type promotion of upper bound does not work inside closures

[jmesserly]

Consider this example:

void f/*<T extends num>*/(T x, T y) {
  var f = () => x;
  f = () => y;
  if (x is int) {
    var q = x;

    // BUG HERE
    // This does not capture the type `T extends int`. Instead the return type
    // is `T extends num`. What happens is we substitute {T/T} on the function
    // type, and the way it is implemented, this leads back to `T extends num`.
    var g = () => x;
    g = f;
    /*info:DYNAMIC_INVOKE*/g()./*error:UNDEFINED_GETTER*/isEven;
    q = /*warning:DOWN_CAST_COMPOSITE*/g();
    int r = x;
  }
}

The substitution does not happen correctly here. Note the lazy substitution is also unnecessary when it's just {T/T}.

[jmesserly]

this is a loose end from the fix to #27040

[jmesserly]

I think this will be fixed in https://codereview.chromium.org/2456803004/
(I'm currently updating the test because it's working now.)

[jmesserly]

This was indeed fixed in f021a70