The @typescript-eslint/require-await rule exists to allow exceptions to the core ESLint require-await rule for async functions that return a promise (where adding an await to the return to suppress the require-await warnings would in turn trigger warnings for no-return-await).

The initial implementation of the @typescript-eslint/require-await rule allowed the following exceptions:

• function expressions that return a promise
• function declarations that return a promise
• arrow function expressions with block bodies that return a promise

(the rule was only checking ReturnStatement nodes)

This PR adds support for:

• arrow function expressions with concise bodies that return a promise

(single-line expressions that don't explicitly include a return statement)

Prior to this PR, the following code would fall through to the core ESLint require-await rule and trigger warnings:

// 1. Async arrow function with promise return
const numberOne = async (): Promise<number> => Promise.resolve(1);

// 2. Async arrow function with async function return
const getAsyncNumber = async function(x: number): Promise<number> {
  return Promise.resolve(x);
}

const numberOne = async (): Promise<number> => getAsyncNumber(1);

// 3. Async arrow function expression with no await
const numberOne = async (): Promise<number> => 1;

After this PR, only the last example should fall through to the core rule and triggers a warning:

// 3. Async arrow function expression with no await
const numberOne = async (): Promise<number> => 1;