Add support for configuration type and bdep-config-link sub-command

35 files changed, 980 insertions, 381 deletions

diff --git a/bdep/build.txx b/bdep/build.txx
index 0090be5..7d17088 100644
--- a/bdep/build.txx
+++ b/bdep/build.txx
@@ -44,56 +44,72 @@ namespace bdep
 
     const dir_path& prj (pp.project);
 
-    // Load the configurations without keeping the database open longer
-    // than necessary.
+    // Load the configurations without keeping the database open longer than
+    // necessary.
     //
     configurations cfgs;
     {
       database db (open (prj, trace));
 
       transaction t (db.begin ());
-      cfgs = find_configurations (o, prj, t);
+      pair<configurations, bool> cs (find_configurations (o, prj, t));
       t.commit ();
-    }
 
-    // If specified, verify packages are present in each configuration.
-    //
-    if (!pp.packages.empty ())
-      verify_project_packages (pp, cfgs);
+      // If specified, verify packages are present in at least one
+      // configuration.
+      //
+      if (!pp.packages.empty ())
+        verify_project_packages (pp, cs);
+
+      cfgs = move (cs.first);
+    }
 
     // If no packages were explicitly specified, then we build all that have
-    // been initialized in each configuration.
+    // been initialized in each configuration. Otherwise, we build only
+    // specified packages initialized in the (specified) configurations.
     //
-    cstrings pkgs;
+    const package_locations& pkgs (pp.packages);
 
-    bool all (pp.packages.empty ());
-    if (!all)
-    {
-      for (const package_location& p: pp.packages)
-        pkgs.push_back (p.name.string ().c_str ());
-    }
+    bool all (pkgs.empty ());
 
-    // Build in each configuration skipping empty ones.
+    // Build in each configuration, skipping those where no packages needs to
+    // be built.
     //
     bool first (true);
     for (const shared_ptr<configuration>& c: cfgs)
     {
-      if (c->packages.empty ())
-      {
-        if (verb)
-          info << "skipping empty configuration " << *c;
+      // Collect packages to build.
+      //
+      cstrings ps;
 
-        continue;
+      for (const package_state& s: c->packages)
+      {
+        if (all ||
+            find_if (pkgs.begin (),
+                     pkgs.end (),
+                     [&s] (const package_location& p)
+                     {
+                       return p.name == s.name;
+                     }) != pkgs.end ())
+          ps.push_back (s.name.string ().c_str ());
       }
 
-      // Collect packages.
-      //
-      if (all)
+      if (ps.empty ())
       {
-        pkgs.clear ();
+        if (verb)
+        {
+          diag_record dr (info);
+
+          dr << "skipping configuration " << *c;
 
-        for (const package_state& p: c->packages)
-          pkgs.push_back (p.name.string ().c_str ());
+          if (c->packages.empty ())
+            dr << info << "configuration is empty";
+          else
+            dr << info << "none of specified packages initialized in this "
+                       << "configuration";
+        }
+
+        continue;
       }
 
       // If we are printing multiple configurations, separate them with a
@@ -107,12 +123,12 @@ namespace bdep
         first = false;
       }
 
-      // Pre-sync the configuration to avoid triggering the build system
-      // hook (see sync for details).
+      // Pre-sync the configuration to avoid triggering the build system hook
+      // (see sync for details).
       //
       cmd_sync (o, prj, c, strings () /* pkg_args */, true /* implicit */);
 
-      build (o, c, pkgs, cfg_vars);
+      build (o, c, ps, cfg_vars);
     }
 
     return 0;
diff --git a/bdep/ci.cli b/bdep/ci.cli
index 08d65cc..5f955ea 100644
--- a/bdep/ci.cli
+++ b/bdep/ci.cli
@@ -20,9 +20,9 @@ namespace bdep
 
      \c{\b{bdep ci} [<options>] [<cfg-spec>] [<pkg-spec>]}
 
-     \c{<pkg-spec> = (\b{--directory}|\b{-d} <pkg-dir>)... | <prj-spec>\n
-        <prj-spec> = \b{--directory}|\b{-d} <prj-dir>\n
-        <cfg-spec> = \b{@}<cfg-name> | \b{--config}|\b{-c} <cfg-dir>}
+     \c{<cfg-spec> = (\b{@}<cfg-name> | \b{--config}|\b{-c} <cfg-dir>)... | \b{--all}|\b{-a}\n
+        <pkg-spec> = (\b{--directory}|\b{-d} <pkg-dir>)... | <prj-spec>\n
+        <prj-spec> = \b{--directory}|\b{-d} <prj-dir>}
 
      \h|DESCRIPTION|
 
@@ -31,10 +31,10 @@ namespace bdep
 
      If no project or package directory is specified, then the current working
      directory is assumed. If no configuration is specified, then the default
-     configuration is used. If the specified directory is a project directory,
-     then all the packages initialized in the configuration are submitted. See
-     \l{bdep-projects-configs(1)} for details on specifying projects and
-     configurations.
+     configurations are used. If the specified directory is a project
+     directory, then all the packages initialized in the configurations are
+     submitted. See \l{bdep-projects-configs(1)} for details on specifying
+     projects and configurations.
 
      A CI request consists of the specified packages and their versions as
      well as the project's remote version control repository URL corresponding
diff --git a/bdep/ci.cxx b/bdep/ci.cxx
index 3b59a30..a4acd94 100644
--- a/bdep/ci.cxx
+++ b/bdep/ci.cxx
@@ -249,10 +249,10 @@ namespace bdep
 
     // If we are submitting the entire project, then we have two choices: we
     // can list all the packages in the project or we can only do so for
-    // packages that were initialized in the (specified) configuration(s?).
+    // packages that were initialized in the specified configurations.
     //
     // Note that other than getting the list of packages, we would only need
-    // the configuration to obtain their versions. Since we can only have one
+    // the configurations to obtain their versions. Since we can only have one
     // version for each package this is not strictly necessary but is sure a
     // good sanity check against local/remote mismatches. Also, it would be
     // nice to print the versions we are submitting in the prompt.
@@ -262,10 +262,14 @@ namespace bdep
     // has configurations for subsets of packages or some such. And in the
     // future, who knows, we could have multi-project CI.
     //
-    // So, let's go with the configuration. Specifically, if packages were
+    // So, let's go with the configurations. Specifically, if packages were
     // explicitly specified, we verify they are initialized. Otherwise, we use
-    // the list of packages that are initialized in a configuration (single
-    // for now).
+    // the list of packages that are initialized in configurations. In both
+    // cases we also verify that for each package only one configuration, it
+    // is initialized in, is specified (while we currently don't need this
+    // restriction, this may change in the future if we decide to support
+    // archive-based CI or some such).
+    //
     //
     // Note also that no pre-sync is needed since we are only getting versions
     // (via the info meta-operation).
@@ -277,51 +281,87 @@ namespace bdep
 
     const dir_path& prj (pp.project);
 
-    shared_ptr<configuration> cfg;
+    configurations cfgs;
     {
       // Don't keep the database open longer than necessary.
       //
       database db (open (prj, trace));
 
       transaction t (db.begin ());
-      configurations cfgs (find_configurations (o, prj, t));
+      cfgs = find_configurations (o, prj, t).first;
       t.commit ();
-
-      if (cfgs.size () > 1)
-        fail << "multiple configurations specified for ci";
-
-      // If specified, verify packages are present in the configuration.
-      //
-      if (!pp.packages.empty ())
-        verify_project_packages (pp, cfgs);
-
-      cfg = move (cfgs[0]);
     }
 
-    // Collect package names and their versions.
+    // Collect package names, versions, and configurations used.
     //
     struct package
     {
-      package_name     name;
-      standard_version version;
+      package_name              name;
+      standard_version          version;
+      shared_ptr<configuration> config;
     };
     vector<package> pkgs;
 
-    auto add_package = [&o, &cfg, &pkgs] (package_name n)
+    // Add a package to the list, suppressing duplicates and verifying that it
+    // is initialized in only one configuration.
+    //
+    auto add_package = [&o, &pkgs] (package_name n,
+                                    shared_ptr<configuration> c)
     {
-      standard_version v (package_version (o, cfg->path, n));
-      pkgs.push_back (package {move (n), move (v)});
+      auto i (find_if (pkgs.begin (),
+                       pkgs.end (),
+                       [&n] (const package& p) {return p.name == n;}));
+
+      if (i != pkgs.end ())
+      {
+        if (i->config == c)
+          return;
+
+        fail << "package " << n << " is initialized in multiple specified "
+             << "configurations" <<
+          info << *i->config <<
+          info << *c;
+      }
+
+      standard_version v (package_version (o, c->path, n));
+      pkgs.push_back (package {move (n), move (v), move (c)});
     };
 
     if (pp.packages.empty ())
     {
-      for (const package_state& p: cfg->packages)
-        add_package (p.name);
+      for (const shared_ptr<configuration>& c: cfgs)
+      {
+        for (const package_state& p: c->packages)
+          add_package (p.name, c);
+      }
     }
     else
     {
       for (package_location& p: pp.packages)
-        add_package (p.name);
+      {
+        bool init (false);
+
+        for (const shared_ptr<configuration>& c: cfgs)
+        {
+          if (find_if (c->packages.begin (),
+                       c->packages.end (),
+                       [&p] (const package_state& s)
+                       {
+                         return p.name == s.name;
+                       }) != c->packages.end ())
+          {
+            // Add the package, but continue the loop to detect a potential
+            // configuration ambiguity.
+            //
+            add_package (p.name, c);
+            init = true;
+          }
+        }
+
+        if (!init)
+          fail << "package " << p.name << " is not initialized in any "
+               << "configuration";
+      }
     }
 
     // Extract the interactive mode configuration and breakpoint from the
diff --git a/bdep/clean.cli b/bdep/clean.cli
index 141d20a..6a2e140 100644
--- a/bdep/clean.cli
+++ b/bdep/clean.cli
@@ -41,9 +41,9 @@ namespace bdep
 
      If no project or package directory is specified, then the current working
      directory is assumed. If no configuration is specified, then the default
-     configuration is assumed. See \l{bdep-projects-configs(1)} for details on
-     specifying projects and configurations. Optional \c{\i{cfg-var}...} are
-     the additional configuration variables to pass to the build system.
+     configurations are assumed. See \l{bdep-projects-configs(1)} for details
+     on specifying projects and configurations. Optional \c{\i{cfg-var}...}
+     are the additional configuration variables to pass to the build system.
      "
   }
 
diff --git a/bdep/config.cli b/bdep/config.cli
index 6d26432..a1cdba2 100644
--- a/bdep/config.cli
+++ b/bdep/config.cli
@@ -19,6 +19,7 @@ namespace bdep
 
      \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 link} \ \ [<options>] [<prj-spec>] <cfg-spec> <cfg-spec>\n
         \b{bdep config list} \ \ [<options>] [<prj-spec>] [<cfg-spec>...]\n
         \b{bdep config move} \ \ [<options>] [<prj-spec>] <cfg-spec> <cfg-dir>\n
         \b{bdep config rename} [<options>] [<prj-spec>] <cfg-spec> <cfg-name>\n
@@ -77,23 +78,31 @@ namespace bdep
          $ bdep config create -- @gcc cc config.cxx=g++  # ../hello-gcc
          \
 
+         A configuration also has a type that is specified with the
+         \cb{--config-type} option. If the type is not specified explicitly,
+         then \cb{target} is assumed. See \l{bpkg-cfg-create(1)} for
+         background on configuration types.
+
          Unless the \cb{--no-default} option is specified, the first added or
-         created build configuration is designated as the default. Several
-         \cb{bdep} commands use such a configuration by default if no
-         configuration was specified explicitly (see
+         created build configuration of each type is designated as the
+         default. Several \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.
-
-         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 designate a non-default
-         configuration as forwarded use the \cb{--forward} option. Note also
-         that it is possible to have multiple forwarded configurations,
-         however, any given package within a project can only be initialized
-         in one such configuration.
+         added configuration the default use the \cb{--default} option. Note
+         also that in case of multiple default configurations any given
+         package within a project can only be initialized in one such
+         configuration.
+
+         The default build configuration of each type is also designated as
+         forwarded unless the \cb{--no-forward} option is specified or another
+         configuration of this type 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 designate a
+         non-default configuration as forwarded use the \cb{--forward}
+         option. Note also that it is possible to have multiple forwarded
+         configurations, however, any given package within a project can only
+         be initialized in one such configuration.
 
          Unless the \cb{--no-auto-sync} option is specified, an added or
          created build configuration will be automatically synchronized on
@@ -102,6 +111,12 @@ namespace bdep
          configuration, then they must have a consistent auto-synchronization
          setting.|
 
+     \li|\cb{link}
+
+         The \cb{link} subcommand links one build configuration with another
+         by executing the \l{bpkg-cfg-link(1)} command. See
+         \l{bpkg-cfg-create(1)} for background on linked configurations.|
+
      \li|\cb{list}
 
          The \cb{list} subcommand prints the list of build configurations
@@ -145,10 +160,11 @@ namespace bdep
          (\c{\b{--}[\b{no-}]\b{forward}}), and auto-synchronization
          (\c{\b{--}[\b{no-}]\b{auto-sync}}) flags. Note that changing any of
          these flags requires an explicit \l{bdep-sync(1)} command to take
-         effect. ||"
+         effect.||"
 
     bool add;
     bool create;
+    bool link;
     bool list;
     bool move;
     bool rename;
@@ -164,7 +180,6 @@ namespace bdep
     "\h|CONFIG OPTIONS|"
   };
 
-
   "
    \h|DEFAULT OPTIONS FILES|
 
diff --git a/bdep/config.cxx b/bdep/config.cxx
index 8d33155..f06bb98 100644
--- a/bdep/config.cxx
+++ b/bdep/config.cxx
@@ -22,7 +22,7 @@ namespace bdep
     if (c->name)
       o << '@' << *c->name << ' ';
 
-    o << c->path << ' ' << *c->id;
+    o << c->path << ' ' << *c->id << ' ' << c->type;
 
     if (flags)
     {
@@ -54,14 +54,15 @@ namespace bdep
     if (o.existing () && o.wipe ())
       fail << "both --existing|-e and --wipe specified";
 
-    return (o.default_ ()     ? "--default"      :
-            o.no_default ()   ? "--no-default"   :
-            o.forward ()      ? "--forward"      :
-            o.no_forward ()   ? "--no-forward"   :
-            o.auto_sync ()    ? "--auto-sync"    :
-            o.no_auto_sync () ? "--no-auto-sync" :
-            o.existing ()     ? "--existing|-e"  :
-            o.wipe ()         ? "--wipe"         : nullptr);
+    return (o.config_type_specified () ? "--config-type"  :
+            o.default_ ()              ? "--default"      :
+            o.no_default ()            ? "--no-default"   :
+            o.forward ()               ? "--forward"      :
+            o.no_forward ()            ? "--no-forward"   :
+            o.auto_sync ()             ? "--auto-sync"    :
+            o.no_auto_sync ()          ? "--no-auto-sync" :
+            o.existing ()              ? "--existing|-e"  :
+            o.wipe ()                  ? "--wipe"         : nullptr);
   }
 
   void
@@ -137,12 +138,14 @@ namespace bdep
   }
 
   shared_ptr<configuration>
-  cmd_config_add (const configuration_add_options& ao,
+  cmd_config_add (const common_options&            co,
+                  const configuration_add_options& ao,
                   const dir_path&                  prj,
                   const package_locations&         pkgs,
                   database&                        db,
                   dir_path                         path,
                   optional<string>                 name,
+                  optional<string>                 type,
                   optional<uint64_t>               id,
                   const char*                      what)
   {
@@ -161,8 +164,53 @@ namespace bdep
 
     verify_configuration_path (path, prj, pkgs);
 
-    optional<dir_path> rel_path;
-    try {rel_path = path.relative (prj);} catch (const invalid_path&) {}
+    // Use bpkg-cfg-info to query the configuration type, unless specified
+    // explicitly.
+    //
+    if (!type)
+    {
+      fdpipe pipe (open_pipe ()); // Text mode seems appropriate.
+
+      process pr (start_bpkg (3,
+                              co,
+                              pipe /* stdout */,
+                              2    /* stderr */,
+                              "cfg-info",
+                              "-d", path));
+
+      // Shouldn't throw, unless something is severely damaged.
+      //
+      pipe.out.close ();
+
+      bool io (false);
+      try
+      {
+        ifdstream is (move (pipe.in), fdstream_mode::skip, ifdstream::badbit);
+
+        for (string l; !eof (getline (is, l)); )
+        {
+          if (l.compare (0, 6, "type: ") == 0)
+          {
+            type = string (l, 6);
+            break;
+          }
+        }
+
+        is.close (); // Detect errors.
+
+        if (!type || type->empty ())
+          fail << "invalid bpkg-cfg-info output: no configuration type";
+      }
+      catch (const io_error&)
+      {
+        // Presumably the child process failed and issued diagnostics so let
+        // finish_bpkg() try to deal with that first.
+        //
+        io = true;
+      }
+
+      finish_bpkg (co, pr, io);
+    }
 
     transaction t (db.begin ());
 
@@ -172,36 +220,43 @@ namespace bdep
     {
       using query = bdep::query<configuration>;
 
-      // By default the first added configuration is the default.
+      // By default the first added for its type configuration is the default.
       //
       if (ao.default_ () || ao.no_default ())
         def = ao.default_ () && !ao.no_default ();
 
       if (!def)
-        def = (db.query_value<count> () == 0);
+        def = (db.query_value<count> (query::type == *type) == 0);
       else if (*def)
       {
-        if (auto p = db.query_one<configuration> (query::default_))
-          fail << "configuration " << *p << " is already the default" <<
+        if (auto p = db.query_one<configuration> (query::default_ &&
+                                                  query::type == *type))
+          fail << "configuration " << *p << " of type " << *type
+               << " 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.
+      // already forwarded for its configuration type.
       //
       if (ao.forward () || ao.no_forward ())
-        fwd = ao.forward ()  && !ao.no_forward ();
+        fwd = ao.forward () && !ao.no_forward ();
 
+      // Note: there can be multiple forwarded configurations for a type.
+      //
       if (!fwd)
-        fwd = *def && db.query_one<configuration> (query::forward) == nullptr;
+        fwd = *def &&
+              db.query_value<count> (query::forward &&
+                                     query::type == *type) == 0;
     }
 
     shared_ptr<configuration> r (
       new configuration {
         id,
         name,
+        move (*type),
         path,
-        move (rel_path),
+        path.try_relative (prj),
         *def,
         *fwd,
         !ao.no_auto_sync (),
@@ -258,6 +313,7 @@ namespace bdep
                      dir_path                         path,
                      const strings&                   args,
                      optional<string>                 name,
+                     string                           type,
                      optional<uint64_t>               id)
   {
     // Similar logic to *_add().
@@ -274,16 +330,22 @@ namespace bdep
               co,
               "create",
               "-d", path,
+              (name
+               ? strings ({"--name", *name})
+               : strings ()),
+              "--type", type,
               (ao.existing () ? "--existing" : nullptr),
               (ao.wipe ()     ? "--wipe"     : nullptr),
               args);
 
-    return cmd_config_add (ao,
+    return cmd_config_add (co,
+                           ao,
                            prj,
                            package_locations {}, // Already verified.
                            db,
                            move (path),
                            move (name),
+                           move (type),
                            id,
                            ao.existing () ? "initialized" : "created");
   }
@@ -324,11 +386,13 @@ namespace bdep
     database db (open (prj, trace));
 
     cmd_config_add (o,
+                    o,
                     prj,
                     load_packages (prj, true /* allow_empty */),
                     db,
                     move (path),
                     move (name),
+                    nullopt,     /* type */
                     move (id));
     return 0;
   }
@@ -382,11 +446,61 @@ namespace bdep
                        move (path),
                        cfg_args,
                        move (name),
+                       o.config_type (),
                        move (id));
     return 0;
   }
 
   static int
+  cmd_config_link (const cmd_config_options& o, cli::scanner&)
+  {
+    tracer trace ("config_link");
+
+    // Load project configurations.
+    //
+    configurations cfgs;
+    {
+      dir_path prj (find_project (o));
+      database db (open (prj, trace));
+
+      transaction t (db.begin ());
+
+      cfgs = find_configurations (o,
+                                  prj,
+                                  t,
+                                  false /* fallback_default */,
+                                  true  /* validate         */).first;
+
+      t.commit ();
+    }
+
+    if (cfgs.size () != 2)
+      fail << "two configurations must be specified for config link";
+
+    const dir_path& cd (cfgs[0]->path);
+    const dir_path& ld (cfgs[1]->path);
+
+    // Call bpkg to link the configurations.
+    //
+    // If possible, rebase the linked configuration directory path relative to
+    // the other configuration path.
+    //
+    run_bpkg (2,
+              o,
+              "cfg-link",
+              ld.try_relative (cd) ? "--relative" : nullptr,
+              "-d", cd,
+              ld);
+
+    if (verb)
+      text << "linked configuration " << *cfgs[0] << " (" << cfgs[0]->type
+           << ") with configuration " << *cfgs[1] << " (" << cfgs[1]->type
+           << ")";
+
+    return 0;
+  }
+
+  static int
   cmd_config_list (const cmd_config_options& o, cli::scanner&)
   {
     tracer trace ("config_list");
@@ -405,7 +519,7 @@ namespace bdep
                                   prj,
                                   t,
                                   false /* fallback_default */,
-                                  false /* validate         */);
+                                  false /* validate         */).first;
     }
     else
     {
@@ -425,7 +539,6 @@ namespace bdep
 
     t.commit ();
 
-
     for (const shared_ptr<configuration>& c: cfgs)
     {
       //@@ TODO: use tabular layout facility when ready.
@@ -467,7 +580,7 @@ namespace bdep
         fail << "invalid configuration directory '" << a << "'";
       }
 
-      try {rel_path = path.relative (prj);} catch (const invalid_path&) {}
+      rel_path = path.try_relative (prj);
     }
 
     database db (open (prj, trace));
@@ -480,7 +593,7 @@ namespace bdep
                            prj,
                            t,
                            false /* fallback_default */,
-                           false /* validate         */));
+                           false /* validate         */).first);
 
     if (cfgs.size () > 1)
       fail << "multiple configurations specified for config move";
@@ -500,6 +613,10 @@ namespace bdep
 
     // Save the old path for diagnostics.
     //
+    // @@ We should probably also adjust explicit and implicit links in the
+    //    respective bpkg configurations, if/when bpkg provides the required
+    //    API.
+    //
     c->path.swap (path);
     c->relative_path = move (rel_path);
 
@@ -567,7 +684,7 @@ namespace bdep
                            prj,
                            t,
                            false /* fallback_default */,
-                           false /* validate         */));
+                           false /* validate         */).first);
 
     if (cfgs.size () > 1)
       fail << "multiple configurations specified for config rename";
@@ -625,7 +742,7 @@ namespace bdep
                            prj,
                            t,
                            false /* fallback_default */,
-                           false /* validate         */));
+                           false /* validate         */).first);
 
     for (const shared_ptr<configuration>& c: cfgs)
     {
@@ -683,19 +800,46 @@ namespace bdep
                            prj,
                            t,
                            false /* fallback_default */,
-                           false /* validate         */));
+                           false /* validate         */).first);
 
     for (const shared_ptr<configuration>& c: cfgs)
     {
       using query = bdep::query<configuration>;
 
+      // Verify that there is no other default or forwarded configuration with
+      // the same package as us.
+      //
+      auto verify = [&c, &db] (const query& q, const char* what)
+      {
+        for (const shared_ptr<configuration>& o:
+               pointer_result (db.query<configuration> (q)))
+        {
+          auto i (find_first_of (
+                    o->packages.begin (), o->packages.end (),
+                    c->packages.begin (), c->packages.end (),
+                    [] (const package_state& x, const package_state& y)
+                    {
+                      return x.name == y.name;
+                    }));
+
+          if (i != o->packages.end ())
+            fail << "configuration " << *o << " is also " << what << " and "
+                 << "also has package " << i->name << " initialized" <<
+              info << "while updating configuration " << *c;
+        }
+      };
+
       if (d)
       {
         if (*d && !c->default_)
         {
-          if (auto p = db.query_one<configuration> (query::default_))
-            fail << "configuration " << *p << " is already the default" <<
+          if (auto p = db.query_one<configuration> (query::default_ &&
+                                                    query::type == c->type))
+            fail << "configuration " << *p << " of type " << p->type
+                 << " is already the default" <<
               info << "while updating configuration " << *c;
+
+          verify (query::default_, "default");
         }
 
         c->default_ = *d;
@@ -704,27 +848,7 @@ namespace bdep
       if (f)
       {
         if (*f && !c->forward)
-        {
-          // Make sure there are no other forwarded configurations with the
-          // same package as us.
-          //
-          for (const shared_ptr<configuration>& o:
-                 pointer_result (db.query<configuration> (query::forward)))
-          {
-            auto i (find_first_of (
-                      o->packages.begin (), o->packages.end (),
-                      c->packages.begin (), c->packages.end (),
-                      [] (const package_state& x, const package_state& y)
-                      {
-                        return x.name == y.name;
-                      }));
-
-            if (i != o->packages.end ())
-              fail << "configuration " << *o << " is also forwarded and "
-                   << "also has package " << i->name << " initialized" <<
-                info << "while updating configuration " << *c;
-          }
-        }
+          verify (query::forward, "forwarded");
 
         c->forward = *f;
       }
@@ -768,6 +892,9 @@ namespace bdep
       if (!c.add () && !c.create () && !c.set ())
         fail << n << " not valid for this subcommand";
 
+      if (o.config_type_specified () && !c.create ())
+        fail << "--config-type is not valid for this subcommand";
+
       if (o.existing () && !c.create ())
         fail << "--existing|-e is not valid for this subcommand";
 
@@ -787,6 +914,7 @@ namespace bdep
     //
     if (c.add    ()) return cmd_config_add    (o, scan);
     if (c.create ()) return cmd_config_create (o, scan);
+    if (c.link   ()) return cmd_config_link   (o, scan);
     if (c.list   ()) return cmd_config_list   (o, scan);
     if (c.move   ()) return cmd_config_move   (o, scan);
     if (c.rename ()) return cmd_config_rename (o, scan);
diff --git a/bdep/config.hxx b/bdep/config.hxx
index 049f030..111ce15 100644
--- a/bdep/config.hxx
+++ b/bdep/config.hxx
@@ -12,13 +12,17 @@
 
 namespace bdep
 {
+  // If type is nullopt, then query the bpkg configuration type.
+  //
   shared_ptr<configuration>
-  cmd_config_add (const configuration_add_options&,
+  cmd_config_add (const common_options&,
+                  const configuration_add_options&,
                   const dir_path&           prj,
                   const package_locations&,
                   database&,
                   dir_path                  path,
                   optional<string>          name,
+                  optional<string>          type,
                   optional<uint64_t>        id = nullopt,
                   const char*               what = "added");
 
@@ -31,6 +35,7 @@ namespace bdep
                      dir_path                  path,
                      const strings&            args,
                      optional<string>          name,
+                     string                    type,
                      optional<uint64_t>        id = nullopt);
 
   int
diff --git a/bdep/database.cxx b/bdep/database.cxx
index 5e0aea5..064f9ed 100644
--- a/bdep/database.cxx
+++ b/bdep/database.cxx
@@ -8,6 +8,8 @@
 
 #include <bdep/diagnostics.hxx>
 
+#include <bdep/project.hxx>
+#include <bdep/project-odb.hxx>
 #include <bdep/database-views.hxx>
 #include <bdep/database-views-odb.hxx>
 
@@ -18,6 +20,22 @@ namespace bdep
   using namespace odb::sqlite;
   using odb::schema_catalog;
 
+  // Register the data migration functions.
+  //
+  template <odb::schema_version v>
+  using migration_entry = odb::data_migration_entry<v, DB_SCHEMA_VERSION_BASE>;
+
+  static const migration_entry<2>
+  migrate_v2 ([] (odb::database& db)
+  {
+    for (const shared_ptr<configuration>& c:
+           pointer_result (db.query<configuration> ()))
+    {
+      c->type = "target";
+      db.update (c);
+    }
+  });
+
   database
   open (const dir_path& d, tracer& tr, bool create)
   {
diff --git a/bdep/deinit.cli b/bdep/deinit.cli
index 6aad32c..e78cdbe 100644
--- a/bdep/deinit.cli
+++ b/bdep/deinit.cli
@@ -32,8 +32,8 @@ namespace bdep
 
      If no project directory is specified, then the current working directory
      is assumed. If no configuration is specified, then the default
-     configuration is assumed. See \l{bdep-projects-configs(1)} for details on
-     specifying projects and configurations.
+     configurations are assumed. See \l{bdep-projects-configs(1)} for details
+     on specifying projects and configurations.
      "
   }
 
diff --git a/bdep/deinit.cxx b/bdep/deinit.cxx
index 598efd5..0018aaf 100644
--- a/bdep/deinit.cxx
+++ b/bdep/deinit.cxx
@@ -113,32 +113,33 @@ namespace bdep
     configurations cfgs;
     {
       transaction t (db.begin ());
-      cfgs = find_configurations (o,
-                                  prj,
-                                  t,
-                                  true   /* fallback_default */,
-                                  !force /* validate */);
+      pair<configurations, bool> cs (
+        find_configurations (o,
+                             prj,
+                             t,
+                             true   /* fallback_default */,
+                             !force /* validate */));
       t.commit ();
-    }
 
-    // If specified, verify packages are present in each configuration.
-    //
-    if (!pp.packages.empty ())
-      verify_project_packages (pp, cfgs);
+      // If specified, verify packages are present in at least one
+      // configuration.
+      //
+      if (!pp.packages.empty ())
+        verify_project_packages (pp, cs);
+
+      cfgs = move (cs.first);
+    }
 
     // If no packages were explicitly specified, then we deinitalize all that
-    // have been initialized in each configuration.
+    // have been initialized in each configuration. Otherwise, we deinitalize
+    // only specified packages initialized in the (specified) configurations.
     //
-    strings pkgs;
+    const package_locations& pkgs (pp.packages);
 
-    bool all (pp.packages.empty ());
-    if (!all)
-    {
-      for (const package_location& p: pp.packages)
-        pkgs.push_back (p.name.string ());
-    }
+    bool all (pkgs.empty ());
 
-    // Deinitialize in each configuration skipping empty ones.
+    // Deinitialize in each configuration, skipping those where no packages
+    // needs to be deinitialized.
     //
     // We do each configuration in a separate transaction so that our state
     // reflects the bpkg configuration as closely as possible.
@@ -146,10 +147,36 @@ namespace bdep
     bool first (true);
     for (const shared_ptr<configuration>& c: cfgs)
     {
-      if (c->packages.empty ())
+      // Collect packages to deinitialize.
+      //
+      strings ps;
+
+      for (const package_state& s: c->packages)
+      {
+        if (all ||
+            find_if (pkgs.begin (),
+                     pkgs.end (),
+                     [&s] (const package_location& p)
+                     {
+                       return p.name == s.name;
+                     }) != pkgs.end ())
+          ps.push_back (s.name.string ());
+      }
+
+      if (ps.empty ())
       {
         if (verb)
-          info << "skipping empty configuration " << *c;
+        {
+          diag_record dr (info);
+
+          dr << "skipping configuration " << *c;
+
+          if (c->packages.empty ())
+            dr << info << "configuration is empty";
+          else
+            dr << info << "none of specified packages initialized in this "
+                       << "configuration";
+        }
 
         continue;
       }
@@ -167,41 +194,33 @@ namespace bdep
 
       transaction t (db.begin ());
 
-      // Collect packages to drop and remove them from the configuration.
+      // Remove collected packages from the configuration.
       //
-      if (all)
-      {
-        pkgs.clear ();
-
-        for (const package_state& p: c->packages)
-          pkgs.push_back (p.name.string ());
-      }
-
       c->packages.erase (
         remove_if (c->packages.begin (),
                    c->packages.end (),
-                   [&pkgs] (const package_state& p)
+                   [&ps] (const package_state& p)
                    {
-                     return find_if (pkgs.begin (),
-                                     pkgs.end (),
+                     return find_if (ps.begin (),
+                                     ps.end (),
                                      [&p] (const string& n)
                                      {
                                        return p.name == n;
-                                     }) != pkgs.end ();
+                                     }) != ps.end ();
                    }),
         c->packages.end ());
 
       // If we are deinitializing multiple packages, print their names.
       //
-      if (verb && pkgs.size () > 1)
+      if (verb && ps.size () > 1)
       {
-        for (const string& n: pkgs)
+        for (const string& n: ps)
           text << "deinitializing package " << n;
       }
 
       // The same story as in init with regard to the state update order.
       //
-      cmd_deinit (o, prj, c, pkgs);
+      cmd_deinit (o, prj, c, ps);
 
       db.update (c);
       t.commit ();
diff --git a/bdep/fetch.cli b/bdep/fetch.cli
index 4349bdd..bfd9c53 100644
--- a/bdep/fetch.cli
+++ b/bdep/fetch.cli
@@ -29,8 +29,8 @@ namespace bdep
 
      If no project or package directory is specified, then the current working
      directory is assumed. If no configuration is specified, then the default
-     configuration is assumed. See \l{bdep-projects-configs(1)} for details on
-     specifying projects and configurations.
+     configurations are assumed. See \l{bdep-projects-configs(1)} for details
+     on specifying projects and configurations.
 
      If the \cb{--full|-F} option is specified, then instead \cb{fetch}
      performs a full re-fetch of all the repositories added to the
diff --git a/bdep/fetch.cxx b/bdep/fetch.cxx
index 93a727f..96bfd4b 100644
--- a/bdep/fetch.cxx
+++ b/bdep/fetch.cxx
@@ -40,7 +40,7 @@ namespace bdep
       database db (open (prj, trace));
 
       transaction t (db.begin ());
-      cfgs = find_configurations (o, prj, t);
+      cfgs = find_configurations (o, prj, t).first;
       t.commit ();
     }
 
diff --git a/bdep/init.cli b/bdep/init.cli
index c8616c3..658c81e 100644
--- a/bdep/init.cli
+++ b/bdep/init.cli
@@ -42,10 +42,11 @@ namespace bdep
 
      If no project directory is specified, then the current working directory
      is assumed. If no configuration is specified, then the default
-     configuration is assumed. See \l{bdep-projects-configs(1)} for details on
-     specifying projects and configurations. Optional <pkg-args> are the
-     additional dependency packages and/or configuration variables to pass
-     to the underlying \l{bpkg-pkg-build(1)} command.
+     configuration is assumed (failing if multiple default configurations are
+     present). See \l{bdep-projects-configs(1)} for details on specifying
+     projects and configurations. Optional <pkg-args> are the additional
+     dependency packages and/or configuration variables to pass to the
+     underlying \l{bpkg-pkg-build(1)} command.
 
      The second form (\cb{--empty} is specified) initializes an empty project
      database that can later be used to first add build configurations
diff --git a/bdep/init.cxx b/bdep/init.cxx
index a3f0859..2dbc1bb 100644
--- a/bdep/init.cxx
+++ b/bdep/init.cxx
@@ -53,7 +53,7 @@ namespace bdep
                    const dir_path& cfg,
                    const strings& args,
                    bool ca,
-                   bool cc)
+                   optional<string> cc)
   {
     const char* m (!ca ? "--config-create" :
                    !cc ? "--config-add"    : nullptr);
@@ -66,8 +66,25 @@ namespace bdep
     cmd_config_validate_add (o, m, nm, id);
 
     return ca
-      ? cmd_config_add    (   ao, prj, ps, db, cfg,       move (nm), move (id))
-      : cmd_config_create (o, ao, prj, ps, db, cfg, args, move (nm), move (id));
+      ? cmd_config_add (o,
+                        ao,
+                        prj,
+                        ps,
+                        db,
+                        cfg,
+                        move (nm),
+                        nullopt    /* type */,
+                        move (id))
+      : cmd_config_create (o,
+                           ao,
+                           prj,
+                           ps,
+                           db,
+                           cfg,
+                           args,
+                           move (nm),
+                           move (*cc),
+                           move (id));
   }
 
   void
@@ -79,6 +96,91 @@ namespace bdep
             const strings& pkg_args,
             bool sync)
   {
+    // Return true if a package is initialized in the specified configuration.
+    //
+    auto initialized = [] (const package_location& p,
+                           const shared_ptr<configuration>& c)
+    {
+      return find_if (c->packages.begin (),
+                      c->packages.end (),
+                      [&p] (const package_state& s)
+                      {
+                        return p.name == s.name;
+                      }) != c->packages.end ();
+    };
+
+    // Verify that as a result of this operation, none of the packages will be
+    // initialized in multiple default or forwarded configurations and fail if
+    // that's not the case.
+    //
+    // Note that we perform verification in a separate loop to make sure that
+    // no actual bpkg commands are executed and no database changes are
+    // committed by the time of potential failure.
+    //
+    {
+      transaction t (db.begin ());
+
+      // For the sake of simplicity, add packages to the configuration
+      // objects, updating their state in the database (so that the changes
+      // are seen by the queries) and rollback the transaction in the
+      // end. Note that by doing so, we can end up modifying passed
+      // configuration objects and then failing, which is probably ok.
+      //
+      for (const shared_ptr<configuration>& c: cfgs)
+      {
+        for (const package_location& p: pkgs)
+        {
+          // Skip the package if it is already initialized in this
+          // configuration.
+          //
+          if (initialized (p, c))
+            continue;
+
+          // Verify that there is no other default or forwarded configuration
+          // that also has this package.
+          //
+          using query = bdep::query<configuration>;
+
+          auto verify = [&c, &p, &db, &initialized] (const query& q,
+                                                     const char* what)
+          {
+            for (const shared_ptr<configuration>& o:
+                   pointer_result (db.query<configuration> (q)))
+            {
+              if (initialized (p, o))
+              {
+                // Differ, since the package is not initialized in `c` (see
+                // above).
+                //
+                assert (o->id != c->id);
+
+                fail << what << " configuration " << *o << " also has package "
+                     << p.name << " initialized" <<
+                  info << "while initializing in " << what << " configuration "
+                     << *c <<
+                  info << "specify packages and configurations explicitly";
+              }
+            }
+          };
+
+          if (c->default_)
+            verify (query::default_, "default");
+
+          if (c->forward)
+            verify (query::forward, "forwarded");
+
+          c->packages.push_back (package_state {p.name});
+        }
+
+        db.update (c);
+      }
+
+      t.rollback ();
+    }
+
+    // Now, execute the actual bpkg commands and update configurations for
+    // real.
+    //
     // We do each configuration in a separate transaction so that our state
     // reflects the bpkg configuration as closely as possible.
     //
@@ -108,14 +210,15 @@ namespace bdep
 
       transaction t (db.begin ());
 
+      // Reload the configuration object that could have been changed during
+      // verification. This is required for skipping the already initialized
+      // packages.
+      //
+      db.reload (*c);
+
       for (const package_location& p: pkgs)
       {
-        if (find_if (c->packages.begin (),
-                     c->packages.end (),
-                     [&p] (const package_state& s)
-                     {
-                       return p.name == s.name;
-                     }) != c->packages.end ())
+        if (initialized (p, c))
         {
           if (verb)
             info << "package " << p.name << " is already initialized";
@@ -123,38 +226,11 @@ namespace bdep
           continue;
         }
 
-        // If this configuration is forwarded, verify there is no other
-        // forwarded configuration that also has this package.
-        //
-        if (c->forward)
-        {
-          using query = bdep::query<configuration>;
-
-          for (const shared_ptr<configuration>& o:
-                 pointer_result (db.query<configuration> (query::forward)))
-          {
-            if (o == c)
-              continue;
-
-            if (find_if (o->packages.begin (),
-                         o->packages.end (),
-                         [&p] (const package_state& s)
-                         {
-                           return p.name == s.name;
-                         }) != o->packages.end ())
-            {
-              fail << "forwarded configuration " << *o << " also has package "
-                   << p.name << " initialized" <<
-                info << "while initializing in forwarded configuration " << *c;
-            }
-          }
-        }
-
         // If we are initializing multiple packages or there will be no sync,
         // print their names.
         //
         if (verb && (pkgs.size () > 1 || !sync))
-          text << "initializing package " << p.name;;
+          text << "initializing package " << p.name;
 
         c->packages.push_back (package_state {p.name});
       }
@@ -190,7 +266,12 @@ namespace bdep
     tracer trace ("init");
 
     bool ca (o.config_add_specified ());
-    bool cc (o.config_create_specified ());
+
+    // Type of configuration being created, if --config-create is specified.
+    //
+    optional<string> cc (o.config_create_specified ()
+                         ? o.config_type ()
+                         : optional<string> ());
 
     if (o.empty ())
     {
@@ -204,6 +285,9 @@ namespace bdep
       if (!ca && !cc)
         fail << n << " specified without --config-(add|create)";
 
+      if (o.config_type_specified () && !cc)
+        fail << "--config-type specified without --config-create";
+
       if (o.existing () && !cc)
         fail << "--existing|-e specified without --config-create";
 
@@ -243,11 +327,6 @@ namespace bdep
 
     configurations cfgs;
     {
-      // Make sure everyone refers to the same objects across all the
-      // transactions.
-      //
-      session s;
-
       // --config-add/create
       //
       if (ca || cc)
@@ -272,7 +351,7 @@ namespace bdep
             ca ? o.config_add () : o.config_create (),
             cfg_args,
             ca,
-            cc));
+            move (cc)));
       }
       else
       {
@@ -280,7 +359,7 @@ namespace bdep
         // wants us to use.
         //
         transaction t (db.begin ());
-        cfgs = find_configurations (o, prj, t);
+        cfgs = find_configurations (o, prj, t).first;
         t.commit ();
       }
     }
diff --git a/bdep/init.hxx b/bdep/init.hxx
index 6a2afd2..fff5f84 100644
--- a/bdep/init.hxx
+++ b/bdep/init.hxx
@@ -23,7 +23,7 @@ namespace bdep
                    const dir_path& cfg,
                    const strings& cfg_args,
                    bool config_add_specified,
-                   bool config_create_specified);
+                   optional<string> config_create_type);
 
   // Initialize each package in each configuration skipping those that are
   // already initialized. Then synchronize each configuration unless sync
diff --git a/bdep/new.cxx b/bdep/new.cxx
index b512497..5998630 100644
--- a/bdep/new.cxx
+++ b/bdep/new.cxx
@@ -242,7 +242,12 @@ cmd_new (cmd_new_options&& o, cli::group_scanner& args)
   // Validate options.
   //
   bool ca (o.config_add_specified ());
-  bool cc (o.config_create_specified ());
+
+  // Type of configuration being created, if --config-create is specified.
+  //
+  optional<string> cc (o.config_create_specified ()
+                       ? o.config_type ()
+                       : optional<string> ());
 
   if (o.subdirectory ())
     fail << "--subdirectory was renamed to --source";
@@ -271,6 +276,9 @@ cmd_new (cmd_new_options&& o, cli::group_scanner& args)
     if (!ca && !cc)
       fail << n << " specified without --config-(add|create)";
 
+    if (o.config_type_specified () && !cc)
+      fail << "--config-type specified without --config-create";
+
     if (o.existing () && !cc)
       fail << "--existing|-e specified without --config-create";
 
@@ -3159,7 +3167,7 @@ cmd_new (cmd_new_options&& o, cli::group_scanner& args)
         ca ? o.config_add () : o.config_create (),
         cfg_args,
         ca,
-        cc)};
+        move (cc))};
 
     cmd_init (o, prj, db, cfgs, pkgs, strings () /* pkg_args */);
   }
diff --git a/bdep/project.cli b/bdep/project.cli
index 1b6c7aa..17ef72e 100644
--- a/bdep/project.cli
+++ b/bdep/project.cli
@@ -11,6 +11,14 @@ namespace bdep
   //
   class configuration_add_options
   {
+    string --config-type = "target"
+    {
+      "<type>",
+      "The type of the configuration being created. By default, configuration
+       of type \cb{target} is created. See \l{bpkg-cfg-create(1)} for
+       background on configuration types."
+    }
+
     bool --default
     {
       "Make the added or created configuration the default."
diff --git a/bdep/project.cxx b/bdep/project.cxx
index 7190045..ace8e3b 100644
--- a/bdep/project.cxx
+++ b/bdep/project.cxx
@@ -16,7 +16,7 @@ using namespace butl;
 
 namespace bdep
 {
-  configurations
+  pair<configurations, bool>
   find_configurations (const project_options& po,
                        const dir_path& prj,
                        transaction& t,
@@ -24,6 +24,7 @@ namespace bdep
                        bool validate)
   {
     configurations r;
+    bool fallback (false);
 
     // Weed out duplicates.
     //
@@ -99,12 +100,16 @@ namespace bdep
     {
       if (fallback_default)
       {
-        if (auto c = db.query_one<configuration> (query::default_))
+        for (shared_ptr<configuration> c:
+               pointer_result (db.query<configuration> (query::default_)))
           add (move (c));
-        else
+
+        if (r.empty ())
           fail << "no default configuration in project " << prj <<
             info << "use (@<cfg-name> | --config|-c <cfg-dir> | --all|-a) to "
-               << "specify configuration explicitly";
+                 << "specify configuration explicitly";
+
+        fallback = true;
       }
       else
         fail << "no configurations specified";
@@ -123,7 +128,7 @@ namespace bdep
       }
     }
 
-    return r;
+    return make_pair (move (r), fallback);
   }
 
   project_package
@@ -400,23 +405,39 @@ namespace bdep
 
   void
   verify_project_packages (const project_packages& pp,
-                           const configurations& cfgs)
+                           const pair<configurations, bool>& cfgs)
   {
-    for (const shared_ptr<configuration>& c: cfgs)
+    for (const package_location& p: pp.packages)
     {
-      for (const package_location& p: pp.packages)
+      bool init (false);
+
+      for (const shared_ptr<configuration>& c: cfgs.first)
       {
         if (find_if (c->packages.begin (),
                      c->packages.end (),
                      [&p] (const package_state& s)
                      {
                        return p.name == s.name;
-                     }) == c->packages.end ())
+                     }) != c->packages.end ())
         {
-          fail << "package " << p.name << " is not initialized "
-               << "in configuration " << *c;
+          init = true;
+          break;
         }
       }
+
+      if (!init)
+      {
+        diag_record dr (fail);
+
+        dr << "package " << p.name << " is not initialized in ";
+
+        if (cfgs.second)
+          dr << "any default configuration(s)";
+        else if (cfgs.first.size () == 1)
+          dr << "configuration " << *cfgs.first.front ();
+        else
+          dr << "any specified configurations";
+      }
     }
   }
 
diff --git a/bdep/project.hxx b/bdep/project.hxx
index 86b833f..5c6be87 100644
--- a/bdep/project.hxx
+++ b/bdep/project.hxx
@@ -15,7 +15,11 @@
 
 #include <bdep/project-options.hxx>
 
-#pragma db model version(1, 1, closed)
+// Used by the data migration entries.
+//
+#define DB_SCHEMA_VERSION_BASE 1
+
+#pragma db model version(DB_SCHEMA_VERSION_BASE, 2, closed)
 
 // Prevent assert() macro expansion in get/set expressions. This should appear
 // after all #include directives since the assert() macro is redefined in each
@@ -85,6 +89,7 @@ namespace bdep
     //
     optional_uint64_t  id;
     optional_string    name;
+    string             type;
     dir_path           path;
     optional_dir_path  relative_path;
 
@@ -122,6 +127,7 @@ namespace bdep
     //
     configuration (optional_uint64_t i,
                    optional_string n,
+                   string t,
                    dir_path p,
                    optional_dir_path rp,
                    bool d,
@@ -130,6 +136,7 @@ namespace bdep
                    vector<package_state> ps)
       : id (i),
         name (move (n)),
+        type (move (t)),
         path (move (p)),
         relative_path (move (rp)),
         default_ (d),
@@ -166,12 +173,15 @@ namespace bdep
 
   // Given the project directory, database, and options resolve all the
   // mentioned configurations or, unless fallback_default is false, find the
-  // default configuration if none were mentioned. Unless validate is false,
+  // default configurations if none were mentioned. Unless validate is false,
   // also validate that the configuration directories still exist.
   //
+  // Besides configurations, also return an indication if they are retrieved
+  // as a fallback to default configurations (true if that's the case).
+  //
   using configurations = vector<shared_ptr<configuration>>;
 
-  configurations
+  pair<configurations, bool>
   find_configurations (const project_options&,
                        const dir_path& prj,
                        transaction&,
@@ -255,10 +265,14 @@ namespace bdep
     return find_project_packages (o, true /* ignore_packages */).project;
   }
 
-  // Verify all the packages are present in all the configurations.
+  // Verify that each package is present in at least one configuration.
+  //
+  // Note that the default configurations fallback indication (see above) is
+  // only used for diagnostics.
   //
   void
-  verify_project_packages (const project_packages&, const configurations&);
+  verify_project_packages (const project_packages&,
+                           const pair<configurations, bool>&);
 
   // Determine the version of a package in the specified package (first
   // version) or configuration (second version) directory.
diff --git a/bdep/project.xml b/bdep/project.xml
index e69af8b..805d741 100644
--- a/bdep/project.xml
+++ b/bdep/project.xml
@@ -1,4 +1,10 @@
 <changelog xmlns="http://www.codesynthesis.com/xmlns/odb/changelog" database="sqlite" version="1">
+  <changeset version="2">
+    <alter-table name="configuration">
+      <add-column name="type" type="TEXT" null="true"/>
+    </alter-table>
+  </changeset>
+
   <model version="1">
     <table name="configuration" kind="object">
       <column name="id" type="INTEGER" null="true"/>
diff --git a/bdep/projects-configs.cli b/bdep/projects-configs.cli
index 72b9736..a5c5808 100644
--- a/bdep/projects-configs.cli
+++ b/bdep/projects-configs.cli
@@ -58,11 +58,12 @@ include <bdep/common-options.hxx>;
   \cb{packages.manifest}).
 
   A project managed by \cb{bdep} has one or more associated build
-  configurations (see \l{bdep-config(1)} for details). One of these
-  configurations can be designated as the default and used if no configuration
-  is specified explicitly. So, for example, running \cb{status} without any
-  arguments in the project directory will show the status of all the project
-  packages initialized in the default configuration.
+  configurations (see \l{bdep-config(1)} for details). Some of these
+  configurations, one per the configuration type, can be designated as default
+  and used if no configuration is specified explicitly. So, for example,
+  running \cb{status} without any arguments in the project directory will show
+  the status of all the project packages initialized in the default
+  configurations.
 
   An associated build configuration can be assigned a name in which case we
   can specify it using the \c{\b{@}\i{cfg-name}} notation. For example:
diff --git a/bdep/publish.cli b/bdep/publish.cli
index d8ecb82..42504ac 100644
--- a/bdep/publish.cli
+++ b/bdep/publish.cli
@@ -23,7 +23,7 @@ namespace bdep
 
      \c{<pkg-spec> = (\b{--directory}|\b{-d} <pkg-dir>)... | <prj-spec>\n
         <prj-spec> = \b{--directory}|\b{-d} <prj-dir>\n
-        <cfg-spec> = \b{@}<cfg-name> | \b{--config}|\b{-c} <cfg-dir> | \b{--forward}}
+        <cfg-spec> = (\b{@}<cfg-name> | \b{--config}|\b{-c} <cfg-dir>)... | \b{--all}|\b{-a} | \b{--forward}}
 
      \h|DESCRIPTION|
 
@@ -32,7 +32,7 @@ namespace bdep
 
      If no project or package directory is specified, then the current working
      directory is assumed. If no configuration is specified, then the default
-     configuration is used to prepare the package distributions. If the
+     configurations are used to prepare the package distributions. If the
      specified directory is a project directory, then all the packages in the
      project are published. See \l{bdep-projects-configs(1)} for details on
      specifying projects and configurations.
diff --git a/bdep/publish.cxx b/bdep/publish.cxx
index d39cbcc..75c38d8 100644
--- a/bdep/publish.cxx
+++ b/bdep/publish.cxx
@@ -48,16 +48,18 @@ namespace bdep
       info << "use --control to specify explicitly" << endf;
   }
 
-  // If cfg is empty, then use each package's (forwarded) source directory.
+  // Distribute packages in the specified (per-package) directories.
   //
   static int
   cmd_publish (const cmd_publish_options& o,
                const dir_path& prj,
-               const dir_path& cfg,
-               package_locations&& pkg_locs)
+               package_locations&& pkg_locs,
+               dir_paths&& dist_dirs)
   {
     using bpkg::package_manifest;
 
+    assert (pkg_locs.size () == dist_dirs.size ()); // Parallel vectors.
+
     const url& repo (o.repository ());
 
     // Control repository URL.
@@ -125,7 +127,7 @@ namespace bdep
     struct package
     {
       package_name     name;
-      dir_path         path;
+      dir_path         dist_dir;
       standard_version version;
       package_name     project;
       string           section; // alpha|beta|stable (or --section)
@@ -158,14 +160,14 @@ namespace bdep
           info << "use --force=uncommitted to publish anyway";
     }
 
-    for (package_location& pl: pkg_locs)
+    for (size_t i (0); i != pkg_locs.size (); ++i)
     {
-      package_name n (move (pl.name));
-      package_name p (pl.project ? move (*pl.project) : n);
+      package_location& pl (pkg_locs[i]);
 
-      standard_version v (cfg.empty ()
-                          ? package_version (o, prj / pl.path)
-                          : package_version (o, cfg, n));
+      package_name     n (move (pl.name));
+      package_name     p (pl.project ? move (*pl.project) : n);
+      dir_path         d (move (dist_dirs[i]));
+      standard_version v (package_version (o, d));
 
       // Should we allow publishing snapshots and, if so, to which section?
       // For example, is it correct to consider a "between betas" snapshot a
@@ -204,7 +206,7 @@ namespace bdep
                 v.beta ()                     ? "beta"  : "stable");
 
       pkgs.push_back (package {move (n),
-                               move (pl.path),
+                               move (d),
                                move (v),
                                move (p),
                                move (s),
@@ -269,13 +271,10 @@ namespace bdep
       // build2's version module by default does not allow distribution of
       // uncommitted projects.
       //
-      dir_path d (cfg.empty ()
-                  ? prj / p.path
-                  : dir_path (cfg) /= p.name.string ());
       run_b (
         o,
         "dist:",
-        "'" + d.representation () + "'",
+        "'" + p.dist_dir.representation () + "'",
         "config.dist.root='" + dr.representation () + "'",
         "config.dist.archives=tar.gz",
         "config.dist.checksums=sha256",
@@ -858,16 +857,17 @@ namespace bdep
 
     const dir_path& prj (pp.project);
 
-    // Unless we are using the forwarded configurations, we need a single
-    // configuration to prepare package distributions.
+    // Collect directories to distribute the packages in. In the forward mode
+    // the packages are distributed in the package's (forwarded) source
+    // directories and in their configuration directories otherwise.
     //
-    dir_path cfg_dir;
+    dir_paths dist_dirs;
 
     if (o.forward ())
     {
       // Note: in this case we don't even open the database.
       //
-      dir_paths cfgs;
+      dir_paths cfgs; // Configuration directories to sync.
 
       for (const package_location& pl: pp.packages)
       {
@@ -883,6 +883,8 @@ namespace bdep
         //
         (pi.out_root /= pi.amalgamation).normalize ();
 
+        dist_dirs.push_back (move (d));
+
         if (find (cfgs.begin (), cfgs.end (), pi.out_root) == cfgs.end ())
           cfgs.push_back (move (pi.out_root));
       }
@@ -895,31 +897,66 @@ namespace bdep
     }
     else
     {
-      shared_ptr<configuration> cfg;
+      configurations cfgs;
       {
         // Don't keep the database open longer than necessary.
         //
         database db (open (prj, trace));
 
         transaction t (db.begin ());
-        configurations cfgs (find_configurations (o, prj, t));
+        cfgs = find_configurations (o, prj, t).first;
         t.commit ();
+      }
 
-        if (cfgs.size () > 1)
-          fail << "multiple configurations specified for publish";
+      // Configurations to sync.
+      //
+      // We could probably unify syncing configuration directories with the
+      // forward mode, however configuration name-based progress indication
+      // feels preferable for the common case.
+      //
+      configurations scs;
 
-        // Verify packages are present in the configuration.
-        //
-        verify_project_packages (pp, cfgs);
+      // Besides collecting the package directories and configurations to
+      // sync, also verify that for each package being published only one
+      // configuration, it is initialized in, is specified.
+      //
+      for (const package_location& p: pp.packages)
+      {
+        shared_ptr<configuration> pc;
 
-        cfg = move (cfgs[0]);
-      }
+        for (const shared_ptr<configuration>& c: cfgs)
+        {
+          if (find_if (c->packages.begin (),
+                       c->packages.end (),
+                       [&p] (const package_state& s)
+                       {
+                         return p.name == s.name;
+                       }) != c->packages.end ())
+          {
+            if (pc != nullptr)
+              fail << "package " << p.name << " is initialized in multiple "
+                   << "specified configurations" <<
+                info << *pc <<
+                info << *c;
+
+            pc = c;
+          }
+        }
+
+        if (pc == nullptr)
+          fail << "package " << p.name << " is not initialized in any "
+               << "configuration";
 
-      cmd_sync (o, prj, cfg, strings () /* pkg_args */, true /* implicit */);
+        dist_dirs.push_back (dir_path (pc->path) /= p.name.string ());
+
+        if (find (scs.begin (), scs.end (), pc) == scs.end ())
+          scs.push_back (move (pc));
+      }
 
-      cfg_dir = cfg->path;
+      for (const shared_ptr<configuration>& c: scs)
+        cmd_sync (o, prj, c, strings () /* pkg_args */, true /* implicit */);
     }
 
-    return cmd_publish (o, prj, cfg_dir, move (pp.packages));
+    return cmd_publish (o, prj, move (pp.packages), move (dist_dirs));
   }
 }
diff --git a/bdep/status.cli b/bdep/status.cli
index 39688cb..38e70e0 100644
--- a/bdep/status.cli
+++ b/bdep/status.cli
@@ -32,8 +32,8 @@ namespace bdep
 
      If no project or package directory is specified, then the current working
      directory is assumed. If no configuration is specified, then the default
-     configuration is assumed. See \l{bdep-projects-configs(1)} for details on
-     specifying projects and configurations.
+     configurations are assumed. See \l{bdep-projects-configs(1)} for details
+     on specifying projects and configurations.
 
      If no <dep-spec> arguments are specified, then \cb{status} prints the
      status of the project's packages. Otherwise, the status of the specified
diff --git a/bdep/status.cxx b/bdep/status.cxx
index 2e60b29..fc07698 100644
--- a/bdep/status.cxx
+++ b/bdep/status.cxx
@@ -50,34 +50,6 @@ namespace bdep
               pkgs);
   }
 
-  static void
-  cmd_status (const cmd_status_options& o,
-              const dir_path& prj,
-              const shared_ptr<configuration>& c,
-              const package_locations& ps,
-              bool fetch)
-  {
-    assert (!c->packages.empty ());
-
-    // If no packages were explicitly specified, then we print the status for
-    // all that have been initialized in the configuration.
-    //
-    strings pkgs;
-
-    if (ps.empty ())
-    {
-      for (const package_state& p: c->packages)
-        pkgs.push_back (p.name.string ());
-    }
-    else
-    {
-      for (const package_location& p: ps)
-        pkgs.push_back (p.name.string ());
-    }
-
-    cmd_status (o, prj, c->path, pkgs, fetch);
-  }
-
   int
   cmd_status (const cmd_status_options& o, cli::scanner& args)
   {
@@ -103,16 +75,23 @@ namespace bdep
 
     database db (open (prj, trace));
 
-    transaction t (db.begin ());
-    configurations cfgs (find_configurations (o, prj, t));
-    t.commit ();
+    configurations cfgs;
+    {
+      transaction t (db.begin ());
+      pair<configurations, bool> cs (find_configurations (o, prj, t));
+      t.commit ();
 
-    // If specified, verify packages are present in each configuration.
-    //
-    if (!pp.packages.empty ())
-      verify_project_packages (pp, cfgs);
+      // If specified, verify packages are present in at least one
+      // configuration.
+      //
+      if (!pp.packages.empty ())
+        verify_project_packages (pp, cs);
+
+      cfgs = move (cs.first);
+    }
 
-    // Print status in each configuration skipping empty ones.
+    // Print status in each configuration, skipping those where no package
+    // statuses needs to be printed.
     //
     bool first (true);
     for (const shared_ptr<configuration>& c: cfgs)
@@ -120,11 +99,50 @@ namespace bdep
       if (c->packages.empty ())
       {
         if (verb)
-          info << "skipping empty configuration " << *c;
+          info << "skipping configuration " << *c <<
+            info << "configuration is empty";
 
         continue;
       }
 
+      // Collect the packages to print, unless the dependency packages are
+      // specified.
+      //
+      // If no packages were explicitly specified, then we print the status
+      // for all that have been initialized in the configuration. Otherwise,
+      // only for specified packages initialized in the (specified)
+      // configurations.
+      //
+      strings pkgs;
+
+      if (dep_pkgs.empty ())
+      {
+        const package_locations& ps (pp.packages);
+        bool all (ps.empty ());
+
+        for (const package_state& s: c->packages)
+        {
+          if (all ||
+              find_if (ps.begin (),
+                       ps.end (),
+                       [&s] (const package_location& p)
+                       {
+                         return p.name == s.name;
+                       }) != ps.end ())
+            pkgs.push_back (s.name.string ());
+        }
+
+        if (pkgs.empty ())
+        {
+          if (verb)
+            info << "skipping configuration " << *c <<
+              info << "none of specified packages initialized in this "
+                   << "configuration";
+
+          continue;
+        }
+      }
+
       // If we are printing multiple configurations, separate them with a
       // blank line and print the configuration name/directory.
       //
@@ -141,10 +159,12 @@ namespace bdep
       if (fetch)
         cmd_fetch (o, prj, c, o.fetch_full ());
 
-      if (dep_pkgs.empty ())
-        cmd_status (o, prj, c, pp.packages, !fetch);
-      else
-        cmd_status (o, prj, c->path, dep_pkgs, !fetch);
+      // Status for either packages or their dependencies must be printed, but
+      // not for both.
+      //
+      assert (pkgs.empty () == !dep_pkgs.empty ());
+
+      cmd_status (o, prj, c->path, !pkgs.empty () ? pkgs : dep_pkgs, !fetch);
     }
 
     return 0;
diff --git a/bdep/sync.cli b/bdep/sync.cli
index 8f806b6..07c46a2 100644
--- a/bdep/sync.cli
+++ b/bdep/sync.cli
@@ -41,8 +41,8 @@ namespace bdep
 
      If no project or package directory is specified, then the current working
      directory is assumed. If no configuration is specified, then the default
-     configuration is assumed. See \l{bdep-projects-configs(1)} for details on
-     specifying projects and configurations. Optional <pkg-args> are the
+     configurations are assumed. See \l{bdep-projects-configs(1)} for details
+     on specifying projects and configurations. Optional <pkg-args> are the
      additional dependency packages and/or configuration variables to pass to
      the underlying \l{bpkg-pkg-build(1)} command.
 
diff --git a/bdep/sync.cxx b/bdep/sync.cxx
index d47cd6c..0d5132f 100644
--- a/bdep/sync.cxx
+++ b/bdep/sync.cxx
@@ -188,7 +188,7 @@ namespace bdep
   // Sync with optional upgrade.
   //
   // If upgrade is not nullopt, then: If there are dep_pkgs, then we are
-  // upgrading specific dependency packages. Othewise -- project packages.
+  // upgrading specific dependency packages. Otherwise -- project packages.
   //
   static void
   cmd_sync (const common_options& co,
@@ -743,12 +743,14 @@ namespace bdep
     if (o.directory_specified () || !o.implicit ())
     {
       // We could be running from a package directory (or the user specified
-      // one with -d) that has not been init'ed in this configuration. Unless
-      // we are upgrading specific dependencies, we want to diagnose that
-      // since such a package will not be present in the bpkg configuration.
-      // But if we are running from the project, then we don't want to treat
-      // all the available packages as specified by the user (thus
-      // load_packages is false).
+      // one with -d) that has not been init'ed in this configuration. This,
+      // however, doesn't really matter since the specified packages are only
+      // used to determine which configuration package dependencies needs to
+      // be ugraded (see cmd_sync() for details).
+      //
+      // If we are running from the project, then we don't want to treat all
+      // the available packages as specified by the user (thus load_packages
+      // is false).
       //
       project_packages pp (
         find_project_packages (o,
@@ -761,21 +763,24 @@ namespace bdep
 
       // Load project configurations.
       //
+      pair<configurations, bool> cs;
       {
         database db (open (pp.project, trace));
 
         transaction t (db.begin ());
-        cfgs = find_configurations (o, pp.project, t);
+        cs = find_configurations (o, pp.project, t);
         t.commit ();
       }
 
-      // If specified, verify packages are present in each configuration.
+      // If specified, verify packages are present in at least one
+      // configuration.
       //
       if (!pp.packages.empty ())
-        verify_project_packages (pp, cfgs);
+        verify_project_packages (pp, cs);
 
       prj = move (pp.project);
       prj_pkgs = move (pp.packages);
+      cfgs = move (cs.first);
     }
     else
     {
@@ -838,7 +843,8 @@ namespace bdep
       if (c != nullptr && c->packages.empty ())
       {
         if (verb)
-          info << "skipping empty configuration " << *c;
+          info << "skipping configuration " << *c <<
+            info << "configuration is empty";
 
         continue;
       }
@@ -857,6 +863,11 @@ namespace bdep
 
       if (!dep_pkgs.empty ())
       {
+        // We ignore the project packages if the dependencies are specified
+        // explicitly (see the above find_project_packages() call).
+        //
+        assert (prj_pkgs.empty ());
+
         // The third form: upgrade of the specified dependencies.
         //
         // Only prompt if upgrading their dependencies.
@@ -873,7 +884,7 @@ namespace bdep
                   !o.patch (), // Upgrade by default unless patch requested.
                   (o.recursive () ? optional<bool> (true)  :
                    o.immediate () ? optional<bool> (false) : nullopt),
-                  prj_pkgs,
+                  package_locations () /* prj_pkgs  */,
                   dep_pkgs);
       }
       else if (o.upgrade () || o.patch ())
diff --git a/bdep/test.cli b/bdep/test.cli
index 18c9b04..a283b1b 100644
--- a/bdep/test.cli
+++ b/bdep/test.cli
@@ -41,9 +41,9 @@ namespace bdep
 
      If no project or package directory is specified, then the current working
      directory is assumed. If no configuration is specified, then the default
-     configuration is assumed. See \l{bdep-projects-configs(1)} for details on
-     specifying projects and configurations. Optional \c{\i{cfg-var}...} are
-     the additional configuration variables to pass to the build system.
+     configurations are assumed. See \l{bdep-projects-configs(1)} for details
+     on specifying projects and configurations. Optional \c{\i{cfg-var}...}
+     are the additional configuration variables to pass to the build system.
      "
   }
 
diff --git a/bdep/update.cli b/bdep/update.cli
index 4a66298..fc3df84 100644
--- a/bdep/update.cli
+++ b/bdep/update.cli
@@ -41,9 +41,9 @@ namespace bdep
 
      If no project or package directory is specified, then the current working
      directory is assumed. If no configuration is specified, then the default
-     configuration is assumed. See \l{bdep-projects-configs(1)} for details on
-     specifying projects and configurations. Optional \c{\i{cfg-var}...} are
-     the additional configuration variables to pass to the build system.
+     configurations are assumed. See \l{bdep-projects-configs(1)} for details
+     on specifying projects and configurations. Optional \c{\i{cfg-var}...}
+     are the additional configuration variables to pass to the build system.
      "
   }
 
diff --git a/tests/ci.testscript b/tests/ci.testscript
index d0407b5..bc3174f 100644
--- a/tests/ci.testscript
+++ b/tests/ci.testscript
@@ -102,7 +102,11 @@ windows = ($cxx.target.class == 'windows')
     $init -C @cfg1 &prj-cfg1/***;
     $init -C @cfg2 &prj-cfg2/***;
 
-    $* --all 2>'error: multiple configurations specified for ci' != 0
+    $* --all 2>>EOE != 0
+      error: package prj is initialized in multiple specified configurations
+        info: @cfg1
+        info: @cfg2
+      EOE
   }
 
   : no-commits
@@ -393,6 +397,26 @@ windows = ($cxx.target.class == 'windows')
       EOE
   }
 
+  : diff-configs
+  :
+  {
+    $clone_prj;
+    $init -C @cfg1 -d prj/libprj &prj-cfg1/***;
+
+    # While at it, test that we fail for uninitialized package.
+    #
+    $* -d prj/prj 2>>EOE != 0;
+      error: package prj is not initialized in any configuration
+      EOE
+
+    $init -C @cfg2 --config-type host -d prj/prj &prj-cfg2/***;
+
+    $* 2>>~%EOE%
+      %CI request is queued.*%
+      %reference: .+%
+      EOE
+  }
+
   : single
   :
   {
diff --git a/tests/config.testscript b/tests/config.testscript
index db02947..cb8ed7e 100644
--- a/tests/config.testscript
+++ b/tests/config.testscript
@@ -22,10 +22,10 @@ deinit += -d prj
     $clone_root_prj;
 
     $* create @cfg cfg-dir $config_cxx 2>>/"EOE" &cfg-dir/***;
-      created configuration @cfg $~/cfg-dir/ 1 default,forwarded,auto-synchronized
+      created configuration @cfg $~/cfg-dir/ 1 target default,forwarded,auto-synchronized
       EOE
 
-    $status 2>'error: package prj is not initialized in configuration @cfg' != 0;
+    $status 2>'error: package prj is not initialized in any default configuration(s)' != 0;
 
     $init @cfg 2>>/~"%EOE%";
       initializing in project $~/prj/
@@ -36,7 +36,7 @@ deinit += -d prj
     $status >'prj configured 0.1.0-a.0.19700101000000';
 
     $* list @cfg >>/"EOO";
-      @cfg $~/cfg-dir/ 1 default,forwarded,auto-synchronized
+      @cfg $~/cfg-dir/ 1 target default,forwarded,auto-synchronized
       EOO
 
     $update @cfg 2>>~%EOE%;
@@ -56,7 +56,7 @@ deinit += -d prj
     $clone_root_prj;
 
     $* create -- @cfg $config_cxx 2>>/"EOE" &prj-cfg/***;
-      created configuration @cfg $~/prj-cfg/ 1 default,forwarded,auto-synchronized
+      created configuration @cfg $~/prj-cfg/ 1 target default,forwarded,auto-synchronized
       EOE
 
     $init @cfg 2>>/~"%EOE%";
@@ -68,7 +68,7 @@ deinit += -d prj
     $status >'prj configured 0.1.0-a.0.19700101000000';
 
     $* list >>/"EOO";
-      @cfg $~/prj-cfg/ 1 default,forwarded,auto-synchronized
+      @cfg $~/prj-cfg/ 1 target default,forwarded,auto-synchronized
       EOO
 
     $update @cfg 2>>~%EOE%;
@@ -88,7 +88,7 @@ deinit += -d prj
     $clone_root_prj;
 
     $* create cfg $config_cxx 2>>/"EOE" &cfg/***;
-      created configuration $~/cfg/ 1 default,forwarded,auto-synchronized
+      created configuration $~/cfg/ 1 target default,forwarded,auto-synchronized
       EOE
 
     $init -c cfg 2>>/~"%EOE%";
@@ -100,7 +100,7 @@ deinit += -d prj
     $status >'prj configured 0.1.0-a.0.19700101000000';
 
     $* list >>/"EOO";
-      $~/cfg/ 1 default,forwarded,auto-synchronized
+      $~/cfg/ 1 target default,forwarded,auto-synchronized
       EOO
 
     $update -c cfg 2>>~%EOE%;
@@ -114,6 +114,38 @@ deinit += -d prj
       EOE
   }
 
+  : type
+  :
+  {
+    $clone_root_prj;
+
+    $* create --config-type host -- @cfg $config_cxx 2>>/"EOE" &prj-cfg/***;
+      created configuration @cfg $~/prj-cfg/ 1 host default,forwarded,auto-synchronized
+      EOE
+
+    $init @cfg 2>>/~"%EOE%";
+      initializing in project $~/prj/
+      synchronizing:
+      %  new prj.+19700101000000%
+      EOE
+
+    $status >'prj configured 0.1.0-a.0.19700101000000';
+
+    $* list @cfg >>/"EOO";
+      @cfg $~/prj-cfg/ 1 host default,forwarded,auto-synchronized
+      EOO
+
+    $update @cfg 2>>~%EOE%;
+      %(mkdir|c\+\+|ld) .+%{3}
+      EOE
+
+    $deinit @cfg 2>>/"EOE"
+      deinitializing in project $~/prj/
+      synchronizing:
+        drop prj
+      EOE
+  }
+
   : wipe
   :
   {
@@ -128,7 +160,7 @@ deinit += -d prj
       EOE
 
     $* create --wipe cfg $config_cxx 2>>/"EOE" &cfg/***
-      created configuration $~/cfg/ 1 default,forwarded,auto-synchronized
+      created configuration $~/cfg/ 1 target default,forwarded,auto-synchronized
       EOE
   }
 }
@@ -144,11 +176,11 @@ deinit += -d prj
   $new -C prj-cfg2 tmp2 $config_cxx 2>! &prj-cfg2/*** &tmp2/***;
 
   $* add @cfg1 prj-cfg1 2>>/"EOE";
-    added configuration @cfg1 $~/prj-cfg1/ 1 default,forwarded,auto-synchronized
+    added configuration @cfg1 $~/prj-cfg1/ 1 target default,forwarded,auto-synchronized
     EOE
 
   $* add @cfg2 prj-cfg2 2>>/"EOE";
-    added configuration @cfg2 $~/prj-cfg2/ 2 auto-synchronized
+    added configuration @cfg2 $~/prj-cfg2/ 2 target auto-synchronized
     EOE
 
   $init --all 2>>/~"%EOE%";
@@ -171,8 +203,8 @@ deinit += -d prj
     EOO
 
   $* list >>/"EOO";
-    @cfg1 $~/prj-cfg1/ 1 default,forwarded,auto-synchronized
-    @cfg2 $~/prj-cfg2/ 2 auto-synchronized
+    @cfg1 $~/prj-cfg1/ 1 target default,forwarded,auto-synchronized
+    @cfg2 $~/prj-cfg2/ 2 target auto-synchronized
     EOO
 
   $update --all 2>>~%EOE%;
@@ -201,7 +233,7 @@ deinit += -d prj
   $clone_root_prj;
 
   $* create -- @cfg $config_cxx &prj-cfg/*** 2>>/"EOE";
-    created configuration @cfg $~/prj-cfg/ 1 default,forwarded,auto-synchronized
+    created configuration @cfg $~/prj-cfg/ 1 target default,forwarded,auto-synchronized
     EOE
 
   $init @cfg 2>>/~"%EOE%";
@@ -213,7 +245,7 @@ deinit += -d prj
   mv prj-cfg prj-cfg2;
 
   $* move @cfg prj-cfg2 2>>/"EOE";
-    moved configuration @cfg $~/prj-cfg/ 1 to $~/prj-cfg2/
+    moved configuration @cfg $~/prj-cfg/ 1 target to $~/prj-cfg2/
     info: explicit sync command is required for changes to take effect
     EOE
 
@@ -234,7 +266,7 @@ deinit += -d prj
   $clone_root_prj;
 
   $* create -- @cfg $config_cxx 2>>/"EOE" &prj-cfg/***;
-    created configuration @cfg $~/prj-cfg/ 1 default,forwarded,auto-synchronized
+    created configuration @cfg $~/prj-cfg/ 1 target default,forwarded,auto-synchronized
     EOE
 
   $init @cfg 2>>/~"%EOE%";
@@ -244,7 +276,7 @@ deinit += -d prj
     EOE
 
   $* rename @cfg cfg2 2>>/"EOE";
-    renamed configuration @cfg $~/prj-cfg/ 1 to @cfg2
+    renamed configuration @cfg $~/prj-cfg/ 1 target to @cfg2
     EOE
 
   $update @cfg2 2>>~%EOE%;
@@ -283,7 +315,7 @@ deinit += -d prj
     EOE
 
   $* remove @cfg1 2>>/"EOE";
-    removed configuration @cfg1 $~/prj-cfg1/ 1
+    removed configuration @cfg1 $~/prj-cfg1/ 1 target
     EOE
 
   $status --all >>EOO;
@@ -291,7 +323,7 @@ deinit += -d prj
     EOO
 
   $* list >>/"EOO";
-    @cfg2 $~/prj-cfg2/ 2 auto-synchronized
+    @cfg2 $~/prj-cfg2/ 2 target auto-synchronized
     EOO
 
   $update 2>>/"EOE" != 0;
@@ -300,12 +332,12 @@ deinit += -d prj
     EOE
 
   $* set @cfg2 --default --forward --no-auto-sync 2>>/"EOE";
-    updated configuration @cfg2 $~/prj-cfg2/ 2 default,forwarded
+    updated configuration @cfg2 $~/prj-cfg2/ 2 target default,forwarded
     info: explicit sync command is required for changes to take effect
     EOE
 
   $* list >>/"EOO";
-    @cfg2 $~/prj-cfg2/ 2 default,forwarded
+    @cfg2 $~/prj-cfg2/ 2 target default,forwarded
     EOO
 
   $update 2>>~%EOE%;
@@ -318,3 +350,16 @@ deinit += -d prj
       drop prj
     EOE
 }
+
+: link
+:
+{
+  $clone_root_prj;
+
+  $* create -- @cfg1 $config_cxx 2>! &prj-cfg1/***;
+  $* create -- @cfg2 $config_cxx 2>! &prj-cfg2/***;
+
+  $* link @cfg1 @cfg2 2>>EOE
+    linked configuration @cfg1 (target) with configuration @cfg2 (target)
+    EOE
+}
diff --git a/tests/init.testscript b/tests/init.testscript
index ba67b56..5192145 100644
--- a/tests/init.testscript
+++ b/tests/init.testscript
@@ -27,7 +27,7 @@ deinit += -d prj
 
     $* -C @cfg $config_cxx 'config.cc.poptions=-DTEST' -- '?sys:libprj/*' 2>>/~"%EOE%" &prj-cfg/***;
       initializing in project $~/prj/
-      created configuration @cfg $~/prj-cfg/ 1 default,forwarded,auto-synchronized
+      created configuration @cfg $~/prj-cfg/ 1 target default,forwarded,auto-synchronized
       synchronizing:
       %  configure sys:libprj.*%
       %  new prj.+19700101000000%
@@ -67,7 +67,7 @@ deinit += -d prj
 
     $* -C @cfg -- $config_cxx 'config.cc.poptions=-DTEST' -- '?sys:libprj/*' 2>>/~"%EOE%" &prj-cfg/***;
       initializing in project $~/prj/
-      created configuration @cfg $~/prj-cfg/ 1 default,forwarded,auto-synchronized
+      created configuration @cfg $~/prj-cfg/ 1 target default,forwarded,auto-synchronized
       synchronizing:
       %  configure sys:libprj.*%
       %  new prj.+19700101000000%
@@ -99,7 +99,7 @@ deinit += -d prj
 
     $* -C @cfg -- -- '?sys:libprj/*' 2>>/~"%EOE%" &prj-cfg/***;
       initializing in project $~/prj/
-      created configuration @cfg $~/prj-cfg/ 1 default,forwarded,auto-synchronized
+      created configuration @cfg $~/prj-cfg/ 1 target default,forwarded,auto-synchronized
       synchronizing:
       %  configure sys:libprj.*%
       %  new prj.+19700101000000%
@@ -125,20 +125,20 @@ deinit += -d prj
 
   # Pre-create configurations.
   #
-  $new  -C prj-cfg1    tmp $config_cxx 2>! &prj-cfg1/*** &tmp/***;
-  $init -C prj-cfg2 -d tmp $config_cxx 2>! &prj-cfg2/***;
+  $new  -C prj-cfg1 --no-default          tmp $config_cxx 2>! &prj-cfg1/*** &tmp/***;
+  $init -C prj-cfg2 --config-type host -d tmp $config_cxx 2>! &prj-cfg2/***;
 
   $* -A @cfg1 '?sys:libprj/*' 2>>/~"%EOE%";
     initializing in project $~/prj/
-    added configuration @cfg1 $~/prj-cfg1/ 1 default,forwarded,auto-synchronized
+    added configuration @cfg1 $~/prj-cfg1/ 1 target default,forwarded,auto-synchronized
     synchronizing:
     %  configure sys:libprj.*%
     %  new prj.+19700101000000%
     EOE
 
-  $* -A prj-cfg2 @cfg2 '?sys:libprj/*' 2>>/~"%EOE%";
+  $* -A prj-cfg2 --no-default @cfg2 '?sys:libprj/*' 2>>/~"%EOE%";
     initializing in project $~/prj/
-    added configuration @cfg2 $~/prj-cfg2/ 2 auto-synchronized
+    added configuration @cfg2 $~/prj-cfg2/ 2 host auto-synchronized
     synchronizing:
     %  configure sys:libprj.*%
     %  new prj.+19700101000000%
@@ -188,7 +188,7 @@ deinit += -d prj
 
   $* -C @cfg $config_cxx 2>>/~"%EOE%" &prj-cfg/***;
     initializing in project $~/prj/
-    created configuration @cfg $~/prj-cfg/ 1 default,forwarded,auto-synchronized
+    created configuration @cfg $~/prj-cfg/ 1 target default,forwarded,auto-synchronized
     synchronizing:
     %  new prj.+19700101000000%
     EOE
diff --git a/tests/new.testscript b/tests/new.testscript
index 4d98feb..727f338 100644
--- a/tests/new.testscript
+++ b/tests/new.testscript
@@ -1836,7 +1836,7 @@ subdir=hello,no-subdir-source                                        \
   {
     $* -C prj-config @cfg prj cc $config_cxx 2>>/~"%EOE%" &prj/*** &prj-config/***;
       created new executable project prj in $~/prj/
-      created configuration @cfg $~/prj-config/ 1 default,forwarded,auto-synchronized
+      created configuration @cfg $~/prj-config/ 1 target default,forwarded,auto-synchronized
       synchronizing:
       %  new prj.+19700101000000%
       EOE
@@ -1858,7 +1858,7 @@ subdir=hello,no-subdir-source                                        \
   {
     $* -C -@cfg prj cc $config_cxx 2>>/~"%EOE%" &prj/*** &prj-cfg/***;
       created new executable project prj in $~/prj/
-      created configuration @cfg $~/prj-cfg/ 1 default,forwarded,auto-synchronized
+      created configuration @cfg $~/prj-cfg/ 1 target default,forwarded,auto-synchronized
       synchronizing:
       %  new prj.+19700101000000%
       EOE
diff --git a/tests/publish.testscript b/tests/publish.testscript
index 8f5ec85..07c3632 100644
--- a/tests/publish.testscript
+++ b/tests/publish.testscript
@@ -33,7 +33,7 @@ g = git -C prj >! 2>!
 # duplicate submissions. We will use unique version for each test,
 # incrementing the patch version for 1.0.X.
 #
-# Next version to use: 1.0.20
+# Next version to use: 1.0.22
 #
 
 # Normally we disable the progress indication that complicates stderr output
@@ -104,7 +104,11 @@ g = git -C prj >! 2>!
       $init -C @cfg1 &prj-cfg1/***;
       $init -C @cfg2 &prj-cfg2/***;
 
-      $* --all 2>'error: multiple configurations specified for publish' != 0
+      $* --all 2>>EOE != 0
+        error: package prj is initialized in multiple specified configurations
+          info: @cfg1
+          info: @cfg2
+        EOE
     }
 
     : snapshot
@@ -152,6 +156,42 @@ g = git -C prj >! 2>!
         EOE
     }
 
+    : diff-configs
+    :
+    {
+      $clone_prj;
+      sed -i -e 's/^(version:) .*$/\1 1.0.20/' prj/libprj/manifest;
+      sed -i -e 's/^(version:) .*$/\1 1.0.20/' prj/prj/manifest;
+
+      $init -C @cfg1                    -d prj/libprj &prj-cfg1/***;
+      $init -C @cfg2 --config-type host -d prj/prj    &prj-cfg2/***;
+
+      $* 2>>~%EOE%
+        %package submission is queued(: \.*libprj/1.0.20)?%d
+        %reference: .{12}%
+        %package submission is queued(: \.*prj/1.0.20)?%d
+        %reference: .{12}%
+        EOE
+    }
+
+    : diff-configs-forward
+    :
+    {
+      $clone_prj;
+      sed -i -e 's/^(version:) .*$/\1 1.0.21/' prj/libprj/manifest;
+      sed -i -e 's/^(version:) .*$/\1 1.0.21/' prj/prj/manifest;
+
+      $init -C @cfg1                    --no-default --forward -d prj/libprj &prj-cfg1/***;
+      $init -C @cfg2 --config-type host --no-default --forward -d prj/prj    &prj-cfg2/***;
+
+      $* --forward 2>>~%EOE%
+        %package submission is queued(: \.*libprj/1.0.21)?%d
+        %reference: .{12}%
+        %package submission is queued(: \.*prj/1.0.21)?%d
+        %reference: .{12}%
+        EOE
+    }
+
     : single
     :
     {
diff --git a/tests/update.testscript b/tests/update.testscript
index 7e03238..3823b9d 100644
--- a/tests/update.testscript
+++ b/tests/update.testscript
@@ -88,3 +88,46 @@ deinit += -d prj
       drop pkg2
     EOE
 }
+
+: multi-default-cfg
+:
+{
+  $new -t empty prj &prj/***;
+
+  $new --package pkg1 -d prj;
+  $new --package pkg2 -d prj;
+
+  $init -C @cfg1 -d prj/pkg1                    &prj-cfg1/***;
+  $init -C @cfg2 -d prj/pkg2 --config-type host &prj-cfg2/***;
+
+  # Update.
+  #
+  $* -d prj 2>>~%EOE%;
+    in configuration @cfg1:
+    %(mkdir|c\+\+|ld) .+pkg1.+%{3}
+
+    in configuration @cfg2:
+    %(mkdir|c\+\+|ld) .+pkg2.+%{3}
+    EOE
+
+  # Clean.
+  #
+  $clean -d prj 2>>~%EOE%;
+    in configuration @cfg1:
+    %rm .+pkg1.+%{3}
+
+    in configuration @cfg2:
+    %rm .+pkg2.+%{3}
+    EOE
+
+  $deinit 2>>/"EOE"
+    deinitializing in project $~/prj/
+    in configuration @cfg1:
+    synchronizing:
+      drop pkg1
+
+    in configuration @cfg2:
+    synchronizing:
+      drop pkg2
+    EOE
+}