Merge pull request #12697 from dotty-staging/fix-parents-of-null

Add Matchable to the parents of Null in explicit nulls
scala · Jun 4, 2021 · cbb1e07 · cbb1e07
2 parents 2ce3e97 + e248658
commit cbb1e07
Show file tree

Hide file tree

Showing 3 changed files with 9 additions and 2 deletions.
diff --git a/compiler/src/dotty/tools/dotc/core/Definitions.scala b/compiler/src/dotty/tools/dotc/core/Definitions.scala
@@ -455,8 +455,9 @@ class Definitions {
     ScalaPackageClass, tpnme.Nothing, AbstractFinal, List(AnyType))
   def NothingType: TypeRef = NothingClass.typeRef
   @tu lazy val NullClass: ClassSymbol = {
-    val parent = if ctx.explicitNulls then AnyType else ObjectType
-    enterCompleteClassSymbol(ScalaPackageClass, tpnme.Null, AbstractFinal, parent :: Nil)
+    // When explicit-nulls is enabled, Null becomes a direct subtype of Any and Matchable
+    val parents = if ctx.explicitNulls then AnyType :: MatchableType :: Nil else ObjectType :: Nil
+    enterCompleteClassSymbol(ScalaPackageClass, tpnme.Null, AbstractFinal, parents)
   }
   def NullType: TypeRef = NullClass.typeRef
 

diff --git a/tests/explicit-nulls/neg/basic.scala b/tests/explicit-nulls/neg/basic.scala
@@ -9,6 +9,9 @@ class Basic {
   val any1: Any  = null
   val any2: Any  = n
 
+  val matchable1: Matchable = null
+  val matchable2: Matchable = n
+
   val s1: String = null // error
   val s2: String = n // error
   val s3: String | Null = null

diff --git a/tests/explicit-nulls/pos/matchable.scala b/tests/explicit-nulls/pos/matchable.scala
@@ -0,0 +1,3 @@
+def foo1[T <: Matchable](t: T) = t match { case t: Null => () }
+
+def foo2[T <: Matchable](t: T) = t match { case null => () }
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1,3 @@
		def foo1[T <: Matchable](t: T) = t match { case t: Null => () }

		def foo2[T <: Matchable](t: T) = t match { case null => () }