1 files changed, 66 insertions, 0 deletions
diff --git a/compiler/src/dotty/tools/dotc/transform/LiftTry.scala b/compiler/src/dotty/tools/dotc/transform/LiftTry.scala
new file mode 100644
index 000000000..6a273b91e
--- /dev/null
+++ b/compiler/src/dotty/tools/dotc/transform/LiftTry.scala
@@ -0,0 +1,66 @@
+package dotty.tools.dotc
+package transform
+
+import TreeTransforms._
+import core.DenotTransformers._
+import core.Symbols._
+import core.Contexts._
+import core.Types._
+import core.Flags._
+import core.Decorators._
+import NonLocalReturns._
+
+/** Lifts try's that might be executed on non-empty expression stacks
+ *  to their own methods. I.e.
+ *
+ *      try body catch handler
+ *
+ *  is lifted to
+ *
+ *      { def liftedTree$n() = try body catch handler; liftedTree$n() }
+ */
+class LiftTry extends MiniPhase with IdentityDenotTransformer { thisTransform =>
+  import ast.tpd._
+
+  /** the following two members override abstract members in Transform */
+  val phaseName: String = "liftTry"
+
+  val treeTransform = new Transform(needLift = false)
+  val liftingTransform = new Transform(needLift = true)
+
+  class Transform(needLift: Boolean) extends TreeTransform {
+    def phase = thisTransform
+
+    override def prepareForApply(tree: Apply)(implicit ctx: Context) =
+      if (tree.fun.symbol.is(Label)) this
+      else liftingTransform
+
+    override def prepareForValDef(tree: ValDef)(implicit ctx: Context) =
+      if (!tree.symbol.exists  ||
+          tree.symbol.isSelfSym ||
+          tree.symbol.owner == ctx.owner.enclosingMethod) this
+      else liftingTransform
+
+    override def prepareForAssign(tree: Assign)(implicit ctx: Context) =
+      if (tree.lhs.symbol.maybeOwner == ctx.owner.enclosingMethod) this
+      else liftingTransform
+
+    override def prepareForReturn(tree: Return)(implicit ctx: Context) =
+      if (!isNonLocalReturn(tree)) this
+      else liftingTransform
+
+    override def prepareForTemplate(tree: Template)(implicit ctx: Context) =
+      treeTransform
+
+    override def transformTry(tree: Try)(implicit ctx: Context, info: TransformerInfo): Tree =
+      if (needLift) {
+        ctx.debuglog(i"lifting tree at ${tree.pos}, current owner = ${ctx.owner}")
+        val fn = ctx.newSymbol(
+          ctx.owner, ctx.freshName("liftedTree").toTermName, Synthetic | Method,
+          MethodType(Nil, tree.tpe), coord = tree.pos)
+        tree.changeOwnerAfter(ctx.owner, fn, thisTransform)
+        Block(DefDef(fn, tree) :: Nil, ref(fn).appliedToNone)
+      }
+      else tree
+  }
+}