add support for emitting typedefs (#387)

* add support for emittig typedefs

* Apply suggestions from code review

suggestions from code review

Co-authored-by: Nate Bosch <nbosch@google.com>

Co-authored-by: Nate Bosch <nbosch@google.com>

Author: devoncarew

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 * Mention how the `allocator` argument relates to imports in the `DartEmitter`
   constructor doc.
+* Add support for emitting typedefs.
 
 ## 4.3.0
 

README.md

@@ -85,7 +85,7 @@ will be on a best-effort basis.
 > format this repository. You can run it simply from the command-line:
 >
 > ```sh
-> $ pub run dart_style:format -w .
+> $ dart pub run dart_style:format -w .
 > ```
 
 [wiki]: https://github.com/dart-lang/code_builder/wiki

lib/code_builder.dart

@@ -57,3 +57,4 @@ export 'src/specs/mixin.dart' show Mixin, MixinBuilder;
 export 'src/specs/reference.dart' show refer, Reference;
 export 'src/specs/type_function.dart' show FunctionType, FunctionTypeBuilder;
 export 'src/specs/type_reference.dart' show TypeReference, TypeReferenceBuilder;
+export 'src/specs/typedef.dart' show TypeDef, TypeDefBuilder;

lib/src/emitter.dart

@@ -18,6 +18,7 @@ import 'specs/mixin.dart';
 import 'specs/reference.dart';
 import 'specs/type_function.dart';
 import 'specs/type_reference.dart';
+import 'specs/typedef.dart';
 import 'visitors.dart';
 
 /// Helper method improving on [StringSink.writeAll].
@@ -514,6 +515,19 @@ class DartEmitter extends Object
     return out;
   }
 
+  @override
+  StringSink visitTypeDef(TypeDef spec, [StringSink? output]) {
+    final out = output ??= StringBuffer();
+    spec.docs.forEach(out.writeln);
+    for (var a in spec.annotations) {
+      visitAnnotation(a, out);
+    }
+    out.write('typedef ${spec.name} = ');
+    spec.definition.accept(this, out);
+    out.writeln(';');
+    return out;
+  }
+
   @override
   StringSink visitMethod(Method spec, [StringSink? output]) {
     output ??= StringBuffer();

lib/src/specs/typedef.dart

@@ -0,0 +1,57 @@
+// Copyright (c) 2022, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:built_collection/built_collection.dart';
+import 'package:built_value/built_value.dart';
+import 'package:meta/meta.dart';
+
+import '../base.dart';
+import '../mixins/annotations.dart';
+import '../mixins/dartdoc.dart';
+import '../visitors.dart';
+import 'expression.dart';
+
+part 'typedef.g.dart';
+
+@immutable
+abstract class TypeDef extends Object
+    with HasAnnotations, HasDartDocs
+    implements Built<TypeDef, TypeDefBuilder>, Spec {
+  factory TypeDef([void Function(TypeDefBuilder)? updates]) = _$TypeDef;
+
+  TypeDef._();
+
+  /// Name of the typedef.
+  String get name;
+
+  /// The right hand side of the typedef.
+  ///
+  /// Typically a reference to a type, or a Function type.
+  Expression get definition;
+
+  @override
+  R accept<R>(
+    SpecVisitor<R> visitor, [
+    R? context,
+  ]) =>
+      visitor.visitTypeDef(this, context);
+}
+
+abstract class TypeDefBuilder extends Object
+    with HasAnnotationsBuilder, HasDartDocsBuilder
+    implements Builder<TypeDef, TypeDefBuilder> {
+  factory TypeDefBuilder() = _$TypeDefBuilder;
+
+  TypeDefBuilder._();
+
+  @override
+  ListBuilder<Expression> annotations = ListBuilder<Expression>();
+
+  @override
+  ListBuilder<String> docs = ListBuilder<String>();
+
+  String? name;
+
+  Expression? definition;
+}

lib/src/specs/typedef.g.dart

@@ -18,6 +18,7 @@ import 'specs/mixin.dart';
 import 'specs/reference.dart';
 import 'specs/type_function.dart';
 import 'specs/type_reference.dart';
+import 'specs/typedef.dart';
 
 @optionalTypeArgs
 abstract class SpecVisitor<T> {
@@ -43,6 +44,8 @@ abstract class SpecVisitor<T> {
 
   T visitFunctionType(FunctionType spec, [T? context]);
 
+  T visitTypeDef(TypeDef spec, [T? context]);
+
   T visitMethod(Method spec, [T? context]);
 
   T visitReference(Reference spec, [T? context]);

lib/src/visitors.dart

@@ -237,6 +237,30 @@ void main() {
     );
   });
 
+  test('should create a typedef to a reference', () {
+    expect(
+      TypeDef((b) => b
+        ..name = 'i32'
+        ..definition = const Reference('int')),
+      equalsDart(r'''
+        typedef i32 = int;
+      '''),
+    );
+  });
+
+  test('should create a typedef to a function type', () {
+    expect(
+      TypeDef((b) => b
+        ..name = 'MyMapper'
+        ..definition = FunctionType((b) => b
+          ..returnType = refer('String')
+          ..optionalParameters.add(refer('int')))),
+      equalsDart(r'''
+        typedef MyMapper = String Function([int]);
+      '''),
+    );
+  });
+
   test('should create a method with a nested function type return type', () {
     expect(
       Method((b) => b