2 files changed, 18 insertions, 3 deletions
diff --git a/src/main/scala/firrtl/Parser.scala b/src/main/scala/firrtl/Parser.scala
index b2d97e86..a4c366ec 100644
--- a/src/main/scala/firrtl/Parser.scala
+++ b/src/main/scala/firrtl/Parser.scala
@@ -10,6 +10,8 @@ import firrtl.parser.Listener
 import firrtl.Utils.time
 import firrtl.antlr.{FIRRTLParser, _}
 
+import scala.util.control.NonFatal
+
 class ParserException(message: String) extends FirrtlUserException(message)
 
 case class ParameterNotSpecifiedException(message: String) extends ParserException(message)
@@ -42,12 +44,25 @@ object Parser extends LazyLogging {
       parser.getInterpreter.setPredictionMode(PredictionMode.SLL)
       parser.addParseListener(listener)
 
-      // Concrete Syntax Tree
-      parser.circuit
+      // Syntax errors may violate assumptions in the Listener and Visitor.
+      // We need to handle these errors gracefully.
+      val throwable =
+        try {
+          parser.circuit
+          None
+        } catch {
+          case e: ParserException => throw e
+          case NonFatal(e) => Some(e)
+        }
 
       val numSyntaxErrors = parser.getNumberOfSyntaxErrors
       if (numSyntaxErrors > 0) throw new SyntaxErrorsException(s"$numSyntaxErrors syntax error(s) detected")
 
+      // Note that this should never happen because any throwables caught should be due to syntax
+      // errors that are reported above. This is just to ensure that we don't accidentally mask any
+      // bugs in the Parser, Listener, or Visitor.
+      if (throwable.nonEmpty) Utils.throwInternalError(exception = throwable)
+
       listener.getCircuit
     }
 
diff --git a/src/main/scala/firrtl/Utils.scala b/src/main/scala/firrtl/Utils.scala
index ec68d4eb..9e267a39 100644
--- a/src/main/scala/firrtl/Utils.scala
+++ b/src/main/scala/firrtl/Utils.scala
@@ -165,7 +165,7 @@ object Utils extends LazyLogging {
     * @param message - possible string to emit,
     * @param exception - possible exception triggering the error.
     */
-  def throwInternalError(message: String = "", exception: Option[Exception] = None) = {
+  def throwInternalError(message: String = "", exception: Option[Throwable] = None) = {
     // We'll get the first exception in the chain, keeping it intact.
     val first = true
     val throwable = getThrowable(exception, true)