fix: allow enums to be appended

Dockerfile

@@ -1,7 +1,7 @@
 FROM openjdk:8-jdk-slim AS build
 WORKDIR /build
-COPY ./ /build
-RUN ./mvnw -V -B -ff -P docker package -q
+COPY ./ .
+RUN sh ./mvnw -V -B -ff -P docker package -q
 
 FROM openjdk:8-jre-slim
 WORKDIR /app

core/src/main/java/org/openapitools/openapidiff/core/model/schema/ChangedEnum.java

@@ -13,8 +13,12 @@ public ChangedEnum(List<T> oldValue, List<T> newValue, DiffContext context) {
 
   @Override
   public DiffResult isItemsChanged() {
-    if (context.isRequest() && getMissing().isEmpty()
-        || context.isResponse() && getIncreased().isEmpty()) {
+
+    if (
+      (context.isRequest() && getMissing().isEmpty() || context.isResponse())
+      && newValue.containsAll(oldValue)
+    ) 
+    {
       return DiffResult.COMPATIBLE;
     }
     return DiffResult.INCOMPATIBLE;

core/src/test/java/org/openapitools/openapidiff/core/EnumDiffTest.java

@@ -0,0 +1,21 @@
+package org.openapitools.openapidiff.core;
+
+import org.junit.jupiter.api.Test;
+import static org.openapitools.openapidiff.core.TestUtils.assertOpenApiAreEquals;
+import static org.openapitools.openapidiff.core.TestUtils.assertOpenApiBackwardCompatible;
+
+class EnumDiffTest {
+
+  private final String OPENAPI_PATH1 = "enum_1.yaml";
+  private final String OPENAPI_PATH2 = "enum_2.yaml";
+
+  @Test
+  public void testDiffSame() {
+    assertOpenApiAreEquals(OPENAPI_PATH1, OPENAPI_PATH1);
+  }
+
+  @Test
+  void appendedEnumsAreNotBreakingChanges() {
+    assertOpenApiBackwardCompatible(OPENAPI_PATH1, OPENAPI_PATH2, false);
+  }
+}

core/src/test/resources/enum_1.yaml

@@ -0,0 +1,48 @@
+openapi: 3.0.0
+servers:
+  - url: 'http://petstore.swagger.io/v2'
+info:
+  description: 'This is a sample server Petstore server.  You can find out more about Swagger at [http://swagger.io](http://swagger.io) or on [irc.freenode.net, #swagger](http://swagger.io/irc/).  For this sample, you can use the api key `special-key` to test the authorization filters.'
+  version: 1.0.0
+  title: Swagger Petstore
+  termsOfService: 'http://swagger.io/terms/'
+  contact:
+    email: apiteam@swagger.io
+  license:
+    name: Apache 2.0
+    url: 'http://www.apache.org/licenses/LICENSE-2.0.html'
+paths:
+  '/pet/{petId}':
+    get:
+      tags:
+        - pet
+      summary: gets a pet by id
+      description: ''
+      operationId: updatePetWithForm
+      parameters:
+        - name: petId
+          in: path
+          description: ID of pet that needs to be updated
+          required: true
+          schema:
+            type: integer
+      responses:
+        '200':
+          description: ''
+          content:
+            application/json:
+              schema:
+                $ref: '#/components/schemas/Pet'
+components:
+  schemas:
+    Pet:
+      title: Pet
+      type: object
+      properties:
+        name:
+          type: string
+          enum:
+            - Cat
+            - Dog
+      required:
+        - name

core/src/test/resources/enum_2.yaml

@@ -0,0 +1,49 @@
+openapi: 3.0.0
+servers:
+  - url: 'http://petstore.swagger.io/v2'
+info:
+  description: 'This is a sample server Petstore server.  You can find out more about Swagger at [http://swagger.io](http://swagger.io) or on [irc.freenode.net, #swagger](http://swagger.io/irc/).  For this sample, you can use the api key `special-key` to test the authorization filters.'
+  version: 1.0.0
+  title: Swagger Petstore
+  termsOfService: 'http://swagger.io/terms/'
+  contact:
+    email: apiteam@swagger.io
+  license:
+    name: Apache 2.0
+    url: 'http://www.apache.org/licenses/LICENSE-2.0.html'
+paths:
+  '/pet/{petId}':
+    get:
+      tags:
+        - pet
+      summary: gets a pet by id
+      description: ''
+      operationId: updatePetWithForm
+      parameters:
+        - name: petId
+          in: path
+          description: ID of pet that needs to be updated
+          required: true
+          schema:
+            type: integer
+      responses:
+        '200':
+          description: ''
+          content:
+            application/json:
+              schema:
+                $ref: '#/components/schemas/Pet'
+components:
+  schemas:
+    Pet:
+      title: Pet
+      type: object
+      properties:
+        name:
+          type: string
+          enum:
+            - Cat
+            - Dog
+            - Lemon
+      required:
+        - name

mvnw

@@ -17,7 +17,6 @@
 # specific language governing permissions and limitations
 # under the License.
 # ----------------------------------------------------------------------------
-
 # ----------------------------------------------------------------------------
 # Maven2 Start Up Batch script
 #
@@ -33,7 +32,6 @@
 #       set MAVEN_OPTS=-Xdebug -Xrunjdwp:transport=dt_socket,server=y,suspend=y,address=8000
 #   MAVEN_SKIP_RC - flag to disable loading of mavenrc files
 # ----------------------------------------------------------------------------
-
 if [ -z "$MAVEN_SKIP_RC" ] ; then
 
   if [ -f /etc/mavenrc ] ; then