fix: additionalItems must be ignored when items != array

Author: sagold

src/SchemaNode.ts

@@ -114,7 +114,18 @@ export interface SchemaNode extends SchemaNodeMethodsType {
     $id?: string;
     $defs?: Record<string, SchemaNode>;
     $ref?: string;
-    /** only used for draft <= 2019-09 */
+    /**
+     * # Items-object schema for additional items for drafts <= 2019-09
+     *
+     * - `additionalItems` is ignored when items-schema is not an array
+     *
+     *  If `items` is present, and its annotation result is a number, validation succeeds if every
+     *  instance element at an index greater than that number validates against "additionalItems".
+     *  Otherwise, if `items` is absent or its annotation result is the boolean true,
+     * `additionalItems` is ignored.
+     *
+     * [Specification](https://json-schema.org/draft/2019-09/draft-handrews-json-schema-02#additionalItems)
+     */
     additionalItems?: SchemaNode;
     additionalProperties?: SchemaNode;
     allOf?: SchemaNode[];
@@ -124,7 +135,39 @@ export interface SchemaNode extends SchemaNodeMethodsType {
     dependentSchemas?: Record<string, SchemaNode | boolean>;
     else?: SchemaNode;
     if?: SchemaNode;
+    /**
+     * # Items-array schema for all drafts
+     *
+     * - for drafts prior 2020-12 items[]-schema stored as `prefixItems`
+     *
+     * Validation succeeds if each element of the instance validates against the schema at the
+     * same position, if any.
+     *
+     * The `prefixItems` keyword restricts a number of items from the start of an array instance
+     * to validate against the given sequence of subschemas, where the item at a given index in
+     * the array instance is evaluated against the subschema at the given index in the `prefixItems`
+     * array, if any. Array items outside the range described by the `prefixItems` keyword is
+     * evaluated against the items keyword, if present.
+     *
+     * [Docs](https://www.learnjsonschema.com/2020-12/applicator/prefixitems/)
+     * | [Examples](https://json-schema.org/understanding-json-schema/reference/array#tupleValidation)
+     */
     prefixItems?: SchemaNode[];
+    /**
+     * # Items-object schema
+     *
+     * - ⚠️ For drafts < 2020-12, `additionalItems` is still used and must be referenced by `node.additionalItems`
+     *
+     * Validation succeeds if each element of the instance not covered by `prefixItems` validates
+     * against this schema.
+     *
+     * The items keyword restricts array instance items not described by the sibling `prefixItems`
+     * keyword (if any), to validate against the given subschema. Whetherthis keyword was evaluated
+     * against any item of the array instance is reported using annotations.
+     *
+     * [Docs](https://www.learnjsonschema.com/2020-12/applicator/items/)
+     * | [Examples](https://json-schema.org/understanding-json-schema/reference/array#items)
+     */
     items?: SchemaNode;
     not?: SchemaNode;
     oneOf?: SchemaNode[];

src/draft2019-09/keywords/additionalItems.ts

@@ -12,17 +12,14 @@ export const additionalItemsKeyword: Keyword = {
     addResolve: (node: SchemaNode) => node.additionalItems != null,
     resolve: additionalItemsResolver,
     addValidate: ({ schema }) =>
-        schema.additionalItems != null &&
-        schema.additionalItems !== true &&
-        schema.items != null &&
-        !isObject(schema.items),
+        schema.additionalItems != null && schema.additionalItems !== true && Array.isArray(schema.items),
     validate: validateAdditionalItems
 };
 
 // must come as last resolver
 export function parseAdditionalItems(node: SchemaNode) {
     const { schema, evaluationPath, schemaLocation } = node;
-    if (isObject(schema.additionalItems) || schema.additionalItems === true) {
+    if ((isObject(schema.additionalItems) || schema.additionalItems === true) && Array.isArray(schema.items)) {
         node.additionalItems = node.compileSchema(
             schema.additionalItems,
             `${evaluationPath}/additionalItems`,

src/draft2019-09/methods/getChildSchemaSelection.test.ts

@@ -129,6 +129,7 @@ describe("getChildSelection (2019)", () => {
             const result = compileSchema({
                 $schema: "draft-2019-09",
                 type: "array",
+                items: [],
                 additionalItems: { id: "number", type: "number", default: 2 }
             }).getChildSelection(1);
 

src/draft2019-09/methods/getData.test.ts

@@ -835,6 +835,7 @@ describe("getData (2019)", () => {
                     $schema: "draft-2019-09",
                     type: "array",
                     minItems: 2,
+                    items: [],
                     additionalItems: {
                         type: "number",
                         default: 2