CFE gives incorrect type error for constant argument to extension type constructor.

[lrhn]

Example:

extension type const N(Null _) {}
void main() {
  var n = N(null); // Works.
  const cn = N(null); // compile-time error.
}

This gives the errors:

badnone.dart:4:14: Error: Constant evaluation error:
  const cn = N(null); // compile-time error.
             ^
badnone.dart:1:23: Context: Expected constant 'null' to be of type 'N', but was of type 'Null'.
extension type const N(Null _) {}
                      ^
badnone.dart:4:9: Context: While analyzing:
  const cn = N(null); // compile-time error.
        ^

Analyzer has no error

Not sure which constant has which type, but the code is correct as written.
It seems to be a bug only in the constant evaluation, which does some type check using the wrong type.

[lrhn]

I keep hitting this issue with my attempts to write extension type examples.

If the constant evaluator effectively erases extension types, because it looks at the actual "runtime type" of the value for "runtime" type checks performed during constant evaluation, then it needs to do so consistently, also erasing in the type being checked against.