Merge pull request #13837 from dotty-staging/fix-anyval-or-null

Fix comparing AnyVal | Null to Null and selecting in UnsafeNulls

Author: smarter

compiler/src/dotty/tools/dotc/core/Types.scala

@@ -853,18 +853,23 @@ object Types {
       def goAnd(l: Type, r: Type) =
         go(l).meet(go(r), pre, safeIntersection = ctx.base.pendingMemberSearches.contains(name))
 
-      def goOr(tp: OrType) = tp match {
-        case OrNull(tp1) if Nullables.unsafeNullsEnabled =>
-          // Selecting `name` from a type `T | Null` is like selecting `name` from `T`, if
-          // unsafeNulls is enabled. This can throw at runtime, but we trade soundness for usability.
-          tp1.findMember(name, pre.stripNull, required, excluded)
-        case _ =>
+      def goOr(tp: OrType) =
+        inline def searchAfterJoin =
           // we need to keep the invariant that `pre <: tp`. Branch `union-types-narrow-prefix`
           // achieved that by narrowing `pre` to each alternative, but it led to merge errors in
           // lots of places. The present strategy is instead of widen `tp` using `join` to be a
           // supertype of `pre`.
           go(tp.join)
-      }
+
+        if Nullables.unsafeNullsEnabled then tp match
+          case OrNull(tp1) if tp1 <:< defn.ObjectType  =>
+            // Selecting `name` from a type `T | Null` is like selecting `name` from `T`, if
+            // unsafeNulls is enabled and T is a subtype of AnyRef.
+            // This can throw at runtime, but we trade soundness for usability.
+            tp1.findMember(name, pre.stripNull, required, excluded)
+          case _ =>
+            searchAfterJoin
+        else searchAfterJoin
 
       val recCount = ctx.base.findMemberCount
       if (recCount >= Config.LogPendingFindMemberThreshold)

compiler/src/dotty/tools/dotc/typer/TypeAssigner.scala

@@ -162,7 +162,7 @@ trait TypeAssigner {
     val qualType = qual.tpe.widenIfUnstable
     def kind = if tree.isType then "type" else "value"
     val foundWithoutNull = qualType match
-      case OrNull(qualType1) =>
+      case OrNull(qualType1) if qualType1 <:< defn.ObjectType =>
         val name = tree.name
         val pre = maybeSkolemizePrefix(qualType1, name)
         reallyExists(qualType1.findMember(name, pre))

compiler/src/dotty/tools/dotc/typer/Typer.scala

@@ -626,7 +626,7 @@ class Typer extends Namer
       val qual = typedExpr(tree.qualifier, shallowSelectionProto(tree.name, pt, this))
       val qual1 = if Nullables.unsafeNullsEnabled then
         qual.tpe match {
-          case OrNull(tpe1) =>
+          case OrNull(tpe1) if tpe1 <:< defn.ObjectType =>
             qual.cast(AndType(qual.tpe, tpe1))
           case tp =>
             if tp.isNullType

tests/explicit-nulls/neg/AnyValOrNullSelect.scala

@@ -0,0 +1,13 @@
+case class MyVal(i: Int) extends AnyVal:
+  def printVal: Unit =
+    println(i)
+
+class Test:
+  val v: MyVal | Null = MyVal(1)
+
+  def f1 =
+    v.printVal // error: value printVal is not a member of MyVal | Null
+
+  def f1 =
+    import scala.language.unsafeNulls
+    v.printVal // error: value printVal is not a member of MyVal | Null

tests/explicit-nulls/pos/AnyValOrNull.scala

@@ -0,0 +1,36 @@
+case class MyVal(i: Boolean) extends AnyVal
+
+class Test1:
+
+  def test1 =
+    val v: AnyVal | Null = null
+    if v == null then
+      println("null")
+
+  def test2 =
+    val v: Int | Null = 1
+    if v != null then
+      println(v)
+
+  def test3 =
+    val v: MyVal | Null = MyVal(false)
+    if v != null then
+      println(v)
+
+class Test2:
+  import scala.language.unsafeNulls
+
+  def test1 =
+    val v: AnyVal | Null = null
+    if v == null then
+      println("null")
+
+  def test2 =
+    val v: Int | Null = 1
+    if v != null then
+      println(v)
+
+  def test3 =
+    val v: MyVal | Null = MyVal(false)
+    if v != null then
+      println(v)