Make errors are not swept under the carpet

Typer#ensureReported's comment outlines an example where errors
could go unreported, resulting in error trees after typer without
any reported error messages. This commit makes sure that at least
one error is reported if a tree node has an error type.

Fixes #1802.

1 files changed, 6 insertions, 5 deletions

diff --git a/compiler/src/dotty/tools/dotc/core/SymDenotations.scala b/compiler/src/dotty/tools/dotc/core/SymDenotations.scala
index e2bb0ac1a..aaae78c57 100644
--- a/compiler/src/dotty/tools/dotc/core/SymDenotations.scala
+++ b/compiler/src/dotty/tools/dotc/core/SymDenotations.scala
@@ -1937,12 +1937,12 @@ object SymDenotations {
   /** A completer for missing references */
   class StubInfo() extends LazyType {
 
-    def initializeToDefaults(denot: SymDenotation)(implicit ctx: Context) = {
+    def initializeToDefaults(denot: SymDenotation, errMsg: => String)(implicit ctx: Context) = {
       denot.info = denot match {
         case denot: ClassDenotation =>
           ClassInfo(denot.owner.thisType, denot.classSymbol, Nil, EmptyScope)
         case _ =>
-          ErrorType
+          new ErrorType(errMsg)
       }
       denot.privateWithin = NoSymbol
     }
@@ -1954,13 +1954,14 @@ object SymDenotations {
         if (file != null) (s" in $file", file.toString)
         else ("", "the signature")
       val name = ctx.fresh.setSetting(ctx.settings.debugNames, true).nameString(denot.name)
-      ctx.error(
+      def errMsg =
         i"""bad symbolic reference. A signature$location
            |refers to $name in ${denot.owner.showKind} ${denot.owner.showFullName} which is not available.
            |It may be completely missing from the current classpath, or the version on
-           |the classpath might be incompatible with the version used when compiling $src.""")
+           |the classpath might be incompatible with the version used when compiling $src."""
+      ctx.error(errMsg)
       if (ctx.debug) throw new Error()
-      initializeToDefaults(denot)
+      initializeToDefaults(denot, errMsg)
     }
   }