close #3667.

scala> def ser(o: AnyRef) = new java.io.ObjectOutputStream(new java.io.ByteArrayOutputStream()).writeObject(o)
ser: (o: AnyRef)Unit

scala> @serializable class Outer {
     |   case class Inner(x: Int)
     | }
defined class Outer

scala> val o = new Outer
o: Outer = Outer@34469729

scala> ser(new o.Inner(1))

scala> o.Inner // initialize the Inner$module field of o

res1: o.Inner.type = Inner

scala> ser(new o.Inner(1))
java.io.NotSerializableException: Outer$Inner$

review by extempore.

1 files changed, 45 insertions, 0 deletions

diff --git a/test/files/run/t3667.scala b/test/files/run/t3667.scala
new file mode 100644
index 0000000000..804432c516
--- /dev/null
+++ b/test/files/run/t3667.scala
@@ -0,0 +1,45 @@
+object Test {
+  def main(args: Array[String]) {
+    val o1 = new Outer1
+    val o2 = new Outer2
+    val o3 = new Outer3
+
+    println(1)
+    ser(new o1.Inner(1))
+    o1.Inner // make sure the Inner$module field of the Outer1 instance is initialized!
+    ser(new o1.Inner(1))
+
+    println(2)
+    ser(new o2.Inner(1))
+    o2.Inner
+    ser(new o2.Inner(1))
+
+    println(3)
+    ser(new o3.Inner(1))
+    o3.Inner
+    ser(new o3.Inner(1))
+  }
+
+  def ser(o: AnyRef) {
+    val oos = new java.io.ObjectOutputStream(new java.io.ByteArrayOutputStream())
+    oos.writeObject(o)
+    oos.close()
+  }
+
+}
+
+@serializable
+class Outer1 {
+  @serializable
+  class Inner(x: Int = 1)
+}
+
+@serializable
+class Outer2 {
+  case class Inner(x: Int = 1)
+}
+
+@serializable
+class Outer3 {
+  case class Inner(x: Int)
+}