Fix sindresorhus#80

source/index.ts

@@ -103,6 +103,7 @@ export default class Conf<T extends Record<string, any> = Record<string, unknown
 			const schema: JSONSchema = {
 				type: 'object',
 				properties: options.schema,
+				...options.rootSchema,
 			};
 
 			this.#validator = ajv.compile(schema);
@@ -112,6 +113,8 @@ export default class Conf<T extends Record<string, any> = Record<string, unknown
 					this.#defaultValues[key as keyof T] = value.default; // eslint-disable-line @typescript-eslint/no-unsafe-assignment
 				}
 			}
+		} else if (options.rootSchema) {
+			throw new TypeError('`schema` option required to use `rootSchema`.');
 		}
 
 		if (options.defaults) {

source/types.ts

@@ -50,6 +50,13 @@ export type Options<T extends Record<string, any>> = {
 	*/
 	schema?: Schema<T>;
 
+	/**
+	Top-level properties for the schema.
+
+	Requires a `schema` option to be provided, and cannot contain a `properties` field.
+	*/
+	rootSchema?: Omit<TypedJSONSchema, 'properties'>;
+
 	/**
 	Name of the config file (without extension).
 

test/index.ts

@@ -787,6 +787,28 @@ test('schema - validate Conf default', t => {
 	}, {message: 'Config schema violation: `foo` must be string'});
 });
 
+test('schema - rootSchema without schema', t => {
+	t.throws(() => {
+		new Conf({
+			cwd: temporaryDirectory(),
+			rootSchema: {},
+		});
+	}, {message: '`schema` option required to use `rootSchema`.'});
+});
+
+test('schema - validate rootSchema', t => {
+	t.throws(() => {
+		const config = new Conf({
+			cwd: temporaryDirectory(),
+			schema: {},
+			rootSchema: {
+				additionalProperties: false,
+			},
+		});
+		config.set('foo', 'bar');
+	}, {message: 'Config schema violation: `` must NOT have additional properties'});
+});
+
 test('.get() - without dot notation', t => {
 	t.is(t.context.configWithoutDotNotation.get('foo'), undefined);
 	t.is(t.context.configWithoutDotNotation.get('foo', '🐴'), '🐴');