Confusing error message when using spread operator

[Quantumplation]

What Git revision are you using?

$ aiken --version
aiken v1.0.11-alpha unknown

What operating system are you using, and which version?

NixOS

Describe what the problem is?

When I have the following definition

pub type Redeemer {
  First(Int),
  Second
}

and I attempt to pattern match on it like so

when redeemer is {
  First(..) -> todo
  Second -> todo
}

I get the following confusing error message

aiken::check::arity::pattern (link)

  × While trying to make sense of your code...
  ╰─▶ I saw a pattern on a constructor that has 1 field(s) be matched with 0 argument(s).
      
    ╭─[/home/pi/proj/example.ak:21:1]
 21 │         )
 22 │       First(..) ->
    ·       ──────┬─────
    ·             ╰── Try instead: First(..)
 23 │         dict.has_key(
    ╰────
  help: When pattern-matching on constructors, you must either match the exact number of fields, or use the spread operator '..'. Note that unused fields must be discarded by prefixing their name with '_'.

Here are the things that are confusing about this:

• I saw a pattern on a constructor that has 1 field(s); based on a discussion with @rvcas, my understanding is that "constructor that has 1 field(s)" would be something defined with First { field: Int }, so it's odd that it's referring to a constructor with 1 field here.
• be matched with 0 argument(s). I don't believe this to be true, considering I'm using the spread operator
• Try instead: First(..) it suggests that I use the exact same code that I have written

Note that even doing

First { .. } ->

Doesn't seem to work, and gives a similar error message (but with Try instead: First { .. }, for bonus points!)

What should be the expected behavior?

First, I would expect to be able to use the spread operator to ignore () style arguments as well, instead of being forced to _name, _each, _one.

Second, if that's not possible, I would expect the error message to be something like:

aiken::check::arity::pattern (link)

  × While trying to make sense of your code...
  ╰─▶ I saw a pattern on a constructor that has 1 argument(s) (defined positionally, between parentheses) be matched with a spread operator.
      
    ╭─[/home/pi/proj/example.ak:21:1]
 21 │         )
 22 │       First(..) ->
    ·       ──────┬─────
    ·             ╰── Try instead: First(_) ->
 23 │         dict.has_key(
    ╰────
  help: When pattern-matching on constructors with positional arguments, you cannot use the spread operator.

or something similar.

[rvcas]

Cool

As an initial first improvement we can make the error message more clear and probably allow the spread for none labeled constructors. Eventually I want to just have these two different forms be captured as two different AST nodes allowing for more fine grained error messages.