Add key information to instance location when validating required fields of a schema

Package.swift

@@ -5,7 +5,7 @@ import PackageDescription
 let package = Package(
   name: "JSONSchema",
   platforms: [
-    .macOS(.v10_13),
+    .macOS(.v10_13), .iOS(.v11), .tvOS(.v11)
   ],
   products: [
     .library(name: "JSONSchema", targets: ["JSONSchema"]),

Sources/RefResolver.swift

@@ -1,9 +1,15 @@
 import Foundation
 
 func urlSplitFragment(url: String) -> (String, String) {
+  #if swift(>=5.0)
+  guard let hashIndex = url.firstIndex(of: "#") else {
+    return (url, "")
+  }
+  #else
   guard let hashIndex = url.index(of: "#") else {
     return (url, "")
   }
+  #endif
 
   return (
     String(url.prefix(upTo: hashIndex)),

Sources/Validation/required.swift

@@ -10,6 +10,8 @@ func required(context: Context, required: Any, instance: Any, schema: [String: A
 
   return AnySequence(required.compactMap { key -> ValidationError? in
     guard !instance.keys.contains(key) else { return nil }
+    context.instanceLocation.push(key)
+    defer { context.instanceLocation.pop() }
     return ValidationError(
       "Required property '\(key)' is missing",
       instanceLocation: context.instanceLocation,

Tests/JSONSchemaTests/Validation/TestRequired.swift

@@ -21,7 +21,7 @@ public let testRequired: ((ContextType) -> Void) = {
       let error = errors[0]
 
       try expect(error.description) == "Required property 'test' is missing"
-      try expect(error.instanceLocation.path) == "/0"
+      try expect(error.instanceLocation.path) == "/0/test"
       try expect(error.keywordLocation.path) == "#/items/required"
     }
   }