Expr Ops not handling variance (opaque types)

[ivan-klass]

Currently we have:

override implicit def ExprStringOpsConv(v: Expr[String]): PostgresDialect.ExprStringOps[String] =
    new PostgresDialect.ExprStringOps(v)

So methods .contains or .like are not picked up for refined string:

opaque type PetName <: String = String


// fails
Pet.select.filter(_.name.contains("ffy"))

I believe this could be easily fixed with something like

override implicit def ExprStringOpsConv[V <: String](v: Expr[V]): PostgresDialect.ExprStringOps[V] =
    new PostgresDialect.ExprStringOps(v)

[ivan-klass]

Another option would be to add variance parent(s) for Expr, like

trait ExprCo[+V] {
  // methods for V in "output" meaning 
}

trait Expr[V] extends ExprCo[V] {
  // invariant methods
}

So such extensions are applied to base ExprCo, not Expr