analyzer: Using a const instance as the "bitwise or expression" in a relational pattern reports a weird error

[srawlins]

Take this slight modification to the Relational pattern example from the spec:

class MyInt {
  const MyInt(int i);
  
  bool operator <(MyInt other) => false;
}

String asciiCharType(int char) {
  const space = MyInt(32);
  const zero = 48;
  const nine = 57;

  return switch (char) {
    < space => 'control', // error
    == space => 'space',
    > space && < zero => 'punctuation', // error
    >= zero && <= nine => 'digit'
    // Etc...
  };
}

This code (today on DartPad) results in an odd error on the // error lines:

The argument type 'MyInt' can't be assigned to the parameter type 'num'.

I don't understand this message:

• I don't think the "bitwise or expression" has to be a num, so I don't know where 'num' is coming from.
• I don't think there is any 'MyInt' argument, or any 'num' parameter, in a pattern.

CC @scheglov @munificent

[scheglov]

Here we match char against space.
This means matching int < MyInt.
This means invocation of int.<(num).
And we try to pass MyInt where num is expected, so the error.

I don't understand the portion about "bitwise or expression", there are no || anywhere.

[srawlins]

This means invocation of int.<(num).

Ah I see. This makes sense. If I change the parameter to MyInt char, then the errors go away.

I still hope we can separate into a different error message, other than "The argument type 'MyInt' can't be assigned to the parameter type 'num'." Perhaps something like "The constant expression type 'MyInt' can't be used in this relational pattern against a 'num'"?

I don't know all of the terms we're using for patterns and errors.

I don't understand the portion about "bitwise or expression", there are no || anywhere.

I don't understand it either, I'm just using the name from the spec. Maybe a typo.

[bwilkerson]

Not a typo. That's a grammar production, so it means you can use any expression whose precedence is less than or equal to the precedence of the bitwise-or operator.

[srawlins]

Ah I see. Sounds good.

[scheglov]

https://dart-review.googlesource.com/c/sdk/+/287940