Reflection Overview reflectClass Error

[jacobhjkim]

Issue description

When I follow the runtime reflection example, I get an error as shown below.
https://docs.scala-lang.org/overviews/reflection/overview.html#examples

Welcome to Scala 2.13.3 (OpenJDK 64-Bit Server VM, Java 1.8.0_252).
Type in expressions for evaluation. Or try :help.

scala> import scala.reflect.runtime.{universe => ru}
import scala.reflect.runtime.{universe=>ru}

scala>  case class Person(name: String)
class Person

scala> val m = ru.runtimeMirror(getClass.getClassLoader)
val m: reflect.runtime.universe.Mirror = JavaMirror with scala.tools.nsc.interpreter.IMain$TranslatingClassLoader@4b20ca2b of type class scala.tools.nsc.interpreter.IMain$TranslatingClassLoader with classpath [(memory)] and parent being scala.reflect.internal.util.ScalaClassLoader$URLClassLoader@682af059 of type class scala.reflect.internal.util.ScalaClassLoader$URLClassLoader with classpath [file:/Library/Java/JavaVirtualMachines/adoptopenjdk-8.jdk/Contents/Home/jre/lib/resources.jar,file:/Library/Java/JavaVirtualMachines/adoptopenjdk-8.jdk/Contents/Home/jre/lib/rt.jar,file:/Library/Java/JavaVirtualMachines/adoptopenjdk-8.jdk/Contents/Home/jre/lib/jsse.jar,file:/Library/Java/JavaVirtualMachines/adoptopenjdk-8.jdk/Contents/Home/jre/lib/jce.jar,file:/Library/Jav...

scala> val classPerson = ru.typeOf[Person].typeSymbol.asClass
val classPerson: reflect.runtime.universe.ClassSymbol = class Person

scala> val cm = m.reflectClass(classPerson)
scala.ScalaReflectionException: class Person is an inner class, use reflectClass on an InstanceMirror to obtain its ClassMirror
  at scala.reflect.runtime.JavaMirrors$JavaMirror.ErrorInnerClass(JavaMirrors.scala:156)
  at scala.reflect.runtime.JavaMirrors$JavaMirror.reflectClass(JavaMirrors.scala:226)
  at scala.reflect.runtime.JavaMirrors$JavaMirror.reflectClass(JavaMirrors.scala:70)
  ... 32 elided

Using InstanceMirror also results in an error.

scala> val person = Person("John Doe")
val person: Person = Person(John Doe)

scala> val cm = m.reflect(person).reflectClass(classPerson)
scala.ScalaReflectionException: expected a member of class Person, you provided class Person
  at scala.reflect.runtime.JavaMirrors$JavaMirror.ErrorNotMember(JavaMirrors.scala:156)
  at scala.reflect.runtime.JavaMirrors$JavaMirror.$anonfun$checkMemberOf$1(JavaMirrors.scala:257)
  at scala.reflect.runtime.JavaMirrors$JavaMirror.scala$reflect$runtime$JavaMirrors$JavaMirror$$checkMemberOf(JavaMirrors.scala:247)
  at scala.reflect.runtime.JavaMirrors$JavaMirror$JavaInstanceMirror.reflectClass(JavaMirrors.scala:295)
  at scala.reflect.runtime.JavaMirrors$JavaMirror$JavaInstanceMirror.reflectClass(JavaMirrors.scala:276)
  ... 32 elided

[som-snytt]

The easy workaround is to use scala -Yrepl-class-based:false, which used to be the default.

[jacobhjkim]

That worked!

scala>  val cm = m.reflectClass(classPerson)
val cm: reflect.runtime.universe.ClassMirror = class mirror for Person (bound to null)

Should I add scala -Yrepl-class-based:false to the docs?

[som-snytt]

That would be helpful. Maybe there is one place to add that info.

[jacobhjkim]

Hi, @som-snytt. I did open a PR #1781. Let me know if there is a better place to add this info. I will close this issue since it's solved.