Adding a value to an enum is now a dangerous change.

src/utilities/__tests__/findBreakingChanges-test.js

@@ -32,6 +32,7 @@ import {
   findTypesRemovedFromUnions,
   findTypesThatChangedKind,
   findValuesRemovedFromEnums,
+  findValuesAddedToEnums,
   findArgChanges,
   findInterfacesRemovedFromObjectTypes,
 } from '../findBreakingChanges';
@@ -1349,7 +1350,63 @@ describe('findDangerousChanges', () => {
     });
   });
 
+  it('should detect if a value was added to an enum type', () => {
+    const oldEnumType = new GraphQLEnumType({
+      name: 'EnumType1',
+      values: {
+        VALUE0: { value: 0 },
+        VALUE1: { value: 1 },
+      }
+    });
+    const newEnumType = new GraphQLEnumType({
+      name: 'EnumType1',
+      values: {
+        VALUE0: { value: 0 },
+        VALUE1: { value: 1 },
+        VALUE2: { value: 2 },
+      }
+    });
+
+    const oldSchema = new GraphQLSchema({
+      query: queryType,
+      types: [
+        oldEnumType,
+      ]
+    });
+    const newSchema = new GraphQLSchema({
+      query: queryType,
+      types: [
+        newEnumType,
+      ]
+    });
+
+    expect(findValuesAddedToEnums(oldSchema, newSchema)).to.eql(
+      [
+        {
+          type: DangerousChangeType.VALUE_ADDED_TO_ENUM,
+          description: 'VALUE2 was added to enum type EnumType1.',
+        }
+      ]
+    );
+  });
+
   it('should find all dangerous changes', () => {
+    const enumThatGainsAValueOld = new GraphQLEnumType({
+      name: 'EnumType1',
+      values: {
+        VALUE0: { value: 0 },
+        VALUE1: { value: 1 },
+      }
+    });
+    const enumThatGainsAValueNew = new GraphQLEnumType({
+      name: 'EnumType1',
+      values: {
+        VALUE0: { value: 0 },
+        VALUE1: { value: 1 },
+        VALUE2: { value: 2 },
+      }
+    });
+
     const oldType = new GraphQLObjectType({
       name: 'Type1',
       fields: {
@@ -1384,20 +1441,26 @@ describe('findDangerousChanges', () => {
       query: queryType,
       types: [
         oldType,
+        enumThatGainsAValueOld
       ]
     });
 
     const newSchema = new GraphQLSchema({
       query: queryType,
       types: [
         newType,
+        enumThatGainsAValueNew
       ]
     });
 
     const expectedDangerousChanges = [
       {
         description: 'Type1.field1 arg name has changed defaultValue',
         type: 'ARG_DEFAULT_VALUE_CHANGE'
+      },
+      {
+        description: 'VALUE2 was added to enum type EnumType1.',
+        type: 'VALUE_ADDED_TO_ENUM',
       }
     ];
 

src/utilities/findBreakingChanges.js

@@ -44,6 +44,7 @@ export const BreakingChangeType = {
 
 export const DangerousChangeType = {
   ARG_DEFAULT_VALUE_CHANGE: 'ARG_DEFAULT_VALUE_CHANGE',
+  VALUE_ADDED_TO_ENUM: 'VALUE_ADDED_TO_ENUM'
 };
 
 export type BreakingChange = {
@@ -85,6 +86,7 @@ export function findDangerousChanges(
 ): Array<DangerousChange> {
   return [
     ...findArgChanges(oldSchema, newSchema).dangerousChanges,
+    ...findValuesAddedToEnums(oldSchema, newSchema)
   ];
 }
 
@@ -542,6 +544,42 @@ export function findValuesRemovedFromEnums(
   return valuesRemovedFromEnums;
 }
 
+/**
+ * Given two schemas, returns an Array containing descriptions of any dangerous
+ * changes in the newSchema related to adding values to an enum type.
+ */
+export function findValuesAddedToEnums(
+  oldSchema: GraphQLSchema,
+  newSchema: GraphQLSchema
+): Array<DangerousChange> {
+  const oldTypeMap = oldSchema.getTypeMap();
+  const newTypeMap = newSchema.getTypeMap();
+
+  const valuesAddedToEnums = [];
+  Object.keys(oldTypeMap).forEach(typeName => {
+    const oldType = oldTypeMap[typeName];
+    const newType = newTypeMap[typeName];
+    if (!(oldType instanceof GraphQLEnumType) ||
+        !(newType instanceof GraphQLEnumType)) {
+      return;
+    }
+
+    const valuesInOldEnum = Object.create(null);
+    oldType.getValues().forEach(value => {
+      valuesInOldEnum[value.name] = true;
+    });
+    newType.getValues().forEach(value => {
+      if (!valuesInOldEnum[value.name]) {
+        valuesAddedToEnums.push({
+          type: DangerousChangeType.VALUE_ADDED_TO_ENUM,
+          description: `${value.name} was added to enum type ${typeName}.`
+        });
+      }
+    });
+  });
+  return valuesAddedToEnums;
+}
+
 export function findInterfacesRemovedFromObjectTypes(
   oldSchema: GraphQLSchema,
   newSchema: GraphQLSchema