support $anchor

src/jsonSchema.ts

@@ -62,6 +62,7 @@ export interface JSONSchema {
 	dependentRequired?: { [prop: string]: string[] };
 	dependentSchemas?: JSONSchemaMap;
 	$defs?: { [name: string]: JSONSchema };
+	$anchor?: string;
 
 	// schema 2020-12
 	prefixItems?: JSONSchemaRef[];

src/services/jsonSchemaService.ts

@@ -12,7 +12,7 @@ import { SchemaRequestService, WorkspaceContextService, PromiseConstructor, Then
 
 import * as nls from 'vscode-nls';
 import { createRegex } from '../utils/glob';
-import { isObject } from '../utils/objects';
+import { isObject, isString } from '../utils/objects';
 
 const localize = nls.loadMessageBundle();
 
@@ -520,12 +520,10 @@ export class JSONSchemaService implements IJSONSchemaService {
 			const result = new Map<string, JSONSchema>();
 			this.traverseNodes(root, next => {
 				const id = next.$id || next.id;
-				if (typeof id === 'string' && id.charAt(0) === '#') {
-					// delete next.$id;
-					// delete next.id;
-					const anchor = id.substring(1);
+				const anchor = isString(id) && id.charAt(0) === '#' ? id.substring(1) : next.$anchor;
+				if (anchor) {
 					if (result.has(anchor)) {
-						resolveErrors.push(localize('json.schema.duplicateid', 'Duplicate id declaration: \'{0}\'', id));
+						resolveErrors.push(localize('json.schema.duplicateid', 'Duplicate anchor declaration: \'{0}\'', anchor));
 					} else {
 						result.set(anchor, next);
 					}

src/test/schema.test.ts

@@ -312,6 +312,46 @@ suite('JSON Schema', () => {
 		});
 	});
 
+	test('Resolving $refs to local $anchors', async function () {
+		const service = new SchemaService.JSONSchemaService(newMockRequestService(), workspaceContext);
+
+		service.setSchemaContributions({
+			schemas: {
+				"https://example.com/schemas/address": {
+					"$id": "https://example.com/schemas/address",
+
+					"type": "object",
+					"properties": {
+						"street_address":
+						{
+							"$anchor": "street_address",
+							"type": "string"
+						},
+						"city": { "type": "string" },
+						"state": { "type": "string" }
+					},
+					"required": ["street_address", "city", "state"]
+				},
+				"https://example.com/schemas/customer": {
+					"$id": "https://example.com/schemas/customer",
+
+					"type": "object",
+					"properties": {
+						"first_name": { "type": "string" },
+						"last_name": { "type": "string" },
+						"street_address": { "$ref": "/schemas/address#street_address" },
+					}
+				}
+			}
+		});
+
+		const fs = await service.getResolvedSchema('https://example.com/schemas/customer');
+		assert.deepStrictEqual(fs?.schema.properties?.street_address, {
+			type: 'string',
+			$anchor: "street_address"
+		});
+	});
+
 	test('Resolving $refs to external $ids', async function () {
 		const service = new SchemaService.JSONSchemaService(newMockRequestService(), workspaceContext);
 		service.setSchemaContributions({