From b4d7ab3caab6b4e1b00d29071ebee7f0372f3512 Mon Sep 17 00:00:00 2001
From: Andreas Rumpf <rumpf_a@web.de>
Date: Fri, 26 Aug 2016 17:29:56 +0200
Subject: [PATCH] fixes #4179; disallow assignments to openarrays

---
 compiler/semexprs.nim | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/compiler/semexprs.nim b/compiler/semexprs.nim
index 16dc159bd..274bb15b9 100644
--- a/compiler/semexprs.nim
+++ b/compiler/semexprs.nim
@@ -1400,8 +1400,9 @@ proc semAsgn(c: PContext, n: PNode; mode=asgnNormal): PNode =
   # a = b # both are vars, means: a[] = b[]
   # a = b # b no 'var T' means: a = addr(b)
   var le = a.typ
-  if skipTypes(le, {tyGenericInst}).kind != tyVar and
-      isAssignable(c, a) == arNone:
+  if (skipTypes(le, {tyGenericInst}).kind != tyVar and
+        isAssignable(c, a) == arNone) or
+      skipTypes(le, abstractVar).kind in {tyOpenArray, tyVarargs}:
     # Direct assignment to a discriminant is allowed!
     localError(a.info, errXCannotBeAssignedTo,
                renderTree(a, {renderNoComments}))