How to avoid required type narrowing for (Deno.PermissionStatus).state?

[jsejcksn]

Using this example:

example.ts:

export async function ensurePermission<T extends Deno.PermissionDescriptor>(
  descriptor: T,
): Promise<Deno.PermissionStatus> {
  const status = await Deno.permissions.query(descriptor);
  if (status.state === "granted") return status;
  await Deno.permissions.request(descriptor);
  // It would be nice to not have to use this assertion:
  // if ((status.state as Deno.PermissionState) === "granted") return status; // ✅ Ok
  if (status.state === "granted") return status; // ❌ Compile error: deno-ts(2367)
  throw new Deno.errors.PermissionDenied("Permission denied");
}

async function greet(): Promise<void> {
  const variable = "USER";
  const desc: Deno.EnvPermissionDescriptor = { name: "env", variable };
  let user: string;
  try {
    await ensurePermission(desc);
    user = Deno.env.get(variable)?.trim() || "anonymous user";
  } catch (ex) {
    if (ex instanceof Deno.errors.PermissionDenied) user = "skeptical user";
    else throw ex;
  }
  const message = `hello ${user}`;
  console.log(message);
}

if (import.meta.main) greet();

Note the commented lines in the function ensurePermission. If I try to run the script, I get the following compilation error:

% deno run example.ts
Check file:///Users/jesse/example/example.ts
error: TS2367 [ERROR]: This condition will always return 'false' since the types '"denied" | "prompt"' and '"granted"' have no overlap.
  if (status.state === "granted") return status; // ❌ Compile error: deno-ts(2367)
      ~~~~~~~~~~~~~~~~~~~~~~~~~~
    at file:///Users/jesse/example/example.ts:9:7

but if I comment the line in the message and uncomment the line above it, everything works fine:

  if ((status.state as Deno.PermissionState) === "granted") return status; // ✅ Ok
  // if (status.state === "granted") return status; // ❌ Compile error: deno-ts(2367)

% deno run example.ts
Check file:///Users/jesse/example/example.ts
⚠️  ️Deno requests env access to "USER". Grant? [g/d (g = grant, d = deny)] g
hello jesse

Is there a way that the state property/getter of PermissionStatus can be refactored in order to avoid requiring this kind of assertion or is it simply an upstream limitation of TypeScript's CFA?

I am using Deno v1.9.0

% deno --version
deno 1.9.0 (release, x86_64-apple-darwin)
v8 9.1.269.5
typescript 4.2.2