Make rules const throughout

9 files changed, 30 insertions, 23 deletions

diff --git a/build2/bin/init.cxx b/build2/bin/init.cxx
index eaded2a..913c887 100644
--- a/build2/bin/init.cxx
+++ b/build2/bin/init.cxx
@@ -24,8 +24,8 @@ namespace build2
 {
   namespace bin
   {
-    static obj_rule obj_;
-    static lib_rule lib_;
+    static const obj_rule obj_;
+    static const lib_rule lib_;
 
     // Default config.bin.*.lib values.
     //
diff --git a/build2/cc/module.cxx b/build2/cc/module.cxx
index e63f740..3e20694 100644
--- a/build2/cc/module.cxx
+++ b/build2/cc/module.cxx
@@ -363,9 +363,9 @@ namespace build2
         //
         // @@ Should we check if install module was loaded (see bin)?
         //
-        compile& cr (*this);
-        link&    lr (*this);
-        install& ir (*this);
+        const compile& cr (*this);
+        const link&    lr (*this);
+        const install& ir (*this);
 
         r.insert<obje> (perform_update_id,    x_compile, cr);
         r.insert<obje> (perform_clean_id,     x_compile, cr);
diff --git a/build2/cli/init.cxx b/build2/cli/init.cxx
index 45e2655..b34711d 100644
--- a/build2/cli/init.cxx
+++ b/build2/cli/init.cxx
@@ -23,7 +23,7 @@ namespace build2
 {
   namespace cli
   {
-    static compile compile_;
+    static const compile compile_;
 
     bool
     config_init (scope& rs,
diff --git a/build2/dist/init.cxx b/build2/dist/init.cxx
index f185145..901e9c2 100644
--- a/build2/dist/init.cxx
+++ b/build2/dist/init.cxx
@@ -20,7 +20,7 @@ namespace build2
 {
   namespace dist
   {
-    static rule rule_;
+    static const rule rule_;
 
     void
     boot (scope& r, const location&, unique_ptr<module_base>&)
diff --git a/build2/install/init.cxx b/build2/install/init.cxx
index 5281d38..8c28dad 100644
--- a/build2/install/init.cxx
+++ b/build2/install/init.cxx
@@ -120,8 +120,8 @@ namespace build2
         var_pool.insert<bool> (string ("install.") + n + ".subdirs");
     }
 
-    static alias_rule alias_;
-    static file_rule file_;
+    static const alias_rule alias_;
+    static const file_rule file_;
 
     void
     boot (scope& r, const location&, unique_ptr<module_base>&)
diff --git a/build2/rule b/build2/rule
index 015cf1a..fbf3dcc 100644
--- a/build2/rule
+++ b/build2/rule
@@ -29,6 +29,10 @@ namespace build2
     match_result (bool r, action a): result (r), recipe_action (a) {}
   };
 
+  // Once a rule is registered (for a scope), it is treated as immutable. If
+  // you need to modify some state (e.g., counters or some such), then make
+  // sure it is MT-safe.
+  //
   class rule
   {
   public:
@@ -50,7 +54,7 @@ namespace build2
     virtual recipe
     apply (action, target&) const override;
 
-    static file_rule instance;
+    static const file_rule instance;
   };
 
   class alias_rule: public rule
@@ -62,7 +66,7 @@ namespace build2
     virtual recipe
     apply (action, target&) const override;
 
-    static alias_rule instance;
+    static const alias_rule instance;
   };
 
   class fsdir_rule: public rule
@@ -80,7 +84,7 @@ namespace build2
     static target_state
     perform_clean (action, target&);
 
-    static fsdir_rule instance;
+    static const fsdir_rule instance;
   };
 
   // Fallback rule that always matches and does nothing.
@@ -94,7 +98,7 @@ namespace build2
     virtual recipe
     apply (action, target&) const override {return noop_recipe;}
 
-    static fallback_rule instance;
+    static const fallback_rule instance;
   };
 }
 
diff --git a/build2/rule-map b/build2/rule-map
index c1b757b..b7397a0 100644
--- a/build2/rule-map
+++ b/build2/rule-map
@@ -21,7 +21,7 @@ namespace build2
   using target_type_rule_map = std::map<
     const target_type*,
     butl::prefix_map<string, // Rule hint.
-                     reference_wrapper<rule>, '.'>>;
+                     reference_wrapper<const rule>, '.'>>;
 
   // This is an "indexed map" with operation_id being the index. Entry
   // with id 0 is a wildcard.
@@ -31,7 +31,7 @@ namespace build2
   public:
     template <typename T>
     void
-    insert (operation_id oid, const char* hint, rule& r)
+    insert (operation_id oid, const char* hint, const rule& r)
     {
       // 3 is the number of builtin operations.
       //
@@ -69,14 +69,17 @@ namespace build2
 
     template <typename T>
     void
-    insert (action_id a, const char* hint, rule& r)
+    insert (action_id a, const char* hint, const rule& r)
     {
       insert<T> (a >> 4, a & 0x0F, hint, r);
     }
 
     template <typename T>
     void
-    insert (meta_operation_id mid, operation_id oid, const char* hint, rule& r)
+    insert (meta_operation_id mid,
+            operation_id oid,
+            const char* hint,
+            const rule& r)
     {
       if (mid_ == mid)
         map_.insert<T> (oid, hint, r);
diff --git a/build2/rule.cxx b/build2/rule.cxx
index 1c0e08c..42d5eb8 100644
--- a/build2/rule.cxx
+++ b/build2/rule.cxx
@@ -110,7 +110,7 @@ namespace build2
     return default_recipe;
   }
 
-  file_rule file_rule::instance;
+  const file_rule file_rule::instance;
 
   // alias_rule
   //
@@ -132,7 +132,7 @@ namespace build2
     return default_recipe;
   }
 
-  alias_rule alias_rule::instance;
+  const alias_rule alias_rule::instance;
 
   // fsdir_rule
   //
@@ -222,9 +222,9 @@ namespace build2
     return ts;
   }
 
-  fsdir_rule fsdir_rule::instance;
+  const fsdir_rule fsdir_rule::instance;
 
   // fallback_rule
   //
-  fallback_rule fallback_rule::instance;
+  const fallback_rule fallback_rule::instance;
 }
diff --git a/build2/test/init.cxx b/build2/test/init.cxx
index 4338231..94e4073 100644
--- a/build2/test/init.cxx
+++ b/build2/test/init.cxx
@@ -146,8 +146,8 @@ namespace build2
       // Register rules.
       //
       {
-        rule& r (m);
-        alias_rule& ar (m);
+        const rule&        r (m);
+        const alias_rule& ar (m);
 
         // Register our test running rule.
         //