Added testing hooks for unpickler

New option -Ytest-pickler compares trees before and after pickling.

1 files changed, 26 insertions, 16 deletions

diff --git a/src/dotty/tools/dotc/core/pickling/PositionPickler.scala b/src/dotty/tools/dotc/core/pickling/PositionPickler.scala
index 6215a452d..8ee70719e 100644
--- a/src/dotty/tools/dotc/core/pickling/PositionPickler.scala
+++ b/src/dotty/tools/dotc/core/pickling/PositionPickler.scala
@@ -41,24 +41,34 @@ class PositionPickler(pickler: TastyPickler, addrOfTree: Tree => Option[Addr]) {
   val buf = new TastyBuffer(100000)
   pickler.newSection("Positions", buf)
   import buf._
-  
-  private def record(tree: Tree, parentPos: Position): Unit = {
-    assert(tree.pos.exists)
-    val startDelta = tree.pos.start - parentPos.start
-    val endDelta = tree.pos.end - parentPos.end
-    if (startDelta != 0 || endDelta != 0)
-      for (addr <- addrOfTree(tree)) {
-        buf.writeInt(addr.index)
-        if (startDelta != 0) buf.writeInt(startDelta)
-        if (endDelta != 0) {
-          assert(endDelta < 0)
-          buf.writeInt(endDelta)
-        } else assert(startDelta >= 0)
-      }
-    
-  }
     
   def picklePositions(roots: List[Tree], totalRange: Position)(implicit ctx: Context) = {
+    var lastIndex = 0
+    def record(tree: Tree, parentPos: Position): Unit =
+      if (tree.pos.exists) {
+        def msg = s"failure to pickle $tree at ${tree.pos}, parent = $parentPos"
+        val endPos = tree.pos.end min parentPos.end 
+          // end positions can be larger than their parents
+          // e.g. in the case of synthetic empty ranges, which are placed at the next token after
+          // the current construct.
+        val endDelta = endPos - parentPos.end
+        val startPos = 
+          if (endDelta == 0) tree.pos.start max parentPos.start else tree.pos.start min endPos
+          // Since end positions are corrected above, start positions have to follow suit.
+        val startDelta = startPos - parentPos.start
+        if (startDelta != 0 || endDelta != 0)
+          for (addr <- addrOfTree(tree)) {
+            buf.writeInt(addr.index - lastIndex)
+            lastIndex = addr.index
+            if (startDelta != 0) buf.writeInt(startDelta)
+            if (endDelta != 0) {
+              assert(endDelta < 0, msg)
+              buf.writeInt(endDelta)
+            } else
+              assert(startDelta >= 0, msg)
+          }
+      }
+    
     buf.writeNat(totalRange.end)
     traverse(roots, totalRange, record)
   }