Issue 16394: Fix uncompileable java client code from composed schema

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

@@ -561,6 +561,9 @@ public Map<String, ModelsMap> postProcessAllModels(Map<String, ModelsMap> objs)
             }
         }
 
+
+
+
         return objs;
     }
 
@@ -3576,12 +3579,13 @@ protected CodegenDiscriminator createDiscriminator(String schemaName, Schema sch
                 .orElseGet(() -> typeMapping.get("string"));
         discriminator.setPropertyType(propertyType);
 
-        // check to see if the discriminator property is an enum string
-        if (schema.getProperties() != null &&
-                schema.getProperties().get(discriminatorPropertyName) instanceof StringSchema) {
-            StringSchema s = (StringSchema) schema.getProperties().get(discriminatorPropertyName);
-            if (s.getEnum() != null && !s.getEnum().isEmpty()) { // it's an enum string
-                discriminator.setIsEnum(true);
+
+        // sometimes the discriminator is directly described in the properties
+        discriminator.setIsEnum(discriminatorIsEnumString(schema, discriminatorPropertyName));
+        if (ModelUtils.isComposedSchema(schema)) {
+            // other times the properties are null and only the parent contains data about if the discriminator is an enum
+            for(Schema s: getModelNameToSchemaCache().values()) {
+                discriminator.setIsEnum(discriminatorIsEnumString(s, discriminatorPropertyName));
             }
         }
 
@@ -3639,6 +3643,16 @@ protected CodegenDiscriminator createDiscriminator(String schemaName, Schema sch
         return discriminator;
     }
 
+    private static boolean discriminatorIsEnumString(Schema schema, String discriminatorPropertyName) {
+        if (schema.getProperties() != null && schema.getProperties().get(discriminatorPropertyName) instanceof StringSchema) {
+            StringSchema s = (StringSchema) schema.getProperties().get(discriminatorPropertyName);
+            if (s.getEnum() != null && !s.getEnum().isEmpty()) { // it's an enum string
+                return true;
+            }
+        }
+        return false;
+    }
+
     /**
      * Handle the model for the 'additionalProperties' keyword in the OAS schema.
      *

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

@@ -45,6 +45,7 @@
 import org.openapitools.codegen.DefaultGenerator;
 import org.openapitools.codegen.TestUtils;
 import org.openapitools.codegen.config.CodegenConfigurator;
+import org.openapitools.codegen.config.GlobalSettings;
 import org.openapitools.codegen.java.assertions.JavaFileAssert;
 import org.openapitools.codegen.languages.AbstractJavaCodegen;
 import org.openapitools.codegen.languages.JavaClientCodegen;
@@ -2384,4 +2385,32 @@ public void testEnumCaseSensitive_issue8084() throws IOException {
             .bodyContainsLines("if (b.value.equals(value)) {");
     }
 
+    @Test
+    public void testIfJavaCodeWithDiscriminatorWillCompile_issue16394() throws IOException {
+        Map<String, Object> properties = new HashMap<>();
+        properties.put(CodegenConstants.API_PACKAGE, "xyz.abcdef.api");
+        properties.put(JavaClientCodegen.OKHTTP_GSON, true);
+
+        File output = Files.createTempDirectory("test").toFile();
+        output.deleteOnExit();
+
+        final CodegenConfigurator configurator = new CodegenConfigurator()
+                .setGeneratorName("java")
+                .setInputSpec("src/test/resources/bugs/issue_16394.yaml")
+                .setOutputDir(output.getAbsolutePath().replace("\\", "/"));
+
+        GlobalSettings.setProperty("debugModels", "true");
+        DefaultGenerator generator = new DefaultGenerator();
+        List<File> files = generator.opts(configurator.toClientOptInput()).generate();
+        files.forEach(File::deleteOnExit);
+
+        for(File f: files) {
+            // a rather fragile way of determining if the code won't compile. a better approach would be a reusable
+            // utility to determine this, similar to how validateJavaSourceFiles checks the syntax.
+            if("Cat.java".equals(f.getName())) {
+                String fileContents = new String(Files.readAllBytes(f.toPath()), StandardCharsets.UTF_8);
+                Assert.assertFalse(fileContents.contains("this.petType = this.getClass().getSimpleName()"));
+            }
+        }
+    }
 }

modules/openapi-generator/src/test/resources/bugs/issue_16394.yaml

@@ -0,0 +1,63 @@
+---
+openapi: 3.0.3
+info:
+  title: example of a parent schema with discriminator property that is an enum
+  version: 2.0
+paths:
+  "/pet/{petId}":
+    get:
+      summary: Find pet by id
+      operationId: getBetById
+      parameters:
+        - name: petId
+          in: path
+          required: true
+          schema:
+            type: string
+      responses:
+        '200':
+          description: OK - The request has succeeded.
+          content:
+            application/json:
+              schema:
+                type: array
+                items:
+                  "$ref": "#/components/schemas/Pet"
+components:
+  schemas:
+    Pet:
+      type: object
+      required:
+        - petType
+      properties:
+        petType:
+          type: string
+          enum: [ Cat, Dog, Lizard ]
+      discriminator:
+        propertyName: petType
+        mapping:
+          dog: Dog
+    Cat:
+      allOf:
+        - $ref: '#/components/schemas/Pet'
+        - type: object
+          # all other properties specific to a `Cat`
+          properties:
+            name:
+              type: string
+    Dog:
+      allOf:
+        - $ref: '#/components/schemas/Pet'
+        - type: object
+          # all other properties specific to a `Dog`
+          properties:
+            bark:
+              type: string
+    Lizard:
+      allOf:
+        - $ref: '#/components/schemas/Pet'
+        - type: object
+          # all other properties specific to a `Lizard`
+          properties:
+            lovesRocks:
+              type: boolean