Add union types to the analysis server API spec.

pkg/analysis_server/tool/spec/api.dart

 // Copyright (c) 2014, 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.
 
 /**
  * Data structures representing an API definition, and visitor base classes
  * for visiting those data structures.
  */
 library api;
 
 import 'dart:collection';
 
 import 'package:html5lib/dom.dart' as dom;
 
 /**
  * Base class for visiting the API definition.
  */
 abstract class ApiVisitor<T> {
   T visitTypeReference(TypeReference typeReference);
+  T visitTypeUnion(TypeUnion typeUnion);
   T visitTypeObject(TypeObject typeObject);
   T visitTypeList(TypeList typeList);
   T visitTypeMap(TypeMap typeMap);
   T visitTypeEnum(TypeEnum typeEnum);
 
   /**
    * Dispatch the given [type] to the visitor.
    */
   T visitTypeDecl(TypeDecl type) => type.accept(this);
 }
@@ skipping 81 matching lines @@
   }
 
   void visitTypeObjectField(TypeObjectField typeObjectField) {
     visitTypeDecl(typeObjectField.type);
   }
 
   @override
   void visitTypeReference(TypeReference typeReference) {
   }
 
+  @override
+  void visitTypeUnion(TypeUnion typeUnion) {
+    typeUnion.choices.forEach(visitTypeDecl);
+  }
+
   /**
    * If [type] is a [TypeReference] that is defined in the API, follow the
    * chain until a non-[TypeReference] is found, if possible.
    *
    * If it is not possible (because the chain ends with a [TypeReference] that
    * is not defined in the API), then that final [TypeReference] is returned.
    */
   TypeDecl resolveTypeReferenceChain(TypeDecl type) {
     while (type is TypeReference && api.types.containsKey(type.typeName)) {
       type = api.types[(type as TypeReference).typeName].type;
@@ skipping 228 matching lines @@
   TypeReference(this.typeName, dom.Element html) : super(html) {
     if (typeName.isEmpty) {
       throw new Exception('Empty type name');
     }
   }
 
   accept(ApiVisitor visitor) => visitor.visitTypeReference(this);
 }
 
 /**
+ * Type which represents a union among multiple choices.
+ */
+class TypeUnion extends TypeDecl {
+  final List<TypeDecl> choices;
+
+  TypeUnion(this.choices, dom.Element html) : super(html);
+
+  accept(ApiVisitor visitor) => visitor.visitTypeUnion(this);
+}
+
+/**
  * Type of a JSON object with specified fields, some of which may be optional.
  */
 class TypeObject extends TypeDecl {
   final List<TypeObjectField> fields;
 
   TypeObject(this.fields, dom.Element html) : super(html);
 
   accept(ApiVisitor visitor) => visitor.visitTypeObject(this);
 }
 
@@ skipping 59 matching lines @@
 }
 
 /**
  * Description of a single allowed value for an enum.
  */
 class TypeEnumValue extends ApiNode {
   final String value;
 
   TypeEnumValue(this.value, dom.Element html) : super(html);
 }