allow optional discriminator in oneOf

src/main/java/com/qdesrame/openapi/diff/compare/schemadiffresult/ComposedSchemaDiffResult.java

@@ -42,15 +42,15 @@ public <T extends Schema<X>, X> Optional<ChangedSchema> diff(
 
         Discriminator leftDis = leftComposedSchema.getDiscriminator();
         Discriminator rightDis = rightComposedSchema.getDiscriminator();
-        if (leftDis == null
-            || rightDis == null
-            || leftDis.getPropertyName() == null
-            || rightDis.getPropertyName() == null) {
-          throw new IllegalArgumentException(
-              "discriminator or property not found for oneOf schema");
-        } else if (!leftDis.getPropertyName().equals(rightDis.getPropertyName())
-            || (CollectionUtils.isEmpty(leftComposedSchema.getOneOf())
-                || CollectionUtils.isEmpty(rightComposedSchema.getOneOf()))) {
+        if ((leftDis == null && rightDis != null)
+        ||  (leftDis != null && rightDis == null)
+        ||  (leftDis != null && rightDis != null && (
+                (leftDis.getPropertyName() == null && rightDis.getPropertyName() != null)
+            ||  (leftDis.getPropertyName() != null && rightDis.getPropertyName() == null)
+            ||  (leftDis.getPropertyName() != null && rightDis.getPropertyName() != null &&
+                    !leftDis.getPropertyName().equals(rightDis.getPropertyName()))
+            ))
+        ) {
           changedSchema.setOldSchema(left);
           changedSchema.setNewSchema(right);
           changedSchema.setDiscriminatorPropertyChanged(true);
@@ -109,7 +109,7 @@ private Map<String, String> getMapping(ComposedSchema composedSchema) {
       reverseMapping.put(ref, schemaName);
     }
 
-    if (composedSchema.getDiscriminator().getMapping() != null) {
+    if (composedSchema.getDiscriminator() != null && composedSchema.getDiscriminator().getMapping() != null) {
       for (String ref : composedSchema.getDiscriminator().getMapping().keySet()) {
         reverseMapping.put(composedSchema.getDiscriminator().getMapping().get(ref), ref);
       }

src/test/java/com/qdesrame/openapi/test/OneOfDiffTest.java

@@ -16,6 +16,8 @@ public class OneOfDiffTest {
   private final String OPENAPI_DOC5 = "composed_schema_2.yaml";
   private final String OPENAPI_DOC6 = "oneOf_discriminator-changed_1.yaml";
   private final String OPENAPI_DOC7 = "oneOf_discriminator-changed_2.yaml";
+  private final String OPENAPI_DOC8 = "oneOf_discriminator-missing_1.yaml";
+  private final String OPENAPI_DOC9 = "oneOf_discriminator-missing_2.yaml";
 
   @Test
   public void testDiffSame() {
@@ -42,4 +44,14 @@ public void testOneOfDiscrimitatorChanged() {
     // The oneOf 'discriminator' changed: 'realtype' -> 'othertype':
     assertOpenApiBackwardIncompatible(OPENAPI_DOC6, OPENAPI_DOC7);
   }
+
+  @Test
+  public void testOneOfDiscrimitatorMissingSameOrder() {
+    assertOpenApiAreEquals(OPENAPI_DOC8, OPENAPI_DOC8);
+  }
+
+  @Test
+  public void testOneOfDiscrimitatorMissingDifferentOrder() {
+    assertOpenApiAreEquals(OPENAPI_DOC8, OPENAPI_DOC9);
+  }
 }

src/test/resources/oneOf_discriminator-missing_1.yaml

@@ -0,0 +1,44 @@
+openapi: 3.0.1
+info:
+  title: oneOf test for issue 29
+  version: '1.0'
+servers:
+  - url: 'http://localhost:8000/'
+paths:
+  /state:
+    post:
+      operationId: update
+      requestBody:
+        content:
+            application/json:
+              schema:
+                oneOf:
+                  - $ref: '#/components/schemas/A'
+                  - $ref: '#/components/schemas/B'
+        required: true
+      responses:
+        '201':
+          description: OK
+components:
+  schemas:
+    A:
+      type: object
+      properties:
+        realtype:
+          type: string
+        othertype:
+          type: string
+        message:
+          type: string
+    B:
+      type: object
+      properties:
+        realtype:
+          type: string
+        othertype:
+          type: string
+        description:
+          type: string
+        code:
+          type: integer
+          format: int32 

src/test/resources/oneOf_discriminator-missing_2.yaml

@@ -0,0 +1,44 @@
+openapi: 3.0.1
+info:
+  title: oneOf test for issue 29
+  version: '1.0'
+servers:
+  - url: 'http://localhost:8000/'
+paths:
+  /state:
+    post:
+      operationId: update
+      requestBody:
+        content:
+            application/json:
+              schema:
+                oneOf:
+                  - $ref: '#/components/schemas/B'
+                  - $ref: '#/components/schemas/A'
+        required: true
+      responses:
+        '201':
+          description: OK
+components:
+  schemas:
+    A:
+      type: object
+      properties:
+        realtype:
+          type: string
+        othertype:
+          type: string
+        message:
+          type: string
+    B:
+      type: object
+      properties:
+        realtype:
+          type: string
+        othertype:
+          type: string
+        description:
+          type: string
+        code:
+          type: integer
+          format: int32