TASTY 3.0: Distinguish SHARED terms from types

In general, this makes things easier to debug at virtually no cost. It
also makes it much easier to properly set positions on unpickled
TypeTrees: in TreeUnpickler#readTpt we can know make sure that the
position of the TypeTree is unpickled from the address found after
following all shared terms but before following any shared type.

Note that the major version bump could have been avoided by adding some
compatibility code, but that doesn't seem worthwhile until Tasty is used
in the wild.

Author: smarter

compiler/src/dotty/tools/dotc/core/tasty/TastyFormat.scala

@@ -108,7 +108,7 @@ Standard-Section: "ASTs" TopLevelStat*
                   ORtpt          Length left_Term right_Term
                   BYNAMEtpt             underlying_Term
                   EMPTYTREE
-                  SHARED                term_ASTRef
+                  SHAREDterm            term_ASTRef
                   HOLE           Length idx_Nat arg_Tree*
   Application   = APPLY          Length fn_Term arg_Term*
 
@@ -125,7 +125,7 @@ Standard-Section: "ASTs" TopLevelStat*
                   TERMREF               possiblySigned_NameRef qual_Type
                   THIS                  clsRef_Type
                   RECthis               recType_ASTRef
-                  SHARED                path_ASTRef
+                  SHAREDtype            path_ASTRef
 
   Constant      = UNITconst
                   FALSEconst
@@ -165,7 +165,7 @@ Standard-Section: "ASTs" TopLevelStat*
                   POLYtype       Length result_Type NamesTypes
                   METHODtype     Length result_Type NamesTypes      // needed for refinements
                   TYPELAMBDAtype Length result_Type NamesTypes      // variance encoded in front of name: +/-/(nothing)
-                  SHARED                type_ASTRef
+                  SHAREDtype            type_ASTRef
   NamesTypes    = NameType*
   NameType      = paramName_NameRef typeOrBounds_ASTRef
 
@@ -226,8 +226,8 @@ Standard Section: "Positions" Assoc*
 object TastyFormat {
 
   final val header = Array(0x5C, 0xA1, 0xAB, 0x1F)
-  val MajorVersion = 2
-  val MinorVersion = 1
+  val MajorVersion = 3
+  val MinorVersion = 0
 
   /** Tags used to serialize names */
   class NameTags {
@@ -302,23 +302,24 @@ object TastyFormat {
 
   // Cat. 2:    tag Nat
 
-  final val SHARED = 50
-  final val TERMREFdirect = 51
-  final val TYPEREFdirect = 52
-  final val TERMREFpkg = 53
-  final val TYPEREFpkg = 54
-  final val RECthis = 55
-  final val BYTEconst = 56
-  final val SHORTconst = 57
-  final val CHARconst = 58
-  final val INTconst = 59
-  final val LONGconst = 60
-  final val FLOATconst = 61
-  final val DOUBLEconst = 62
-  final val STRINGconst = 63
-  final val IMPORTED = 64
-  final val RENAMED = 65
-  final val SYMBOLconst = 66
+  final val SHAREDterm = 50
+  final val SHAREDtype = 51
+  final val TERMREFdirect = 52
+  final val TYPEREFdirect = 53
+  final val TERMREFpkg = 54
+  final val TYPEREFpkg = 55
+  final val RECthis = 56
+  final val BYTEconst = 57
+  final val SHORTconst = 58
+  final val CHARconst = 59
+  final val INTconst = 60
+  final val LONGconst = 61
+  final val FLOATconst = 62
+  final val DOUBLEconst = 63
+  final val STRINGconst = 64
+  final val IMPORTED = 65
+  final val RENAMED = 66
+  final val SYMBOLconst = 67
 
   // Cat. 3:    tag AST
 
@@ -402,7 +403,7 @@ object TastyFormat {
   final val HOLE = 255
 
   final val firstSimpleTreeTag = UNITconst
-  final val firstNatTreeTag = SHARED
+  final val firstNatTreeTag = SHAREDterm
   final val firstASTTreeTag = THIS
   final val firstNatASTTreeTag = IDENT
   final val firstLengthTreeTag = PACKAGE
@@ -492,7 +493,8 @@ object TastyFormat {
     case DEFAULTparameterized => "DEFAULTparameterized"
     case STABLE => "STABLE"
 
-    case SHARED => "SHARED"
+    case SHAREDterm => "SHAREDterm"
+    case SHAREDtype => "SHAREDtype"
     case TERMREFdirect => "TERMREFdirect"
     case TYPEREFdirect => "TYPEREFdirect"
     case TERMREFpkg => "TERMREFpkg"

compiler/src/dotty/tools/dotc/core/tasty/TreePickler.scala

@@ -143,7 +143,7 @@ class TreePickler(pickler: TastyPickler) {
         pickleNewType(tpe, richTypes)
       }
       else {
-        writeByte(SHARED)
+        writeByte(SHAREDtype)
         writeRef(prev.asInstanceOf[Addr])
       }
     } catch {
@@ -330,7 +330,7 @@ class TreePickler(pickler: TastyPickler) {
   def pickleTree(tree: Tree)(implicit ctx: Context): Unit = {
     val addr = registerTreeAddr(tree)
     if (addr != currentAddr) {
-      writeByte(SHARED)
+      writeByte(SHAREDterm)
       writeRef(addr)
     }
     else

compiler/src/dotty/tools/dotc/core/tasty/TreeUnpickler.scala

@@ -152,7 +152,7 @@ class TreeUnpickler(reader: TastyReader,
     /** The next tag, following through SHARED tags */
     def nextUnsharedTag: Int = {
       val tag = nextByte
-      if (tag == SHARED) {
+      if (tag == SHAREDtype || tag == SHAREDterm) {
         val lookAhead = fork
         lookAhead.reader.readByte()
         forkAt(lookAhead.reader.readAddr()).nextUnsharedTag
@@ -321,7 +321,7 @@ class TreeUnpickler(reader: TastyReader,
           readTypeRef().asInstanceOf[RecType].recThis
         case TYPEALIAS =>
           TypeAlias(readType())
-        case SHARED =>
+        case SHAREDtype =>
           val ref = readAddr()
           typeAtAddr.getOrElseUpdate(ref, forkAt(ref).readType())
         case UNITconst =>
@@ -899,7 +899,7 @@ class TreeUnpickler(reader: TastyReader,
       }
 
       def readSimpleTerm(): Tree = tag match {
-        case SHARED =>
+        case SHAREDterm =>
           forkAt(readAddr()).readTerm()
         case IDENT =>
           untpd.Ident(readName()).withType(readType())
@@ -1051,16 +1051,16 @@ class TreeUnpickler(reader: TastyReader,
     }
 
     def readTpt()(implicit ctx: Context) =
-      if (isTypeTreeTag(nextUnsharedTag)) readTerm()
+      if (nextByte == SHAREDterm || isTypeTreeTag(nextUnsharedTag)) readTerm()
       else {
         val start = currentAddr
         val tp = readType()
         if (tp.exists) setPos(start, TypeTree(tp)) else EmptyTree
       }
 
     def readCases(end: Addr)(implicit ctx: Context): List[CaseDef] =
-      collectWhile((nextByte == CASEDEF || nextByte == SHARED) && currentAddr != end) {
-        if (nextByte == SHARED) {
+      collectWhile((nextByte == CASEDEF || nextByte == SHAREDterm) && currentAddr != end) {
+        if (nextByte == SHAREDterm) {
           readByte()
           forkAt(readAddr()).readCase()(ctx.fresh.setNewScope)
         }