Make namedTrees surivive TypeErrors

Same principle as for completions applies.

Author: odersky

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

@@ -62,6 +62,9 @@ object Interactive {
       sourceSymbol(sym.owner)
     else sym
 
+  private def safely[T](default: T)(op: => T) =
+    try op catch { case ex: TypeError => default }
+
   /** Possible completions at position `pos` */
   def completions(trees: List[SourceTree], pos: SourcePosition)(implicit ctx: Context): List[Symbol] = {
     val path = pathTo(trees, pos)
@@ -85,16 +88,13 @@ object Interactive {
   }
 
   /** Possible completions of members of `prefix` which are accessible when called inside `boundary` */
-  def completions(prefix: Type, boundary: Symbol)(implicit ctx: Context): List[Symbol] = {
-    val boundaryCtx = ctx.withOwner(boundary)
-    try
+  def completions(prefix: Type, boundary: Symbol)(implicit ctx: Context): List[Symbol] =
+    safely(Nil) {
+      val boundaryCtx = ctx.withOwner(boundary)
       prefix.memberDenots(completionsFilter, (name, buf) =>
         buf ++= prefix.member(name).altsWith(d => !d.isAbsent && d.symbol.isAccessibleFrom(prefix)(boundaryCtx))
       ).map(_.symbol).toList
-    catch {
-      case ex: TypeError => Nil
     }
-  }
 
   /** Filter for names that should appear when looking for completions. */
   private[this] object completionsFilter extends NameFilter {
@@ -131,7 +131,7 @@ object Interactive {
    *  @param includeReferences  If true, include references and not just definitions
    */
   def namedTrees(trees: List[SourceTree], includeReferences: Boolean, treePredicate: NameTree => Boolean)
-    (implicit ctx: Context): List[SourceTree] = {
+    (implicit ctx: Context): List[SourceTree] = safely(Nil) {
     val buf = new mutable.ListBuffer[SourceTree]
 
     trees foreach { case SourceTree(topTree, source) =>