Move version build system module to separate library

13 files changed, 1354 insertions, 0 deletions

diff --git a/libbuild2/version/buildfile b/libbuild2/version/buildfile
new file mode 100644
index 0000000..e9d4905
--- /dev/null
+++ b/libbuild2/version/buildfile
@@ -0,0 +1,66 @@
+# file      : libbuild2/version/buildfile
+# copyright : Copyright (c) 2014-2019 Code Synthesis Ltd
+# license   : MIT; see accompanying LICENSE file
+
+import int_libs = libbutl%lib{butl}
+
+include ../
+int_libs += ../lib{build2}
+
+include ../in/
+int_libs += ../in/lib{build2-in}
+
+./: lib{build2-version}: libul{build2-version}: \
+  {hxx ixx txx cxx}{** -**.test...}             \
+  $int_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-version}: bin.whole = false
+}
+
+# Build options.
+#
+obja{*}: cxx.poptions += -DLIBBUILD2_VERSION_STATIC_BUILD
+objs{*}: cxx.poptions += -DLIBBUILD2_VERSION_SHARED_BUILD
+
+# Export options.
+#
+lib{build2-version}:
+{
+  cxx.export.poptions = "-I$out_root" "-I$src_root"
+  cxx.export.libs = $int_libs
+}
+
+liba{build2-version}: cxx.export.poptions += -DLIBBUILD2_VERSION_STATIC
+libs{build2-version}: cxx.export.poptions += -DLIBBUILD2_VERSION_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.
+#
+if $version.pre_release
+  lib{build2-version}: bin.lib.version = @"-$version.project_id"
+else
+  lib{build2-version}: bin.lib.version = @"-$version.major.$version.minor"
+
+# Install into the libbuild2/version/ subdirectory of, say, /usr/include/
+# recreating subdirectories.
+#
+{hxx ixx txx}{*}:
+{
+  install         = include/libbuild2/version/
+  install.subdirs = true
+}
diff --git a/libbuild2/version/export.hxx b/libbuild2/version/export.hxx
new file mode 100644
index 0000000..c76cd8a
--- /dev/null
+++ b/libbuild2/version/export.hxx
@@ -0,0 +1,34 @@
+#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_VERSION_STATIC)         // Using static.
+#  define LIBBUILD2_VERSION_SYMEXPORT
+#elif defined(LIBBUILD2_VERSION_STATIC_BUILD) // Building static.
+#  define LIBBUILD2_VERSION_SYMEXPORT
+#elif defined(LIBBUILD2_VERSION_SHARED)       // Using shared.
+#  ifdef _WIN32
+#    define LIBBUILD2_VERSION_SYMEXPORT __declspec(dllimport)
+#  else
+#    define LIBBUILD2_VERSION_SYMEXPORT
+#  endif
+#elif defined(LIBBUILD2_VERSION_SHARED_BUILD) // Building shared.
+#  ifdef _WIN32
+#    define LIBBUILD2_VERSION_SYMEXPORT __declspec(dllexport)
+#  else
+#    define LIBBUILD2_VERSION_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_VERSION_SYMEXPORT         // Using static or shared.
+#endif
diff --git a/libbuild2/version/init.cxx b/libbuild2/version/init.cxx
new file mode 100644
index 0000000..8adbb29
--- /dev/null
+++ b/libbuild2/version/init.cxx
@@ -0,0 +1,407 @@
+// file      : libbuild2/version/init.cxx -*- C++ -*-
+// copyright : Copyright (c) 2014-2019 Code Synthesis Ltd
+// license   : MIT; see accompanying LICENSE file
+
+#include <libbuild2/version/init.hxx>
+
+#include <libbutl/manifest-parser.mxx>
+
+#include <libbuild2/scope.hxx>
+#include <libbuild2/context.hxx>
+#include <libbuild2/variable.hxx>
+#include <libbuild2/diagnostics.hxx>
+
+#include <libbuild2/config/utility.hxx>
+
+#include <libbuild2/dist/module.hxx>
+
+#include <libbuild2/version/rule.hxx>
+#include <libbuild2/version/module.hxx>
+#include <libbuild2/version/utility.hxx>
+#include <libbuild2/version/snapshot.hxx>
+
+using namespace std;
+using namespace butl;
+
+namespace build2
+{
+  namespace version
+  {
+    static const path manifest_file ("manifest");
+
+    static const in_rule in_rule_;
+    static const manifest_install_rule manifest_install_rule_;
+
+    bool
+    boot (scope& rs, const location& l, unique_ptr<module_base>& mod)
+    {
+      tracer trace ("version::boot");
+      l5 ([&]{trace << "for " << rs;});
+
+      // Extract the version from the manifest file. As well as summary and
+      // url while at it.
+      //
+      // Also, as a sanity check, verify the package name matches the build
+      // system project name.
+      //
+      string sum;
+      string url;
+
+      standard_version v;
+      dependencies ds;
+      {
+        path f (rs.src_path () / manifest_file);
+
+        try
+        {
+          if (!file_exists (f))
+            fail (l) << "no manifest file in " << rs.src_path ();
+
+          ifdstream ifs (f);
+          manifest_parser p (ifs, f.string ());
+
+          manifest_name_value nv (p.next ());
+          if (!nv.name.empty () || nv.value != "1")
+            fail (l) << "unsupported manifest format in " << f;
+
+          for (nv = p.next (); !nv.empty (); nv = p.next ())
+          {
+            if (nv.name == "name")
+            {
+              auto& pn (cast<project_name> (rs.vars[var_project]));
+
+              if (nv.value != pn.string ())
+              {
+                path bf (rs.src_path () / rs.root_extra->bootstrap_file);
+                location ml (&f, nv.value_line, nv.value_column);
+                location bl (&bf);
+
+                fail (ml) << "package name " << nv.value << " does not match "
+                          << "build system project name " << pn <<
+                  info (bl) << "build system project name specified here";
+              }
+            }
+            if (nv.name == "summary")
+              sum = move (nv.value);
+            else if (nv.name == "url")
+              url = move (nv.value);
+            else if (nv.name == "version")
+            {
+              try
+              {
+                // Allow the package stub versions in the 0+<revision> form.
+                // While not standard, we want to use the version module for
+                // packaging stubs.
+                //
+                v = standard_version (nv.value, standard_version::allow_stub);
+              }
+              catch (const invalid_argument& e)
+              {
+                fail << "invalid standard version '" << nv.value << "': " << e;
+              }
+            }
+            else if (nv.name == "depends")
+            {
+              // According to the package manifest spec, the format of the
+              // 'depends' value is as follows:
+              //
+              // depends: [?][*] <alternatives> [; <comment>]
+              //
+              // <alternatives> := <dependency> [ '|' <dependency>]*
+              // <dependency>   := <name> [<constraint>]
+              // <constraint>   := <comparison> | <range>
+              // <comparison>   := ('==' | '>' | '<' | '>=' | '<=') <version>
+              // <range>        := ('(' | '[') <version> <version> (')' | ']')
+              //
+              // Note that we don't do exhaustive validation here leaving it
+              // to the package manager.
+              //
+              string v (move (nv.value));
+
+              size_t p;
+
+              // Get rid of the comment.
+              //
+              if ((p = v.find (';')) != string::npos)
+                v.resize (p);
+
+              // Get rid of conditional/runtime markers. Note that enither of
+              // them is valid in the rest of the value.
+              //
+              if ((p = v.find_last_of ("?*")) != string::npos)
+                v.erase (0, p + 1);
+
+              // Parse as |-separated "words".
+              //
+              for (size_t b (0), e (0); next_word (v, b, e, '|'); )
+              {
+                string d (v, b, e - b);
+                trim (d);
+
+                p = d.find_first_of (" \t=<>[(~^");
+                string n (d, 0, p);
+                string c (p != string::npos ? string (d, p) : string ());
+
+                trim (n);
+                trim (c);
+
+                try
+                {
+                  package_name pn (move (n));
+                  string v (pn.variable ());
+
+                  ds.emplace (move (v), dependency {move (pn), move (c)});
+                }
+                catch (const invalid_argument& e)
+                {
+                  fail (l) << "invalid package name for dependency "
+                           << d << ": " << e;
+                }
+              }
+            }
+          }
+        }
+        catch (const manifest_parsing& e)
+        {
+          location l (&f, e.line, e.column);
+          fail (l) << e.description;
+        }
+        catch (const io_error& e)
+        {
+          fail (l) << "unable to read from " << f << ": " << e;
+        }
+        catch (const system_error& e) // EACCES, etc.
+        {
+          fail (l) << "unable to access manifest " << f << ": " << e;
+        }
+
+        if (v.empty ())
+          fail (l) << "no version in " << f;
+      }
+
+      // If this is the latest snapshot (i.e., the -a.1.z kind), then load the
+      // snapshot number and id (e.g., commit date and id from git).
+      //
+      bool committed (true);
+      bool rewritten (false);
+      if (v.snapshot () && v.snapshot_sn == standard_version::latest_sn)
+      {
+        snapshot ss (extract_snapshot (rs));
+
+        if (!ss.empty ())
+        {
+          v.snapshot_sn = ss.sn;
+          v.snapshot_id = move (ss.id);
+          committed = ss.committed;
+          rewritten = true;
+        }
+        else
+          committed = false;
+      }
+
+      // If there is a dependency on the build system itself, check it (so
+      // there is no need for explicit using build@X.Y.Z).
+      //
+      {
+        auto i (ds.find ("build2"));
+
+        if (i != ds.end () && !i->second.constraint.empty ())
+        try
+        {
+          check_build_version (
+            standard_version_constraint (i->second.constraint, v), l);
+        }
+        catch (const invalid_argument& e)
+        {
+          fail (l) << "invalid version constraint for dependency build2 "
+                   << i->second.constraint << ": " << e;
+        }
+      }
+
+      // Set all the version.* variables.
+      //
+      auto& vp (var_pool.rw (rs));
+
+      auto set = [&vp, &rs] (const char* var, auto val)
+      {
+        using T = decltype (val);
+        auto& v (vp.insert<T> (var, variable_visibility::project));
+        rs.assign (v) = move (val);
+      };
+
+      if (!sum.empty ()) rs.assign (var_project_summary) = move (sum);
+      if (!url.empty ()) rs.assign (var_project_url)     = move (url);
+
+      set ("version", v.string ());  // Project version (var_version).
+
+      set ("version.project",        v.string_project ());
+      set ("version.project_number", v.version);
+
+      // Enough of project version for unique identification (can be used in
+      // places like soname, etc).
+      //
+      set ("version.project_id",     v.string_project_id ());
+
+      set ("version.stub", v.stub ()); // bool
+
+      set ("version.epoch", uint64_t (v.epoch));
+
+      set ("version.major", uint64_t (v.major ()));
+      set ("version.minor", uint64_t (v.minor ()));
+      set ("version.patch", uint64_t (v.patch ()));
+
+      optional<uint16_t> a (v.alpha ());
+      optional<uint16_t> b (v.beta ());
+
+      set ("version.alpha",              a.has_value ());
+      set ("version.beta",               b.has_value ());
+      set ("version.pre_release",        v.pre_release ().has_value ());
+      set ("version.pre_release_string", v.string_pre_release ());
+      set ("version.pre_release_number", uint64_t (a ? *a : b ? *b : 0));
+
+      set ("version.snapshot",           v.snapshot ()); // bool
+      set ("version.snapshot_sn",        v.snapshot_sn); // uint64
+      set ("version.snapshot_id",        v.snapshot_id); // string
+      set ("version.snapshot_string",    v.string_snapshot ());
+      set ("version.snapshot_committed", committed);     // bool
+
+      set ("version.revision", uint64_t (v.revision));
+
+      // Create the module.
+      //
+      mod.reset (new module (cast<project_name> (rs.vars[var_project]),
+                             move (v),
+                             committed,
+                             rewritten,
+                             move (ds)));
+
+      return true; // Init first (dist.package, etc).
+    }
+
+    static void
+    dist_callback (const path&, const scope&, void*);
+
+    bool
+    init (scope& rs,
+          scope&,
+          const location& l,
+          unique_ptr<module_base>& mod,
+          bool first,
+          bool,
+          const variable_map&)
+    {
+      tracer trace ("version::init");
+
+      if (!first)
+        fail (l) << "multiple version module initializations";
+
+      // Load in.base (in.* variables, in{} target type).
+      //
+      if (!cast_false<bool> (rs["in.base.loaded"]))
+        load_module (rs, rs, "in.base", l);
+
+      module& m (static_cast<module&> (*mod));
+      const standard_version& v (m.version);
+
+      // If the dist module is used, set its dist.package and register the
+      // post-processing callback.
+      //
+      if (auto* dm = rs.lookup_module<dist::module> (dist::module::name))
+      {
+        // Make sure dist is init'ed, not just boot'ed.
+        //
+        if (!cast_false<bool> (rs["dist.loaded"]))
+          load_module (rs, rs, "dist", l);
+
+        m.dist_uncommitted = cast_false<bool> (rs["config.dist.uncommitted"]);
+
+        // Don't touch if dist.package was set by the user.
+        //
+        value& val (rs.assign (dm->var_dist_package));
+
+        if (!val)
+        {
+          string p (cast<project_name> (rs.vars[var_project]).string ());
+          p += '-';
+          p += v.string ();
+          val = move (p);
+
+          // Only register the post-processing callback if this is a rewritten
+          // snapshot.
+          //
+          if (m.rewritten)
+            dm->register_callback (dir_path (".") / manifest_file,
+                                   &dist_callback,
+                                   &m);
+        }
+      }
+
+      // Register rules.
+      //
+      {
+        auto& r (rs.rules);
+
+        r.insert<file> (perform_update_id,   "version.in", in_rule_);
+        r.insert<file> (perform_clean_id,    "version.in", in_rule_);
+        r.insert<file> (configure_update_id, "version.in", in_rule_);
+
+        if (cast_false<bool> (rs["install.booted"]))
+        {
+          r.insert<manifest> (
+            perform_install_id, "version.manifest", manifest_install_rule_);
+        }
+      }
+
+      return true;
+    }
+
+    static void
+    dist_callback (const path& f, const scope& rs, void* data)
+    {
+      module& m (*static_cast<module*> (data));
+
+      // Complain if this is an uncommitted snapshot.
+      //
+      if (!m.committed && !m.dist_uncommitted)
+        fail << "distribution of uncommitted project " << rs.src_path () <<
+          info << "specify config.dist.uncommitted=true to force";
+
+      // The plan is simple: fixing up the version in a temporary file then
+      // move it to the original.
+      //
+      try
+      {
+        auto_rmfile t (fixup_manifest (f,
+                                       path::temp_path ("manifest"),
+                                       m.version));
+
+        mvfile (t.path, f, (cpflags::overwrite_content |
+                            cpflags::overwrite_permissions));
+        t.cancel ();
+      }
+      catch (const io_error& e)
+      {
+        fail << "unable to overwrite " << f << ": " << e;
+      }
+      catch (const system_error& e) // EACCES, etc.
+      {
+        fail << "unable to overwrite " << f << ": " << e;
+      }
+    }
+
+    static const module_functions mod_functions[] =
+    {
+      // NOTE: don't forget to also update the documentation in init.hxx if
+      //       changing anything here.
+
+      {"version", boot,    init},
+      {nullptr,   nullptr, nullptr}
+    };
+
+    const module_functions*
+    build2_version_load ()
+    {
+      return mod_functions;
+    }
+  }
+}
diff --git a/libbuild2/version/init.hxx b/libbuild2/version/init.hxx
new file mode 100644
index 0000000..68e4def
--- /dev/null
+++ b/libbuild2/version/init.hxx
@@ -0,0 +1,28 @@
+// file      : libbuild2/version/init.hxx -*- C++ -*-
+// copyright : Copyright (c) 2014-2019 Code Synthesis Ltd
+// license   : MIT; see accompanying LICENSE file
+
+#ifndef LIBBUILD2_VERSION_INIT_HXX
+#define LIBBUILD2_VERSION_INIT_HXX
+
+#include <libbuild2/types.hxx>
+#include <libbuild2/utility.hxx>
+
+#include <libbuild2/module.hxx>
+
+#include <libbuild2/version/export.hxx>
+
+namespace build2
+{
+  namespace version
+  {
+    // Module `version` requires bootstrapping.
+    //
+    // No submodules.
+    //
+    extern "C" LIBBUILD2_VERSION_SYMEXPORT const module_functions*
+    build2_version_load ();
+  }
+}
+
+#endif // LIBBUILD2_VERSION_INIT_HXX
diff --git a/libbuild2/version/module.cxx b/libbuild2/version/module.cxx
new file mode 100644
index 0000000..5ee44f7
--- /dev/null
+++ b/libbuild2/version/module.cxx
@@ -0,0 +1,15 @@
+// file      : libbuild2/version/module.cxx -*- C++ -*-
+// copyright : Copyright (c) 2014-2019 Code Synthesis Ltd
+// license   : MIT; see accompanying LICENSE file
+
+#include <libbuild2/version/module.hxx>
+
+using namespace std;
+
+namespace build2
+{
+  namespace version
+  {
+    const string module::name ("version");
+  }
+}
diff --git a/libbuild2/version/module.hxx b/libbuild2/version/module.hxx
new file mode 100644
index 0000000..174da7b
--- /dev/null
+++ b/libbuild2/version/module.hxx
@@ -0,0 +1,64 @@
+// file      : libbuild2/version/module.hxx -*- C++ -*-
+// copyright : Copyright (c) 2014-2019 Code Synthesis Ltd
+// license   : MIT; see accompanying LICENSE file
+
+#ifndef LIBBUILD2_VERSION_MODULE_HXX
+#define LIBBUILD2_VERSION_MODULE_HXX
+
+#include <map>
+
+#include <libbuild2/types.hxx>
+#include <libbuild2/utility.hxx>
+
+#include <libbuild2/module.hxx>
+
+namespace build2
+{
+  namespace version
+  {
+    // A map of package names sanitized for use in variable names to the
+    // 'depends' values from manifest.
+    //
+    using package_name = project_name;
+
+    struct dependency
+    {
+      package_name name;
+      string constraint;
+    };
+
+    using dependencies = std::map<string, dependency>;
+
+    struct module: module_base
+    {
+      using dependencies_type = version::dependencies;
+
+      static const string name;
+
+      // The project variable value sanitized for use in variable names.
+      //
+      const string project;
+
+      butl::standard_version version;
+      bool committed; // Whether this is a committed snapshot.
+      bool rewritten; // Whether this is a rewritten .z snapshot.
+
+      dependencies_type dependencies;
+
+      bool dist_uncommitted = false;
+
+      module (const project_name& p,
+              butl::standard_version v,
+              bool c,
+              bool r,
+              dependencies_type d)
+          : project (p.variable ()),
+            version (move (v)),
+            committed (c),
+            rewritten (r),
+            dependencies (move (d)) {}
+    };
+  }
+}
+
+#endif // LIBBUILD2_VERSION_MODULE_HXX
diff --git a/libbuild2/version/rule.cxx b/libbuild2/version/rule.cxx
new file mode 100644
index 0000000..37e6b0f
--- /dev/null
+++ b/libbuild2/version/rule.cxx
@@ -0,0 +1,334 @@
+// file      : libbuild2/version/rule.cxx -*- C++ -*-
+// copyright : Copyright (c) 2014-2019 Code Synthesis Ltd
+// license   : MIT; see accompanying LICENSE file
+
+#include <libbuild2/version/rule.hxx>
+
+#include <libbuild2/scope.hxx>
+#include <libbuild2/target.hxx>
+#include <libbuild2/diagnostics.hxx>
+
+#include <libbuild2/in/target.hxx>
+
+#include <libbuild2/version/module.hxx>
+#include <libbuild2/version/utility.hxx>
+
+using namespace std;
+using namespace butl;
+
+namespace build2
+{
+  namespace version
+  {
+    using in::in;
+
+    // Return true if this prerequisite is a project's manifest file. To be
+    // sure we would need to search it into target but that we can't do in
+    // match().
+    //
+    static inline bool
+    manifest_prerequisite (const scope& rs, const prerequisite_member& p)
+    {
+      if (!p.is_a<manifest> () || p.name () != "manifest")
+        return false;
+
+      const scope& s (p.scope ());
+
+      if (s.root_scope () == nullptr) // Out of project prerequisite.
+        return false;
+
+      dir_path d (p.dir ());
+      if (d.relative ())
+        d = s.src_path () / d;
+      d.normalize ();
+
+      return d == rs.src_path ();
+    }
+
+    // in_rule
+    //
+    bool in_rule::
+    match (action a, target& xt, const string&) const
+    {
+      tracer trace ("version::in_rule::match");
+
+      file& t (static_cast<file&> (xt));
+      const scope& rs (t.root_scope ());
+
+      bool fm (false); // Found manifest.
+      bool fi (false); // Found in.
+      for (prerequisite_member p: group_prerequisite_members (a, t))
+      {
+        if (include (a, t, p) != include_type::normal) // Excluded/ad hoc.
+          continue;
+
+        fm = fm || manifest_prerequisite (rs, p);
+        fi = fi || p.is_a<in> ();
+      }
+
+      // Note that while normally we print these at verbosity level 4, these
+      // ones get quite noisy since we try this rule any file target.
+      //
+      if (!fm)
+        l5 ([&]{trace << "no manifest prerequisite for target " << t;});
+
+      if (!fi)
+        l5 ([&]{trace << "no in file prerequisite for target " << t;});
+
+      bool r (fm && fi);
+
+      // If we match, lookup and cache the module for the update operation.
+      //
+      if (r && a == perform_update_id)
+        t.data (rs.lookup_module<module> (module::name));
+
+      return r;
+    }
+
+    string in_rule::
+    lookup (const location& l,
+            action a,
+            const target& t,
+            const string& n) const
+    {
+      // Note that this code will be executed during up-to-date check for each
+      // substitution so let's try not to do anything overly sub-optimal here.
+      //
+      const module& m (*t.data<const module*> ());
+
+      // Split it into the package name and the variable/condition name.
+      //
+      // We used to bail if there is no package component but now we treat it
+      // the same as project. This can be useful when trying to reuse existing
+      // .in files (e.g., from autoconf, etc).
+      //
+      size_t p (n.find ('.'));
+
+      if (p == string::npos || n.compare (0, p, m.project) == 0)
+      {
+        return rule::lookup (l, // Standard lookup.
+                             a,
+                             t,
+                             p == string::npos ? n : string (n, p + 1));
+      }
+
+      string pn (n, 0, p);
+      string vn (n, p + 1);
+
+      // Perform substitutions for a dependency. Here we recognize the
+      // following substitutions:
+      //
+      // $libfoo.version$               - textual version constraint.
+      // $libfoo.condition(VER[,SNAP])$ - numeric satisfaction condition.
+      // $libfoo.check(VER[,SNAP])$     - numeric satisfaction check (#if ...).
+      //
+      // Where VER is the version number macro and SNAP is the optional
+      // snapshot number macro (only needed if you plan to include snapshot
+      // informaton in your constraints).
+      //
+      // Note also that the last two (condition and check) can only be used in
+      // the strict substitution mode since in::rule::substitute() will skip
+      // them in the lax mode.
+
+      // For now we re-parse the constraint every time. Firstly because not
+      // all of them are necessarily in the standard form and secondly because
+      // of the MT-safety.
+      //
+      standard_version_constraint dc;
+      const package_name* dn;
+      {
+        auto i (m.dependencies.find (pn));
+
+        if (i == m.dependencies.end ())
+          fail (l) << "unknown dependency '" << pn << "'";
+
+        const dependency& dp (i->second);
+
+        if (dp.constraint.empty ())
+          fail (l) << "no version constraint for dependency " << dp.name;
+
+        try
+        {
+          dc = standard_version_constraint (dp.constraint, m.version);
+        }
+        catch (const invalid_argument& e)
+        {
+          fail (l) << "invalid version constraint for dependency " << dp.name
+                   << " " << dp.constraint << ": " << e;
+        }
+
+        dn = &dp.name;
+      }
+
+      // Now substitute.
+      //
+      size_t i;
+      if (vn == "version")
+      {
+        return dc.string (); // Use normalized representation.
+      }
+      if (vn.compare (0, (i = 6),  "check(")     == 0 ||
+          vn.compare (0, (i = 10), "condition(") == 0)
+      {
+        size_t j (vn.find_first_of (",)", i));
+
+        if (j == string::npos || (vn[j] == ',' && vn.back () != ')'))
+          fail (l) << "missing closing ')'";
+
+        string vm (vn, i, j - i); // VER macro.
+        string sm (vn[j] == ','   // SNAP macro.
+                   ? string (vn, j + 1, vn.size () - j - 2)
+                   : string ());
+
+        trim (vm);
+        trim (sm);
+
+        auto cond = [&l, &dc, &vm, &sm] () -> string
+        {
+          auto& miv (dc.min_version);
+          auto& mav (dc.max_version);
+
+          bool mio (dc.min_open);
+          bool mao (dc.max_open);
+
+          if (sm.empty () &&
+              ((miv && miv->snapshot ()) ||
+               (mav && mav->snapshot ())))
+            fail (l) << "snapshot macro required for " << dc.string ();
+
+          auto cmp = [] (const string& m, const char* o, uint64_t v)
+          {
+            return m + o + to_string (v) + "ULL";
+          };
+
+          // Note that version orders everything among pre-releases (that E
+          // being 0/1). So the snapshot comparison is only necessary "inside"
+          // the same pre-release.
+          //
+          auto max_cmp = [&vm, &sm, mao, &mav, &cmp] (bool p = false)
+          {
+            string r;
+
+            if (mav->snapshot ())
+            {
+              r += (p ? "(" : "");
+
+              r += cmp (vm, " < ", mav->version) + " || (";
+              r += cmp (vm, " == ", mav->version) + " && ";
+              r += cmp (sm, (mao ? " < " : " <= "), mav->snapshot_sn) + ")";
+
+              r += (p ? ")" : "");
+            }
+            else
+              r = cmp (vm, (mao ? " < " : " <= "), mav->version);
+
+            return r;
+          };
+
+          auto min_cmp = [&vm, &sm, mio, &miv, &cmp] (bool p = false)
+          {
+            string r;
+
+            if (miv->snapshot ())
+            {
+              r += (p ? "(" : "");
+
+              r += cmp (vm, " > ", miv->version) + " || (";
+              r += cmp (vm, " == ", miv->version) + " && ";
+              r += cmp (sm, (mio ? " > " : " >= "), miv->snapshot_sn) + ")";
+
+              r += (p ? ")" : "");
+            }
+            else
+              r = cmp (vm, (mio ? " > " : " >= "), miv->version);
+
+            return r;
+          };
+
+          // < / <=
+          //
+          if (!miv)
+            return max_cmp ();
+
+          // > / >=
+          //
+          if (!mav)
+            return min_cmp ();
+
+          // ==
+          //
+          if (*miv == *mav)
+          {
+            string r (cmp (vm, " == ", miv->version));
+
+            if (miv->snapshot ())
+              r += " && " + cmp (sm, " == ", miv->snapshot_sn);
+
+            return r;
+          }
+
+          // range
+          //
+          return min_cmp (true) + " && " + max_cmp (true);
+        };
+
+        if (vn[1] == 'o') // condition
+          return cond ();
+
+        string r;
+
+        // This is tricky: if the version header hasn't been generated yet,
+        // then the check will fail. Maybe a better solution is to disable
+        // diagnostics and ignore (some) errors during dependency extraction.
+        //
+        r += "#ifdef " + vm + "\n";
+        r += "#  if !(" + cond () + ")\n";
+        r += "#    error incompatible " + dn->string () + " version, ";
+        r +=       dn->string () + ' ' + dc.string () + " is required\n";
+        r += "#  endif\n";
+        r += "#endif";
+
+        return r;
+      }
+      else
+        fail (l) << "unknown dependency substitution '" << vn << "'" << endf;
+    }
+
+    // manifest_install_rule
+    //
+    bool manifest_install_rule::
+    match (action a, target& t, const string&) const
+    {
+      // We only match project's manifest.
+      //
+      if (!t.is_a<manifest> () || t.name != "manifest")
+        return false;
+
+      // Must be in project's src_root.
+      //
+      const scope& s (t.base_scope ());
+      if (s.root_scope () != &s || s.src_path () != t.dir)
+        return false;
+
+      return file_rule::match (a, t, "");
+    }
+
+    auto_rmfile manifest_install_rule::
+    install_pre (const file& t, const install_dir&) const
+    {
+      const path& p (t.path ());
+
+      const scope& rs (t.root_scope ());
+      const module& m (*rs.lookup_module<module> (module::name));
+
+      if (!m.rewritten)
+        return auto_rmfile (p, false /* active */);
+
+      // Our options are to use path::temp_path() or to create a .t file in
+      // the out tree. Somehow the latter feels more appropriate (even though
+      // if we crash in between, we won't clean it up).
+      //
+      return fixup_manifest (p, rs.out_path () / "manifest.t", m.version);
+    }
+  }
+}
diff --git a/libbuild2/version/rule.hxx b/libbuild2/version/rule.hxx
new file mode 100644
index 0000000..ce21aa4
--- /dev/null
+++ b/libbuild2/version/rule.hxx
@@ -0,0 +1,52 @@
+// file      : libbuild2/version/rule.hxx -*- C++ -*-
+// copyright : Copyright (c) 2014-2019 Code Synthesis Ltd
+// license   : MIT; see accompanying LICENSE file
+
+#ifndef LIBBUILD2_VERSION_RULE_HXX
+#define LIBBUILD2_VERSION_RULE_HXX
+
+#include <libbuild2/types.hxx>
+#include <libbuild2/utility.hxx>
+
+#include <libbuild2/install/rule.hxx>
+
+#include <libbuild2/in/rule.hxx>
+
+namespace build2
+{
+  namespace version
+  {
+    // Preprocess an .in file that depends on manifest.
+    //
+    class in_rule: public in::rule
+    {
+    public:
+      in_rule (): rule ("version.in 2", "version.in") {}
+
+      virtual bool
+      match (action, target&, const string&) const override;
+
+      virtual string
+      lookup (const location&,
+              action,
+              const target&,
+              const string&) const override;
+    };
+
+    // Pre-process manifest before installation to patch in the version.
+    //
+    class manifest_install_rule: public install::file_rule
+    {
+    public:
+      manifest_install_rule () {}
+
+      virtual bool
+      match (action, target&, const string&) const override;
+
+      virtual auto_rmfile
+      install_pre (const file&, const install_dir&) const override;
+    };
+  }
+}
+
+#endif // LIBBUILD2_VERSION_RULE_HXX
diff --git a/libbuild2/version/snapshot-git.cxx b/libbuild2/version/snapshot-git.cxx
new file mode 100644
index 0000000..b7ca084
--- /dev/null
+++ b/libbuild2/version/snapshot-git.cxx
@@ -0,0 +1,175 @@
+// file      : libbuild2/version/snapshot-git.cxx -*- C++ -*-
+// copyright : Copyright (c) 2014-2019 Code Synthesis Ltd
+// license   : MIT; see accompanying LICENSE file
+
+#include <ctime> // time_t
+
+#include <libbutl/sha1.mxx>
+
+#include <libbuild2/version/snapshot.hxx>
+
+using namespace std;
+using namespace butl;
+
+namespace build2
+{
+  namespace version
+  {
+    snapshot
+    extract_snapshot_git (const dir_path& src_root)
+    {
+      snapshot r;
+      const char* d (src_root.string ().c_str ());
+
+      // First check whether the working directory is clean. There doesn't
+      // seem to be a way to do everything in a single invocation (the
+      // porcelain v2 gives us the commit id but not timestamp).
+      //
+
+      // If git status --porcelain returns anything, then the working
+      // directory is not clean.
+      //
+      {
+        const char* args[] {"git", "-C", d, "status", "--porcelain", nullptr};
+        r.committed = run<string> (
+          3 /* verbosity */,
+          args,
+          [](string& s, bool) {return move (s);}).empty ();
+      }
+
+      // Now extract the commit id and date. One might think that would be
+      // easy... Commit id is a SHA1 hash of the commit object. And commit
+      // object looks like this:
+      //
+      // commit <len>\0
+      // <data>
+      //
+      // Where <len> is the size of <data> and <data> is the output of:
+      //
+      // git cat-file commit HEAD
+      //
+      // There is also one annoying special case: new repository without any
+      // commits. In this case the above command will fail (with diagnostics
+      // and non-zero exit code) because there is no HEAD. Of course, it can
+      // also fail for other reason (like broken repository) which would be
+      // hard to distinguish. Note, however, that we just ran git status and
+      // it would have most likely failed if this were the case. So here we
+      // (reluctantly) assume that the only reason git cat-file fails is if
+      // there is no HEAD (that we equal with the "new repository" condition
+      // which is, strictly speaking, might not be the case either). So we
+      // suppress any diagnostics, and handle non-zero exit code.
+      //
+      string data;
+
+      const char* args[] {
+        "git", "-C", d, "cat-file", "commit", "HEAD", nullptr};
+      process pr (run_start (3     /* verbosity */,
+                             args,
+                             0     /* stdin  */,
+                             -1    /* stdout */,
+                             false /* error  */));
+
+      string l;
+      try
+      {
+        ifdstream is (move (pr.in_ofd), ifdstream::badbit);
+
+        while (!eof (getline (is, l)))
+        {
+          data += l;
+          data += '\n'; // We assume there is always a newline.
+
+          if (r.sn == 0 && l.compare (0, 10, "committer ") == 0)
+          try
+          {
+            // The line format is:
+            //
+            // committer <noise> <timestamp> <timezone>
+            //
+            // For example:
+            //
+            // committer John Doe <john@example.org> 1493117819 +0200
+            //
+            // The timestamp is in seconds since UNIX epoch. The timezone
+            // appears to be always numeric (+0000 for UTC). Note that
+            // timestamp appears to be already in UTC with timezone being just
+            // for information it seems.
+            //
+            size_t p1 (l.rfind (' ')); // Can't be npos.
+
+            size_t p2 (l.rfind (' ', p1 - 1));
+            if (p2 == string::npos)
+              throw invalid_argument ("missing timestamp");
+
+            string ts (l, p2 + 1, p1 - p2 - 1);
+            time_t t (static_cast<time_t> (stoull (ts)));
+
+#if 0
+            string tz (l, p1 + 1);
+
+            if (tz.size () != 5)
+              throw invalid_argument ("invalid timezone");
+
+            unsigned long h (stoul (string (tz, 1, 2)));
+            unsigned long m (stoul (string (tz, 3, 2)));
+            unsigned long s (h * 3600 + m * 60);
+
+            // The timezone indicates where the timestamp was generated so to
+            // convert to UTC we need to invert the sign.
+            //
+            switch (tz[0])
+            {
+            case '+': t -= s; break;
+            case '-': t += s; break;
+            default: throw invalid_argument ("invalid timezone sign");
+            }
+#endif
+            // Represent as YYYYMMDDhhmmss.
+            //
+            r.sn = stoull (to_string (system_clock::from_time_t (t),
+                                      "%Y%m%d%H%M%S",
+                                      false /* special */,
+                                      false /* local (already in UTC) */));
+          }
+          catch (const invalid_argument& e)
+          {
+            fail << "unable to extract git commit date from '" << l << "': "
+                 << e;
+          }
+        }
+
+        is.close ();
+      }
+      catch (const io_error&)
+      {
+        // Presumably the child process failed. Let run_finish() deal with
+        // that.
+      }
+
+      if (!run_finish (args, pr, false /* error */, l))
+      {
+        // Presumably new repository without HEAD. Return uncommitted snapshot
+        // with UNIX epoch as timestamp.
+        //
+        r.sn = 19700101000000ULL;
+        r.committed = false;
+        return r;
+      }
+
+      if (r.sn == 0)
+        fail << "unable to extract git commit id/date for " << src_root;
+
+      if (r.committed)
+      {
+        sha1 cs;
+        cs.append ("commit " + to_string (data.size ())); // Includes '\0'.
+        cs.append (data.c_str (), data.size ());
+        r.id.assign (cs.string (), 12); // 12-characters abbreviated commit id.
+      }
+      else
+        r.sn++; // Add a second.
+
+      return r;
+    }
+  }
+}
diff --git a/libbuild2/version/snapshot.cxx b/libbuild2/version/snapshot.cxx
new file mode 100644
index 0000000..46b37f3
--- /dev/null
+++ b/libbuild2/version/snapshot.cxx
@@ -0,0 +1,39 @@
+// file      : libbuild2/version/snapshot.cxx -*- C++ -*-
+// copyright : Copyright (c) 2014-2019 Code Synthesis Ltd
+// license   : MIT; see accompanying LICENSE file
+
+#include <libbuild2/version/snapshot.hxx>
+
+#include <libbuild2/filesystem.hxx>
+
+using namespace std;
+
+namespace build2
+{
+  namespace version
+  {
+    snapshot
+    extract_snapshot_git (const dir_path&);
+
+    static const path git (".git");
+
+    snapshot
+    extract_snapshot (const scope& rs)
+    {
+      // Ignore errors when checking for existence since we may be iterating
+      // over directories past any reasonable project boundaries.
+      //
+      for (dir_path d (rs.src_path ()); !d.empty (); d = d.directory ())
+      {
+        // .git can be either a directory or a file in case of a submodule.
+        //
+        if (butl::entry_exists (d / git,
+                                true /* follow_symlinks */,
+                                true /* ignore_errors */))
+          return extract_snapshot_git (d);
+      }
+
+      return snapshot ();
+    }
+  }
+}
diff --git a/libbuild2/version/snapshot.hxx b/libbuild2/version/snapshot.hxx
new file mode 100644
index 0000000..86b6eab
--- /dev/null
+++ b/libbuild2/version/snapshot.hxx
@@ -0,0 +1,34 @@
+// file      : libbuild2/version/snapshot.hxx -*- C++ -*-
+// copyright : Copyright (c) 2014-2019 Code Synthesis Ltd
+// license   : MIT; see accompanying LICENSE file
+
+#ifndef LIBBUILD2_VERSION_SNAPSHOT_HXX
+#define LIBBUILD2_VERSION_SNAPSHOT_HXX
+
+#include <libbuild2/types.hxx>
+#include <libbuild2/utility.hxx>
+
+#include <libbuild2/scope.hxx>
+
+namespace build2
+{
+  namespace version
+  {
+    struct snapshot
+    {
+      uint64_t sn = 0;
+      string id;
+      bool committed = false;
+
+      bool
+      empty () const {return sn == 0;}
+    };
+
+    // Return empty snapshot if unknown scm or uncommitted.
+    //
+    snapshot
+    extract_snapshot (const scope& rs);
+  }
+}
+
+#endif // LIBBUILD2_VERSION_SNAPSHOT_HXX
diff --git a/libbuild2/version/utility.cxx b/libbuild2/version/utility.cxx
new file mode 100644
index 0000000..c93a251
--- /dev/null
+++ b/libbuild2/version/utility.cxx
@@ -0,0 +1,81 @@
+// file      : libbuild2/version/utility.cxx -*- C++ -*-
+// copyright : Copyright (c) 2014-2019 Code Synthesis Ltd
+// license   : MIT; see accompanying LICENSE file
+
+#include <libbuild2/version/utility.hxx>
+
+#include <libbutl/manifest-parser.mxx>
+#include <libbutl/manifest-serializer.mxx>
+
+#include <libbuild2/diagnostics.hxx>
+
+using namespace butl;
+
+namespace build2
+{
+  namespace version
+  {
+    auto_rmfile
+    fixup_manifest (const path& in, path out, const standard_version& v)
+    {
+      auto_rmfile r (move (out), !dry_run /* active */);
+
+      if (!dry_run)
+      {
+        try
+        {
+          permissions perm (path_permissions (in));
+
+          ifdstream ifs (in);
+          manifest_parser p (ifs, in.string ());
+
+          auto_fd ofd (fdopen (r.path,
+                               fdopen_mode::out       |
+                               fdopen_mode::create    |
+                               fdopen_mode::exclusive |
+                               fdopen_mode::binary,
+                               perm));
+
+          ofdstream ofs (move (ofd));
+          manifest_serializer s (ofs, r.path.string ());
+
+          manifest_name_value nv (p.next ());
+          assert (nv.name.empty () && nv.value == "1"); // We just loaded it.
+          s.next (nv.name, nv.value);
+
+          for (nv = p.next (); !nv.empty (); nv = p.next ())
+          {
+            if (nv.name == "version")
+              nv.value = v.string ();
+
+            s.next (nv.name, nv.value);
+          }
+
+          s.next (nv.name, nv.value); // End of manifest.
+          s.next (nv.name, nv.value); // End of stream.
+
+          ofs.close ();
+          ifs.close ();
+        }
+        catch (const manifest_parsing& e)
+        {
+          location l (&in, e.line, e.column);
+          fail (l) << e.description;
+        }
+        catch (const manifest_serialization& e)
+        {
+          location l (&r.path);
+          fail (l) << e.description;
+        }
+        catch (const io_error& e)
+        {
+          fail << "io error: " << e <<
+            info << "while reading " << in <<
+            info << "while writing " << r.path;
+        }
+      }
+
+      return r;
+    }
+  }
+}
diff --git a/libbuild2/version/utility.hxx b/libbuild2/version/utility.hxx
new file mode 100644
index 0000000..16e8c78
--- /dev/null
+++ b/libbuild2/version/utility.hxx
@@ -0,0 +1,25 @@
+// file      : libbuild2/version/utility.hxx -*- C++ -*-
+// copyright : Copyright (c) 2014-2019 Code Synthesis Ltd
+// license   : MIT; see accompanying LICENSE file
+
+#ifndef LIBBUILD2_VERSION_UTILITY_HXX
+#define LIBBUILD2_VERSION_UTILITY_HXX
+
+#include <libbuild2/types.hxx>
+#include <libbuild2/utility.hxx>
+
+#include <libbuild2/filesystem.hxx>
+
+namespace build2
+{
+  namespace version
+  {
+    // Re-serialize the manifest fixing up the version. Note that this will
+    // not preserve comments. Probably acceptable for snapshots.
+    //
+    auto_rmfile
+    fixup_manifest (const path& in, path out, const standard_version&);
+  }
+}
+
+#endif // LIBBUILD2_VERSION_UTILITY_HXX