+  newParsers['protobuf-enum-style'] = protobufEnumStyleParser;
+
   if (genericOptionsParser(request, response, newParsers)) {
     return GenerationOptions(
       useGrpc: grpcOptionParser.grpcEnabled,
       generateMetadata: generateMetadataParser.generateKytheInfo,
       disableConstructorArgs: disableConstructorArgsParser.value,
+      protobufEnumStyle: protobufEnumStyleParser.protobufEnumStyleEnabled,
     );
   }
   return null;

protoc_plugin/test/enum_generator_test.dart

@@ -42,4 +42,126 @@ void main() {
     expectGolden(writer.emitSource(format: false), 'enum.pbenum.dart');
     expectGolden(writer.sourceLocationInfo.toString(), 'enum.pbenum.dart.meta');
   });
+
+  test('testEnumGeneratorWithProtobufEnumStyle', () {
+    // Create an enum with protobuf-style names (enum name prefixed values)
+    final ed =
+        EnumDescriptorProto()
+          ..name = 'PhoneType'
+          ..value.addAll([
+            EnumValueDescriptorProto()
+              ..name = 'PHONE_TYPE_UNSPECIFIED'
+              ..number = 0,
+            EnumValueDescriptorProto()
+              ..name = 'PHONE_TYPE_MOBILE'
+              ..number = 1,
+            EnumValueDescriptorProto()
+              ..name = 'PHONE_TYPE_HOME'
+              ..number = 2,
+            EnumValueDescriptorProto()
+              ..name = 'PHONE_TYPE_WORK'
+              ..number = 3,
+          ]);
+
+    final writer = IndentingWriter(
+      generateMetadata: true,
+      fileName: 'sample.proto',
+    );
+
+    // Test with protobuf enum style enabled - this should strip prefixes
+    final optionsWithProtobufStyle = GenerationOptions(protobufEnumStyle: true);
+    final fg = FileGenerator(FileDescriptorProto(), optionsWithProtobufStyle);
+    final eg = EnumGenerator.topLevel(ed, fg, <String>{}, 0);
+    eg.generate(writer);
+
+    expectGolden(
+      writer.emitSource(format: false),
+      'enum_protobuf_style.pbenum.dart',
+    );
+    expectGolden(
+      writer.sourceLocationInfo.toString(),
+      'enum_protobuf_style.pbenum.dart.meta',
+    );
+  });
+
+  test('testEnumGeneratorWithoutProtobufEnumStyle', () {
+    // Same enum with protobuf-style names but without the flag
+    final ed =
+        EnumDescriptorProto()
+          ..name = 'PhoneType'
+          ..value.addAll([
+            EnumValueDescriptorProto()
+              ..name = 'PHONE_TYPE_UNSPECIFIED'
+              ..number = 0,
+            EnumValueDescriptorProto()
+              ..name = 'PHONE_TYPE_MOBILE'
+              ..number = 1,
+          ]);
+
+    final writer = IndentingWriter(
+      generateMetadata: true,
+      fileName: 'sample.proto',
+    );
+
+    // Test without protobuf enum style - should use names as-is
+    final optionsWithoutProtobufStyle = GenerationOptions(
+      protobufEnumStyle: false,
+    );
+    final fg = FileGenerator(
+      FileDescriptorProto(),
+      optionsWithoutProtobufStyle,
+    );
+    final eg = EnumGenerator.topLevel(ed, fg, <String>{}, 0);
+    eg.generate(writer);
+
+    expectGolden(
+      writer.emitSource(format: false),
+      'enum_without_protobuf_style.pbenum.dart',
+    );
+    expectGolden(
+      writer.sourceLocationInfo.toString(),
+      'enum_without_protobuf_style.pbenum.dart.meta',
+    );
+  });
+
+  test('testEnumGeneratorWithComplexProtobufEnumStyle', () {
+    // Test with more complex enum names to verify camelCase conversion
+    final ed =
+        EnumDescriptorProto()
+          ..name = 'HTTPStatusCode'
+          ..value.addAll([
+            EnumValueDescriptorProto()
+              ..name = 'HTTP_STATUS_CODE_UNSPECIFIED'
+              ..number = 0,
+            EnumValueDescriptorProto()
+              ..name = 'HTTP_STATUS_CODE_NOT_FOUND'
+              ..number = 1,
+            EnumValueDescriptorProto()
+              ..name = 'HTTP_STATUS_CODE_INTERNAL_SERVER_ERROR'
+              ..number = 2,
+            EnumValueDescriptorProto()
+              ..name = 'HTTP_STATUS_CODE_OK'
+              ..number = 3,
+          ]);
+
+    final writer = IndentingWriter(
+      generateMetadata: true,
+      fileName: 'sample.proto',
+    );
+
+    // Test with protobuf enum style enabled
+    final optionsWithProtobufStyle = GenerationOptions(protobufEnumStyle: true);
+    final fg = FileGenerator(FileDescriptorProto(), optionsWithProtobufStyle);
+    final eg = EnumGenerator.topLevel(ed, fg, <String>{}, 0);
+    eg.generate(writer);
+
+    expectGolden(
+      writer.emitSource(format: false),
+      'enum_complex_protobuf_style.pbenum.dart',
+    );
+    expectGolden(
+      writer.sourceLocationInfo.toString(),
+      'enum_complex_protobuf_style.pbenum.dart.meta',
+    );
+  });
 }

protoc_plugin/test/goldens/enum_complex_protobuf_style.pbenum.dart

@@ -0,0 +1,21 @@
+class HTTPStatusCode extends $pb.ProtobufEnum {
+  static const HTTPStatusCode unspecified = HTTPStatusCode._(0, _omitEnumNames ? '' : 'HTTP_STATUS_CODE_UNSPECIFIED');
+  static const HTTPStatusCode notFound = HTTPStatusCode._(1, _omitEnumNames ? '' : 'HTTP_STATUS_CODE_NOT_FOUND');
+  static const HTTPStatusCode internalServerError = HTTPStatusCode._(2, _omitEnumNames ? '' : 'HTTP_STATUS_CODE_INTERNAL_SERVER_ERROR');
+  static const HTTPStatusCode ok = HTTPStatusCode._(3, _omitEnumNames ? '' : 'HTTP_STATUS_CODE_OK');
+
+  static const $core.List<HTTPStatusCode> values = <HTTPStatusCode> [
+    unspecified,
+    notFound,
+    internalServerError,
+    ok,
+  ];
+
+  static final $core.List<HTTPStatusCode?> _byValue = $pb.ProtobufEnum.$_initByValueList(values, 3);
+  static HTTPStatusCode? valueOf($core.int value) =>  value < 0 || value >= _byValue.length ? null : _byValue[value];
+
+  const HTTPStatusCode._(super.value, super.name);
+}
+
+
+const $core.bool _omitEnumNames = $core.bool.fromEnvironment('protobuf.omit_enum_names');

protoc_plugin/test/goldens/enum_complex_protobuf_style.pbenum.dart.meta

@@ -0,0 +1,43 @@
+annotation: {
+  path: 5
+  path: 0
+  sourceFile: sample.proto
+  begin: 6
+  end: 20
+}
+annotation: {
+  path: 5
+  path: 0
+  path: 2
+  path: 0
+  sourceFile: sample.proto
+  begin: 78
+  end: 89
+}
+annotation: {
+  path: 5
+  path: 0
+  path: 2
+  path: 1
+  sourceFile: sample.proto
+  begin: 197
+  end: 205
+}
+annotation: {
+  path: 5
+  path: 0
+  path: 2
+  path: 2
+  sourceFile: sample.proto
+  begin: 311
+  end: 330
+}
+annotation: {
+  path: 5
+  path: 0
+  path: 2
+  path: 3
+  sourceFile: sample.proto
+  begin: 448
+  end: 450
+}

protoc_plugin/test/goldens/enum_protobuf_style.pbenum.dart

@@ -0,0 +1,21 @@
+class PhoneType extends $pb.ProtobufEnum {
+  static const PhoneType unspecified = PhoneType._(0, _omitEnumNames ? '' : 'PHONE_TYPE_UNSPECIFIED');
+  static const PhoneType mobile = PhoneType._(1, _omitEnumNames ? '' : 'PHONE_TYPE_MOBILE');
+  static const PhoneType home = PhoneType._(2, _omitEnumNames ? '' : 'PHONE_TYPE_HOME');
+  static const PhoneType work = PhoneType._(3, _omitEnumNames ? '' : 'PHONE_TYPE_WORK');
+
+  static const $core.List<PhoneType> values = <PhoneType> [
+    unspecified,
+    mobile,
+    home,
+    work,
+  ];
+
+  static final $core.List<PhoneType?> _byValue = $pb.ProtobufEnum.$_initByValueList(values, 3);
+  static PhoneType? valueOf($core.int value) =>  value < 0 || value >= _byValue.length ? null : _byValue[value];
+
+  const PhoneType._(super.value, super.name);
+}
+
+
+const $core.bool _omitEnumNames = $core.bool.fromEnvironment('protobuf.omit_enum_names');