SI-9946 make nullification of lazy val dependencies module aware

If a non-transient lazy val is the only user of a private field in
a class, the field is nulled out at the end of the lazy initializer.
This is tested in the existing test `run/lazy-leaks.scala`.

The analysis of which fields could be nulled out was recently moved
from `mixin` to the new `fields` phase. This introduced a regression
as a it didn't account for the richer pallete of trees and symbols
at that juncture.

This commit excludes references to private member modules from
collection of private fields, thus avoiding a later compiler
crash in the backend due to a nonsense tree trying to null
out the module symbol. It might make sense to null out the module
var, but I've opted to limit the scope of this analysis to
paramaccessors and regular fields.

1 files changed, 14 insertions, 0 deletions

diff --git a/test/files/run/t9946a.scala b/test/files/run/t9946a.scala
new file mode 100644
index 0000000000..491fb31f7b
--- /dev/null
+++ b/test/files/run/t9946a.scala
@@ -0,0 +1,14 @@
+package p1 {
+  object O {
+    private case class N(a: Any)
+    lazy val x: AnyRef = N
+    lazy val y: AnyRef = new { assert(N != null) }
+  }
+}
+
+object Test {
+  def main(args: Array[String]): Unit = {
+    p1.O.x
+    p1.O.y
+  }
+}