Tighten type checking config (#1071)

* Use more restrictive type signatures
* Don't rely on broken expect.error()

lib/modules/types.js

@@ -15,6 +15,8 @@ const Utils = require('../utils');
 const internals = {
     compiler: {
         strict: true,
+        noUncheckedIndexedAccess: true,
+        exactOptionalPropertyTypes: true,
         jsx: Ts.JsxEmit.React,
         lib: ['lib.es2020.d.ts'],
         module: Ts.ModuleKind.CommonJS,

package.json

@@ -33,7 +33,7 @@
     },
     "peerDependencies": {
         "@hapi/eslint-plugin": "^7.0.0",
-        "typescript": ">=3.6.5"
+        "typescript": ">=4.4.0"
     },
     "peerDependenciesMeta": {
         "typescript": {

test/types.js

@@ -98,6 +98,18 @@ describe('Types', () => {
                 line: 3,
                 column: 4
             },
+            {
+                filename: 'test/restrict.ts',
+                message: `Type 'undefined' is not assignable to type 'string' with 'exactOptionalPropertyTypes: true'. Consider adding 'undefined' to the type of the target.`,
+                line: 10,
+                column: 0
+            },
+            {
+                filename: 'test/restrict.ts',
+                message: `'unchecked.b' is possibly 'undefined'.`,
+                line: 15,
+                column: 0
+            },
             {
                 filename: 'test/syntax.ts',
                 message: `')' expected.`,

test/types/errors/lib/index.d.ts

@@ -8,3 +8,14 @@ export default add;
 export const sample: { readonly x: string };
 
 export function hasProperty(property: { name: string }): boolean;
+
+export interface UsesExactOptionalPropertyTypes {
+	a?: boolean | undefined;
+	b?: string;
+}
+
+export interface UncheckedIndexedAccess {
+	a: UsesExactOptionalPropertyTypes;
+
+	[prop: string]: UsesExactOptionalPropertyTypes;
+}

test/types/errors/test/restrict.ts

@@ -0,0 +1,15 @@
+import * as Lab from '../../../..';
+import type { UncheckedIndexedAccess, UsesExactOptionalPropertyTypes } from '../lib/index';
+
+const { expect } = Lab.types;
+
+const exact: UsesExactOptionalPropertyTypes = { a: true };
+
+exact.a = undefined;
+exact.b = 'ok';
+exact.b = undefined;      // Fails
+
+const unchecked: UncheckedIndexedAccess = { a: exact, b: {} };
+
+unchecked.a.a;
+unchecked.b.a;      // Fails