feat: support keywordLocation for $ref relative

Author: kylef

Sources/Validator.swift

@@ -34,6 +34,8 @@ class Context {
     if validator is Draft4Validator || validator is Draft6Validator {
       // Older versions of JSON Schema, $ref ignores any alongside keywords
       if let ref = schema["$ref"] as? String {
+        keywordLocation.push("$ref")
+        defer { keywordLocation.pop() }
         let validation = validator.validations["$ref"]!
         return try validation(self, ref, instance, schema)
       }

Tests/JSONSchemaTests/Validation/TestRef.swift

@@ -0,0 +1,33 @@
+import XCTest
+@testable import JSONSchema
+
+
+class RefTests: XCTestCase {
+  func testRefWithErrorInSubschema() throws {
+    let schema: [String: Any] = [
+      "$schema": "http://json-schema.org/draft-07/schema#",
+      "items": [
+        "$ref": "#/definitions/name",
+      ],
+      "definitions": [
+        "name": [
+          "type": "string",
+        ],
+      ],
+    ]
+
+    let result = try validate([true], schema: schema)
+
+    switch result {
+    case .valid:
+      XCTFail("Validation should fail")
+    case .invalid(let errors):
+      XCTAssertEqual(errors.count, 1)
+      let error = errors[0]
+
+      XCTAssertEqual(error.description, "'true' is not of type 'string'")
+      XCTAssertEqual(error.instanceLocation.path, "/0")
+      XCTAssertEqual(error.keywordLocation.path, "#/items/$ref/type")
+    }
+  }
+}