Sdk: Null-coalescing operator with a "throw" expression messes with dart2js ineterceptors

[greglittlefield-wf]

Reduced test case (see on Dartpad: https://dartpad.dartlang.org/35b1478eec218cf4275a588ff7e679c8)

main() {
  var mayBeNull = new DateTime.now().millisecondsSinceEpoch != 1 ? 'foo bar baz' : null;
  var nullCoalescedString = mayBeNull ?? (throw new Error());
  print(nullCoalescedString.runtimeType); // prints 'String'
  print(nullCoalescedString.indexOf('bar')); // prints `null` unexpectedly
}

Replacing (throw new Error()) with other expressions results in correct behavior, with the indexOf line printing 4 instead of null. Expressions I tried:

• a number literal (this is a strong mode error, so it's not completely relevant)
• a call to a void function (this is a strong mode error, so it's not completely relevant)
• a string literal
• null

[greglittlefield-wf]

Interestingly enough, it also happens in this simplified case... (thanks @georgelesica-wf)

main() {
  var nullCoalescedString = 'foo bar baz' ?? (throw new Error());
  print(nullCoalescedString.runtimeType); // prints 'String'
  print(nullCoalescedString.indexOf('bar')); // prints `null` unexpectedly
}

[natebosch]

On DartPad today the second example prints 4 instead of null so it looks like this was fixed.