Tweaks relative to error reporting

Author: odersky

src/dotty/tools/dotc/ast/Desugar.scala

@@ -786,7 +786,7 @@ object desugar {
             New(ref(defn.RepeatedAnnot.typeRef), Nil :: Nil),
             AppliedTypeTree(ref(seqClass.typeRef), t))
         } else {
-          assert(ctx.mode.isExpr, ctx.mode)
+          assert(ctx.mode.isExpr || ctx.reporter.hasErrors, ctx.mode)
           Select(t, op)
         }
       case PrefixOp(op, t) =>

src/dotty/tools/dotc/typer/Checking.scala

@@ -232,7 +232,7 @@ trait Checking {
 
   /** Check that type `tp` is stable. */
   def checkStable(tp: Type, pos: Position)(implicit ctx: Context): Unit =
-    if (!tp.isStable)
+    if (!tp.isStable && !tp.isErroneous)
       ctx.error(d"$tp is not stable", pos)
 
   /** Check that type `tp` is a legal prefix for '#'.