[core] Resolve primitive aliases for the oneOf discriminator property type

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

@@ -3916,6 +3916,9 @@ protected String getCommonSchemaType(List<Schema> schemas) {
 
                 Schema first = schemas.get(0);
                 try {
+                    // a $ref to an alias of a primitive type has no model: use the aliased type,
+                    // like the type of the property in the concrete models
+                    first = unaliasSchema(first);
                     if (StringUtils.isNotEmpty(first.get$ref())) {
                         return toModelName(ModelUtils.getSimpleRef(first.get$ref()));
                     }

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

@@ -1385,6 +1385,34 @@ public void testOneOfAllOfInlineStringWithFormatDiscriminatorInheritance() {
         assertEquals("URI", catModel.discriminator.getPropertyType());
     }
 
+    @Test
+    public void testOneOfDiscriminatorPropertyIsRefToPrimitiveAlias() {
+        final OpenAPI openAPI = TestUtils.parseFlattenSpec("src/test/resources/3_0/oneOf_issue_25226.yaml");
+        new OpenAPINormalizer(openAPI, Map.of()).normalize();
+        DefaultCodegen codegen = new DefaultCodegen();
+        codegen.setUseOneOfInterfaces(true);
+        codegen.setOpenAPI(openAPI);
+
+        // no model is generated for an alias of a primitive type: the aliased type is used, like for the subtypes
+        verifyOneOfDiscriminatorPropertyType(codegen, openAPI, "Shape", "String");
+        verifyOneOfDiscriminatorPropertyType(codegen, openAPI, "Vehicle", "Integer");
+        verifyOneOfDiscriminatorPropertyType(codegen, openAPI, "Document", "UUID");
+        verifyOneOfDiscriminatorPropertyType(codegen, openAPI, "Fruit", "String");
+        verifyOneOfDiscriminatorPropertyType(codegen, openAPI, "Animal", "String");
+        // each subtype has its own alias
+        verifyOneOfDiscriminatorPropertyType(codegen, openAPI, "Tool", "String");
+        // an enum, or an alias of an enum, is generated as a model
+        verifyOneOfDiscriminatorPropertyType(codegen, openAPI, "Pet", "BreedEnum");
+        verifyOneOfDiscriminatorPropertyType(codegen, openAPI, "Toy", "ToyKind");
+    }
+
+    private void verifyOneOfDiscriminatorPropertyType(DefaultCodegen codegen, OpenAPI openAPI, String schemaName,
+                                                      String expectedPropertyType) {
+        CodegenModel model = codegen.fromModel(schemaName, openAPI.getComponents().getSchemas().get(schemaName));
+        assertTrue(model.getHasDiscriminatorWithNonEmptyMapping(), schemaName);
+        assertEquals(expectedPropertyType, model.discriminator.getPropertyType(), schemaName);
+    }
+
     @Test
     public void testParentName() {
         final OpenAPI openAPI = TestUtils.parseFlattenSpec("src/test/resources/3_0/allOf.yaml");

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

@@ -10249,6 +10249,40 @@ public void oneOfDiscriminatorType(String filename, boolean resolveInlineEnum, S
                 .fileContains(expectedContains);
     }
 
+    @Test
+    public void issue_25226() throws IOException {
+        Map<String, File> files = generateFromContract(
+                "src/test/resources/3_0/oneOf_issue_25226.yaml", SPRING_BOOT,
+                Map.of(USE_SPRING_BOOT4, true)
+        );
+
+        // no model is generated for an alias of a primitive type
+        assertThat(files).doesNotContainKeys("ShapeKind.java", "Wheels.java", "SchemaId.java", "Species.java",
+                "BreedAlias.java", "AnimalGroup.java");
+
+        // the getter of the oneOf interface uses the aliased type, like the subtypes
+        JavaFileAssert.assertThat(files.get("Shape.java"))
+                .fileContains("public String getKind();");
+        JavaFileAssert.assertThat(files.get("Circle.java"))
+                .fileContains("public String getKind() {");
+        JavaFileAssert.assertThat(files.get("Vehicle.java"))
+                .fileContains("public Integer getWheels();");
+        JavaFileAssert.assertThat(files.get("Document.java"))
+                .fileContains("public UUID getSchemaId();");
+        JavaFileAssert.assertThat(files.get("Fruit.java"))
+                .fileContains("public String getSpecies();");
+        JavaFileAssert.assertThat(files.get("Animal.java"))
+                .fileContains("public String getGroup();");
+        JavaFileAssert.assertThat(files.get("Tool.java"))
+                .fileContains("public String getCategory();");
+
+        // an enum, or an alias of an enum, is generated as a model
+        JavaFileAssert.assertThat(files.get("Pet.java"))
+                .fileContains("public BreedEnum getBreed();");
+        JavaFileAssert.assertThat(files.get("Toy.java"))
+                .fileContains("public ToyKind getKind();");
+    }
+
     @Test
     void listItems_annotated_with_x_field_extra_annotation() throws IOException {
         Map<String, File> files = generateFromContract("src/test/resources/3_0/issue_23705.yaml", SPRING_BOOT,

modules/openapi-generator/src/test/resources/3_0/oneOf_issue_25226.yaml

@@ -0,0 +1,282 @@
+openapi: 3.0.3
+info:
+  title: oneOf discriminator property typed by a $ref to a primitive alias
+  description: >
+    The discriminator property of the oneOf subtypes is a $ref. When the referenced schema is an alias of
+    a primitive type (e.g. a plain `type: string`), no model is generated for it and the getter of the
+    generated oneOf interface must use the aliased type, like the implementing classes do.
+  version: 1.0.0
+paths:
+  /all:
+    get:
+      operationId: getAll
+      responses:
+        '200':
+          description: All the oneOf parents
+          content:
+            application/json:
+              schema:
+                $ref: '#/components/schemas/Holder'
+components:
+  schemas:
+    Holder:
+      type: object
+      properties:
+        shape:
+          $ref: '#/components/schemas/Shape'
+        vehicle:
+          $ref: '#/components/schemas/Vehicle'
+        document:
+          $ref: '#/components/schemas/Document'
+        fruit:
+          $ref: '#/components/schemas/Fruit'
+        pet:
+          $ref: '#/components/schemas/Pet'
+        toy:
+          $ref: '#/components/schemas/Toy'
+        tool:
+          $ref: '#/components/schemas/Tool'
+        animal:
+          $ref: '#/components/schemas/Animal'
+
+    # Both subtypes share the same alias of a string
+    Shape:
+      oneOf:
+        - $ref: '#/components/schemas/Circle'
+        - $ref: '#/components/schemas/Square'
+      discriminator:
+        propertyName: kind
+        mapping:
+          circle: '#/components/schemas/Circle'
+          square: '#/components/schemas/Square'
+    ShapeKind:
+      type: string
+      description: The kind of shape.
+    Circle:
+      type: object
+      required:
+        - kind
+      properties:
+        kind:
+          $ref: '#/components/schemas/ShapeKind'
+        radius:
+          type: number
+    Square:
+      type: object
+      required:
+        - kind
+      properties:
+        kind:
+          $ref: '#/components/schemas/ShapeKind'
+        side:
+          type: number
+
+    # Alias of an integer
+    Vehicle:
+      oneOf:
+        - $ref: '#/components/schemas/Car'
+        - $ref: '#/components/schemas/Bike'
+      discriminator:
+        propertyName: wheels
+        mapping:
+          '4': '#/components/schemas/Car'
+          '2': '#/components/schemas/Bike'
+    Wheels:
+      type: integer
+      format: int32
+    Car:
+      type: object
+      required:
+        - wheels
+      properties:
+        wheels:
+          $ref: '#/components/schemas/Wheels'
+    Bike:
+      type: object
+      required:
+        - wheels
+      properties:
+        wheels:
+          $ref: '#/components/schemas/Wheels'
+
+    # Alias of a formatted string
+    Document:
+      oneOf:
+        - $ref: '#/components/schemas/Memo'
+        - $ref: '#/components/schemas/Note'
+      discriminator:
+        propertyName: schemaId
+        mapping:
+          memo: '#/components/schemas/Memo'
+          note: '#/components/schemas/Note'
+    SchemaId:
+      type: string
+      format: uuid
+    Memo:
+      type: object
+      required:
+        - schemaId
+      properties:
+        schemaId:
+          $ref: '#/components/schemas/SchemaId'
+    Note:
+      type: object
+      required:
+        - schemaId
+      properties:
+        schemaId:
+          $ref: '#/components/schemas/SchemaId'
+
+    # Alias of an alias
+    Fruit:
+      oneOf:
+        - $ref: '#/components/schemas/Apple'
+        - $ref: '#/components/schemas/Pear'
+      discriminator:
+        propertyName: species
+        mapping:
+          apple: '#/components/schemas/Apple'
+          pear: '#/components/schemas/Pear'
+    SpeciesBase:
+      type: string
+    Species:
+      $ref: '#/components/schemas/SpeciesBase'
+    Apple:
+      type: object
+      required:
+        - species
+      properties:
+        species:
+          $ref: '#/components/schemas/Species'
+    Pear:
+      type: object
+      required:
+        - species
+      properties:
+        species:
+          $ref: '#/components/schemas/Species'
+
+    # Alias of an enum: the enum model is generated, so it must be used
+    Pet:
+      oneOf:
+        - $ref: '#/components/schemas/Dog'
+        - $ref: '#/components/schemas/Cat'
+      discriminator:
+        propertyName: breed
+        mapping:
+          dog: '#/components/schemas/Dog'
+          cat: '#/components/schemas/Cat'
+    BreedEnum:
+      type: string
+      enum:
+        - dog
+        - cat
+    BreedAlias:
+      $ref: '#/components/schemas/BreedEnum'
+    Dog:
+      type: object
+      required:
+        - breed
+      properties:
+        breed:
+          $ref: '#/components/schemas/BreedAlias'
+    Cat:
+      type: object
+      required:
+        - breed
+      properties:
+        breed:
+          $ref: '#/components/schemas/BreedAlias'
+
+    # $ref to an enum: the enum model is generated, so it must be used (unchanged behavior)
+    Toy:
+      oneOf:
+        - $ref: '#/components/schemas/Ball'
+        - $ref: '#/components/schemas/Doll'
+      discriminator:
+        propertyName: kind
+        mapping:
+          ball: '#/components/schemas/Ball'
+          doll: '#/components/schemas/Doll'
+    ToyKind:
+      type: string
+      enum:
+        - ball
+        - doll
+    Ball:
+      type: object
+      required:
+        - kind
+      properties:
+        kind:
+          $ref: '#/components/schemas/ToyKind'
+    Doll:
+      type: object
+      required:
+        - kind
+      properties:
+        kind:
+          $ref: '#/components/schemas/ToyKind'
+
+    # Each subtype uses its own alias of a string
+    Tool:
+      oneOf:
+        - $ref: '#/components/schemas/Hammer'
+        - $ref: '#/components/schemas/Saw'
+      discriminator:
+        propertyName: category
+        mapping:
+          hammer: '#/components/schemas/Hammer'
+          saw: '#/components/schemas/Saw'
+    HammerCategory:
+      type: string
+    SawCategory:
+      type: string
+    Hammer:
+      type: object
+      required:
+        - category
+      properties:
+        category:
+          $ref: '#/components/schemas/HammerCategory'
+    Saw:
+      type: object
+      required:
+        - category
+      properties:
+        category:
+          $ref: '#/components/schemas/SawCategory'
+
+    # The alias property is inherited from a shared base schema through allOf
+    Animal:
+      oneOf:
+        - $ref: '#/components/schemas/Bird'
+        - $ref: '#/components/schemas/Fish'
+      discriminator:
+        propertyName: group
+        mapping:
+          bird: '#/components/schemas/Bird'
+          fish: '#/components/schemas/Fish'
+    AnimalGroup:
+      type: string
+    BaseAnimal:
+      type: object
+      required:
+        - group
+      properties:
+        group:
+          $ref: '#/components/schemas/AnimalGroup'
+    Bird:
+      allOf:
+        - $ref: '#/components/schemas/BaseAnimal'
+        - type: object
+          properties:
+            wingspan:
+              type: number
+    Fish:
+      allOf:
+        - $ref: '#/components/schemas/BaseAnimal'
+        - type: object
+          properties:
+            length:
+              type: number