Getting type information inside scala repl via IMain

Question

Intent

I am trying to add support for :kind command to scala repl. Thanks to Eugene Burmako, I was able to get a working prototype. Though it only works with fully qualified names and fails to resolve imported names.

I am now trying to use IMain.exprTyper to do the job, as it is aware of types, imported into the repl. But there is a problem. Everything I've tried returns a ClassInfoType like the following (displayed with showRaw):

ClassInfoType(List(TypeRef(TypeRef(TypeRef(TypeRef(NoPrefix(), package <root>, List()), package java, List()), package lang, List()), class Object, List()), TypeRef(TypeRef(TypeRef(NoPrefix(), package <root>, List()), package scala, List()), trait Serializable, List())), Scope{
  def <init>(): Option.type;
  implicit def option2Iterable(xo: Option): Iterable;
  def apply(x: Object): Option;
  def empty(): Option;
  private def readResolve(): Object
}, object Option)

While the working implementation returns specific Type:

PolyType(List(TypeName("A")), ClassInfoType(List(TypeRef(ThisType(scala), TypeName("AnyRef"), List()), TypeRef(ThisType(scala), scala.Product, List()), TypeRef(ThisType(scala), scala.Serializable, List())), Scope(nme.CONSTRUCTOR, TermName("isEmpty"), TermName("isDefined"), TermName("get"), TermName("getOrElse"), TermName("orNull"), TermName("map"), TermName("fold"), TermName("flatMap"), TermName("flatten"), TermName("filter"), TermName("filterNot"), TermName("nonEmpty"), TermName("withFilter"), TypeName("WithFilter"), TermName("contains"), TermName("exists"), TermName("forall"), TermName("foreach"), TermName("collect"), TermName("orElse"), TermName("iterator"), TermName("toList"), TermName("toRight"), TermName("toLeft")), scala.Option))

Question

I feel like I'm really close. Here's a playground, you can use to try everything yourself:

Welcome to Scala version 2.11.0-20130328-093148-47645c7e7e (OpenJDK 64-Bit Server VM, Java 1.7.0_17).
Type in expressions to have them evaluated.
Type :help for more information.

scala> import scala.reflect.runtime.universe._
import scala.reflect.runtime.universe._

scala> import scala.tools.nsc.interpreter.IMain
import scala.tools.nsc.interpreter.IMain

scala> val mirror = runtimeMirror(getClass.getClassLoader) // Working approach
mirror: reflect.runtime.universe.Mirror = JavaMirror with scala.tools.nsc.interpreter.IMain$TranslatingClassLoader@3d34ec98 of type class scala.tools.nsc.interpreter.IMain$TranslatingClassLoader with classpath [<unknown>] and parent being scala.tools.nsc.util.ScalaClassLoader$URLClassLoader@5d990e8c of type class scala.tools.nsc.util.ScalaClassLoader$URLClassLoader with classpath [file:/usr/lib/jvm/java-7-openjdk/jre/lib/resources.jar,file:/usr/lib/jvm/java-7-openjdk/jre/lib/rt.jar,file:/usr/lib/jvm/java-7-openjdk/jre/lib/jsse.jar,file:/usr/lib/jvm/java-7-openjdk/jre/lib/jce.jar,file:/usr/lib/jvm/java-7-openjdk/jre/lib/charsets.jar,file:/usr/lib/jvm/java-7-openjdk/jre/lib/rhino.jar,file:/home/folone/workspace/scala-myfork/build/pack/lib/jline.jar,file:/home/folone/workspace/scala-myfork...

scala> val typer = new IMain().exprTyper // Not working approach
typer: scala.tools.nsc.interpreter.IMain#exprTyper.type = scala.tools.nsc.interpreter.IMain$exprTyper$@68c181f0

scala> val expr = "scala.Option"
expr: String = scala.Option

scala> showRaw(mirror.staticClass(expr).toType.typeSymbol.typeSignature) // Correct signature
res6: String = PolyType(List(TypeName("A")), ClassInfoType(List(TypeRef(ThisType(scala), TypeName("AnyRef"), List()), TypeRef(ThisType(scala), scala.Product, List()), TypeRef(ThisType(scala), scala.Serializable, List())), Scope(nme.CONSTRUCTOR, TermName("isEmpty"), TermName("isDefined"), TermName("get"), TermName("getOrElse"), TermName("orNull"), TermName("map"), TermName("fold"), TermName("flatMap"), TermName("flatten"), TermName("filter"), TermName("filterNot"), TermName("nonEmpty"), TermName("withFilter"), TypeName("WithFilter"), TermName("contains"), TermName("exists"), TermName("forall"), TermName("foreach"), TermName("collect"), TermName("orElse"), TermName("iterator"), TermName("toList"), TermName("toRight"), TermName("toLeft")), scala.Option))

scala> showRaw(typer.typeOfExpression(expr).typeSymbol.typeSignature) // Wrong signature
res7: String = 
ClassInfoType(List(TypeRef(TypeRef(TypeRef(TypeRef(NoPrefix(), package <root>, List()), package java, List()), package lang, List()), class Object, List()), TypeRef(TypeRef(TypeRef(NoPrefix(), package <root>, List()), package scala, List()), trait Serializable, List())), Scope{
  def <init>(): Option.type;
  implicit def option2Iterable(xo: Option): Iterable;
  def apply(x: Object): Option;
  def empty(): Option;
  private def readResolve(): Object
}, object Option)

How do I transform ClassInfoType into a valid Type containing the needed info? Alternatively, how do I get the Type using IMain in the first place?

Answer 1

How about this? I'm using power mode which gives you access to the global from the currently running REPL, which is a shade more convenient than creating a new IMain.

scala> :power
Already in power mode.

scala> val g = global
g: $r.intp.global.type = <global>

scala> val context = g.analyzer.rootContext(NoCompilationUnit)
context: g.analyzer.Context = Context(<root>@EmptyTree unit=NoCompilationUnit scope=997093283 errors=false, reportErrors=true, throwErrors=false)

// aware imports of scala._, etc.
scala> val sym = context.lookupSymbol("Option": TypeName, _ => true).symbol
sym: g.analyzer.global.Symbol = class Option

scala> sym.tpeHK.typeParams
res21: List[g.analyzer.global.Symbol] = List(type A)

See also:

scala> intp.symbolOfType("Foo")
res26: $r.intp.global.Symbol = class Foo

But I'm not sure how to get at previously imported symbols:

scala> object Bar { class Bop }
defined object Bar

scala> import Bar.Bop
import Bar.Bop

scala> intp.symbolOfType("Bop")
res27: $r.intp.global.Symbol = <none>

Edit:

The reason OP's getting ClassInfoType instead of PolyType is due to phase. To get the same result as the power mode's global, one must set the phase to typer. To quote @retronym's explanation from REPL: intp.global vs "global" available in :power mode:

scala> :power
** Power User mode enabled - BEEP WHIR GYVE **
** :phase has been set to 'typer'.          **
    ^
    `----  this part is relevant

Symbols have an list of types (aka info-s), indexed by compiler phase. (aka TypeHistory). Many compiler phases install InfoTransformers to morph the type. See src/compiler/scala/tools/nsc/transform/InfoTransform.scala for some documentation.

To inspect the type as-at particular phase, you can use methods like 'exitingTyper`.

scala> exitingPostErasure($intp.global.rootMirror.staticClass("scala.Option").typeSignature).getClass
res6: Class[_ <: $intp.global.Type] = class scala.reflect.internal.Types$ClassInfoType

scala> exitingTyper($intp.global.rootMirror.staticClass("scala.Option").typeSignature).getClass
res7: Class[_ <: $intp.global.Type] = class scala.reflect.internal.Types$PolyType

Or, a little more conveniently in :power mode:

scala> :phase typer
Active phase is now: Typer

scala> global.rootMirror.staticClass("scala.Option").typeSignature.getClass
res16: Class[_ <: $r.global.Type] = class scala.reflect.internal.Types$PolyType

scala> :phase cleanup
Active phase is now: Cleanup

scala> global.rootMirror.staticClass("scala.Option").typeSignature.getClass
res17: Class[_ <: $r.global.Type] = class scala.reflect.internal.Types$ClassInfoType