SimpleTable does not work with opaque types

[NovaMage]

The example below is also available as a public repo.
@bishabosha @lihaoyi

// ThisBuild / scalaVersion := "3.7.3"
// val scalaSqlVersion = "0.2.1"
// libraryDependencies += "com.lihaoyi" %% "scalasql" % scalaSqlVersion
// libraryDependencies += "com.lihaoyi" %% "scalasql-namedtuples" % scalaSqlVersion

package com.example

import scalasql.dialects.PostgresDialect.*
import scalasql.simple.{*, given}

opaque type UserId = java.util.UUID

object UserId {

  given TypeMapper[UserId] = new UuidType

}

case class User(id: UserId, firstName: String, lastName: String)

object User extends SimpleTable[User]

def find(id: UserId)(using db: DbApi.Txn): Option[User] = {
  db.run(User.select.filter(_.id === id)).headOption
}

The above won't compile with the following error:

value === is not a member of com.example.UserId match {
  case scalasql.namedtuples.SimpleTable.Nested =>
    scalasql.namedtuples.SimpleTable.Record[com.example.UserId,
      scalasql.core.Expr]
  case Any => scalasql.core.Expr[com.example.UserId]
} <:
  scalasql.namedtuples.SimpleTable.Record[com.example.UserId, scalasql.core.Expr
    ]
 | scalasql.core.Expr[com.example.UserId] - did you mean com.example.UserId match {
  case scalasql.namedtuples.SimpleTable.Nested =>
    scalasql.namedtuples.SimpleTable.Record[com.example.UserId,
      scalasql.core.Expr]
  case Any => scalasql.core.Expr[com.example.UserId]
} <:
  scalasql.namedtuples.SimpleTable.Record[com.example.UserId, scalasql.core.Expr
    ]
 | scalasql.core.Expr[com.example.UserId].==?

As far as I understand, opaque types used in SimpleTables do not reduce appropiately in the Records match types used to convert them into Expr.

This has been stopping us from using SimpleTable as we use opaque types for all ids of models in our system (to avoid passing an incorrect ids anywhere in the system).

[bishabosha]

Unfortunately the match type reducer will give up as soon as you try to compare an abstract type (e.g. any opaque type with Any upper bound) because it does not know if the RHS is actually Nested in this case.

Some solutions:

1. try adding an upper bound, e.g. opaque type UserId <: java.util.UUID = java.util.UUID this still makes the type unique from any other arbitrary UUID. My predicition is as long as the upper bound is disjoint from Nested then it should work
2. introduce a variant of SimpleTable that does not support Nested, therefore no inspection of field types is done
3. Redesign using a macro to generate a "shape" type representing the structure of the classes - that would work with opaque types, but at the expense of more ugly types (e.g. seeing the shape on every inferred type)
4. SIP for variant of match types that doesnt apply the disjointness check (with some restrictions applied such as no dependent methods - which has no consequences for Selectable)