Codefix: convert `Type[]` to `readonly Type[]` - Githubissues

microsoft / TypeScript

TypeScript is a superset of JavaScript that compiles to clean JavaScript output.

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Codefix: convert `Type[]` to `readonly Type[]` #31923

Open JoshuaKGoldberg opened 5 years ago

JoshuaKGoldberg commented 5 years ago

Search Terms

codefix readonlyarray readonly array immutable

Suggestion

It'd be nice to have a codefix for converting non-readonly arrays to readonly.

Use Cases

When converting/refactoring code to be more immutable/readonly-friendly, it's a bit of a pain to manually add these annotations.

Examples

Given this:

function takesArrays(items: /*| |*/string[], moreItems: /*| |*/string[]) { /* ... */ }

...having a codefix to make one or all parameters readonly would be useful:

function takesArrays(items: readonly string[], moreItems: readonly string[]) { /* ... */ }

Checklist

My suggestion meets these guidelines:

[x] This wouldn't be a breaking change in existing TypeScript/JavaScript code
[x] This wouldn't change the runtime behavior of existing JavaScript code
[x] This could be implemented without emitting different JS based on the types of the expressions
[x] This isn't a runtime feature (e.g. library functionality, non-ECMAScript syntax with JavaScript output, etc.)
[x] This feature would agree with the rest of TypeScript's Design Goals.

jcalz commented 5 years ago

I agree, especially with the introduction of const assertions (#29510) and their readonly tuples.