Pickle comments positions

We're not reusing the PositionPickler for this task, because it is very
tied to pickling the positions of `Tree`s, which `Comment`s are not.

We simply pickle the coordinates of the comment, and reconstruct the
position from the coordinates when unpickling.

Author: Duhemm

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

@@ -23,6 +23,7 @@ class CommentPickler(pickler: TastyPickler, addrOfTree: tpd.Tree => Option[Addr]
       buf.writeAddr(addr)
       buf.writeNat(length)
       buf.writeBytes(bytes, length)
+      buf.writeLongInt(cmt.pos.coords)
       buf.writeByte(if (cmt.isExpanded) 1 else 0)
     case other =>
       ()

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

@@ -3,7 +3,7 @@ package dotty.tools.dotc.core.tasty
 import dotty.tools.dotc.core.Comments.Comment
 import dotty.tools.dotc.core.Symbols.Symbol
 import dotty.tools.dotc.core.tasty.TastyBuffer.Addr
-import dotty.tools.dotc.util.Positions
+import dotty.tools.dotc.util.Positions.Position
 
 import scala.collection.mutable.HashMap
 
@@ -19,9 +19,10 @@ class CommentUnpickler(reader: TastyReader) {
       val length = readNat()
       if (length > 0) {
         val bytes = readBytes(length)
+        val position = new Position(readLongInt())
         val expanded = readByte() == 1
         val rawComment = new String(bytes, Charset.forName("UTF-8"))
-        comments(addr) = Comment(Positions.NoPosition, rawComment, expanded = expanded)
+        comments(addr) = Comment(position, rawComment, expanded = expanded)
       }
     }
     comments.toMap

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

@@ -235,8 +235,8 @@ Standard Section: "Positions" Assoc*
 
 Standard Section: "Comments" Comment*
 
-  Comment       = Length Bytes Byte         // Raw comment's bytes encoded as UTF-8, plus a byte indicating
-                                            // whether the comment is expanded (1) or not expanded (0)
+  Comment       = Length Bytes LongInt Byte // Raw comment's bytes encoded as UTF-8, followed by the comment's coordinates,
+                                            // plus a byte indicating whether the comment is expanded (1) or not expanded (0)
 
 
 **************************************************************************************/