loosing promise type when using await

async function foo() {
  let /** null */ x = await Promise.resolve(1); // no type warning
  Promise.resolve(1).then((value) => {x = value}); // type warning
}

https://closure-compiler.appspot.com/home#code%3D%252F%252F%2520%253D%253DClosureCompiler%253D%253D%250A%252F%252F%2520%2540compilation_level%2520ADVANCED_OPTIMIZATIONS%250A%252F%252F%2520%2540output_file_name%2520default.js%250A%252F%252F%2520%253D%253D%252FClosureCompiler%253D%253D%250A%250Aasync%2520function%2520foo()%2520%257B%250A%2520%2520let%2520%252F**%2520null%2520*%252F%2520x%2520%253D%2520await%2520Promise.resolve(1)%253B%250A%2520%2520Promise.resolve(1).then((value)%2520%253D%253E%2520%257Bx%2520%253D%2520value%257D)%253B%250A%257D

[brad4d]

Current status of the work I mentioned is that we’re close to having ES6 class transpilation happen after type checking. Most of what’s left is fixing Google internal code containing type-related errors previously hidden by the transpilation.

After that the next blocker is moving destructuring transpilation. @lauraharker has been very active in making the changes needed to make that happen.

After that moving async function transpilation will be relatively easy, possibly a single commit, because theoretically all the work needed other than moving the other transpilations it depends on is already done.

I expect it all to be done by the end of this quarter.

[brad4d]

We’re actively working to improve type checking for async functions this quarter. I expect this to get fixed as part of that work.