Rule Proposal: require-await

Async functions and await expressions arrived stage 4. We can add the rule for those after our parser supported those.

This proposal is the await version of require-yield rule. It disallows async functions without await expressions.

/*eslint require-await: error*/

//------------------------------------------------------------------------------
// ✔ GOOD
async function foo() {
    await doSomething()
}

async function foo() {
    // do nothing.
}

//------------------------------------------------------------------------------
// ✘ BAD
async function foo() {
    doSomething()
}

[btmills]

After discussion in the 2016-11-10 TSC meeting, the team decided to accept this rule into core.

[nzakas]

I don’t think there’s a clear conflict between these two rules. require-await can be resolved by adding an await at a spot other than right after return.