3 files changed, 44 insertions, 16 deletions
diff --git a/libbuild2/bin/init.cxx b/libbuild2/bin/init.cxx
index 6d2d2c2..ff00e89 100644
--- a/libbuild2/bin/init.cxx
+++ b/libbuild2/bin/init.cxx
@@ -29,7 +29,8 @@ namespace build2
 {
   namespace bin
   {
-    static const fail_rule fail_;
+    static const obj_rule obj_;
+    static const libul_rule libul_;
     static const lib_rule lib_;
 
     // Default config.bin.*.lib values.
@@ -563,17 +564,17 @@ namespace build2
       {
         auto& r (bs.rules);
 
-        r.insert<obj> (perform_update_id, "bin.obj", fail_);
-        r.insert<obj> (perform_clean_id,  "bin.obj", fail_);
+        r.insert<obj> (perform_update_id, "bin.obj", obj_);
+        r.insert<obj> (perform_clean_id,  "bin.obj", obj_);
 
-        r.insert<bmi> (perform_update_id, "bin.bmi", fail_);
-        r.insert<bmi> (perform_clean_id,  "bin.bmi", fail_);
+        r.insert<bmi> (perform_update_id, "bin.bmi", obj_);
+        r.insert<bmi> (perform_clean_id,  "bin.bmi", obj_);
 
-        r.insert<hbmi> (perform_update_id, "bin.hbmi", fail_);
-        r.insert<hbmi> (perform_clean_id,  "bin.hbmi", fail_);
+        r.insert<hbmi> (perform_update_id, "bin.hbmi", obj_);
+        r.insert<hbmi> (perform_clean_id,  "bin.hbmi", obj_);
 
-        r.insert<libul> (perform_update_id, "bin.libul", fail_);
-        r.insert<libul> (perform_clean_id,  "bin.libul", fail_);
+        r.insert<libul> (perform_update_id, "bin.libul", libul_);
+        r.insert<libul> (perform_clean_id,  "bin.libul", libul_);
 
         // Similar to alias.
         //
diff --git a/libbuild2/bin/rule.cxx b/libbuild2/bin/rule.cxx
index 0abfcb5..021a768 100644
--- a/libbuild2/bin/rule.cxx
+++ b/libbuild2/bin/rule.cxx
@@ -17,9 +17,9 @@ namespace build2
 {
   namespace bin
   {
-    // fail_rule
+    // obj_rule
     //
-    bool fail_rule::
+    bool obj_rule::
     match (action a, target& t, const string&) const
     {
       const char* n (t.dynamic_type ().name); // Ignore derived type.
@@ -29,7 +29,19 @@ namespace build2
            << n << "s{} member" << endf;
     }
 
-    recipe fail_rule::
+    recipe obj_rule::
+    apply (action, target&) const {return empty_recipe;}
+
+    // libul_rule
+    //
+    bool libul_rule::
+    match (action a, target& t, const string&) const
+    {
+      fail << diag_doing (a, t) << " target group" <<
+        info << "explicitly select libua{} or libus{} member" << endf;
+    }
+
+    recipe libul_rule::
     apply (action, target&) const {return empty_recipe;}
 
     // lib_rule
diff --git a/libbuild2/bin/rule.hxx b/libbuild2/bin/rule.hxx
index 51693a7..ffb975d 100644
--- a/libbuild2/bin/rule.hxx
+++ b/libbuild2/bin/rule.hxx
@@ -15,13 +15,28 @@ namespace build2
 {
   namespace bin
   {
-    // "Fail rule" for obj{}, [h]bmi{}, and libu{} that issues diagnostics if
-    // someone tries to build any of these groups directly.
+    // "Fail rule" for obj{} and [h]bmi{} that issues diagnostics if someone
+    // tries to build these groups directly.
     //
-    class fail_rule: public simple_rule
+    class obj_rule: public simple_rule
     {
     public:
-      fail_rule () {}
+      obj_rule () {}
+
+      virtual bool
+      match (action, target&, const string&) const override;
+
+      virtual recipe
+      apply (action, target&) const override;
+    };
+
+    // "Fail rule" for libul{} that issues diagnostics if someone tries to
+    // build this group directly.
+    //
+    class libul_rule: public simple_rule
+    {
+    public:
+      libul_rule () {}
 
       virtual bool
       match (action, target&, const string&) const override;