SI-6323 prohibits reflection against free types

One of the use cases for free types is reification of local classes.

The result is very seamless. Despite that local classes are not pickled,
free types recreated the symbols referenced by local classes, so that we
get our own symbol table, which can be analyzed with usual precision of
pickled symbols and types.

However when we try to use those symbols for reflection, we hit a problem.
Scala runtime reflection uses its own mechanism for dealing with non-pickled
types, which is incompatible with mini symbol tables used in free types.

Therefore to prevent confusion, I prohibit using those symbols for reflection.

3 files changed, 42 insertions, 3 deletions

diff --git a/src/reflect/scala/reflect/runtime/JavaMirrors.scala b/src/reflect/scala/reflect/runtime/JavaMirrors.scala
index 9f2c3fc79c..455cc14789 100644
--- a/src/reflect/scala/reflect/runtime/JavaMirrors.scala
+++ b/src/reflect/scala/reflect/runtime/JavaMirrors.scala
@@ -133,6 +133,7 @@ trait JavaMirrors extends internal.SymbolTable with api.JavaUniverse { self: Sym
     """.trim.stripMargin)
     private def ErrorSetImmutableField(wannabe: Symbol) = throw new ScalaReflectionException(s"cannot set an immutable field ${wannabe.name}")
     private def ErrorNotConstructor(wannabe: Symbol, owner: Symbol) = throw new ScalaReflectionException(s"expected a constructor of $owner, you provided $wannabe")
+    private def ErrorFree(member: Symbol, freeType: Symbol) = throw new ScalaReflectionException(s"cannot reflect ${member.kindString} ${member.name}, because it's a member of a free type ${freeType.name}")
 
     def reflect[T: ClassTag](obj: T): InstanceMirror = new JavaInstanceMirror(obj)
 
@@ -154,13 +155,30 @@ trait JavaMirrors extends internal.SymbolTable with api.JavaUniverse { self: Sym
 
     def moduleSymbol(rtcls: RuntimeClass): ModuleSymbol = classToScala(rtcls).companionModule.asModule
 
+    private def ensuringNotFree(wannabe: Symbol)(body: => Any) {
+      val freeType = wannabe.ownerChain find (_.isFreeType)
+      freeType match {
+        case Some(freeType) => ErrorFree(wannabe, freeType)
+        case _ => body
+      }
+    }
+
     private def checkMemberOf(wannabe: Symbol, owner: ClassSymbol) {
       if (wannabe.owner == AnyClass || wannabe.owner == AnyRefClass || wannabe.owner == ObjectClass) {
         // do nothing
       } else if (wannabe.owner == AnyValClass) {
         if (!owner.isPrimitiveValueClass && !owner.isDerivedValueClass) ErrorNotMember(wannabe, owner)
       } else {
-        if (!(owner.info.baseClasses contains wannabe.owner)) ErrorNotMember(wannabe, owner)
+        ensuringNotFree(wannabe) {
+          if (!(owner.info.baseClasses contains wannabe.owner)) ErrorNotMember(wannabe, owner)
+        }
+      }
+    }
+
+    private def checkConstructorOf(wannabe: Symbol, owner: ClassSymbol) {
+      if (!wannabe.isClassConstructor) ErrorNotConstructor(wannabe, owner)
+      ensuringNotFree(wannabe) {
+        if (!owner.info.decls.toList.contains(wannabe)) ErrorNotConstructor(wannabe, owner)
       }
     }
 
@@ -386,8 +404,7 @@ trait JavaMirrors extends internal.SymbolTable with api.JavaUniverse { self: Sym
       def erasure = symbol
       def isStatic = false
       def reflectConstructor(constructor: MethodSymbol) = {
-        if (!constructor.isClassConstructor) ErrorNotConstructor(constructor, symbol)
-        if (!symbol.info.decls.toList.contains(constructor)) ErrorNotConstructor(constructor, symbol)
+        checkConstructorOf(constructor, symbol)
         new JavaConstructorMirror(outer, constructor)
       }
       def companion: Option[ModuleMirror] = symbol.companionModule match {
diff --git a/test/files/run/t6323.check b/test/files/run/t6323.check
new file mode 100644
index 0000000000..2219278a16
--- /dev/null
+++ b/test/files/run/t6323.check
@@ -0,0 +1 @@
+cannot reflect value a, because it's a member of a free type Test

diff --git a/test/files/run/t6323.scala b/test/files/run/t6323.scala
new file mode 100644
index 0000000000..625cfaae20
--- /dev/null
+++ b/test/files/run/t6323.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.typeOf[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)
+    }
+  }
+}
\ No newline at end of file