Add ability to mark config.* variables as "unsaved" (always transient)

5 files changed, 40 insertions, 19 deletions

diff --git a/libbuild2/config/module.cxx b/libbuild2/config/module.cxx
index 6b0c82a..bf68c4e 100644
--- a/libbuild2/config/module.cxx
+++ b/libbuild2/config/module.cxx
@@ -12,7 +12,7 @@ namespace build2
   namespace config
   {
     bool module::
-    save_variable (const variable& var, uint64_t flags)
+    save_variable (const variable& var, optional<uint64_t> flags)
     {
       const string& n (var.name);
 
@@ -39,7 +39,7 @@ namespace build2
 
       if (j != sv.end ())
       {
-        assert (j->flags == flags);
+        assert (!j->flags == !flags && (!flags || *j->flags == *flags));
         return false;
       }
 
@@ -48,7 +48,7 @@ namespace build2
     }
 
     void module::
-    save_variable (scope& rs, const variable& var, uint64_t flags)
+    save_variable (scope& rs, const variable& var, optional<uint64_t> flags)
     {
       if (module* m = rs.find_module<module> (module::name))
         m->save_variable (var, flags);
diff --git a/libbuild2/config/module.hxx b/libbuild2/config/module.hxx
index 96220ac..857a30c 100644
--- a/libbuild2/config/module.hxx
+++ b/libbuild2/config/module.hxx
@@ -25,12 +25,13 @@ namespace build2
     // config.* variables and their "save flags" (see save_variable()) that
     // are used (as opposed to just being specified) in this configuration.
     // Populated by the config utility functions (required(), optional()) and
-    // saved in the order populated.
+    // saved in the order populated. If flags are absent, then this variable
+    // was marked as "unsaved" (always transient).
     //
     struct saved_variable
     {
       reference_wrapper<const variable> var;
-      uint64_t flags;
+      optional<uint64_t> flags;
     };
 
     struct saved_variables: vector<saved_variable>
@@ -75,10 +76,10 @@ namespace build2
       // Return true if variable/module were newly inserted.
       //
       bool
-      save_variable (const variable&, uint64_t flags = 0);
+      save_variable (const variable&, optional<uint64_t> flags);
 
       static void
-      save_variable (scope&, const variable&, uint64_t);
+      save_variable (scope&, const variable&, optional<uint64_t>);
 
       bool
       save_module (const char* name, int prio = 0);
@@ -86,14 +87,18 @@ namespace build2
       static void
       save_module (scope&, const char*, int);
 
-      // Return true if the variable is already saved.
-      //
-      bool
-      saved (const variable& var)
+      const saved_variable*
+      find_variable (const variable& var)
       {
         auto i (saved_modules.find_sup (var.name));
-        return i != saved_modules.end () &&
-          i->second.find (var) != i->second.end ();
+        if (i != saved_modules.end ())
+        {
+          auto j (i->second.find (var));
+          if (j != i->second.end ())
+            return &*j;
+        }
+
+        return nullptr;
       }
 
       // Configure/disfigure hooks.
diff --git a/libbuild2/config/operation.cxx b/libbuild2/config/operation.cxx
index b07df42..963a3e1 100644
--- a/libbuild2/config/operation.cxx
+++ b/libbuild2/config/operation.cxx
@@ -236,7 +236,7 @@ namespace build2
               var->name.compare (0, 14, "config.config.") == 0)
             continue;
 
-          if (mod->saved (*var))
+          if (mod->find_variable (*var)) // Saved or unsaved.
             continue;
 
           const value& v (p.first->second);
@@ -247,7 +247,7 @@ namespace build2
                                                     true  /* unused */));
           if (r.first) // save
           {
-            mod->save_variable (*var);
+            mod->save_variable (*var, 0);
 
             if (r.second) // warn
             {
@@ -291,7 +291,11 @@ namespace build2
           bool first (true); // Separate modules with a blank line.
           for (const saved_variable& sv: svars)
           {
+            if (!sv.flags) // unsaved
+              continue;
+
             const variable& var (sv.var);
+            uint64_t flags (*sv.flags);
 
             pair<lookup, size_t> org (rs.lookup_original (var));
             pair<lookup, size_t> ovr (var.overrides == nullptr
@@ -304,7 +308,7 @@ namespace build2
             // inherited. We might also not have any value at all (see
             // unconfigured()).
             //
-            if (!l.defined () || (l->null && sv.flags & save_null_omitted))
+            if (!l.defined () || (l->null && flags & save_null_omitted))
               continue;
 
             // Handle inherited from outer scope values.
@@ -451,7 +455,7 @@ namespace build2
             //
             if ((org.first.defined () && org.first->extra) && // Default value.
                 org.first == ovr.first &&                     // Not overriden.
-                (sv.flags & save_default_commented) != 0)
+                (flags & save_default_commented) != 0)
             {
               os << '#' << n << " =" << endl;
               continue;
diff --git a/libbuild2/config/utility.cxx b/libbuild2/config/utility.cxx
index b10c980..12ec1fe 100644
--- a/libbuild2/config/utility.cxx
+++ b/libbuild2/config/utility.cxx
@@ -7,7 +7,7 @@ using namespace std;
 
 namespace build2
 {
-  void (*config_save_variable) (scope&, const variable&, uint64_t);
+  void (*config_save_variable) (scope&, const variable&, optional<uint64_t>);
   void (*config_save_module) (scope&, const char*, int);
   const string& (*config_preprocess_create) (context&,
                                              values&,
diff --git a/libbuild2/config/utility.hxx b/libbuild2/config/utility.hxx
index 209ef5c..7d3e18b 100644
--- a/libbuild2/config/utility.hxx
+++ b/libbuild2/config/utility.hxx
@@ -33,7 +33,7 @@ namespace build2
   // attribute). Such flags should start from 0x100000000.
   //
   LIBBUILD2_SYMEXPORT extern void
-  (*config_save_variable) (scope&, const variable&, uint64_t);
+  (*config_save_variable) (scope&, const variable&, optional<uint64_t>);
 
   LIBBUILD2_SYMEXPORT extern void
   (*config_save_module) (scope&, const char*, int);
@@ -65,6 +65,18 @@ namespace build2
         config_save_variable (rs, var, flags);
     }
 
+    // Mark the variable as "unsaved" (always transient).
+    //
+    // Such variables are not very common and are usually used to control the
+    // process of configuration itself.
+    //
+    inline void
+    unsave_variable (scope& rs, const variable& var)
+    {
+      if (config_save_variable != nullptr)
+        config_save_variable (rs, var, nullopt);
+    }
+
     // Establish module save order/priority with INT32_MIN being the highest.
     // Modules with the same priority are saved in the order inserted.
     //