Add ability for module to remember that it is unconfigured

A module can set and then check the config.*.configured special variable
to false.

3 files changed, 35 insertions, 12 deletions

diff --git a/build/config/operation.cxx b/build/config/operation.cxx
index 295a38a..abe4e22 100644
--- a/build/config/operation.cxx
+++ b/build/config/operation.cxx
@@ -101,13 +101,24 @@ namespace build
         {
           const variable& var (p.first->first);
           const value& val (p.first->second);
+          const string& n (var.name);
 
           // Skip special variables.
           //
-          if (var.name == "config.loaded" ||
-              var.name == "config.configured")
+          if (n == "config.loaded" ||
+              n == "config.configured")
             continue;
 
+          // We will only write config.*.configured if it is false
+          // (true is implied by its absence).
+          //
+          if (n.size () > 11 &&
+              n.compare (n.size () - 11, 11, ".configured") == 0)
+          {
+            if (val == nullptr || as<bool> (val))
+              continue;
+          }
+
           // Warn the user if the value that we are saving differs
           // from the one they specified on the command line.
           //
diff --git a/build/config/utility b/build/config/utility
index ece7a88..ee5f50b 100644
--- a/build/config/utility
+++ b/build/config/utility
@@ -83,13 +83,16 @@ namespace build
       return optional_absolute (root, var_pool.find (var));
     }
 
-    // Check whether there are any variables specified from the
-    // config namespace. The idea is that we can check if there
-    // are any, say, config.install.* values. If there are none,
-    // then we can assume this functionality is not (yet) used
-    // and omit writing a whole bunch of NULL config.install.*
-    // values to the config.build file . We call it omitted/
-    // delayed configuration.
+    // Check whether there are any variables specified from the config
+    // namespace. The idea is that we can check if there are any, say,
+    // config.install.* values. If there are none, then we can assume
+    // this functionality is not (yet) used and omit writing a whole
+    // bunch of NULL config.install.* values to the config.build file.
+    // We call it omitted/delayed configuration.
+    //
+    // Note that this function detects and ignores the special
+    // config.*.configured variable which may be used by a module to
+    // "remember" that it is unconfigured.
     //
     bool
     specified (scope& root, const std::string& ns);
diff --git a/build/config/utility.cxx b/build/config/utility.cxx
index c9d7c66..b81cb04 100644
--- a/build/config/utility.cxx
+++ b/build/config/utility.cxx
@@ -60,9 +60,18 @@ namespace build
       //
       for (scope* s (&r); s != nullptr; s = s->parent_scope ())
       {
-        auto p (s->vars.find_namespace (ns));
-        if (p.first != p.second)
-          return true;
+        for (auto p (s->vars.find_namespace (ns));
+             p.first != p.second;
+             ++p.first)
+        {
+          const variable& var (p.first->first);
+
+          // Ignore config.*.configured.
+          //
+          if (var.name.size () < 11 ||
+              var.name.compare (var.name.size () - 11, 11, ".configured") != 0)
+            return true;
+        }
       }
 
       return false;