fix(core): follow ApiResponse $ref in SpecFilter to avoid pruning schemas

Fixes #4960

Author: kuntal1461

modules/swagger-core/src/main/java/io/swagger/v3/core/filter/SpecFilter.java

@@ -36,6 +36,7 @@
 
 public class SpecFilter {
 
+    private OpenAPI _ctxOpenAPI;
     public OpenAPI filter(OpenAPI openAPI, OpenAPISpecFilter filter, Map<String, List<String>> params, Map<String, String> cookies, Map<String, List<String>> headers) {
         OpenAPI filteredOpenAPI = filterOpenAPI(filter, openAPI, params, cookies, headers);
         if (filteredOpenAPI == null) {
@@ -399,6 +400,26 @@ private void addPathItemSchemaRef(PathItem pathItem, Set<String> referencedDefin
     }
 
     private void addApiResponseSchemaRef(ApiResponse response, Set<String> referencedDefinitions) {
+       if (response == null)  return;
+       String respRef = response.get$ref();
+       if (respRef != null && !respRef.isEmpty() && _ctxOpenAPI != null) {
+        String name = (String) RefUtils.extractSimpleName(respRef).getLeft();
+        referencedDefinitions.add(name);
+        Components comps = _ctxOpenAPI.getComponents();
+        ApiResponse resolved = (comps != null && comps.getResponses() != null)
+                ? comps.getResponses().get(name)
+                : null;
+        if (resolved != null) {
+            if (resolved.getHeaders() != null) {
+                for (Header h : resolved.getHeaders().values()) {
+                    addHeaderSchemaRef(h, referencedDefinitions);
+                }
+            }
+            addContentSchemaRef(resolved.getContent(), referencedDefinitions);
+        }
+        return;
+       }
+       
         if (response.getHeaders() != null) {
             for (String keyHeaders : response.getHeaders().keySet()) {
                 Header header = response.getHeaders().get(keyHeaders);
@@ -469,7 +490,7 @@ private void addComponentsSchemaRef(Components components, Set<String> reference
     }
 
     protected OpenAPI removeBrokenReferenceDefinitions(OpenAPI openApi) {
-
+        this._ctxOpenAPI = openApi;
         if (openApi == null || openApi.getComponents() == null || openApi.getComponents().getSchemas() == null) {
             return openApi;
         }
@@ -499,6 +520,7 @@ protected OpenAPI removeBrokenReferenceDefinitions(OpenAPI openApi) {
                 .retainAll(referencedDefinitions.stream()
                         .map(s -> (String) RefUtils.extractSimpleName(s).getLeft())
                         .collect(Collectors.toSet()));
+        this._ctxOpenAPI = null;
         return openApi;
     }