Refactor JavaNullInterop to reflect new usage

Author: HarrisL2

compiler/src/dotty/tools/dotc/core/JavaNullInterop.scala renamed to compiler/src/dotty/tools/dotc/core/ImplicitNullInterop.scala

@@ -35,7 +35,7 @@ import dotty.tools.dotc.core.Decorators.i
  *   to handle the full spectrum of Scala types. Additionally, some kinds of symbols like constructors and
  *   enum instances get special treatment.
  */
-object JavaNullInterop {
+object ImplicitNullInterop {
 
   /** Transforms the type `tp` of Java member `sym` to be explicitly nullable.
    *  `tp` is needed because the type inside `sym` might not be set when this method is called.
@@ -55,7 +55,6 @@ object JavaNullInterop {
    */
   def nullifyMember(sym: Symbol, tp: Type, isEnumValueDef: Boolean)(using Context): Type = trace(i"nullifyMember ${sym}, ${tp}"){
     assert(ctx.explicitNulls)
-    // assert(sym.is(JavaDefined), "can only nullify java-defined members")
 
     // Some special cases when nullifying the type
     if isEnumValueDef || sym.name == nme.TYPE_ // Don't nullify the `TYPE` field in every class and Java enum instances
@@ -81,14 +80,14 @@ object JavaNullInterop {
    *  but the result type is not nullable.
    */
   private def nullifyExceptReturnType(tp: Type)(using Context): Type =
-    new JavaNullMap(outermostLevelAlreadyNullable = true)(tp)
+    new ImplicitNullMap(outermostLevelAlreadyNullable = true)(tp)
 
-  /** Nullifies a Java type by adding `| Null` in the relevant places. */
+  /** Nullifies a type by adding `| Null` in the relevant places. */
   private def nullifyType(tp: Type)(using Context): Type =
-    new JavaNullMap(outermostLevelAlreadyNullable = false)(tp)
+    new ImplicitNullMap(outermostLevelAlreadyNullable = false)(tp)
 
-  /** A type map that implements the nullification function on types. Given a Java-sourced type, this adds `| Null`
-   *  in the right places to make the nulls explicit in Scala.
+  /** A type map that implements the nullification function on types. Given a Java-sourced type or an
+   *  implicitly null type, this adds `| Null` in the right places to make the nulls explicit.
    *
    *  @param outermostLevelAlreadyNullable whether this type is already nullable at the outermost level.
    *                                       For example, `Array[String] | Null` is already nullable at the
@@ -98,7 +97,7 @@ object JavaNullInterop {
    *                                       This is useful for e.g. constructors, and also so that `A & B` is nullified
    *                                       to `(A & B) | Null`, instead of `(A | Null & B | Null) | Null`.
    */
-  private class JavaNullMap(var outermostLevelAlreadyNullable: Boolean)(using Context) extends TypeMap {
+  private class ImplicitNullMap(var outermostLevelAlreadyNullable: Boolean)(using Context) extends TypeMap {
     def nullify(tp: Type): Type = if ctx.flexibleTypes then FlexibleType(tp) else OrNull(tp)
 
     /** Should we nullify `tp` at the outermost level? */

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

@@ -3427,6 +3427,7 @@ object Types extends TypeUtils {
         // flexible type is always a subtype of the original type and the Object type.
         // It is not necessary according to the use cases, so we choose to use a simpler
         // rule.
+        assert(!tp.isInstanceOf[LazyType])
         FlexibleType(OrNull(tp), tp)
     }
   }

compiler/src/dotty/tools/dotc/core/classfile/ClassfileParser.scala

@@ -525,7 +525,7 @@ class ClassfileParser(
       denot.info = translateTempPoly(attrCompleter.complete(denot.info, isVarargs))
       if (isConstructor) normalizeConstructorInfo()
 
-      if (ctx.explicitNulls) denot.info = JavaNullInterop.nullifyMember(denot.symbol, denot.info, isEnum)
+      if (ctx.explicitNulls) denot.info = ImplicitNullInterop.nullifyMember(denot.symbol, denot.info, isEnum)
 
       // seal java enums
       if (isEnum) {

compiler/src/dotty/tools/dotc/core/tasty/TreeUnpickler.scala

@@ -985,7 +985,7 @@ class TreeUnpickler(reader: TastyReader,
       // If explicit nulls is enabled, and the source file did not have explicit
       // nulls enabled, nullify the member to allow for compatibility.
       if (ctx.explicitNulls && !explicitNulls) then
-        sym.info = JavaNullInterop.nullifyMember(sym, sym.info, sym.is(Enum))
+        sym.info = ImplicitNullInterop.nullifyMember(sym, sym.info, sym.is(Enum))
 
       goto(end)
       setSpan(start, tree)

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

@@ -1879,7 +1879,7 @@ class Namer { typer: Typer =>
 
     val mbrTpe = paramFn(checkSimpleKinded(typedAheadType(mdef.tpt, tptProto)).tpe)
     if (ctx.explicitNulls && mdef.mods.is(JavaDefined))
-      JavaNullInterop.nullifyMember(sym, mbrTpe, mdef.mods.isAllOf(JavaEnumValue))
+      ImplicitNullInterop.nullifyMember(sym, mbrTpe, mdef.mods.isAllOf(JavaEnumValue))
     else mbrTpe
   }