feat(eslint-plugin): [prefer-readonly-parameter-types] add ignoreInferredTypes option (#2668)

Author: eyelidlessness

Diff for: packages/eslint-plugin/docs/rules/prefer-readonly-parameter-types.md

@@ -124,10 +124,12 @@ interface Foo {
 ```ts
 interface Options {
   checkParameterProperties?: boolean;
+  ignoreInferredTypes?: boolean;
 }
 
 const defaultOptions: Options = {
   checkParameterProperties: true,
+  ignoreInferredTypes: false,
 };
 ```
 
@@ -162,3 +164,53 @@ class Foo {
   ) {}
 }
 ```
+
+### `ignoreInferredTypes`
+
+This option allows you to ignore parameters which don't explicitly specify a type. This may be desirable in cases where an external dependency specifies a callback with mutable parameters, and manually annotating the callback's parameters is undesirable.
+
+Examples of **incorrect** code for this rule with `{ignoreInferredTypes: true}`:
+
+```ts
+import { acceptsCallback, CallbackOptions } from 'external-dependency';
+
+acceceptsCallback((options: CallbackOptions) => {});
+```
+
+<details>
+<summary>external-dependency.d.ts</summary>
+
+```ts
+export interface CallbackOptions {
+  prop: string;
+}
+type Callback = (options: CallbackOptions) => void;
+type AcceptsCallback = (callback: Callback) => void;
+
+export const acceptsCallback: AcceptsCallback;
+```
+
+</details>
+
+Examples of **correct** code for this rule with `{ignoreInferredTypes: true}`:
+
+```ts
+import { acceptsCallback } from 'external-dependency';
+
+acceceptsCallback(options => {});
+```
+
+<details>
+<summary>external-dependency.d.ts</summary>
+
+```ts
+export interface CallbackOptions {
+  prop: string;
+}
+type Callback = (options: CallbackOptions) => void;
+type AcceptsCallback = (callback: Callback) => void;
+
+export const acceptsCallback: AcceptsCallback;
+```
+
+</details>

Diff for: packages/eslint-plugin/src/rules/prefer-readonly-parameter-types.ts

@@ -7,6 +7,7 @@ import * as util from '../util';
 type Options = [
   {
     checkParameterProperties?: boolean;
+    ignoreInferredTypes?: boolean;
   },
 ];
 type MessageIds = 'shouldBeReadonly';
@@ -30,6 +31,9 @@ export default util.createRule<Options, MessageIds>({
           checkParameterProperties: {
             type: 'boolean',
           },
+          ignoreInferredTypes: {
+            type: 'boolean',
+          },
         },
       },
     ],
@@ -40,9 +44,11 @@ export default util.createRule<Options, MessageIds>({
   defaultOptions: [
     {
       checkParameterProperties: true,
+      ignoreInferredTypes: false,
     },
   ],
-  create(context, [{ checkParameterProperties }]) {
+  create(context, options) {
+    const [{ checkParameterProperties, ignoreInferredTypes }] = options;
     const { esTreeNodeToTSNodeMap, program } = util.getParserServices(context);
     const checker = program.getTypeChecker();
 
@@ -81,6 +87,11 @@ export default util.createRule<Options, MessageIds>({
             param.type === AST_NODE_TYPES.TSParameterProperty
               ? param.parameter
               : param;
+
+          if (ignoreInferredTypes && actualParam.typeAnnotation == null) {
+            continue;
+          }
+
           const tsNode = esTreeNodeToTSNodeMap.get(actualParam);
           const type = checker.getTypeAtLocation(tsNode);
           const isReadOnly = util.isTypeReadonly(checker, type);

Diff for: packages/eslint-plugin/tests/rules/prefer-readonly-parameter-types.test.ts

@@ -247,6 +247,24 @@ ruleTester.run('prefer-readonly-parameter-types', rule, {
 
       const willNotCrash = (foo: Readonly<WithSymbol>) => {};
     `,
+    {
+      code: `
+        type Callback<T> = (options: T) => void;
+
+        declare const acceptsCallback: <T>(callback: Callback<T>) => void;
+
+        interface CallbackOptions {
+          prop: string;
+        }
+
+        acceptsCallback<CallbackOptions>(options => {});
+      `,
+      options: [
+        {
+          ignoreInferredTypes: true,
+        },
+      ],
+    },
   ],
   invalid: [
     // arrays
@@ -671,5 +689,31 @@ ruleTester.run('prefer-readonly-parameter-types', rule, {
         },
       ],
     },
+    {
+      code: `
+        type Callback<T> = (options: T) => void;
+
+        declare const acceptsCallback: <T>(callback: Callback<T>) => void;
+
+        interface CallbackOptions {
+          prop: string;
+        }
+
+        acceptsCallback<CallbackOptions>((options: CallbackOptions) => {});
+      `,
+      options: [
+        {
+          ignoreInferredTypes: true,
+        },
+      ],
+      errors: [
+        {
+          messageId: 'shouldBeReadonly',
+          line: 10,
+          column: 43,
+          endColumn: 67,
+        },
+      ],
+    },
   ],
 });