[pigeon] unnamed arguments and nonnull typeArguments

packages/pigeon/lib/ast.dart

@@ -80,14 +80,14 @@ class TypeDeclaration {
   TypeDeclaration({
     required this.baseName,
     required this.isNullable,
-    this.typeArguments,
+    this.typeArguments = const <TypeDeclaration>[],
   });
 
   /// The base name of the [TypeDeclaration] (ex 'Foo' to 'Foo<Bar>?').
   final String baseName;
 
   /// The type arguments to the entity (ex 'Bar' to 'Foo<Bar>?').
-  final List<TypeDeclaration>? typeArguments;
+  final List<TypeDeclaration> typeArguments;
 
   /// True if the type is nullable.
   final bool isNullable;

packages/pigeon/lib/dart_generator.dart

@@ -94,16 +94,16 @@ void _writeCodec(Indent indent, String codecName, Api api) {
 
 /// Creates a Dart type where all type arguments are [Objects].
 String _makeGenericTypeArguments(TypeDeclaration type, String nullTag) {
-  return type.typeArguments != null
-      ? '${type.baseName}<${type.typeArguments!.map<String>((TypeDeclaration e) => 'Object$nullTag').join(', ')}>'
+  return type.typeArguments.isNotEmpty
+      ? '${type.baseName}<${type.typeArguments.map<String>((TypeDeclaration e) => 'Object$nullTag').join(', ')}>'
       : _addGenericTypes(type, nullTag);
 }
 
 /// Creates a `.cast<>` call for an type. Returns an empty string if the
 /// type has no type arguments.
 String _makeGenericCastCall(TypeDeclaration type, String nullTag) {
-  return type.typeArguments != null
-      ? '.cast<${_flattenTypeArguments(type.typeArguments!, nullTag)}>()'
+  return type.typeArguments.isNotEmpty
+      ? '.cast<${_flattenTypeArguments(type.typeArguments, nullTag)}>()'
       : '';
 }
 
@@ -293,23 +293,23 @@ void _writeFlutterApi(
 /// used in Dart code.
 String _flattenTypeArguments(List<TypeDeclaration> args, String nullTag) {
   return args
-      .map<String>((TypeDeclaration arg) => arg.typeArguments == null
+      .map<String>((TypeDeclaration arg) => arg.typeArguments.isEmpty
           ? '${arg.baseName}$nullTag'
-          : '${arg.baseName}<${_flattenTypeArguments(arg.typeArguments!, nullTag)}>$nullTag')
+          : '${arg.baseName}<${_flattenTypeArguments(arg.typeArguments, nullTag)}>$nullTag')
       .join(', ');
 }
 
 /// Creates the type declaration for use in Dart code from a [NamedType] making sure
 /// that type arguments are used for primitive generic types.
 String _addGenericTypes(TypeDeclaration type, String nullTag) {
-  final List<TypeDeclaration>? typeArguments = type.typeArguments;
+  final List<TypeDeclaration> typeArguments = type.typeArguments;
   switch (type.baseName) {
     case 'List':
-      return (typeArguments == null)
+      return (typeArguments.isEmpty)
           ? 'List<Object$nullTag>'
           : 'List<${_flattenTypeArguments(typeArguments, nullTag)}>';
     case 'Map':
-      return (typeArguments == null)
+      return (typeArguments.isEmpty)
           ? 'Map<Object$nullTag, Object$nullTag>'
           : 'Map<${_flattenTypeArguments(typeArguments, nullTag)}>';
     default:
@@ -412,7 +412,7 @@ pigeonMap['${field.name}'] != null
 pigeonMap['${field.name}'] != null
 \t\t? ${field.type.baseName}.values[pigeonMap['${field.name}']$unwrapOperator as int]
 \t\t: null''', leadingSpace: false, trailingNewline: false);
-            } else if (field.type.typeArguments != null) {
+            } else if (field.type.typeArguments.isNotEmpty) {
               final String genericType =
                   _makeGenericTypeArguments(field.type, nullTag);
               final String castCall = _makeGenericCastCall(field.type, nullTag);

packages/pigeon/lib/java_generator.dart

@@ -305,10 +305,10 @@ String? _javaTypeForBuiltinDartType(TypeDeclaration type) {
   if (javaTypeForDartTypeMap.containsKey(type.baseName)) {
     return javaTypeForDartTypeMap[type.baseName];
   } else if (type.baseName == 'List') {
-    if (type.typeArguments == null) {
+    if (type.typeArguments.isEmpty) {
       return 'List<Object>';
     } else {
-      return 'List<${_flattenTypeArguments(type.typeArguments!)}>';
+      return 'List<${_flattenTypeArguments(type.typeArguments)}>';
     }
   } else {
     return null;

packages/pigeon/lib/objc_generator.dart

@@ -98,9 +98,9 @@ String? _objcTypePtrForPrimitiveDartType(String? classPrefix, NamedType field) {
 /// _objcTypeForDartType(null, 'int') => 'NSNumber'.
 String _objcTypeForDartType(String? classPrefix, TypeDeclaration field) {
   return _objcTypeForDartTypeMap.containsKey(field.baseName)
-      ? field.typeArguments == null
+      ? field.typeArguments.isEmpty
           ? _objcTypeForDartTypeMap[field.baseName]!
-          : '${_objcTypeForDartTypeMap[field.baseName]}<${_flattenTypeArguments(classPrefix, field.typeArguments!)}>'
+          : '${_objcTypeForDartTypeMap[field.baseName]}<${_flattenTypeArguments(classPrefix, field.typeArguments)}>'
       : _className(classPrefix, field.baseName);
 }
 

packages/pigeon/lib/pigeon_lib.dart

@@ -385,7 +385,7 @@ List<Error> _validateAst(Root root, String source) {
   for (final Class klass in root.classes) {
     for (final NamedType field in klass.fields) {
       if (field.type.typeArguments != null) {
-        for (final TypeDeclaration typeArgument in field.type.typeArguments!) {
+        for (final TypeDeclaration typeArgument in field.type.typeArguments) {
           if (!typeArgument.isNullable) {
             result.add(Error(
               message:
@@ -443,6 +443,14 @@ List<Error> _validateAst(Root root, String source) {
           lineNumber: _calculateLineNumberNullable(source, method.offset),
         ));
       }
+      for (final NamedType unnamedType in method.arguments
+          .where((NamedType element) => element.type.baseName.isEmpty)) {
+        result.add(Error(
+          message:
+              'Arguments must specify their type in method "${method.name}" in API: "${api.name}"',
+          lineNumber: _calculateLineNumberNullable(source, unnamedType.offset),
+        ));
+      }
     }
   }
 
@@ -648,20 +656,27 @@ class _RootBuilder extends dart_ast_visitor.RecursiveAstVisitor<Object?> {
   }
 
   NamedType formalParameterToField(dart_ast.FormalParameter parameter) {
-    final dart_ast.TypeName typeName = parameter.childEntities.firstWhere(
-        (dart_ast_syntactic_entity.SyntacticEntity e) =>
-            e is dart_ast.TypeName) as dart_ast.TypeName;
-    final String argTypeBaseName = typeName.name.name;
-    final bool isNullable = typeName.question != null;
-    final List<TypeDeclaration>? argTypeArguments =
-        typeAnnotationsToTypeArguments(typeName.typeArguments);
-    return NamedType(
-        type: TypeDeclaration(
-            baseName: argTypeBaseName,
-            isNullable: isNullable,
-            typeArguments: argTypeArguments),
-        name: parameter.identifier?.name ?? '',
-        offset: null);
+    final dart_ast.TypeName? typeName =
+        getFirstChildOfType<dart_ast.TypeName>(parameter);
+    if (typeName != null) {
+      final String argTypeBaseName = typeName.name.name;
+      final bool isNullable = typeName.question != null;
+      final List<TypeDeclaration> argTypeArguments =
+          typeAnnotationsToTypeArguments(typeName.typeArguments);
+      return NamedType(
+          type: TypeDeclaration(
+              baseName: argTypeBaseName,
+              isNullable: isNullable,
+              typeArguments: argTypeArguments),
+          name: parameter.identifier?.name ?? '',
+          offset: parameter.offset);
+    } else {
+      return NamedType(
+        name: '',
+        type: TypeDeclaration(baseName: '', isNullable: false),
+        offset: parameter.offset,
+      );
+    }
   }
 
   static T? getFirstChildOfType<T>(dart_ast.AstNode entity) {
@@ -716,13 +731,12 @@ class _RootBuilder extends dart_ast_visitor.RecursiveAstVisitor<Object?> {
     return null;
   }
 
-  List<TypeDeclaration>? typeAnnotationsToTypeArguments(
+  List<TypeDeclaration> typeAnnotationsToTypeArguments(
       dart_ast.TypeArgumentList? typeArguments) {
-    List<TypeDeclaration>? result;
+    final List<TypeDeclaration> result = <TypeDeclaration>[];
     if (typeArguments != null) {
       for (final Object x in typeArguments.childEntities) {
         if (x is dart_ast.TypeName) {
-          result ??= <TypeDeclaration>[];
           result.add(TypeDeclaration(
               baseName: x.name.name,
               isNullable: x.question != null,