From 4ef67884962b6aac61cc895aaa3ba16aa892ecf4 Mon Sep 17 00:00:00 2001
From: ulrichb <ulrich.b@gmx.at>
Date: Tue, 21 Apr 2020 18:30:43 +0200
Subject: [PATCH] feat(experimental-utils): allow rule options to be a readonly
 tuple (#1924)

---
 .../experimental-utils/src/eslint-utils/RuleCreator.ts    | 2 +-
 .../experimental-utils/src/eslint-utils/applyDefault.ts   | 8 ++++++--
 2 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/packages/experimental-utils/src/eslint-utils/RuleCreator.ts b/packages/experimental-utils/src/eslint-utils/RuleCreator.ts
index f9278dc8154..4dede52bd7c 100644
--- a/packages/experimental-utils/src/eslint-utils/RuleCreator.ts
+++ b/packages/experimental-utils/src/eslint-utils/RuleCreator.ts
@@ -17,7 +17,7 @@ function RuleCreator(urlCreator: (ruleName: string) => string) {
   // This function will get much easier to call when this is merged https://github.com/Microsoft/TypeScript/pull/26349
   // TODO - when the above PR lands; add type checking for the context.report `data` property
   return function createRule<
-    TOptions extends unknown[],
+    TOptions extends readonly unknown[],
     TMessageIds extends string,
     TRuleListener extends RuleListener = RuleListener
   >({
diff --git a/packages/experimental-utils/src/eslint-utils/applyDefault.ts b/packages/experimental-utils/src/eslint-utils/applyDefault.ts
index 142c8d1a746..9b4f6513ecc 100644
--- a/packages/experimental-utils/src/eslint-utils/applyDefault.ts
+++ b/packages/experimental-utils/src/eslint-utils/applyDefault.ts
@@ -7,12 +7,14 @@ import { deepMerge, isObjectNotArray } from './deepMerge';
  * @param userOptions the user opts
  * @returns the options with defaults
  */
-function applyDefault<TUser extends unknown[], TDefault extends TUser>(
+function applyDefault<TUser extends readonly unknown[], TDefault extends TUser>(
   defaultOptions: TDefault,
   userOptions: TUser | null,
 ): TDefault {
   // clone defaults
-  const options: TDefault = JSON.parse(JSON.stringify(defaultOptions));
+  const options: AsMutable<TDefault> = JSON.parse(
+    JSON.stringify(defaultOptions),
+  );
 
   if (userOptions === null || userOptions === undefined) {
     return options;
@@ -33,4 +35,6 @@ function applyDefault<TUser extends unknown[], TDefault extends TUser>(
   return options;
 }
 
+type AsMutable<T extends {}> = { -readonly [TKey in keyof T]: T[TKey] };
+
 export { applyDefault };