Implement optional module loading

The syntax is:

using? cli

Now each module use results in two bool variables: <module>.loaded and
<module>.configured.

Also implement variable visibility (the above two variables are limited
to project).

2 files changed, 20 insertions, 10 deletions

diff --git a/build/cli/module b/build/cli/module
index cf6258f..221e6a0 100644
--- a/build/cli/module
+++ b/build/cli/module
@@ -6,14 +6,17 @@
 #define BUILD_CLI_MODULE
 
 #include <build/types>
+#include <build/utility>
+
 #include <build/module>
 
 namespace build
 {
   namespace cli
   {
-    extern "C" void
-    cli_init (scope&, scope&, const location&, std::unique_ptr<module>&, bool);
+    extern "C" bool
+    cli_init (
+    scope&, scope&, const location&, unique_ptr<module>&, bool, bool);
   }
 }
 
diff --git a/build/cli/module.cxx b/build/cli/module.cxx
index 64e95a8..081980b 100644
--- a/build/cli/module.cxx
+++ b/build/cli/module.cxx
@@ -28,12 +28,13 @@ namespace build
   {
     static compile compile_;
 
-    extern "C" void
+    extern "C" bool
     cli_init (scope& root,
               scope& base,
-              const location& l,
+              const location& loc,
               std::unique_ptr<module>&,
-              bool first)
+              bool first,
+              bool)
     {
       tracer trace ("cli::init");
       level5 ([&]{trace << "for " << base.out_path ();});
@@ -44,8 +45,12 @@ namespace build
       // semantics. So it is better to let the user load cxx
       // explicitly.
       //
-      if (base.find_target_type ("cxx") == nullptr)
-        fail (l) << "cxx module must be initialized before cli";
+      {
+        auto l (base["cxx.loaded"]);
+
+        if (!l || !as<bool> (*l))
+          fail (loc) << "cxx module must be loaded before cli";
+      }
 
       // Register target types.
       //
@@ -84,10 +89,10 @@ namespace build
       //
       if (first)
       {
-        variable_pool.find ("config.cli", string_type); //@@ VAR type
+        var_pool.find ("config.cli", string_type); //@@ VAR type
 
-        variable_pool.find ("config.cli.options", strings_type);
-        variable_pool.find ("cli.options", strings_type);
+        var_pool.find ("config.cli.options", strings_type);
+        var_pool.find ("cli.options", strings_type);
       }
 
       // Configure.
@@ -156,6 +161,8 @@ namespace build
       //
       if (const value& v = config::optional (root, "config.cli.options"))
         base.assign ("cli.options") += as<strings> (v);
+
+      return true;
     }
   }
 }