Implement support for importing installed libraries

9 files changed, 1056 insertions, 613 deletions

diff --git a/build/cxx/compile b/build/cxx/compile
new file mode 100644
index 0000000..1cc91ab
--- /dev/null
+++ b/build/cxx/compile
@@ -0,0 +1,30 @@
+// file      : build/cxx/compile -*- C++ -*-
+// copyright : Copyright (c) 2014-2015 Code Synthesis Ltd
+// license   : MIT; see accompanying LICENSE file
+
+#ifndef BUILD_CXX_COMPILE
+#define BUILD_CXX_COMPILE
+
+#include <build/types>
+#include <build/rule>
+
+namespace build
+{
+  namespace cxx
+  {
+    class compile: public rule
+    {
+    public:
+      virtual match_result
+      match (action, target&, const std::string& hint) const;
+
+      virtual recipe
+      apply (action, target&, const match_result&) const;
+
+      static target_state
+      perform_update (action, target&);
+    };
+  }
+}
+
+#endif // BUILD_CXX_COMPILE
diff --git a/build/cxx/rule.cxx b/build/cxx/compile.cxx
index 9228994..d0e6526 100644
--- a/build/cxx/rule.cxx
+++ b/build/cxx/compile.cxx
@@ -1,19 +1,18 @@
-// file      : build/cxx/rule.cxx -*- C++ -*-
+// file      : build/cxx/compile.cxx -*- C++ -*-
 // copyright : Copyright (c) 2014-2015 Code Synthesis Ltd
 // license   : MIT; see accompanying LICENSE file
 
-#include <build/cxx/rule>
+#include <build/cxx/compile>
 
 #include <map>
 #include <string>
 #include <cstddef>  // size_t
-#include <cstdlib>  // exit
+#include <cstdlib>  // exit()
 #include <utility>  // move()
 
 #include <butl/process>
 #include <butl/utility>  // reverse_iterate
 #include <butl/fdstream>
-#include <butl/optional>
 #include <butl/path-map>
 
 #include <build/types>
@@ -26,7 +25,8 @@
 #include <build/bin/target>
 #include <build/cxx/target>
 
-#include <build/config/utility>
+#include <build/cxx/utility>
+#include <build/cxx/link>
 
 using namespace std;
 using namespace butl;
@@ -37,48 +37,6 @@ namespace build
   {
     using namespace bin;
 
-    using config::append_options;
-
-    static void
-    append_std (cstrings& args, target& t, string& opt)
-    {
-      if (auto val = t["cxx.std"])
-      {
-        const string& v (val.as<const string&> ());
-
-        // Translate 11 to 0x and 14 to 1y for compatibility with
-        // older versions of the compiler.
-        //
-        opt = "-std=c++";
-
-        if (v == "11")
-          opt += "0x";
-        else if (v == "14")
-          opt += "1y";
-        else
-          opt += v;
-
-        args.push_back (opt.c_str ());
-      }
-    }
-
-    // Append library options from one of the cxx.export.* variables
-    // recursively, prerequisite libraries first.
-    //
-    static void
-    append_lib_options (cstrings& args, target& l, const char* var)
-    {
-      for (target* t: l.prerequisite_targets)
-      {
-        if (t->is_a<lib> () || t->is_a<liba> () || t->is_a<libso> ())
-          append_lib_options (args, *t, var);
-      }
-
-      append_options (args, l, var);
-    }
-
-    // compile
-    //
     match_result compile::
     match (action a, target& t, const string&) const
     {
@@ -133,31 +91,49 @@ namespace build
         ? nullptr
         : &t.strong_scope ().path ());
 
+      link::search_paths_cache lib_paths; // Extract lazily.
+
       for (prerequisite_member p: group_prerequisite_members (a, t))
       {
-        target& pt (p.search ());
-
-        if (a.operation () == clean_id && !pt.dir.sub (*amlg))
-          continue;
-
         // A dependency on a library is there so that we can get its
         // cxx.export.poptions. In particular, making sure it is
         // executed before us will only restrict parallelism. But we
         // do need to match it in order to get its prerequisite_targets
         // populated; see append_lib_options() above.
         //
-        if (pt.is_a<lib> () || pt.is_a<liba> () || pt.is_a<libso> ())
+        if (p.is_a<lib> () || p.is_a<liba> () || p.is_a<libso> ())
         {
-          // @@ The fact that we match but never execute messes up
-          //    the dependents count. This is a workaround, not a
-          //    solution.
-          //
           if (a.operation () == update_id)
+          {
+            // Handle imported libraries.
+            //
+            if (p.proj () != nullptr)
+            {
+              // We know that for such libraries we don't need to do
+              // match() in order to get options (if any, they would
+              // be set by search_library()).
+              //
+              if (link::search_library (lib_paths, p.prerequisite) != nullptr)
+                continue;
+            }
+
+            target& pt (p.search ());
+
+            // @@ The fact that we match but never execute messes up
+            //    the dependents count. This is a workaround, not a
+            //    solution.
+            //
             build::match (a, pt);
+          }
 
           continue;
         }
 
+        target& pt (p.search ());
+
+        if (a.operation () == clean_id && !pt.dir.sub (*amlg))
+          continue;
+
         build::match (a, pt);
         t.prerequisite_targets.push_back (&pt);
       }
@@ -493,7 +469,7 @@ namespace build
             getline (is, l);
 
             if (is.fail () && !is.eof ())
-              fail << "io error while parsing g++ -M output";
+              fail << "error reading C++ compiler -M output";
 
             size_t pos (0);
 
@@ -802,499 +778,5 @@ namespace build
         throw failed ();
       }
     }
-
-    // link
-    //
-    inline link::type link::
-    link_type (target& t)
-    {
-      return t.is_a<exe> () ? type::e : (t.is_a<liba> () ? type::a : type::so);
-    }
-
-    link::order link::
-    link_order (target& t)
-    {
-      const char* var;
-
-      switch (link_type (t))
-      {
-      case type::e:  var = "bin.exe.lib";   break;
-      case type::a:  var = "bin.liba.lib";  break;
-      case type::so: var = "bin.libso.lib"; break;
-      }
-
-      const list_value& lv (t[var].as<const list_value&> ());
-      return lv[0].value == "shared"
-        ? lv.size () > 1 && lv[1].value == "static" ? order::so_a : order::so
-        : lv.size () > 1 && lv[1].value == "shared" ? order::a_so : order::a;
-    }
-
-    match_result link::
-    match (action a, target& t, const string& hint) const
-    {
-      tracer trace ("cxx::link::match");
-
-      // @@ TODO:
-      //
-      // - check prerequisites: object files, libraries
-      // - if path already assigned, verify extension?
-      //
-      // @@ Q:
-      //
-      // - if there is no .o, are we going to check if the one derived
-      //   from target exist or can be built? A: No.
-      //   What if there is a library. Probably ok if .a, not if .so.
-      //   (i.e., a utility library).
-      //
-
-      bool so (t.is_a<libso> ());
-
-      // Scan prerequisites and see if we can work with what we've got.
-      //
-      bool seen_cxx (false), seen_c (false), seen_obj (false),
-        seen_lib (false);
-
-      for (prerequisite_member p: group_prerequisite_members (a, t))
-      {
-        if (p.is_a<cxx> ())
-        {
-          seen_cxx = seen_cxx || true;
-        }
-        else if (p.is_a<c> ())
-        {
-          seen_c = seen_c || true;
-        }
-        else if (p.is_a<obja> ())
-        {
-          if (so)
-            fail << "shared library " << t << " prerequisite " << p
-                 << " is static object";
-
-          seen_obj = seen_obj || true;
-        }
-        else if (p.is_a<objso> () ||
-                 p.is_a<obj> ())
-        {
-          seen_obj = seen_obj || true;
-        }
-        else if (p.is_a<liba> ()  ||
-                 p.is_a<libso> () ||
-                 p.is_a<lib> ())
-        {
-          seen_lib = seen_lib || true;
-        }
-        else if (p.is_a<h> ()   ||
-                 p.is_a<hxx> () ||
-                 p.is_a<ixx> () ||
-                 p.is_a<txx> () ||
-                 p.is_a<fsdir> ())
-          ;
-        else
-        {
-          level3 ([&]{trace << "unexpected prerequisite type " << p.type ();});
-          return nullptr;
-        }
-      }
-
-      // We will only chain a C source if there is also a C++ source or we
-      // were explicitly told to.
-      //
-      if (seen_c && !seen_cxx && hint < "cxx")
-      {
-        level3 ([&]{trace << "c prerequisite(s) without c++ or hint";});
-        return nullptr;
-      }
-
-      return seen_cxx || seen_c || seen_obj || seen_lib ? &t : nullptr;
-    }
-
-    recipe link::
-    apply (action a, target& xt, const match_result&) const
-    {
-      tracer trace ("cxx::link::apply");
-
-      path_target& t (static_cast<path_target&> (xt));
-
-      type lt (link_type (t));
-      bool so (lt == type::so);
-      optional<order> lo; // Link-order.
-
-      // Derive file name from target name.
-      //
-      if (t.path ().empty ())
-      {
-        switch (lt)
-        {
-        case type::e:  t.derive_path (""         ); break;
-        case type::a:  t.derive_path ("a",  "lib"); break;
-        case type::so: t.derive_path ("so", "lib"); break;
-        }
-      }
-
-      // Inject dependency on the output directory.
-      //
-      inject_parent_fsdir (a, t);
-
-      // We may need the project roots for rule chaining (see below).
-      // We will resolve them lazily only if needed.
-      //
-      scope* root (nullptr);
-      const dir_path* out_root (nullptr);
-      const dir_path* src_root (nullptr);
-
-      // Process prerequisites: do rule chaining for C and C++ source
-      // files as well as search and match.
-      //
-      // When cleaning, ignore prerequisites that are not in the same
-      // or a subdirectory of our strong amalgamation.
-      //
-      const dir_path* amlg (
-        a.operation () != clean_id
-        ? nullptr
-        : &t.strong_scope ().path ());
-
-      for (prerequisite_member p: group_prerequisite_members (a, t))
-      {
-        bool group (!p.prerequisite.belongs (t)); // Group's prerequisite.
-        target* pt (nullptr);
-
-        if (!p.is_a<c> () && !p.is_a<cxx> ())
-        {
-          // The same basic logic as in search_and_match().
-          //
-          pt = &p.search ();
-
-          if (a.operation () == clean_id && !pt->dir.sub (*amlg))
-            continue; // Skip.
-
-          // If this is the obj{} or lib{} target group, then pick the
-          // appropriate member and make sure it is searched and matched.
-          //
-          if (obj* o = pt->is_a<obj> ())
-          {
-            pt = so ? static_cast<target*> (o->so) : o->a;
-
-            if (pt == nullptr)
-              pt = &search (so ? objso::static_type : obja::static_type,
-                            p.key ());
-          }
-          else if (lib* l = pt->is_a<lib> ())
-          {
-            // Determine the library type to link.
-            //
-            bool lso (true);
-            const string& at ((*l)["bin.lib"].as<const string&> ());
-
-            if (!lo)
-              lo = link_order (t);
-
-            switch (*lo)
-            {
-            case order::a:
-            case order::a_so:
-              lso = false; // Fall through.
-            case order::so:
-            case order::so_a:
-              {
-                if (lso ? at == "static" : at == "shared")
-                {
-                  if (*lo == order::a_so || *lo == order::so_a)
-                    lso = !lso;
-                  else
-                    fail << (lso ? "shared" : "static") << " build of " << *l
-                         << " is not available";
-                }
-              }
-            }
-
-            pt = lso ? static_cast<target*> (l->so) : l->a;
-
-            if (pt == nullptr)
-              pt = &search (lso ? libso::static_type : liba::static_type,
-                            p.key ());
-          }
-
-          build::match (a, *pt);
-          t.prerequisite_targets.push_back (pt);
-          continue;
-        }
-
-        if (root == nullptr)
-        {
-          // Which scope shall we use to resolve the root? Unlikely,
-          // but possible, the prerequisite is from a different project
-          // altogether. So we are going to use the target's project.
-          //
-          root = &t.root_scope ();
-          out_root = &root->path ();
-          src_root = &root->src_path ();
-        }
-
-        const prerequisite_key& cp (p.key ()); // c(xx){} prerequisite key.
-        const target_type& o_type (
-          group
-          ? obj::static_type
-          : (so ? objso::static_type : obja::static_type));
-
-        // Come up with the obj*{} target. The c(xx){} prerequisite
-        // directory can be relative (to the scope) or absolute. If it is
-        // relative, then use it as is. If it is absolute, then translate
-        // it to the corresponding directory under out_root. While the
-        // c(xx){} directory is most likely under src_root, it is also
-        // possible it is under out_root (e.g., generated source).
-        //
-        dir_path d;
-        {
-          const dir_path& cpd (*cp.tk.dir);
-
-          if (cpd.relative () || cpd.sub (*out_root))
-            d = cpd;
-          else
-          {
-            if (!cpd.sub (*src_root))
-              fail << "out of project prerequisite " << cp <<
-                info << "specify corresponding " << o_type.name << "{} "
-                   << "target explicitly";
-
-            d = *out_root / cpd.leaf (*src_root);
-          }
-        }
-
-        target& ot (search (o_type, d, *cp.tk.name, nullptr, cp.scope));
-
-        // If we are cleaning, check that this target is in the same or
-        // a subdirectory of our strong amalgamation.
-        //
-        if (a.operation () == clean_id && !ot.dir.sub (*amlg))
-        {
-          // If we shouldn't clean obj{}, then it is fair to assume
-          // we shouldn't clean cxx{} either (generated source will
-          // be in the same directory as obj{} and if not, well, go
-          // find yourself another build system ;-)).
-          //
-          continue; // Skip.
-        }
-
-        // If we have created the obj{} target group, pick one of its
-        // members; the rest would be primarily concerned with it.
-        //
-        if (group)
-        {
-          obj& o (static_cast<obj&> (ot));
-          pt = so ? static_cast<target*> (o.so) : o.a;
-
-          if (pt == nullptr)
-            pt = &search (so ? objso::static_type : obja::static_type,
-                          o.dir, o.name, o.ext, nullptr);
-        }
-        else
-          pt = &ot;
-
-        // If this obj*{} target already exists, then it needs to be
-        // "compatible" with what we are doing here.
-        //
-        // This gets a bit tricky. We need to make sure the source files
-        // are the same which we can only do by comparing the targets to
-        // which they resolve. But we cannot search the ot's prerequisites
-        // -- only the rule that matches can. Note, however, that if all
-        // this works out, then our next step is to match the obj*{}
-        // target. If things don't work out, then we fail, in which case
-        // searching and matching speculatively doesn't really hurt.
-        //
-        bool found (false);
-        for (prerequisite_member p1:
-               reverse_group_prerequisite_members (a, *pt))
-        {
-          // Ignore some known target types (fsdir, headers, libraries).
-          //
-          if (p1.is_a<fsdir> () ||
-              p1.is_a<h> ()     ||
-              (p.is_a<cxx> () && (p1.is_a<hxx> () ||
-                                  p1.is_a<ixx> () ||
-                                  p1.is_a<txx> ())) ||
-              p1.is_a<lib> ()  ||
-              p1.is_a<liba> () ||
-              p1.is_a<libso> ())
-          {
-            continue;
-          }
-
-          if (!p1.is_a<cxx> ())
-            fail << "synthesized target for prerequisite " << cp
-                 << " would be incompatible with existing target " << *pt <<
-              info << "unexpected existing prerequisite type " << p1 <<
-              info << "specify corresponding obj{} target explicitly";
-
-          if (!found)
-          {
-            build::match (a, *pt); // Now p1 should be resolved.
-
-            // Searching our own prerequisite is ok.
-            //
-            if (&p.search () != &p1.search ())
-              fail << "synthesized target for prerequisite " << cp << " would "
-                   << "be incompatible with existing target " << *pt <<
-                info << "existing prerequisite " << p1 << " does not match "
-                   << cp <<
-                info << "specify corresponding " << o_type.name << "{} target "
-                   << "explicitly";
-
-            found = true;
-            // Check the rest of the prerequisites.
-          }
-        }
-
-        if (!found)
-        {
-          // Note: add the source to the group, not the member.
-          //
-          ot.prerequisites.emplace_back (p.as_prerequisite (trace));
-
-          // Add our lib*{} prerequisites to the object file (see
-          // cxx.export.poptions above for details). Note: no need
-          // to go into group members.
-          //
-          // Initially, we were only adding imported libraries, but
-          // there is a problem with this approach: the non-imported
-          // library might depend on the imported one(s) which we will
-          // never "see" unless we start with this library.
-          //
-          for (prerequisite& p: group_prerequisites (t))
-          {
-            if (p.is_a<lib> () || p.is_a<liba> () || p.is_a<libso> ())
-              ot.prerequisites.emplace_back (p);
-          }
-
-          build::match (a, *pt);
-        }
-
-        t.prerequisite_targets.push_back (pt);
-      }
-
-      switch (a)
-      {
-      case perform_update_id: return &perform_update;
-      case perform_clean_id: return &perform_clean;
-      default: return default_recipe; // Forward to prerequisites.
-      }
-    }
-
-    target_state link::
-    perform_update (action a, target& xt)
-    {
-      path_target& t (static_cast<path_target&> (xt));
-
-      type lt (link_type (t));
-      bool so (lt == type::so);
-
-      if (!execute_prerequisites (a, t, t.mtime ()))
-        return target_state::unchanged;
-
-      // Translate paths to relative (to working directory) ones. This
-      // results in easier to read diagnostics.
-      //
-      path relt (relative (t.path ()));
-
-      scope& rs (t.root_scope ());
-      cstrings args;
-      string storage1;
-
-      if (lt == type::a)
-      {
-        //@@ ranlib
-        //
-        args.push_back ("ar");
-        args.push_back ("-rc");
-        args.push_back (relt.string ().c_str ());
-      }
-      else
-      {
-        args.push_back (rs["config.cxx"].as<const string&> ().c_str ());
-
-        append_options (args, t, "cxx.coptions");
-
-        append_std (args, t, storage1);
-
-        if (so)
-          args.push_back ("-shared");
-
-        args.push_back ("-o");
-        args.push_back (relt.string ().c_str ());
-
-        append_options (args, t, "cxx.loptions");
-      }
-
-      // Reserve enough space so that we don't reallocate. Reallocating
-      // means pointers to elements may no longer be valid.
-      //
-      paths relo;
-      relo.reserve (t.prerequisite_targets.size ());
-
-      for (target* pt: t.prerequisite_targets)
-      {
-        path_target* ppt;
-
-        if ((ppt = pt->is_a<obja> ()))
-          ;
-        else if ((ppt = pt->is_a<objso> ()))
-          ;
-        else if ((ppt = pt->is_a<liba> ()))
-          ;
-        else if ((ppt = pt->is_a<libso> ()))
-        {
-          // Use absolute path for the shared libraries since that's
-          // the path the runtime loader will use to try to find it.
-          // This is probably temporary until we get into the whole
-          // -soname/-rpath mess.
-          //
-          args.push_back (ppt->path ().string ().c_str ());
-          continue;
-        }
-        else
-          continue;
-
-        relo.push_back (relative (ppt->path ()));
-        args.push_back (relo.back ().string ().c_str ());
-      }
-
-      if (lt != type::a)
-        append_options (args, t, "cxx.libs");
-
-      args.push_back (nullptr);
-
-      if (verb)
-        print_process (args);
-      else
-        text << "ld " << t;
-
-      try
-      {
-        process pr (args.data ());
-
-        if (!pr.wait ())
-          throw failed ();
-
-        // Should we go to the filesystem and get the new mtime? We
-        // know the file has been modified, so instead just use the
-        // current clock time. It has the advantage of having the
-        // subseconds precision.
-        //
-        t.mtime (system_clock::now ());
-        return target_state::changed;
-      }
-      catch (const process_error& e)
-      {
-        error << "unable to execute " << args[0] << ": " << e.what ();
-
-        // In a multi-threaded program that fork()'ed but did not exec(),
-        // it is unwise to try to do any kind of cleanup (like unwinding
-        // the stack and running destructors).
-        //
-        if (e.child ())
-          exit (1);
-
-        throw failed ();
-      }
-    }
   }
 }
diff --git a/build/cxx/link b/build/cxx/link
new file mode 100644
index 0000000..75223fc
--- /dev/null
+++ b/build/cxx/link
@@ -0,0 +1,46 @@
+// file      : build/cxx/link -*- C++ -*-
+// copyright : Copyright (c) 2014-2015 Code Synthesis Ltd
+// license   : MIT; see accompanying LICENSE file
+
+#ifndef BUILD_CXX_LINK
+#define BUILD_CXX_LINK
+
+#include <vector>
+
+#include <butl/optional>
+
+#include <build/types>
+#include <build/rule>
+
+namespace build
+{
+  namespace cxx
+  {
+    class link: public rule
+    {
+    public:
+      virtual match_result
+      match (action, target&, const std::string& hint) const;
+
+      virtual recipe
+      apply (action, target&, const match_result&) const;
+
+      static target_state
+      perform_update (action, target&);
+
+    private:
+      friend class compile;
+
+      using search_paths = std::vector<dir_path>;
+      using search_paths_cache = butl::optional<search_paths>;
+
+      static target*
+      search_library (search_paths_cache&, prerequisite&);
+
+      static search_paths
+      extract_library_paths (scope&);
+    };
+  }
+}
+
+#endif // BUILD_CXX_LINK
diff --git a/build/cxx/link.cxx b/build/cxx/link.cxx
new file mode 100644
index 0000000..f37ef58
--- /dev/null
+++ b/build/cxx/link.cxx
@@ -0,0 +1,843 @@
+// file      : build/cxx/link.cxx -*- C++ -*-
+// copyright : Copyright (c) 2014-2015 Code Synthesis Ltd
+// license   : MIT; see accompanying LICENSE file
+
+#include <build/cxx/link>
+
+#include <vector>
+#include <string>
+#include <cstddef>  // size_t
+#include <cstdlib>  // exit()
+#include <utility>  // move()
+
+#include <butl/process>
+#include <butl/utility>  // reverse_iterate
+#include <butl/fdstream>
+#include <butl/optional>
+#include <butl/path-map>
+#include <butl/filesystem>
+
+#include <build/types>
+#include <build/scope>
+#include <build/variable>
+#include <build/algorithm>
+#include <build/diagnostics>
+#include <build/context>
+
+#include <build/bin/target>
+#include <build/cxx/target>
+
+#include <build/cxx/utility>
+
+using namespace std;
+using namespace butl;
+
+namespace build
+{
+  namespace cxx
+  {
+    using namespace bin;
+
+    enum class type {e, a, so};
+    enum class order {a, so, a_so, so_a};
+
+    static inline type
+    link_type (target& t)
+    {
+      return t.is_a<exe> () ? type::e : (t.is_a<liba> () ? type::a : type::so);
+    }
+
+    static order
+    link_order (target& t)
+    {
+      const char* var;
+
+      switch (link_type (t))
+      {
+      case type::e:  var = "bin.exe.lib";   break;
+      case type::a:  var = "bin.liba.lib";  break;
+      case type::so: var = "bin.libso.lib"; break;
+      }
+
+      const list_value& lv (t[var].as<const list_value&> ());
+      return lv[0].value == "shared"
+        ? lv.size () > 1 && lv[1].value == "static" ? order::so_a : order::so
+        : lv.size () > 1 && lv[1].value == "shared" ? order::a_so : order::a;
+    }
+
+    link::search_paths link::
+    extract_library_paths (scope& bs)
+    {
+      search_paths r;
+      scope& rs (*bs.root_scope ());
+
+      // Extract user-supplied search paths (i.e., -L).
+      //
+      if (auto val = bs["cxx.loptions"])
+      {
+        const list_value& l (val.as<const list_value&> ());
+
+        for (auto i (l.begin ()), e (l.end ()); i != e; ++i)
+        {
+          if (!i->simple ())
+            continue;
+
+          // -L can either be in the -Lfoo or -L foo form.
+          //
+          dir_path d;
+          if (i->value == "-L")
+          {
+            if (++i == e)
+              break; // Let the compiler complain.
+
+            if (i->simple ())
+              d = dir_path (i->value);
+            else if (i->directory ())
+              d = i->dir;
+            else
+              break; // Let the compiler complain.
+          }
+          else if (i->value.compare (0, 2, "-L") == 0)
+            d = dir_path (i->value, 2, string::npos);
+          else
+            continue;
+
+          // Ignore relative paths. Or maybe we should warn?
+          //
+          if (!d.relative ())
+            r.push_back (move (d));
+        }
+      }
+
+      // Extract system search paths.
+      //
+      cstrings args;
+      string std_storage;
+
+      args.push_back (rs["config.cxx"].as<const string&> ().c_str ());
+      append_options (args, bs, "cxx.coptions");
+      append_std (args, bs, std_storage);
+      append_options (args, bs, "cxx.loptions");
+      args.push_back ("-print-search-dirs");
+      args.push_back (nullptr);
+
+      if (verb >= 5)
+        print_process (args);
+
+      string l;
+      try
+      {
+        process pr (args.data (), false, false, true);
+        ifdstream is (pr.in_ofd);
+
+        while (!is.eof ())
+        {
+          string s;
+          getline (is, s);
+
+          if (is.fail () && !is.eof ())
+            fail << "error reading C++ compiler -print-search-dirs output";
+
+          if (s.compare (0, 12, "libraries: =") == 0)
+          {
+            l.assign (s, 12, string::npos);
+            break;
+          }
+        }
+
+        is.close (); // Don't block.
+
+        if (!pr.wait ())
+          throw failed ();
+      }
+      catch (const process_error& e)
+      {
+        error << "unable to execute " << args[0] << ": " << e.what ();
+
+        if (e.child ())
+          exit (1);
+
+        throw failed ();
+      }
+
+      if (l.empty ())
+        fail << "unable to extract C++ compiler system library paths";
+
+      // Now the fun part: figuring out which delimiter is used.
+      // Normally it is ':' but on Windows it is ';' (or can be;
+      // who knows for sure). Also note that these paths are
+      // absolute (or should be). So here is what we are going
+      // to do: first look for ';'. If found, then that's the
+      // delimiter. If not found, then there are two cases:
+      // it is either a single Windows path or the delimiter
+      // is ':'. To distinguish these two cases we check if
+      // the path starts with a Windows drive.
+      //
+      char d (';');
+      string::size_type e (l.find (d));
+
+      if (e == string::npos &&
+          (l.size () < 2 || l[0] == '/' || l[1] != ':'))
+      {
+        d = ':';
+        e = l.find (d);
+      }
+
+      // Now chop it up. We already have the position of the
+      // first delimiter (if any).
+      //
+      for (string::size_type b (0);; e = l.find (d, (b = e + 1)))
+      {
+        r.emplace_back (l, b, (e != string::npos ? e - b : e));
+        r.back ().normalize ();
+
+        if (e == string::npos)
+          break;
+      }
+
+      return r;
+    }
+
+    target* link::
+    search_library (search_paths_cache& spc, prerequisite& p)
+    {
+      tracer trace ("cxx::link::search_library");
+
+      // First check the cache.
+      //
+      if (p.target != nullptr)
+        return p.target;
+
+      bool l (p.is_a<lib> ());
+      const string* ext (l ? nullptr : p.ext); // Only for liba/libso.
+
+      // Then figure out what we need to search for.
+      //
+
+      // liba
+      //
+      path an;
+      const string* ae;
+
+      if (l || p.is_a<liba> ())
+      {
+        an = path ("lib" + p.name);
+
+        // Note that p.scope should be the same as the target's for
+        // which we are looking for this library. The idea here is
+        // that we have to use the same "extension configuration" as
+        // the target's.
+        //
+        ae = ext == nullptr
+          ? &liba::static_type.extension (p.key ().tk, p.scope)
+          : ext;
+
+        if (!ae->empty ())
+        {
+          an += '.';
+          an += *ae;
+        }
+      }
+
+      // libso
+      //
+      path sn;
+      const string* se;
+
+      if (l || p.is_a<libso> ())
+      {
+        sn = path ("lib" + p.name);
+        se = ext == nullptr
+          ? &libso::static_type.extension (p.key ().tk, p.scope)
+          : ext;
+
+        if (!se->empty ())
+        {
+          sn += '.';
+          sn += *se;
+        }
+      }
+
+      // Now search.
+      //
+      if (!spc)
+        spc = extract_library_paths (p.scope);
+
+      liba* a (nullptr);
+      libso* s (nullptr);
+
+      path f; // Reuse the buffer.
+      const dir_path* pd;
+      for (const dir_path& d: *spc)
+      {
+        timestamp mt;
+
+        // liba
+        //
+        if (!an.empty ())
+        {
+          f = d;
+          f /= an;
+
+          text << "trying " << f;
+
+          if ((mt = file_mtime (f)) != timestamp_nonexistent)
+          {
+            // Enter the target. Note that because the search paths are
+            // normalized, the result is automatically normalized as well.
+            //
+            a = &targets.insert<liba> (d, p.name, ae, trace);
+
+            if (a->path ().empty ())
+              a->path (move (f));
+
+            a->mtime (mt);
+          }
+        }
+
+        // libso
+        //
+        if (!sn.empty ())
+        {
+          f = d;
+          f /= sn;
+
+          text << "trying " << f;
+
+          if ((mt = file_mtime (f)) != timestamp_nonexistent)
+          {
+            s = &targets.insert<libso> (d, p.name, se, trace);
+
+            if (s->path ().empty ())
+              s->path (move (f));
+
+            s->mtime (mt);
+          }
+        }
+
+        if (a != nullptr || s != nullptr)
+        {
+          pd = &d;
+          break;
+        }
+      }
+
+      if (a == nullptr && s == nullptr)
+        return nullptr;
+
+      if (l)
+      {
+        // Enter the target group.
+        //
+        lib& l (targets.insert<lib> (*pd, p.name, p.ext, trace));
+
+        // It should automatically link-up to the members we have found.
+        //
+        assert (l.a == a);
+        assert (l.so == s);
+
+        // Set the bin.lib variable to indicate what's available.
+        //
+        const char* bl (a != nullptr
+                        ? (s != nullptr ? "both" : "static")
+                        : "shared");
+        l.assign ("bin.lib") = bl;
+
+        p.target = &l;
+      }
+      else
+        p.target = p.is_a<liba> () ? static_cast<target*> (a) : s;
+
+      return p.target;
+    }
+
+    match_result link::
+    match (action a, target& t, const string& hint) const
+    {
+      tracer trace ("cxx::link::match");
+
+      // @@ TODO:
+      //
+      // - check prerequisites: object files, libraries
+      // - if path already assigned, verify extension?
+      //
+      // @@ Q:
+      //
+      // - if there is no .o, are we going to check if the one derived
+      //   from target exist or can be built? A: No.
+      //   What if there is a library. Probably ok if .a, not if .so.
+      //   (i.e., a utility library).
+      //
+
+      bool so (t.is_a<libso> ());
+
+      // Scan prerequisites and see if we can work with what we've got.
+      //
+      bool seen_cxx (false), seen_c (false), seen_obj (false),
+        seen_lib (false);
+
+      for (prerequisite_member p: group_prerequisite_members (a, t))
+      {
+        if (p.is_a<cxx> ())
+        {
+          seen_cxx = seen_cxx || true;
+        }
+        else if (p.is_a<c> ())
+        {
+          seen_c = seen_c || true;
+        }
+        else if (p.is_a<obja> ())
+        {
+          if (so)
+            fail << "shared library " << t << " prerequisite " << p
+                 << " is static object";
+
+          seen_obj = seen_obj || true;
+        }
+        else if (p.is_a<objso> () ||
+                 p.is_a<obj> ())
+        {
+          seen_obj = seen_obj || true;
+        }
+        else if (p.is_a<liba> ()  ||
+                 p.is_a<libso> () ||
+                 p.is_a<lib> ())
+        {
+          seen_lib = seen_lib || true;
+        }
+        else if (p.is_a<h> ()   ||
+                 p.is_a<hxx> () ||
+                 p.is_a<ixx> () ||
+                 p.is_a<txx> () ||
+                 p.is_a<fsdir> ())
+          ;
+        else
+        {
+          level3 ([&]{trace << "unexpected prerequisite type " << p.type ();});
+          return nullptr;
+        }
+      }
+
+      // We will only chain a C source if there is also a C++ source or we
+      // were explicitly told to.
+      //
+      if (seen_c && !seen_cxx && hint < "cxx")
+      {
+        level3 ([&]{trace << "c prerequisite(s) without c++ or hint";});
+        return nullptr;
+      }
+
+      return seen_cxx || seen_c || seen_obj || seen_lib ? &t : nullptr;
+    }
+
+    recipe link::
+    apply (action a, target& xt, const match_result&) const
+    {
+      tracer trace ("cxx::link::apply");
+
+      path_target& t (static_cast<path_target&> (xt));
+
+      type lt (link_type (t));
+      bool so (lt == type::so);
+      optional<order> lo; // Link-order.
+
+      // Derive file name from target name.
+      //
+      if (t.path ().empty ())
+      {
+        switch (lt)
+        {
+        case type::e:  t.derive_path (""         ); break;
+        case type::a:  t.derive_path ("a",  "lib"); break;
+        case type::so: t.derive_path ("so", "lib"); break;
+        }
+      }
+
+      // Inject dependency on the output directory.
+      //
+      inject_parent_fsdir (a, t);
+
+      // We may need the project roots for rule chaining (see below).
+      // We will resolve them lazily only if needed.
+      //
+      scope* root (nullptr);
+      const dir_path* out_root (nullptr);
+      const dir_path* src_root (nullptr);
+
+      search_paths_cache lib_paths; // Extract lazily.
+
+      // Process prerequisites: do rule chaining for C and C++ source
+      // files as well as search and match.
+      //
+      // When cleaning, ignore prerequisites that are not in the same
+      // or a subdirectory of our strong amalgamation.
+      //
+      const dir_path* amlg (
+        a.operation () != clean_id
+        ? nullptr
+        : &t.strong_scope ().path ());
+
+      for (prerequisite_member p: group_prerequisite_members (a, t))
+      {
+        bool group (!p.prerequisite.belongs (t)); // Group's prerequisite.
+        target* pt (nullptr);
+
+        if (!p.is_a<c> () && !p.is_a<cxx> ())
+        {
+          // Handle imported libraries. Essentially, we want to replicate
+          // the -lfoo functionality but as part of our import support.
+          //
+          if (p.proj () != nullptr &&
+              (p.is_a<lib> () || p.is_a<liba> () || p.is_a<libso> ()))
+          {
+            pt = search_library (lib_paths, p.prerequisite);
+
+            // We only need this target if we are updating (remember, like
+            // -lfoo). The question is why search in the first place? The
+            // reason is the "not found" situation, in which someone else
+            // (i.e., the import phase 2) could resolve it to something
+            // that, who knows, might need cleaning, for example.
+            //
+            if (pt != nullptr && a.operation () != update_id)
+              continue; // Skip.
+          }
+
+          // The rest is the same basic logic as in search_and_match().
+          //
+          if (pt == nullptr) // Could've been resolved by search_library().
+            pt = &p.search ();
+
+          if (a.operation () == clean_id && !pt->dir.sub (*amlg))
+            continue; // Skip.
+
+          // If this is the obj{} or lib{} target group, then pick the
+          // appropriate member and make sure it is searched and matched.
+          //
+          if (obj* o = pt->is_a<obj> ())
+          {
+            pt = so ? static_cast<target*> (o->so) : o->a;
+
+            if (pt == nullptr)
+              pt = &search (so ? objso::static_type : obja::static_type,
+                            p.key ());
+          }
+          else if (lib* l = pt->is_a<lib> ())
+          {
+            // Determine the library type to link.
+            //
+            bool lso (true);
+            const string& at ((*l)["bin.lib"].as<const string&> ());
+
+            if (!lo)
+              lo = link_order (t);
+
+            switch (*lo)
+            {
+            case order::a:
+            case order::a_so:
+              lso = false; // Fall through.
+            case order::so:
+            case order::so_a:
+              {
+                if (lso ? at == "static" : at == "shared")
+                {
+                  if (*lo == order::a_so || *lo == order::so_a)
+                    lso = !lso;
+                  else
+                    fail << (lso ? "shared" : "static") << " build of " << *l
+                         << " is not available";
+                }
+              }
+            }
+
+            pt = lso ? static_cast<target*> (l->so) : l->a;
+
+            if (pt == nullptr)
+              pt = &search (lso ? libso::static_type : liba::static_type,
+                            p.key ());
+          }
+
+          build::match (a, *pt);
+          t.prerequisite_targets.push_back (pt);
+          continue;
+        }
+
+        if (root == nullptr)
+        {
+          // Which scope shall we use to resolve the root? Unlikely,
+          // but possible, the prerequisite is from a different project
+          // altogether. So we are going to use the target's project.
+          //
+          root = &t.root_scope ();
+          out_root = &root->path ();
+          src_root = &root->src_path ();
+        }
+
+        const prerequisite_key& cp (p.key ()); // c(xx){} prerequisite key.
+        const target_type& o_type (
+          group
+          ? obj::static_type
+          : (so ? objso::static_type : obja::static_type));
+
+        // Come up with the obj*{} target. The c(xx){} prerequisite
+        // directory can be relative (to the scope) or absolute. If it is
+        // relative, then use it as is. If it is absolute, then translate
+        // it to the corresponding directory under out_root. While the
+        // c(xx){} directory is most likely under src_root, it is also
+        // possible it is under out_root (e.g., generated source).
+        //
+        dir_path d;
+        {
+          const dir_path& cpd (*cp.tk.dir);
+
+          if (cpd.relative () || cpd.sub (*out_root))
+            d = cpd;
+          else
+          {
+            if (!cpd.sub (*src_root))
+              fail << "out of project prerequisite " << cp <<
+                info << "specify corresponding " << o_type.name << "{} "
+                   << "target explicitly";
+
+            d = *out_root / cpd.leaf (*src_root);
+          }
+        }
+
+        target& ot (search (o_type, d, *cp.tk.name, nullptr, cp.scope));
+
+        // If we are cleaning, check that this target is in the same or
+        // a subdirectory of our strong amalgamation.
+        //
+        if (a.operation () == clean_id && !ot.dir.sub (*amlg))
+        {
+          // If we shouldn't clean obj{}, then it is fair to assume
+          // we shouldn't clean cxx{} either (generated source will
+          // be in the same directory as obj{} and if not, well, go
+          // find yourself another build system ;-)).
+          //
+          continue; // Skip.
+        }
+
+        // If we have created the obj{} target group, pick one of its
+        // members; the rest would be primarily concerned with it.
+        //
+        if (group)
+        {
+          obj& o (static_cast<obj&> (ot));
+          pt = so ? static_cast<target*> (o.so) : o.a;
+
+          if (pt == nullptr)
+            pt = &search (so ? objso::static_type : obja::static_type,
+                          o.dir, o.name, o.ext, nullptr);
+        }
+        else
+          pt = &ot;
+
+        // If this obj*{} target already exists, then it needs to be
+        // "compatible" with what we are doing here.
+        //
+        // This gets a bit tricky. We need to make sure the source files
+        // are the same which we can only do by comparing the targets to
+        // which they resolve. But we cannot search the ot's prerequisites
+        // -- only the rule that matches can. Note, however, that if all
+        // this works out, then our next step is to match the obj*{}
+        // target. If things don't work out, then we fail, in which case
+        // searching and matching speculatively doesn't really hurt.
+        //
+        bool found (false);
+        for (prerequisite_member p1:
+               reverse_group_prerequisite_members (a, *pt))
+        {
+          // Ignore some known target types (fsdir, headers, libraries).
+          //
+          if (p1.is_a<fsdir> () ||
+              p1.is_a<h> ()     ||
+              (p.is_a<cxx> () && (p1.is_a<hxx> () ||
+                                  p1.is_a<ixx> () ||
+                                  p1.is_a<txx> ())) ||
+              p1.is_a<lib> ()  ||
+              p1.is_a<liba> () ||
+              p1.is_a<libso> ())
+          {
+            continue;
+          }
+
+          if (!p1.is_a<cxx> ())
+            fail << "synthesized target for prerequisite " << cp
+                 << " would be incompatible with existing target " << *pt <<
+              info << "unexpected existing prerequisite type " << p1 <<
+              info << "specify corresponding obj{} target explicitly";
+
+          if (!found)
+          {
+            build::match (a, *pt); // Now p1 should be resolved.
+
+            // Searching our own prerequisite is ok.
+            //
+            if (&p.search () != &p1.search ())
+              fail << "synthesized target for prerequisite " << cp << " would "
+                   << "be incompatible with existing target " << *pt <<
+                info << "existing prerequisite " << p1 << " does not match "
+                   << cp <<
+                info << "specify corresponding " << o_type.name << "{} target "
+                   << "explicitly";
+
+            found = true;
+            // Check the rest of the prerequisites.
+          }
+        }
+
+        if (!found)
+        {
+          // Note: add the source to the group, not the member.
+          //
+          ot.prerequisites.emplace_back (p.as_prerequisite (trace));
+
+          // Add our lib*{} prerequisites to the object file (see
+          // cxx.export.poptions above for details). Note: no need
+          // to go into group members.
+          //
+          // Initially, we were only adding imported libraries, but
+          // there is a problem with this approach: the non-imported
+          // library might depend on the imported one(s) which we will
+          // never "see" unless we start with this library.
+          //
+          for (prerequisite& p: group_prerequisites (t))
+          {
+            if (p.is_a<lib> () || p.is_a<liba> () || p.is_a<libso> ())
+              ot.prerequisites.emplace_back (p);
+          }
+
+          build::match (a, *pt);
+        }
+
+        t.prerequisite_targets.push_back (pt);
+      }
+
+      switch (a)
+      {
+      case perform_update_id: return &perform_update;
+      case perform_clean_id: return &perform_clean;
+      default: return default_recipe; // Forward to prerequisites.
+      }
+    }
+
+    target_state link::
+    perform_update (action a, target& xt)
+    {
+      path_target& t (static_cast<path_target&> (xt));
+
+      type lt (link_type (t));
+      bool so (lt == type::so);
+
+      if (!execute_prerequisites (a, t, t.mtime ()))
+        return target_state::unchanged;
+
+      // Translate paths to relative (to working directory) ones. This
+      // results in easier to read diagnostics.
+      //
+      path relt (relative (t.path ()));
+
+      scope& rs (t.root_scope ());
+      cstrings args;
+      string storage1;
+
+      if (lt == type::a)
+      {
+        //@@ ranlib
+        //
+        args.push_back ("ar");
+        args.push_back ("-rc");
+        args.push_back (relt.string ().c_str ());
+      }
+      else
+      {
+        args.push_back (rs["config.cxx"].as<const string&> ().c_str ());
+
+        append_options (args, t, "cxx.coptions");
+
+        append_std (args, t, storage1);
+
+        if (so)
+          args.push_back ("-shared");
+
+        args.push_back ("-o");
+        args.push_back (relt.string ().c_str ());
+
+        append_options (args, t, "cxx.loptions");
+      }
+
+      // Reserve enough space so that we don't reallocate. Reallocating
+      // means pointers to elements may no longer be valid.
+      //
+      paths relo;
+      relo.reserve (t.prerequisite_targets.size ());
+
+      for (target* pt: t.prerequisite_targets)
+      {
+        path_target* ppt;
+
+        if ((ppt = pt->is_a<obja> ()))
+          ;
+        else if ((ppt = pt->is_a<objso> ()))
+          ;
+        else if ((ppt = pt->is_a<liba> ()))
+          ;
+        else if ((ppt = pt->is_a<libso> ()))
+        {
+          // Use absolute path for the shared libraries since that's
+          // the path the runtime loader will use to try to find it.
+          // This is probably temporary until we get into the whole
+          // -soname/-rpath mess.
+          //
+          args.push_back (ppt->path ().string ().c_str ());
+          continue;
+        }
+        else
+          continue;
+
+        relo.push_back (relative (ppt->path ()));
+        args.push_back (relo.back ().string ().c_str ());
+      }
+
+      if (lt != type::a)
+        append_options (args, t, "cxx.libs");
+
+      args.push_back (nullptr);
+
+      if (verb)
+        print_process (args);
+      else
+        text << "ld " << t;
+
+      try
+      {
+        process pr (args.data ());
+
+        if (!pr.wait ())
+          throw failed ();
+
+        // Should we go to the filesystem and get the new mtime? We
+        // know the file has been modified, so instead just use the
+        // current clock time. It has the advantage of having the
+        // subseconds precision.
+        //
+        t.mtime (system_clock::now ());
+        return target_state::changed;
+      }
+      catch (const process_error& e)
+      {
+        error << "unable to execute " << args[0] << ": " << e.what ();
+
+        // In a multi-threaded program that fork()'ed but did not exec(),
+        // it is unwise to try to do any kind of cleanup (like unwinding
+        // the stack and running destructors).
+        //
+        if (e.child ())
+          exit (1);
+
+        throw failed ();
+      }
+    }
+  }
+}
diff --git a/build/cxx/module.cxx b/build/cxx/module.cxx
index ce7c968..3975ac5 100644
--- a/build/cxx/module.cxx
+++ b/build/cxx/module.cxx
@@ -14,8 +14,9 @@
 
 #include <build/bin/target>
 
-#include <build/cxx/rule>
 #include <build/cxx/target>
+#include <build/cxx/compile>
+#include <build/cxx/link>
 
 using namespace std;
 using namespace butl;
diff --git a/build/cxx/rule b/build/cxx/rule
deleted file mode 100644
index 2bd344d..0000000
--- a/build/cxx/rule
+++ /dev/null
@@ -1,60 +0,0 @@
-// file      : build/cxx/rule -*- C++ -*-
-// copyright : Copyright (c) 2014-2015 Code Synthesis Ltd
-// license   : MIT; see accompanying LICENSE file
-
-#ifndef BUILD_CXX_RULE
-#define BUILD_CXX_RULE
-
-#include <build/types>
-#include <build/rule>
-
-namespace build
-{
-  class scope;
-
-  namespace cxx
-  {
-    class cxx;
-
-    // @@ Can't we do match(obj&) and then registration code extracts
-    // that. And no virtuals?
-    //
-    class compile: public rule
-    {
-    public:
-      virtual match_result
-      match (action, target&, const std::string& hint) const;
-
-      virtual recipe
-      apply (action, target&, const match_result&) const;
-
-      static target_state
-      perform_update (action, target&);
-    };
-
-    class link: public rule
-    {
-    public:
-      virtual match_result
-      match (action, target&, const std::string& hint) const;
-
-      virtual recipe
-      apply (action, target&, const match_result&) const;
-
-      static target_state
-      perform_update (action, target&);
-
-    private:
-      enum class type {e, a, so};
-      enum class order {a, so, a_so, so_a};
-
-      static type
-      link_type (target&);
-
-      static order
-      link_order (target&);
-    };
-  }
-}
-
-#endif // BUILD_CXX_RULE
diff --git a/build/cxx/utility b/build/cxx/utility
new file mode 100644
index 0000000..53e80e1
--- /dev/null
+++ b/build/cxx/utility
@@ -0,0 +1,37 @@
+// file      : build/cxx/utility -*- C++ -*-
+// copyright : Copyright (c) 2014-2015 Code Synthesis Ltd
+// license   : MIT; see accompanying LICENSE file
+
+#ifndef BUILD_CXX_UTILITY
+#define BUILD_CXX_UTILITY
+
+#include <string>
+
+#include <build/types>
+#include <build/target>
+
+#include <build/config/utility>
+
+namespace build
+{
+  namespace cxx
+  {
+    using config::append_options;
+
+    // T is either target or scope.
+    //
+    template <typename T>
+    void
+    append_std (cstrings& args, T&, std::string& storage);
+
+    // Append library options from one of the cxx.export.* variables
+    // recursively, prerequisite libraries first.
+    //
+    void
+    append_lib_options (cstrings& args, target&, const char* variable);
+  }
+}
+
+#include <build/cxx/utility.txx>
+
+#endif // BUILD_CXX_UTILITY
diff --git a/build/cxx/utility.cxx b/build/cxx/utility.cxx
new file mode 100644
index 0000000..830ee76
--- /dev/null
+++ b/build/cxx/utility.cxx
@@ -0,0 +1,29 @@
+// file      : build/cxx/utility.cxx -*- C++ -*-
+// copyright : Copyright (c) 2014-2015 Code Synthesis Ltd
+// license   : MIT; see accompanying LICENSE file
+
+#include <build/cxx/utility>
+
+#include <build/bin/target>
+
+using namespace std;
+
+namespace build
+{
+  namespace cxx
+  {
+    void
+    append_lib_options (cstrings& args, target& l, const char* var)
+    {
+      using namespace bin;
+
+      for (target* t: l.prerequisite_targets)
+      {
+        if (t->is_a<lib> () || t->is_a<liba> () || t->is_a<libso> ())
+          append_lib_options (args, *t, var);
+      }
+
+      append_options (args, l, var);
+    }
+  }
+}
diff --git a/build/cxx/utility.txx b/build/cxx/utility.txx
new file mode 100644
index 0000000..7d9d686
--- /dev/null
+++ b/build/cxx/utility.txx
@@ -0,0 +1,35 @@
+// file      : build/cxx/utility.txx -*- C++ -*-
+// copyright : Copyright (c) 2014-2015 Code Synthesis Ltd
+// license   : MIT; see accompanying LICENSE file
+
+using namespace std;
+
+namespace build
+{
+  namespace cxx
+  {
+    template <typename T>
+    void
+    append_std (cstrings& args, T& t, std::string& s)
+    {
+      if (auto val = t["cxx.std"])
+      {
+        const std::string& v (val.template as<const string&> ());
+
+        // Translate 11 to 0x and 14 to 1y for compatibility with
+        // older versions of the compiler.
+        //
+        s = "-std=c++";
+
+        if (v == "11")
+          s += "0x";
+        else if (v == "14")
+          s += "1y";
+        else
+          s += v;
+
+        args.push_back (s.c_str ());
+      }
+    }
+  }
+}