Add rule @typescript-eslint/prefer-readonly

Author: Shinigami92

src/rules/typescript-eslint/index.d.ts

@@ -9,6 +9,7 @@ import type { NoUnsafeAssignmentRule } from './no-unsafe-assignment';
 import type { NoUnusedVarsRule } from './no-unused-vars';
 import type { PreferNullishCoalescingRule } from './prefer-nullish-coalescing';
 import type { PreferOptionalChainRule } from './prefer-optional-chain';
+import type { PreferReadonlyRule } from './prefer-readonly';
 
 /**
  * All @typescript-eslint rules.
@@ -23,4 +24,5 @@ export type TypeScriptEslintRules = BanTsCommentRule &
   NoUnsafeAssignmentRule &
   NoUnusedVarsRule &
   PreferNullishCoalescingRule &
-  PreferOptionalChainRule;
+  PreferOptionalChainRule &
+  PreferReadonlyRule;

src/rules/typescript-eslint/prefer-readonly.d.ts

@@ -0,0 +1,39 @@
+import type { RuleConfig } from '../rule-config';
+
+/**
+ * Option.
+ */
+export type PreferReadonlyOption = {
+  /**
+   * You may pass `"onlyInlineLambdas": true` as a rule option within an object to restrict checking only to members immediately assigned a lambda value.
+   *
+   * @see [onlyInlineLambdas](https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/docs/rules/prefer-readonly.md#onlyinlinelambdas)
+   */
+  onlyInlineLambdas?: boolean;
+};
+
+/**
+ * Options.
+ */
+export type PreferReadonlyOptions = [PreferReadonlyOption?];
+
+/**
+ * Requires that private members are marked as `readonly` if they're never modified outside of the constructor.
+ *
+ * @see [prefer-readonly](https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/docs/rules/prefer-readonly.md)
+ */
+export type PreferReadonlyRuleConfig = RuleConfig<PreferReadonlyOptions>;
+
+/**
+ * Requires that private members are marked as `readonly` if they're never modified outside of the constructor.
+ *
+ * @see [prefer-readonly](https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/docs/rules/prefer-readonly.md)
+ */
+export interface PreferReadonlyRule {
+  /**
+   * Requires that private members are marked as `readonly` if they're never modified outside of the constructor.
+   *
+   * @see [prefer-readonly](https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/docs/rules/prefer-readonly.md)
+   */
+  '@typescript-eslint/prefer-readonly': PreferReadonlyRuleConfig;
+}