fix(kotlin): redefined vars should be marked as inherited so that override modifier is added on children class. closes #22216

Author: Sylvain-maillard

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

@@ -859,6 +859,28 @@ public CodegenModel fromModel(String name, Schema schema) {
                 .collect(Collectors.toMap(CodegenProperty::getBaseName, Function.identity()));
         allVarsMap.keySet()
                 .removeAll(m.vars.stream().map(CodegenProperty::getBaseName).collect(Collectors.toSet()));
+
+        // if there is a parent, find the redefined vars
+        if (m.parent != null && m.parentSchema != null) {
+
+            // get the parent schema
+            Schema<?> parentSchema = ModelUtils.getSchemas(this.openAPI).get(m.parentSchema);
+
+            // if parent schema has properties, find the intersection
+            if (parentSchema != null && parentSchema.getProperties() != null) {
+                Set<String> varNames = parentSchema.getProperties().keySet();
+
+                // compute intersection of m.allVars and parent properties, this will give us the overridden properties
+                Map<String, CodegenProperty> overriddenProperties = m.allVars.stream()
+                        .filter(p -> varNames.contains(p.getBaseName()))
+                        .collect(Collectors.toMap(CodegenProperty::getBaseName, Function.identity()));
+
+                // overridden properties contain the properties that are redefined in the child model.
+                // add them to allVarsMap so that they are marked as inherited.
+                allVarsMap.putAll(overriddenProperties);
+            }
+        }
+
         // Update the allVars
         allVarsMap.values().forEach(p -> p.isInherited = true);
         // Update any other vars (requiredVars, optionalVars)

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

@@ -574,6 +574,32 @@ private void givenSchemaObjectPropertyNameContainsDollarSignWhenGenerateThenDoll
         Assert.assertEquals(customKotlinParseListener.getStringReferenceCount(), 0);
     }
 
+    @Test(description = "add override on reference specialisation")
+    public void polymorphicReferenceOverrides() throws IOException {
+        File output = Files.createTempDirectory("test").toFile();
+        output.deleteOnExit();
+//        File output = Paths.get("/Users/sylvain_maillard/workspaces/openapi-generator/modules/openapi-generator/target/test").toFile();
+
+        final CodegenConfigurator configurator = new CodegenConfigurator()
+                .setGeneratorName("kotlin")
+                .setInputSpec("src/test/resources/3_1/issue_22216.yaml")
+                .setOutputDir(output.getAbsolutePath().replace("\\", "/"));
+
+        final ClientOptInput clientOptInput = configurator.toClientOptInput();
+        DefaultGenerator generator = new DefaultGenerator();
+        List<File> files = generator.opts(clientOptInput).generate();
+
+        Assert.assertEquals(files.size(), 36);
+
+        final Path carFile = Paths.get(output + "/src/main/kotlin/org/openapitools/client/models/Car.kt");
+        final Path vehicleFile = Paths.get(output + "/src/main/kotlin/org/openapitools/client/models/Vehicle.kt");
+        // file should contain override keyword for inherited properties ref
+        TestUtils.assertFileContains(carFile, "override val requiredProperty: kotlin.String,");
+        TestUtils.assertFileContains(carFile, "override val optionalProperty: kotlin.String? = null");
+        // file should not contain override keyword for own properties
+        TestUtils.assertFileNotContains(carFile, "override val color: kotlin.String? = null");
+    }
+
     @Test(description = "generate polymorphic kotlinx_serialization model")
     public void polymorphicKotlinxSerialization() throws IOException {
         File output = Files.createTempDirectory("test").toFile();

modules/openapi-generator/src/test/resources/3_1/issue_22216.yaml

@@ -0,0 +1,40 @@
+openapi: 3.1.0
+
+info:
+  title: Title
+  description: Title
+  version: 1.0.0
+
+paths:
+  /example:
+    get:
+      responses:
+        "200":
+          description: "A successful response"
+          content:
+            application/json:
+              schema:
+                $ref: '#/components/schemas/Vehicle'
+
+components:
+  schemas:
+    Vehicle:
+      type: object
+      additionalProperties: false
+      discriminator: { propertyName: objectType }
+      required: [ objectType, requiredProperty ]
+      properties:
+        objectType: { type: string }
+        requiredProperty: { type: object }
+        optionalProperty: { type: object }
+
+    Car:
+      allOf:
+        - $ref: '#/components/schemas/Vehicle'
+        - type: object
+          additionalProperties: false
+          required: [ objectType, requiredProperty ]
+          properties:
+            color: { type: string }
+            requiredProperty: { type: string }
+            optionalProperty: { type: string }