Json backward compatability fix for type keyword

Motivation: #2835

Author: YangSan0622

schema-util/json/src/main/java/io/apicurio/registry/rules/compatibility/jsonschema/diff/ObjectSchemaDiffVisitor.java

@@ -17,10 +17,13 @@
 package io.apicurio.registry.rules.compatibility.jsonschema.diff;
 
 import io.apicurio.registry.rules.compatibility.jsonschema.JsonSchemaWrapperVisitor;
+import io.apicurio.registry.rules.compatibility.jsonschema.wrapper.CombinedSchemaWrapper;
 import io.apicurio.registry.rules.compatibility.jsonschema.wrapper.ObjectSchemaWrapper;
 import io.apicurio.registry.rules.compatibility.jsonschema.wrapper.SchemaWrapper;
+import org.everit.json.schema.CombinedSchema;
 import org.everit.json.schema.ObjectSchema;
 import org.everit.json.schema.Schema;
+import org.everit.json.schema.StringSchema;
 
 import java.util.ArrayList;
 import java.util.HashSet;
@@ -300,8 +303,18 @@ public void visitPropertySchemas(Map<String, SchemaWrapper> propertySchemas) {
     @Override
     public void visitPropertySchema(String propertyName, SchemaWrapper schema) {
         if (original.getPropertySchemas().containsKey(propertyName)) {
+            Schema originalPropertySchema = original.getPropertySchemas().get(propertyName);
+            if (originalPropertySchema instanceof StringSchema
+                && schema instanceof CombinedSchemaWrapper) {
+                originalPropertySchema = CombinedSchema
+                    .builder()
+                    .criterion(CombinedSchema.ANY_CRITERION)
+                    .subschema(originalPropertySchema)
+                    .build();
+            }
+
             schema.accept(new SchemaDiffVisitor(ctx.sub("properties/" + propertyName),
-                original.getPropertySchemas().get(propertyName))); // TODO null/invalid schema
+                originalPropertySchema)); // TODO null/invalid schema
         }
         super.visitPropertySchema(propertyName, schema);
     }

schema-util/json/src/test/resources/io/apicurio/registry/rules/compatibility/jsonschema/compatibility-test-data.json

@@ -3385,6 +3385,63 @@
           }
         }
       }
+    },
+    {
+      "enabled": true,
+      "id": "Properties: type keyword from string to array compatability 1",
+      "compatibility": "backward",
+      "original": {
+        "$schema": "http://json-schema.org/draft-07/schema#",
+        "title": "Person",
+        "type": "object",
+        "properties": {
+          "test": {
+            "type": "string"
+          }
+        }
+      },
+      "updated": {
+        "$schema": "http://json-schema.org/draft-07/schema#",
+        "title": "Person",
+        "type": "object",
+        "properties": {
+          "test": {
+            "anyOf": [
+              {
+                "type": "string"
+              },
+              {
+                "type": "number"
+              }
+            ]
+          }
+        }
+      }
+    },
+    {
+      "enabled": true,
+      "id": "Properties: type keyword from string to array compatability 2",
+      "compatibility": "backward",
+      "original": {
+        "$schema": "http://json-schema.org/draft-07/schema#",
+        "title": "Person",
+        "type": "object",
+        "properties": {
+          "test": {
+            "type": "string"
+          }
+        }
+      },
+      "updated": {
+        "$schema": "http://json-schema.org/draft-07/schema#",
+        "title": "Person",
+        "type": "object",
+        "properties": {
+          "test": {
+            "type": ["string", "number"]
+          }
+        }
+      }
     }
   ]
 }