fix: unwrap single non-object array items in allOf

docs/customization.md

@@ -588,6 +588,13 @@ Example:
 java -jar modules/openapi-generator-cli/target/openapi-generator-cli.jar generate -g java -i modules/openapi-generator/src/test/resources/3_0/simplifyOneOfAnyOf_test.yaml -o /tmp/java-okhttp/ --openapi-normalizer SIMPLIFY_ONEOF_ANYOF=true
 ```
 
+- `SIMPLIFY_ALLOF`: when set to `true`, simplify allOf by 1) removing null (sub-schema) or enum of null (sub-schema) and setting nullable to true instead, and 2) simplifying allOf with a single sub-schema to just the sub-schema itself.
+
+Example:
+```
+java -jar modules/openapi-generator-cli/target/openapi-generator-cli.jar generate -g java -i modules/openapi-generator/src/test/resources/3_0/simplifyAllOf_test.yaml -o /tmp/java-okhttp/ --openapi-normalizer SIMPLIFY_ALLOF=true
+```
+
 - `KEEP_ONLY_FIRST_TAG_IN_OPERATION`: when set to `true`, only keep the first tag in operation if there are more than one tag defined.
 
 Example:

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

@@ -41,7 +41,7 @@
 import java.util.stream.Collectors;
 
 import static org.openapitools.codegen.CodegenConstants.*;
-import static org.openapitools.codegen.utils.ModelUtils.simplifyOneOfAnyOfWithOnlyOneNonNullSubSchema;
+import static org.openapitools.codegen.utils.ModelUtils.simplifyOneOfAnyOfAllOfWithOnlyOneNonNullSubSchema;
 import static org.openapitools.codegen.utils.StringUtils.getUniqueString;
 
 public class OpenAPINormalizer {
@@ -75,7 +75,7 @@ public class OpenAPINormalizer {
     // 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";
 
-    // when set to true, complex composed schemas (a mix of oneOf/anyOf/anyOf and properties) with
+    // when set to true, complex composed schemas (a mix of oneOf/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
     final String REMOVE_ANYOF_ONEOF_AND_KEEP_PROPERTIES_ONLY = "REMOVE_ANYOF_ONEOF_AND_KEEP_PROPERTIES_ONLY";
@@ -93,6 +93,11 @@ public class OpenAPINormalizer {
     // and if sub-schema contains enum of "null", remove it and set nullable to true instead
     final String SIMPLIFY_ONEOF_ANYOF = "SIMPLIFY_ONEOF_ANYOF";
 
+    // when set to true, allOf schema with only one sub-schema is simplified to just the sub-schema
+    // and if sub-schema contains "null", remove it and set nullable to true instead
+    // and if sub-schema contains enum of "null", remove it and set nullable to true instead
+    final String SIMPLIFY_ALLOF = "SIMPLIFY_ALLOF";
+
     // when set to true, boolean enum will be converted to just boolean
     final String SIMPLIFY_BOOLEAN_ENUM = "SIMPLIFY_BOOLEAN_ENUM";
 
@@ -206,6 +211,7 @@ public OpenAPINormalizer(OpenAPI openAPI, Map<String, String> inputRules) {
         ruleNames.add(REMOVE_ANYOF_ONEOF_AND_KEEP_PROPERTIES_ONLY);
         ruleNames.add(SIMPLIFY_ANYOF_STRING_AND_ENUM_STRING);
         ruleNames.add(SIMPLIFY_ONEOF_ANYOF);
+        ruleNames.add(SIMPLIFY_ALLOF);
         ruleNames.add(SIMPLIFY_BOOLEAN_ENUM);
         ruleNames.add(KEEP_ONLY_FIRST_TAG_IN_OPERATION);
         ruleNames.add(SET_TAGS_FOR_ALL_OPERATIONS);
@@ -929,7 +935,7 @@ public Schema normalizeSchema(Schema schema, Set<Schema> visitedSchemas) {
 
         if (ModelUtils.isArraySchema(schema)) { // array
             Schema result = normalizeArraySchema(schema);
-            normalizeSchema(result.getItems(), visitedSchemas);
+            result.setItems(normalizeSchema(result.getItems(), visitedSchemas));
             return result;
         } else if (ModelUtils.isOneOf(schema)) { // oneOf
             return normalizeOneOf(schema, visitedSchemas);
@@ -1203,6 +1209,7 @@ protected Schema normalizeAllOf(Schema schema, Set<Schema> visitedSchemas) {
 
         // process rules here
         processUseAllOfRefAsParent(schema);
+        schema = processSimplifyAllOf(schema);
 
         return schema;
     }
@@ -1306,6 +1313,43 @@ protected Schema normalizeComplexComposedSchema(Schema schema, Set<Schema> visit
     // ===================== a list of rules =====================
     // all rules (functions ) start with the word "process"
 
+
+    /**
+     * If the schema is allOf and the sub-schemas is null, set `nullable: true`
+     * instead.
+     * If there's only one sub-schema, simply return the sub-schema directly.
+     *
+     * @param schema Schema
+     * @return Schema
+     */
+    protected Schema processSimplifyAllOf(Schema schema) {
+        List<Schema> allOfSchemas = schema.getAllOf();
+        if (allOfSchemas == null) {
+            return schema;
+        }
+
+        // allOf containing $refs is intentional composition (inheritance, or $ref+sibling wrapping
+        // from normalizeReferenceSchema) — never simplify these, as the referenced schema may have
+        // no type/description yet still be a real model (e.g. after oneOf removal by discriminator mapping)
+        if (allOfSchemas.stream().anyMatch(s -> StringUtils.isNotEmpty(s.get$ref()))) {
+            return schema;
+        }
+        schema = simplifyOneOfAnyOfAllOfWithOnlyOneNonNullSubSchema(openAPI, schema, allOfSchemas);
+
+        if (!getRule(SIMPLIFY_ALLOF)) {
+            return schema;
+        }
+
+        // clear allOf on primitive types (opt-in)
+        if (ModelUtils.isIntegerSchema(schema) || ModelUtils.isNumberSchema(schema) || ModelUtils.isStringSchema(schema) || ModelUtils.isBooleanSchema(schema)) {
+            if (schema.getSpecVersion().equals(SpecVersion.V30)) {
+                schema.setAllOf(null);
+            }
+        }
+
+        return schema;
+    }
+
     /**
      * Child schemas in `allOf` is considered a parent if it's a `$ref` (instead of inline schema).
      *
@@ -1736,8 +1780,8 @@ protected Schema processSimplifyOneOf(Schema schema) {
                 }
             }
 
-            schema = simplifyOneOfAnyOfWithOnlyOneNonNullSubSchema(openAPI, schema, oneOfSchemas);
-            if (ModelUtils.isIntegerSchema(schema) || ModelUtils.isNumberSchema(schema) || ModelUtils.isStringSchema(schema)) {
+            schema = simplifyOneOfAnyOfAllOfWithOnlyOneNonNullSubSchema(openAPI, schema, oneOfSchemas);
+            if (ModelUtils.isIntegerSchema(schema) || ModelUtils.isNumberSchema(schema) || ModelUtils.isStringSchema(schema) || ModelUtils.isBooleanSchema(schema)) {
                 if (schema.getSpecVersion().equals(SpecVersion.V30)) {
                     schema.setOneOf(null);
                 } //else {
@@ -2104,7 +2148,7 @@ protected Schema processSimplifyAnyOf(Schema schema) {
                 }
             }
 
-            schema = simplifyOneOfAnyOfWithOnlyOneNonNullSubSchema(openAPI, schema, anyOfSchemas);
+            schema = simplifyOneOfAnyOfAllOfWithOnlyOneNonNullSubSchema(openAPI, schema, anyOfSchemas);
         }
 
         return schema;

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

@@ -2323,7 +2323,7 @@ public static Schema cloneSchema(Schema schema, boolean openapi31) {
      * @param subSchemas The oneOf or AnyOf schemas
      * @return The simplified schema
      */
-    public static Schema simplifyOneOfAnyOfWithOnlyOneNonNullSubSchema(OpenAPI openAPI, Schema schema, List<Schema> subSchemas) {
+    public static Schema simplifyOneOfAnyOfAllOfWithOnlyOneNonNullSubSchema(OpenAPI openAPI, Schema schema, List<Schema> subSchemas) {
         if (subSchemas.removeIf(subSchema -> isNullTypeSchema(openAPI, subSchema))) {
             schema.setNullable(true);
         }

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

@@ -353,6 +353,49 @@ public void testOpenAPINormalizerSimplifyOneOfAnyOf() {
         assertEquals(schema20.getEnum().size(), 2);
     }
 
+    @Test
+    public void testOpenAPINormalizerSimplifyAllOf() {
+        OpenAPI openAPI = TestUtils.parseSpec("src/test/resources/3_0/simplifyAllOf_test.yaml");
+
+        Schema schema = openAPI.getComponents().getSchemas().get("AllOfTest");
+        assertEquals(schema.getAllOf().size(), 4);
+        assertNull(schema.getNullable());
+
+        Schema schema3 = openAPI.getComponents().getSchemas().get("SingleAllOfTest");
+        assertEquals(schema3.getAllOf().size(), 1);
+
+        Schema schema5 = openAPI.getComponents().getSchemas().get("ArrayAllOfTest");
+        Schema schema5_outer = ((Schema) schema5.getProperties().get("outer"));
+        assertNotNull(schema5_outer.getItems().getAllOf());
+        assertEquals(schema5_outer.getItems().getAllOf().size(), 1);
+        Schema schema5_outer_first = (Schema) schema5_outer.getItems().getAllOf().get(0);
+        assertEquals(schema5_outer_first.getType(), "array");
+        assertEquals(schema5_outer_first.getMinItems(), 1);
+        assertEquals(schema5_outer_first.getItems().getType(), "string");
+
+        Map<String, String> options = new HashMap<>();
+        options.put("SIMPLIFY_ALLOF", "true");
+        OpenAPINormalizer openAPINormalizer = new OpenAPINormalizer(openAPI, options);
+        openAPINormalizer.normalize();
+
+        Schema schema2 = openAPI.getComponents().getSchemas().get("AllOfTest");
+        assertNull(schema2.getAllOf());
+        assertTrue(schema2 instanceof StringSchema);
+        assertTrue(schema2.getNullable());
+
+        Schema schema4 = openAPI.getComponents().getSchemas().get("SingleAllOfTest");
+        assertEquals(schema4.getAllOf(), null);
+        assertEquals(schema4.getType(), "string");
+        assertEquals(schema4.getEnum().size(), 2);
+
+        Schema schema6 = openAPI.getComponents().getSchemas().get("ArrayAllOfTest");
+        Schema schema6_outer = ((Schema) schema6.getProperties().get("outer"));
+        assertNull(schema6_outer.getItems().getAllOf());
+        assertEquals(schema6_outer.getItems().getType(), "array");
+        assertEquals(schema6_outer.getItems().getMinItems(), 1);
+        assertEquals(schema6_outer.getItems().getItems().getType(), "string");
+    }
+
     @Test
     public void testOpenAPINormalizerSimplifyOneOfWithSingleRef() {
         OpenAPI openAPI = TestUtils.parseSpec("src/test/resources/3_0/simplifyOneOfAnyOf_test.yaml");

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

@@ -487,39 +487,39 @@ public void simplifyOneOfAnyOfWithOnlyOneNonNullSubSchema() {
 
         Schema anyOfWithSeveralSubSchemasButSingleNonNull = ModelUtils.getSchema(openAPI, "AnyOfTest");
         subSchemas = anyOfWithSeveralSubSchemasButSingleNonNull.getAnyOf();
-        schema = ModelUtils.simplifyOneOfAnyOfWithOnlyOneNonNullSubSchema(openAPI, anyOfWithSeveralSubSchemasButSingleNonNull, subSchemas);
+        schema = ModelUtils.simplifyOneOfAnyOfAllOfWithOnlyOneNonNullSubSchema(openAPI, anyOfWithSeveralSubSchemasButSingleNonNull, subSchemas);
         assertNull(schema.getOneOf());
         assertNull(schema.getAnyOf());
         assertTrue(schema.getNullable());
         assertEquals("string", schema.getType());
 
         Schema anyOfWithSingleNonNullSubSchema = ModelUtils.getSchema(openAPI, "Parent");
         subSchemas = ((Schema) anyOfWithSingleNonNullSubSchema.getProperties().get("number")).getAnyOf();
-        schema = ModelUtils.simplifyOneOfAnyOfWithOnlyOneNonNullSubSchema(openAPI, anyOfWithSingleNonNullSubSchema, subSchemas);
+        schema = ModelUtils.simplifyOneOfAnyOfAllOfWithOnlyOneNonNullSubSchema(openAPI, anyOfWithSingleNonNullSubSchema, subSchemas);
         assertNull(schema.getOneOf());
         assertNull(schema.getAnyOf());
         assertNull(schema.getNullable());
         assertEquals(schema.get$ref(), "#/components/schemas/Number");
 
         Schema oneOfWithSeveralSubSchemasButSingleNonNull = ModelUtils.getSchema(openAPI, "OneOfTest");
         subSchemas = oneOfWithSeveralSubSchemasButSingleNonNull.getOneOf();
-        schema = ModelUtils.simplifyOneOfAnyOfWithOnlyOneNonNullSubSchema(openAPI, oneOfWithSeveralSubSchemasButSingleNonNull, subSchemas);
+        schema = ModelUtils.simplifyOneOfAnyOfAllOfWithOnlyOneNonNullSubSchema(openAPI, oneOfWithSeveralSubSchemasButSingleNonNull, subSchemas);
         assertNull(schema.getOneOf());
         assertNull(schema.getAnyOf());
         assertTrue(schema.getNullable());
         assertEquals("integer", schema.getType());
 
         Schema oneOfWithSingleNonNullSubSchema = ModelUtils.getSchema(openAPI, "ParentWithOneOfProperty");
         subSchemas = ((Schema) oneOfWithSingleNonNullSubSchema.getProperties().get("number")).getOneOf();
-        schema = ModelUtils.simplifyOneOfAnyOfWithOnlyOneNonNullSubSchema(openAPI, oneOfWithSingleNonNullSubSchema, subSchemas);
+        schema = ModelUtils.simplifyOneOfAnyOfAllOfWithOnlyOneNonNullSubSchema(openAPI, oneOfWithSingleNonNullSubSchema, subSchemas);
         assertNull(schema.getOneOf());
         assertNull(schema.getAnyOf());
         assertNull(schema.getNullable());
         assertEquals(schema.get$ref(), "#/components/schemas/Number");
 
         Schema oneOfWithSeveralSubSchemas = ModelUtils.getSchema(openAPI, "ParentWithPluralOneOfProperty");
         subSchemas = ((Schema) oneOfWithSeveralSubSchemas.getProperties().get("number")).getOneOf();
-        schema = ModelUtils.simplifyOneOfAnyOfWithOnlyOneNonNullSubSchema(openAPI, oneOfWithSeveralSubSchemas, subSchemas);
+        schema = ModelUtils.simplifyOneOfAnyOfAllOfWithOnlyOneNonNullSubSchema(openAPI, oneOfWithSeveralSubSchemas, subSchemas);
         assertNull(schema.getOneOf());
         assertNotNull(oneOfWithSeveralSubSchemas.getProperties().get("number"));
         assertNull(schema.getAnyOf());
@@ -536,7 +536,7 @@ public void simplifyOneOfWithOnlyOneNonNullSubSchemaKeepsReadOnlyWriteOnlyAttrib
         Schema oneOfWithNullAndRefSubSchema = ModelUtils.getSchema(openAPI, "OneOfParentRefTest");
         Schema numberPropertySchema = ((Schema) oneOfWithNullAndRefSubSchema.getProperties().get("number"));
         subSchemas = numberPropertySchema.getOneOf();
-        schema = ModelUtils.simplifyOneOfAnyOfWithOnlyOneNonNullSubSchema(openAPI, numberPropertySchema, subSchemas);
+        schema = ModelUtils.simplifyOneOfAnyOfAllOfWithOnlyOneNonNullSubSchema(openAPI, numberPropertySchema, subSchemas);
         assertNull(schema.getOneOf());
         assertNull(schema.getAnyOf());
         assertTrue(schema.getNullable());
@@ -546,7 +546,7 @@ public void simplifyOneOfWithOnlyOneNonNullSubSchemaKeepsReadOnlyWriteOnlyAttrib
 
         Schema number2PropertySchema = ((Schema) oneOfWithNullAndRefSubSchema.getProperties().get("number2"));
         subSchemas = number2PropertySchema.getOneOf();
-        schema = ModelUtils.simplifyOneOfAnyOfWithOnlyOneNonNullSubSchema(openAPI, number2PropertySchema, subSchemas);
+        schema = ModelUtils.simplifyOneOfAnyOfAllOfWithOnlyOneNonNullSubSchema(openAPI, number2PropertySchema, subSchemas);
         assertNull(schema.getOneOf());
         assertNull(schema.getAnyOf());
         assertTrue(schema.getNullable());
@@ -564,7 +564,7 @@ public void simplifyAnyOfWithOnlyOneNonNullSubSchemaKeepsReadOnlyWriteOnlyAttrib
         Schema anyOfWithNullAndRefSubSchema = ModelUtils.getSchema(openAPI, "AnyOfParentRefTest");
         Schema numberPropertySchema = ((Schema) anyOfWithNullAndRefSubSchema.getProperties().get("number"));
         subSchemas = numberPropertySchema.getAnyOf();
-        schema = ModelUtils.simplifyOneOfAnyOfWithOnlyOneNonNullSubSchema(openAPI, numberPropertySchema, subSchemas);
+        schema = ModelUtils.simplifyOneOfAnyOfAllOfWithOnlyOneNonNullSubSchema(openAPI, numberPropertySchema, subSchemas);
         assertNull(schema.getOneOf());
         assertNull(schema.getAnyOf());
         assertTrue(schema.getNullable());
@@ -574,7 +574,7 @@ public void simplifyAnyOfWithOnlyOneNonNullSubSchemaKeepsReadOnlyWriteOnlyAttrib
 
         Schema number2PropertySchema = ((Schema) anyOfWithNullAndRefSubSchema.getProperties().get("number2"));
         subSchemas = number2PropertySchema.getAnyOf();
-        schema = ModelUtils.simplifyOneOfAnyOfWithOnlyOneNonNullSubSchema(openAPI, number2PropertySchema, subSchemas);
+        schema = ModelUtils.simplifyOneOfAnyOfAllOfWithOnlyOneNonNullSubSchema(openAPI, number2PropertySchema, subSchemas);
         assertNull(schema.getOneOf());
         assertNull(schema.getAnyOf());
         assertTrue(schema.getNullable());
@@ -592,23 +592,23 @@ public void simplifyOneOfAnyOfWithOnlyOneNonNullSubSchemaKeepsParentDescription(
                 new StringSchema(),
                 new Schema<>().type("null")
         )));
-        Schema anyOfSchema = ModelUtils.simplifyOneOfAnyOfWithOnlyOneNonNullSubSchema(openAPI, anyOfParent, anyOfParent.getAnyOf());
+        Schema anyOfSchema = ModelUtils.simplifyOneOfAnyOfAllOfWithOnlyOneNonNullSubSchema(openAPI, anyOfParent, anyOfParent.getAnyOf());
         assertEquals(anyOfSchema.getDescription(), "Access token");
 
         Schema oneOfParent = new Schema().description("Expires at");
         oneOfParent.setOneOf(new ArrayList<>(Arrays.asList(
                 new IntegerSchema(),
                 new Schema<>().type("null")
         )));
-        Schema oneOfSchema = ModelUtils.simplifyOneOfAnyOfWithOnlyOneNonNullSubSchema(openAPI, oneOfParent, oneOfParent.getOneOf());
+        Schema oneOfSchema = ModelUtils.simplifyOneOfAnyOfAllOfWithOnlyOneNonNullSubSchema(openAPI, oneOfParent, oneOfParent.getOneOf());
         assertEquals(oneOfSchema.getDescription(), "Expires at");
 
         Schema anyOfParentWithChildDescription = new Schema().description("Parent description");
         anyOfParentWithChildDescription.setAnyOf(new ArrayList<>(Arrays.asList(
                 new StringSchema().description("Child description"),
                 new Schema<>().type("null")
         )));
-        Schema anyOfSchemaWithChildDescription = ModelUtils.simplifyOneOfAnyOfWithOnlyOneNonNullSubSchema(
+        Schema anyOfSchemaWithChildDescription = ModelUtils.simplifyOneOfAnyOfAllOfWithOnlyOneNonNullSubSchema(
                 openAPI,
                 anyOfParentWithChildDescription,
                 anyOfParentWithChildDescription.getAnyOf());

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

@@ -0,0 +1,53 @@
+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:
+      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/AllOfTest"
+components:
+  schemas:
+    AllOfTest:
+      description: to test allOf
+      allOf:
+        - type: string
+        - type: 'null'
+        - type: null
+        - $ref: null
+    SingleAllOfTest:
+      description: to test allOf (enum string only)
+      allOf:
+        - type: string
+          enum:
+            - A
+            - B
+    ArrayAllOfTest:
+      type: object
+      properties:
+        outer:
+          type: array
+          items:
+            allOf:
+              - type: array
+                minItems: 1
+                items:
+                  type: string

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

@@ -45,6 +45,13 @@ components:
       oneOf:
         - type: string
         - type: 'null'
+    AllOfTest:
+      description: to test allOf
+      allOf:
+        - type: string
+        - type: 'null'
+        - type: null
+        - $ref: null
     OneOfNullableTest:
       description: to test oneOf nullable
       oneOf:
@@ -58,6 +65,13 @@ components:
           enum:
             - A
             - B
+    SingleAllOfTest:
+      description: to test allOf (enum string only)
+      allOf:
+        - type: string
+          enum:
+            - A
+            - B
     Parent:
       type: object
       properties: