add a rule to keep only the first tag (#14465)

modules/openapi-generator/src/main/java/org/openapitools/codegen/OpenAPINormalizer.java

@@ -48,6 +48,10 @@ public class OpenAPINormalizer {
     final String REF_AS_PARENT_IN_ALLOF = "REF_AS_PARENT_IN_ALLOF";
     boolean enableRefAsParentInAllOf;
 
+    // when set to true, only keep the first tag in operation if there are more than one tag defined.
+    final String KEEP_ONLY_FIRST_TAG_IN_OPERATION = "KEEP_ONLY_FIRST_TAG_IN_OPERATION";
+    boolean enableKeepOnlyFirstTagInOperation;
+
     // when set to true, complex composed schemas (a mix of oneOf/anyOf/anyOf and properties) with
     // oneOf/anyOf containing only `required` and no properties (these are properties inter-dependency rules)
     // are removed as most generators cannot handle such case at the moment
@@ -91,6 +95,10 @@ public class OpenAPINormalizer {
             enableRefAsParentInAllOf = true;
         }
 
+        if (enableAll || "true".equalsIgnoreCase(rules.get(KEEP_ONLY_FIRST_TAG_IN_OPERATION))) {
+            enableKeepOnlyFirstTagInOperation = true;
+        }
+
         if (enableAll || "true".equalsIgnoreCase(rules.get(REMOVE_ANYOF_ONEOF_AND_KEEP_PROPERTIES_ONLY))) {
             removeAnyOfOneOfAndKeepPropertiesOnly = true;
         }
@@ -146,6 +154,7 @@ public class OpenAPINormalizer {
             }
 
             for (Operation operation : operations) {
+                normalizeOperation(operation);
                 normalizeRequestBody(operation);
                 normalizeParameters(operation);
                 normalizeResponses(operation);
@@ -153,6 +162,15 @@ public class OpenAPINormalizer {
         }
     }
 
+    /**
+     * Normalizes operation
+     *
+     * @param operation Operation
+     */
+    private void normalizeOperation(Operation operation) {
+        processKeepOnlyFirstTagInOperation(operation);
+    }
+
     /**
      * Normalizes schemas in content
      *
@@ -432,6 +450,25 @@ public class OpenAPINormalizer {
         }
     }
 
+    /**
+     * Keep only first tag in the operation if the operation has more than
+     * one tag.
+     *
+     * @param operation Operation
+     */
+    private void processKeepOnlyFirstTagInOperation(Operation operation) {
+        if (!enableKeepOnlyFirstTagInOperation) {
+            return;
+        }
+
+        if (operation.getTags() != null && !operation.getTags().isEmpty() && operation.getTags().size() > 1) {
+            // has more than 1 tag
+            String firstTag = operation.getTags().get(0);
+            operation.setTags(null);
+            operation.addTagsItem(firstTag);
+        }
+    }
+
     /**
      * If the schema contains anyOf/oneOf and properties, remove oneOf/anyOf as these serve as rules to
      * ensure inter-dependency between properties. It's a workaround as such validation is not supported at the moment.

modules/openapi-generator/src/test/java/org/openapitools/codegen/DefaultCodegenTest.java

@@ -4326,6 +4326,23 @@ public class DefaultCodegenTest {
         assertEquals(schema5.getExtensions().get("x-parent"), "abstract");
     }
 
+    @Test
+    public void testOpenAPINormalizerEnableKeepOnlyFirstTagInOperation() {
+        OpenAPI openAPI = TestUtils.parseSpec("src/test/resources/3_0/enableKeepOnlyFirstTagInOperation_test.yaml");
+
+        assertEquals(openAPI.getPaths().get("/person/display/{personId}").getGet().getTags().size(), 2);
+        assertEquals(openAPI.getPaths().get("/person/display/{personId}").getDelete().getTags().size(), 1);
+
+        Map<String, String> options = new HashMap<>();
+        options.put("KEEP_ONLY_FIRST_TAG_IN_OPERATION", "true");
+        OpenAPINormalizer openAPINormalizer = new OpenAPINormalizer(openAPI, options);
+        openAPINormalizer.normalize();
+
+        assertEquals(openAPI.getPaths().get("/person/display/{personId}").getGet().getTags().size(), 1);
+        assertEquals(openAPI.getPaths().get("/person/display/{personId}").getDelete().getTags().size(), 1);
+        assertEquals(openAPI.getPaths().get("/person/display/{personId}").getGet().getTags().get(0), "person");
+    }
+
     @Test
     public void testOpenAPINormalizerRemoveAnyOfOneOfAndKeepPropertiesOnly() {
         // to test the rule REMOVE_ANYOF_ONEOF_AND_KEEP_PROPERTIIES_ONLY
@@ -4359,6 +4376,5 @@ public class DefaultCodegenTest {
         Schema schema3 = openAPI.getComponents().getSchemas().get("AnyOfTest");
         assertNull(schema3.getAnyOf());
         assertTrue(schema3 instanceof StringSchema);
-
     }
 }

modules/openapi-generator/src/test/resources/3_0/enableKeepOnlyFirstTagInOperation_test.yaml

@@ -0,0 +1,59 @@
+openapi: 3.0.1
+info:
+  version: 1.0.0
+  title: Example
+  license:
+    name: MIT
+servers:
+  - url: http://api.example.xyz/v1
+paths:
+  /person/display/{personId}:
+    get:
+      tags:
+        - person
+        - basic
+      parameters:
+        - name: personId
+          in: path
+          required: true
+          description: The id of the person to retrieve
+          schema:
+            type: string
+      operationId: list
+      responses:
+        '200':
+          description: OK
+          content:
+            application/json:
+              schema:
+                $ref: "#/components/schemas/Person"
+    delete:
+      tags:
+        - person
+      parameters:
+        - name: personId
+          in: path
+          required: true
+          description: The id of the person to retrieve
+          schema:
+            type: string
+      operationId: delete
+      responses:
+        '200':
+          description: OK
+          content:
+            application/json:
+              schema:
+                $ref: "#/components/schemas/Person"
+components:
+  schemas:
+    Person:
+      description: person
+      type: object
+      properties:
+        $_type:
+          type: string
+        lastName:
+          type: string
+        firstName:
+          type: string