[pigeon] Use a const for custom type ids for gobject generated files (#156100)

Adds a custom type identifier to generated gobject headers for the user. Calling fl_value_new_custom_object is now possible with that constant.
This fixes flutter/flutter#156100

Also updated the CONTRIBUTING.md file to include the gobject generator.

Author: JesseRiemens

packages/pigeon/CHANGELOG.md

@@ -1,5 +1,6 @@
-## NEXT
+## 25.4.0
 
+* [gobject] Adds type id constants in header files so that they can be used by the user.
 * Updates minimum supported SDK version to Flutter 3.27/Dart 3.6.
 
 ## 25.3.2

packages/pigeon/CONTRIBUTING.md

@@ -19,13 +19,14 @@ generators with that AST.
 ## Source Index
 
 * [ast.dart](./lib/src/ast.dart) - The data structure for representing the Abstract Syntax Tree.
-* [dart_generator.dart](./lib/src/dart_generator.dart) - The Dart code generator.
-* [java_generator.dart](./lib/src/java_generator.dart) - The Java code generator.
-* [kotlin_generator.dart](./lib/src/kotlin_generator.dart) - The Kotlin code generator.
-* [objc_generator.dart](./lib/src/objc_generator.dart) - The Objective-C code
+* [dart_generator.dart](./lib/src/dart/dart_generator.dart) - The Dart code generator.
+* [java_generator.dart](./lib/src/java/java_generator.dart) - The Java code generator.
+* [kotlin_generator.dart](./lib/src/kotlin/kotlin_generator.dart) - The Kotlin code generator.
+* [objc_generator.dart](./lib/src/objc/objc_generator.dart) - The Objective-C code
   generator (header and source files).
-* [swift_generator.dart](./lib/src/swift_generator.dart) - The Swift code generator.
-* [cpp_generator.dart](./lib/src/cpp_generator.dart) - The C++ code generator.
+* [swift_generator.dart](./lib/src/swift/swift_generator.dart) - The Swift code generator.
+* [cpp_generator.dart](./lib/src/cpp/cpp_generator.dart) - The C++ code generator.
+* [gobject_generator.dart](./lib/src/gobject/gobject_generator.dart) - The GObject code generator.
 * [generator_tools.dart](./lib/src/generator_tools.dart) - Shared code between generators.
 * [pigeon_cl.dart](./lib/src/pigeon_cl.dart) - The top-level function executed by
   the command line tool in [bin/][./bin].

packages/pigeon/example/app/linux/messages.g.cc

@@ -91,7 +91,8 @@ static FlValue* pigeon_example_package_message_data_to_list(
                                    ? fl_value_new_string(self->description)
                                    : fl_value_new_null());
   fl_value_append_take(values,
-                       fl_value_new_custom(129, fl_value_new_int(self->code),
+                       fl_value_new_custom(pigeon_example_package_code_type_id,
+                                           fl_value_new_int(self->code),
                                            (GDestroyNotify)fl_value_unref));
   fl_value_append_take(values, fl_value_ref(self->data));
   return values;
@@ -126,11 +127,14 @@ G_DEFINE_TYPE(PigeonExamplePackageMessageCodec,
               pigeon_example_package_message_codec,
               fl_standard_message_codec_get_type())
 
+const int pigeon_example_package_code_type_id = 129;
+const int pigeon_example_package_message_data_type_id = 130;
+
 static gboolean
 pigeon_example_package_message_codec_write_pigeon_example_package_code(
     FlStandardMessageCodec* codec, GByteArray* buffer, FlValue* value,
     GError** error) {
-  uint8_t type = 129;
+  uint8_t type = pigeon_example_package_code_type_id;
   g_byte_array_append(buffer, &type, sizeof(uint8_t));
   return fl_standard_message_codec_write_value(codec, buffer, value, error);
 }
@@ -139,7 +143,7 @@ static gboolean
 pigeon_example_package_message_codec_write_pigeon_example_package_message_data(
     FlStandardMessageCodec* codec, GByteArray* buffer,
     PigeonExamplePackageMessageData* value, GError** error) {
-  uint8_t type = 130;
+  uint8_t type = pigeon_example_package_message_data_type_id;
   g_byte_array_append(buffer, &type, sizeof(uint8_t));
   g_autoptr(FlValue) values =
       pigeon_example_package_message_data_to_list(value);
@@ -151,13 +155,13 @@ static gboolean pigeon_example_package_message_codec_write_value(
     GError** error) {
   if (fl_value_get_type(value) == FL_VALUE_TYPE_CUSTOM) {
     switch (fl_value_get_custom_type(value)) {
-      case 129:
+      case pigeon_example_package_code_type_id:
         return pigeon_example_package_message_codec_write_pigeon_example_package_code(
             codec, buffer,
             reinterpret_cast<FlValue*>(
                 const_cast<gpointer>(fl_value_get_custom_value(value))),
             error);
-      case 130:
+      case pigeon_example_package_message_data_type_id:
         return pigeon_example_package_message_codec_write_pigeon_example_package_message_data(
             codec, buffer,
             PIGEON_EXAMPLE_PACKAGE_MESSAGE_DATA(
@@ -176,7 +180,8 @@ pigeon_example_package_message_codec_read_pigeon_example_package_code(
     FlStandardMessageCodec* codec, GBytes* buffer, size_t* offset,
     GError** error) {
   return fl_value_new_custom(
-      129, fl_standard_message_codec_read_value(codec, buffer, offset, error),
+      pigeon_example_package_code_type_id,
+      fl_standard_message_codec_read_value(codec, buffer, offset, error),
       (GDestroyNotify)fl_value_unref);
 }
 
@@ -198,17 +203,18 @@ pigeon_example_package_message_codec_read_pigeon_example_package_message_data(
     return nullptr;
   }
 
-  return fl_value_new_custom_object(130, G_OBJECT(value));
+  return fl_value_new_custom_object(pigeon_example_package_message_data_type_id,
+                                    G_OBJECT(value));
 }
 
 static FlValue* pigeon_example_package_message_codec_read_value_of_type(
     FlStandardMessageCodec* codec, GBytes* buffer, size_t* offset, int type,
     GError** error) {
   switch (type) {
-    case 129:
+    case pigeon_example_package_code_type_id:
       return pigeon_example_package_message_codec_read_pigeon_example_package_code(
           codec, buffer, offset, error);
-    case 130:
+    case pigeon_example_package_message_data_type_id:
       return pigeon_example_package_message_codec_read_pigeon_example_package_message_data(
           codec, buffer, offset, error);
     default:

packages/pigeon/example/app/linux/messages.g.h

@@ -95,6 +95,16 @@ G_DECLARE_FINAL_TYPE(PigeonExamplePackageMessageCodec,
                      PIGEON_EXAMPLE_PACKAGE, MESSAGE_CODEC,
                      FlStandardMessageCodec)
 
+/**
+ * Custom type ID constants:
+ *
+ * Constants used to identify custom types in the codec.
+ * They are used in the codec to encode and decode custom types.
+ * They may be used in custom object creation functions to identify the type.
+ */
+extern const int pigeon_example_package_code_type_id;
+extern const int pigeon_example_package_message_data_type_id;
+
 G_DECLARE_FINAL_TYPE(PigeonExamplePackageExampleHostApi,
                      pigeon_example_package_example_host_api,
                      PIGEON_EXAMPLE_PACKAGE, EXAMPLE_HOST_API, GObject)

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 = '25.3.2';
+const String pigeonVersion = '25.4.0';
 
 /// Read all the content from [stdin] to a String.
 String readStdin() {

packages/pigeon/lib/src/gobject/gobject_generator.dart

@@ -338,6 +338,28 @@ class GObjectHeaderGenerator
     indent.newln();
     _writeDeclareFinalType(indent, module, _codecBaseName,
         parentClassName: _standardCodecName);
+
+    final Iterable<EnumeratedType> customTypes =
+        getEnumeratedTypes(root, excludeSealedClasses: true);
+
+    if (customTypes.isNotEmpty) {
+      indent.newln();
+      addDocumentationComments(
+          indent,
+          <String>[
+            'Custom type ID constants:',
+            '',
+            'Constants used to identify custom types in the codec.',
+            'They are used in the codec to encode and decode custom types.',
+            'They may be used in custom object creation functions to identify the type.',
+          ],
+          _docCommentSpec);
+    }
+
+    for (final EnumeratedType customType in customTypes) {
+      final String customTypeId = _getCustomTypeId(module, customType);
+      indent.writeln('extern const int $customTypeId;');
+    }
   }
 
   @override
@@ -1019,18 +1041,26 @@ class GObjectSourceGenerator
     _writeDefineType(indent, module, _codecBaseName,
         parentType: 'fl_standard_message_codec_get_type()');
 
+    indent.newln();
+    for (final EnumeratedType customType in customTypes) {
+      final String customTypeId = _getCustomTypeId(module, customType);
+      indent.writeln('const int $customTypeId = ${customType.enumeration};');
+    }
+
     for (final EnumeratedType customType in customTypes) {
       final String customTypeName = _getClassName(module, customType.name);
       final String snakeCustomTypeName =
           _snakeCaseFromCamelCase(customTypeName);
+      final String customTypeId = _getCustomTypeId(module, customType);
+
       indent.newln();
       final String valueType = customType.type == CustomTypes.customClass
           ? '$customTypeName*'
           : 'FlValue*';
       indent.writeScoped(
           'static gboolean ${codecMethodPrefix}_write_$snakeCustomTypeName($_standardCodecName* codec, GByteArray* buffer, $valueType value, GError** error) {',
           '}', () {
-        indent.writeln('uint8_t type = ${customType.enumeration};');
+        indent.writeln('uint8_t type = $customTypeId;');
         indent.writeln('g_byte_array_append(buffer, &type, sizeof(uint8_t));');
         if (customType.type == CustomTypes.customClass) {
           indent.writeln(
@@ -1053,7 +1083,8 @@ class GObjectSourceGenerator
         indent.writeScoped('switch (fl_value_get_custom_type(value)) {', '}',
             () {
           for (final EnumeratedType customType in customTypes) {
-            indent.writeln('case ${customType.enumeration}:');
+            final String customTypeId = _getCustomTypeId(module, customType);
+            indent.writeln('case $customTypeId:');
             indent.nest(1, () {
               final String customTypeName =
                   _getClassName(module, customType.name);
@@ -1082,6 +1113,7 @@ class GObjectSourceGenerator
       final String customTypeName = _getClassName(module, customType.name);
       final String snakeCustomTypeName =
           _snakeCaseFromCamelCase(customTypeName);
+      final String customTypeId = _getCustomTypeId(module, customType);
       indent.newln();
       indent.writeScoped(
           'static FlValue* ${codecMethodPrefix}_read_$snakeCustomTypeName($_standardCodecName* codec, GBytes* buffer, size_t* offset, GError** error) {',
@@ -1102,10 +1134,10 @@ class GObjectSourceGenerator
           });
           indent.newln();
           indent.writeln(
-              'return fl_value_new_custom_object(${customType.enumeration}, G_OBJECT(value));');
+              'return fl_value_new_custom_object($customTypeId, G_OBJECT(value));');
         } else if (customType.type == CustomTypes.customEnum) {
           indent.writeln(
-              'return fl_value_new_custom(${customType.enumeration}, fl_standard_message_codec_read_value(codec, buffer, offset, error), (GDestroyNotify)fl_value_unref);');
+              'return fl_value_new_custom($customTypeId, fl_standard_message_codec_read_value(codec, buffer, offset, error), (GDestroyNotify)fl_value_unref);');
         }
       });
     }
@@ -1117,9 +1149,10 @@ class GObjectSourceGenerator
       indent.writeScoped('switch (type) {', '}', () {
         for (final EnumeratedType customType in customTypes) {
           final String customTypeName = _getClassName(module, customType.name);
+          final String customTypeId = _getCustomTypeId(module, customType);
           final String snakeCustomTypeName =
               _snakeCaseFromCamelCase(customTypeName);
-          indent.writeln('case ${customType.enumeration}:');
+          indent.writeln('case $customTypeId:');
           indent.nest(1, () {
             indent.writeln(
                 'return ${codecMethodPrefix}_read_$snakeCustomTypeName(codec, buffer, offset, error);');
@@ -1922,6 +1955,16 @@ String _getMethodPrefix(String module, String name) {
   return _snakeCaseFromCamelCase(className);
 }
 
+// Returns the code for the custom type id definition for [customType].
+String _getCustomTypeId(String module, EnumeratedType customType) {
+  final String customTypeName = _getClassName(module, customType.name);
+
+  final String snakeCustomTypeName = _snakeCaseFromCamelCase(customTypeName);
+
+  final String customTypeId = '${snakeCustomTypeName}_type_id';
+  return customTypeId;
+}
+
 // Returns an enumeration value in C++ form.
 String _getEnumValue(String module, String enumName, String memberName) {
   final String snakeEnumName = _snakeCaseFromCamelCase(enumName);
@@ -2062,12 +2105,14 @@ String _referenceValue(String module, TypeDeclaration type, String variableName,
   }
 }
 
-int _getTypeEnumeration(Root root, TypeDeclaration type) {
-  return getEnumeratedTypes(root, excludeSealedClasses: true)
-      .firstWhere((EnumeratedType t) =>
-          (type.isClass && t.associatedClass == type.associatedClass) ||
-          (type.isEnum && t.associatedEnum == type.associatedEnum))
-      .enumeration;
+String _getCustomTypeIdFromDeclaration(
+    Root root, TypeDeclaration type, String module) {
+  return _getCustomTypeId(
+      module,
+      getEnumeratedTypes(root, excludeSealedClasses: true).firstWhere(
+          (EnumeratedType t) =>
+              (type.isClass && t.associatedClass == type.associatedClass) ||
+              (type.isEnum && t.associatedEnum == type.associatedEnum)));
 }
 
 // Returns code to convert the native data type stored in [variableName] to a FlValue.
@@ -2078,12 +2123,15 @@ String _makeFlValue(
     {String? lengthVariableName}) {
   final String value;
   if (type.isClass) {
-    final int enumeration = _getTypeEnumeration(root, type);
-    value = 'fl_value_new_custom_object($enumeration, G_OBJECT($variableName))';
+    final String customTypeId =
+        _getCustomTypeIdFromDeclaration(root, type, module);
+    value =
+        'fl_value_new_custom_object($customTypeId, G_OBJECT($variableName))';
   } else if (type.isEnum) {
-    final int enumeration = _getTypeEnumeration(root, type);
+    final String customTypeId =
+        _getCustomTypeIdFromDeclaration(root, type, module);
     value =
-        'fl_value_new_custom($enumeration, fl_value_new_int(${type.isNullable ? '*$variableName' : variableName}), (GDestroyNotify)fl_value_unref)';
+        'fl_value_new_custom($customTypeId, fl_value_new_int(${type.isNullable ? '*$variableName' : variableName}), (GDestroyNotify)fl_value_unref)';
   } else if (_isFlValueWrappedType(type)) {
     value = 'fl_value_ref($variableName)';
   } else if (type.baseName == 'void') {