New phase: RestoreScopes

Cleans up after LambdaLift and Flatten. RestoreScopes exhibited a problem (double definition)
when compiling Unpickler. The root of the problem was in Applications.scala. The effect was
that arguments woulkd be lifted out, but then the argument expression would be used anyway. That caused
a closure to be present twice which caused the double def error much later. -Ycheck did not catch it because
the two closure expressions were in non-overlapping scopes.

Author: odersky

src/dotty/tools/dotc/Compiler.scala

@@ -56,7 +56,8 @@ class Compiler {
       List(new CapturedVars,
            new Constructors),
       List(new LambdaLift,
-           new Flatten)
+           new Flatten,
+           new RestoreScopes)
     )
 
   var runId = 1

src/dotty/tools/dotc/transform/RestoreScopes.scala

@@ -0,0 +1,36 @@
+package dotty.tools.dotc
+package transform
+
+import core._
+import DenotTransformers.IdentityDenotTransformer
+import Contexts.Context
+import Symbols._
+import Scopes._
+import collection.mutable
+import TreeTransforms.MiniPhaseTransform
+import ast.Trees._
+import TreeTransforms.TransformerInfo
+
+/** The preceding lambda lift and flatten phases move symbols to different scopes
+ *  and rename them. This miniphase cleans up afterwards and makes sure that all
+ *  class scopes contain the symbols defined in them.
+ */
+class RestoreScopes extends MiniPhaseTransform with IdentityDenotTransformer { thisTransform =>
+  import ast.tpd._
+  override def phaseName = "restoreScopes"
+
+  override def treeTransformPhase = thisTransform.next
+
+  override def transformTypeDef(tree: TypeDef)(implicit ctx: Context, info: TransformerInfo) = {
+    val TypeDef(_, _, Template(constr, _, _, body)) = tree
+    val restoredDecls = newScope
+    for (stat <- constr :: body)
+      if (stat.isInstanceOf[MemberDef] && stat.symbol.exists)
+        restoredDecls.enter(stat.symbol)
+    val cinfo = tree.symbol.asClass.classInfo
+    tree.symbol.copySymDenotation(
+      info = cinfo.derivedClassInfo( // Dotty deviation: Cannot expand cinfo inline without a type error
+        decls = restoredDecls: Scope)).installAfter(thisTransform)
+    tree
+  }
+}

src/dotty/tools/dotc/typer/Applications.scala

@@ -461,7 +461,7 @@ trait Applications extends Compatibility { self: Typer =>
 
     val result = {
       var typedArgs = typedArgBuf.toList
-      val app0 = cpy.Apply(app)(normalizedFun, typedArgs)
+      def app0 = cpy.Apply(app)(normalizedFun, typedArgs) // needs to be a `def` because typedArgs can change later
       val app1 =
         if (!success) app0.withType(ErrorType)
         else {

test/dotc/tests.scala

@@ -15,7 +15,7 @@ class tests extends CompilerTest {
 
   implicit val defaultOptions = noCheckOptions ++ List(
       "-Yno-deep-subtypes",
-      "-Ycheck:patternMatcher,gettersSetters,flatten"
+      "-Ycheck:patternMatcher,gettersSetters,restoreScopes"
   )
 
   val twice = List("#runs", "2", "-YnoDoubleBindings")