fix hashCode for value classes with null argument: return 0

Author: VladimirNik

src/dotty/runtime/vc/VCPrototype.scala

@@ -85,7 +85,7 @@ final class VCFloatArray[T <: VCFloatPrototype] (val arr: Array[Float], val ct:
 
 abstract class VCObjectPrototype(val underlying: Object) extends VCPrototype {
   override def hashCode(): Int = {
-    underlying.hashCode()
+    if (underlying == null) 0 else underlying.hashCode()
   }
 }
 
@@ -94,7 +94,7 @@ abstract class VCObjectCasePrototype(underlying: Object) extends VCObjectPrototy
   final def _1: Object = underlying
 
   override final def hashCode(): Int = {
-    underlying.hashCode()
+    if (underlying == null) 0 else underlying.hashCode()
   }
 
   override def toString: String = {

test/dotc/tests.scala

@@ -112,6 +112,7 @@ class tests extends CompilerTest {
   @Test def pos_vc_array_int = compileFile(runDir, "valueclasses-array-int", args = "-Ycheck:all" :: Nil)
   @Test def pos_vc_array_object = compileFile(runDir, "valueclasses-array-object", args = "-Ycheck:all" :: Nil)
   @Test def pos_vc_array_newarray = compileFile(runDir, "valueclasses-array-newarray", args = "-Ycheck:all" :: Nil)
+  @Test def pos_vc_underlying_null = compileFile(runDir, "valueclasses-underlying-null", args = "-Ycheck:all" :: Nil)
 
   @Test def pos_all = compileFiles(posDir) // twice omitted to make tests run faster
 

tests/run/valueclasses-underlying-null.check

@@ -0,0 +1,3 @@
+0
+0
+Set(Y@0)

tests/run/valueclasses-underlying-null.scala

@@ -0,0 +1,13 @@
+class X(val x: Object) extends AnyVal
+class Y(val y: String) extends AnyVal
+object Test {
+  def main(args: Array[String]) = {
+    val x = new X(null)
+    val y = new Y(null)
+    println(x.hashCode())
+    println(y.hashCode())
+
+    val r = Set(new Y(null))
+    println(r.toString)
+  }
+}