'Infer function return type' quick fix generates invalid code for arrow functions without parens

[mjbvz]

Bug Report

🔎 Search Terms

• Quick fix
• code action
• infer function return type

🕗 Version & Regression Information

TypeScript version: 4.2.0-dev.20210125

💻 Code

const a = async x => {
    return 1; 
}

Trigger the infer function return type fix here

🙁 Actual behavior

This results in:

const a = async x: Promise<number> => {
    return 1;
}

🙂 Expected behavior

Instead a set of parameter parens needs to be added in this case:

const a = async (x): Promise<number> => {
    return 1;
}