No analyzer error for [expression][unary_operator][expression]

[greglittlefield-wf]

While editing some code, I accidentally removed an &&, and the code ended up something like this:

if (a !b && c && d) {}

I got a runtime error for a !b, but didn't receive an analyzer error as I'd expect to.

This also reproduces with the ~ operator:

main() {
  var a, b;
  // No analyzer error
  // Runtime error: "Error: The string '!' isn't a user-definable operator."
  var result1 = a !b;
  // No analyzer error
  // Runtime error: "Error: The string '~' isn't a user-definable operator."
  var result2 = a ~b;
}

---

Reproducible in Dart 2.2.0

[lrhn]

@askeksa-google @peter-ahe-google
The front end could perhaps also do with a more precise error message.

[peter-ahe-google]

The example program above leads to a spurious error about non-nullable types and causes an infinite loop in the parser.

@danrubel