Give attribute a semantic kind

Author: nicolasstucki

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

@@ -3,7 +3,7 @@ package dotty.tools.dotc.core.tasty
 import dotty.tools.dotc.ast.{tpd, untpd}
 
 import dotty.tools.tasty.TastyBuffer
-import dotty.tools.tasty.TastyFormat.AttributesSection
+import dotty.tools.tasty.TastyFormat, TastyFormat.AttributesSection
 
 import java.nio.charset.StandardCharsets
 
@@ -19,6 +19,7 @@ object AttributePickler:
           val bytes = attribute.getBytes(StandardCharsets.UTF_8).nn
           val length = bytes.length
           assert("[a-zA-Z0-9]+".r.matches(attribute), s"Malformed attribute: $attribute\n. Attribute must match [a-zA-Z0-9]+")
+          buf.writeNat(TastyFormat.FLAGattr)
           buf.writeNat(length)
           buf.writeBytes(bytes, length)
   end pickleAttributes

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

@@ -13,6 +13,8 @@ class AttributeUnpickler(reader: TastyReader):
   private[tasty] lazy val attributes: List[String] = {
     val attributesBuilder = List.newBuilder[String]
     while (!isAtEnd) {
+      val kind = readNat()
+      assert(kind == TastyFormat.FLAGattr, "Malformed attribute kind")
       val length = readNat()
       val bytes = readBytes(length)
       val attribute = new String(bytes, StandardCharsets.UTF_8)

tasty/src/dotty/tools/tasty/TastyFormat.scala

@@ -270,7 +270,7 @@ Standard Section: "Comments" Comment*
 
 Standard Section: "Attributes" Attribute*
 ```none
-  Attribute     = UTF8                      // attributes match the regex [a-zA-Z0-9]+
+  Attribute     = FLAGattr UTF8             // attributes match the regex [a-zA-Z0-9]+
 ```
 
 **************************************************************************************/
@@ -606,6 +606,11 @@ object TastyFormat {
   final val firstNatASTTreeTag = IDENT
   final val firstLengthTreeTag = PACKAGE
 
+
+  // Attribute tags
+
+  final val FLAGattr = 1
+
   /** Useful for debugging */
   def isLegalTag(tag: Int): Boolean =
     firstSimpleTreeTag <= tag && tag <= SPLITCLAUSE ||