`undefined` error if enable coverage

[xuwei-k]

Compiler version

• 3.5.2-RC1
• 3.6.0-RC1-bin-20241001-8244d67-NIGHTLY

Minimized code

build.sbt

scalacOptions ++= Seq("-coverage-out:coverage-out")

libraryDependencies += "io.grpc" % "grpc-services" % "1.68.0"

scalaVersion := "3.5.2-RC1"

MyServer.scala

package example

import io.grpc.Server
import io.grpc.ServerBuilder
import io.grpc.ServerInterceptors
import io.grpc.ServerServiceDefinition
import io.grpc.protobuf.services.ProtoReflectionService
import io.grpc.util.TransmitStatusRuntimeExceptionInterceptor

object MyServer {

  def createServer(port: Int, services: List[ServerServiceDefinition]): Server = {
    services
      .foldLeft(ServerBuilder.forPort(port))((builder, service) =>
        builder.addService(
          ServerInterceptors.intercept(
            service,
            TransmitStatusRuntimeExceptionInterceptor.instance()
          )
        )
      )
      .addService(ProtoReflectionService.newInstance())
      .build()
  }

}

Output (click arrow to expand)

[error] -- Error: scala3-coverage-bug/MyServer.scala:23:12 ----------------
[error] 13 |    services
[error] 14 |      .foldLeft(ServerBuilder.forPort(port))((builder, service) =>
[error] 15 |        builder.addService(
[error] 16 |          ServerInterceptors.intercept(
[error] 17 |            service,
[error] 18 |            TransmitStatusRuntimeExceptionInterceptor.instance()
[error] 19 |          )
[error] 20 |        )
[error] 21 |      )
[error] 22 |      .addService(ProtoReflectionService.newInstance())
[error] 23 |      .build()
[error]    |    ^
[error]    |undefined: {
[error]    |  val $3$: io.grpc.ServerBuilder[?] =
[error]    |    {
[error]    |      val z$1: io.grpc.ServerBuilder[?] =
[error]    |        {
[error]    |          scala.runtime.coverage.Invoker.invoked(3, "coverage-out")
[error]    |          io.grpc.ServerBuilder.forPort(port)
[error]    |        }
[error]    |      val op$1:
[error]    |        ((io.grpc.ServerBuilder[?], io.grpc.ServerServiceDefinition) =>
[error]    |          io.grpc.ServerBuilder[?])
[error]    |       =
[error]    |        {
[error]    |          def $anonfun(builder: io.grpc.ServerBuilder[?],
[error]    |            service: io.grpc.ServerServiceDefinition): io.grpc.ServerBuilder[?]
[error]    |             =
[error]    |            {
[error]    |              val $2$: io.grpc.ServerServiceDefinition =
[error]    |                {
[error]    |                  val $1$: Seq[io.grpc.ServerInterceptor] =
[error]    |                    [
[error]    |                      {
[error]    |                        scala.runtime.coverage.Invoker.invoked(6, "coverage-out"
[error]    |                          )
[error]    |                        io.grpc.util.TransmitStatusRuntimeExceptionInterceptor.
[error]    |                          instance()
[error]    |                      }
[error]    |                     : io.grpc.ServerInterceptor]
[error]    |                  scala.runtime.coverage.Invoker.invoked(5, "coverage-out")
[error]    |                  io.grpc.ServerInterceptors.intercept(service, $1$*)
[error]    |                }
[error]    |              scala.runtime.coverage.Invoker.invoked(4, "coverage-out")
[error]    |              builder.addService($2$)
[error]    |            }
[error]    |          closure($anonfun)
[error]    |        }
[error]    |      scala.runtime.coverage.Invoker.invoked(2, "coverage-out")
[error]    |      services.foldLeft[io.grpc.ServerBuilder[?]](z$1)(op$1)
[error]    |    }
[error]    |  val $4$: io.grpc.BindableService =
[error]    |    {
[error]    |      scala.runtime.coverage.Invoker.invoked(7, "coverage-out")
[error]    |      io.grpc.protobuf.services².ProtoReflectionService.newInstance()
[error]    |    }
[error]    |  scala.runtime.coverage.Invoker.invoked(1, "coverage-out")
[error]    |  $3$.addService²($4$)
[error]    |}.build # -1: TermRef(TypeRef(ThisType(TypeRef(NoPrefix,module class <special-ops>)),type <FromJavaObject>),build) at instrumentCoverage
[error]    |
[error]    |where:    addService  is a method in class ServerBuilder
[error]    |          addService² is a method in class ServerBuilder
[error]    |          services    is a parameter in method createServer
[error]    |          services²   is a package in package io.grpc.protobuf
[error] one error found
[error] (Compile / compileIncremental) Compilation failed

[Gedochao]

Scala CLI example, for convenience:

//> using options -coverage-out:coverage-out
//> using dep io.grpc:grpc-services:1.68.0
import io.grpc.Server
import io.grpc.ServerBuilder
import io.grpc.ServerInterceptors
import io.grpc.ServerServiceDefinition
import io.grpc.protobuf.services.ProtoReflectionService
import io.grpc.util.TransmitStatusRuntimeExceptionInterceptor

object MyServer {
  def createServer(
      port: Int,
      services: List[ServerServiceDefinition]
  ): Server = {
    services
      .foldLeft(ServerBuilder.forPort(port))((builder, service) =>
        builder.addService(
          ServerInterceptors.intercept(
            service,
            TransmitStatusRuntimeExceptionInterceptor.instance()
          )
        )
      )
      .addService(ProtoReflectionService.newInstance())
      .build()
  }
}

BTW it's not actually a compiler crash, we get an actual (if cryptic) error.
Optimally, we'd like it minimized without the io.grpc:grpc-services:1.68.0 dependency.

[xuwei-k]

Optimally, we'd like it minimized without the io.grpc:grpc-services:1.68.0 dependency.

Builder.java

package example;

public abstract class Builder<T extends Builder<T>> {
  public abstract String build();
  public abstract T addService(Service service);
}

Service.java

package example;

public class Service{}

A.scala

package example

trait A {
  def x1: Builder[?]
  def x2: Service

  def create: String =
    x1.addService(x2).build()
}

[error] 8 |    x1.addService(x2).build()
[error]   |    ^^^^^^^^^^^^^^^^^^^^^^^^^
[error]   |undefined: {
[error]   |  val $1$: example.Builder[?] =
[error]   |    {
[error]   |      scala.runtime.coverage.Invoker.invoked(2, "coverage-out")
[error]   |      this.x1
[error]   |    }
[error]   |  val service$1: example.Service =
[error]   |    {
[error]   |      scala.runtime.coverage.Invoker.invoked(3, "coverage-out")
[error]   |      this.x2
[error]   |    }
[error]   |  scala.runtime.coverage.Invoker.invoked(1, "coverage-out")
[error]   |  $1$.addService(service$1)
[error]   |}.build # -1: TermRef(TypeRef(ThisType(TypeRef(NoPrefix,module class scala)),class Any),build) at instrumentCoverage
[error] one error found
[error] (Compile / compileIncremental) Compilation failed

[odersky]

The error is procduced in Line 170 of ErrorReporting.scala:

    def takesNoParamsMsg(tree: Tree, kind: String): Message =
      if (tree.tpe.widen.exists)
        em"${exprStr(tree)} does not take ${kind}parameters"
      else {
        em"undefined: $tree # ${tree.uniqueId}: ${tree.tpe.toString} at ${ctx.phase}"
      }

That happens if something that gets applied does not have a valid type (which should not happen). We can try to improve the error message to explain this. But it would be better to figure out who produced this tree without a valid type. Looking at the stacktrace after -Xprompt would help.