1 files changed, 67 insertions, 0 deletions
diff --git a/src/dotty/tools/dotc/core/pickling/PositionReader.scala b/src/dotty/tools/dotc/core/pickling/PositionReader.scala
new file mode 100644
index 000000000..5acb3c6d8
--- /dev/null
+++ b/src/dotty/tools/dotc/core/pickling/PositionReader.scala
@@ -0,0 +1,67 @@
+package dotty.tools
+package dotc
+package core
+package pickling
+
+import java.io.IOException
+
+import Contexts._
+import ast.tpd
+import ast.Trees.{Lazy,WithLazyField}
+import TastyBuffer._
+import Traversals._
+import util.Positions._
+
+/** Unpickler for start or end offset of tree positions */
+class PositionReader(reader: TastyReader, startOffset: Int, initNextOffset: Int, initNextAddr: Int) {
+  import reader._
+  import tpd._
+      
+  def this(reader: TastyReader) = {
+    this(reader, 0, 0, 0)
+    next()
+  }
+  
+  var lastOffset: Int = startOffset
+  var nextOffset = initNextOffset
+  var nextAddr = initNextAddr
+  
+  private def fork = 
+    new PositionReader(subReader(currentAddr, endAddr), lastOffset, nextOffset, nextAddr)
+  
+  private def next() = {
+    lastOffset = nextOffset
+    if (!isAtEnd) {
+      nextOffset += readInt()
+      nextAddr += readInt()
+    }
+  }  
+
+  def readStart(tree: Tree) = 
+    if (tree.pos.exists) { // TODO assign positions of tree nodes with NoPosition afterwards based on the context.
+      val addr = tree.pos.end
+      if (addr == nextAddr) next()
+      tree.setPosUnchecked(tree.pos.withStart(lastOffset))
+    }
+  
+  def readEnd(tree: Tree) = {
+    if (tree.pos.exists) {
+      val addr = tree.pos.end
+      tree match {
+        case tree: WithLazyField[_] =>
+          tree.unforced match {
+            case rdr: TreeUnpickler#LazyReader[_] =>
+              rdr.posReader = Some(fork)
+              while (addr != nextAddr) next()
+            case _ =>
+          }
+        case _ =>
+      }
+      if (addr == nextAddr) next()
+      tree.setPosUnchecked(tree.pos.withEnd(lastOffset))
+    }
+  }
+  
+  def unpickle(x: Any) =
+    traverse(x, readStart, readEnd)
+}
+\ No newline at end of file