Never create inline model for allOf with single $ref (#18945)

Fixes #15077

The previous fix for this in #16096 is incomplete because it still
generates unnecessary inline models when readOnly or
nullable is used in conjunction with other properties like
description.
This commit fixes the logic error and adds testcases.

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

@@ -231,7 +231,9 @@ public class InlineModelResolver {
                 if (schema.equals(c)) {
                     return isModelNeeded((Schema) schema.getAllOf().get(0), visitedSchemas);
                 }
-            } else if (isSingleAllOf && StringUtils.isNotEmpty(((Schema) schema.getAllOf().get(0)).get$ref())) {
+            }
+
+            if (isSingleAllOf && StringUtils.isNotEmpty(((Schema) schema.getAllOf().get(0)).get$ref())) {
                 // single allOf and it's a ref
                 return isModelNeeded((Schema) schema.getAllOf().get(0), visitedSchemas);
             }

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

@@ -1171,4 +1171,30 @@ public class InlineModelResolverTest {
                 ((Schema) inlineFormParaemter.getProperties().get("enum_form_string")).get$ref());
 
     }
+
+    @Test
+    public void doNotWrapSingleAllOfRefs() {
+        OpenAPI openAPI = TestUtils.parseSpec("src/test/resources/3_0/issue_15077.yaml");
+        new InlineModelResolver().flatten(openAPI);
+
+        // None of these cases should be wrapped in an inline schema and should reference the original schema "NumberRange"
+        Schema limitsModel = (Schema) openAPI.getComponents().getSchemas().get("Limits");
+        final String numberRangeRef = "#/components/schemas/NumberRange";
+
+        Schema allOfRef = (Schema) limitsModel.getProperties().get("allOfRef");
+        assertNotNull(allOfRef.getAllOf());
+        assertEquals(numberRangeRef, ((Schema) allOfRef.getAllOf().get(0)).get$ref());
+
+        Schema allOfRefWithDescription = (Schema) limitsModel.getProperties().get("allOfRefWithDescription");
+        assertNotNull(allOfRefWithDescription.getAllOf());
+        assertEquals(numberRangeRef, ((Schema) allOfRefWithDescription.getAllOf().get(0)).get$ref());
+
+        Schema allOfRefWithReadonly = (Schema) limitsModel.getProperties().get("allOfRefWithReadonly");
+        assertNotNull(allOfRefWithReadonly.getAllOf());
+        assertEquals(numberRangeRef, ((Schema) allOfRefWithReadonly.getAllOf().get(0)).get$ref());
+
+        Schema allOfRefWithDescriptionAndReadonly = (Schema) limitsModel.getProperties().get("allOfRefWithDescriptionAndReadonly");
+        assertNotNull(allOfRefWithDescriptionAndReadonly.getAllOf());
+        assertEquals(numberRangeRef, ((Schema) allOfRefWithDescriptionAndReadonly.getAllOf().get(0)).get$ref());
+    }
 }

modules/openapi-generator/src/test/resources/3_0/issue_15077.yaml

@@ -0,0 +1,53 @@
+openapi: 3.0.0
+info:
+  version: 1.0.0
+  title: Property refs using allOf
+paths:
+  /limits:
+    get:
+      operationId: getLimits
+      responses:
+        '200':
+          description: OK
+          content:
+            application/json:
+              schema:
+                $ref: '#/components/schemas/Limits'
+components:
+  schemas:
+    NumberRange:
+      type: object
+      properties:
+        min:
+          type: number
+        max:
+          type: number
+      required:
+        - min
+        - max
+    Limits:
+      type: object
+      properties:
+        allOfRef:
+          allOf:
+            - $ref: '#/components/schemas/NumberRange'
+        allOfRefWithDescription:
+          description: |
+            Description for this property
+          allOf:
+            - $ref: '#/components/schemas/NumberRange'
+        allOfRefWithReadonly:
+          readOnly: true
+          allOf:
+            - $ref: '#/components/schemas/NumberRange'
+        allOfRefWithDescriptionAndReadonly:
+          description: |
+            Description for this readonly property
+          readOnly: true
+          allOf:
+            - $ref: '#/components/schemas/NumberRange'
+      required:
+        - allOfRef
+        - allOfRefWithDescription
+        - allOfRefWithReadonly
+        - allOfRefWithDescriptionAndReadonly

modules/openapi-generator/src/test/resources/3_0/java/petstore-with-fake-endpoints-models-for-testing-okhttp-gson.yaml

@@ -1217,7 +1217,7 @@ paths:
       operationId: getParameterNameMapping
       parameters:
         - name: _type
-          in: header 
+          in: header
           description: _type
           required: true
           schema:
@@ -1230,7 +1230,7 @@ paths:
           schema:
             type: string
         - name: type_
-          in: header 
+          in: header
           description: type_
           required: true
           schema:
@@ -1246,7 +1246,7 @@ paths:
       operationId: getParameterStringNumber
       parameters:
         - name: string_number
-          in: header 
+          in: header
           description: string number
           required: true
           schema:
@@ -2600,6 +2600,17 @@ components:
         category_allOf_ref:
           allOf:
             - $ref: '#/components/schemas/Category'
+        category_allOf_ref_description:
+          description: |
+            Adding description to property using allOf
+          allOf:
+            - $ref: '#/components/schemas/Category'
+        category_allOf_ref_description_readonly:
+          description: |
+            Adding description to readonly property using allOf
+          readOnly: true
+          allOf:
+            - $ref: '#/components/schemas/Category'
         name:
           type: string
           example: doggie