Unpickle a single tree

Author: nicolasstucki

compiler/src/dotty/tools/dotc/ast/tpd.scala

@@ -892,20 +892,16 @@ object tpd extends Trees.Instance[Type] with TypedTreeInfo {
 
   /** A trait for loaders that compute trees. Currently implemented just by DottyUnpickler. */
   trait TreeProvider {
-    protected def computeTrees(implicit ctx: Context): List[Tree]
+    protected def computeTree(implicit ctx: Context): Tree
 
-    private[this] var myTrees: List[Tree] = null
-
-    /** Get trees defined by this provider. Cache them if -Yretain-trees is set. */
-    def trees(implicit ctx: Context): List[Tree] =
-      if (ctx.settings.YretainTrees.value) {
-        if (myTrees == null) myTrees = computeTrees
-        myTrees
-      } else computeTrees
+    private[this] var myTree: Tree = null
 
     /** Get first tree defined by this provider, or EmptyTree if none exists */
     def tree(implicit ctx: Context): Tree =
-      trees.headOption.getOrElse(EmptyTree)
+      if (ctx.settings.YretainTrees.value) {
+        if (myTree == null) myTree = computeTree
+        myTree
+      } else computeTree
 
     /** Is it possible that the tree to load contains a definition of or reference to `id`? */
     def mightContain(id: String)(implicit ctx: Context) = true

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

@@ -50,7 +50,7 @@ class DottyUnpickler(bytes: Array[Byte]) extends ClassfileParser.Embedded with t
     new TreeSectionUnpickler(posUnpicklerOpt)
   }
 
-  protected def computeTrees(implicit ctx: Context) = treeUnpickler.unpickle()
+  protected def computeTree(implicit ctx: Context) = treeUnpickler.unpickle()
 
   private[this] var ids: Array[String] = null
 

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

@@ -79,12 +79,12 @@ class TreeUnpickler(reader: TastyReader,
       rdr.indexStats(reader.endAddr)
   }
 
-  /** The unpickled trees */
-  def unpickle()(implicit ctx: Context): List[Tree] = {
+  /** The unpickled tree */
+  def unpickle()(implicit ctx: Context): Tree = {
     assert(roots != null, "unpickle without previous enterTopLevel")
     val rdr = new TreeReader(reader)
-    if (rdr.isTopLevel) rdr.readTopLevel()
-    else rdr.readTerm() :: Nil
+    if (rdr.isTopLevel) rdr.readTopLevel().head
+    else rdr.readTerm()
   }
 
   class Completer(owner: Symbol, reader: TastyReader) extends LazyType {

compiler/src/dotty/tools/dotc/transform/Pickler.scala

@@ -99,7 +99,7 @@ class Pickler extends Phase {
       }
     pickling.println("************* entered toplevel ***********")
     for ((cls, unpickler) <- unpicklers) {
-      val unpickled = unpickler.trees
+      val unpickled = unpickler.tree
       testSame(i"$unpickled%\n%", beforePickling(cls), cls)
     }
   }