[pigeon] implement generics in primitives

packages/pigeon/CHANGELOG.md

@@ -5,6 +5,7 @@
 * [front-end] Added more errors for incorrect usage of Pigeon (previously they were just ignored).
 * Moved Pigeon to using a custom codec which allows collection types to contain custom classes.
 * Started allowing primitive data types as arguments and return types.
+* Started supporting generics' type arguments for fields in classes.
 
 ## 0.3.0
 

packages/pigeon/lib/ast.dart

@@ -20,27 +20,19 @@ class Method extends Node {
   Method({
     required this.name,
     required this.returnType,
-    required this.argType,
-    this.isArgNullable = false,
+    required this.arguments,
     this.isAsynchronous = false,
-    this.isReturnNullable = false,
     this.offset,
   });
 
   /// The name of the method.
   String name;
 
   /// The data-type of the return value.
-  String returnType;
-
-  /// True if the method can return a null value.
-  bool isReturnNullable;
+  Field returnType;
 
   /// The data-type of the argument.
-  String argType;
-
-  /// True if the argument has a null tag `?`.
-  bool isArgNullable;
+  List<Field> arguments;
 
   /// Whether the receiver of this method is expected to return synchronously or not.
   bool isAsynchronous;
@@ -50,7 +42,7 @@ class Method extends Node {
 
   @override
   String toString() {
-    return '(Api name:$name returnType:$returnType argType:$argType isAsynchronous:$isAsynchronous)';
+    return '(Method name:$name returnType:$returnType argType:$arguments isAsynchronous:$isAsynchronous)';
   }
 }
 
@@ -82,8 +74,47 @@ class Api extends Node {
   }
 }
 
+/// An entity that represents a typed concept, like a [TypeArgument] or [Field].
+abstract class TypedEntity {
+  /// The data-type of the entity (ex 'String' or 'int').
+  String get dataType;
+
+  /// The type arguments to the entity.
+  List<TypeArgument>? get typeArguments;
+
+  /// True if the type is nullable.
+  bool get isNullable;
+}
+
+/// A parameter to a generic entity.  For example, "String" to "List<String>".
+class TypeArgument implements TypedEntity {
+  /// Constructor for [TypeArgument].
+  TypeArgument({
+    required this.dataType,
+    required this.isNullable,
+    this.typeArguments,
+  });
+
+  /// A string representation of the base datatype.
+  @override
+  final String dataType;
+
+  /// The type arguments to this [TypeArgument].
+  @override
+  final List<TypeArgument>? typeArguments;
+
+  /// True if the type is nullable.
+  @override
+  final bool isNullable;
+
+  @override
+  String toString() {
+    return '(TypeArgument dataType:$dataType isNullable:$isNullable typeArguments:$typeArguments)';
+  }
+}
+
 /// Represents a field on a [Class].
-class Field extends Node {
+class Field extends Node implements TypedEntity {
   /// Parametric constructor for [Field].
   Field({
     required this.name,
@@ -97,20 +128,23 @@ class Field extends Node {
   String name;
 
   /// The data-type of the field (ex 'String' or 'int').
+  @override
   String dataType;
 
   /// The offset in the source file where the field appears.
   int? offset;
 
   /// True if the datatype is nullable (ex `int?`).
+  @override
   bool isNullable;
 
   /// Type parameters used for generics.
-  List<Field>? typeArguments;
+  @override
+  List<TypeArgument>? typeArguments;
 
   @override
   String toString() {
-    return '(Field name:$name dataType:$dataType)';
+    return '(Field name:$name dataType:$dataType typeArguments:$typeArguments)';
   }
 }
 

packages/pigeon/lib/dart_generator.dart

@@ -92,6 +92,18 @@ void _writeCodec(Indent indent, String codecName, Api api) {
   });
 }
 
+String _makeGenericTypeArguments(TypedEntity entity, String nullTag) {
+  return entity.typeArguments != null
+      ? '${entity.dataType}<${entity.typeArguments!.map((TypeArgument e) => 'Object$nullTag').reduce((String value, String element) => '$value, $element')}>'
+      : _addGenericTypes(entity, nullTag);
+}
+
+String _makeGenericCastCall(TypedEntity entity, String nullTag) {
+  return entity.typeArguments != null
+      ? '.cast<${_flattenTypeArguments(entity.typeArguments!, nullTag)}>()'
+      : '';
+}
+
 void _writeHostApi(DartOptions opt, Indent indent, Api api) {
   assert(api.location == ApiLocation.host);
   final String codecName = _getCodecName(api);
@@ -121,12 +133,12 @@ final BinaryMessenger$nullTag _binaryMessenger;
       }
       String argSignature = '';
       String sendArgument = 'null';
-      if (func.argType != 'void') {
-        argSignature = '${func.argType} arg';
+      if (func.arguments.isNotEmpty) {
+        argSignature = '${_addGenericTypes(func.arguments[0], nullTag)} arg';
         sendArgument = 'arg';
       }
       indent.write(
-        'Future<${func.returnType}> ${func.name}($argSignature) async ',
+        'Future<${_addGenericTypes(func.returnType, nullTag)}> ${func.name}($argSignature) async ',
       );
       indent.scoped('{', '}', () {
         final String channelName = makeChannelName(api, func);
@@ -137,9 +149,12 @@ final BinaryMessenger$nullTag _binaryMessenger;
             '\'$channelName\', codec, binaryMessenger: _binaryMessenger);',
           );
         });
-        final String returnStatement = func.returnType == 'void'
+        final String returnType =
+            _makeGenericTypeArguments(func.returnType, nullTag);
+        final String castCall = _makeGenericCastCall(func.returnType, nullTag);
+        final String returnStatement = func.returnType.dataType == 'void'
             ? '// noop'
-            : 'return (replyMap[\'${Keys.result}\'] as ${func.returnType}$nullTag)$unwrapOperator;';
+            : 'return (replyMap[\'${Keys.result}\'] as $returnType$nullTag)$unwrapOperator$castCall;';
         indent.format('''
 final Map<Object$nullTag, Object$nullTag>$nullTag replyMap =\n\t\tawait channel.send($sendArgument) as Map<Object$nullTag, Object$nullTag>$nullTag;
 if (replyMap == null) {
@@ -181,10 +196,12 @@ void _writeFlutterApi(
     indent.addln('');
     for (final Method func in api.methods) {
       final bool isAsync = func.isAsynchronous;
-      final String returnType =
-          isAsync ? 'Future<${func.returnType}>' : func.returnType;
-      final String argSignature =
-          func.argType == 'void' ? '' : '${func.argType} arg';
+      final String returnType = isAsync
+          ? 'Future<${_addGenericTypes(func.returnType, nullTag)}>'
+          : _addGenericTypes(func.returnType, nullTag);
+      final String argSignature = func.arguments.isEmpty
+          ? ''
+          : '${_addGenericTypes(func.arguments[0], nullTag)} arg';
       indent.writeln('$returnType ${func.name}($argSignature);');
     }
     indent.write('static void setup(${api.name}$nullTag api) ');
@@ -215,19 +232,21 @@ void _writeFlutterApi(
               'channel.$messageHandlerSetter((Object$nullTag message) async ',
             );
             indent.scoped('{', '});', () {
-              final String argType = func.argType;
-              final String returnType = func.returnType;
+              final String returnType =
+                  _addGenericTypes(func.returnType, nullTag);
               final bool isAsync = func.isAsynchronous;
               final String emptyReturnStatement = isMockHandler
                   ? 'return <Object$nullTag, Object$nullTag>{};'
-                  : func.returnType == 'void'
+                  : func.returnType.dataType == 'void'
                       ? 'return;'
                       : 'return null;';
               String call;
-              if (argType == 'void') {
+              if (func.arguments.isEmpty) {
                 indent.writeln('// ignore message');
                 call = 'api.${func.name}()';
               } else {
+                final String argType =
+                    _addGenericTypes(func.arguments[0], nullTag);
                 indent.writeln(
                   'assert(message != null, \'Argument for $channelName was null. Expected $argType.\');',
                 );
@@ -263,17 +282,37 @@ void _writeFlutterApi(
   });
 }
 
-String _addGenericTypes(String dataType, String nullTag) {
-  switch (dataType) {
+/// Converts a [List] of [TypeArgument]s to a comma separated [String] to be
+/// used in Dart code.
+String _flattenTypeArguments(List<TypeArgument> args, String nullTag) {
+  return args
+      .map((TypeArgument arg) => arg.typeArguments == null
+          ? '${arg.dataType}$nullTag'
+          : '${arg.dataType}<${_flattenTypeArguments(arg.typeArguments!, nullTag)}>$nullTag')
+      .reduce((String value, String element) => '$value, $element');
+}
+
+/// Creates the type declaration for use in Dart code from a [Field] making sure
+/// that type arguments are used for primitive generic types.
+String _addGenericTypes(TypedEntity entity, String nullTag) {
+  switch (entity.dataType) {
     case 'List':
-      return 'List<Object$nullTag>$nullTag';
+      return (entity.typeArguments == null)
+          ? 'List<Object$nullTag>'
+          : 'List<${_flattenTypeArguments(entity.typeArguments!, nullTag)}>';
     case 'Map':
-      return 'Map<Object$nullTag, Object$nullTag>$nullTag';
+      return (entity.typeArguments == null)
+          ? 'Map<Object$nullTag, Object$nullTag>'
+          : 'Map<${_flattenTypeArguments(entity.typeArguments!, nullTag)}>';
     default:
-      return '$dataType$nullTag';
+      return entity.dataType;
   }
 }
 
+String _addGenericTypesNullable(Field field, String nullTag) {
+  return '${_addGenericTypes(field, nullTag)}$nullTag';
+}
+
 /// Generates Dart source code for the given AST represented by [root],
 /// outputting the code to [sink].
 void generateDart(DartOptions opt, Root root, StringSink sink) {
@@ -315,7 +354,7 @@ void generateDart(DartOptions opt, Root root, StringSink sink) {
     indent.write('class ${klass.name} ');
     indent.scoped('{', '}', () {
       for (final Field field in klass.fields) {
-        final String datatype = _addGenericTypes(field.dataType, nullTag);
+        final String datatype = _addGenericTypesNullable(field, nullTag);
         indent.writeln('$datatype ${field.name};');
       }
       if (klass.fields.isNotEmpty) {
@@ -365,9 +404,16 @@ pigeonMap['${field.name}'] != null
 pigeonMap['${field.name}'] != null
 \t\t? ${field.dataType}.values[pigeonMap['${field.name}']$unwrapOperator as int]
 \t\t: null''', leadingSpace: false, trailingNewline: false);
+            } else if (field.typeArguments != null) {
+              final String genericType =
+                  _makeGenericTypeArguments(field, nullTag);
+              final String castCall = _makeGenericCastCall(field, nullTag);
+              indent.add(
+                '(pigeonMap[\'${field.name}\'] as $genericType$nullTag)$nullTag$castCall',
+              );
             } else {
               indent.add(
-                'pigeonMap[\'${field.name}\'] as ${_addGenericTypes(field.dataType, nullTag)}',
+                'pigeonMap[\'${field.name}\'] as ${_addGenericTypesNullable(field, nullTag)}',
               );
             }
             indent.addln(index == klass.fields.length - 1 ? ';' : '');

packages/pigeon/lib/generator_tools.dart

@@ -159,9 +159,9 @@ class HostDatatype {
 /// `builtinResolver` will return the host datatype for the Dart datatype for
 /// builtin types.  `customResolver` can modify the datatype of custom types.
 HostDatatype getHostDatatype(Field field, List<Class> classes, List<Enum> enums,
-    String? Function(String) builtinResolver,
+    String? Function(Field) builtinResolver,
     {String Function(String)? customResolver}) {
-  final String? datatype = builtinResolver(field.dataType);
+  final String? datatype = builtinResolver(field);
   if (datatype == null) {
     if (classes.map((Class x) => x.name).contains(field.dataType)) {
       final String customName = customResolver != null
@@ -285,8 +285,10 @@ const int _minimumCodecFieldKey = 128;
 Iterable<EnumeratedClass> getCodecClasses(Api api) sync* {
   final Set<String> names = <String>{};
   for (final Method method in api.methods) {
-    names.add(method.returnType);
-    names.add(method.argType);
+    names.add(method.returnType.dataType);
+    if (method.arguments.isNotEmpty) {
+      names.add(method.arguments[0].dataType);
+    }
   }
   final List<String> sortedNames = names
       .where((String element) =>