Allow for target group members to remain unresolved

This, for example, can happen when we have a fallback rule for dist(update)
or configure(update).

1 files changed, 12 insertions, 3 deletions

diff --git a/build/target.ixx b/build/target.ixx
index 3ae9660..3d48904 100644
--- a/build/target.ixx
+++ b/build/target.ixx
@@ -57,17 +57,26 @@ namespace build
   }
 
   template <typename T>
-  inline void prerequisite_members_range<T>::iterator::
+  inline bool prerequisite_members_range<T>::iterator::
   switch_members ()
   {
-    j_ = 1;
-
     do
     {
       g_ = resolve_group_members (r_->a_, search (*i_));
+
+      // If members are not know, iterate over the group as itself.
+      //
+      if (g_.members == nullptr)
+      {
+        g_.count = 0;
+        return false;
+      }
     }
     while (g_.count == 0  && // Skip empty groups.
            ++i_ != r_->e_ &&
            i_->get ().type.see_through);
+
+    j_ = 1; // Start from the first group member.
+    return true;
   }
 }