From 4ce9366b563ceb4939403dbf498b6a5126661ee0 Mon Sep 17 00:00:00 2001
From: Boris Kolpackov <boris@codesynthesis.com>
Date: Thu, 9 Aug 2018 09:34:24 +0200
Subject: Fix issue with concatenating empty typed LHS

---
 build2/parser.cxx | 17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/build2/parser.cxx b/build2/parser.cxx
index d2cf38a..caf970e 100644
--- a/build2/parser.cxx
+++ b/build2/parser.cxx
@@ -3510,10 +3510,21 @@ namespace build2
 
       if (!vnull)
       {
-        untypify (rhs);
+        if (vtype != nullptr)
+          untypify (rhs);
+
         names& d (rhs.as<names> ());
-        assert (d.size () == 1); // Must be single value.
-        concat_data = move (d[0]);
+
+        // If the value is empty, then untypify() will (typically; no pun
+        // intended) represent it as an empty sequence of names rather than
+        // a sequence of one empty name. This is usually what we need (see
+        // simple_reverse() for details) but not in this case.
+        //
+        if (!d.empty ())
+        {
+          assert (d.size () == 1); // Must be a single value.
+          concat_data = move (d[0]);
+        }
       }
     };
 
-- 
cgit v1.1