CombinedSchema#equals() fix (#498)

Fixes #497  - makes subschema sorting deterministic in CombinedSchema to resolve issue with equals() being unreliable.

Co-authored-by: tkledkov <[email protected]>

Author: erosb

core/pom.xml

@@ -259,7 +259,7 @@
         <dependency>
             <groupId>nl.jqno.equalsverifier</groupId>
             <artifactId>equalsverifier</artifactId>
-            <version>3.8.2</version>
+            <version>3.15.3</version>
             <scope>test</scope>
         </dependency>
         <dependency>

core/src/main/java/org/everit/json/schema/CombinedSchema.java

@@ -172,9 +172,12 @@ public CombinedSchema(Builder builder) {
     }
 
     private static int compareBySchemaType(Schema lschema, Schema rschema) {
-        return lschema instanceof CombinedSchema ?
-                (rschema instanceof CombinedSchema ? 0 : -1) :
-                (rschema instanceof CombinedSchema ? 1 : 0);
+        boolean leftSchemaIsCombined = lschema instanceof CombinedSchema;
+        boolean rightIsCombined = rschema instanceof CombinedSchema;
+        int defaultRetval = lschema.hashCode() - rschema.hashCode();
+        return leftSchemaIsCombined ?
+                (rightIsCombined ? defaultRetval : -1) :
+                (rightIsCombined ? 1 : defaultRetval);
     }
 
     // ensure subschemas of type CombinedSchema are always visited first

core/src/test/java/org/everit/json/schema/loader/CombinedSchemaLoaderTest.java

@@ -7,6 +7,7 @@
 import static org.junit.jupiter.api.Assertions.*;
 
 import java.util.HashSet;
+import java.util.Objects;
 import java.util.Set;
 
 import org.everit.json.schema.BooleanSchema;
@@ -16,6 +17,7 @@
 import org.everit.json.schema.SchemaLocation;
 import org.everit.json.schema.StringSchema;
 import org.json.JSONObject;
+import org.json.JSONTokener;
 import org.junit.jupiter.api.Test;
 
 /**
@@ -75,4 +77,19 @@ public void multipleCombinedSchemasAtTheSameNestingLevel() {
         assertEquals(expected, actual);
     }
 
+    @Test
+    public void loadTheSameCombinedSeveralTimes() {
+        JSONObject json = new JSONObject(new JSONTokener("{\"enum\": [\"V1\", \"V2\", \"V3\"],\"type\": \"string\"}"));
+
+        for (int i = 0; i < 100000; ++i) {
+            Schema s0 = SchemaLoader.load(json);
+            Schema s1 = SchemaLoader.load(json);
+
+            System.out.println("Iter: " + i + ", equals=" + Objects.equals(s0, s1));
+
+            if (i > 10) {
+                assertEquals(s0, s1);
+            }
+        }
+    }
 }