Add support for forwarded configurations

18 files changed, 423 insertions, 161 deletions

diff --git a/bdep/bdep.cli b/bdep/bdep.cli
index 19c79af..d7ce274 100644
--- a/bdep/bdep.cli
+++ b/bdep/bdep.cli
@@ -217,7 +217,17 @@ namespace bdep
          -a} in the previous example), then it will print a line identifying
          each configuration before printing the command's result.
 
-         @@ build and run?
+         By default the project's source directory is configured to forward to
+         the default build configuration. That is, we can run the build system
+         in the source directory and it will automatically build in the
+         forwarded configuration as well as link the results back to the
+         source directory using symlinks or a another suitable mechanism (see
+         \l{bdep-config(1)} for details). For example:
+
+         \
+         $ b        # build in gcc
+         $ ./hello  # run the result
+         \
 
          |
 
@@ -272,6 +282,8 @@ namespace bdep
            libhello >= 1.0.0 configured 1.0.0
          \
 
+         @@ TODO: build system hook.
+
          |
 
      \li|\b{Upgrade or Downgrade Dependencies}\n
diff --git a/bdep/config.cli b/bdep/config.cli
index 62ef5da..c9b2ce8 100644
--- a/bdep/config.cli
+++ b/bdep/config.cli
@@ -24,13 +24,22 @@ namespace bdep
     // @@ Should we be able to remove config with init'ed packages? Who
     //    is going to drop them in configs? Or require them to be de-init'ed?
     //
+    // @@ Should set be able to alter forward flag? This will require both
+    //    disfiguring forward on old and configuring on new. Perhaps best
+    //    done by sync? I.e., for this change to take effect, one has to
+    //    run sync on both configs? Then sync would somehow need to know
+    //    to remove forwards. Maybe it should always check for stray
+    //    forwards (via out-root.build).
+    //
     "\h|SYNOPSIS|
 
      \c{\b{bdep config add} \ \ \ [<options>] [<prj-spec>] [\b{@}<cfg-name>] <cfg-dir>\n
         \b{bdep config create} [<options>] [<prj-spec>] [\b{@}<cfg-name>] <cfg-dir> [<cfg-args>]\n
         \b{bdep config remove} [<options>] [<prj-spec>] <cfg-spec>... | \b{--all}|\b{-a}\n
         \b{bdep config rename} [<options>] [<prj-spec>] <cfg-spec> <cfg-name>\n
-        \b{bdep config set} \ \ \ [<options>] [<prj-spec>] <cfg-spec> \b{--}[\b{no-}]\b{default}}
+        \b{bdep config set} \ \ \ [<options>] [<prj-spec>] <cfg-spec>\n
+        \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ [\b{--}[\b{no-}]\b{default}]\n
+        \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ [\b{--}[\b{no-}]\b{forward}]}
 
      \c{<cfg-spec> = \b{@}<cfg-name> | \b{--config}|\b{-c} <cfg-dir>\n
         <prj-spec> = \b{--directory}|\b{-d} <prj-dir>\n
@@ -72,7 +81,15 @@ namespace bdep
          \cb{bdep} commands use such a configuration by default if no
          configuration was specified explicitly (see
          \l{bdep-projects-configs(1)} for details). To make a subsequently
-         added configuration the default use the \cb{--default} option.|
+         added configuration the default use the \cb{--default} option.
+
+         The default build configuration is also designated as forwarded
+         unless the \cb{--no-forward} option is specified or another
+         configuration is already designated as forwarded. When a project is
+         initialized in a forwarded build configuration, its source directory
+         is configured to forward to this configuration (see \l{b(1)} for
+         details on forwarded configurations). To forward to a non-default
+         configuration use the \cb{--forward} option.|
 
      \li|\cb{remove}
 
@@ -89,8 +106,10 @@ namespace bdep
      \li|\cb{set}
 
          The \cb{set} subcommand sets various properties of the specified
-         build configuration. These include the default flag
-         (\c{\b{--}[\b{no-}]\b{default}}).||"
+         build configuration. These include the default
+         (\c{\b{--}[\b{no-}]\b{default}}) and forward
+         (\c{\b{--}[\b{no-}]\b{forward}}) flags. Note that changing the
+         forward flag requires an explicit \cb{sync} command to take effect.||"
 
     bool add;
     bool create;
@@ -102,18 +121,8 @@ namespace bdep
   // Note that not all project/configuration options are valid for all
   // subcommands.
   //
-  class cmd_config_options: project_options
+  class cmd_config_options: configuration_add_options, project_options
   {
     "\h|CONFIG OPTIONS|"
-
-    bool --default
-    {
-      "Make the added or created configuration the default."
-    }
-
-    bool --no-default
-    {
-      "Don't make the first added or created configuration then default."
-    }
   };
 }
diff --git a/bdep/config.cxx b/bdep/config.cxx
index 0acd227..0dcea48 100644
--- a/bdep/config.cxx
+++ b/bdep/config.cxx
@@ -18,6 +18,7 @@ namespace bdep
                   dir_path           path,
                   optional<string>   name,
                   optional<bool>     def,
+                  optional<bool>     fwd,
                   optional<uint64_t> id,
                   const char*        what)
   {
@@ -27,19 +28,32 @@ namespace bdep
     transaction t (db.begin ());
 
     using count = configuration_count;
-    using query = bdep::query<count>;
 
-    // By default the first added configuration is the default.
-    //
-    if (!def)
-      def = (db.query_value<count> () == 0);
-    else if (*def)
     {
       using query = bdep::query<configuration>;
 
-      if (auto p = db.query_one<configuration> (query::default_))
-        fail << "configuration " << *p << " is already the default" <<
-          info << "use 'bdep config set --no-default' to clear";
+      // By default the first added configuration is the default.
+      //
+      if (!def)
+        def = (db.query_value<count> () == 0);
+      else if (*def)
+      {
+        if (auto p = db.query_one<configuration> (query::default_))
+          fail << "configuration " << *p << " is already the default" <<
+            info << "use 'bdep config set --no-default' to clear";
+      }
+
+      // By default the default configuration is forwarded unless another
+      // is already forwarded.
+      //
+      if (!fwd)
+        fwd = *def && db.query_one<configuration> (query::forward) == nullptr;
+      else if (*fwd)
+      {
+        if (auto p = db.query_one<configuration> (query::forward))
+          fail << "configuration " << *p << " is already forwarded" <<
+            info << "use 'bdep config set --no-forward' to clear";
+      }
     }
 
     // Make sure the configuration path is absolute and normalized. Also
@@ -58,6 +72,7 @@ namespace bdep
         path,
         move (rel_path),
         *def,
+        *fwd,
         {} /* packages */});
 
     try
@@ -66,6 +81,8 @@ namespace bdep
     }
     catch (const odb::exception&)
     {
+      using query = bdep::query<count>;
+
       // See if this is id, name, or path conflict.
       //
       if (id && db.query_value<count> (query::id == *id) != 0)
@@ -94,6 +111,7 @@ namespace bdep
       if (r->name)     dr << '@' << *r->name << ' ';
       /*            */ dr << r->path << " (" << *r->id;
       if (r->default_) dr << ", default";
+      if (r->forward)  dr << ", forwarded";
       /*            */ dr << ')';
     }
 
@@ -114,6 +132,7 @@ namespace bdep
                      cli::scanner&         cfg_args,
                      optional<string>      name,
                      optional<bool>        def,
+                     optional<bool>        fwd,
                      optional<uint64_t>    id)
   {
     // Call bpkg to create the configuration.
@@ -131,6 +150,7 @@ namespace bdep
                            move (path),
                            move (name),
                            def,
+                           fwd,
                            id,
                            "created");
   }
@@ -159,6 +179,25 @@ namespace bdep
     fail << "@@ TODO" << endf;
   }
 
+  const char*
+  cmd_config_validate_add (const configuration_add_options& o)
+  {
+    // --[no-]default
+    //
+    if (o.default_ () && o.no_default ())
+      fail << "both --default and --no-default specified";
+
+    // --[no-]forward
+    //
+    if (o.forward () && o.no_forward ())
+      fail << "both --forward and --no-forward specified";
+
+    return (o.default_ ()   ? "--default"    :
+            o.forward ()    ? "--forward"    :
+            o.no_default () ? "--no-default" :
+            o.no_forward () ? "--no-forward" : nullptr);
+  }
+
   int
   cmd_config (const cmd_config_options& o, cli::scanner& scan)
   {
@@ -171,14 +210,7 @@ namespace bdep
 
     // Validate options/subcommands.
     //
-
-    // --[no-]default
-    //
-    if (o.default_ () && o.no_default ())
-      fail << "both --default and --no-default specified";
-
-    if (const char* n = (o.default_ ()   ? "--default"    :
-                         o.no_default () ? "--no-default" : nullptr))
+    if (const char* n = cmd_config_validate_add (o))
     {
       if (!(c.add () || c.create () || c.set ()))
         fail << n << " not valid for this command";
diff --git a/bdep/config.hxx b/bdep/config.hxx
index 2ebda45..b521bac 100644
--- a/bdep/config.hxx
+++ b/bdep/config.hxx
@@ -19,6 +19,7 @@ namespace bdep
                   dir_path           path,
                   optional<string>   name,
                   optional<bool>     default_ = nullopt,
+                  optional<bool>     forward  = nullopt,
                   optional<uint64_t> id = nullopt,
                   const char*        what = "added");
 
@@ -30,10 +31,16 @@ namespace bdep
                      cli::scanner&          args,
                      optional<string>       name,
                      optional<bool>         default_ = nullopt,
+                     optional<bool>         forward  = nullopt,
                      optional<uint64_t>     id = nullopt);
 
   int
   cmd_config (const cmd_config_options&, cli::scanner& args);
+
+  // Validate returning one of the options or NULL if none specified.
+  //
+  const char*
+  cmd_config_validate_add (const configuration_add_options&);
 }
 
 #endif // BDEP_CONFIG_HXX
diff --git a/bdep/init.cli b/bdep/init.cli
index c72e4c3..57b1abb 100644
--- a/bdep/init.cli
+++ b/bdep/init.cli
@@ -137,7 +137,7 @@ namespace bdep
      "
   }
 
-  class cmd_init_options: project_options
+  class cmd_init_options: configuration_add_options, project_options
   {
     "\h|INIT OPTIONS|"
 
@@ -157,19 +157,5 @@ namespace bdep
       "<dir>",
       "Create a new build configuration in <dir>."
     }
-
-    bool --default
-    {
-      "Make the added or created configuration the default. Only valid with
-       \cb{--config-add} or \cb{--config-create}, see \l{bdep-config(1)} for
-       details."
-    }
-
-    bool --no-default
-    {
-      "Don't make the first added or created configuration then default. Only
-       valid with \cb{--config-add} or \cb{--config-create}, see
-       \l{bdep-config(1)} for details."
-    }
   };
 }
diff --git a/bdep/init.cxx b/bdep/init.cxx
index 49a2de4..1875c42 100644
--- a/bdep/init.cxx
+++ b/bdep/init.cxx
@@ -24,7 +24,8 @@ namespace bdep
                    cli::scanner& args,
                    bool ca,
                    bool cc,
-                   optional<bool> cd)
+                   optional<bool> cd,
+                   optional<bool> cf)
   {
     const char* m (!ca ? "--config-create" :
                    !cc ? "--config-add"    : nullptr);
@@ -32,13 +33,13 @@ namespace bdep
     if (m == nullptr)
       fail << "both --config-add and --config-create specified";
 
-    optional<string> name;
+    optional<string> nm;
     if (size_t n = o.config_name ().size ())
     {
       if (n > 1)
         fail << "multiple configuration names specified for " << m;
 
-      name = o.config_name ()[0];
+      nm = o.config_name ()[0];
     }
 
     optional<uint64_t> id;
@@ -51,8 +52,8 @@ namespace bdep
     }
 
     return ca
-      ? cmd_config_add    (   prj, db, cfg,       move (name), cd, move (id))
-      : cmd_config_create (o, prj, db, cfg, args, move (name), cd, move (id));
+      ? cmd_config_add    (   prj, db, cfg,       move (nm), cd, cf, move (id))
+      : cmd_config_create (o, prj, db, cfg, args, move (nm), cd, cf, move (id));
   }
 
   void
@@ -128,24 +129,18 @@ namespace bdep
     bool ca (o.config_add_specified ());
     bool cc (o.config_create_specified ());
 
-    optional<bool> cd;
-    if (o.default_ () || o.no_default ())
-    {
-      if (!ca && !cc)
-        fail << "--[no-]default specified without --config-(add|create)";
-
-      if (o.default_ () && o.no_default ())
-        fail << "both --default and --no-default specified";
-
-      cd = o.default_ () && !o.no_default ();
-    }
-
     if (o.empty ())
     {
       if (ca) fail << "both --empty and --config-add specified";
       if (cc) fail << "both --empty and --config-create specified";
     }
 
+    if (const char* n = cmd_config_validate_add (o))
+    {
+      if (!ca && !cc)
+        fail << n << " specified without --config-(add|create)";
+    }
+
     project_packages pp (
       find_project_packages (o, o.empty () /* ignore_packages */));
 
@@ -186,6 +181,14 @@ namespace bdep
     configurations cfgs;
     if (ca || cc)
     {
+      optional<bool> cd;
+      if (o.default_ () || o.no_default ())
+        cd = o.default_ () && !o.no_default ();
+
+      optional<bool> cf;
+      if (o.forward () || o.no_forward ())
+        cf = o.forward ()  && !o.no_forward ();
+
       cfgs.push_back (
         cmd_init_config (
           o,
@@ -195,7 +198,8 @@ namespace bdep
           args,
           ca,
           cc,
-          cd));
+          cd,
+          cf));
 
       // Fall through.
     }
diff --git a/bdep/init.hxx b/bdep/init.hxx
index 7905306..6e52737 100644
--- a/bdep/init.hxx
+++ b/bdep/init.hxx
@@ -23,7 +23,8 @@ namespace bdep
                    cli::scanner& cfg_args,
                    bool config_add_specified,
                    bool config_create_specified,
-                   optional<bool> config_default);
+                   optional<bool> config_default,
+                   optional<bool> config_forward);
 
   // Initialize each package in each configuration skipping those that are
   // already initialized. Then synchronize each configuration.
diff --git a/bdep/new.cli b/bdep/new.cli
index 377dbec..f5f2a14 100644
--- a/bdep/new.cli
+++ b/bdep/new.cli
@@ -145,7 +145,7 @@ namespace bdep
   {
   };
 
-  class cmd_new_options: configuration_name_options
+  class cmd_new_options: configuration_add_options, configuration_name_options
   {
     "\h|NEW OPTIONS|"
 
@@ -189,19 +189,5 @@ namespace bdep
        \cb{git} (default) and \cb{none}. Valid values for <opt> are
        system-specific."
     }
-
-    bool --default
-    {
-      "Make the added or created configuration the default. Only valid with
-       \cb{--config-add} or \cb{--config-create}, see \l{bdep-config(1)} for
-       details."
-    }
-
-    bool --no-default
-    {
-      "Don't make the first added or created configuration then default. Only
-       valid with \cb{--config-add} or \cb{--config-create}, see
-       \l{bdep-config(1)} for details."
-    }
   };
 }
diff --git a/bdep/new.cxx b/bdep/new.cxx
index 97c8352..5f99e6c 100644
--- a/bdep/new.cxx
+++ b/bdep/new.cxx
@@ -9,6 +9,7 @@
 #include <bdep/diagnostics.hxx>
 
 #include <bdep/init.hxx>
+#include <bdep/config.hxx>
 
 using namespace std;
 
@@ -26,24 +27,18 @@ namespace bdep
     bool ca (o.config_add_specified ());
     bool cc (o.config_create_specified ());
 
-    optional<bool> cd;
-    if (o.default_ () || o.no_default ())
-    {
-      if (!ca && !cc)
-        fail << "--[no-]default specified without --config-(add|create)";
-
-      if (o.default_ () && o.no_default ())
-        fail << "both --default and --no-default specified";
-
-      cd = o.default_ () && !o.no_default ();
-    }
-
     if (o.no_init ())
     {
       if (ca) fail << "both --no-init and --config-add specified";
       if (cc) fail << "both --no-init and --config-create specified";
     }
 
+    if (const char* n = cmd_config_validate_add (o))
+    {
+      if (!ca && !cc)
+        fail << n << " specified without --config-(add|create)";
+    }
+
     // Validate type options.
     //
     const type& t (o.type ());
@@ -621,6 +616,14 @@ namespace bdep
 
     if (ca || cc)
     {
+      optional<bool> cd;
+      if (o.default_ () || o.no_default ())
+        cd = o.default_ () && !o.no_default ();
+
+      optional<bool> cf;
+      if (o.forward () || o.no_forward ())
+        cf = o.forward ()  && !o.no_forward ();
+
       configurations cfgs {
         cmd_init_config (
           o,
@@ -630,7 +633,8 @@ namespace bdep
           args,
           ca,
           cc,
-          cd)};
+          cd,
+          cf)};
 
       package_locations pkgs {{n, dir_path ()}}; // project == package
 
diff --git a/bdep/project.cli b/bdep/project.cli
index 15faea8..137c77d 100644
--- a/bdep/project.cli
+++ b/bdep/project.cli
@@ -8,6 +8,31 @@ include <bdep/common.cli>;
 
 namespace bdep
 {
+  // Common options for commands that add/create configurations.
+  //
+  class configuration_add_options
+  {
+    bool --default
+    {
+      "Make the added or created configuration the default."
+    }
+
+    bool --no-default
+    {
+      "Don't make the first added or created configuration then default."
+    }
+
+    bool --forward
+    {
+      "Make the added or created configuration forwarded."
+    }
+
+    bool --no-forward
+    {
+      "Don't make the added or created configuration forwarded."
+    }
+  };
+
   // Common options for commands that accept --config-id and @<cfg-name>.
   //
   class configuration_name_options: common_options
diff --git a/bdep/project.cxx b/bdep/project.cxx
index 6b5ee30..8d922b6 100644
--- a/bdep/project.cxx
+++ b/bdep/project.cxx
@@ -110,7 +110,7 @@ namespace bdep
     return r;
   }
 
-  // Given a directory which can a project root, a package root, or one of
+  // Given a directory which can be a project root, a package root, or one of
   // their subdirectories, return the absolute project (first) and relative
   // package (second) directories. The package directory may be absent if the
   // given directory is not within a package root or empty if the project and
@@ -186,6 +186,69 @@ namespace bdep
     return project_package {move (prj), move (pkg)};
   }
 
+  static package_locations
+  load_package_locations (const dir_path& prj)
+  {
+    package_locations pls;
+
+    // If exists, load packages.manifest from the project root. Otherwise,
+    // this must be a simple, single-package project.
+    //
+    path f (prj / packages_file);
+
+    if (exists (f))
+    {
+      using bpkg::package_manifest;
+      using bpkg::dir_package_manifests;
+
+      auto ms (parse_manifest<dir_package_manifests> (f, "packages"));
+
+      // While an empty repository is legal, in our case it doesn't make much
+      // sense and will just further complicate things.
+      //
+      if (ms.empty ())
+        fail << "no packages listed in " << f;
+
+      for (package_manifest& m: ms)
+      {
+        // Convert the package location from POSIX to the host form and make
+        // sure the current directory is represented as an empty path.
+        //
+        assert (m.location);
+        dir_path d (path_cast<dir_path> (move (*m.location)));
+        d.normalize (false /* actualize */, true /* cur_empty */);
+
+        pls.push_back (package_location {string (), move (d)});
+      }
+    }
+    else
+      pls.push_back (package_location {string (), dir_path ()});
+
+    return pls;
+  }
+
+  static void
+  load_package_names (const dir_path& prj, package_locations& pls)
+  {
+    // Load each package's manifest and obtain its name (name is normally the
+    // first value so we could optimize this, if necessary).
+    //
+    for (package_location& pl: pls)
+    {
+      path f (prj / pl.path / manifest_file);
+      auto m (parse_manifest<bpkg::package_manifest> (f, "package"));
+      pl.name = move (m.name);
+    }
+  }
+
+  package_locations
+  load_packages (const dir_path& prj)
+  {
+    package_locations pls (load_package_locations (prj));
+    load_package_names (prj, pls);
+    return pls;
+  }
+
   project_packages
   find_project_packages (const project_options& po,
                          bool ignore_packages,
@@ -246,82 +309,37 @@ namespace bdep
 
     if (!ignore_packages)
     {
-      // If exists, load packages.manifest from the project root and either
-      // verify that the discovered packages are in it or, if nothing was
-      // discovered, use it as the source for the package list.
+      // Load the package locations and either verify that the discovered
+      // packages are in it or, if nothing was discovered, use it as the
+      // source for the package list.
       //
-      path f (r.project / packages_file);
+      package_locations pls (load_package_locations (r.project));
 
-      if (exists (f))
+      if (!r.packages.empty ())
       {
-        using bpkg::package_manifest;
-        using bpkg::dir_package_manifests;
-
-        auto ms (parse_manifest<dir_package_manifests> (f, "packages"));
-
-        // While an empty repository is legal, in our case it doesn't make
-        // much sense and will just further complicate things.
-        //
-        if (ms.empty ())
-          fail << "no packages listed in " << f;
-
-        // Convert the package location from POSIX to the host form and make
-        // sure the current directory is represented as an empty path.
-        //
-        auto location = [] (const package_manifest& m)
+        for (const package_location& x: r.packages)
         {
-          assert (m.location);
-          dir_path d (path_cast<dir_path> (*m.location));
-          d.normalize (false /* actualize */, true /* cur_empty */);
-          return d;
-        };
-
-        if (!r.packages.empty ())
-        {
-          // It could be costly to normalize the location for each
-          // comparison. We, however, do not expect more than a handful of
-          // packages so we are probably ok.
-          //
-          for (const package_location& pl: r.packages)
+          if (find_if (pls.begin (),
+                       pls.end (),
+                       [&x] (const package_location& y)
+                       {
+                         return x.path == y.path;
+                       }) == pls.end ())
           {
-            const dir_path& p (pl.path);
-
-            if (find_if (ms.begin (),
-                         ms.end (),
-                         [&p, &location] (const package_manifest& m)
-                         {
-                           return p == location (m);
-                         }) == ms.end ())
-            {
-              fail << "package directory " << p << " is not listed in " << f;
-            }
+            fail << "package directory " << x.path << " is not listed in "
+                 << r.project;
           }
         }
-        else if (load_packages)
-        {
-          // Name is to be extracted later.
-          //
-          for (package_manifest& m: ms)
-            r.packages.push_back (package_location {"", location (m)});
-        }
       }
-      else
+      else if (load_packages)
       {
-        // If packages.manifest does not exist, then this must be a simple
-        // project.
+        // Names to be extracted later.
         //
-        assert (r.packages.size () == 1 && r.packages[0].path.empty ());
+        r.packages = move (pls);
       }
 
-      // Load each package's manifest and obtain its name (name is normally
-      // the first value so we could optimize this, if necessary).
-      //
-      for (package_location& pl: r.packages)
-      {
-        path f (r.project / pl.path / manifest_file);
-        auto m (parse_manifest<bpkg::package_manifest> (f, "package"));
-        pl.name = move (m.name);
-      }
+      if (!r.packages.empty ())
+        load_package_names (r.project, r.packages);
     }
 
     return r;
diff --git a/bdep/project.hxx b/bdep/project.hxx
index 2b1894c..2e8d366 100644
--- a/bdep/project.hxx
+++ b/bdep/project.hxx
@@ -78,6 +78,7 @@ namespace bdep
     optional_dir_path  relative_path;
 
     bool default_;
+    bool forward;
 
     // We made it a vector instead of set/map since we are unlikely to have
     // more than a handful of packages. We may, however, want to use a change-
@@ -162,6 +163,9 @@ namespace bdep
 
   using package_locations = vector<package_location>;
 
+  package_locations
+  load_packages (const dir_path& prj);
+
   struct project_packages
   {
     dir_path          project;
diff --git a/bdep/project.xml b/bdep/project.xml
index 5685945..8d1bf26 100644
--- a/bdep/project.xml
+++ b/bdep/project.xml
@@ -6,6 +6,7 @@
       <column name="path" type="TEXT" null="true"/>
       <column name="relative_path" type="TEXT" null="true"/>
       <column name="default" type="INTEGER" null="true"/>
+      <column name="forward" type="INTEGER" null="true"/>
       <primary-key auto="true">
         <column name="id"/>
       </primary-key>
diff --git a/bdep/sync.cxx b/bdep/sync.cxx
index 370e4f4..6c29a50 100644
--- a/bdep/sync.cxx
+++ b/bdep/sync.cxx
@@ -70,7 +70,7 @@ namespace bdep
                      }) != prj_pkgs.end ())
         {
           // The project package itself must always be upgraded to the latest
-          // version/iteration. So we have to translate our option to their
+          // version/iteration. So we have to translate our options to their
           // dependency-only --{upgrade,patch}-{recursive,immediate}.
           //
           args.push_back ("{");
@@ -119,6 +119,82 @@ namespace bdep
               "--plan", "synchronizing:",
               (yes ? "--yes" : nullptr),
               args);
+
+
+    // Handle configuration forwarding.
+    //
+    // We do it here (instead of, say init) because a change in a package may
+    // introduce new subprojects. Though it would be nice to only do this if
+    // the package was upgraded (probably by comparing before/after versions
+    // @@ TODO: changed flag below).
+    //
+    // Also, the current thinking is that config set --[no-]forward is best
+    // implemented by just changing the flag on the configuration and then
+    // requiring an explicit sync to configure/disfigure forwards.
+    //
+    // @@ TODO: could optimize out version query/comparison if pkg-build
+    //    signalled that nothing has changed (the --exit-result idea). Would
+    //    be nice to optimize the whole thing. Maybe --force flag (for things
+    //    like config set --no-forward)? Or maybe we should require explicit
+    //    sync for certain changes (and pass --implicit or some such in hook
+    //    -- after all, configuring forward of a project being bootstrapped
+    //    might get tricky).
+    //
+    package_locations pls (load_packages (prj));
+
+    for (const package_state& p: c->packages)
+    {
+      // If this is a forwarded configuration, make sure forwarding is
+      // configured and is up-to-date. Otherwise, make sure it is disfigured
+      // (the config set --no-forward case).
+      //
+      dir_path src (prj);
+      {
+        auto i (find_if (pls.begin (),
+                         pls.end (),
+                         [&p] (const package_location& pl)
+                         {
+                           return p.name == pl.name;
+                         }));
+
+        if (i == pls.end ())
+          fail << "package " << p.name << " is not listed in " << prj;
+
+        src /= i->path;
+      }
+
+      // We could run 'b info' and used the 'forwarded' value but this is
+      // both faster and simpler.
+      //
+      path f (src / "build" / "bootstrap" / "out-root.build");
+      bool e (exists (f));
+
+      const char* o (nullptr);
+      if (c->forward)
+      {
+        bool changed (true);
+
+        if (changed || !e)
+          o = "configure:";
+      }
+      else
+      {
+        //@@ This is broken: we will disfigure forwards to other configs.
+        //   Looks like we will need to test that the forward is to this
+        //   config. 'b info' here we come?
+
+        //if (e)
+        //  o = "disfigure:";
+      }
+
+      if (o != nullptr)
+      {
+        dir_path out (dir_path (c->path) /= p.name);
+        string arg (src.representation () + '@' + out.representation () +
+                    ",forward");
+        run_b (co, o, arg);
+      }
+    }
   }
 
   void
diff --git a/bdep/utility.cxx b/bdep/utility.cxx
index f8ef1df..a902273 100644
--- a/bdep/utility.cxx
+++ b/bdep/utility.cxx
@@ -107,4 +107,12 @@ namespace bdep
       ? co.bpkg ().string ().c_str ()
       : "bpkg" BDEP_EXE_SUFFIX;
   }
+
+  const char*
+  name_b (const common_options& co)
+  {
+    return co.build_specified ()
+      ? co.build ().string ().c_str ()
+      : "b" BDEP_EXE_SUFFIX;
+  }
 }
diff --git a/bdep/utility.hxx b/bdep/utility.hxx
index 4831bab..31cd0cb 100644
--- a/bdep/utility.hxx
+++ b/bdep/utility.hxx
@@ -114,6 +114,19 @@ namespace bdep
   void
   run_bpkg (const common_options&, A&&... args);
 
+  // Run the b process.
+  //
+  const char*
+  name_b (const common_options&);
+
+  template <typename O, typename E, typename... A>
+  process
+  start_b (const common_options&, O&& out, E&& err, A&&... args);
+
+  template <typename... A>
+  void
+  run_b (const common_options&, A&&... args);
+
   // Manifest parsing and serialization.
   //
   // For parsing, if path is '-', then read from stdin.
diff --git a/bdep/utility.txx b/bdep/utility.txx
index 2d6de1d..aa75952 100644
--- a/bdep/utility.txx
+++ b/bdep/utility.txx
@@ -144,6 +144,81 @@ namespace bdep
     }
   }
 
+  // *_b()
+  //
+  template <typename O, typename E, typename... A>
+  process
+  start_b (const common_options& co,
+              O&& out,
+              E&& err,
+              A&&... args)
+  {
+    const char* b (name_b (co));
+
+    try
+    {
+      process_path pp (process::path_search (b, exec_dir));
+
+      small_vector<const char*, 1> ops;
+
+      // Map verbosity level. If we are running quiet or at level 1, then run
+      // b quiet. Otherwise, run it at the same level as us.
+      //
+      bool quiet (true); // Maybe will become an argument one day.
+
+      string vl;
+      switch (verb)
+      {
+      case  0:            ops.push_back ("-q"); break;
+      case  1: if (quiet) ops.push_back ("-q"); break;
+      case  2:            ops.push_back ("-v"); break;
+      default:
+        {
+          vl = to_string (verb);
+          ops.push_back ("--verbose");
+          ops.push_back (vl.c_str ());
+        }
+      }
+
+      return process_start_callback (
+        [] (const char* const args[], size_t n)
+        {
+          if (verb >= 2)
+            print_process (args, n);
+        },
+        0 /* stdin */,
+        forward<O> (out),
+        forward<E> (err),
+        pp,
+        ops,
+        co.build_option (),
+        forward<A> (args)...);
+    }
+    catch (const process_error& e)
+    {
+      fail << "unable to execute " << b << ": " << e << endf;
+    }
+  }
+
+  template <typename... A>
+  void
+  run_b (const common_options& co, A&&... args)
+  {
+    process pr (start_b (co,
+                         1 /* stdout */,
+                         2 /* stderr */,
+                         forward<A> (args)...));
+    if (!pr.wait ())
+    {
+      const process_exit& e (*pr.exit);
+
+      if (e.normal ())
+        throw failed (); // Assume the child issued diagnostics.
+
+      fail << "process " << name_b (co) << " " << e;
+    }
+  }
+
   // *_manifest()
   //
   template <typename T>
diff --git a/doc/cli.sh b/doc/cli.sh
index fb19aa2..e51aacf 100755
--- a/doc/cli.sh
+++ b/doc/cli.sh
@@ -39,6 +39,7 @@ function compile ()
   cli -I .. -v project="bdep" -v version="$version" -v date="$date" \
 --include-base-last "${o[@]}" --generate-html --html-prologue-file \
 man-prologue.xhtml --html-epilogue-file man-epilogue.xhtml --html-suffix .xhtml \
+--link-regex '%b([-.].+)%../../build2/doc/b$1%' \
 --link-regex '%bpkg([-.].+)%../../bpkg/doc/bpkg$1%' \
 --link-regex '%bpkg(#.+)?%../../bpkg/doc/build2-package-manager-manual.xhtml$1%' \
 --link-regex '%bdep(#.+)?%build2-project-manager-manual.xhtml$1%' \