Change Tasty parameter encoding

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

@@ -69,9 +69,10 @@ Standard-Section: "ASTs" TopLevelStat*
                   BOUNDED               type_Term                                  -- type bound
 
   TypeParam     = TYPEPARAM      Length NameRef type_Term Modifier*                -- modifiers name bounds
-  Params        = PARAMS         Length Param*
   Param         = PARAM          Length NameRef type_Term rhs_Term? Modifier*      -- modifiers name : type (= rhs_Term)?. `rhsTerm` is present in the case of an aliased class parameter
-  Template      = TEMPLATE       Length TypeParam* Params* parent_Term* Self? Stat* -- [typeparams] paramss extends parents { self => stats }, where Stat* always starts with the primary constructor.
+                  PARAMEND                                                         -- ends a parameter clause
+                                                																   -- needed if previous parameter clause is empty or another parameter clause follows
+  Template      = TEMPLATE       Length TypeParam* Param* parent_Term* Self? Stat* -- [typeparams] paramss extends parents { self => stats }, where Stat* always starts with the primary constructor.
   Self          = SELFDEF               selfName_NameRef selfType_Term             -- selfName : selfType
 
   Term          = Path                                                             -- Paths represent both types and terms
@@ -252,7 +253,7 @@ Standard Section: "Comments" Comment*
 object TastyFormat {
 
   final val header: Array[Int] = Array(0x5C, 0xA1, 0xAB, 0x1F)
-  val MajorVersion: Int = 17
+  val MajorVersion: Int = 18
   val MinorVersion: Int = 0
 
   /** Tags used to serialize names */
@@ -273,7 +274,7 @@ object TastyFormat {
     final val DEFAULTGETTER = 11     // The name `<meth-name>$default$<param-num>`
                                      // of a default getter that returns a default argument.
 
-    final val VARIANT = 12           // A name `+<name>` o `-<name>` indicating
+    final val VARIANT = 12           // A name `+<name>` or `-<name>` indicating
                                      // a co- or contra-variant parameter of a type lambda.
 
     final val SUPERACCESSOR = 20     // The name of a super accessor `super$name` created by SuperAccesors.
@@ -334,6 +335,7 @@ object TastyFormat {
   final val PARAMsetter = 38
   final val EXPORTED = 39
   final val OPEN = 40
+  final val PARAMEND = 41
 
   // Cat. 2:    tag Nat
 
@@ -394,8 +396,7 @@ object TastyFormat {
   final val TYPEDEF = 131
   final val IMPORT = 132
   final val TYPEPARAM = 133
-  final val PARAMS = 134
-  final val PARAM = 135
+  final val PARAM = 134
   final val APPLY = 136
   final val TYPEAPPLY = 137
   final val TYPED = 138
@@ -462,7 +463,7 @@ object TastyFormat {
 
   /** Useful for debugging */
   def isLegalTag(tag: Int): Boolean =
-    firstSimpleTreeTag <= tag && tag <= OPEN ||
+    firstSimpleTreeTag <= tag && tag <= PARAMEND ||
     firstNatTreeTag <= tag && tag <= RENAMED ||
     firstASTTreeTag <= tag && tag <= BOUNDED ||
     firstNatASTTreeTag <= tag && tag <= NAMEDARG ||
@@ -569,6 +570,7 @@ object TastyFormat {
     case PARAMsetter => "PARAMsetter"
     case EXPORTED => "EXPORTED"
     case OPEN => "OPEN"
+    case PARAMEND => "PARAMEND"
 
     case SHAREDterm => "SHAREDterm"
     case SHAREDtype => "SHAREDtype"
@@ -602,7 +604,6 @@ object TastyFormat {
     case TYPEDEF => "TYPEDEF"
     case IMPORT => "IMPORT"
     case TYPEPARAM => "TYPEPARAM"
-    case PARAMS => "PARAMS"
     case PARAM => "PARAM"
     case IMPORTED => "IMPORTED"
     case RENAMED => "RENAMED"

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

@@ -494,13 +494,15 @@ class TreePickler(pickler: TastyPickler) {
         case tree: ValDef =>
           pickleDef(VALDEF, tree.symbol, tree.tpt, tree.rhs)
         case tree: DefDef =>
-          def pickleAllParams = {
+          def pickleParamss(paramss: List[List[ValDef]]): Unit = paramss match
+            case Nil =>
+            case params :: rest =>
+              pickleParams(params)
+              if params.isEmpty || rest.nonEmpty then writeByte(PARAMEND)
+              pickleParamss(rest)
+          def pickleAllParams =
             pickleParams(tree.tparams)
-            for (vparams <- tree.vparamss) {
-              writeByte(PARAMS)
-              withLength { pickleParams(vparams) }
-            }
-          }
+            pickleParamss(tree.vparamss)
           pickleDef(DEFDEF, tree.symbol, tree.tpt, tree.rhs, pickleAllParams)
         case tree: TypeDef =>
           pickleDef(TYPEDEF, tree.symbol, tree.rhs)

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

@@ -131,7 +131,10 @@ class TreeUnpickler(reader: TastyReader,
     def skipTree(): Unit = skipTree(readByte())
 
     def skipParams(): Unit =
-      while (nextByte == PARAMS || nextByte == TYPEPARAM) skipTree()
+      while
+        val tag = nextByte
+        tag == PARAM || tag == TYPEPARAM || tag == PARAMEND
+      do skipTree()
 
     /** Record all directly nested definitions and templates in current tree
      *  as `OwnerTree`s in `buf`.
@@ -747,12 +750,12 @@ class TreeUnpickler(reader: TastyReader,
       val tag = readByte()
       val end = readEnd()
 
-      def readParamss(implicit ctx: Context): List[List[ValDef]] =
-        collectWhile(nextByte == PARAMS) {
-          readByte()
-          readEnd()
-          readParams[ValDef](PARAM)
-        }
+      def readParamss(implicit ctx: Context): List[List[ValDef]] = nextByte match
+        case PARAM | PARAMEND =>
+          readParams[ValDef](PARAM) ::
+            (if nextByte == PARAMEND then { readByte(); readParamss } else Nil)
+        case _ =>
+          Nil
 
       val localCtx = localContext(sym)
 
@@ -987,10 +990,11 @@ class TreeUnpickler(reader: TastyReader,
     def readIndexedParams[T <: MemberDef](tag: Int)(implicit ctx: Context): List[T] =
       collectWhile(nextByte == tag) { readIndexedDef().asInstanceOf[T] }
 
-    def readParams[T <: MemberDef](tag: Int)(implicit ctx: Context): List[T] = {
-      fork.indexParams(tag)
-      readIndexedParams(tag)
-    }
+    def readParams[T <: MemberDef](tag: Int)(implicit ctx: Context): List[T] =
+      if nextByte == tag then
+        fork.indexParams(tag)
+        readIndexedParams(tag)
+      else Nil
 
 // ------ Reading trees -----------------------------------------------------