Extend comment about @quoteTypeTag

Author: nicolasstucki

compiler/src/dotty/tools/dotc/core/quoted/PickledQuotes.scala

@@ -80,7 +80,11 @@ object PickledQuotes {
     val unpickled = unpickle(tastyBytes, args, isType = true)(ctx.addMode(Mode.ReadPositions))
     val tpt = unpickled match {
       case Block(aliases, tpt) =>
-        // `@quoteTypeTag type` aliasses are not required after unpickling
+        // `@quoteTypeTag type` aliases are not required after unpickling.
+        // Type definitions are placeholders for type holes in the pickled quote, at this point
+        // those holes have been filled. As we already dealias al references to them in `dealiasTypeTags`
+        // there is no need to keep their definitions in the tree. As artifacts of quote reification
+        // they also do not have a meaningful position in the source.
         val aliases1 = aliases.filter(!_.symbol.hasAnnotation(defn.InternalQuoted_QuoteTypeTagAnnot))
         seq(aliases1, tpt)
       case tpt => tpt