Merge pull request scala#37 from noti0na1/dotty-explicit-nulls

Fix nullification of type arguments

Author: noti0na1

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

@@ -114,27 +114,23 @@ object JavaNullInterop {
         case _ => true
       })
 
-    /** Should we nullify the type arguments to the given generic `tp`?
-     *  We only nullify the inside of Scala-defined generics.
-     *  This is because Java classes are _all_ nullified, so both `java.util.List[String]` and
-     *  `java.util.List[String|Null]` contain nullable elements.
-     */
-    def needsNullArgs(tp: AppliedType): Boolean = !tp.classSymbol.is(JavaDefined)
-
     override def apply(tp: Type): Type = {
       // Fast version of Type::toJavaNullableUnion that doesn't check whether the type
       // is already a union.
       def toJavaNullableUnion(tpe: Type): Type = OrType(tpe, defn.JavaNullAliasType)
 
       tp match {
         case tp: TypeRef if needsNull(tp) => toJavaNullableUnion(tp)
-        case appTp @ AppliedType(tycons, targs) =>
+        case appTp @ AppliedType(tycon, targs) =>
           val oldOutermostNullable = outermostLevelAlreadyNullable
-          outermostLevelAlreadyNullable = false
-          val targs2 = if (needsNullArgs(appTp)) targs map this else targs
+          // We don't make the outmost levels of type arguements nullable if tycon is Java-defined.
+          // This is because Java classes are _all_ nullified, so both `java.util.List[String]` and
+          // `java.util.List[String|Null]` contain nullable elements.
+          outermostLevelAlreadyNullable = tp.classSymbol.is(JavaDefined)
+          val targs2 = targs map this
           outermostLevelAlreadyNullable = oldOutermostNullable
-          val appTp2 = derivedAppliedType(appTp, tycons, targs2)
-          if (needsNull(tycons)) toJavaNullableUnion(appTp2) else appTp2
+          val appTp2 = derivedAppliedType(appTp, tycon, targs2)
+          if (needsNull(tycon)) toJavaNullableUnion(appTp2) else appTp2
         case ptp: PolyType =>
           derivedLambdaType(ptp)(ptp.paramInfos, this(ptp.resType))
         case mtp: MethodType =>

tests/explicit-nulls/pos/interop-poly-src/J.java

@@ -1,14 +1,29 @@
+import java.util.*;
 
 class JavaCat<T> {
-	T prop;
+  T prop;
 }
 
 class J {
-	static <T> ScalaCat<T> getScalaCat() {
-		return null;
-	}
+  static <T> ScalaCat<T> getScalaCat() {
+    return null;
+  }
 
-	static <T> JavaCat<T> getJavaCat() {
-		return null;
-	}
+  static <T> JavaCat<T> getJavaCat() {
+    return null;
+  }
+
+  static List<String[]> getListOfStringArray() {
+    List<String[]> as = new ArrayList<String[]>();
+    as.add(new String[1]);
+    return as;
+  }
+
+  static List<String>[] getArrayOfStringList() {
+    return (List<String>[]) new List[1];
+  }
+
+  static List<List<String[]>[]> getComplexStrings() {
+    return new ArrayList<List<String[]>[]>();
+  }
 }

tests/explicit-nulls/pos/interop-poly-src/S.scala

@@ -9,6 +9,12 @@ class Test {
   // because JavaCat, being a Java class, _already_ nullifies its
   // fields.
   val jc: JavaCat[String]|Null = J.getJavaCat[String]()
-  // ScalaCat is Java-defined, so we need the inner |Null.
+  // ScalaCat is Scala-defined, so we need the inner |Null.
   val sc: ScalaCat[String|Null]|Null = J.getScalaCat[String]()
+
+  import java.util.List
+
+  val las: List[Array[String|Null]]|Null = J.getListOfStringArray()
+  val als: Array[List[String]|Null]|Null = J.getArrayOfStringList()
+  val css: List[Array[List[Array[String|Null]]|Null]]|Null = J.getComplexStrings()
 }