Add utility functions to compare schemas (#508)

* Add utility functions to compare schemas

* Add top level check that invokes other sub checks

* Return Arrays instead of Sets, forEach instead of for in, other tweaks

* Return a BreakingChange object rather than just a string

* Only expose findBreakingChanges; other minor changes

* Add static prettyName property to Type classes

Author: sam-swarr

src/index.js

@@ -203,4 +203,7 @@ export {
 
   // Asserts a string is a valid GraphQL name.
   assertValidName,
+
+  // Compares two GraphQLSchemas and detects breaking changes.
+  findBreakingChanges,
 } from './utilities';

src/type/definition.js

@@ -223,6 +223,8 @@ export class GraphQLScalarType {
 
   _scalarConfig: GraphQLScalarTypeConfig<*, *>;
 
+  static prettyName: string = 'Scalar';
+
   constructor(config: GraphQLScalarTypeConfig<*, *>) {
     invariant(config.name, 'Type must be named.');
     assertValidName(config.name);
@@ -324,6 +326,8 @@ export class GraphQLObjectType {
   _fields: GraphQLFieldDefinitionMap;
   _interfaces: Array<GraphQLInterfaceType>;
 
+  static prettyName: string = 'Object';
+
   constructor(config: GraphQLObjectTypeConfig<*>) {
     invariant(config.name, 'Type must be named.');
     assertValidName(config.name);
@@ -570,6 +574,8 @@ export class GraphQLInterfaceType {
   _typeConfig: GraphQLInterfaceTypeConfig;
   _fields: GraphQLFieldDefinitionMap;
 
+  static prettyName: string = 'Interface';
+
   constructor(config: GraphQLInterfaceTypeConfig) {
     invariant(config.name, 'Type must be named.');
     assertValidName(config.name);
@@ -641,6 +647,8 @@ export class GraphQLUnionType {
   _types: Array<GraphQLObjectType>;
   _possibleTypeNames: {[typeName: string]: boolean};
 
+  static prettyName: string = 'Union';
+
   constructor(config: GraphQLUnionTypeConfig) {
     invariant(config.name, 'Type must be named.');
     assertValidName(config.name);
@@ -742,6 +750,8 @@ export class GraphQLEnumType/* <T> */ {
   _valueLookup: Map<any/* T */, GraphQLEnumValueDefinition>;
   _nameLookup: { [valueName: string]: GraphQLEnumValueDefinition };
 
+  static prettyName: string = 'Enum';
+
   constructor(config: GraphQLEnumTypeConfig/* <T> */) {
     this.name = config.name;
     assertValidName(config.name);
@@ -893,6 +903,8 @@ export class GraphQLInputObjectType {
   _typeConfig: InputObjectConfig;
   _fields: InputObjectFieldMap;
 
+  static prettyName: string = 'InputObject';
+
   constructor(config: InputObjectConfig) {
     invariant(config.name, 'Type must be named.');
     assertValidName(config.name);