Infra work for customizable config var persistence (config.config.persist)

4 files changed, 74 insertions, 40 deletions

diff --git a/libbuild2/config/init.cxx b/libbuild2/config/init.cxx
index 9fc914c..1f053e9 100644
--- a/libbuild2/config/init.cxx
+++ b/libbuild2/config/init.cxx
@@ -47,14 +47,23 @@ namespace build2
       //
       auto& vp (rs.ctx.var_pool.rw (rs));
 
-      // While config.config.load could theoretically be specified in a
-      // buildfile, config.config.save is expected to always be specified as a
-      // command line override.
+      // While config.config.load (see below) could theoretically be specified
+      // in a buildfile, config.config.save is expected to always be specified
+      // as a command line override.
       //
       // Note: must be entered during bootstrap since we need it in
       // configure_execute().
       //
-      vp.insert<path>  ("config.config.save", true /* ovr */);
+      vp.insert<path> ("config.config.save", true /* ovr */);
+
+      // @@ TODO
+      //
+      // Use the NULL value to clear.
+      //
+      auto& c_p (vp.insert<vector<pair<string, string>>> (
+                   "config.config.persist",
+                   true /* ovr */,
+                   variable_visibility::project));
 
       // Only create the module if we are configuring or creating or if it was
       // requested with config.config.module (useful if we need to call
@@ -78,11 +87,14 @@ namespace build2
 
         unique_ptr<module> m (new module);
 
-        // Adjust priority for the import pseudo-module so that
-        // config.import.* values come first in config.build.
+        // Adjust priority for the config module and import pseudo-module so
+        // that their variables come first in config.build.
         //
+        m->save_module ("config", INT32_MIN);
         m->save_module ("import", INT32_MIN);
 
+        m->save_variable (c_p, omit_null);
+
         mod = move (m);
       }
 
@@ -109,7 +121,7 @@ namespace build2
     init (scope& rs,
           scope&,
           const location& l,
-          unique_ptr<module_base>&,
+          unique_ptr<module_base>& mod,
           bool first,
           bool,
           const variable_map& config_hints)
@@ -224,6 +236,15 @@ namespace build2
         }
       }
 
+      // Cache the config.config.persist value, if any.
+      //
+      if (mod != nullptr)
+      {
+        static_cast<module&> (*mod).persist =
+          cast_null<vector<pair<string, string>>> (
+            rs["config.config.persist"]);
+      }
+
       // Register alias and fallback rule for the configure meta-operation.
       //
       // We need this rule for out-of-any-project dependencies (e.g.,
diff --git a/libbuild2/config/module.hxx b/libbuild2/config/module.hxx
index 296dec5..eccd61b 100644
--- a/libbuild2/config/module.hxx
+++ b/libbuild2/config/module.hxx
@@ -86,6 +86,10 @@ namespace build2
       bool
       save_module (const char* name, int prio = 0);
 
+      // Cached (during init) config.config.persist value, if defined.
+      //
+      const vector<pair<string, string>>* persist = nullptr;
+
       static const string name;
       static const uint64_t version;
     };
diff --git a/libbuild2/config/operation.cxx b/libbuild2/config/operation.cxx
index 21bf8c1..5f1c8cd 100644
--- a/libbuild2/config/operation.cxx
+++ b/libbuild2/config/operation.cxx
@@ -85,20 +85,18 @@ namespace build2
 
     using project_set = set<const scope*>; // Use pointers to get comparison.
 
-    // Mark all the config.import.* variables defined in this variable map as
-    // saved optionally issuing a warning if the variable would otherwise be
-    // unsaved.
+    // Mark all the config.import.* variables defined on this scope as saved
+    // optionally warning if the variable would otherwise be dropped.
     //
     static void
-    save_config_import (context& ctx,
-                        module& m,
-                        const variable_map& vars,
-                        bool warning = false,
-                        const location& loc = location ())
+    save_config_import (module& m,
+                        const scope& rs,
+                        const location& loc,
+                        bool warning)
     {
-      auto& vp (ctx.var_pool);
+      auto& vp (rs.ctx.var_pool);
 
-      for (auto p (vars.find_namespace (*vp.find ("config.import")));
+      for (auto p (rs.vars.find_namespace (*vp.find ("config.import")));
            p.first != p.second;
            ++p.first)
       {
@@ -111,7 +109,22 @@ namespace build2
           var = vp.find (string (var->name, 0, n));
 
         if (m.save_variable (*var) && warning)
+        {
+          // Consistently with save_config() below we don't warn about an
+          // overriden variable.
+          //
+          if (var->overrides != nullptr)
+          {
+            lookup l {p.first->second, *var, rs.vars};
+            pair<lookup, size_t> org {l, 1 /* depth */};
+            pair<lookup, size_t> ovr (rs.find_override (*var, org));
+
+            if (org.first != ovr.first)
+              continue;
+          }
+
           warn (loc) << "keeping potentially no longer used variable " << *var;
+        }
       }
     }
 
@@ -155,8 +168,8 @@ namespace build2
           }
         }
 
-        // Mark all the config.import.* variables defined on our root scope as
-        // saved.
+        // Pre-mark all the config.import.* variables defined on our root
+        // scope as saved.
         //
         // This is in contrast to module-specific config variables (and later
         // probably to project-specific) where by default we drop no longer
@@ -168,7 +181,8 @@ namespace build2
         //
         // Note that in the future we may make these defaults configurable.
         //
-        save_config_import (ctx, *mod, rs.vars, true /* warn */, location (on));
+        if (mod->persist) //@@ TMP
+          save_config_import (*mod, rs, location (on), false /* warn */);
 
         // Save config variables.
         //
@@ -195,7 +209,7 @@ namespace build2
             // inherited. We might also not have any value at all (see
             // unconfigured()).
             //
-            if (!l.defined ())
+            if (!l.defined () || (l->null && sv.flags & omit_null))
               continue;
 
             // Handle inherited from outer scope values.
@@ -256,7 +270,7 @@ namespace build2
                       // outer project is reconfigured). Feels like this will
                       // be quite obscure and error-prone.
                       //
-                      if (!found)
+                      if (!found && m->persist) //@@ TMP
                         found = var.name.compare (0, 14, "config.import.") == 0;
 
                       // Handle that other case: if this is an override but
@@ -504,8 +518,8 @@ namespace build2
           dir_path out_nroot (out_root / pd);
           const scope& nrs (ctx.scopes.find (out_nroot));
 
-          // @@ Strictly speaking we need to check whether the config
-          // module was loaded for this subproject.
+          // @@ Strictly speaking we need to check whether the config module
+          //    was loaded for this subproject.
           //
           if (nrs.out_path () != out_nroot) // This subproject not loaded.
             continue;
@@ -1002,29 +1016,23 @@ namespace build2
     {
       // Since there aren't any sub-projects yet, any config.import.* values
       // that the user may want to specify won't be saved in config.build. So
-      // let's go ahead and mark them all to be saved. To do this, however, we
-      // need the config module (which is where this information is stored).
-      // And the module is created by init() during bootstrap. So what we are
-      // going to do is bootstrap the newly created project, similar to the
-      // way main() does it.
+      // we go ahead and add them to config.config.persist (unless overriden).
+      // To do this, however, we need the project's root scope (which is where
+      // this information is stored). So what we are going to do is bootstrap
+      // the newly created project, similar to the way main() does it.
       //
       scope& gs (ctx.global_scope.rw ());
       scope& rs (load_project (gs, d, d, false /* fwd */, false /* load */));
-      module& m (*rs.lookup_module<module> (module::name));
 
-      // Save all the global config.import.* variables.
+      // Add the default config.config.persist value unless there is a custom
+      // one (specified as a command line override).
       //
-      save_config_import (ctx, m, gs.vars);
+      const variable& var (*ctx.var_pool.find ("config.config.persist"));
 
-      // Now project-specific. For now we just save all of them and let
-      // save_config() above weed out the ones that do not apply.
-      //
-      for (const variable_override& vo: ctx.var_overrides)
+      if (!rs[var].defined ())
       {
-        const variable& var (vo.var);
-
-        if (var.name.compare (0, 14, "config.import.") == 0)
-          m.save_variable (var);
+        rs.assign (var) = vector<pair<string, string>> {
+          pair<string, string> {"config.import.*", "unused=keep"}};
       }
     }
 
diff --git a/libbuild2/config/utility.hxx b/libbuild2/config/utility.hxx
index 2a0909f..7774b68 100644
--- a/libbuild2/config/utility.hxx
+++ b/libbuild2/config/utility.hxx
@@ -143,6 +143,7 @@ namespace build2
     // config::module for details.
     //
     const uint64_t save_commented = 0x01; // Save default value as commented.
+    const uint64_t omit_null      = 0x02; // Treat NULL as undefined.
 
     LIBBUILD2_SYMEXPORT void
     save_variable (scope& root, const variable&, uint64_t flags = 0);