Bad inferences with error TS2365

[ghost]

TypeScript Version: 2.2.1

Code

class Foo {
  _elements: string[];

  constructor(input: string) {
    this._elements = input.split("");
  }

  get top(): string {
    return (this._elements.length > 0) ?
      this._elements[this._elements.length - 1] :
      "";
  }

  strip(): number {
    if (this.top == "$") {
      this._elements.pop(); // $
      let count = 0;
      while (this.top != "^") { // XXX TS2365
        ++count;
        this._elements.pop();
      }
      this._elements.pop(); // ^
      return count;
    }

    return 0;
  }
}

let f = new Foo("ba^z$");
console.log(f.strip());

Expected behavior:

Clean compilation, with no errors or warnings.

Actual behavior:

foo.ts(18,14): error TS2365: Operator '!=' cannot be applied to types '"$"' and '"^"'.

[ghost]

This may be related to issue #12794, or maybe not, but even if so, it looks like there's a lot of noise and casted aspersions wrt the testcases in that issue, rather than engineering.

[gcnew]

It is. See #9998 (comment)

[RyanCavanaugh]

Duplicate #13904 / we don't keep open issues from 👻 s, too spooky