TypesScript types issue with node with readonly array and .map, .each on AstPath

[timotheeguerin]

Environments:

• Prettier Version: 3.0.0
• Running Prettier via: n/a / TypeScript
• Runtime: Node v18.16.0, Typescript 5.1
• Operating System: MacOS
• Prettier plugins (if any): Issue happen when writing a plugin

Typescript produce an error when trying to use .map for a property that is a readonly array.

Steps to reproduce:

Using the following typescript code will produce an error when trying to .map a property that is a readonly array(same for .each)

import { AstPath } from "prettier";

interface TestNode {
  regularArray: string[];
  readonlyArray: readonly string[];
}

const path: AstPath<TestNode> = undefined as any;

// Works fine
path.map(() => "", "regularArray");
// Ts error
path.map(() => "", "readonlyArray");
//                 ^ Argument of type '"readonlyArray"' is not assignable to parameter of type '"regularArray"'.ts(2345)

Expected behavior:
Should not be any difference between a readonly and regular array.

Actual behavior:
Typescript produce an error when trying to use .map for a property that is a readonly array.

[auvred]

It guess that to fix this issue it is enough to add readonly here:

prettier/src/index.d.ts

Line 36 in 6e5dee0

[K in keyof T]: NonNullable<T[K]> extends any[] ? K : never;

type ArrayProperties<T> = { 
   [K in keyof T]: NonNullable<T[K]> extends readonly any[] ? K : never; 
 }[keyof T];  //                               ^ here

TS Playground

If this is correct, I can submit a PR

[timotheeguerin]

yeah, i copied the types after and adding that readonly works, though got into some very bad performance issue in the IDE. Not sure if that was related or due to something else at the same time.

Edit: perf issue seems to have been caused by using both prettier.AstPath and my copy if it at the same time. Typescript didn't seem to like converting between those 2 complex types.