Reverse empty simple values as an empty names sequence rather than empty name

This way we get:

config.import.foo =

Rather than:

config.import.foo = {}

1 files changed, 15 insertions, 1 deletions

diff --git a/build2/variable.txx b/build2/variable.txx
index f1335b4..95e4f0a 100644
--- a/build2/variable.txx
+++ b/build2/variable.txx
@@ -148,7 +148,21 @@ namespace build2
   names_view
   simple_reverse (const value& v, names& s)
   {
-    s.emplace_back (value_traits<T>::reverse (v.as<T> ()));
+    const T& x (v.as<T> ());
+
+    // Represent an empty simple value as empty name sequence rather than
+    // a single empty name. This way, for example, during serialization we
+    // end up with a much saner looking:
+    //
+    // config.import.foo =
+    //
+    // Rather than:
+    //
+    // config.import.foo = {}
+    //
+    if (!value_traits<T>::empty (x))
+      s.emplace_back (value_traits<T>::reverse (x));
+
     return s;
   }