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).

5 files changed, 27 insertions, 17 deletions

diff --git a/build/algorithm b/build/algorithm
index 375cebb..d144d6c 100644
--- a/build/algorithm
+++ b/build/algorithm
@@ -121,8 +121,10 @@ namespace build
   void
   search_and_match_prerequisite_members (action, target&, const dir_path&);
 
-  // Unless already available, match, and, if necessary, execute
-  // the group in order to obtain its members list.
+  // Unless already available, match, and, if necessary, execute the group
+  // in order to obtain its members list. Note that even after that the
+  // member's list might still not be available (e.g., if some wildcard/
+  // fallback rule matched).
   //
   group_view
   resolve_group_members (action, target&);
diff --git a/build/algorithm.cxx b/build/algorithm.cxx
index fb6c72a..6c3374e 100644
--- a/build/algorithm.cxx
+++ b/build/algorithm.cxx
@@ -272,8 +272,7 @@ namespace build
     execute_direct (a, g);
 
     r = g.group_members (a);
-    assert (r.members != nullptr); // What "next step" did the group expect?
-    return r;
+    return r; // Might still be unresolved.
   }
 
   void
diff --git a/build/cli/module.cxx b/build/cli/module.cxx
index 240aaa7..05abb94 100644
--- a/build/cli/module.cxx
+++ b/build/cli/module.cxx
@@ -72,10 +72,6 @@ namespace build
 
         rs.insert<cxx::ixx> (perform_id, update_id, "cli", compile_);
         rs.insert<cxx::ixx> (perform_id, clean_id, "cli", compile_);
-
-        // We may need to resolve group members.
-        //
-        rs.insert<cli_cxx> (configure_id, update_id, "cli", compile_);
       }
 
       // Enter module variables.
diff --git a/build/target b/build/target
index f2b093e..d451851 100644
--- a/build/target
+++ b/build/target
@@ -609,14 +609,18 @@ namespace build
         g_.count = 1;
       }
 
-      // Iterate over this group's members. Similar to leave_group(),
-      // you should increment the iterator after calling this function.
+      // Iterate over this group's members. Return false if the member
+      // information is not available. Similar to leave_group(), you
+      // should increment the iterator after calling this function
+      // (provided it returned true).
       //
-      void
+      bool
       enter_group ()
       {
-        switch_members ();
-        --j_; // Compensate for the increment that will follow.
+        bool r (switch_members ());
+        if (r)
+          --j_; // Compensate for the increment that will follow.
+        return r;
       }
 
       value_type operator* () const
@@ -646,7 +650,7 @@ namespace build
       operator!= (const iterator& x, const iterator& y) {return !(x == y);}
 
     private:
-      void
+      bool
       switch_members ();
 
     private:
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;
   }
 }