Introduce notion of build context

All non-const global state is now in class context and we can now have
multiple independent builds going on at the same time.

21 files changed, 326 insertions, 263 deletions

diff --git a/build2/b.cxx b/build2/b.cxx
index f359dbc..51b024e 100644
--- a/build2/b.cxx
+++ b/build2/b.cxx
@@ -107,12 +107,15 @@ namespace build2
 
       if (ops.structured_result ())
       {
+        const target& t (at.as_target ());
+        context& ctx (t.ctx);
+
         cout << at.state
-             << ' ' << current_mif->name
-             << ' ' << current_inner_oif->name;
+             << ' ' << ctx.current_mif->name
+             << ' ' << ctx.current_inner_oif->name;
 
-        if (current_outer_oif != nullptr)
-          cout << '(' << current_outer_oif->name << ')';
+        if (ctx.current_outer_oif != nullptr)
+          cout << '(' << ctx.current_outer_oif->name << ')';
 
         // There are two ways one may wish to identify the target of the
         // operation: as something specific but inherently non-portable (say,
@@ -131,7 +134,7 @@ namespace build2
         stream_verbosity sv (stream_verb (cout));
         stream_verb (cout, stream_verbosity (1, 0));
 
-        cout << ' ' << at.as_target () << endl;
+        cout << ' ' << t << endl;
 
         stream_verb (cout, sv);
       }
@@ -222,6 +225,8 @@ main (int argc, char* argv[])
          << system_error (errno, generic_category ()); // Sanitize.
 #endif
 
+  scheduler sched;
+
   // Parse the command line.
   //
   try
@@ -475,7 +480,6 @@ main (int argc, char* argv[])
     //
     init (&::terminate,
           argv[0],
-          !ops.serial_stop (), ops.dry_run (),
           (ops.mtime_check ()    ? optional<bool> (true)  :
            ops.no_mtime_check () ? optional<bool> (false) : nullopt),
           (ops.config_sub_specified ()
@@ -490,7 +494,7 @@ main (int argc, char* argv[])
     // current and child processes unless we are in the stop mode. Failed that
     // we may have multiple dialog boxes popping up.
     //
-    if (keep_going)
+    if (!ops.serial_stop ())
       SetErrorMode (SetErrorMode (0) | // Returns the current mode.
                     SEM_FAILCRITICALERRORS | SEM_NOGPFAULTERRORBOX);
 #endif
@@ -582,14 +586,16 @@ main (int argc, char* argv[])
         fail << "invalid --max-jobs|-J value";
     }
 
-    sched.startup (jobs,
-                   1,
-                   max_jobs,
-                   jobs * ops.queue_depth (),
-                   (ops.max_stack_specified ()
-                    ? optional<size_t> (ops.max_stack () * 1024)
-                    : nullopt));
+     sched.startup (jobs,
+                    1,
+                    max_jobs,
+                    jobs * ops.queue_depth (),
+                    (ops.max_stack_specified ()
+                     ? optional<size_t> (ops.max_stack () * 1024)
+                     : nullopt));
 
+    // @@ CTX: should these be per-context?
+    //
     variable_cache_mutex_shard_size = sched.shard_size ();
     variable_cache_mutex_shard.reset (
       new shared_mutex[variable_cache_mutex_shard_size]);
@@ -606,10 +612,21 @@ main (int argc, char* argv[])
       trace << "jobs: " << jobs;
     }
 
-    // Set the build state before parsing the buildspec since it relies on
-    // global scope being setup.
+    // Set the build context before parsing the buildspec since it relies on
+    // the global scope being setup. We reset it for every meta-operation (see
+    // below).
     //
-    variable_overrides var_ovs (reset (cmd_vars));
+    unique_ptr<context> ctx;
+    auto new_context = [&ctx, &sched, &cmd_vars]
+    {
+      ctx = nullptr; // Free first.
+      ctx.reset (new context (sched,
+                              cmd_vars,
+                              ops.dry_run (),
+                              !ops.serial_stop () /* keep_going */));
+    };
+
+    new_context ();
 
     // Parse the buildspec.
     //
@@ -619,7 +636,7 @@ main (int argc, char* argv[])
       istringstream is (args);
       is.exceptions (istringstream::failbit | istringstream::badbit);
 
-      parser p;
+      parser p (*ctx);
       bspec = p.parse_buildspec (is, path ("<buildspec>"));
     }
     catch (const io_error&)
@@ -745,13 +762,13 @@ main (int argc, char* argv[])
       else
         opspecs.assign (lifted, 1);
 
-      // Reset the build state for each meta-operation since there is no
+      // Reset the build context for each meta-operation since there is no
       // guarantee their assumptions (e.g., in the load callback) are
       // compatible.
       //
       if (dirty)
       {
-        var_ovs = reset (cmd_vars);
+        new_context ();
         dirty = false;
       }
 
@@ -769,24 +786,25 @@ main (int argc, char* argv[])
       values& mparams (lifted == nullptr ? mit->params : lifted->params);
       string  mname   (lifted == nullptr ? mit->name   : lifted->name);
 
-      current_mname = mname; // Set early.
+      ctx->current_mname = mname; // Set early.
 
       if (!mname.empty ())
       {
-        if (meta_operation_id m = meta_operation_table.find (mname))
+        if (meta_operation_id m = ctx->meta_operation_table.find (mname))
         {
           // Can modify params, opspec, change meta-operation name.
           //
-          if (auto f = meta_operation_table[m].process)
-            mname = current_mname =
-              f (var_ovs, mparams, opspecs, lifted != nullptr, l);
+          if (auto f = ctx->meta_operation_table[m].process)
+            mname = ctx->current_mname = f (
+              *ctx, mparams, opspecs, lifted != nullptr, l);
         }
       }
 
       // Expose early so can be used during bootstrap (with the same
       // limitations as for pre-processing).
       //
-      global_scope->rw ().assign (var_build_meta_operation) = mname;
+      scope& gs (ctx->global_scope.rw ());
+      gs.assign (ctx->var_build_meta_operation) = mname;
 
       for (auto oit (opspecs.begin ()); oit != opspecs.end (); ++oit)
       {
@@ -797,7 +815,7 @@ main (int argc, char* argv[])
         const values& oparams (lifted == nullptr ? os.params : values ());
         const string& oname   (lifted == nullptr ? os.name   : empty_string);
 
-        current_oname = oname; // Set early.
+        ctx->current_oname = oname; // Set early.
 
         if (lifted != nullptr)
           lifted = nullptr; // Clear for the next iteration.
@@ -817,9 +835,11 @@ main (int argc, char* argv[])
 
         // Return true if this operation is lifted.
         //
-        auto lift = [&oname, &mname, &os, &mit, &lifted, &skip, &l, &trace] ()
+        auto lift = [&ctx,
+                     &oname, &mname,
+                     &os, &mit, &lifted, &skip, &l, &trace] ()
         {
-          meta_operation_id m (meta_operation_table.find (oname));
+          meta_operation_id m (ctx->meta_operation_table.find (oname));
 
           if (m != 0)
           {
@@ -978,7 +998,7 @@ main (int argc, char* argv[])
               // Handle a forwarded configuration. Note that if we've changed
               // out_root then we also have to remap out_base.
               //
-              out_root = bootstrap_fwd (src_root, altn);
+              out_root = bootstrap_fwd (*ctx, src_root, altn);
               if (src_root != out_root)
               {
                 out_base = out_root / out_base.leaf (src_root);
@@ -1023,8 +1043,7 @@ main (int argc, char* argv[])
           // use to the bootstrap files (other than src-root.build, which,
           // BTW, doesn't need to exist if src_root == out_root).
           //
-          scope& rs (
-            create_root (*scope::global_, out_root, src_root)->second);
+          scope& rs (create_root (gs, out_root, src_root)->second);
 
           bool bstrapped (bootstrapped (rs));
 
@@ -1034,7 +1053,7 @@ main (int argc, char* argv[])
 
             // See if the bootstrap process set/changed src_root.
             //
-            value& v (rs.assign (var_src_root));
+            value& v (rs.assign (ctx->var_src_root));
 
             if (v)
             {
@@ -1062,8 +1081,8 @@ main (int argc, char* argv[])
                        << (forwarded ? "forwarded " : "specified ")
                        << src_root;
 
-                new_src_root = src_root;
-                old_src_root = move (p);
+                ctx->new_src_root = src_root;
+                ctx->old_src_root = move (p);
                 p = src_root;
               }
             }
@@ -1096,7 +1115,7 @@ main (int argc, char* argv[])
             // command line and import).
             //
             if (forwarded)
-              rs.assign (var_forwarded) = true;
+              rs.assign (ctx->var_forwarded) = true;
 
             // Sync local variable that are used below with actual values.
             //
@@ -1133,7 +1152,7 @@ main (int argc, char* argv[])
           // Note that the subprojects variable has already been processed
           // and converted to a map by the bootstrap_src() call above.
           //
-          if (auto l = rs.vars[var_subprojects])
+          if (auto l = rs.vars[ctx->var_subprojects])
           {
             for (const auto& p: cast<subprojects> (l))
             {
@@ -1148,8 +1167,8 @@ main (int argc, char* argv[])
           // all be known. We store the combined action id in uint8_t;
           // see <operation> for details.
           //
-          assert (operation_table.size () <= 128);
-          assert (meta_operation_table.size () <= 128);
+          assert (ctx->operation_table.size () <= 128);
+          assert (ctx->meta_operation_table.size () <= 128);
 
           // Since we now know all the names of meta-operations and
           // operations, "lift" names that we assumed (from buildspec syntax)
@@ -1166,7 +1185,7 @@ main (int argc, char* argv[])
 
             if (!mname.empty ())
             {
-              m = meta_operation_table.find (mname);
+              m = ctx->meta_operation_table.find (mname);
 
               if (m == 0)
                 fail (l) << "unknown meta-operation " << mname;
@@ -1174,7 +1193,7 @@ main (int argc, char* argv[])
 
             if (!oname.empty ())
             {
-              o = operation_table.find (oname);
+              o = ctx->operation_table.find (oname);
 
               if (o == 0)
                 fail (l) << "unknown operation " << oname;
@@ -1197,7 +1216,7 @@ main (int argc, char* argv[])
 
               if (mif == nullptr)
                 fail (l) << "target " << tn << " does not support meta-"
-                         << "operation " << meta_operation_table[m].name;
+                         << "operation " << ctx->meta_operation_table[m].name;
             }
             //
             // Otherwise, check that all the targets in a meta-operation
@@ -1210,7 +1229,7 @@ main (int argc, char* argv[])
 
               if (mi == nullptr)
                 fail (l) << "target " << tn << " does not support meta-"
-                         << "operation " << meta_operation_table[mid].name;
+                         << "operation " << ctx->meta_operation_table[mid].name;
 
               if (mi != mif)
                 fail (l) << "different implementations of meta-operation "
@@ -1238,7 +1257,7 @@ main (int argc, char* argv[])
                 fail (l) << "unexpected parameters for meta-operation "
                          << mif->name;
 
-              set_current_mif (*mif);
+              ctx->current_meta_operation (*mif);
               dirty = true;
             }
 
@@ -1247,16 +1266,16 @@ main (int argc, char* argv[])
             //
             if (oid == 0)
             {
-              auto lookup =
-                [&rs, &l, &tn] (operation_id o) -> const operation_info*
-                {
-                  const operation_info* r (rs.root_extra->operations[o]);
+              auto lookup = [&ctx, &rs, &l, &tn] (operation_id o) ->
+                const operation_info*
+              {
+                const operation_info* r (rs.root_extra->operations[o]);
 
-                  if (r == nullptr)
-                    fail (l) << "target " << tn << " does not support "
-                             << "operation " << operation_table[o];
-                  return r;
-                };
+                if (r == nullptr)
+                  fail (l) << "target " << tn << " does not support "
+                           << "operation " << ctx->operation_table[o];
+                return r;
+              };
 
               if (o == 0)
                 o = default_id;
@@ -1324,19 +1343,19 @@ main (int argc, char* argv[])
             //
             else
             {
-              auto check =
-                [&rs, &l, &tn] (operation_id o, const operation_info* i)
-                {
-                  const operation_info* r (rs.root_extra->operations[o]);
+              auto check = [&ctx, &rs, &l, &tn] (operation_id o,
+                                                 const operation_info* i)
+              {
+                const operation_info* r (rs.root_extra->operations[o]);
 
-                  if (r == nullptr)
-                    fail (l) << "target " << tn << " does not support "
-                             << "operation " << operation_table[o];
+                if (r == nullptr)
+                  fail (l) << "target " << tn << " does not support "
+                           << "operation " << ctx->operation_table[o];
 
-                  if (r != i)
-                    fail (l) << "different implementations of operation "
-                             << i->name << " in the same operation batch";
-                };
+                if (r != i)
+                  fail (l) << "different implementations of operation "
+                           << i->name << " in the same operation batch";
+              };
 
               check (orig_oid, oif);
 
@@ -1406,7 +1425,7 @@ main (int argc, char* argv[])
             trace << "  out_root:     " << out_root;
             trace << "  src_root:     " << src_root;
             trace << "  forwarded:    " << (forwarded ? "true" : "false");
-            if (auto l = rs.vars[var_amalgamation])
+            if (auto l = rs.vars[ctx->var_amalgamation])
             {
               trace << "  amalgamation: " << cast<dir_path> (l);
               trace << "  strong scope: " << *rs.strong_scope ();
@@ -1427,9 +1446,9 @@ main (int argc, char* argv[])
           // So we split it into two passes.
           //
           {
-            auto& sm (scope_map::instance);
+            auto& sm (ctx->scopes.rw ());
 
-            for (const variable_override& o: var_ovs)
+            for (const variable_override& o: ctx->var_overrides)
             {
               if (o.ovr.visibility != variable_visibility::normal)
                 continue;
@@ -1450,7 +1469,7 @@ main (int argc, char* argv[])
               v = o.val;
             }
 
-            for (const variable_override& o: var_ovs)
+            for (const variable_override& o: ctx->var_overrides)
             {
               // Ours is either project (%foo) or scope (/foo).
               //
@@ -1504,7 +1523,7 @@ main (int argc, char* argv[])
           // building before we know how to for all the targets in this
           // operation batch.
           //
-          const scope& bs (scopes.find (ts.out_base));
+          const scope& bs (ctx->scopes.find (ts.out_base));
 
           // Find the target type and extract the extension.
           //
@@ -1546,7 +1565,7 @@ main (int argc, char* argv[])
         } // target
 
         if (dump_load)
-          dump ();
+          dump (*ctx);
 
         // Finally, match the rules and perform the operation.
         //
@@ -1558,7 +1577,7 @@ main (int argc, char* argv[])
           if (mif->operation_pre != nullptr)
             mif->operation_pre (mparams, pre_oid); // Cannot be translated.
 
-          set_current_oif (*pre_oif, oif);
+          ctx->current_operation (*pre_oif, oif);
 
           action a (mid, pre_oid, oid);
 
@@ -1570,7 +1589,7 @@ main (int argc, char* argv[])
               mif->match (mparams, a, tgs, diag, true /* progress */);
 
             if (dump_match)
-              dump (a);
+              dump (*ctx, a);
 
             if (mif->execute != nullptr && !ops.match_only ())
               mif->execute (mparams, a, tgs, diag, true /* progress */);
@@ -1585,7 +1604,7 @@ main (int argc, char* argv[])
           tgs.reset ();
         }
 
-        set_current_oif (*oif, outer_oif);
+        ctx->current_operation (*oif, outer_oif);
 
         action a (mid, oid, oif->outer_id);
 
@@ -1597,7 +1616,7 @@ main (int argc, char* argv[])
             mif->match (mparams, a, tgs, diag, true /* progress */);
 
           if (dump_match)
-            dump (a);
+            dump (*ctx, a);
 
           if (mif->execute != nullptr && !ops.match_only ())
             mif->execute (mparams, a, tgs, diag, true /* progress */);
@@ -1613,7 +1632,7 @@ main (int argc, char* argv[])
           if (mif->operation_pre != nullptr)
             mif->operation_pre (mparams, post_oid); // Cannot be translated.
 
-          set_current_oif (*post_oif, oif);
+          ctx->current_operation (*post_oif, oif);
 
           action a (mid, post_oid, oid);
 
@@ -1625,7 +1644,7 @@ main (int argc, char* argv[])
               mif->match (mparams, a, tgs, diag, true /* progress */);
 
             if (dump_match)
-              dump (a);
+              dump (*ctx, a);
 
             if (mif->execute != nullptr && !ops.match_only ())
               mif->execute (mparams, a, tgs, diag, true /* progress */);
diff --git a/build2/bin/init.cxx b/build2/bin/init.cxx
index b46d643..4e80834 100644
--- a/build2/bin/init.cxx
+++ b/build2/bin/init.cxx
@@ -56,7 +56,7 @@ namespace build2
       // Target is a string and not target_triplet because it can be
       // specified by the user.
       //
-      auto& vp (var_pool.rw (rs));
+      auto& vp (rs.ctx.var_pool.rw (rs));
 
       vp.insert<string>    ("config.bin.target",   true);
       vp.insert<string>    ("config.bin.pattern",  true);
@@ -266,7 +266,7 @@ namespace build2
         // config.bin.target
         //
         {
-          const variable& var (var_pool["config.bin.target"]);
+          const variable& var (rs.ctx.var_pool["config.bin.target"]);
 
           // We first see if the value was specified via the configuration
           // mechanism.
@@ -343,7 +343,7 @@ namespace build2
         // config.bin.pattern
         //
         {
-          const variable& var (var_pool["config.bin.pattern"]);
+          const variable& var (rs.ctx.var_pool["config.bin.pattern"]);
 
           // We first see if the value was specified via the configuration
           // mechanism.
@@ -568,7 +568,7 @@ namespace build2
       //
       if (first)
       {
-        auto& v (var_pool.rw (rs));
+        auto& v (rs.ctx.var_pool.rw (rs));
 
         v.insert<process_path> ("bin.ar.path");
         v.insert<process_path> ("bin.ranlib.path");
@@ -744,7 +744,7 @@ namespace build2
       //
       if (first)
       {
-        auto& v (var_pool.rw (rs));
+        auto& v (rs.ctx.var_pool.rw (rs));
 
         v.insert<process_path> ("bin.ld.path");
         v.insert<path>         ("config.bin.ld", true);
@@ -857,7 +857,7 @@ namespace build2
       //
       if (first)
       {
-        auto& v (var_pool.rw (rs));
+        auto& v (rs.ctx.var_pool.rw (rs));
 
         v.insert<process_path> ("bin.rc.path");
         v.insert<path>         ("config.bin.rc", true);
diff --git a/build2/bin/target.cxx b/build2/bin/target.cxx
index ec4a0ef..9074317 100644
--- a/build2/bin/target.cxx
+++ b/build2/bin/target.cxx
@@ -88,11 +88,12 @@ namespace build2
     //
     template <typename M, typename G>
     static target*
-    m_factory (const target_type&, dir_path dir, dir_path out, string n)
+    m_factory (context& ctx,
+               const target_type&, dir_path dir, dir_path out, string n)
     {
-      const G* g (targets.find<G> (dir, out, n));
+      const G* g (ctx.targets.find<G> (dir, out, n));
 
-      M* m (new M (move (dir), move (out), move (n)));
+      M* m (new M (ctx, move (dir), move (out), move (n)));
       m->group = g;
 
       return m;
@@ -104,8 +105,8 @@ namespace build2
       &objx::static_type,
       &m_factory<obje, obj>,
       nullptr, /* fixed_extension */
-      &target_extension_var<var_extension, nullptr>,
-      &target_pattern_var<var_extension, nullptr>,
+      &target_extension_var<nullptr>,
+      &target_pattern_var<nullptr>,
       nullptr,
       &target_search, // Note: not _file(); don't look for an existing file.
       false
@@ -117,8 +118,8 @@ namespace build2
       &bmix::static_type,
       &m_factory<bmie, bmi>,
       nullptr, /* fixed_extension */
-      &target_extension_var<var_extension, nullptr>,
-      &target_pattern_var<var_extension, nullptr>,
+      &target_extension_var<nullptr>,
+      &target_pattern_var<nullptr>,
       nullptr,
       &target_search, // Note: not _file(); don't look for an existing file.
       false
@@ -130,8 +131,8 @@ namespace build2
       &hbmix::static_type,
       &m_factory<hbmie, hbmi>,
       nullptr, /* fixed_extension */
-      &target_extension_var<var_extension, nullptr>,
-      &target_pattern_var<var_extension, nullptr>,
+      &target_extension_var<nullptr>,
+      &target_pattern_var<nullptr>,
       nullptr,
       &target_search, // Note: not _file(); don't look for an existing file.
       false
@@ -143,8 +144,8 @@ namespace build2
       &objx::static_type,
       &m_factory<obja, obj>,
       nullptr, /* fixed_extension */
-      &target_extension_var<var_extension, nullptr>,
-      &target_pattern_var<var_extension, nullptr>,
+      &target_extension_var<nullptr>,
+      &target_pattern_var<nullptr>,
       nullptr,
       &target_search, // Note: not _file(); don't look for an existing file.
       false
@@ -156,8 +157,8 @@ namespace build2
       &bmix::static_type,
       &m_factory<bmia, bmi>,
       nullptr, /* fixed_extension */
-      &target_extension_var<var_extension, nullptr>,
-      &target_pattern_var<var_extension, nullptr>,
+      &target_extension_var<nullptr>,
+      &target_pattern_var<nullptr>,
       nullptr,
       &target_search, // Note: not _file(); don't look for an existing file.
       false
@@ -169,8 +170,8 @@ namespace build2
       &hbmix::static_type,
       &m_factory<hbmia, hbmi>,
       nullptr, /* fixed_extension */
-      &target_extension_var<var_extension, nullptr>,
-      &target_pattern_var<var_extension, nullptr>,
+      &target_extension_var<nullptr>,
+      &target_pattern_var<nullptr>,
       nullptr,
       &target_search, // Note: not _file(); don't look for an existing file.
       false
@@ -182,8 +183,8 @@ namespace build2
       &objx::static_type,
       &m_factory<objs, obj>,
       nullptr, /* fixed_extension */
-      &target_extension_var<var_extension, nullptr>,
-      &target_pattern_var<var_extension, nullptr>,
+      &target_extension_var<nullptr>,
+      &target_pattern_var<nullptr>,
       nullptr,
       &target_search, // Note: not _file(); don't look for an existing file.
       false
@@ -195,8 +196,8 @@ namespace build2
       &bmix::static_type,
       &m_factory<bmis, bmi>,
       nullptr, /* fixed_extension */
-      &target_extension_var<var_extension, nullptr>,
-      &target_pattern_var<var_extension, nullptr>,
+      &target_extension_var<nullptr>,
+      &target_pattern_var<nullptr>,
       nullptr,
       &target_search, // Note: not _file(); don't look for an existing file.
       false
@@ -208,8 +209,8 @@ namespace build2
       &hbmix::static_type,
       &m_factory<hbmis, hbmi>,
       nullptr, /* fixed_extension */
-      &target_extension_var<var_extension, nullptr>,
-      &target_pattern_var<var_extension, nullptr>,
+      &target_extension_var<nullptr>,
+      &target_pattern_var<nullptr>,
       nullptr,
       &target_search, // Note: not _file(); don't look for an existing file.
       false
@@ -221,8 +222,8 @@ namespace build2
       &libux::static_type,
       &target_factory<libue>,
       nullptr, /* fixed_extension */
-      &target_extension_var<var_extension, nullptr>,
-      &target_pattern_var<var_extension, nullptr>,
+      &target_extension_var<nullptr>,
+      &target_pattern_var<nullptr>,
       nullptr,
       &target_search, // Note: not _file(); don't look for an existing file.
       false
@@ -234,8 +235,8 @@ namespace build2
       &libux::static_type,
       &m_factory<libua, libul>,
       nullptr, /* fixed_extension */
-      &target_extension_var<var_extension, nullptr>,
-      &target_pattern_var<var_extension, nullptr>,
+      &target_extension_var<nullptr>,
+      &target_pattern_var<nullptr>,
       nullptr,
       &target_search, // Note: not _file(); don't look for an existing file.
       false
@@ -247,8 +248,8 @@ namespace build2
       &libux::static_type,
       &m_factory<libus, libul>,
       nullptr, /* fixed_extension */
-      &target_extension_var<var_extension, nullptr>,
-      &target_pattern_var<var_extension, nullptr>,
+      &target_extension_var<nullptr>,
+      &target_pattern_var<nullptr>,
       nullptr,
       &target_search, // Note: not _file(); don't look for an existing file.
       false
@@ -258,21 +259,22 @@ namespace build2
     //
     template <typename G, typename E, typename A, typename S>
     static target*
-    g_factory (const target_type&, dir_path dir, dir_path out, string n)
+    g_factory (context& ctx,
+               const target_type&, dir_path dir, dir_path out, string n)
     {
       // Casts are MT-aware (during serial load).
       //
-      E* e (phase == run_phase::load
-            ? const_cast<E*> (targets.find<E> (dir, out, n))
+      E* e (ctx.phase == run_phase::load
+            ? const_cast<E*> (ctx.targets.find<E> (dir, out, n))
             : nullptr);
-      A* a (phase == run_phase::load
-            ? const_cast<A*> (targets.find<A> (dir, out, n))
+      A* a (ctx.phase == run_phase::load
+            ? const_cast<A*> (ctx.targets.find<A> (dir, out, n))
             : nullptr);
-      S* s (phase == run_phase::load
-            ? const_cast<S*> (targets.find<S> (dir, out, n))
+      S* s (ctx.phase == run_phase::load
+            ? const_cast<S*> (ctx.targets.find<S> (dir, out, n))
             : nullptr);
 
-      G* g (new G (move (dir), move (out), move (n)));
+      G* g (new G (ctx, move (dir), move (out), move (n)));
 
       if (e != nullptr) e->group = g;
       if (a != nullptr) a->group = g;
@@ -323,16 +325,17 @@ namespace build2
     // The same as g_factory() but without E.
     //
     static target*
-    libul_factory (const target_type&, dir_path dir, dir_path out, string n)
+    libul_factory (context& ctx,
+                   const target_type&, dir_path dir, dir_path out, string n)
     {
-      libua* a (phase == run_phase::load
-                ? const_cast<libua*> (targets.find<libua> (dir, out, n))
+      libua* a (ctx.phase == run_phase::load
+                ? const_cast<libua*> (ctx.targets.find<libua> (dir, out, n))
                 : nullptr);
-      libus* s (phase == run_phase::load
-                ? const_cast<libus*> (targets.find<libus> (dir, out, n))
+      libus* s (ctx.phase == run_phase::load
+                ? const_cast<libus*> (ctx.targets.find<libus> (dir, out, n))
                 : nullptr);
 
-      libul* g (new libul (move (dir), move (out), move (n)));
+      libul* g (new libul (ctx, move (dir), move (out), move (n)));
 
       if (a != nullptr) a->group = g;
       if (s != nullptr) s->group = g;
@@ -369,8 +372,8 @@ namespace build2
       &file::static_type,
       &m_factory<liba, lib>,
       nullptr, /* fixed_extension */
-      &target_extension_var<var_extension, nullptr>,
-      &target_pattern_var<var_extension, nullptr>,
+      &target_extension_var<nullptr>,
+      &target_pattern_var<nullptr>,
       nullptr,
       &file_search,
       false
@@ -382,8 +385,8 @@ namespace build2
       &file::static_type,
       &m_factory<libs, lib>,
       nullptr, /* fixed_extension */
-      &target_extension_var<var_extension, nullptr>,
-      &target_pattern_var<var_extension, nullptr>,
+      &target_extension_var<nullptr>,
+      &target_pattern_var<nullptr>,
       nullptr,
       &file_search,
       false
@@ -403,18 +406,19 @@ namespace build2
     }
 
     static target*
-    lib_factory (const target_type&, dir_path dir, dir_path out, string n)
+    lib_factory (context& ctx,
+                 const target_type&, dir_path dir, dir_path out, string n)
     {
       // Casts are MT-aware (during serial load).
       //
-      liba* a (phase == run_phase::load
-               ? const_cast<liba*> (targets.find<liba> (dir, out, n))
+      liba* a (ctx.phase == run_phase::load
+               ? const_cast<liba*> (ctx.targets.find<liba> (dir, out, n))
                : nullptr);
-      libs* s (phase == run_phase::load
-               ? const_cast<libs*> (targets.find<libs> (dir, out, n))
+      libs* s (ctx.phase == run_phase::load
+               ? const_cast<libs*> (ctx.targets.find<libs> (dir, out, n))
                : nullptr);
 
-      lib* l (new lib (move (dir), move (out), move (n)));
+      lib* l (new lib (ctx, move (dir), move (out), move (n)));
 
       if (a != nullptr) a->group = l;
       if (s != nullptr) s->group = l;
@@ -443,8 +447,8 @@ namespace build2
       &file::static_type,
       &target_factory<libi>,
       nullptr, /* fixed_extension */
-      &target_extension_var<var_extension, nullptr>,
-      &target_pattern_var<var_extension, nullptr>,
+      &target_extension_var<nullptr>,
+      &target_pattern_var<nullptr>,
       nullptr,
       &file_search,
       false
diff --git a/build2/c/init.cxx b/build2/c/init.cxx
index 5c55281..ff9cc58 100644
--- a/build2/c/init.cxx
+++ b/build2/c/init.cxx
@@ -145,7 +145,7 @@ namespace build2
 
       // Enter all the variables and initialize the module data.
       //
-      auto& v (var_pool.rw (rs));
+      auto& v (rs.ctx.var_pool.rw (rs));
 
       cc::config_data d {
         cc::lang::c,
diff --git a/build2/cc/common.cxx b/build2/cc/common.cxx
index aa0eb89..4f5db4c 100644
--- a/build2/cc/common.cxx
+++ b/build2/cc/common.cxx
@@ -87,7 +87,7 @@ namespace build2
       bool impl (proc_impl && proc_impl (l, la));
       bool cc (false), same (false);
 
-      auto& vp (var_pool);
+      auto& vp (top_bs.ctx.var_pool);
       lookup c_e_libs;
       lookup x_e_libs;
 
@@ -221,7 +221,7 @@ namespace build2
         : &cast<dir_paths> (
           bs.root_scope ()->vars[same
                                  ? x_sys_lib_dirs
-                                 : var_pool[*t + ".sys_lib_dirs"]]);
+                                 : bs.ctx.var_pool[*t + ".sys_lib_dirs"]]);
       };
 
       auto find_linfo = [top_li, t, cc, &bs, &l, &li] ()
@@ -474,7 +474,7 @@ namespace build2
         if (xt == nullptr)
         {
           if (n.qualified ())
-            xt = import_existing (pk);
+            xt = import_existing (s.ctx, pk);
         }
 
         if (xt == nullptr)
@@ -494,20 +494,21 @@ namespace build2
     //
     template <typename T>
     ulock common::
-    insert_library (T*& r,
+    insert_library (context& ctx,
+                    T*& r,
                     const string& name,
                     const dir_path& d,
                     optional<string> ext,
                     bool exist,
                     tracer& trace)
     {
-      auto p (targets.insert_locked (T::static_type,
-                                     d,
-                                     dir_path (),
-                                     name,
-                                     move (ext),
-                                     true, // Implied.
-                                     trace));
+      auto p (ctx.targets.insert_locked (T::static_type,
+                                         d,
+                                         dir_path (),
+                                         name,
+                                         move (ext),
+                                         true, // Implied.
+                                         trace));
 
       assert (!exist || !p.second.owns_lock ());
       r = &p.first.template as<T> ();
@@ -626,6 +627,8 @@ namespace build2
                     &name, ext,
                     &p, &f, exist, &trace, this] (const dir_path& d) -> bool
       {
+        context& ctx (p.scope->ctx);
+
         timestamp mt;
 
         // libs
@@ -648,9 +651,10 @@ namespace build2
             if (tclass == "windows")
             {
               libi* i (nullptr);
-              insert_library (i, name, d, se, exist, trace);
+              insert_library (ctx, i, name, d, se, exist, trace);
 
-              ulock l (insert_library (s, name, d, nullopt, exist, trace));
+              ulock l (
+                insert_library (ctx, s, name, d, nullopt, exist, trace));
 
               if (!exist)
               {
@@ -677,7 +681,7 @@ namespace build2
             }
             else
             {
-              insert_library (s, name, d, se, exist, trace);
+              insert_library (ctx, s, name, d, se, exist, trace);
 
               s->mtime (mt);
               s->path (move (f));
@@ -697,7 +701,7 @@ namespace build2
 
             if (mt != timestamp_nonexistent)
             {
-              insert_library (s, name, d, se, exist, trace);
+              insert_library (ctx, s, name, d, se, exist, trace);
 
               s->mtime (mt);
               s->path (move (f));
@@ -722,7 +726,7 @@ namespace build2
             // Note that this target is outside any project which we treat
             // as out trees.
             //
-            insert_library (a, name, d, ae, exist, trace);
+            insert_library (ctx, a, name, d, ae, exist, trace);
             a->mtime (mt);
             a->path (move (f));
           }
@@ -760,14 +764,14 @@ namespace build2
 
             if (na && !r.first.empty ())
             {
-              insert_library (a, name, d, nullopt, exist, trace);
+              insert_library (ctx, a, name, d, nullopt, exist, trace);
               a->mtime (timestamp_unreal);
               a->path (empty_path);
             }
 
             if (ns && !r.second.empty ())
             {
-              insert_library (s, name, d, nullopt, exist, trace);
+              insert_library (ctx, s, name, d, nullopt, exist, trace);
               s->mtime (timestamp_unreal);
               s->path (empty_path);
             }
@@ -821,7 +825,8 @@ namespace build2
       // Enter (or find) the lib{} target group.
       //
       lib* lt;
-      insert_library (lt, name, *pd, l ? p.tk.ext : nullopt, exist, trace);
+      insert_library (
+        p.scope->ctx, lt, name, *pd, l ? p.tk.ext : nullopt, exist, trace);
 
       // Result.
       //
diff --git a/build2/cc/common.hxx b/build2/cc/common.hxx
index c58a7f3..b24eb7d 100644
--- a/build2/cc/common.hxx
+++ b/build2/cc/common.hxx
@@ -8,6 +8,7 @@
 #include <libbuild2/types.hxx>
 #include <libbuild2/utility.hxx>
 
+#include <libbuild2/context.hxx>
 #include <libbuild2/variable.hxx>
 
 #include <build2/bin/target.hxx>
@@ -278,7 +279,8 @@ namespace build2
 
       template <typename T>
       static ulock
-      insert_library (T*&,
+      insert_library (context&,
+                      T*&,
                       const string&,
                       const dir_path&,
                       optional<string>,
diff --git a/build2/cc/compile-rule.cxx b/build2/cc/compile-rule.cxx
index 833fd44..fa43533 100644
--- a/build2/cc/compile-rule.cxx
+++ b/build2/cc/compile-rule.cxx
@@ -365,7 +365,9 @@ namespace build2
         const variable& var (
           com
           ? c_export_poptions
-          : (t == x ? x_export_poptions : var_pool[t + ".export.poptions"]));
+          : (t == x
+             ? x_export_poptions
+             : l.ctx.var_pool[t + ".export.poptions"]));
 
         append_options (args, l, var);
       };
@@ -418,7 +420,9 @@ namespace build2
         const variable& var (
           com
           ? c_export_poptions
-          : (t == x ? x_export_poptions : var_pool[t + ".export.poptions"]));
+          : (t == x
+             ? x_export_poptions
+             : l.ctx.var_pool[t + ".export.poptions"]));
 
         hash_options (cs, l, var);
       };
@@ -472,7 +476,9 @@ namespace build2
         const variable& var (
           com
           ? c_export_poptions
-          : (t == x ? x_export_poptions : var_pool[t + ".export.poptions"]));
+          : (t == x
+             ? x_export_poptions
+             : l.ctx.var_pool[t + ".export.poptions"]));
 
         append_prefixes (m, l, var);
       };
@@ -553,7 +559,7 @@ namespace build2
         // @@ MT perf: so we are going to switch the phase and execute for
         //    any generated header.
         //
-        phase_switch ps (run_phase::execute);
+        phase_switch ps (t.ctx, run_phase::execute);
         target_state ns (execute_direct (a, t));
 
         if (ns != os && ns != target_state::unchanged)
@@ -577,6 +583,8 @@ namespace build2
 
       match_data& md (t.data<match_data> ());
 
+      context& ctx (t.ctx);
+
       // Note: until refined below, non-BMI-generating translation unit is
       // assumed non-modular.
       //
@@ -692,7 +700,7 @@ namespace build2
       // Start asynchronous matching of prerequisites. Wait with unlocked
       // phase to allow phase switching.
       //
-      wait_guard wg (target::count_busy (), t[a].task_count, true);
+      wait_guard wg (ctx, ctx.count_busy (), t[a].task_count, true);
 
       size_t start (pts.size ()); // Index of the first to be added.
       for (prerequisite_member p: group_prerequisite_members (a, t))
@@ -754,7 +762,7 @@ namespace build2
             continue;
         }
 
-        match_async (a, *pt, target::count_busy (), t[a].task_count);
+        match_async (a, *pt, ctx.count_busy (), t[a].task_count);
         pts.push_back (prerequisite_target (pt, pi));
       }
 
@@ -1142,7 +1150,7 @@ namespace build2
         // to keep re-validating the file on every subsequent dry-run as well
         // on the real run).
         //
-        if (u && dd.reading () && !dry_run)
+        if (u && dd.reading () && !ctx.dry_run)
           dd.touch = true;
 
         dd.close ();
@@ -2161,7 +2169,7 @@ namespace build2
         //
         small_vector<const target_type*, 2> tts;
 
-        const scope& bs (scopes.find (d));
+        const scope& bs (t.ctx.scopes.find (d));
         if (const scope* rs = bs.root_scope ())
         {
           tts = map_extension (bs, n, e);
@@ -2201,7 +2209,7 @@ namespace build2
           // absolute path with a spelled-out extension to multiple targets.
           //
           for (const target_type* tt: tts)
-            if ((r = targets.find (*tt, d, out, n, e, trace)) != nullptr)
+            if ((r = t.ctx.targets.find (*tt, d, out, n, e, trace)) != nullptr)
               break;
 
           // Note: we can't do this because of the in-source builds where
@@ -2887,7 +2895,7 @@ namespace build2
                     // See if this path is inside a project with an out-of-
                     // tree build and is in the out directory tree.
                     //
-                    const scope& bs (scopes.find (d));
+                    const scope& bs (t.ctx.scopes.find (d));
                     if (bs.root_scope () != nullptr)
                     {
                       const dir_path& bp (bs.out_path ());
@@ -5101,18 +5109,18 @@ namespace build2
                    modules_sidebuild_dir /=
                    x);
 
-      const scope* ps (&scopes.find (pd));
+      const scope* ps (&rs.ctx.scopes.find (pd));
 
       if (ps->out_path () != pd)
       {
         // Switch the phase to load then create and load the subproject.
         //
-        phase_switch phs (run_phase::load);
+        phase_switch phs (rs.ctx, run_phase::load);
 
         // Re-test again now that we are in exclusive phase (another thread
         // could have already created and loaded the subproject).
         //
-        ps = &scopes.find (pd);
+        ps = &rs.ctx.scopes.find (pd);
 
         if (ps->out_path () != pd)
         {
@@ -5200,7 +5208,7 @@ namespace build2
       // exists then we assume all this is already done (otherwise why would
       // someone have created such a target).
       //
-      if (const file* bt = targets.find<file> (
+      if (const file* bt = bs.ctx.targets.find<file> (
             tt,
             pd,
             dir_path (), // Always in the out tree.
@@ -5237,13 +5245,14 @@ namespace build2
         }
       }
 
-      auto p (targets.insert_locked (tt,
-                                     move (pd),
-                                     dir_path (), // Always in the out tree.
-                                     move (mf),
-                                     nullopt,     // Use default extension.
-                                     true,        // Implied.
-                                     trace));
+      auto p (bs.ctx.targets.insert_locked (
+                tt,
+                move (pd),
+                dir_path (), // Always in the out tree.
+                move (mf),
+                nullopt,     // Use default extension.
+                true,        // Implied.
+                trace));
       file& bt (static_cast<file&> (p.first));
 
       // Note that this is racy and someone might have created this target
@@ -5295,7 +5304,7 @@ namespace build2
 
       const target_type& tt (compile_types (li.type).hbmi);
 
-      if (const file* bt = targets.find<file> (
+      if (const file* bt = bs.ctx.targets.find<file> (
             tt,
             pd,
             dir_path (), // Always in the out tree.
@@ -5307,13 +5316,14 @@ namespace build2
       prerequisites ps;
       ps.push_back (prerequisite (ht));
 
-      auto p (targets.insert_locked (tt,
-                                     move (pd),
-                                     dir_path (), // Always in the out tree.
-                                     move (mf),
-                                     nullopt,     // Use default extension.
-                                     true,        // Implied.
-                                     trace));
+      auto p (bs.ctx.targets.insert_locked (
+                tt,
+                move (pd),
+                dir_path (), // Always in the out tree.
+                move (mf),
+                nullopt,     // Use default extension.
+                true,        // Implied.
+                trace));
       file& bt (static_cast<file&> (p.first));
 
       // Note that this is racy and someone might have created this target
@@ -5550,6 +5560,8 @@ namespace build2
       match_data md (move (t.data<match_data> ()));
       unit_type ut (md.type);
 
+      context& ctx (t.ctx);
+
       // While all our prerequisites are already up-to-date, we still have to
       // execute them to keep the dependency counts straight. Actually, no, we
       // may also have to update the modules.
@@ -5575,9 +5587,9 @@ namespace build2
       {
         if (md.touch)
         {
-          touch (tp, false, 2);
+          touch (ctx, tp, false, 2);
           t.mtime (system_clock::now ());
-          skip_count.fetch_add (1, memory_order_relaxed);
+          ctx.skip_count.fetch_add (1, memory_order_relaxed);
         }
         // Note: else mtime should be cached.
 
@@ -5592,7 +5604,7 @@ namespace build2
                        ? system_clock::now ()
                        : timestamp_unknown);
 
-      touch (md.dd, false, verb_never);
+      touch (ctx, md.dd, false, verb_never);
 
       const scope& bs (t.base_scope ());
       const scope& rs (*bs.root_scope ());
@@ -5941,7 +5953,7 @@ namespace build2
       // translation unit (i.e., one of the imported module's has BMIs
       // changed).
       //
-      if (!dry_run)
+      if (!ctx.dry_run)
       {
         try
         {
@@ -6020,7 +6032,7 @@ namespace build2
         if (verb >= 2)
           print_process (args);
 
-        if (!dry_run)
+        if (!ctx.dry_run)
         {
           // Remove the target file if this fails. If we don't do that, we
           // will end up with a broken build that is up-to-date.
@@ -6053,7 +6065,7 @@ namespace build2
 
       timestamp now (system_clock::now ());
 
-      if (!dry_run)
+      if (!ctx.dry_run)
         depdb::check_mtime (start, md.dd, tp, now);
 
       // Should we go to the filesystem and get the new mtime? We know the
diff --git a/build2/cc/init.cxx b/build2/cc/init.cxx
index e22ece7..c83d5ed 100644
--- a/build2/cc/init.cxx
+++ b/build2/cc/init.cxx
@@ -26,27 +26,29 @@ namespace build2
     static target_state
     clean_module_sidebuilds (action, const scope& rs, const dir&)
     {
+      context& ctx (rs.ctx);
+
       const dir_path& out_root (rs.out_path ());
 
       dir_path d (out_root / rs.root_extra->build_dir / modules_sidebuild_dir);
 
       if (exists (d))
       {
-        if (build2::rmdir_r (d))
+        if (rmdir_r (ctx, d))
         {
           // Clean up cc/ if it became empty.
           //
           d = out_root / rs.root_extra->build_dir / module_dir;
           if (empty (d))
           {
-            rmdir (d);
+            rmdir (ctx, d);
 
             // And build/ if it also became empty (e.g., in case of a build
             // with a transient configuration).
             //
             d = out_root / rs.root_extra->build_dir;
             if (empty (d))
-              rmdir (d);
+              rmdir (ctx, d);
           }
 
           return target_state::changed;
@@ -77,7 +79,7 @@ namespace build2
 
       // Enter variables. Note: some overridable, some not.
       //
-      auto& v (var_pool.rw (rs));
+      auto& v (rs.ctx.var_pool.rw (rs));
 
       auto v_t (variable_visibility::target);
 
@@ -276,7 +278,8 @@ namespace build2
         // Prepare configuration hints. They are only used on the first load
         // of bin.config so we only populate them on our first load.
         //
-        variable_map h;
+        variable_map h (rs.ctx);
+
         if (first)
         {
           // Note that all these variables have already been registered.
diff --git a/build2/cc/link-rule.cxx b/build2/cc/link-rule.cxx
index bb91722..bfc31d7 100644
--- a/build2/cc/link-rule.cxx
+++ b/build2/cc/link-rule.cxx
@@ -165,14 +165,15 @@ namespace build2
                 // otherwise the above search would have returned the member
                 // target.
                 //
-                pt = search_existing (p.prerequisite.key (tt));
+                pt = search_existing (t.ctx, p.prerequisite.key (tt));
               }
             }
             else if (!p.is_a<libue> ())
             {
               // See if we also/instead have a group.
               //
-              pg = search_existing (p.prerequisite.key (libul::static_type));
+              pg = search_existing (t.ctx,
+                                    p.prerequisite.key (libul::static_type));
 
               if (pt == nullptr)
                 swap (pt, pg);
@@ -483,6 +484,7 @@ namespace build2
       tracer trace (x, "link_rule::apply");
 
       file& t (xt.as<file> ());
+      context& ctx (t.ctx);
 
       // Note that for_install is signalled by install_rule and therefore
       // can only be relied upon during execute.
@@ -697,7 +699,7 @@ namespace build2
               // Note that ad hoc inputs have to be explicitly marked with the
               // include=adhoc prerequisite-specific variable.
               //
-              if (current_outer_oif != nullptr)
+              if (ctx.current_outer_oif != nullptr)
                 continue;
             }
 
@@ -945,7 +947,7 @@ namespace build2
             // Windows.
             //
 #ifdef _WIN32
-            dir.state[a].assign (var_backlink) = "copy";
+            dir.state[a].assign (ctx.var_backlink) = "copy";
 #endif
           }
         }
@@ -1163,7 +1165,7 @@ namespace build2
           bool u;
           if ((u = pt->is_a<libux> ()) || pt->is_a<liba> ())
           {
-            const variable& var (var_pool["bin.whole"]); // @@ Cache.
+            const variable& var (ctx.var_pool["bin.whole"]); // @@ Cache.
 
             // See the bin module for the lookup semantics discussion. Note
             // that the variable is not overridable so we omit find_override()
@@ -1197,7 +1199,7 @@ namespace build2
 
       // Wait with unlocked phase to allow phase switching.
       //
-      wait_guard wg (target::count_busy (), t[a].task_count, true);
+      wait_guard wg (ctx, ctx.count_busy (), t[a].task_count, true);
 
       i = start;
       for (prerequisite_member p: group_prerequisite_members (a, t))
@@ -1229,7 +1231,7 @@ namespace build2
           }
         }
 
-        match_async (a, *pt, target::count_busy (), t[a].task_count);
+        match_async (a, *pt, ctx.count_busy (), t[a].task_count);
         mark (pt, m);
       }
 
@@ -1473,7 +1475,7 @@ namespace build2
             ? (exp ? c_export_loptions : c_loptions)
             : (t == x
                ? (exp ? x_export_loptions : x_loptions)
-               : var_pool[t + (exp ? ".export.loptions" : ".loptions")]));
+               : l.ctx.var_pool[t + (exp ? ".export.loptions" : ".loptions")]));
 
           append_options (d.args, *g, var);
         }
@@ -1575,7 +1577,7 @@ namespace build2
             ? (exp ? c_export_loptions : c_loptions)
             : (t == x
                ? (exp ? x_export_loptions : x_loptions)
-               : var_pool[t + (exp ? ".export.loptions" : ".loptions")]));
+               : l.ctx.var_pool[t + (exp ? ".export.loptions" : ".loptions")]));
 
           hash_options (d.cs, *g, var);
         }
@@ -1747,6 +1749,8 @@ namespace build2
       const file& t (xt.as<file> ());
       const path& tp (t.path ());
 
+      context& ctx (t.ctx);
+
       const scope& bs (t.base_scope ());
       const scope& rs (*bs.root_scope ());
 
@@ -1866,7 +1870,7 @@ namespace build2
             if (verb >= 3)
               print_process (args);
 
-            if (!dry_run)
+            if (!ctx.dry_run)
             {
               auto_rmfile rm (of);
 
@@ -1966,7 +1970,7 @@ namespace build2
         const string& cs (
           cast<string> (
             rs[tsys == "win32-msvc"
-               ? var_pool["bin.ld.checksum"]
+               ? ctx.var_pool["bin.ld.checksum"]
                : x_checksum]));
 
         if (dd.expect (cs) != nullptr)
@@ -2726,7 +2730,7 @@ namespace build2
       //
       auto_rmfile rm;
 
-      if (!dry_run)
+      if (!ctx.dry_run)
       {
         rm = auto_rmfile (relt);
 
@@ -2823,7 +2827,7 @@ namespace build2
         if (verb >= 2)
           print_process (args);
 
-        if (!dry_run)
+        if (!ctx.dry_run)
           run (rl, args);
       }
 
@@ -2843,12 +2847,12 @@ namespace build2
         // For shared libraries we may need to create a bunch of symlinks (or
         // fallback to hardlinks/copies on Windows).
         //
-        auto ln = [] (const path& f, const path& l)
+        auto ln = [&ctx] (const path& f, const path& l)
         {
           if (verb >= 3)
             text << "ln -sf " << f << ' ' << l;
 
-          if (dry_run)
+          if (ctx.dry_run)
             return;
 
           try
@@ -2908,12 +2912,12 @@ namespace build2
         //
         if (tsys == "darwin" && cast<string> (rs["bin.ar.id"]) == "generic")
         {
-          if (!dry_run)
-            touch (tp, false /* create */, verb_never);
+          if (!ctx.dry_run)
+            touch (ctx, tp, false /* create */, verb_never);
         }
       }
 
-      if (!dry_run)
+      if (!ctx.dry_run)
       {
         rm.cancel ();
         dd.check_mtime (tp);
diff --git a/build2/cc/module.cxx b/build2/cc/module.cxx
index 36cdd1a..064d954 100644
--- a/build2/cc/module.cxx
+++ b/build2/cc/module.cxx
@@ -41,9 +41,13 @@ namespace build2
 
       config::save_module (rs, x, 250);
 
-      const variable& config_c_poptions (var_pool["config.cc.poptions"]);
-      const variable& config_c_coptions (var_pool["config.cc.coptions"]);
-      const variable& config_c_loptions (var_pool["config.cc.loptions"]);
+      auto& vp (rs.ctx.var_pool.rw (rs));
+
+      // Must already exist.
+      //
+      const variable& config_c_poptions (vp["config.cc.poptions"]);
+      const variable& config_c_coptions (vp["config.cc.coptions"]);
+      const variable& config_c_loptions (vp["config.cc.loptions"]);
 
       // config.x
       //
@@ -63,8 +67,6 @@ namespace build2
         //
         if (!cc_loaded)
         {
-          auto& vp (var_pool.rw (rs));
-
           for (const char* const* pm (x_hinters); *pm != nullptr; ++pm)
           {
             string m (*pm);
@@ -201,7 +203,7 @@ namespace build2
       {
         // Prepare configuration hints.
         //
-        variable_map h;
+        variable_map h (rs.ctx);
 
         // Note that all these variables have already been registered.
         //
@@ -545,7 +547,7 @@ namespace build2
       //
       if (!cast_false<bool> (rs["cc.core.config.loaded"]))
       {
-        variable_map h;
+        variable_map h (rs.ctx);
 
         if (!ci.bin_pattern.empty ())
           h.assign ("config.bin.pattern") = ci.bin_pattern;
diff --git a/build2/cc/msvc.cxx b/build2/cc/msvc.cxx
index 6125fdd..7d8c3f5 100644
--- a/build2/cc/msvc.cxx
+++ b/build2/cc/msvc.cxx
@@ -365,6 +365,7 @@ namespace build2
     {
       // Pretty similar logic to search_library().
       //
+      assert (p.scope != nullptr);
 
       const optional<string>& ext (p.tk.ext);
       const string& name (*p.tk.name);
@@ -403,7 +404,7 @@ namespace build2
         // Enter the target.
         //
         T* t;
-        common::insert_library (t, name, d, e, exist, trace);
+        common::insert_library (p.scope->ctx, t, name, d, e, exist, trace);
 
         t->mtime (mt);
         t->path (move (f));
@@ -453,6 +454,8 @@ namespace build2
     {
       tracer trace (x, "msvc_search_shared");
 
+      assert (pk.scope != nullptr);
+
       libs* s (nullptr);
 
       auto search = [&s, &ld, &d, &pk, exist, &trace] (
@@ -461,7 +464,9 @@ namespace build2
         if (libi* i = msvc_search_library<libi> (
               ld, d, pk, otype::s, pf, sf, exist, trace))
         {
-          ulock l (insert_library (s, *pk.tk.name, d, nullopt, exist, trace));
+          ulock l (
+            insert_library (
+              pk.scope->ctx, s, *pk.tk.name, d, nullopt, exist, trace));
 
           if (!exist)
           {
diff --git a/build2/cc/pkgconfig.cxx b/build2/cc/pkgconfig.cxx
index c23b746..3b4c711 100644
--- a/build2/cc/pkgconfig.cxx
+++ b/build2/cc/pkgconfig.cxx
@@ -1027,7 +1027,7 @@ namespace build2
 
       // Parse modules and add them to the prerequisites.
       //
-      auto parse_modules = [&trace, &next, this]
+      auto parse_modules = [&trace, &next, &s, this]
         (const pkgconf& pc, prerequisites& ps)
       {
         string mstr (pc.variable ("cxx_modules"));
@@ -1057,7 +1057,7 @@ namespace build2
           // For now there are only C++ modules.
           //
           auto tl (
-            targets.insert_locked (
+            s.ctx.targets.insert_locked (
               *x_mod,
               mp.directory (),
               dir_path (),
@@ -1228,6 +1228,8 @@ namespace build2
     {
       tracer trace (x, "pkgconfig_save");
 
+      context& ctx (l.ctx);
+
       const scope& bs (l.base_scope ());
       const scope& rs (*bs.root_scope ());
 
@@ -1246,7 +1248,7 @@ namespace build2
       if (verb >= 2)
         text << "cat >" << p;
 
-      if (dry_run)
+      if (ctx.dry_run)
         return;
 
       auto_rmfile arm (p);
@@ -1256,9 +1258,12 @@ namespace build2
         ofdstream os (p);
 
         {
-          const project_name& n (cast<project_name> (rs.vars[var_project]));
+          const project_name& n (project (rs));
+
+          if (n.empty ())
+            fail << "no project name in " <<  rs;
 
-          lookup vl (rs.vars[var_version]);
+          lookup vl (rs.vars[ctx.var_version]);
           if (!vl)
             fail << "no version variable in project " << n <<
               info << "while generating " << p;
@@ -1271,12 +1276,12 @@ namespace build2
           // This one is required so make something up if unspecified.
           //
           os << "Description: ";
-          if (const string* s = cast_null<string> (rs[var_project_summary]))
+          if (const string* s = cast_null<string> (rs[ctx.var_project_summary]))
             os << *s << endl;
           else
             os << n << ' ' << v << endl;
 
-          if (const string* u = cast_null<string> (rs[var_project_url]))
+          if (const string* u = cast_null<string> (rs[ctx.var_project_url]))
             os << "URL: " << *u << endl;
         }
 
diff --git a/build2/cc/target.cxx b/build2/cc/target.cxx
index c637e60..89b9391 100644
--- a/build2/cc/target.cxx
+++ b/build2/cc/target.cxx
@@ -33,8 +33,8 @@ namespace build2
       &cc::static_type,
       &target_factory<h>,
       nullptr, /* fixed_extension */
-      &target_extension_var<var_extension, h_ext_def>,
-      &target_pattern_var<var_extension, h_ext_def>,
+      &target_extension_var<h_ext_def>,
+      &target_pattern_var<h_ext_def>,
       nullptr,
       &file_search,
       false
@@ -48,8 +48,8 @@ namespace build2
       &cc::static_type,
       &target_factory<c>,
       nullptr, /* fixed_extension */
-      &target_extension_var<var_extension, c_ext_def>,
-      &target_pattern_var<var_extension, c_ext_def>,
+      &target_extension_var<c_ext_def>,
+      &target_pattern_var<c_ext_def>,
       nullptr,
       &file_search,
       false
diff --git a/build2/cc/utility.cxx b/build2/cc/utility.cxx
index 3271f7c..e9d4ce3 100644
--- a/build2/cc/utility.cxx
+++ b/build2/cc/utility.cxx
@@ -70,9 +70,9 @@ namespace build2
 
         // Called by the compile rule during execute.
         //
-        return phase == run_phase::match && !exist
+        return x.ctx.phase == run_phase::match && !exist
           ? &search (x, tt, x.dir, x.out, x.name)
-          : search_existing (tt, x.dir, x.out, x.name);
+          : search_existing (x.ctx, tt, x.dir, x.out, x.name);
       }
       else
       {
diff --git a/build2/cc/windows-manifest.cxx b/build2/cc/windows-manifest.cxx
index da12f0f..733cae5 100644
--- a/build2/cc/windows-manifest.cxx
+++ b/build2/cc/windows-manifest.cxx
@@ -119,7 +119,7 @@ namespace build2
       if (verb >= 3)
         text << "cat >" << mf;
 
-      if (!dry_run)
+      if (!t.ctx.dry_run)
       {
         auto_rmfile rm (mf);
 
diff --git a/build2/cc/windows-rpath.cxx b/build2/cc/windows-rpath.cxx
index d81e3b0..4478f7d 100644
--- a/build2/cc/windows-rpath.cxx
+++ b/build2/cc/windows-rpath.cxx
@@ -281,7 +281,7 @@ namespace build2
       // simpler.
       //
       {
-        rmdir_status s (build2::rmdir_r (ad, empty, 3));
+        rmdir_status s (rmdir_r (t.ctx, ad, empty, 3));
 
         if (empty)
           return;
@@ -362,7 +362,7 @@ namespace build2
       if (verb >= 3)
         text << "cat >" << am;
 
-      if (dry_run)
+      if (t.ctx.dry_run)
         return;
 
       auto_rmfile rm (am);
diff --git a/build2/cli/init.cxx b/build2/cli/init.cxx
index 6d20aa0..2e553f7 100644
--- a/build2/cli/init.cxx
+++ b/build2/cli/init.cxx
@@ -43,7 +43,7 @@ namespace build2
       //
       if (first)
       {
-        auto& v (var_pool.rw (rs));
+        auto& v (rs.ctx.var_pool.rw (rs));
 
         // Note: some overridable, some not.
         //
diff --git a/build2/cli/rule.cxx b/build2/cli/rule.cxx
index f6bebee..4ccafc9 100644
--- a/build2/cli/rule.cxx
+++ b/build2/cli/rule.cxx
@@ -112,7 +112,7 @@ namespace build2
 
         // Check if there is a corresponding cli.cxx{} group.
         //
-        const cli_cxx* g (targets.find<cli_cxx> (t.dir, t.out, t.name));
+        const cli_cxx* g (t.ctx.targets.find<cli_cxx> (t.dir, t.out, t.name));
 
         // If not or if it has no prerequisites (happens when we use it to
         // set cli.options) and this target has a cli{} prerequisite, then
@@ -124,7 +124,7 @@ namespace build2
                 prerequisite_members (a, t)))
           {
             if (g == nullptr)
-              g = &targets.insert<cli_cxx> (t.dir, t.out, t.name, trace);
+              g = &t.ctx.targets.insert<cli_cxx> (t.dir, t.out, t.name, trace);
 
             g->prerequisites (prerequisites {p->as_prerequisite ()});
           }
@@ -322,7 +322,7 @@ namespace build2
       else if (verb)
         text << "cli " << s;
 
-      if (!dry_run)
+      if (!t.ctx.dry_run)
       {
         run (cli, args);
         dd.check_mtime (tp);
diff --git a/build2/cli/target.cxx b/build2/cli/target.cxx
index 096295a..2fd70f7 100644
--- a/build2/cli/target.cxx
+++ b/build2/cli/target.cxx
@@ -23,8 +23,8 @@ namespace build2
       &file::static_type,
       &target_factory<cli>,
       nullptr, /* fixed_extension */
-      &target_extension_var<var_extension, cli_ext_def>,
-      &target_pattern_var<var_extension, cli_ext_def>,
+      &target_extension_var<cli_ext_def>,
+      &target_pattern_var<cli_ext_def>,
       nullptr,
       &file_search,
       false
@@ -45,7 +45,8 @@ namespace build2
     }
 
     static target*
-    cli_cxx_factory (const target_type&, dir_path d, dir_path o, string n)
+    cli_cxx_factory (context& ctx,
+                     const target_type&, dir_path d, dir_path o, string n)
     {
       tracer trace ("cli::cli_cxx_factory");
 
@@ -55,11 +56,11 @@ namespace build2
       //
       // Also required for the src-out remapping logic.
       //
-      targets.insert<cxx::hxx> (d, o, n, trace);
-      targets.insert<cxx::cxx> (d, o, n, trace);
-      targets.insert<cxx::ixx> (d, o, n, trace);
+      ctx.targets.insert<cxx::hxx> (d, o, n, trace);
+      ctx.targets.insert<cxx::cxx> (d, o, n, trace);
+      ctx.targets.insert<cxx::ixx> (d, o, n, trace);
 
-      return new cli_cxx (move (d), move (o), move (n));
+      return new cli_cxx (ctx, move (d), move (o), move (n));
     }
 
     const target_type cli_cxx::static_type
diff --git a/build2/cxx/init.cxx b/build2/cxx/init.cxx
index c355763..1ffa098 100644
--- a/build2/cxx/init.cxx
+++ b/build2/cxx/init.cxx
@@ -62,7 +62,8 @@ namespace build2
       //
       auto enter = [&rs] (const char* v) -> const variable&
       {
-        return var_pool.rw (rs).insert<bool> (v, variable_visibility::project);
+        return rs.ctx.var_pool.rw (rs).insert<bool> (
+          v, variable_visibility::project);
       };
 
       // NOTE: see also module sidebuild subproject if changing anything about
@@ -370,7 +371,7 @@ namespace build2
 
       // Enter all the variables and initialize the module data.
       //
-      auto& v (var_pool.rw (rs));
+      auto& v (rs.ctx.var_pool.rw (rs));
 
       cc::config_data d {
         cc::lang::cxx,
@@ -572,7 +573,7 @@ namespace build2
 
       config_module& cm (*rs.lookup_module<config_module> ("cxx.guess"));
 
-      auto& vp (var_pool.rw (rs));
+      auto& vp (rs.ctx.var_pool.rw (rs));
 
       bool modules (cast<bool> (rs["cxx.features.modules"]));
 
diff --git a/build2/cxx/target.cxx b/build2/cxx/target.cxx
index 025bf9d..45463f3 100644
--- a/build2/cxx/target.cxx
+++ b/build2/cxx/target.cxx
@@ -19,8 +19,8 @@ namespace build2
       &cc::static_type,
       &target_factory<hxx>,
       nullptr, /* fixed_extension */
-      &target_extension_var<var_extension, hxx_ext_def>,
-      &target_pattern_var<var_extension, hxx_ext_def>,
+      &target_extension_var<hxx_ext_def>,
+      &target_pattern_var<hxx_ext_def>,
       nullptr,
       &file_search,
       false
@@ -33,8 +33,8 @@ namespace build2
       &cc::static_type,
       &target_factory<ixx>,
       nullptr, /* fixed_extension */
-      &target_extension_var<var_extension, ixx_ext_def>,
-      &target_pattern_var<var_extension, ixx_ext_def>,
+      &target_extension_var<ixx_ext_def>,
+      &target_pattern_var<ixx_ext_def>,
       nullptr,
       &file_search,
       false
@@ -47,8 +47,8 @@ namespace build2
       &cc::static_type,
       &target_factory<txx>,
       nullptr, /* fixed_extension */
-      &target_extension_var<var_extension, txx_ext_def>,
-      &target_pattern_var<var_extension, txx_ext_def>,
+      &target_extension_var<txx_ext_def>,
+      &target_pattern_var<txx_ext_def>,
       nullptr,
       &file_search,
       false
@@ -61,8 +61,8 @@ namespace build2
       &cc::static_type,
       &target_factory<cxx>,
       nullptr, /* fixed_extension */
-      &target_extension_var<var_extension, cxx_ext_def>,
-      &target_pattern_var<var_extension, cxx_ext_def>,
+      &target_extension_var<cxx_ext_def>,
+      &target_pattern_var<cxx_ext_def>,
       nullptr,
       &file_search,
       false
@@ -75,8 +75,8 @@ namespace build2
       &cc::static_type,
       &target_factory<mxx>,
       nullptr, /* fixed_extension */
-      &target_extension_var<var_extension, mxx_ext_def>,
-      &target_pattern_var<var_extension, mxx_ext_def>,
+      &target_extension_var<mxx_ext_def>,
+      &target_pattern_var<mxx_ext_def>,
       nullptr,
       &file_search,
       false