SI-6323 outlaws free types from TypeTag

Free types are no longer acceptable in normal type tags.
Like type parameters or abstract type members they don't map on any real type,
therefore I think this is a justified change.

The main reason for doing is this is to prohibit people from using `typeOf`
on local classes. Sure, the guard introduced in the previous commit will raise
runtime errors about that, but this commit provides static checking.

Those especially persistent might use `absTypeOf` and then try to play around
with the weak type it returns, but that's advanced usage scenario, and I don't
worry much about it.

Bottom line: `typeOf` should just work.
Things that work with additional effort should be explicitly marked as such.

src/compiler/scala/reflect/reify/Errors.scala

@@ -27,8 +27,8 @@ trait Errors {
     throw new ReificationError(defaultErrorPosition, msg)
   }
 
-  def CannotReifyTypeTagHavingUnresolvedTypeParameters(tpe: Type) = {
-    val msg = "cannot reify TypeTag having unresolved type parameter %s".format(tpe)
+  def CannotReifyWeakType(details: Any) = {
+    val msg = "cannot create a TypeTag" + details
     throw new ReificationError(defaultErrorPosition, msg)
   }
 

src/compiler/scala/reflect/reify/States.scala

@@ -34,9 +34,11 @@ trait States {
     def reificationIsConcrete_=(value: Boolean): Unit = {
       _reificationIsConcrete = value
       if (!value && concrete) {
-        assert(current.isInstanceOf[Type], current)
-        val offender = current.asInstanceOf[Type]
-        CannotReifyTypeTagHavingUnresolvedTypeParameters(offender)
+        current match {
+          case tpe: Type => CannotReifyWeakType(s" having unresolved type parameter $tpe")
+          case sym: Symbol => CannotReifyWeakType(s" referring to local ${sym.kindString} ${sym.fullName}")
+          case _ => CannotReifyWeakType("")
+        }
       }
     }
     var reifyStack = reifee :: Nil

src/compiler/scala/reflect/reify/codegen/GenSymbols.scala

@@ -112,6 +112,7 @@ trait GenSymbols {
   def reifyFreeType(binding: Tree): Tree =
     reifyIntoSymtab(binding.symbol) { sym =>
       if (reifyDebug) println("Free type: %s (%s)".format(sym, sym.accurateKindString))
+      state.reificationIsConcrete = false
       val name = newTermName(nme.REIFY_FREE_PREFIX + sym.name)
       Reification(name, binding, mirrorBuildCall(nme.newFreeType, reify(sym.name.toString), mirrorBuildCall(nme.flagsFromBits, reify(sym.flags)), reify(origin(sym))))
     }

src/compiler/scala/reflect/reify/utils/SymbolTables.scala

@@ -17,6 +17,7 @@ trait SymbolTables {
     private[SymbolTable] val original: Option[List[Tree]] = None) {
 
     def syms: List[Symbol] = symtab.keys.toList
+    def isConcrete: Boolean = symtab.values forall (sym => !FreeTypeDef.unapply(sym).isDefined)
 
 //    def aliases: Map[Symbol, List[TermName]] = aliases.distinct groupBy (_._1) mapValues (_ map (_._2))
 

test/files/neg/t6323a.check

@@ -0,0 +1,9 @@
+t6323a.scala:11: `package`.this.materializeTypeTag[Test](scala.reflect.runtime.`package`.universe) is not a valid implicit value for reflect.runtime.universe.TypeTag[Test] because:
+failed to typecheck the materialized tag: 
+cannot create a TypeTag referring to local class Test.Test
+      val value = u.typeOf[Test]
+                          ^
+t6323a.scala:11: error: No TypeTag available for Test
+      val value = u.typeOf[Test]
+                          ^
+one error found

test/files/neg/t6323a.flags

@@ -0,0 +1 @@
+-Xlog-implicits

test/files/run/t6323.scala → test/files/neg/t6323a.scala

@@ -15,7 +15,7 @@ object Test extends App {
       val thisShouldBeA = aAccessor.apply()
       println(thisShouldBeA)
     } catch {
-      case ScalaReflectionException(msg) =>  println(msg)
+      case ScalaReflectionException(msg) => println(msg)
     }
   }
 }

test/files/run/t6323b.scala

@@ -0,0 +1,21 @@
+import scala.reflect.runtime.universe._
+import scala.reflect.runtime.{currentMirror => m}
+import scala.reflect.runtime.{universe => u}
+
+object Test extends App {
+  locally {
+    try {
+      case class Test(a:String,b:List[Int])
+
+      val lookAtMe = m.reflect(Test("a",List(5)))
+      val value = u.absTypeOf[Test]
+      val members = value.members
+      val member = value.members.filter(_.name.encoded == "a")
+      val aAccessor = lookAtMe.reflectMethod(member.head.asMethod)
+      val thisShouldBeA = aAccessor.apply()
+      println(thisShouldBeA)
+    } catch {
+      case ScalaReflectionException(msg) => println(msg)
+    }
+  }
+}