Replaced overridden init methods with prepareForUnit.

This allows to move to a functional implementation later.
Only exception: CapturedVars still uses init() because it
contains a (dubious!) interaction with intialization and
transformSym. Looking at this next.

Author: odersky

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

@@ -26,9 +26,10 @@ import dotty.tools.dotc.config.JavaPlatform
 class CollectEntryPoints extends MiniPhaseTransform {
 
   /** perform context-dependant initialization */
-  override def init(implicit ctx: Context, info: TransformerInfo): Unit = {
+  override def prepareForUnit(tree: tpd.Tree)(implicit ctx: Context) = {
     entryPoints = collection.immutable.TreeSet.empty[Symbol](new SymbolOrdering())
     assert(ctx.platform.isInstanceOf[JavaPlatform], "Java platform specific phase")
+    this
   }
 
   private var entryPoints: Set[Symbol] = _

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

@@ -53,11 +53,12 @@ class InterceptedMethods extends MiniPhaseTransform {
   private var primitiveGetClassMethods: Set[Symbol] = _
 
   /** perform context-dependant initialization */
-  override def init(implicit ctx: Context, info: TransformerInfo): Unit = {
+  override def prepareForUnit(tree: Tree)(implicit ctx: Context) = {
     poundPoundMethods = Set(defn.Any_##)
     Any_comparisons = Set(defn.Any_==, defn.Any_!=)
     interceptedMethods = poundPoundMethods ++ Any_comparisons
     primitiveGetClassMethods = Set[Symbol]() ++ defn.ScalaValueClasses.map(x => x.requiredMethod(nme.getClass_))
+    this
   }
 
   // this should be removed if we have guarantee that ## will get Apply node

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

@@ -278,20 +278,26 @@ class LambdaLift extends MiniPhaseTransform with IdentityDenotTransformer { this
     }
   }
 
-  override def init(implicit ctx: Context, info: TransformerInfo) =
+  override def prepareForUnit(tree: Tree)(implicit ctx: Context) = {
     ctx.atPhase(thisTransform) { implicit ctx =>
-      free.clear()
-      proxyMap.clear()
-      called.clear()
-      calledFromInner.clear()
-      liftedOwner.clear()
-      liftedDefs.clear()
       (new CollectDependencies).traverse(NoSymbol, ctx.compilationUnit.tpdTree)
       computeFreeVars()
       computeLiftedOwners()
       generateProxies()(ctx.withPhase(thisTransform.next))
       liftLocals()(ctx.withPhase(thisTransform.next))
     }
+    this
+  }
+
+  override def transformUnit(tree: Tree)(implicit ctx: Context, info: TransformerInfo) = {
+    free.clear()
+    proxyMap.clear()
+    called.clear()
+    calledFromInner.clear()
+    liftedOwner.clear()
+    liftedDefs.clear()
+    tree
+  }
 
   private def currentEnclosure(implicit ctx: Context) =
     ctx.owner.enclosingMethod.skipConstructor

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

@@ -39,9 +39,10 @@ class SyntheticMethods extends MiniPhaseTransform with IdentityDenotTransformer
   private var valueSymbols: List[Symbol] = _
   private var caseSymbols: List[Symbol] = _
 
-  override def init(implicit ctx: Context, info: TransformerInfo) = {
+  override def prepareForUnit(tree: Tree)(implicit ctx: Context) = {
     valueSymbols = List(defn.Any_hashCode, defn.Any_equals)
     caseSymbols = valueSymbols ++ List(defn.Any_toString, defn.Product_canEqual, defn.Product_productArity)
+    this
   }
 
   /** The synthetic methods of the case or value class `clazz`.