feat: support prefixItems for draft 2020-12

Author: kylef

Sources/Applicators/items.swift

@@ -3,16 +3,26 @@ func items(context: Context, items: Any, instance: Any, schema: [String: Any]) t
     return AnySequence(EmptyCollection())
   }
 
+  let instances: [(Int, Any)]
+  if let prefixItems = schema["prefixItems"] as? [Any] {
+    guard instance.count > prefixItems.count else {
+      return AnySequence(EmptyCollection())
+    }
+    instances = Array(Array(instance.enumerated())[prefixItems.count...])
+  } else {
+    instances = Array(instance.enumerated())
+  }
+
   if let items = items as? [String: Any] {
-    return try AnySequence(Array(instance.enumerated()).map { (index, instance) throws -> AnySequence<ValidationError> in
+    return try AnySequence(instances.map { (index, instance) throws -> AnySequence<ValidationError> in
       context.instanceLocation.push(index.description)
       defer { context.instanceLocation.pop() }
       return try context.descend(instance: instance, subschema: items)
     }.joined())
   }
 
   if let items = items as? Bool {
-    return try AnySequence(Array(instance.enumerated()).map { (index, instance) throws -> AnySequence<ValidationError> in
+    return try AnySequence(instances.map { (index, instance) throws -> AnySequence<ValidationError> in
       context.instanceLocation.push(index.description)
       defer { context.instanceLocation.pop() }
       return try context.descend(instance: instance, subschema: items)
@@ -22,7 +32,7 @@ func items(context: Context, items: Any, instance: Any, schema: [String: Any]) t
   if let items = items as? [Any] {
     var results = [AnySequence<ValidationError>]()
 
-    for (index, item) in instance.enumerated() where index < items.count {
+    for (index, item) in instances where index < items.count {
       context.instanceLocation.push(index.description)
       defer { context.instanceLocation.pop() }
       results.append(try context.descend(instance: item, subschema: items[index]))

Sources/Draft202012Validator.swift

@@ -36,7 +36,7 @@ public class Draft202012Validator: Validator {
     "minProperties": minProperties,
     "maxProperties": maxProperties,
     "items": items,
-    "additionalItems": additionalItems,
+    "prefixItems": prefixItems,
     "patternProperties": patternProperties,
     "additionalProperties": additionalProperties,
     "$ref": ref,

Tests/JSONSchemaTests/JSONSchemaCases.swift

@@ -196,10 +196,7 @@ class JSONSchemaCases: XCTestCase {
       "id.json",
 
       "ref.json",
-      "uniqueItems.json",
-      "prefixItems.json",
       "dynamicRef.json",
-      "items.json",
 
       // unsupported
       "unevaluatedProperties.json",