Cannot create an instance of the case class with some encoded field names

[plokhotnyuk]

It looks like a bug in scalac and affects case classes which have 2 fields where name of one is a prefix for the another name that contains a character that should be encoded immediately after the prefix (like o and o-o).

For 2.11.12 I got a compilation error:

[error] scala.reflect.internal.Types$TypeError: type mismatch;
[error]  found   : Int
[error]  required: Seq
[error] 	at scala.tools.nsc.typechecker.Contexts$ThrowingReporter.handleError(Contexts.scala:1402)
[error] 	at scala.tools.nsc.typechecker.Contexts$ContextReporter.issue(Contexts.scala:1254)
[error] 	at scala.tools.nsc.typechecker.Contexts$Context.issue(Contexts.scala:573)
[error] 	at scala.tools.nsc.typechecker.ContextErrors$ErrorUtils$.issueTypeError(ContextErrors.scala:106)

While in 2.12 it fails in the runtime during a call of the constructor:

java.lang.Integer cannot be cast to scala.collection.Seq
java.lang.ClassCastException: java.lang.Integer cannot be cast to scala.collection.Seq
	at Publication.<init>(KebabFieldNameSpec.scala:3)
	at KebabFieldNameSpec.$anonfun$new$2(KebabFieldNameSpec.scala:8)
	at org.scalatest.OutcomeOf.outcomeOf(OutcomeOf.scala:85)
	at org.scalatest.OutcomeOf.outcomeOf$(OutcomeOf.scala:83)
	at org.scalatest.OutcomeOf$.outcomeOf(OutcomeOf.scala:104)
	at org.scalatest.Transformer.apply(Transformer.scala:22)

Code to reproduce:

import org.scalatest.{Matchers, WordSpec}

case class Publication(title: String, author: String, `reference-count`: Int, reference: Seq[String])

class KebabFieldNameSpec extends WordSpec with Matchers {
  "Publication" should {
    "be created by the constructor" in {
      new Publication("", "", 0, Nil)
    }
  }
}

[plokhotnyuk]

W/a for this scalac bug is to move a definition of the field with encoded chars (`reference-count` in our case) to be after the field that is affected by the exception (after the reference field):

case class Publication(title: String, author: String, reference: Seq[String], `reference-count`: Int)

[hrhino]

    // The constructor parameter with given name. This means the parameter
    // has given name, or starts with given name, and continues with a `$` afterwards.
    def parameterNamed(name: Name): Symbol = {
      def matchesName(param: Symbol) = param.name == name || param.name.startsWith(name + nme.NAME_JOIN_STRING) // nme.NAME_JOIN_STRING = "$"

      primaryConstrParams filter matchesName match {
        case Nil    => abort(name + " not in " + primaryConstrParams)
        case p :: _ => p
      }

More fallout from using $ for everything name-y. (#2806) This may hail from '06: scala/scala@cb7711d.

[som-snytt]

Probably the same problem as #10625 where Constructors looks at prefixes.

[som-snytt]

Another symptom #8831

[som-snytt]

@hrhino should this and 10625 also be closed in favor of 8831 as an umbrella issue? Asking in case you understand any nuances. I haven't re-read the issues.

[hrhino]

I'm not a very nuanced person. Re-rereading the issues, this is almost certainly a duplicate of #8831, and has the same root cause as #10625 (IIRC, if I remember constructors) but I don't feel confident saying, externally, that it's a duplicate. Not sure what the criteria for that are.

[hrhino]

Also, what happened to the touted GitHub "duplicate of" feature from a few months ago? Did it get rebased away?

[som-snytt]

I'll take a @hrhino "almost certainly" and "don't feel confident" any day. I think the issue that says "bizarre" always takes priority.

On github, it's easy to navigate between linked issues, so I won't try to copy/paste to #8831.