Add ability for module to remember that it is unconfigured

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

5 files changed, 65 insertions, 24 deletions

diff --git a/build/cli/module.cxx b/build/cli/module.cxx
index 7ce4235..c44d670 100644
--- a/build/cli/module.cxx
+++ b/build/cli/module.cxx
@@ -65,6 +65,8 @@ namespace build
       //
       if (first)
       {
+        var_pool.find ("config.cli.configured", bool_type);
+
         var_pool.find ("config.cli", string_type); //@@ VAR type
 
         var_pool.find ("config.cli.options", strings_type);
@@ -73,17 +75,26 @@ namespace build
 
       // Configure.
       //
-      // The plan is as follows: try to configure the module. If this
-      // fails with the default values and the module is optional,
-      // leave it unconfigured.
+      // The plan is as follows: try to configure the module. If this fails,
+      // we are using default values, and the module is optional, leave it
+      // unconfigured.
       //
-      bool r (true);
 
       // We will only honor optional if the user didn't specify any cli
       // configuration explicitly.
       //
       optional = optional && !config::specified (root, "config.cli");
 
+      // Don't re-run tests if the configuration says we are unconfigured.
+      //
+      if (optional)
+      {
+        auto l (root["config.cli.configured"]);
+
+        if (l && !as<bool> (*l))
+          return false;
+      }
+
       // config.cli
       //
       if (first)
@@ -148,10 +159,15 @@ namespace build
 
           if (ver.empty ())
           {
-            r = false;
+            // Note that we are unconfigured so that we don't keep re-testing
+            // this on each run.
+            //
+            root.assign ("config.cli.configured") = false;
 
             if (verb >= 2)
               text << cli << " not found, leaving cli module unconfigured";
+
+            return false;
           }
           else
           {
@@ -175,6 +191,10 @@ namespace build
           }
         }
 
+        // Clear the unconfigured flag, if any.
+        //
+        root.assign ("config.cli.configured") = true;
+
         if (!ver.empty () && verb >= 2)
           text << cli << " " << ver;
       }
@@ -185,15 +205,11 @@ namespace build
       // cli.* variables. See the cxx module for more information on
       // this merging semantics and some of its tricky aspects.
       //
-      if (r)
-      {
-        if (const value& v = config::optional (root, "config.cli.options"))
-          base.assign ("cli.options") += as<strings> (v);
-      }
+      if (const value& v = config::optional (root, "config.cli.options"))
+        base.assign ("cli.options") += as<strings> (v);
 
       // Register our rules.
       //
-      if (r)
       {
         auto& rs (base.rules);
 
@@ -216,7 +232,7 @@ namespace build
         rs.insert<cli_cxx> (configure_id, update_id, "cli", compile_);
       }
 
-      return r;
+      return true;
     }
   }
 }
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;
diff --git a/build/variable b/build/variable
index 5d0b175..51d748d 100644
--- a/build/variable
+++ b/build/variable
@@ -119,6 +119,8 @@ namespace build
     bool empty () const {return state_ == state_type::empty;}
 
     explicit operator bool () const {return !null ();}
+    bool operator== (std::nullptr_t) const {return null ();}
+    bool operator!= (std::nullptr_t) const {return !null ();}
 
     // Raw data read interface.
     //