fix(converter): keep x-nullable in shared $ref responses

modules/swagger-parser-v2-converter/src/main/java/io/swagger/v3/parser/converter/SwaggerConverter.java

@@ -59,15 +59,13 @@
 
 
 import java.math.BigDecimal;
-import java.util.ArrayList;
-import java.util.HashMap;
-import java.util.LinkedHashMap;
-import java.util.List;
-import java.util.Map;
-import java.util.Optional;
+import java.util.*;
 import java.util.stream.Collectors;
 
 public class SwaggerConverter implements SwaggerParserExtension {
+
+    private static final Set<String> STRIPPED_EXTENSION_KEYS = Collections.unmodifiableSet(new HashSet<>(Arrays.asList("x-example", "x-examples", "x-nullable")));
+
     private List<String> globalConsumes = new ArrayList<>();
     private List<String> globalProduces = new ArrayList<>();
     private Components components = new Components();
@@ -654,14 +652,17 @@ public Operation convert(io.swagger.models.Operation v2Operation) {
     }
 
     private Map<String, Object> convert(Map<String, Object> vendorExtensions) {
-        if (vendorExtensions != null && vendorExtensions.size() > 0) {
-            vendorExtensions.entrySet().removeIf(extension -> (
-                    extension.getKey().equals("x-example")) ||
-                    extension.getKey().equals("x-examples") ||
-                    extension.getKey().equals("x-nullable"));
+        if (vendorExtensions == null || vendorExtensions.isEmpty()) {
+            return vendorExtensions;
         }
 
-        return vendorExtensions;
+        Map<String, Object> result = new LinkedHashMap<>();
+        for (Map.Entry<String, Object> entry : vendorExtensions.entrySet()) {
+            if (!STRIPPED_EXTENSION_KEYS.contains(entry.getKey())) {
+                result.put(entry.getKey(), entry.getValue());
+            }
+        }
+        return result;
     }
 
     private Schema convertFormDataToSchema(io.swagger.models.parameters.Parameter formParam) {

modules/swagger-parser-v2-converter/src/test/java/io/swagger/parser/test/V2ConverterTest.java

@@ -100,6 +100,7 @@ public class V2ConverterTest {
 
     private static final String ISSUE_1767_YAML = "issue-1767.yaml";
     private static final String ISSUE_1796_YAML = "issue-1796.yaml";
+    private static final String ISSUE_2269_YAML = "issue-2269.yaml";
 
     private static final String API_BATCH_PATH = "/api/batch/";
     private static final String PETS_PATH = "/pets";
@@ -928,6 +929,42 @@ public void testConvertFormDataAsObjectSchema() throws Exception {
 
     }
 
+    @Test
+    public void testIssue2269SharedResponseNullable() {
+        SwaggerConverter converter = new SwaggerConverter();
+        ParseOptions parseOptions = new ParseOptions();
+        parseOptions.setResolve(true);
+        parseOptions.setResolveFully(true);
+        SwaggerParseResult result = converter.readLocation(
+                "src/test/resources/" + ISSUE_2269_YAML, null, parseOptions);
+        assertNotNull(result);
+        OpenAPI oas = result.getOpenAPI();
+        assertNotNull(oas);
+
+        for (String endpoint : Arrays.asList("/endpoint1", "/endpoint2")) {
+            Map<String, Schema> properties = oas.getPaths().get(endpoint).getGet()
+                    .getResponses().get("200").getContent().values().iterator().next()
+                    .getSchema().getProperties();
+            assertNotNull(properties, endpoint + " schema properties must not be null");
+
+            Schema nullableField = properties.get("nullable_field");
+            assertNotNull(nullableField, endpoint + " must have nullable_field");
+            assertEquals(nullableField.getNullable(), Boolean.TRUE,
+                    endpoint + " nullable_field must have nullable: true");
+            assertNotNull(nullableField.getExtensions(), endpoint + " nullable_field must retain extensions");
+            assertEquals(nullableField.getExtensions().get("x-internal-note"), "abc",
+                    endpoint + " nullable_field must retain x-internal-note extension");
+
+            Schema nonNullableField = properties.get("non_nullable_field");
+            assertNotNull(nonNullableField, endpoint + " must have non_nullable_field");
+            assertEquals(nonNullableField.getNullable(), Boolean.FALSE,
+                    endpoint + " non_nullable_field must have nullable: false");
+            assertNotNull(nonNullableField.getExtensions(), endpoint + " non_nullable_field must retain extensions");
+            assertEquals(nonNullableField.getExtensions().get("x-internal-note"), "def",
+                    endpoint + " non_nullable_field must retain x-internal-note extension");
+        }
+    }
+
     /**
      * A clone (almost) of {@link OpenAPIV3Parser#readContents(String, List, ParseOptions)}.
      */

modules/swagger-parser-v2-converter/src/test/resources/issue-2269.yaml

@@ -0,0 +1,41 @@
+swagger: '2.0'
+info:
+  version: 1.0.0
+  title: Issue 2269 - x-nullable preservation for shared $ref responses
+
+responses:
+  SharedResponse:
+    description: A shared response with multiple fields using x-nullable
+    schema:
+      type: object
+      properties:
+        data:
+          type: string
+          description: Required field
+        nullable_field:
+          type: integer
+          x-nullable: true
+          x-internal-note: abc
+        non_nullable_field:
+          type: integer
+          x-nullable: false
+          x-internal-note: def
+      required:
+        - data
+
+paths:
+  /endpoint1:
+    get:
+      operationId: endpoint1
+      summary: First endpoint using shared response
+      responses:
+        '200':
+          $ref: '#/responses/SharedResponse'
+
+  /endpoint2:
+    get:
+      operationId: endpoint2
+      summary: Second endpoint using shared response
+      responses:
+        '200':
+          $ref: '#/responses/SharedResponse'

modules/swagger-parser/src/test/java/io/swagger/parser/OpenAPIParserTest.java

@@ -686,6 +686,32 @@ public void testIssue1552() throws Exception {
         assertNotNull(schema.getProperties().get("foo"));
     }
 
+    @Test(description = "Issue 2269: preserve x-nullable in shared responses for swagger 2.0 specs")
+    public void testSwagger2SharedResponseNullable() {
+        ParseOptions options = new ParseOptions();
+        options.setResolve(true);
+        options.setResolveFully(true);
+
+        SwaggerParseResult result = new OpenAPIParser().readLocation("issue2269.yaml", null, options);
+
+        assertNotNull(result);
+        assertNotNull(result.getOpenAPI());
+        OpenAPI openAPI = result.getOpenAPI();
+
+        Schema endpoint1Field = (Schema) openAPI.getPaths().get("/endpoint1").getGet()
+                .getResponses().get("200").getContent().values().iterator().next()
+                .getSchema().getProperties().get("optional_field");
+        assertNotNull(endpoint1Field, "Endpoint 1 should have optional_field");
+        assertEquals(endpoint1Field.getNullable(), Boolean.TRUE, "Endpoint 1 optional_field should be nullable");
+
+        Schema endpoint2Field = (Schema) openAPI.getPaths().get("/endpoint2").getGet()
+                .getResponses().get("200").getContent().values().iterator().next()
+                .getSchema().getProperties().get("optional_field");
+        assertNotNull(endpoint2Field, "Endpoint 2 should have optional_field");
+        assertEquals(endpoint2Field.getNullable(), Boolean.TRUE, "Endpoint 2 optional_field should be nullable");
+
+    }
+
     @org.testng.annotations.Test(description = "convert response schema")
     public void testIssue1552AdditionalProps() throws Exception {
         ParseOptions options = new ParseOptions();

modules/swagger-parser/src/test/resources/issue2269.yaml

@@ -0,0 +1,38 @@
+swagger: '2.0'
+info:
+  version: 1.0.0
+  title: Swagger 2.0 Shared Response Test
+  description: Test case for verifying x-nullable is preserved when multiple endpoints share the same response definition
+
+responses:
+  SharedResponse:
+    description: A shared response with nullable field
+    schema:
+      type: object
+      properties:
+        data:
+          type: string
+          description: Required field
+        optional_field:
+          type: integer
+          description: Optional nullable field
+          x-nullable: true
+      required:
+        - data
+
+paths:
+  /endpoint1:
+    get:
+      operationId: endpoint1
+      summary: First endpoint using shared response
+      responses:
+        '200':
+          $ref: '#/responses/SharedResponse'
+
+  /endpoint2:
+    get:
+      operationId: endpoint2
+      summary: Second endpoint using shared response
+      responses:
+        '200':
+          $ref: '#/responses/SharedResponse'