Avoid capturing context in lazy trees

Lazy trees can live longer than runs, so it is important
that they capture as little as possible. In particular they
should not capture contexts.

This change led with a ripple through effect to many changes
where operations now have to parameterzied with contexts, in
particular in what concerns tree folding.

The changes in turn uncovered some areas where dotc was
incompatible with scalac, and flagged correct things as errors.
These will be fixed in the next commits.

Another small twist: EmptyTrees will not be read in delayed mode,
so that one can check for lacking definitions without deserializing
the rhs.

1 files changed, 1 insertions, 1 deletions

diff --git a/src/dotty/tools/dotc/typer/Checking.scala b/src/dotty/tools/dotc/typer/Checking.scala
index 1354b8926..f7502d56d 100644
--- a/src/dotty/tools/dotc/typer/Checking.scala
+++ b/src/dotty/tools/dotc/typer/Checking.scala
@@ -169,7 +169,7 @@ object Checking {
     val checkTree = new TreeAccumulator[Unit] {
       def checkRef(tree: Tree, sym: Symbol) =
         if (sym.maybeOwner == refineCls && !seen(sym)) forwardRef(tree)
-      def apply(x: Unit, tree: Tree) = tree match {
+      def apply(x: Unit, tree: Tree)(implicit ctx: Context) = tree match {
         case tree: MemberDef =>
           foldOver(x, tree)
           seen += tree.symbol