fix(#845): Proposed solution to disable BC on pattern change

core/src/main/java/org/openapitools/openapidiff/core/model/BackwardIncompatibleProp.java

@@ -53,6 +53,7 @@ public enum BackwardIncompatibleProp {
   SECURITY_SCHEME_SCOPES_INCREASED("incompatible.security.scheme.scopes.increased", true),
   SCHEMA_DISCRIMINATOR_CHANGED("incompatible.schema.discriminator.changed", true),
   SCHEMA_TYPE_CHANGED("incompatible.schema.type.changed", true),
+  SCHEMA_PATTERN_CHANGED("incompatible.schema.pattern.changed", true),
   ;
 
   private final String propertyName;

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

@@ -1,5 +1,7 @@
 package org.openapitools.openapidiff.core.model.schema;
 
+import static org.openapitools.openapidiff.core.model.BackwardIncompatibleProp.SCHEMA_PATTERN_CHANGED;
+
 import java.util.Objects;
 import org.openapitools.openapidiff.core.model.Changed;
 import org.openapitools.openapidiff.core.model.DiffContext;
@@ -18,7 +20,13 @@ public ChangedPattern(String oldPattern, String newPattern, DiffContext context)
 
   @Override
   public DiffResult isChanged() {
-    return Objects.equals(oldPattern, newPattern) ? DiffResult.NO_CHANGES : DiffResult.INCOMPATIBLE;
+    if (Objects.equals(oldPattern, newPattern)) {
+      return DiffResult.NO_CHANGES;
+    } else if (SCHEMA_PATTERN_CHANGED.enabled(context)) {
+      return DiffResult.INCOMPATIBLE;
+    } else {
+      return DiffResult.COMPATIBLE;
+    }
   }
 
   @Override

core/src/test/java/org/openapitools/openapidiff/core/backcompat/SchemaBCTest.java

@@ -6,6 +6,7 @@
 import static org.openapitools.openapidiff.core.TestUtils.assertSpecUnchanged;
 import static org.openapitools.openapidiff.core.model.BackwardIncompatibleProp.RESPONSE_REQUIRED_DECREASED;
 import static org.openapitools.openapidiff.core.model.BackwardIncompatibleProp.SCHEMA_DISCRIMINATOR_CHANGED;
+import static org.openapitools.openapidiff.core.model.BackwardIncompatibleProp.SCHEMA_PATTERN_CHANGED;
 import static org.openapitools.openapidiff.core.model.BackwardIncompatibleProp.SCHEMA_TYPE_CHANGED;
 
 import org.junit.jupiter.api.Test;
@@ -69,4 +70,10 @@ public void typeChanged() {
     BackwardIncompatibleProp prop = SCHEMA_TYPE_CHANGED;
     assertSpecIncompatible(BASE, "bc_schema_type_changed.yaml", prop);
   }
+
+  @Test
+  public void patternChanged() {
+    BackwardIncompatibleProp prop = SCHEMA_PATTERN_CHANGED;
+    assertSpecIncompatible(BASE, "bc_schema_pattern_changed.yaml", prop);
+  }
 }

core/src/test/resources/bc_schema_pattern_changed.yaml

@@ -0,0 +1,116 @@
+openapi: 3.0.0
+info:
+  description: myDesc
+  title: myTitle
+  version: 1.0.0
+paths:
+  /widgets:
+    post:
+      operationId: widgetCreate
+      requestBody:
+        content:
+          application/json:
+            schema:
+              $ref: '#/components/schemas/WidgetCreateRequest'
+      responses:
+        '200':
+          description: successful operation
+          content:
+            application/json:
+              schema:
+                $ref: '#/components/schemas/WidgetCreateResponse'
+    put:
+      operationId: widgetUpdate
+      requestBody:
+        content:
+          application/json:
+            schema:
+              type: object
+              properties:
+                put_prop1:
+                  type: string
+                put_prop2:
+                  type: string
+      responses:
+        '200':
+          description: successful operation
+          content:
+            application/json:
+              schema:
+                type: string
+components:
+  schemas:
+    WidgetCreateRequest:
+      type: object
+      properties:
+        to_create:
+          $ref: '#/components/schemas/Widget_Polymorphic'
+        request_prop1:
+          type: integer
+          format: int32
+        request_prop2:
+          type: integer
+          format: int64
+      required:
+        - to_create
+        - request_prop1
+    WidgetCreateResponse:
+      type: object
+      properties:
+        created:
+          $ref: '#/components/schemas/Widget_Polymorphic'
+        response_prop1:
+          type: integer
+          format: int32
+        response_prop2:
+          type: integer
+          format: int64
+      required:
+        - created
+        - response_prop1
+    Widget_Polymorphic:
+      type: object
+      oneOf:
+        - $ref: '#/components/schemas/Doodad'
+        - $ref: '#/components/schemas/Gadget'
+      discriminator:
+        propertyName: '@type'
+    Widget:
+      type: object
+      properties:
+        '@type':
+          type: string
+        prop1:
+          type: string
+          pattern: '[A-Za-z0-9#$]$'
+        prop2:
+          type: integer
+          format: int32
+          deprecated: true
+      required:
+        - '@type'
+        - prop1
+    Doodad:
+      type: object
+      allOf:
+        - $ref: '#/components/schemas/Widget'
+        - type: object
+          properties:
+            doodad_prop1:
+              type: string
+    Gadget:
+      type: object
+      allOf:
+        - $ref: '#/components/schemas/Widget'
+        - type: object
+          properties:
+            gadget_prop1:
+              type: string
+    Gizmo:
+      type: object
+      allOf:
+        - $ref: '#/components/schemas/Widget'
+        - type: object
+          properties:
+            gizmo_prop1:
+              type: string