Clarify methodTypeTag

Author: odersky

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

@@ -441,10 +441,10 @@ object TastyFormat {
   final val MATCHtype = 190
   final val MATCHtpt = 191
 
-  def methodType(isContextual: Boolean, isImplicit: Boolean, isErased: Boolean): Int = {
+  def methodTypeTag(isContextual: Boolean, isOldImplicit: Boolean, isErased: Boolean): Int = {
     val implicitOffset =
       if (isContextual) 2
-      else if (isImplicit) { assert(!isErased); 4 }
+      else if (isOldImplicit) { assert(!isErased); 4 }
       else 0
     val erasedOffset = if (isErased) 1 else 0
     METHODtype + erasedOffset + implicitOffset

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

@@ -259,7 +259,11 @@ class TreePickler(pickler: TastyPickler) {
     case tpe: PolyType if richTypes =>
       pickleMethodic(POLYtype, tpe)
     case tpe: MethodType if richTypes =>
-      pickleMethodic(methodType(tpe.isContextual, tpe.isImplicitMethod, tpe.isErasedMethod), tpe)
+      val tag = methodTypeTag(
+        isContextual = tpe.isContextual,
+        isOldImplicit = tpe.isImplicitMethod && !tpe.isContextual,
+        isErased = tpe.isErasedMethod)
+      pickleMethodic(tag, tpe)
     case tpe: ParamRef =>
       assert(pickleParamRef(tpe), s"orphan parameter reference: $tpe")
     case tpe: LazyRef =>