Move config, dist, test, and install modules into library

8 files changed, 1983 insertions, 0 deletions

diff --git a/libbuild2/install/functions.cxx b/libbuild2/install/functions.cxx
new file mode 100644
index 0000000..f067918
--- /dev/null
+++ b/libbuild2/install/functions.cxx
@@ -0,0 +1,33 @@
+// file      : libbuild2/install/functions.cxx -*- C++ -*-
+// copyright : Copyright (c) 2014-2019 Code Synthesis Ltd
+// license   : MIT; see accompanying LICENSE file
+
+#include <libbuild2/function.hxx>
+#include <libbuild2/variable.hxx>
+
+#include <libbuild2/install/utility.hxx>
+
+using namespace std;
+
+namespace build2
+{
+  namespace install
+  {
+    void
+    functions ()
+    {
+      function_family f ("install");
+
+      // Resolve potentially relative install.* value to an absolute directory
+      // based on (other) install.* values visible from the calling scope.
+      //
+      f[".resolve"] = [] (const scope* s, dir_path d)
+      {
+        if (s == nullptr)
+          fail << "install.resolve() called out of scope" << endf;
+
+        return resolve_dir (*s, move (d));
+      };
+    }
+  }
+}
diff --git a/libbuild2/install/init.cxx b/libbuild2/install/init.cxx
new file mode 100644
index 0000000..fb3d9ea
--- /dev/null
+++ b/libbuild2/install/init.cxx
@@ -0,0 +1,309 @@
+// file      : libbuild2/install/init.cxx -*- C++ -*-
+// copyright : Copyright (c) 2014-2019 Code Synthesis Ltd
+// license   : MIT; see accompanying LICENSE file
+
+#include <libbuild2/install/init.hxx>
+
+#include <libbuild2/scope.hxx>
+#include <libbuild2/target.hxx>
+#include <libbuild2/rule.hxx>
+#include <libbuild2/function.hxx>
+#include <libbuild2/operation.hxx>
+#include <libbuild2/diagnostics.hxx>
+
+#include <libbuild2/config/utility.hxx>
+
+#include <libbuild2/install/rule.hxx>
+#include <libbuild2/install/utility.hxx>
+#include <libbuild2/install/operation.hxx>
+
+using namespace std;
+using namespace butl;
+
+namespace build2
+{
+  namespace install
+  {
+    // Set install.<name>.* values based on config.install.<name>.* ones
+    // or the defaults. If none of config.install.* values were specified,
+    // then we do omitted/delayed configuration. Note that we still need
+    // to set all the install.* values to defaults, as if we had the
+    // default configuration.
+    //
+    // If override is true, then override values that came from outer
+    // configurations. We have to do this for paths that contain the
+    // package name.
+    //
+    // For global values we only set config.install.* variables. Non-global
+    // values with NULL defaults are omitted.
+    //
+    template <typename T, typename CT>
+    static void
+    set_var (bool spec,
+             scope& r,
+             const char* name,
+             const char* var,
+             const CT* dv,
+             bool override = false)
+    {
+      string vn;
+      lookup l;
+
+      bool global (*name == '\0');
+
+      if (spec)
+      {
+        // Note: overridable.
+        //
+        vn = "config.install";
+        if (!global)
+        {
+          vn += '.';
+          vn += name;
+        }
+        vn += var;
+        const variable& vr (var_pool.rw (r).insert<CT> (move (vn), true));
+
+        l = dv != nullptr
+          ? config::required (r, vr, *dv, override).first
+          : (global
+             ? config::optional (r, vr)
+             : config::omitted (r, vr).first);
+      }
+
+      if (global)
+        return;
+
+      // Note: not overridable.
+      //
+      vn = "install.";
+      vn += name;
+      vn += var;
+      const variable& vr (var_pool.rw (r).insert<T> (move (vn)));
+
+      value& v (r.assign (vr));
+
+      if (spec)
+      {
+        if (l)
+          v = cast<T> (l); // Strip CT to T.
+      }
+      else
+      {
+        if (dv != nullptr)
+          v = *dv;
+      }
+    }
+
+    template <typename T>
+    static void
+    set_dir (bool s,                                  // specified
+             scope& r,                                // root scope
+             const char* n,                           // var name
+             const T& p,                              // path
+             bool o = false,                          // override
+             const string& fm = string (),            // file mode
+             const string& dm = string (),            // dir mode
+             const build2::path& c = build2::path ()) // command
+    {
+      using build2::path;
+
+      bool global (*n == '\0');
+
+      if (!global)
+        set_var<dir_path> (s, r, n, "",        p.empty ()  ? nullptr : &p, o);
+
+      set_var<path>     (s, r, n, ".cmd",      c.empty ()  ? nullptr : &c);
+      set_var<strings>  (s, r, n, ".options",  (strings*) (nullptr));
+      set_var<string>   (s, r, n, ".mode",     fm.empty () ? nullptr : &fm);
+      set_var<string>   (s, r, n, ".dir_mode", dm.empty () ? nullptr : &dm);
+      set_var<string>   (s, r, n, ".sudo",     (string*) (nullptr));
+
+      // This one doesn't have config.* value (only set in a buildfile).
+      //
+      if (!global)
+        var_pool.rw (r).insert<bool> (string ("install.") + n + ".subdirs");
+    }
+
+    void
+    functions (); // functions.cxx
+
+    bool
+    boot (scope& rs, const location&, unique_ptr<module_base>&)
+    {
+      tracer trace ("install::boot");
+      l5 ([&]{trace << "for " << rs;});
+
+      // Register install function family if this is the first instance of the
+      // install modules.
+      //
+      if (!function_family::defined ("install"))
+        functions ();
+
+      // Register our operations.
+      //
+      rs.insert_operation (install_id,            op_install);
+      rs.insert_operation (uninstall_id,          op_uninstall);
+      rs.insert_operation (update_for_install_id, op_update_for_install);
+
+      return false;
+    }
+
+    static const path cmd ("install");
+
+    static const dir_path dir_root ("root");
+
+    static const dir_path dir_sbin      (dir_path ("exec_root") /= "sbin");
+    static const dir_path dir_bin       (dir_path ("exec_root") /= "bin");
+    static const dir_path dir_lib       (dir_path ("exec_root") /= "lib");
+    static const dir_path dir_libexec   (dir_path ("exec_root") /= "libexec");
+    static const dir_path dir_pkgconfig (dir_path ("lib") /= "pkgconfig");
+
+    static const dir_path dir_data    (dir_path ("data_root") /= "share");
+    static const dir_path dir_include (dir_path ("data_root") /= "include");
+
+    static const dir_path dir_doc  (dir_path (dir_data) /= "doc");
+    static const dir_path dir_man  (dir_path (dir_data) /= "man");
+    static const dir_path dir_man1 (dir_path ("man") /= "man1");
+
+    static const group_rule group_rule_ (true /* see_through_only */);
+
+    bool
+    init (scope& rs,
+          scope& bs,
+          const location& l,
+          unique_ptr<module_base>&,
+          bool first,
+          bool,
+          const variable_map& config_hints)
+    {
+      tracer trace ("install::init");
+
+      if (!first)
+      {
+        warn (l) << "multiple install module initializations";
+        return true;
+      }
+
+      const dir_path& out_root (rs.out_path ());
+      l5 ([&]{trace << "for " << out_root;});
+
+      assert (config_hints.empty ()); // We don't known any hints.
+
+      // Enter module variables.
+      //
+      auto& vp (var_pool.rw (rs));
+
+      // Note that the set_dir() calls below enter some more.
+      //
+      {
+        // Note: not overridable.
+        //
+        // The install variable is a path, not dir_path, since it can be used
+        // to both specify the target directory (to install with the same file
+        // name) or target file (to install with a different name). And the
+        // way we distinguish between the two is via the presence/absence of
+        // the trailing directory separator.
+        //
+        vp.insert<path>   ("install",         variable_visibility::target);
+        vp.insert<string> ("install.mode",    variable_visibility::project);
+        vp.insert<bool>   ("install.subdirs", variable_visibility::project);
+      }
+
+      // Register our rules.
+      //
+      {
+        auto& r (bs.rules);
+
+        const auto& ar (alias_rule::instance);
+        const auto& dr (fsdir_rule::instance);
+        const auto& fr (file_rule::instance);
+        const auto& gr (group_rule_);
+
+        r.insert<alias> (perform_install_id,   "install.alias", ar);
+        r.insert<alias> (perform_uninstall_id, "uninstall.alias", ar);
+
+        r.insert<fsdir> (perform_install_id,   "install.fsdir", dr);
+        r.insert<fsdir> (perform_uninstall_id, "install.fsdir", dr);
+
+        r.insert<file> (perform_install_id,   "install.file", fr);
+        r.insert<file> (perform_uninstall_id, "uninstall.file", fr);
+
+        r.insert<target> (perform_install_id,   "install.file", gr);
+        r.insert<target> (perform_uninstall_id, "uninstall.file", gr);
+     }
+
+      // Configuration.
+      //
+      // Note that we don't use any defaults for root -- the location
+      // must be explicitly specified or the installer will complain
+      // if and when we try to install.
+      //
+      {
+        using build2::path;
+
+        bool s (config::specified (rs, "install"));
+
+        // Adjust module priority so that the (numerous) config.install.*
+        // values are saved at the end of config.build.
+        //
+        if (s)
+          config::save_module (rs, "install", INT32_MAX);
+
+        const string& n (project (rs).string ());
+
+        // Global config.install.* values.
+        //
+        set_dir (s, rs, "",          abs_dir_path (), false, "644", "755", cmd);
+
+        set_dir (s, rs, "root",      abs_dir_path ());
+
+        set_dir (s, rs, "data_root", dir_root);
+        set_dir (s, rs, "exec_root", dir_root, false, "755");
+
+        set_dir (s, rs, "sbin",      dir_sbin);
+        set_dir (s, rs, "bin",       dir_bin);
+        set_dir (s, rs, "lib",       dir_lib);
+        set_dir (s, rs, "libexec",   dir_path (dir_libexec) /= n, true);
+        set_dir (s, rs, "pkgconfig", dir_pkgconfig, false, "644");
+
+        set_dir (s, rs, "data",      dir_path (dir_data) /= n, true);
+        set_dir (s, rs, "include",   dir_include);
+
+        set_dir (s, rs, "doc",       dir_path (dir_doc) /= n, true);
+        set_dir (s, rs, "man",       dir_man);
+        set_dir (s, rs, "man1",      dir_man1);
+
+        // Support for chroot'ed install (aka DESTDIR).
+        //
+        {
+          auto& var  (vp.insert<dir_path>     (       "install.chroot"));
+          auto& cvar (vp.insert<abs_dir_path> ("config.install.chroot", true));
+
+          value& v (rs.assign (var));
+
+          if (s)
+          {
+            if (lookup l = config::optional (rs, cvar))
+              v = cast<dir_path> (l); // Strip abs_dir_path.
+          }
+        }
+      }
+
+      // Configure "installability" for built-in target types.
+      //
+      install_path<exe>  (bs, dir_path ("bin"));  // Install into install.bin.
+      install_path<doc>  (bs, dir_path ("doc"));  // Install into install.doc.
+      install_path<man>  (bs, dir_path ("man"));  // Install into install.man.
+      install_path<man1> (bs, dir_path ("man1")); // Install into install.man1.
+
+      return true;
+    }
+
+    module_functions
+    build2_install_load ()
+    {
+      return module_functions {&boot, &init};
+    }
+  }
+}
diff --git a/libbuild2/install/init.hxx b/libbuild2/install/init.hxx
new file mode 100644
index 0000000..fa0a1e1
--- /dev/null
+++ b/libbuild2/install/init.hxx
@@ -0,0 +1,36 @@
+// file      : libbuild2/install/init.hxx -*- C++ -*-
+// copyright : Copyright (c) 2014-2019 Code Synthesis Ltd
+// license   : MIT; see accompanying LICENSE file
+
+#ifndef LIBBUILD2_INSTALL_INIT_HXX
+#define LIBBUILD2_INSTALL_INIT_HXX
+
+#include <libbuild2/types.hxx>
+#include <libbuild2/utility.hxx>
+
+#include <libbuild2/module.hxx>
+
+#include <libbuild2/export.hxx>
+
+namespace build2
+{
+  namespace install
+  {
+    bool
+    boot (scope&, const location&, unique_ptr<module_base>&);
+
+    bool
+    init (scope&,
+          scope&,
+          const location&,
+          unique_ptr<module_base>&,
+          bool,
+          bool,
+          const variable_map&);
+
+    extern "C" LIBBUILD2_SYMEXPORT module_functions
+    build2_install_load ();
+  }
+}
+
+#endif // LIBBUILD2_INSTALL_INIT_HXX
diff --git a/libbuild2/install/operation.cxx b/libbuild2/install/operation.cxx
new file mode 100644
index 0000000..1135ad6
--- /dev/null
+++ b/libbuild2/install/operation.cxx
@@ -0,0 +1,84 @@
+// file      : libbuild2/install/operation.cxx -*- C++ -*-
+// copyright : Copyright (c) 2014-2019 Code Synthesis Ltd
+// license   : MIT; see accompanying LICENSE file
+
+#include <libbuild2/install/operation.hxx>
+
+using namespace std;
+using namespace butl;
+
+namespace build2
+{
+  namespace install
+  {
+    static operation_id
+    install_pre (const values& params, meta_operation_id mo, const location& l)
+    {
+      if (!params.empty ())
+        fail (l) << "unexpected parameters for operation install";
+
+      // Run update as a pre-operation, unless we are disfiguring.
+      //
+      return mo != disfigure_id ? update_id : 0;
+    }
+
+    // Note that we run both install and uninstall serially. The reason for
+    // this is all the fuzzy things we are trying to do like removing empty
+    // outer directories if they are empty. If we do this in parallel, then
+    // those things get racy. Also, since all we do here is creating/removing
+    // files, there is not going to be much speedup from doing it in parallel.
+
+    const operation_info op_install {
+      install_id,
+      0,
+      "install",
+      "install",
+      "installing",
+      "installed",
+      "has nothing to install", // We cannot "be installed".
+      execution_mode::first,
+      0,
+      &install_pre,
+      nullptr
+    };
+
+    // Note that we run update as a pre-operation, just like install. Which
+    // may seem bizarre at first. We do it to obtain the exact same dependency
+    // graph as install so that we uninstall exactly the same set of files as
+    // install would install. Note that just matching the rules without
+    // executing them may not be enough: for example, a presence of an ad hoc
+    // group member may only be discovered after executing the rule (e.g., VC
+    // link.exe only creates a DLL's import library if there are any exported
+    // symbols).
+    //
+    const operation_info op_uninstall {
+      uninstall_id,
+      0,
+      "uninstall",
+      "uninstall",
+      "uninstalling",
+      "uninstalled",
+      "is not installed",
+      execution_mode::last,
+      0,
+      &install_pre,
+      nullptr
+    };
+
+    // Also the explicit update-for-install operation alias.
+    //
+    const operation_info op_update_for_install {
+      update_id, // Note: not update_for_install_id.
+      install_id,
+      op_update.name,
+      op_update.name_do,
+      op_update.name_doing,
+      op_update.name_did,
+      op_update.name_done,
+      op_update.mode,
+      op_update.concurrency,
+      op_update.pre,
+      op_update.post
+    };
+  }
+}
diff --git a/libbuild2/install/operation.hxx b/libbuild2/install/operation.hxx
new file mode 100644
index 0000000..40cf25d
--- /dev/null
+++ b/libbuild2/install/operation.hxx
@@ -0,0 +1,23 @@
+// file      : libbuild2/install/operation.hxx -*- C++ -*-
+// copyright : Copyright (c) 2014-2019 Code Synthesis Ltd
+// license   : MIT; see accompanying LICENSE file
+
+#ifndef LIBBUILD2_INSTALL_OPERATION_HXX
+#define LIBBUILD2_INSTALL_OPERATION_HXX
+
+#include <libbuild2/types.hxx>
+#include <libbuild2/utility.hxx>
+
+#include <libbuild2/operation.hxx>
+
+namespace build2
+{
+  namespace install
+  {
+    extern const operation_info op_install;
+    extern const operation_info op_uninstall;
+    extern const operation_info op_update_for_install;
+  }
+}
+
+#endif // LIBBUILD2_INSTALL_OPERATION_HXX
diff --git a/libbuild2/install/rule.cxx b/libbuild2/install/rule.cxx
new file mode 100644
index 0000000..0b34832
--- /dev/null
+++ b/libbuild2/install/rule.cxx
@@ -0,0 +1,1223 @@
+// file      : libbuild2/install/rule.cxx -*- C++ -*-
+// copyright : Copyright (c) 2014-2019 Code Synthesis Ltd
+// license   : MIT; see accompanying LICENSE file
+
+#include <libbuild2/install/rule.hxx>
+#include <libbuild2/install/utility.hxx> // resolve_dir() declaration
+
+#include <libbutl/filesystem.mxx> // dir_exists(), file_exists()
+
+#include <libbuild2/scope.hxx>
+#include <libbuild2/target.hxx>
+#include <libbuild2/algorithm.hxx>
+#include <libbuild2/filesystem.hxx>
+#include <libbuild2/diagnostics.hxx>
+
+using namespace std;
+using namespace butl;
+
+namespace build2
+{
+  namespace install
+  {
+    // Lookup the install or install.* variable. Return NULL if not found or
+    // if the value is the special 'false' name (which means do not install;
+    // so the result can be used as bool). T is either scope or target.
+    //
+    template <typename P, typename T>
+    static const P*
+    lookup_install (T& t, const string& var)
+    {
+      auto l (t[var]);
+
+      if (!l)
+        return nullptr;
+
+      const P& r (cast<P> (l));
+      return r.simple () && r.string () == "false" ? nullptr : &r;
+    }
+
+    // alias_rule
+    //
+    const alias_rule alias_rule::instance;
+
+    bool alias_rule::
+    match (action, target&, const string&) const
+    {
+      // We always match.
+      //
+      // Note that we are called both as the outer part during the update-for-
+      // un/install pre-operation and as the inner part during the un/install
+      // operation itself.
+      //
+      return true;
+    }
+
+    const target* alias_rule::
+    filter (action a, const target& t, prerequisite_iterator& i) const
+    {
+      assert (i->member == nullptr);
+      return filter (a, t, i->prerequisite);
+    }
+
+    const target* alias_rule::
+    filter (action, const target& t, const prerequisite& p) const
+    {
+      const target& pt (search (t, p));
+      return pt.in (t.weak_scope ()) ? &pt : nullptr;
+    }
+
+    recipe alias_rule::
+    apply (action a, target& t) const
+    {
+      tracer trace ("install::alias_rule::apply");
+
+      // Pass-through to our installable prerequisites.
+      //
+      // @@ Shouldn't we do match in parallel (here and below)?
+      //
+      auto& pts (t.prerequisite_targets[a]);
+
+      auto pms (group_prerequisite_members (a, t, members_mode::never));
+      for (auto i (pms.begin ()), e (pms.end ()); i != e; ++i)
+      {
+        const prerequisite& p (i->prerequisite);
+
+        // Ignore excluded.
+        //
+        include_type pi (include (a, t, p));
+
+        if (!pi)
+          continue;
+
+        // Ignore unresolved targets that are imported from other projects.
+        // We are definitely not installing those.
+        //
+        if (p.proj)
+          continue;
+
+        // Let a customized rule have its say.
+        //
+        // Note: we assume that if the filter enters the group, then it
+        // iterates over all its members.
+        //
+        const target* pt (filter (a, t, i));
+        if (pt == nullptr)
+        {
+          l5 ([&]{trace << "ignoring " << p << " (filtered out)";});
+          continue;
+        }
+
+        // Check if this prerequisite is explicitly "not installable", that
+        // is, there is the 'install' variable and its value is false.
+        //
+        // At first, this might seem redundand since we could have let the
+        // file_rule below take care of it. The nuance is this: this
+        // prerequsite can be in a different subproject that hasn't loaded the
+        // install module (and therefore has no file_rule registered). The
+        // typical example would be the 'tests' subproject.
+        //
+        // Note: not the same as lookup_install() above.
+        //
+        auto l ((*pt)["install"]);
+        if (l && cast<path> (l).string () == "false")
+        {
+          l5 ([&]{trace << "ignoring " << *pt << " (not installable)";});
+          continue;
+        }
+
+        // If this is not a file-based target (e.g., a target group such as
+        // libu{}) then ignore it if there is no rule to install.
+        //
+        if (pt->is_a<file> ())
+          build2::match (a, *pt);
+        else if (!try_match (a, *pt).first)
+        {
+          l5 ([&]{trace << "ignoring " << *pt << " (no rule)";});
+          pt = nullptr;
+        }
+
+        if (pt != nullptr)
+          pts.push_back (prerequisite_target (pt, pi));
+      }
+
+      return default_recipe;
+    }
+
+    // fsdir_rule
+    //
+    const fsdir_rule fsdir_rule::instance;
+
+    bool fsdir_rule::
+    match (action, target&, const string&) const
+    {
+      // We always match.
+      //
+      // Note that we are called both as the outer part during the update-for-
+      // un/install pre-operation and as the inner part during the un/install
+      // operation itself.
+      //
+      return true;
+    }
+
+    recipe fsdir_rule::
+    apply (action a, target& t) const
+    {
+      // If this is outer part of the update-for-un/install, delegate to the
+      // default fsdir rule. Otherwise, this is a noop (we don't install
+      // fsdir{}).
+      //
+      // For now we also assume we don't need to do anything for prerequisites
+      // (the only sensible prerequisite of fsdir{} is another fsdir{}).
+      //
+      if (a.operation () == update_id)
+      {
+        match_inner (a, t);
+        return &execute_inner;
+      }
+      else
+        return noop_recipe;
+    }
+
+    // group_rule
+    //
+    const group_rule group_rule::instance (false /* see_through_only */);
+
+    bool group_rule::
+    match (action a, target& t, const string& h) const
+    {
+      return (!see_through || t.type ().see_through) &&
+        alias_rule::match (a, t, h);
+    }
+
+    const target* group_rule::
+    filter (action, const target&, const target& m) const
+    {
+      return &m;
+    }
+
+    recipe group_rule::
+    apply (action a, target& t) const
+    {
+      tracer trace ("install::group_rule::apply");
+
+      // Resolve group members.
+      //
+      // Remember that we are called twice: first during update for install
+      // (pre-operation) and then during install. During the former, we rely
+      // on the normall update rule to resolve the group members. During the
+      // latter, there will be no rule to do this but the group will already
+      // have been resolved by the pre-operation.
+      //
+      // If the rule could not resolve the group, then we ignore it.
+      //
+      group_view gv (a.outer ()
+                     ? resolve_members (a, t)
+                     : t.group_members (a));
+
+      if (gv.members != nullptr)
+      {
+        auto& pts (t.prerequisite_targets[a]);
+
+        for (size_t i (0); i != gv.count; ++i)
+        {
+          const target* m (gv.members[i]);
+
+          if (m == nullptr)
+            continue;
+
+          // Let a customized rule have its say.
+          //
+          const target* mt (filter (a, t, *m));
+          if (mt == nullptr)
+          {
+            l5 ([&]{trace << "ignoring " << *m << " (filtered out)";});
+            continue;
+          }
+
+          // See if we were explicitly instructed not to touch this target
+          // (the same semantics as in the prerequisites match).
+          //
+          // Note: not the same as lookup_install() above.
+          //
+          auto l ((*mt)["install"]);
+          if (l && cast<path> (l).string () == "false")
+          {
+            l5 ([&]{trace << "ignoring " << *mt << " (not installable)";});
+            continue;
+          }
+
+          build2::match (a, *mt);
+          pts.push_back (mt); // Never ad hoc.
+        }
+      }
+
+      // Delegate to the base rule.
+      //
+      return alias_rule::apply (a, t);
+    }
+
+
+    // file_rule
+    //
+    const file_rule file_rule::instance;
+
+    bool file_rule::
+    match (action, target&, const string&) const
+    {
+      // We always match, even if this target is not installable (so that we
+      // can ignore it; see apply()).
+      //
+      return true;
+    }
+
+    const target* file_rule::
+    filter (action a, const target& t, prerequisite_iterator& i) const
+    {
+      assert (i->member == nullptr);
+      return filter (a, t, i->prerequisite);
+    }
+
+    const target* file_rule::
+    filter (action, const target& t, const prerequisite& p) const
+    {
+      const target& pt (search (t, p));
+      return pt.in (t.root_scope ()) ? &pt : nullptr;
+    }
+
+    recipe file_rule::
+    apply (action a, target& t) const
+    {
+      tracer trace ("install::file_rule::apply");
+
+      // Note that we are called both as the outer part during the update-for-
+      // un/install pre-operation and as the inner part during the un/install
+      // operation itself.
+      //
+      // In both cases we first determine if the target is installable and
+      // return noop if it's not. Otherwise, in the first case (update-for-
+      // un/install) we delegate to the normal update and in the second
+      // (un/install) -- perform the test.
+      //
+      if (!lookup_install<path> (t, "install"))
+        return noop_recipe;
+
+      // In both cases, the next step is to search, match, and collect all the
+      // installable prerequisites.
+      //
+      // But first, in case of the update pre-operation, match the inner rule
+      // (actual update). We used to do this after matching the prerequisites
+      // but the inner rule may provide some rule-specific information (like
+      // the target extension for exe{}) that may be required during the
+      // prerequisite search (like the base name for in{}).
+      //
+      optional<bool> unchanged;
+      if (a.operation () == update_id)
+        unchanged = match_inner (a, t, unmatch::unchanged);
+
+      auto& pts (t.prerequisite_targets[a]);
+
+      auto pms (group_prerequisite_members (a, t, members_mode::never));
+      for (auto i (pms.begin ()), e (pms.end ()); i != e; ++i)
+      {
+        const prerequisite& p (i->prerequisite);
+
+        // Ignore excluded.
+        //
+        include_type pi (include (a, t, p));
+
+        if (!pi)
+          continue;
+
+        // Ignore unresolved targets that are imported from other projects.
+        // We are definitely not installing those.
+        //
+        if (p.proj)
+          continue;
+
+        // Let a customized rule have its say.
+        //
+        // Note: we assume that if the filter enters the group, then it
+        // iterates over all its members.
+        //
+        const target* pt (filter (a, t, i));
+        if (pt == nullptr)
+        {
+          l5 ([&]{trace << "ignoring " << p << " (filtered out)";});
+          continue;
+        }
+
+        // See if we were explicitly instructed not to touch this target (the
+        // same semantics as in alias_rule).
+        //
+        // Note: not the same as lookup_install() above.
+        //
+        auto l ((*pt)["install"]);
+        if (l && cast<path> (l).string () == "false")
+        {
+          l5 ([&]{trace << "ignoring " << *pt << " (not installable)";});
+          continue;
+        }
+
+        if (pt->is_a<file> ())
+        {
+          // If the matched rule returned noop_recipe, then the target state
+          // is set to unchanged as an optimization. Use this knowledge to
+          // optimize things on our side as well since this will help a lot
+          // when updating static installable content (headers, documentation,
+          // etc).
+          //
+          if (build2::match (a, *pt, unmatch::unchanged))
+            pt = nullptr;
+        }
+        else if (!try_match (a, *pt).first)
+        {
+          l5 ([&]{trace << "ignoring " << *pt << " (no rule)";});
+          pt = nullptr;
+        }
+
+        if (pt != nullptr)
+          pts.push_back (prerequisite_target (pt, pi));
+      }
+
+      if (a.operation () == update_id)
+      {
+        return *unchanged
+          ? (pts.empty () ? noop_recipe : default_recipe)
+          : &perform_update;
+      }
+      else
+      {
+        return [this] (action a, const target& t)
+        {
+          return a.operation () == install_id
+            ? perform_install   (a, t)
+            : perform_uninstall (a, t);
+        };
+      }
+    }
+
+    target_state file_rule::
+    perform_update (action a, const target& t)
+    {
+      // First execute the inner recipe then prerequisites.
+      //
+      target_state ts (execute_inner (a, t));
+
+      if (t.prerequisite_targets[a].size () != 0)
+        ts |= straight_execute_prerequisites (a, t);
+
+      return ts;
+    }
+
+    bool file_rule::
+    install_extra (const file&, const install_dir&) const
+    {
+      return false;
+    }
+
+    bool file_rule::
+    uninstall_extra (const file&, const install_dir&) const
+    {
+      return false;
+    }
+
+    auto_rmfile file_rule::
+    install_pre (const file& t, const install_dir&) const
+    {
+      return auto_rmfile (t.path (), false /* active */);
+    }
+
+    bool file_rule::
+    install_post (const file& t, const install_dir& id, auto_rmfile&&) const
+    {
+      return install_extra (t, id);
+    }
+
+    struct install_dir
+    {
+      dir_path dir;
+
+      // If not NULL, then point to the corresponding install.* value.
+      //
+      const string*  sudo     = nullptr;
+      const path*    cmd      = nullptr;
+      const strings* options  = nullptr;
+      const string*  mode     = nullptr;
+      const string*  dir_mode = nullptr;
+
+      explicit
+      install_dir (dir_path d = dir_path ()): dir (move (d)) {}
+
+      install_dir (dir_path d, const install_dir& b)
+          : dir (move (d)),
+            sudo (b.sudo),
+            cmd (b.cmd),
+            options (b.options),
+            mode (b.mode),
+            dir_mode (b.dir_mode) {}
+    };
+
+    using install_dirs = vector<install_dir>;
+
+    // Calculate a subdirectory based on l's location (*.subdirs) and if not
+    // empty add it to install_dirs. Return the new last element.
+    //
+    static install_dir&
+    resolve_subdir (install_dirs& rs,
+                    const target& t,
+                    const scope& s,
+                    const lookup& l)
+    {
+      // Find the scope from which this value came and use as a base
+      // to calculate the subdirectory.
+      //
+      for (const scope* p (&s); p != nullptr; p = p->parent_scope ())
+      {
+        if (l.belongs (*p, true)) // Include target type/pattern-specific.
+        {
+          // The target can be in out or src.
+          //
+          const dir_path& d (t.out_dir ().leaf (p->out_path ()));
+
+          // Add it as another leading directory rather than modifying
+          // the last one directly; somehow, it feels right.
+          //
+          if (!d.empty ())
+            rs.emplace_back (rs.back ().dir / d, rs.back ());
+          break;
+        }
+      }
+
+      return rs.back ();
+    }
+
+    // Resolve installation directory name to absolute directory path. Return
+    // all the super-directories leading up to the destination (last).
+    //
+    // If target is not NULL, then also handle the subdirs logic.
+    //
+    static install_dirs
+    resolve (const scope& s,
+             const target* t,
+             dir_path d,
+             bool fail_unknown = true,
+             const string* var = nullptr)
+    {
+      install_dirs rs;
+
+      if (d.absolute ())
+        rs.emplace_back (move (d.normalize ()));
+      else
+      {
+        // If it is relative, then the first component is treated as the
+        // installation directory name, e.g., bin, sbin, lib, etc. Look it
+        // up and recurse.
+        //
+        if (d.empty ())
+          fail << "empty installation directory name";
+
+        const string& sn (*d.begin ());
+        const string var ("install." + sn);
+        if (const dir_path* dn = lookup_install<dir_path> (s, var))
+        {
+          if (dn->empty ())
+            fail << "empty installation directory for name " << sn <<
+              info << "did you specified empty config." << var << "?";
+
+          rs = resolve (s, t, *dn, fail_unknown, &var);
+
+          if (rs.empty ())
+          {
+            assert (!fail_unknown);
+            return rs; // Empty.
+          }
+
+          d = rs.back ().dir / dir_path (++d.begin (), d.end ());
+          rs.emplace_back (move (d.normalize ()), rs.back ());
+        }
+        else
+        {
+          if (fail_unknown)
+            fail << "unknown installation directory name '" << sn << "'" <<
+              info << "did you forget to specify config." << var << "?";
+
+          return rs; // Empty.
+        }
+      }
+
+      install_dir* r (&rs.back ());
+
+      // Override components in install_dir if we have our own.
+      //
+      if (var != nullptr)
+      {
+        if (auto l = s[*var + ".sudo"])     r->sudo     = &cast<string> (l);
+        if (auto l = s[*var + ".cmd"])      r->cmd      = &cast<path> (l);
+        if (auto l = s[*var + ".mode"])     r->mode     = &cast<string> (l);
+        if (auto l = s[*var + ".dir_mode"]) r->dir_mode = &cast<string> (l);
+        if (auto l = s[*var + ".options"])  r->options  = &cast<strings> (l);
+
+        if (t != nullptr)
+        {
+          if (auto l = s[*var + ".subdirs"])
+          {
+            if (cast<bool> (l))
+              r = &resolve_subdir (rs, *t, s, l);
+          }
+        }
+      }
+
+      // Set globals for unspecified components.
+      //
+      if (r->sudo == nullptr)
+        r->sudo = cast_null<string> (s["config.install.sudo"]);
+
+      if (r->cmd == nullptr)
+        r->cmd = &cast<path> (s["config.install.cmd"]);
+
+      if (r->options == nullptr)
+        r->options = cast_null<strings> (s["config.install.options"]);
+
+      if (r->mode == nullptr)
+        r->mode = &cast<string> (s["config.install.mode"]);
+
+      if (r->dir_mode == nullptr)
+        r->dir_mode = &cast<string> (s["config.install.dir_mode"]);
+
+      return rs;
+    }
+
+    static inline install_dirs
+    resolve (const target& t, dir_path d, bool fail_unknown = true)
+    {
+      return resolve (t.base_scope (), &t, d, fail_unknown);
+    }
+
+    dir_path
+    resolve_dir (const target& t, dir_path d, bool fail_unknown)
+    {
+      install_dirs r (resolve (t, move (d), fail_unknown));
+      return r.empty () ? dir_path () : move (r.back ().dir);
+    }
+
+    dir_path
+    resolve_dir (const scope& s, dir_path d, bool fail_unknown)
+    {
+      install_dirs r (resolve (s, nullptr, move (d), fail_unknown));
+      return r.empty () ? dir_path () : move (r.back ().dir);
+    }
+
+    path
+    resolve_file (const file& f)
+    {
+      // Note: similar logic to perform_install().
+      //
+      const path* p (lookup_install<path> (f, "install"));
+
+      if (p == nullptr) // Not installable.
+        return path ();
+
+      bool n (!p->to_directory ());
+      dir_path d (n ? p->directory () : path_cast<dir_path> (*p));
+
+      install_dirs ids (resolve (f, d));
+
+      if (!n)
+      {
+        if (auto l = f["install.subdirs"])
+        {
+          if (cast<bool> (l))
+            resolve_subdir (ids, f, f.base_scope (), l);
+        }
+      }
+
+      return ids.back ().dir / (n ? p->leaf () : f.path ().leaf ());
+    }
+
+    // On Windows we use MSYS2 install.exe and MSYS2 by default ignores
+    // filesystem permissions (noacl mount option). And this means, for
+    // example, that .exe that we install won't be runnable by Windows (MSYS2
+    // itself will still run them since it recognizes the file extension).
+    //
+    // NOTE: this is no longer the case and we now use noacl (and acl causes
+    // other problems; see baseutils fstab for details).
+    //
+    // The way we work around this (at least in our distribution of the MSYS2
+    // tools) is by changing the mount option for cygdrives (/c, /d, etc) to
+    // acl. But that's not all: we also have to install via a path that "hits"
+    // one of those mount points, c:\foo won't work, we have to use /c/foo.
+    // So this function translates an absolute Windows path to its MSYS
+    // representation.
+    //
+    // Note that we return the result as a string, not dir_path since path
+    // starting with / are illegal on Windows. Also note that the result
+    // doesn't have the trailing slash.
+    //
+    static string
+    msys_path (const dir_path& d)
+    {
+      assert (d.absolute ());
+      string s (d.representation ());
+
+      // First replace ':' with the drive letter (so the path is no longer
+      // absolute) but postpone setting the first character to / until we are
+      // a string.
+      //
+      s[1] = lcase (s[0]);
+      s = dir_path (move (s)).posix_string ();
+      s[0] = '/';
+
+      return s;
+    }
+
+    // Given an abolute path return its chroot'ed version, if any, accoring to
+    // install.chroot.
+    //
+    template <typename P>
+    static inline P
+    chroot_path (const scope& rs, const P& p)
+    {
+      if (const dir_path* d = cast_null<dir_path> (rs["install.chroot"]))
+      {
+        dir_path r (p.root_directory ());
+        assert (!r.empty ()); // Must be absolute.
+
+        return *d / p.leaf (r);
+      }
+
+      return p;
+    }
+
+    // install -d <dir>
+    //
+    static void
+    install_d (const scope& rs,
+               const install_dir& base,
+               const dir_path& d,
+               bool verbose = true)
+    {
+      // Here is the problem: if this is a dry-run, then we will keep showing
+      // the same directory creation commands over and over again (because we
+      // don't actually create them). There are two alternative ways to solve
+      // this: actually create the directories or simply don't show anything.
+      // While we use the former approach during update (see mkdir() in
+      // filesystem), here it feels like we really shouldn't be touching the
+      // destination filesystem. Plus, not showing anything will be symmetric
+      // with uninstall since the directories won't be empty (because we don't
+      // actually uninstall any files).
+      //
+      if (dry_run)
+        return;
+
+      dir_path chd (chroot_path (rs, d));
+
+      try
+      {
+        if (dir_exists (chd)) // May throw (e.g., EACCES).
+          return;
+      }
+      catch (const system_error& e)
+      {
+        fail << "invalid installation directory " << chd << ": " << e;
+      }
+
+      // While install -d will create all the intermediate components between
+      // base and dir, we do it explicitly, one at a time. This way the output
+      // is symmetrical to uninstall() below.
+      //
+      // Note that if the chroot directory does not exist, then install -d
+      // will create it and we don't bother removing it.
+      //
+      if (d != base.dir)
+      {
+        dir_path pd (d.directory ());
+
+        if (pd != base.dir)
+          install_d (rs, base, pd, verbose);
+      }
+
+      cstrings args;
+
+      string reld (
+        cast<string> ((*global_scope)["build.host.class"]) == "windows"
+        ? msys_path (chd)
+        : relative (chd).string ());
+
+      if (base.sudo != nullptr)
+        args.push_back (base.sudo->c_str ());
+
+      args.push_back (base.cmd->string ().c_str ());
+      args.push_back ("-d");
+
+      if (base.options != nullptr)
+        append_options (args, *base.options);
+
+      args.push_back ("-m");
+      args.push_back (base.dir_mode->c_str ());
+      args.push_back (reld.c_str ());
+      args.push_back (nullptr);
+
+      process_path pp (run_search (args[0]));
+
+      if (verb >= 2)
+        print_process (args);
+      else if (verb && verbose)
+        text << "install " << chd;
+
+      run (pp, args);
+    }
+
+    // install <file> <dir>/
+    // install <file> <file>
+    //
+    static void
+    install_f (const scope& rs,
+               const install_dir& base,
+               const path& name,
+               const file& t,
+               const path& f,
+               bool verbose)
+    {
+      path relf (relative (f));
+
+      dir_path chd (chroot_path (rs, base.dir));
+
+      string reld (
+        cast<string> ((*global_scope)["build.host.class"]) == "windows"
+        ? msys_path (chd)
+        : relative (chd).string ());
+
+      if (!name.empty ())
+      {
+        reld += path::traits_type::directory_separator;
+        reld += name.string ();
+      }
+
+      cstrings args;
+
+      if (base.sudo != nullptr)
+        args.push_back (base.sudo->c_str ());
+
+      args.push_back (base.cmd->string ().c_str ());
+
+      if (base.options != nullptr)
+        append_options (args, *base.options);
+
+      args.push_back ("-m");
+      args.push_back (base.mode->c_str ());
+      args.push_back (relf.string ().c_str ());
+      args.push_back (reld.c_str ());
+      args.push_back (nullptr);
+
+      process_path pp (run_search (args[0]));
+
+      if (verb >= 2)
+        print_process (args);
+      else if (verb && verbose)
+        text << "install " << t;
+
+      if (!dry_run)
+        run (pp, args);
+    }
+
+    void file_rule::
+    install_l (const scope& rs,
+               const install_dir& base,
+               const path& target,
+               const path& link,
+               bool verbose)
+    {
+      path rell (relative (chroot_path (rs, base.dir)));
+      rell /= link;
+
+      // We can create a symlink directly without calling ln. This, however,
+      // won't work if we have sudo. Also, we would have to deal with existing
+      // destinations (ln's -f takes care of that). So we are just going to
+      // always use ln.
+      //
+      const char* args_a[] = {
+        base.sudo != nullptr ? base.sudo->c_str () : nullptr,
+        "ln",
+        "-sf",
+        target.string ().c_str (),
+        rell.string ().c_str (),
+        nullptr};
+
+      const char** args (&args_a[base.sudo == nullptr ? 1 : 0]);
+
+      process_path pp (run_search (args[0]));
+
+      if (verb >= 2)
+        print_process (args);
+      else if (verb && verbose)
+        text << "install " << rell << " -> " << target;
+
+      if (!dry_run)
+        run (pp, args);
+    }
+
+    target_state file_rule::
+    perform_install (action a, const target& xt) const
+    {
+      const file& t (xt.as<file> ());
+      const path& tp (t.path ());
+
+      // Path should have been assigned by update unless it is unreal.
+      //
+      assert (!tp.empty () || t.mtime () == timestamp_unreal);
+
+      const scope& rs (t.root_scope ());
+
+      auto install_target = [&rs, this] (const file& t,
+                                         const path& p,
+                                         bool verbose)
+      {
+        // Note: similar logic to resolve_file().
+        //
+        bool n (!p.to_directory ());
+        dir_path d (n ? p.directory () : path_cast<dir_path> (p));
+
+        // Resolve target directory.
+        //
+        install_dirs ids (resolve (t, d));
+
+        // Handle install.subdirs if one was specified. Unless the target path
+        // includes the file name in which case we assume it's a "final" path.
+        //
+        if (!n)
+        {
+          if (auto l = t["install.subdirs"])
+          {
+            if (cast<bool> (l))
+              resolve_subdir (ids, t, t.base_scope (), l);
+          }
+        }
+
+        // Create leading directories. Note that we are using the leading
+        // directory (if there is one) for the creation information (mode,
+        // sudo, etc).
+        //
+        for (auto i (ids.begin ()), j (i); i != ids.end (); j = i++)
+          install_d (rs, *j, i->dir, verbose); // install -d
+
+        install_dir& id (ids.back ());
+
+        // Override mode if one was specified.
+        //
+        if (auto l = t["install.mode"])
+          id.mode = &cast<string> (l);
+
+        // Install the target.
+        //
+        auto_rmfile f (install_pre (t, id));
+
+        // If install_pre() returned a different file name, make sure we
+        // install it as the original.
+        //
+        const path& tp (t.path ());
+        const path& fp (f.path);
+
+        install_f (
+          rs,
+          id,
+          n ? p.leaf () : fp.leaf () != tp.leaf () ? tp.leaf () : path (),
+          t,
+          f.path,
+          verbose);
+
+        install_post (t, id, move (f));
+      };
+
+      // First handle installable prerequisites.
+      //
+      target_state r (straight_execute_prerequisites (a, t));
+
+      // Then installable ad hoc group members, if any.
+      //
+      for (const target* m (t.member); m != nullptr; m = m->member)
+      {
+        if (const path* p = lookup_install<path> (*m, "install"))
+        {
+          install_target (m->as<file> (), *p, tp.empty () /* verbose */);
+          r |= target_state::changed;
+        }
+      }
+
+      // Finally install the target itself (since we got here we know the
+      // install variable is there).
+      //
+      if (!tp.empty ())
+      {
+        install_target (t, cast<path> (t["install"]), true /* verbose */);
+        r |= target_state::changed;
+      }
+
+      return r;
+    }
+
+    // uninstall -d <dir>
+    //
+    // We try to remove all the directories between base and dir but not base
+    // itself unless base == dir. Return false if nothing has been removed
+    // (i.e., the directories do not exist or are not empty).
+    //
+    static bool
+    uninstall_d (const scope& rs,
+                 const install_dir& base,
+                 const dir_path& d,
+                 bool verbose)
+    {
+      // See install_d() for the rationale.
+      //
+      if (dry_run)
+        return false;
+
+      dir_path chd (chroot_path (rs, d));
+
+      // Figure out if we should try to remove this directory. Note that if
+      // it doesn't exist, then we may still need to remove outer ones.
+      //
+      bool r (false);
+      try
+      {
+        if ((r = dir_exists (chd))) // May throw (e.g., EACCES).
+        {
+          if (!dir_empty (chd)) // May also throw.
+            return false; // Won't be able to remove any outer directories.
+        }
+      }
+      catch (const system_error& e)
+      {
+        fail << "invalid installation directory " << chd << ": " << e;
+      }
+
+      if (r)
+      {
+        dir_path reld (relative (chd));
+
+        // Normally when we need to remove a file or directory we do it
+        // directly without calling rm/rmdir. This however, won't work if we
+        // have sudo. So we are going to do it both ways.
+        //
+        // While there is no sudo on Windows, deleting things that are being
+        // used can get complicated. So we will always use rm/rmdir there.
+        //
+#ifndef _WIN32
+        if (base.sudo == nullptr)
+        {
+          if (verb >= 2)
+            text << "rmdir " << reld;
+          else if (verb && verbose)
+            text << "uninstall " << reld;
+
+          try
+          {
+            try_rmdir (chd);
+          }
+          catch (const system_error& e)
+          {
+            fail << "unable to remove directory " << chd << ": " << e;
+          }
+        }
+        else
+#endif
+        {
+          const char* args_a[] = {
+            base.sudo != nullptr ? base.sudo->c_str () : nullptr,
+            "rmdir",
+            reld.string ().c_str (),
+            nullptr};
+
+          const char** args (&args_a[base.sudo == nullptr ? 1 : 0]);
+
+          process_path pp (run_search (args[0]));
+
+          if (verb >= 2)
+            print_process (args);
+          else if (verb && verbose)
+            text << "uninstall " << reld;
+
+          run (pp, args);
+        }
+      }
+
+      // If we have more empty directories between base and dir, then try
+      // to clean them up as well.
+      //
+      if (d != base.dir)
+      {
+        dir_path pd (d.directory ());
+
+        if (pd != base.dir)
+          r = uninstall_d (rs, base, pd, verbose) || r;
+      }
+
+      return r;
+    }
+
+    bool file_rule::
+    uninstall_f (const scope& rs,
+                 const install_dir& base,
+                 const file* t,
+                 const path& name,
+                 bool verbose)
+    {
+      assert (t != nullptr || !name.empty ());
+      path f (chroot_path (rs, base.dir) /
+              (name.empty () ? t->path ().leaf () : name));
+
+      try
+      {
+        // Note: don't follow symlinks so if the target is a dangling symlinks
+        // we will proceed to removing it.
+        //
+        if (!file_exists (f, false)) // May throw (e.g., EACCES).
+          return false;
+      }
+      catch (const system_error& e)
+      {
+        fail << "invalid installation path " << f << ": " << e;
+      }
+
+      path relf (relative (f));
+
+      if (verb == 1 && verbose)
+      {
+        if (t != nullptr)
+          text << "uninstall " << *t;
+        else
+          text << "uninstall " << relf;
+      }
+
+      // The same story as with uninstall -d.
+      //
+#ifndef _WIN32
+      if (base.sudo == nullptr)
+      {
+        if (verb >= 2)
+          text << "rm " << relf;
+
+        if (!dry_run)
+        {
+          try
+          {
+            try_rmfile (f);
+          }
+          catch (const system_error& e)
+          {
+            fail << "unable to remove file " << f << ": " << e;
+          }
+        }
+      }
+      else
+#endif
+      {
+        const char* args_a[] = {
+          base.sudo != nullptr ? base.sudo->c_str () : nullptr,
+          "rm",
+          "-f",
+          relf.string ().c_str (),
+          nullptr};
+
+        const char** args (&args_a[base.sudo == nullptr ? 1 : 0]);
+
+        process_path pp (run_search (args[0]));
+
+        if (verb >= 2)
+          print_process (args);
+
+        if (!dry_run)
+          run (pp, args);
+      }
+
+      return true;
+    }
+
+    target_state file_rule::
+    perform_uninstall (action a, const target& xt) const
+    {
+      const file& t (xt.as<file> ());
+      const path& tp (t.path ());
+
+      // Path should have been assigned by update unless it is unreal.
+      //
+      assert (!tp.empty () || t.mtime () == timestamp_unreal);
+
+      const scope& rs (t.root_scope ());
+
+      auto uninstall_target = [&rs, this] (const file& t,
+                                           const path& p,
+                                           bool verbose) -> target_state
+      {
+        bool n (!p.to_directory ());
+        dir_path d (n ? p.directory () : path_cast<dir_path> (p));
+
+        // Resolve target directory.
+        //
+        install_dirs ids (resolve (t, d));
+
+        // Handle install.subdirs if one was specified.
+        //
+        if (!n)
+        {
+          if (auto l = t["install.subdirs"])
+          {
+            if (cast<bool> (l))
+              resolve_subdir (ids, t, t.base_scope (), l);
+          }
+        }
+
+        // Remove extras and the target itself.
+        //
+        const install_dir& id (ids.back ());
+
+        target_state r (uninstall_extra (t, id)
+                        ? target_state::changed
+                        : target_state::unchanged);
+
+        if (uninstall_f (rs, id, &t, n ? p.leaf () : path (), verbose))
+          r |= target_state::changed;
+
+        // Clean up empty leading directories (in reverse).
+        //
+        // Note that we are using the leading directory (if there is one)
+        // for the clean up information (sudo, etc).
+        //
+        for (auto i (ids.rbegin ()), j (i), e (ids.rend ()); i != e; j = ++i)
+        {
+          if (install::uninstall_d (rs, ++j != e ? *j : *i, i->dir, verbose))
+            r |= target_state::changed;
+        }
+
+        return r;
+      };
+
+      // Reverse order of installation: first the target itself (since we got
+      // here we know the install variable is there).
+      //
+      target_state r (target_state::unchanged);
+
+      if (!tp.empty ())
+        r |= uninstall_target (t, cast<path> (t["install"]), true);
+
+      // Then installable ad hoc group members, if any. To be anally precise
+      // we would have to do it in reverse, but that's not easy (it's a
+      // single-linked list).
+      //
+      for (const target* m (t.member); m != nullptr; m = m->member)
+      {
+        if (const path* p = lookup_install<path> (*m, "install"))
+          r |= uninstall_target (m->as<file> (),
+                                 *p,
+                                 tp.empty () || r != target_state::changed);
+      }
+
+      // Finally handle installable prerequisites.
+      //
+      r |= reverse_execute_prerequisites (a, t);
+
+      return r;
+    }
+  }
+}
diff --git a/libbuild2/install/rule.hxx b/libbuild2/install/rule.hxx
new file mode 100644
index 0000000..ff99c6e
--- /dev/null
+++ b/libbuild2/install/rule.hxx
@@ -0,0 +1,197 @@
+// file      : libbuild2/install/rule.hxx -*- C++ -*-
+// copyright : Copyright (c) 2014-2019 Code Synthesis Ltd
+// license   : MIT; see accompanying LICENSE file
+
+#ifndef LIBBUILD2_INSTALL_RULE_HXX
+#define LIBBUILD2_INSTALL_RULE_HXX
+
+#include <libbuild2/types.hxx>
+#include <libbuild2/utility.hxx>
+
+#include <libbuild2/rule.hxx>
+#include <libbuild2/action.hxx>
+#include <libbuild2/target.hxx>
+#include <libbuild2/filesystem.hxx>
+
+#include <libbuild2/export.hxx>
+
+namespace build2
+{
+  namespace install
+  {
+    class LIBBUILD2_SYMEXPORT alias_rule: public rule
+    {
+    public:
+      virtual bool
+      match (action, target&, const string&) const override;
+
+      // Return NULL if this prerequisite should be ignored and pointer to its
+      // target otherwise. The default implementation accepts all prerequsites
+      // from the target's (weak) amalgamation.
+      //
+      // The prerequisite is passed as an iterator allowing the filter to
+      // "see" inside groups.
+      //
+      using prerequisite_iterator =
+        prerequisite_members_range<group_prerequisites>::iterator;
+
+      virtual const target*
+      filter (action, const target&, prerequisite_iterator&) const;
+
+      virtual const target*
+      filter (action, const target&, const prerequisite&) const;
+
+      virtual recipe
+      apply (action, target&) const override;
+
+      alias_rule () {}
+      static const alias_rule instance;
+    };
+
+    class fsdir_rule: public rule
+    {
+    public:
+      virtual bool
+      match (action, target&, const string&) const override;
+
+      virtual recipe
+      apply (action, target&) const override;
+
+      fsdir_rule () {}
+      static const fsdir_rule instance;
+    };
+
+    // In addition to the alias rule's semantics, this rule sees through to
+    // the group's members.
+    //
+    // The default group_rule::instance matches any target for which it was
+    // registered. It is to be used for non-see-through groups that should
+    // exhibit the see-through behavior for install (see lib{} in the bin
+    // module for an example).
+    //
+    // We also register (for all targets) another instance of this rule that
+    // only matches see-through groups.
+    //
+    class LIBBUILD2_SYMEXPORT group_rule: public alias_rule
+    {
+    public:
+      virtual bool
+      match (action, target&, const string&) const override;
+
+      // Return NULL if this group member should be ignored and pointer to its
+      // target otherwise. The default implementation accepts all members.
+      //
+      virtual const target*
+      filter (action, const target&, const target& group_member) const;
+
+      using alias_rule::filter; // "Unhide" to make Clang happy.
+
+      virtual recipe
+      apply (action, target&) const override;
+
+      group_rule (bool see_through_only): see_through (see_through_only) {}
+      static const group_rule instance;
+
+      bool see_through;
+    };
+
+    struct install_dir;
+
+    class LIBBUILD2_SYMEXPORT file_rule: public rule
+    {
+    public:
+      virtual bool
+      match (action, target&, const string&) const override;
+
+      // Return NULL if this prerequisite should be ignored and pointer to its
+      // target otherwise. The default implementation ignores prerequsites
+      // that are outside of this target's project.
+      //
+      // @@ I wonder why we do weak amalgamation for alias but project for
+      //    file? And then override this for prerequisite libraries/modules
+      //    in cc::install_rule and bash::install_rule...
+      //
+      // The prerequisite is passed as an iterator allowing the filter to
+      // "see" inside groups.
+      //
+      using prerequisite_iterator =
+        prerequisite_members_range<group_prerequisites>::iterator;
+
+      virtual const target*
+      filter (action, const target&, prerequisite_iterator&) const;
+
+      virtual const target*
+      filter (action, const target&, const prerequisite&) const;
+
+      virtual recipe
+      apply (action, target&) const override;
+
+      static target_state
+      perform_update (action, const target&);
+
+      // Extra un/installation hooks. Return true if anything was actually
+      // un/installed.
+      //
+      using install_dir = install::install_dir; // For derived rules.
+
+      virtual bool
+      install_extra (const file&, const install_dir&) const;
+
+      virtual bool
+      uninstall_extra (const file&, const install_dir&) const;
+
+      // Lower-level pre/post installation hooks that can be used to override
+      // the source file path being installed (for example, to implement
+      // post-processing, etc).
+      //
+      // Note that one cannot generally perform post-processing in-place
+      // because of permissions.
+      //
+      virtual auto_rmfile
+      install_pre (const file&, const install_dir&) const;
+
+      virtual bool
+      install_post (const file&, const install_dir&, auto_rmfile&&) const;
+
+      // Installation/uninstallation "commands".
+      //
+      // If verbose is false, then only print the command at verbosity level 2
+      // or higher. Note that these functions respect the dry_run flag.
+
+      // Install a symlink: base/link -> target.
+      //
+      static void
+      install_l (const scope& rs,
+                 const install_dir& base,
+                 const path& target,
+                 const path& link,
+                 bool verbose);
+
+      // Uninstall a file or symlink:
+      //
+      // uninstall <target> <base>/  rm <base>/<target>.leaf (); name empty
+      // uninstall <target> <name>   rm <base>/<name>; target can be NULL
+      //
+      // Return false if nothing has been removed (i.e., the file does not
+      // exist).
+      //
+      static bool
+      uninstall_f (const scope& rs,
+                   const install_dir& base,
+                   const file* target,
+                   const path& name,
+                   bool verbose);
+
+      target_state
+      perform_install (action, const target&) const;
+
+      target_state
+      perform_uninstall (action, const target&) const;
+
+      static const file_rule instance;
+      file_rule () {}
+    };
+  }
+}
+
+#endif // LIBBUILD2_INSTALL_RULE_HXX
diff --git a/libbuild2/install/utility.hxx b/libbuild2/install/utility.hxx
new file mode 100644
index 0000000..13fcceb
--- /dev/null
+++ b/libbuild2/install/utility.hxx
@@ -0,0 +1,78 @@
+// file      : libbuild2/install/utility.hxx -*- C++ -*-
+// copyright : Copyright (c) 2014-2019 Code Synthesis Ltd
+// license   : MIT; see accompanying LICENSE file
+
+#ifndef LIBBUILD2_INSTALL_UTILITY_HXX
+#define LIBBUILD2_INSTALL_UTILITY_HXX
+
+#include <libbuild2/types.hxx>
+#include <libbuild2/utility.hxx>
+
+#include <libbuild2/scope.hxx>
+#include <libbuild2/target.hxx>
+
+#include <libbuild2/export.hxx>
+
+namespace build2
+{
+  namespace install
+  {
+    // Set install path, mode for a target type.
+    //
+    inline void
+    install_path (scope& s, const target_type& tt, dir_path d)
+    {
+      auto r (
+        s.target_vars[tt]["*"].insert (
+          var_pool.rw (s).insert ("install")));
+
+      if (r.second) // Already set by the user?
+        r.first.get () = path_cast<path> (move (d));
+    }
+
+    template <typename T>
+    inline void
+    install_path (scope& s, dir_path d)
+    {
+      return install_path (s, T::static_type, move (d));
+    }
+
+    inline void
+    install_mode (scope& s, const target_type& tt, string m)
+    {
+      auto r (
+        s.target_vars[tt]["*"].insert (
+          var_pool.rw (s).insert ("install.mode")));
+
+      if (r.second) // Already set by the user?
+        r.first.get () = move (m);
+    }
+
+    template <typename T>
+    inline void
+    install_mode (scope& s, string m)
+    {
+      return install_mode (s, T::static_type, move (m));
+    }
+
+    // Resolve relative installation directory path (e.g., include/libfoo) to
+    // its absolute directory path (e.g., /usr/include/libfoo). If the
+    // resolution encountered an unknown directory, issue diagnostics and fail
+    // unless fail_unknown is false, in which case return empty directory.
+    //
+    // Note: implemented in rule.cxx.
+    //
+    LIBBUILD2_SYMEXPORT dir_path
+    resolve_dir (const target&, dir_path, bool fail_unknown = true);
+
+    LIBBUILD2_SYMEXPORT dir_path
+    resolve_dir (const scope&, dir_path, bool fail_unknown = true);
+
+    // Resolve file installation path returning empty path if not installable.
+    //
+    LIBBUILD2_SYMEXPORT path
+    resolve_file (const file&); // rule.cxx
+  }
+}
+
+#endif // LIBBUILD2_INSTALL_UTILITY_HXX