Move cli module to libbuild2-cli library

This is a temporary measure (until we unboundle this module) needed for
in-process configure support in bpkg.

11 files changed, 980 insertions, 1 deletions

diff --git a/libbuild2/buildfile b/libbuild2/buildfile
index 6707b05..b3a9c52 100644
--- a/libbuild2/buildfile
+++ b/libbuild2/buildfile
@@ -4,7 +4,7 @@
 # NOTE: remember to update bundled_modules in libbuild2/module.cxx if adding a
 #       new module.
 #
-bundled_modules = bash/ bin/ c/ cc/ cxx/ in/ version/
+bundled_modules = bash/ bin/ c/ cc/ cli/ cxx/ in/ version/
 
 ./: lib{build2} $bundled_modules
 
diff --git a/libbuild2/cli/buildfile b/libbuild2/cli/buildfile
new file mode 100644
index 0000000..9b6e4eb
--- /dev/null
+++ b/libbuild2/cli/buildfile
@@ -0,0 +1,71 @@
+# file      : libbuild2/cli/buildfile
+# license   : MIT; see accompanying LICENSE file
+
+# NOTE: shared imports should go into root.build.
+#
+include ../
+impl_libs = ../lib{build2} # Implied interface dependency.
+
+include ../cxx/
+intf_libs = ../cxx/lib{build2-cxx}
+
+./: lib{build2-cli}: libul{build2-cli}: {hxx ixx txx cxx}{** -**.test...} \
+  $intf_libs $impl_libs
+
+# Unit tests.
+#
+exe{*.test}:
+{
+  test = true
+  install = false
+}
+
+for t: cxx{**.test...}
+{
+  d = $directory($t)
+  n = $name($t)...
+
+  ./: $d/exe{$n}: $t $d/{hxx ixx txx}{+$n} $d/testscript{+$n}
+  $d/exe{$n}: libul{build2-cli}: bin.whole = false
+}
+
+# Build options.
+#
+obja{*}: cxx.poptions += -DLIBBUILD2_CLI_STATIC_BUILD
+objs{*}: cxx.poptions += -DLIBBUILD2_CLI_SHARED_BUILD
+
+# Export options.
+#
+lib{build2-cli}:
+{
+  cxx.export.poptions = "-I$out_root" "-I$src_root"
+  cxx.export.libs = $intf_libs
+}
+
+liba{build2-cli}: cxx.export.poptions += -DLIBBUILD2_CLI_STATIC
+libs{build2-cli}: cxx.export.poptions += -DLIBBUILD2_CLI_SHARED
+
+# For pre-releases use the complete version to make sure they cannot be used
+# in place of another pre-release or the final version. See the version module
+# for details on the version.* variable values.
+#
+# And because this is a build system module, we also embed the same value as
+# the interface version (note that we cannot use build.version.interface for
+# bundled modules because we could be built with a different version of the
+# build system).
+#
+ver = ($version.pre_release    \
+       ? "$version.project_id" \
+       : "$version.major.$version.minor")
+
+lib{build2-cli}: bin.lib.version = @"-$ver"
+libs{build2-cli}: bin.lib.load_suffix = "-$ver"
+
+# Install into the libbuild2/cli/ subdirectory of, say, /usr/include/
+# recreating subdirectories.
+#
+{hxx ixx txx}{*}:
+{
+  install         = include/libbuild2/cli/
+  install.subdirs = true
+}
diff --git a/libbuild2/cli/export.hxx b/libbuild2/cli/export.hxx
new file mode 100644
index 0000000..67c1eb9
--- /dev/null
+++ b/libbuild2/cli/export.hxx
@@ -0,0 +1,37 @@
+// file      : libbuild2/cli/export.hxx -*- C++ -*-
+// license   : MIT; see accompanying LICENSE file
+
+#pragma once
+
+// Normally we don't export class templates (but do complete specializations),
+// inline functions, and classes with only inline member functions. Exporting
+// classes that inherit from non-exported/imported bases (e.g., std::string)
+// will end up badly. The only known workarounds are to not inherit or to not
+// export. Also, MinGW GCC doesn't like seeing non-exported functions being
+// used before their inline definition. The workaround is to reorder code. In
+// the end it's all trial and error.
+
+#if defined(LIBBUILD2_CLI_STATIC)         // Using static.
+#  define LIBBUILD2_CLI_SYMEXPORT
+#elif defined(LIBBUILD2_CLI_STATIC_BUILD) // Building static.
+#  define LIBBUILD2_CLI_SYMEXPORT
+#elif defined(LIBBUILD2_CLI_SHARED)       // Using shared.
+#  ifdef _WIN32
+#    define LIBBUILD2_CLI_SYMEXPORT __declspec(dllimport)
+#  else
+#    define LIBBUILD2_CLI_SYMEXPORT
+#  endif
+#elif defined(LIBBUILD2_CLI_SHARED_BUILD) // Building shared.
+#  ifdef _WIN32
+#    define LIBBUILD2_CLI_SYMEXPORT __declspec(dllexport)
+#  else
+#    define LIBBUILD2_CLI_SYMEXPORT
+#  endif
+#else
+// If none of the above macros are defined, then we assume we are being used
+// by some third-party build system that cannot/doesn't signal the library
+// type. Note that this fallback works for both static and shared but in case
+// of shared will be sub-optimal compared to having dllimport.
+//
+#  define LIBBUILD2_CLI_SYMEXPORT         // Using static or shared.
+#endif
diff --git a/libbuild2/cli/init.cxx b/libbuild2/cli/init.cxx
new file mode 100644
index 0000000..581fdaf
--- /dev/null
+++ b/libbuild2/cli/init.cxx
@@ -0,0 +1,287 @@
+// file      : libbuild2/cli/init.cxx -*- C++ -*-
+// license   : MIT; see accompanying LICENSE file
+
+#include <libbuild2/cli/init.hxx>
+
+#include <libbuild2/file.hxx>
+#include <libbuild2/scope.hxx>
+#include <libbuild2/target.hxx>
+#include <libbuild2/variable.hxx>
+#include <libbuild2/diagnostics.hxx>
+
+#include <libbuild2/config/utility.hxx>
+
+#include <libbuild2/cxx/target.hxx>
+
+#include <libbuild2/cli/rule.hxx>
+#include <libbuild2/cli/module.hxx>
+#include <libbuild2/cli/target.hxx>
+
+namespace build2
+{
+  namespace cli
+  {
+    // Remaining issues/semantics change:
+    //
+    // @@ Unconfigured caching.
+    //
+    // @@ Default-found cli used to result in config.cli=cli and now it's just
+    //    omitted (and default-not-found -- in config.cli.configured=false).
+    //
+    //    - Writing any default will take precedence over config.import.cli.
+    //      In fact, this duality is a bigger problem: if we have a config
+    //      that uses config.cli there is no way to reconfigure it to use
+    //      config.import.cli.
+    //
+    //    - We could have saved it commented.
+    //
+    //    - We could do this at the module level only since we also have
+    //      config.cli.options?
+    //
+    //    - Note that in the CLI compiler itself we now rely on default cli
+    //      being NULL/undefined. So if faving, should probably be commented
+    //      out. BUT: it will still be defined, so will need to be defined
+    //      NULL. Note also that long term the CLI compiler will not use the
+    //      module relying on an ad hoc recipe instead.
+    //
+    //    ! Maybe reserving NULL (instead of making it the same as NULL) for
+    //      this "configured to default" state and saving commented is not a
+    //      bad idea. Feels right to have some marker in config.build that
+    //      things are in effect. And I believe if config.import.cli is
+    //      specified, it will just be dropped.
+
+    bool
+    guess_init (scope& rs,
+                scope& bs,
+                const location& loc,
+                bool,
+                bool opt,
+                module_init_extra& extra)
+    {
+      tracer trace ("cli::guess_init");
+      l5 ([&]{trace << "for " << rs;});
+
+      // We only support root loading (which means there can only be one).
+      //
+      if (rs != bs)
+        fail (loc) << "cli.guess module must be loaded in project root";
+
+      // Adjust module config.build save priority (code generator).
+      //
+      config::save_module (rs, "cli", 150);
+
+      // Enter metadata variables.
+      //
+      // They are all qualified so go straight for the public variable pool.
+      //
+      auto& vp (rs.var_pool (true /* public */));
+
+      auto& v_ver (vp.insert<string> ("cli.version"));
+      auto& v_sum (vp.insert<string> ("cli.checksum"));
+
+      // Import the CLI compiler target.
+      //
+      // Note that the special config.cli=false value (recognized by the
+      // import machinery) is treated as an explicit request to leave the
+      // module unconfigured.
+      //
+      bool new_cfg (false);
+      import_result<exe> ir (
+        import_direct<exe> (
+          new_cfg,
+          rs,
+          name ("cli", dir_path (), "exe", "cli"), // cli%exe{cli}
+          true      /* phase2 */,
+          opt,
+          true      /* metadata */,
+          loc,
+          "module load"));
+
+      const exe* tgt (ir.target);
+
+      // Extract metadata.
+      //
+      auto* ver (tgt != nullptr ? &cast<string> (tgt->vars[v_ver]) : nullptr);
+      auto* sum (tgt != nullptr ? &cast<string> (tgt->vars[v_sum]) : nullptr);
+
+      // Print the report.
+      //
+      // If this is a configuration with new values, then print the report
+      // at verbosity level 2 and up (-v).
+      //
+      if (verb >= (new_cfg ? 2 : 3))
+      {
+        diag_record dr (text);
+        dr << "cli " << project (rs) << '@' << rs << '\n';
+
+        if (tgt != nullptr)
+          dr << "  cli        " << ir << '\n'
+             << "  version    " << *ver << '\n'
+             << "  checksum   " << *sum;
+        else
+          dr << "  cli        " << "not found, leaving unconfigured";
+      }
+
+      if (tgt == nullptr)
+        return false;
+
+      // The cli variable (untyped) is an imported compiler target name.
+      //
+      rs.assign ("cli") = move (ir.name);
+      rs.assign (v_sum) = *sum;
+      rs.assign (v_ver) = *ver;
+
+      {
+        standard_version v (*ver);
+
+        rs.assign<uint64_t> ("cli.version.number") = v.version;
+        rs.assign<uint64_t> ("cli.version.major") = v.major ();
+        rs.assign<uint64_t> ("cli.version.minor") = v.minor ();
+        rs.assign<uint64_t> ("cli.version.patch") = v.patch ();
+      }
+
+      // Cache some values in the module for easier access in the rule.
+      //
+      extra.set_module (new module (data {*tgt, *sum}));
+
+      return true;
+    }
+
+    bool
+    config_init (scope& rs,
+                 scope& bs,
+                 const location& loc,
+                 bool,
+                 bool opt,
+                 module_init_extra& extra)
+    {
+      tracer trace ("cli::config_init");
+      l5 ([&]{trace << "for " << rs;});
+
+      // We only support root loading (which means there can only be one).
+      //
+      if (rs != bs)
+        fail (loc) << "cli.config module must be loaded in project root";
+
+      // Load cli.guess and share its module instance as ours.
+      //
+      if (optional<shared_ptr<build2::module>> r = load_module (
+            rs, rs, "cli.guess", loc, opt, extra.hints))
+      {
+        extra.module = *r;
+      }
+      else
+      {
+        // This can happen if someone already optionally loaded cli.guess
+        // and it has failed to configure.
+        //
+        if (!opt)
+          fail (loc) << "cli could not be configured" <<
+            info << "re-run with -V for more information";
+
+        return false;
+      }
+
+      // Configuration.
+      //
+      using config::append_config;
+
+      // config.cli.options
+      //
+      // Note that we merge it into the corresponding cli.* variable.
+      //
+      append_config<strings> (rs, rs, "cli.options", nullptr);
+
+      return true;
+    }
+
+    bool
+    init (scope& rs,
+          scope& bs,
+          const location& loc,
+          bool,
+          bool opt,
+          module_init_extra& extra)
+    {
+      tracer trace ("cli::init");
+      l5 ([&]{trace << "for " << rs;});
+
+      // We only support root loading (which means there can only be one).
+      //
+      if (rs != bs)
+        fail (loc) << "cli module must be loaded in project root";
+
+      // Make sure the cxx module has been loaded since we need its targets
+      // types (?xx{}). Note that we don't try to load it ourselves because of
+      // the non-trivial variable merging semantics. So it is better to let
+      // the user load cxx explicitly. @@ Not sure the reason still holds
+      // though it might still make sense to expect the user to load cxx.
+      //
+      if (!cast_false<bool> (rs["cxx.loaded"]))
+        fail (loc) << "cxx module must be loaded before cli";
+
+      // Load cli.config and get its module instance.
+      //
+      if (optional<shared_ptr<build2::module>> r = load_module (
+            rs, rs, "cli.config", loc, opt, extra.hints))
+      {
+        extra.module = *r;
+      }
+      else
+      {
+        // This can happen if someone already optionally loaded cli.config
+        // and it has failed to configure.
+        //
+        if (!opt)
+          fail (loc) << "cli could not be configured" <<
+            info << "re-run with -V for more information";
+
+        return false;
+      }
+
+      auto& m (extra.module_as<module> ());
+
+      // Register target types.
+      //
+      rs.insert_target_type<cli> ();
+      rs.insert_target_type<cli_cxx> ();
+
+      // Register our rules.
+      //
+      // Other rules (e.g., cc::compile) may need to have the group members
+      // resolved/linked up. Looks like a general pattern: groups should
+      // resolve on *(update).
+      {
+        auto reg = [&rs, &m] (meta_operation_id mid, operation_id oid)
+        {
+          rs.insert_rule<cli_cxx>  (mid, oid, "cli.compile", m);
+          rs.insert_rule<cxx::hxx> (mid, oid, "cli.compile", m);
+          rs.insert_rule<cxx::cxx> (mid, oid, "cli.compile", m);
+          rs.insert_rule<cxx::ixx> (mid, oid, "cli.compile", m);
+        };
+
+        reg (0 /* wildcard */, update_id);
+        reg (perform_id,       clean_id);
+      }
+
+      return true;
+    }
+
+    static const module_functions mod_functions[] =
+    {
+      // NOTE: don't forget to also update the documentation in init.hxx if
+      //       changing anything here.
+
+      {"cli.guess",  nullptr, guess_init},
+      {"cli.config", nullptr, config_init},
+      {"cli",        nullptr, init},
+      {nullptr,      nullptr, nullptr}
+    };
+
+    const module_functions*
+    build2_cli_load ()
+    {
+      return mod_functions;
+    }
+  }
+}
diff --git a/libbuild2/cli/init.hxx b/libbuild2/cli/init.hxx
new file mode 100644
index 0000000..6d23795
--- /dev/null
+++ b/libbuild2/cli/init.hxx
@@ -0,0 +1,31 @@
+// file      : libbuild2/cli/init.hxx -*- C++ -*-
+// license   : MIT; see accompanying LICENSE file
+
+#ifndef LIBBUILD2_CLI_INIT_HXX
+#define LIBBUILD2_CLI_INIT_HXX
+
+#include <libbuild2/types.hxx>
+#include <libbuild2/utility.hxx>
+
+#include <libbuild2/module.hxx>
+
+#include <libbuild2/cli/export.hxx>
+
+namespace build2
+{
+  namespace cli
+  {
+    // Module `cli` does not require bootstrapping.
+    //
+    // Submodules:
+    //
+    // `cli.guess`  -- set variables describing the compiler.
+    // `cli.config` -- load `cli.guess` and set the rest of the variables.
+    // `cli`        -- load `cli.config` and register targets and rules.
+    //
+    extern "C" LIBBUILD2_CLI_SYMEXPORT const module_functions*
+    build2_cli_load ();
+  }
+}
+
+#endif // LIBBUILD2_CLI_INIT_HXX
diff --git a/libbuild2/cli/module.hxx b/libbuild2/cli/module.hxx
new file mode 100644
index 0000000..ba10540
--- /dev/null
+++ b/libbuild2/cli/module.hxx
@@ -0,0 +1,30 @@
+// file      : libbuild2/cli/module.hxx -*- C++ -*-
+// license   : MIT; see accompanying LICENSE file
+
+#ifndef LIBBUILD2_CLI_MODULE_HXX
+#define LIBBUILD2_CLI_MODULE_HXX
+
+#include <libbuild2/types.hxx>
+#include <libbuild2/utility.hxx>
+
+#include <libbuild2/module.hxx>
+
+#include <libbuild2/cli/rule.hxx>
+
+namespace build2
+{
+  namespace cli
+  {
+    class module: public build2::module,
+                  public virtual data,
+                  public compile_rule
+    {
+    public:
+      explicit
+      module (data&& d)
+          : data (move (d)), compile_rule (move (d)) {}
+    };
+  }
+}
+
+#endif // LIBBUILD2_CLI_MODULE_HXX
diff --git a/libbuild2/cli/rule.cxx b/libbuild2/cli/rule.cxx
new file mode 100644
index 0000000..996ca51
--- /dev/null
+++ b/libbuild2/cli/rule.cxx
@@ -0,0 +1,340 @@
+// file      : libbuild2/cli/rule.cxx -*- C++ -*-
+// license   : MIT; see accompanying LICENSE file
+
+#include <libbuild2/cli/rule.hxx>
+
+#include <libbuild2/depdb.hxx>
+#include <libbuild2/scope.hxx>
+#include <libbuild2/target.hxx>
+#include <libbuild2/context.hxx>
+#include <libbuild2/algorithm.hxx>
+#include <libbuild2/filesystem.hxx>
+#include <libbuild2/diagnostics.hxx>
+
+#include <libbuild2/cli/target.hxx>
+
+namespace build2
+{
+  namespace cli
+  {
+    // Figure out if name contains stem and, optionally, calculate prefix and
+    // suffix.
+    //
+    static bool
+    match_stem (const string& name, const string& stem,
+                string* prefix = nullptr, string* suffix = nullptr)
+    {
+      size_t p (name.find (stem));
+
+      if (p != string::npos)
+      {
+        if (prefix != nullptr)
+          prefix->assign (name, 0, p);
+
+        if (suffix != nullptr)
+          suffix->assign (name, p + stem.size (), string::npos);
+
+        return true;
+      }
+
+      return false;
+    }
+
+    bool compile_rule::
+    match (action a, target& t) const
+    {
+      tracer trace ("cli::compile_rule::match");
+
+      // Find the .cli source file.
+      //
+      auto find = [&trace, a, &t] (auto&& r) -> optional<prerequisite_member>
+      {
+        for (prerequisite_member p: r)
+        {
+          // If excluded or ad hoc, then don't factor it into our tests.
+          //
+          if (include (a, t, p) != include_type::normal)
+            continue;
+
+          if (p.is_a<cli> ())
+          {
+            // Check that the stem match.
+            //
+            if (match_stem (t.name, p.name ()))
+              return p;
+
+            l4 ([&]{trace << ".cli file stem '" << p.name () << "' "
+                          << "doesn't match target " << t;});
+          }
+        }
+
+        return nullopt;
+      };
+
+      if (cli_cxx* pt = t.is_a<cli_cxx> ())
+      {
+        // The cli.cxx{} group.
+        //
+        cli_cxx& t (*pt);
+
+        // See if we have a .cli source file.
+        //
+        if (!find (group_prerequisite_members (a, t)))
+        {
+          l4 ([&]{trace << "no .cli source file for target " << t;});
+          return false;
+        }
+
+        // Figure out the member list.
+        //
+        // At this stage, no further changes to cli.options are possible and
+        // we can determine whether the --suppress-inline option is present.
+        //
+        // Passing the group as a "reference target" is a bit iffy,
+        // conceptually.
+        //
+        t.h = &search<cxx::hxx> (t, t.dir, t.out, t.name);
+        t.c = &search<cxx::cxx> (t, t.dir, t.out, t.name);
+        t.i = find_option ("--suppress-inline", t, "cli.options")
+          ? nullptr
+          : &search<cxx::ixx> (t, t.dir, t.out, t.name);
+
+        return true;
+      }
+      else
+      {
+        // One of the ?xx{} members.
+        //
+
+        // Check if there is a corresponding cli.cxx{} group.
+        //
+        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
+        // synthesize the dependency.
+        //
+        if (g == nullptr || !g->has_prerequisites ())
+        {
+          if (optional<prerequisite_member> p = find (
+                prerequisite_members (a, t)))
+          {
+            if (g == nullptr)
+              g = &t.ctx.targets.insert<cli_cxx> (t.dir, t.out, t.name, trace);
+
+            prerequisites ps;
+            ps.push_back (p->as_prerequisite ());
+            g->prerequisites (move (ps));
+          }
+        }
+
+        if (g == nullptr)
+          return false;
+
+        // For ixx{}, verify it is part of the group (i.e., not disabled
+        // via --suppress-inline).
+        //
+        if (t.is_a<cxx::ixx> () &&
+            find_option ("--suppress-inline", *g, "cli.options"))
+          return false;
+
+        t.group = g;
+        return true;
+      }
+    }
+
+    recipe compile_rule::
+    apply (action a, target& xt) const
+    {
+      if (cli_cxx* pt = xt.is_a<cli_cxx> ())
+      {
+        cli_cxx& t (*pt);
+
+        // Derive file names for the members.
+        //
+        t.h->derive_path ();
+        t.c->derive_path ();
+        if (t.i != nullptr)
+          t.i->derive_path ();
+
+        // Inject dependency on the output directory.
+        //
+        inject_fsdir (a, t);
+
+        // Match prerequisites.
+        //
+        match_prerequisite_members (a, t);
+
+        // For update inject dependency on the CLI compiler target.
+        //
+        if (a == perform_update_id)
+          inject (a, t, ctgt);
+
+        switch (a)
+        {
+        case perform_update_id: return [this] (action a, const target& t)
+          {
+            return perform_update (a, t);
+          };
+        case perform_clean_id:  return &perform_clean_group_depdb;
+        default:                return noop_recipe; // Configure/dist update.
+        }
+      }
+      else
+      {
+        const cli_cxx& g (xt.group->as<cli_cxx> ());
+        match_sync (a, g);
+        return group_recipe; // Execute the group's recipe.
+      }
+    }
+
+    static void
+    append_extension (cstrings& args,
+                      const path_target& t,
+                      const char* option,
+                      const char* default_extension)
+    {
+      const string* e (t.ext ());
+      assert (e != nullptr); // Should have been figured out in apply().
+
+      if (*e != default_extension)
+      {
+        // CLI needs the extension with the leading dot (unless it is empty)
+        // while we store the extension without. But if there is an extension,
+        // then we can get it (with the dot) from the file name.
+        //
+        args.push_back (option);
+        args.push_back (e->empty ()
+                        ? e->c_str ()
+                        : t.path ().extension_cstring () - 1);
+      }
+    }
+
+    target_state compile_rule::
+    perform_update (action a, const target& xt) const
+    {
+      tracer trace ("cli::compile_rule::perform_update");
+
+      // The rule has been matched which means the members should be resolved
+      // and paths assigned. We use the header file as our "target path" for
+      // timestamp, depdb, etc.
+      //
+      const cli_cxx& t (xt.as<cli_cxx> ());
+      const path& tp (t.h->path ());
+
+      context& ctx (t.ctx);
+
+      // Update prerequisites and determine if any relevant ones render us
+      // out-of-date. Note that currently we treat all the prerequisites as
+      // potentially affecting the result (think prologues/epilogues, CLI
+      // compiler target itself, etc).
+      //
+      timestamp mt (t.load_mtime (tp));
+      auto pr (execute_prerequisites<cli> (a, t, mt));
+
+      bool update (!pr.first);
+      target_state ts (update ? target_state::changed : *pr.first);
+
+      const cli& s (pr.second);
+
+      // We use depdb to track changes to the .cli file name, options,
+      // compiler, etc.
+      //
+      depdb dd (tp + ".d");
+      {
+        // First should come the rule name/version.
+        //
+        if (dd.expect ("cli.compile 1") != nullptr)
+          l4 ([&]{trace << "rule mismatch forcing update of " << t;});
+
+        // Then the compiler checksum.
+        //
+        if (dd.expect (csum) != nullptr)
+          l4 ([&]{trace << "compiler mismatch forcing update of " << t;});
+
+        // Then the options checksum.
+        //
+        sha256 cs;
+        append_options (cs, t, "cli.options");
+
+        if (dd.expect (cs.string ()) != nullptr)
+          l4 ([&]{trace << "options mismatch forcing update of " << t;});
+
+        // Finally the .cli input file.
+        //
+        if (dd.expect (s.path ()) != nullptr)
+          l4 ([&]{trace << "input file mismatch forcing update of " << t;});
+      }
+
+      // Update if depdb mismatch.
+      //
+      if (dd.writing () || dd.mtime > mt)
+        update = true;
+
+      dd.close ();
+
+      // If nothing changed, then we are done.
+      //
+      if (!update)
+        return ts;
+
+      // Translate paths to relative (to working directory). This results in
+      // easier to read diagnostics.
+      //
+      path relo (relative (t.dir));
+      path rels (relative (s.path ()));
+
+      const process_path& pp (ctgt.process_path ());
+      cstrings args {pp.recall_string ()};
+
+      // See if we need to pass --output-{prefix,suffix}
+      //
+      string prefix, suffix;
+      match_stem (t.name, s.name, &prefix, &suffix);
+
+      if (!prefix.empty ())
+      {
+        args.push_back ("--output-prefix");
+        args.push_back (prefix.c_str ());
+      }
+
+      if (!suffix.empty ())
+      {
+        args.push_back ("--output-suffix");
+        args.push_back (suffix.c_str ());
+      }
+
+      // See if we need to pass any --?xx-suffix options.
+      //
+      append_extension (args, *t.h, "--hxx-suffix", "hxx");
+      append_extension (args, *t.c, "--cxx-suffix", "cxx");
+      if (t.i != nullptr)
+        append_extension (args, *t.i, "--ixx-suffix", "ixx");
+
+      append_options (args, t, "cli.options");
+
+      if (!relo.empty ())
+      {
+        args.push_back ("-o");
+        args.push_back (relo.string ().c_str ());
+      }
+
+      args.push_back (rels.string ().c_str ());
+      args.push_back (nullptr);
+
+      if (verb >= 2)
+        print_process (args);
+      else if (verb)
+        print_diag ("cli", s, t);
+
+      if (!ctx.dry_run)
+      {
+        run (ctx, pp, args, 1 /* finish_verbosity */);
+        dd.check_mtime (tp);
+      }
+
+      t.mtime (system_clock::now ());
+      return target_state::changed;
+    }
+  }
+}
diff --git a/libbuild2/cli/rule.hxx b/libbuild2/cli/rule.hxx
new file mode 100644
index 0000000..0132b44
--- /dev/null
+++ b/libbuild2/cli/rule.hxx
@@ -0,0 +1,46 @@
+// file      : libbuild2/cli/rule.hxx -*- C++ -*-
+// license   : MIT; see accompanying LICENSE file
+
+#ifndef LIBBUILD2_CLI_RULE_HXX
+#define LIBBUILD2_CLI_RULE_HXX
+
+#include <libbuild2/types.hxx>
+#include <libbuild2/utility.hxx>
+
+#include <libbuild2/rule.hxx>
+
+#include <libbuild2/cli/export.hxx>
+
+namespace build2
+{
+  namespace cli
+  {
+    // Cached data shared between rules and the module.
+    //
+    struct data
+    {
+      const exe&    ctgt; // CLI compiler target.
+      const string& csum; // CLI compiler checksum.
+    };
+
+    // @@ Redo as two separate rules?
+    //
+    class LIBBUILD2_CLI_SYMEXPORT compile_rule: public simple_rule,
+                                                private virtual data
+    {
+    public:
+      compile_rule (data&& d): data (move (d)) {}
+
+      virtual bool
+      match (action, target&) const override;
+
+      virtual recipe
+      apply (action, target&) const override;
+
+      target_state
+      perform_update (action, const target&) const;
+    };
+  }
+}
+
+#endif // LIBBUILD2_CLI_RULE_HXX
diff --git a/libbuild2/cli/target.cxx b/libbuild2/cli/target.cxx
new file mode 100644
index 0000000..22ae75c
--- /dev/null
+++ b/libbuild2/cli/target.cxx
@@ -0,0 +1,75 @@
+// file      : libbuild2/cli/target.cxx -*- C++ -*-
+// license   : MIT; see accompanying LICENSE file
+
+#include <libbuild2/cli/target.hxx>
+
+#include <libbuild2/context.hxx>
+
+namespace build2
+{
+  namespace cli
+  {
+    // cli
+    //
+    extern const char cli_ext_def[] = "cli";
+
+    const target_type cli::static_type
+    {
+      "cli",
+      &file::static_type,
+      &target_factory<cli>,
+      nullptr, /* fixed_extension */
+      &target_extension_var<cli_ext_def>,
+      &target_pattern_var<cli_ext_def>,
+      nullptr,
+      &file_search,
+      target_type::flag::none
+    };
+
+    // cli.cxx
+    //
+    group_view cli_cxx::
+    group_members (action) const
+    {
+      static_assert (sizeof (cli_cxx_members) == sizeof (const target*) * 3,
+                     "member layout incompatible with array");
+
+      return h != nullptr
+        ? group_view {reinterpret_cast<const target* const*> (&h),
+                      (i != nullptr ? 3U : 2U)}
+        : group_view {nullptr, 0};
+    }
+
+    static target*
+    cli_cxx_factory (context& ctx,
+                     const target_type&, dir_path d, dir_path o, string n)
+    {
+      tracer trace ("cli::cli_cxx_factory");
+
+      // Pre-enter (potential) members as targets. The main purpose of doing
+      // this is to avoid searching for existing files in src_base if the
+      // buildfile mentions some of them explicitly as prerequisites.
+      //
+      // Also required for the src-out remapping logic.
+      //
+      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 (ctx, move (d), move (o), move (n));
+    }
+
+    const target_type cli_cxx::static_type
+    {
+      "cli.cxx",
+      &mtime_target::static_type,
+      &cli_cxx_factory,
+      nullptr,
+      nullptr,
+      nullptr,
+      nullptr,
+      &target_search,
+      target_type::flag::see_through // Group with "see through" iteration.
+    };
+  }
+}
diff --git a/libbuild2/cli/target.hxx b/libbuild2/cli/target.hxx
new file mode 100644
index 0000000..8efb837
--- /dev/null
+++ b/libbuild2/cli/target.hxx
@@ -0,0 +1,61 @@
+// file      : libbuild2/cli/target.hxx -*- C++ -*-
+// license   : MIT; see accompanying LICENSE file
+
+#ifndef LIBBUILD2_CLI_TARGET_HXX
+#define LIBBUILD2_CLI_TARGET_HXX
+
+#include <libbuild2/types.hxx>
+#include <libbuild2/utility.hxx>
+
+#include <libbuild2/target.hxx>
+
+#include <libbuild2/cxx/target.hxx>
+
+#include <libbuild2/cli/export.hxx>
+
+namespace build2
+{
+  namespace cli
+  {
+    class LIBBUILD2_CLI_SYMEXPORT cli: public file
+    {
+    public:
+      cli (context& c, dir_path d, dir_path o, string n)
+          : file (c, move (d), move (o), move (n))
+      {
+        dynamic_type = &static_type;
+      }
+
+    public:
+      static const target_type static_type;
+    };
+
+    // Standard layout type compatible with group_view's const target*[3].
+    //
+    struct cli_cxx_members
+    {
+      const cxx::hxx* h = nullptr;
+      const cxx::cxx* c = nullptr;
+      const cxx::ixx* i = nullptr;
+    };
+
+    class LIBBUILD2_CLI_SYMEXPORT cli_cxx: public mtime_target,
+                                           public cli_cxx_members
+    {
+    public:
+      cli_cxx (context& c, dir_path d, dir_path o, string n)
+          : mtime_target (c, move (d), move (o), move (n))
+      {
+        dynamic_type = &static_type;
+      }
+
+      virtual group_view
+      group_members (action) const override;
+
+    public:
+      static const target_type static_type;
+    };
+  }
+}
+
+#endif // LIBBUILD2_CLI_TARGET_HXX
diff --git a/libbuild2/module.cxx b/libbuild2/module.cxx
index 0928307..4c1271c 100644
--- a/libbuild2/module.cxx
+++ b/libbuild2/module.cxx
@@ -50,6 +50,7 @@ namespace build2
     "bin",
     "c",
     "cc",
+    "cli",
     "cxx",
     "in",
     "version"