Fix #4535: Handle Null and Nothing in completions

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

@@ -270,7 +270,7 @@ class Definitions {
     lazy val Any_getClass: TermSymbol = enterMethod(AnyClass, nme.getClass_, MethodType(Nil, ClassClass.typeRef.appliedTo(TypeBounds.empty)), Final)
     lazy val Any_isInstanceOf: TermSymbol = enterT1ParameterlessMethod(AnyClass, nme.isInstanceOf_, _ => BooleanType, Final)
     lazy val Any_asInstanceOf: TermSymbol = enterT1ParameterlessMethod(AnyClass, nme.asInstanceOf_, _.paramRefs(0), Final)
-    lazy val Any_typeTest: TermSymbol = enterT1ParameterlessMethod(AnyClass, nme.isInstanceOfPM, _ => BooleanType, Final | Synthetic)
+    lazy val Any_typeTest: TermSymbol = enterT1ParameterlessMethod(AnyClass, nme.isInstanceOfPM, _ => BooleanType, Final | Synthetic | Artifact)
       // generated by pattern matcher, eliminated by erasure
 
     def AnyMethods: List[TermSymbol] = List(Any_==, Any_!=, Any_equals, Any_hashCode,

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

@@ -1,5 +1,7 @@
 package dotty.tools.dotc.interactive
 
+import java.nio.charset.Charset
+
 import dotty.tools.dotc.ast.Trees._
 import dotty.tools.dotc.config.Printers.interactiv
 import dotty.tools.dotc.core.Contexts.{Context, NoContext}
@@ -10,13 +12,13 @@ import dotty.tools.dotc.core.Flags._
 import dotty.tools.dotc.core.Names.{Name, TermName}
 import dotty.tools.dotc.core.NameKinds.SimpleNameKind
 import dotty.tools.dotc.core.NameOps.NameDecorator
-import dotty.tools.dotc.core.Symbols.{defn, NoSymbol, Symbol}
+import dotty.tools.dotc.core.Symbols.{NoSymbol, Symbol, defn}
 import dotty.tools.dotc.core.Scopes
 import dotty.tools.dotc.core.StdNames.{nme, tpnme}
 import dotty.tools.dotc.core.TypeError
-import dotty.tools.dotc.core.Types.{NameFilter, NamedType, Type, NoType}
+import dotty.tools.dotc.core.Types.{NameFilter, NamedType, NoType, Type}
 import dotty.tools.dotc.printing.Texts._
-import dotty.tools.dotc.util.{NoSourcePosition, SourcePosition}
+import dotty.tools.dotc.util.{NameTransformer, NoSourcePosition, SourcePosition}
 
 import scala.collection.mutable
 
@@ -150,7 +152,8 @@ object Completion {
       nameToSymbols.map { case (name, symbols) =>
         val typesFirst = symbols.sortWith((s1, s2) => s1.isType && !s2.isType)
         val desc = description(typesFirst)
-        Completion(name.toString, desc, typesFirst)
+        val label = NameTransformer.decodeIllegalChars(name.toString)
+        Completion(label, desc, typesFirst)
       }
     }
 
@@ -207,11 +210,13 @@ object Completion {
      * considered.
      */
     def addMemberCompletions(qual: Tree)(implicit ctx: Context): Unit = {
-      addAccessibleMembers(qual.tpe)
-      if (!mode.is(Mode.Import)) {
-        // Implicit conversions do not kick in when importing
-        implicitConversionTargets(qual)(ctx.fresh.setExploreTyperState())
-          .foreach(addAccessibleMembers)
+      if (!qual.tpe.widenDealias.isBottomType) {
+        addAccessibleMembers(qual.tpe)
+        if (!mode.is(Mode.Import) && !qual.tpe.isRef(defn.NullClass)) {
+          // Implicit conversions do not kick in when importing
+          implicitConversionTargets(qual)(ctx.fresh.setExploreTyperState())
+            .foreach(addAccessibleMembers)
+        }
       }
     }
 

compiler/src/dotty/tools/dotc/util/NameTransformer.scala

@@ -55,6 +55,29 @@ object NameTransformer {
     else name
   }
 
+  /** Decode expanded characters starting with `$u`, followed by the character's unicode expansion. */
+  def decodeIllegalChars(name: String): String = {
+    if (name.contains("$u")) {
+      val sb = new mutable.StringBuilder()
+      var i = 0
+      while (i < name.length - 5) {
+        if (name(i) == '$' && name(i + 1) == 'u') {
+          sb.append(Integer.valueOf(name.substring(i + 2, i + 6), 16).toChar)
+          i += 6
+        } else {
+          sb.append(name(i))
+          i += 1
+        }
+      }
+      while (i < name.length) {
+        sb.append(name(i))
+        i += 1
+      }
+      sb.result()
+    }
+    else name
+  }
+
   /** Replace operator symbols by corresponding expansion strings.
    *
    *  @param name the string to encode

compiler/test/dotty/tools/repl/TabcompleteTests.scala

@@ -103,4 +103,25 @@ class TabcompleteTests extends ReplTest {
     assertEquals(comp.find(_.startsWith("<")), None)
     assert(!comp.contains("package"))
   }
+
+  @Test def `null` = fromInitialState { implicit s =>
+    val comp = tabComplete("null.")
+    assertEquals(
+      List("!=", "##", "==", "asInstanceOf", "clone", "eq", "equals", "finalize", "getClass", "hashCode",
+          "isInstanceOf", "ne", "notify", "notifyAll", "synchronized", "toString", "wait"),
+      comp.distinct.sorted)
+  }
+
+  @Test def anyRef = fromInitialState { implicit s =>
+    val comp = tabComplete("(null: AnyRef).")
+    assertEquals(
+      List("!=", "##", "+", "->", "==", "asInstanceOf", "clone", "ensuring", "eq", "equals", "finalize", "formatted",
+          "getClass", "hashCode", "isInstanceOf", "ne", "notify", "notifyAll", "synchronized", "toString", "wait", "→"),
+      comp.distinct.sorted)
+  }
+
+  @Test def `???` = fromInitialState { implicit s =>
+    val comp = tabComplete("???.")
+    assertEquals(Nil, comp)
+  }
 }