From 0c289c54fb0a31491aa1d2b030851337430ccd71 Mon Sep 17 00:00:00 2001
From: Mark Wooding <mdw@distorted.org.uk>
Date: Mon, 9 Jul 2018 13:04:38 +0100
Subject: [PATCH] src/module-parse.lisp (parse-class-body): Check for duplicate
 superclasses.

It turns out that this is a thing that can happen.  Catch it early
rather than waiting for a less helpful message during CPL construction.
---
 src/module-parse.lisp | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/src/module-parse.lisp b/src/module-parse.lisp
index 0a3cd28..747bdf7 100644
--- a/src/module-parse.lisp
+++ b/src/module-parse.lisp
@@ -267,7 +267,14 @@
 				  (continue ()
 				    (setf duff t)
 				    (list (find-sod-class "SodObject"))))))
-	      superclasses))
+	      (find-duplicates (lambda (first second)
+				 (declare (ignore second))
+				 (setf duff t)
+				 (cerror* "Class `~A' has duplicate ~
+					   direct superclass `~A'"
+					  name first))
+			       superclasses)
+	      (delete-duplicates superclasses)))
 	   (synthetic-name (or name
 			       (let ((var (synthetic-name)))
 				 (unless pset
-- 
2.11.0