feat: dereference.preservedProperties for preserving data during dereferencing

docs/options.md

@@ -83,3 +83,4 @@ The `dereference` options control how JSON Schema $Ref Parser will dereference `
 | `excludedPathMatcher` | `(string) => boolean` | A function, called for each path, which can return true to stop this path and all subpaths from being dereferenced further. This is useful in schemas where some subpaths contain literal `$ref` keys that should not be dereferenced. |
 | `onCircular` | `(string) => void` | A function, called immediately after detecting a circular `$ref` with the circular `$ref` in question. |
 | `onDereference` | `(string, JSONSchemaObjectType, JSONSchemaObjectType, string) => void` | A function, called immediately after dereferencing, with: the resolved JSON Schema value, the `$ref` being dereferenced, the object holding the dereferenced prop, the dereferenced prop name. |
+| `preservedProperties` | `string[]` | An array of properties to preserve when dereferencing a `$ref` schema. Useful if you want to enforce non-standard dereferencing behavior like present in the OpenAPI 3.1 specification where `description` and `summary` properties are preserved when alongside a `$ref` pointer. |

lib/dereference.ts

@@ -123,7 +123,27 @@ function crawl<S extends object = JSONSchema, O extends ParserOptions<S> = Parse
  circular = dereferenced.circular;
  // Avoid pointless mutations; breaks frozen objects to no profit
  if (obj[key] !== dereferenced.value) {
+ // If we have properties we want to preserve from our derefernced schema then we need
+ // to copy them over to our new object.
+ const preserved: Map<string, unknown> = new Map();
+ if (typeof obj[key] === "object" && !Array.isArray(obj[key])) {
+ (derefOptions?.preservedProperties || []).forEach((prop) => {
+ if (prop in obj[key]) {
+ preserved.set(prop, obj[key][prop]);
+ }
+ });
+ }
+
  obj[key] = dereferenced.value;
+
+ // If we have data to preserve and our dereferenced object is still an object then
+ // we need copy back our preserved data into our dereferenced schema.
+ if (preserved.size && typeof obj[key] === "object" && !Array.isArray(obj[key])) {
+ preserved.forEach((value, prop) => {
+ obj[key][prop] = value;
+ });
+ }
+
  derefOptions?.onDereference?.(value.$ref, obj[key], obj, key);
  }
  } else {

lib/options.ts

@@ -46,6 +46,16 @@ export interface DereferenceOptions {
  */
  onDereference?(path: string, value: JSONSchemaObject, parent?: JSONSchemaObject, parentPropName?: string): void;
 
+ /**
+ * An array of properties to preserve when dereferencing a `$ref` schema. Useful if you want to
+ * enforce non-standard dereferencing behavior like present in the OpenAPI 3.1 specification where
+ * `description` and `summary` properties are preserved when alongside a `$ref` pointer.
+ *
+ * If none supplied then no properties will be preserved and the object will be fully replaced
+ * with the dereferenced `$ref`.
+ */
+ preservedProperties?: string[];
+
  /**
  * Whether a reference should resolve relative to its directory/path, or from the cwd
  *

lib/util/errors.ts

@@ -126,7 +126,7 @@ export class MissingPointerError extends JSONParserError {
  public targetToken: any;
  public targetRef: string;
  public targetFound: string;
- public parentPath: string; 
+ public parentPath: string;
  constructor(token: any, path: any, targetRef: any, targetFound: any, parentPath: any) {
  super(`Missing $ref pointer "${getHash(path)}". Token "${token}" does not exist.`, stripHash(path));
 

test/specs/dereference-preservedProperties/dereference-preservedProperties.spec.ts

@@ -0,0 +1,41 @@
+import { describe, it } from "vitest";
+import $RefParser from "../../../lib/index.js";
+import pathUtils from "../../utils/path.js";
+
+import { expect } from "vitest";
+import type { Options } from "../../../lib/options";
+
+describe("dereference.preservedProperties", () => {
+ it("should preserve properties", async () => {
+ const parser = new $RefParser();
+ const schema = pathUtils.rel("test/specs/dereference-preservedProperties/dereference-preservedProperties.yaml");
+ const options = {
+ dereference: {
+ preservedProperties: ["description"],
+ },
+ } as Options;
+ const res = await parser.dereference(schema, options);
+
+ expect(res).to.deep.equal({
+ title: "Person",
+ required: ["name"],
+ type: "object",
+ definitions: {
+ name: {
+ type: "string",
+ description: "Someone's name",
+ },
+ },
+ properties: {
+ name: {
+ type: "string",
+ description: "Someone's name",
+ },
+ secretName: {
+ type: "string",
+ description: "Someone's secret name",
+ },
+ },
+ });
+ });
+});

test/specs/dereference-preservedProperties/dereference-preservedProperties.yaml

@@ -0,0 +1,16 @@
+title: Person
+required:
+ - name
+type: object
+definitions:
+ name:
+ type: string
+ description: Someone's name
+properties:
+ name:
+ $ref: "#/definitions/name"
+ secretName:
+ $ref: "#/definitions/name"
+ # Despite "Someone's name" being the description of the referenced `name` schema our overwritten
+ # description should be preserved instead.
+ description: Someone's secret name