add comments for extractors

Author: noti0na1

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

@@ -8,9 +8,6 @@ import dotty.tools.dotc.core.Types.{AndType, ClassInfo, ConstantType, OrType, Ty
 object NullOpsDecorator {
 
   implicit class NullOps(val self: Type) {
-    /** Is this type a reference to `Null`, possibly after aliasing? */
-    def isNullType(implicit ctx: Context): Boolean = self.isRef(defn.NullClass)
-
     /** Is this type exactly `JavaNull` (no vars, aliases, refinements etc allowed)? */
     def isJavaNullType(implicit ctx: Context): Boolean = {
       assert(ctx.explicitNulls)

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

@@ -1445,9 +1445,7 @@ object Types {
     }
 
     /** Is this (an alias of) the `scala.Null` type? */
-    final def isNull(given Context) =
-      isRef(defn.NullClass)
-      || classSymbol.name == tpnme.Null // !!! temporary kludge for being able to test without the explicit nulls PR
+    final def isNullType(given Context) = isRef(defn.NullClass)
 
     /** The resultType of a LambdaType, or ExprType, the type itself for others */
     def resultType(implicit ctx: Context): Type = this
@@ -2936,6 +2934,13 @@ object Types {
       else apply(tp1, tp2)
   }
 
+  /** An extractor object to pattern match against a nullable union.
+   *  e.g.
+   *
+   *  (tp: Type) match
+   *    case OrNull(tp1) => // tp had the form `tp1 | Null`
+   *    case _ => // tp was not a nullable union
+   */
   object OrNull {
     def apply(tp: Type)(given Context) =
       OrType(tp, defn.NullType)
@@ -2947,6 +2952,13 @@ object Types {
     else None
   }
 
+  /** An extractor object to pattern match against a Java-nullable union.
+   *  e.g.
+   *
+   *  (tp: Type) match
+   *    case OrJavaNull(tp1) => // tp had the form `tp1 | JavaNull`
+   *    case _ => // tp was not a Java-nullable union
+   */
   object OrJavaNull {
     def apply(tp: Type)(given Context) =
       OrType(tp, defn.JavaNullAliasType)

compiler/src/dotty/tools/dotc/interactive/Completion.scala

@@ -207,7 +207,7 @@ object Completion {
     def addMemberCompletions(qual: Tree)(implicit ctx: Context): Unit =
       if (!qual.tpe.widenDealias.isBottomType) {
         addAccessibleMembers(qual.tpe)
-        if (!mode.is(Mode.Import) && !qual.tpe.isNull)
+        if (!mode.is(Mode.Import) && !qual.tpe.isNullType)
           // Implicit conversions do not kick in when importing
           // and for `NullClass` they produce unapplicable completions (for unclear reasons)
           implicitConversionTargets(qual)(ctx.fresh.setExploreTyperState())