Incorrect tuple union type deduction

[pavel]

TypeScript Version: 3.3.3 and 3.4.0-dev.20190220 with --strictNullChecks

Search Terms:
tuple, union, type deduction, destructuring

Code

function fn(): [null, number] | [string, null] {
  if (Math.random() > 0.5) {
    return [null, 2]
  }
  return ["Str", null]
}

// l: string | null (correct)
// r: number | null (correct)
const [l, r] = fn()
if (l === null) {
  // r: number | null (incorrect)
  console.log(r + 2)
} else {
  // l: string (correct)
  // r: number | null (incorrect)
  console.log(l.toLowerCase(), r === null)
}

Expected behavior:
No compilation errors. Correct type hints.

Actual behavior:
Compilation error:

TS2531: Object is possibly 'null'.

at console.log(r + 2). Incorrect type hints.

Playground Link:
Playground link. Make sure to enable "strictNullChecks".

Related Issues:
Did not find anything exactly like this issue.

[jack-williams]

This is tracked by this #12184. If you go to the linked issue #28981 the example is more-or-less the same as the one you provide.

[pavel]

Thanks.