Simplifications to TASTy format

1) Drop the length field of BYNAMEparam
2) Eliminate EMPTYTREE

Author: odersky

src/dotty/tools/dotc/core/pickling/PickleFormat.scala

@@ -137,7 +137,8 @@ Standard-Section: "ASTs" TopLevelStat*
                   ORtype         Length left_Type right_Type
                   BIND           Length boundName_NameRef bounds_Type selfRef_Type
                                         // for type-variables defined in a type pattern
-                                        // bounds = type bounds, selfRef = reference to type itself.                  BYNAMEtype    Length underlying_Type
+                                        // bounds = type bounds, selfRef = reference to type itself.                  
+                  BYNAMEtype            underlying_Type
                   POLYtype       Length result_Type NamesTypes      // needed for refinements
                   METHODtype     Length result_Type NamesTypes      // needed for refinements
                   PARAMtype      Length binder_ASTref paramNum_Nat  // needed for refinements
@@ -224,7 +225,6 @@ object PickleFormat {
 
 // AST tags
 
-  final val EMPTYTREE = 0
   final val NOTYPE = 1
   final val UNITconst = 2
   final val FALSEconst = 3
@@ -278,10 +278,11 @@ object PickleFormat {
   final val THIS = 96
   final val CLASSconst = 97
   final val ENUMconst = 98
-  final val NEW = 99
-  final val IMPLICITarg = 100
-  final val PRIVATEqualified = 101
-  final val PROTECTEDqualified = 102
+  final val BYNAMEtype = 99
+  final val NEW = 100
+  final val IMPLICITarg = 101
+  final val PRIVATEqualified = 102
+  final val PROTECTEDqualified = 103
 
   final val IDENT = 112
   final val SELECT = 113
@@ -327,13 +328,12 @@ object PickleFormat {
   final val TYPEALIAS = 170
   final val ANDtype = 171
   final val ORtype = 172
-  final val BYNAMEtype = 173
   final val METHODtype = 174
   final val POLYtype = 175
   final val PARAMtype = 176
   final val ANNOTATION = 178
 
-  final val firstSimpleTreeTag = EMPTYTREE
+  final val firstSimpleTreeTag = NOTYPE
   final val firstNatTreeTag = SHARED
   final val firstASTTreeTag = THIS
   final val firstNatASTTreeTag = IDENT
@@ -387,7 +387,6 @@ object PickleFormat {
   }
 
   def astTagToString(tag: Int): String = tag match {
-    case EMPTYTREE => "EMPTYTREE"
     case NOTYPE => "NOTYPE"
     case UNITconst => "UNITconst"
     case FALSEconst => "FALSEconst"

src/dotty/tools/dotc/core/pickling/TreePickler.scala

@@ -230,7 +230,7 @@ class TreePickler(pickler: TastyPickler) {
         withLength { pickleType(tpe.tp1, richTypes); pickleType(tpe.tp2, richTypes) }
       case tpe: ExprType =>
         writeByte(BYNAMEtype)
-        withLength { pickleType(tpe.underlying) }
+        pickleType(tpe.underlying)
       case tpe: MethodType if richTypes =>
         writeByte(METHODtype)
         pickleMethodic(tpe.resultType, tpe.paramNames, tpe.paramTypes)
@@ -448,8 +448,6 @@ class TreePickler(pickler: TastyPickler) {
       case PackageDef(pid, stats) =>
         writeByte(PACKAGE)
         withLength { pickleType(pid.tpe); pickleStats(stats) }
-      case EmptyTree =>
-        writeByte(EMPTYTREE)
     }}
     catch {
       case ex: AssertionError =>
@@ -486,7 +484,7 @@ class TreePickler(pickler: TastyPickler) {
 
     def pickleStats(stats: List[Tree]) = {
       stats.foreach(preRegister)
-      stats.foreach(pickleTree)
+      stats.foreach(stat => if (!stat.isEmpty) pickleTree(stat))
     }
 
     def pickleModifiers(sym: Symbol): Unit = {
@@ -534,7 +532,7 @@ class TreePickler(pickler: TastyPickler) {
       withLength { pickleType(ann.symbol.typeRef); pickleTree(ann.tree) }
     }
 
-    trees.foreach(pickleTree)
+    trees.foreach(tree => if (!tree.isEmpty) pickleTree(tree))
     assert(forwardSymRefs.isEmpty, i"unresolved symbols: ${forwardSymRefs.keySet.toList}%, %")
     compactify()
   }  

src/dotty/tools/dotc/core/pickling/TreeUnpickler.scala

@@ -204,8 +204,6 @@ class TreeUnpickler(reader: TastyReader, tastyName: TastyName.Table) {
               symAtAddr(start) = 
                 ctx.newSymbol(ctx.owner, readName().toTypeName, BindDefinedType, readType())
               readType()
-            case BYNAMEtype =>
-              ExprType(readType())
             case POLYtype =>
               val (names, paramReader) = readNamesSkipParams[TypeName]
               val result = PolyType(names)(
@@ -298,6 +296,8 @@ class TreeUnpickler(reader: TastyReader, tastyName: TastyName.Table) {
           ConstantType(Constant(readName().toString))
         case NULLconst =>
           ConstantType(Constant(null))
+        case BYNAMEtype =>
+          ExprType(readType())
       }
 
       if (tag < firstLengthTreeTag) readSimpleType() else readLengthType()
@@ -464,7 +464,7 @@ class TreeUnpickler(reader: TastyReader, tastyName: TastyName.Table) {
           nextByte match {
             case VALDEF | DEFDEF | TYPEDEF | TYPEPARAM | PARAM => 
               createSymbol() 
-            case EMPTYTREE | IMPORT => 
+            case IMPORT => 
               skipTree()
               true
             case PACKAGE => 
@@ -706,8 +706,6 @@ class TreeUnpickler(reader: TastyReader, tastyName: TastyName.Table) {
 
         case NEW =>
           New(readTpt())
-        case EMPTYTREE =>
-          EmptyTree
         case _ =>
           readPathTerm()
       }