Implement support for C compilation

We now have two new modules: cc (c-common) and c.

1 files changed, 0 insertions, 1497 deletions

diff --git a/build2/cxx/compile.cxx b/build2/cxx/compile.cxx
deleted file mode 100644
index 56c518b..0000000
--- a/build2/cxx/compile.cxx
+++ /dev/null
@@ -1,1497 +0,0 @@
-// file      : build2/cxx/compile.cxx -*- C++ -*-
-// copyright : Copyright (c) 2014-2016 Code Synthesis Ltd
-// license   : MIT; see accompanying LICENSE file
-
-#include <build2/cxx/compile>
-
-#include <map>
-#include <limits>   // numeric_limits
-#include <cstdlib>  // exit()
-#include <iostream> // cerr
-
-#include <butl/path-map>
-
-#include <build2/depdb>
-#include <build2/scope>
-#include <build2/context>
-#include <build2/variable>
-#include <build2/algorithm>
-#include <build2/diagnostics>
-
-#include <build2/bin/target>
-#include <build2/cxx/target>
-
-#include <build2/cxx/link>
-#include <build2/cxx/common>
-#include <build2/cxx/utility>
-
-
-using namespace std;
-using namespace butl;
-
-namespace build2
-{
-  namespace cxx
-  {
-    using namespace bin;
-
-    match_result compile::
-    match (action a, target& t, const string&) const
-    {
-      tracer trace ("cxx::compile::match");
-
-      // @@ TODO:
-      //
-      // - check prerequisites: single source file
-      // - if path already assigned, verify extension?
-      //
-
-      // See if we have a C++ source file. Iterate in reverse so that
-      // a source file specified for an obj*{} member overrides the one
-      // specified for the group. Also "see through" groups.
-      //
-      for (prerequisite_member p: reverse_group_prerequisite_members (a, t))
-      {
-        if (p.is_a<cxx> ())
-          return p;
-      }
-
-      l4 ([&]{trace << "no c++ source file for target " << t;});
-      return nullptr;
-    }
-
-    static void
-    inject_prerequisites (action, target&, lorder, cxx&, scope&, depdb&);
-
-    recipe compile::
-    apply (action a, target& xt, const match_result& mr) const
-    {
-      tracer trace ("cxx::compile");
-
-      file& t (static_cast<file&> (xt));
-
-      scope& bs (t.base_scope ());
-      scope& rs (*bs.root_scope ());
-
-      const string& cid (cast<string> (rs["cxx.id"]));
-      const string& tsys (cast<string> (rs["cxx.target.system"]));
-      const string& tclass (cast<string> (rs["cxx.target.class"]));
-
-      otype ct (compile_type (t));
-
-      // Derive file name from target name.
-      //
-      if (t.path ().empty ())
-      {
-        const char* e (nullptr);
-
-        if (tsys == "win32-msvc")
-        {
-          switch (ct)
-          {
-          case otype::e: e = "exe.obj"; break;
-          case otype::a: e = "lib.obj"; break;
-          case otype::s: e = "dll.obj"; break;
-          }
-        }
-        else if (tsys == "mingw32")
-        {
-          switch (ct)
-          {
-          case otype::e: e = "exe.o"; break;
-          case otype::a: e = "a.o";   break;
-          case otype::s: e = "dll.o"; break;
-          }
-        }
-        else if (tsys == "darwin")
-        {
-          switch (ct)
-          {
-          case otype::e: e = "o";       break;
-          case otype::a: e = "a.o";     break;
-          case otype::s: e = "dylib.o"; break;
-          }
-        }
-        else
-        {
-          switch (ct)
-          {
-          case otype::e: e = "o"; break;
-          case otype::a: e = "a.o"; break;
-          case otype::s: e = "so.o"; break;
-          }
-        }
-
-        t.derive_path (e);
-      }
-
-      // Inject dependency on the output directory.
-      //
-      fsdir* dir (inject_fsdir (a, t));
-
-      // Search and match all the existing prerequisites. The injection
-      // code (below) takes care of the ones it is adding.
-      //
-      // When cleaning, ignore prerequisites that are not in the same
-      // or a subdirectory of our project root.
-      //
-      optional<dir_paths> lib_paths; // Extract lazily.
-
-      for (prerequisite_member p: group_prerequisite_members (a, t))
-      {
-        // A dependency on a library is there so that we can get its
-        // cxx.export.poptions. In particular, making sure it is
-        // executed before us will only restrict parallelism. But we
-        // do need to pre-match it in order to get its
-        // prerequisite_targets populated. This is the "library
-        // meta-information protocol". See also append_lib_options()
-        // above.
-        //
-        if (p.is_a<lib> () || p.is_a<liba> () || p.is_a<libs> ())
-        {
-          if (a.operation () == update_id)
-          {
-            // Handle imported libraries. We know that for such libraries
-            // we don't need to do match() in order to get options (if
-            // any, they would be set by search_library()).
-            //
-            if (p.proj () == nullptr ||
-                link::search_library (lib_paths, p.prerequisite) == nullptr)
-            {
-              match_only (a, p.search ());
-            }
-          }
-
-          continue;
-        }
-
-        target& pt (p.search ());
-
-        if (a.operation () == clean_id && !pt.dir.sub (rs.out_path ()))
-          continue;
-
-        build2::match (a, pt);
-        t.prerequisite_targets.push_back (&pt);
-      }
-
-      // Inject additional prerequisites. We only do it when performing update
-      // since chances are we will have to update some of our prerequisites in
-      // the process (auto-generated source code).
-      //
-      if (a == perform_update_id)
-      {
-        // The cached prerequisite target should be the same as what is in
-        // t.prerequisite_targets since we used standard search() and match()
-        // above.
-        //
-        // @@ Ugly.
-        //
-        cxx& st (
-          dynamic_cast<cxx&> (
-            mr.target != nullptr ? *mr.target : *mr.prerequisite->target));
-
-        // Make sure the output directory exists.
-        //
-        // Is this the right thing to do? It does smell a bit, but then we do
-        // worse things in inject_prerequisites() below. There is also no way
-        // to postpone this until update since we need to extract and inject
-        // header dependencies now (we don't want to be calling search() and
-        // match() in update), which means we need to cache them now as well.
-        // So the only alternative, it seems, is to cache the updates to the
-        // database until later which will sure complicate (and slow down)
-        // things.
-        //
-        if (dir != nullptr)
-          execute_direct (a, *dir);
-
-        depdb dd (t.path () + ".d");
-
-        // First should come the rule name/version.
-        //
-        if (dd.expect ("cxx.compile 1") != nullptr)
-          l4 ([&]{trace << "rule mismatch forcing update of " << t;});
-
-        // Then the compiler checksum. Note that here we assume it
-        // incorporates the (default) target so that if the compiler changes
-        // but only in what it targets, then the checksum will still change.
-        //
-        if (dd.expect (cast<string> (rs["cxx.checksum"])) != nullptr)
-          l4 ([&]{trace << "compiler mismatch forcing update of " << t;});
-
-        // Then the options checksum.
-        //
-        // The idea is to keep them exactly as they are passed to the compiler
-        // since the order may be significant.
-        //
-        sha256 cs;
-
-        // Hash cxx.export.poptions from prerequisite libraries.
-        //
-        lorder lo (link_order (bs, ct));
-        for (prerequisite& p: group_prerequisites (t))
-        {
-          target* pt (p.target); // Already searched and matched.
-
-          if (lib* l = pt->is_a<lib> ())
-            pt = &link_member (*l, lo);
-
-          if (pt->is_a<liba> () || pt->is_a<libs> ())
-            hash_lib_options (cs, *pt, "cxx.export.poptions", lo);
-        }
-
-        hash_options (cs, t, "cxx.poptions");
-        hash_options (cs, t, "cxx.coptions");
-        hash_std (cs, rs, cid, t);
-
-        if (ct == otype::s)
-        {
-          // On Darwin, Win32 -fPIC is the default.
-          //
-          if (tclass == "linux" || tclass == "freebsd")
-            cs.append ("-fPIC");
-        }
-
-        if (dd.expect (cs.string ()) != nullptr)
-          l4 ([&]{trace << "options mismatch forcing update of " << t;});
-
-        // Finally the source file.
-        //
-        if (dd.expect (st.path ()) != nullptr)
-          l4 ([&]{trace << "source file mismatch forcing update of " << t;});
-
-        // If any of the above checks resulted in a mismatch (different
-        // compiler, options, or source file), or if the database is newer
-        // than the target (interrupted update) then force the target update.
-        //
-        if (dd.writing () || dd.mtime () > t.mtime ())
-          t.mtime (timestamp_nonexistent);
-
-        inject_prerequisites (a, t, lo, st, mr.prerequisite->scope, dd);
-
-        dd.close ();
-      }
-
-      switch (a)
-      {
-      case perform_update_id: return &perform_update;
-      case perform_clean_id: return &perform_clean;
-      default: return noop_recipe; // Configure update.
-      }
-    }
-
-    // Reverse-lookup target type from extension.
-    //
-    static const target_type*
-    map_extension (scope& s, const string& n, const string& e)
-    {
-      // We will just have to try all of the possible ones, in the
-      // "most likely to match" order.
-      //
-      const variable& var (var_pool.find ("extension"));
-
-      auto test = [&s, &n, &e, &var] (const target_type& tt)
-        -> const target_type*
-      {
-        if (auto l = s.find (var, tt, n))
-          if (cast<string> (l) == e)
-            return &tt;
-
-        return nullptr;
-      };
-
-      if (auto r = test (hxx::static_type)) return r;
-      if (auto r = test (h::static_type))   return r;
-      if (auto r = test (ixx::static_type)) return r;
-      if (auto r = test (txx::static_type)) return r;
-      if (auto r = test (cxx::static_type)) return r;
-      if (auto r = test (c::static_type))   return r;
-
-      return nullptr;
-    }
-
-    // Mapping of include prefixes (e.g., foo in <foo/bar>) for auto-
-    // generated headers to directories where they will be generated.
-    //
-    // We are using a prefix map of directories (dir_path_map) instead
-    // of just a map in order also cover sub-paths (e.g., <foo/more/bar>
-    // if we continue with the example). Specifically, we need to make
-    // sure we don't treat foobar as a sub-directory of foo.
-    //
-    // @@ The keys should be canonicalized.
-    //
-    using prefix_map = dir_path_map<dir_path>;
-
-    static void
-    append_prefixes (prefix_map& m, target& t, const char* var)
-    {
-      tracer trace ("cxx::append_prefixes");
-
-      // If this target does not belong to any project (e.g, an
-      // "imported as installed" library), then it can't possibly
-      // generate any headers for us.
-      //
-      scope* rs (t.base_scope ().root_scope ());
-      if (rs == nullptr)
-        return;
-
-      const dir_path& out_base (t.dir);
-      const dir_path& out_root (rs->out_path ());
-
-      if (auto l = t[var])
-      {
-        const auto& v (cast<strings> (l));
-
-        for (auto i (v.begin ()), e (v.end ()); i != e; ++i)
-        {
-          // -I can either be in the "-Ifoo" or "-I foo" form. For VC it can
-          // also be /I.
-          //
-          const string& o (*i);
-
-          if (o.size () < 2 || (o[0] != '-' && o[0] != '/') || o[1] != 'I')
-            continue;
-
-          dir_path d;
-          if (o.size () == 2)
-          {
-            if (++i == e)
-              break; // Let the compiler complain.
-
-            d = dir_path (*i);
-          }
-          else
-            d = dir_path (*i, 2, string::npos);
-
-          l6 ([&]{trace << "-I '" << d << "'";});
-
-          // If we are relative or not inside our project root, then
-          // ignore.
-          //
-          if (d.relative () || !d.sub (out_root))
-            continue;
-
-          // If the target directory is a sub-directory of the include
-          // directory, then the prefix is the difference between the
-          // two. Otherwise, leave it empty.
-          //
-          // The idea here is to make this "canonical" setup work auto-
-          // magically:
-          //
-          // 1. We include all files with a prefix, e.g., <foo/bar>.
-          // 2. The library target is in the foo/ sub-directory, e.g.,
-          //    /tmp/foo/.
-          // 3. The poptions variable contains -I/tmp.
-          //
-          dir_path p (out_base.sub (d) ? out_base.leaf (d) : dir_path ());
-
-          auto j (m.find (p));
-
-          if (j != m.end ())
-          {
-            if (j->second != d)
-            {
-              // We used to reject duplicates but it seems this can
-              // be reasonably expected to work according to the order
-              // of the -I options.
-              //
-              if (verb >= 4)
-                trace << "overriding dependency prefix '" << p << "'\n"
-                      << "  old mapping to " << j->second << "\n"
-                      << "  new mapping to " << d;
-
-              j->second = d;
-            }
-          }
-          else
-          {
-            l6 ([&]{trace << "'" << p << "' = '" << d << "'";});
-            m.emplace (move (p), move (d));
-          }
-        }
-      }
-    }
-
-    // Append library prefixes based on the cxx.export.poptions variables
-    // recursively, prerequisite libraries first.
-    //
-    static void
-    append_lib_prefixes (prefix_map& m, target& l, lorder lo)
-    {
-      for (target* t: l.prerequisite_targets)
-      {
-        if (t == nullptr)
-          continue;
-
-        if (lib* l = t->is_a<lib> ())
-          t = &link_member (*l, lo); // Pick one of the members.
-
-        if (t->is_a<liba> () || t->is_a<libs> ())
-          append_lib_prefixes (m, *t, lo);
-      }
-
-      append_prefixes (m, l, "cxx.export.poptions");
-    }
-
-    static prefix_map
-    build_prefix_map (target& t, lorder lo)
-    {
-      prefix_map m;
-
-      // First process the include directories from prerequisite
-      // libraries. Note that here we don't need to see group
-      // members (see apply()).
-      //
-      for (prerequisite& p: group_prerequisites (t))
-      {
-        target* pt (p.target); // Already searched and matched.
-
-        if (lib* l = pt->is_a<lib> ())
-          pt = &link_member (*l, lo); // Pick one of the members.
-
-        if (pt->is_a<liba> () || pt->is_a<libs> ())
-          append_lib_prefixes (m, *pt, lo);
-      }
-
-      // Then process our own.
-      //
-      append_prefixes (m, t, "cxx.poptions");
-
-      return m;
-    }
-
-    // Return the next make prerequisite starting from the specified
-    // position and update position to point to the start of the
-    // following prerequisite or l.size() if there are none left.
-    //
-    static string
-    next_make (const string& l, size_t& p)
-    {
-      size_t n (l.size ());
-
-      // Skip leading spaces.
-      //
-      for (; p != n && l[p] == ' '; p++) ;
-
-      // Lines containing multiple prerequisites are 80 characters max.
-      //
-      string r;
-      r.reserve (n);
-
-      // Scan the next prerequisite while watching out for escape sequences.
-      //
-      for (; p != n && l[p] != ' '; p++)
-      {
-        char c (l[p]);
-
-        if (p + 1 != n)
-        {
-          if (c == '$')
-          {
-            // Got to be another (escaped) '$'.
-            //
-            if (l[p + 1] == '$')
-              ++p;
-          }
-          else if (c == '\\')
-          {
-            // This may or may not be an escape sequence depending on whether
-            // what follows is "escapable".
-            //
-            switch (c = l[++p])
-            {
-            case '\\': break;
-            case ' ': break;
-            default: c = '\\'; --p; // Restore.
-            }
-          }
-        }
-
-        r += c;
-      }
-
-      // Skip trailing spaces.
-      //
-      for (; p != n && l[p] == ' '; p++) ;
-
-      // Skip final '\'.
-      //
-      if (p == n - 1 && l[p] == '\\')
-        p++;
-
-      return r;
-    }
-
-    // Extract the include path from the VC++ /showIncludes output line.
-    // Return empty string if the line is not an include note or include
-    // error. Set the good_error flag if it is an include error (which means
-    // the process will terminate with the error status that needs to be
-    // ignored).
-    //
-    static string
-    next_show (const string& l, bool& good_error)
-    {
-      // The include error should be the last line that we handle.
-      //
-      assert (!good_error);
-
-      // VC++ /showIncludes output. The first line is the file being
-      // compiled. Then we have the list of headers, one per line, in this
-      // form (text can presumably be translated):
-      //
-      // Note: including file: C:\Program Files (x86)\[...]\iostream
-      //
-      // Finally, if we hit a non-existent header, then we end with an error
-      // line in this form:
-      //
-      // x.cpp(3): fatal error C1083: Cannot open include file: 'd/h.hpp':
-      // No such file or directory
-      //
-
-      // Distinguishing between the include note and the include error is
-      // easy: we can just check for C1083. Distinguising between the note and
-      // other errors/warnings is harder: an error could very well end with
-      // what looks like a path so we cannot look for the note but rather have
-      // to look for an error. Here we assume that a line containing ' CNNNN:'
-      // is an error. Should be robust enough in the face of language
-      // translation, etc.
-      //
-      size_t p (l.find (':'));
-      size_t n (l.size ());
-
-      for (; p != string::npos; p = ++p != n ? l.find (':', p) : string::npos)
-      {
-        auto isnum = [](char c) {return c >= '0' && c <= '9';};
-
-        if (p > 5 &&
-            l[p - 6] == ' '  &&
-            l[p - 5] == 'C'  &&
-            isnum (l[p - 4]) &&
-            isnum (l[p - 3]) &&
-            isnum (l[p - 2]) &&
-            isnum (l[p - 1]))
-        {
-          p -= 4; // Start of the error code.
-          break;
-        }
-      }
-
-      if (p == string::npos)
-      {
-        // Include note. We assume the path is always at the end but
-        // need to handle both absolute Windows and POSIX ones.
-        //
-        size_t p (l.rfind (':'));
-
-        if (p != string::npos)
-        {
-          // See if this one is part of the Windows drive letter.
-          //
-          if (p > 1 && p + 1 < n && // 2 chars before, 1 after.
-              l[p - 2] == ' ' &&
-              alpha (l[p - 1]) &&
-              path::traits::is_separator (l[p + 1]))
-            p = l.rfind (':', p - 2);
-        }
-
-        if (p != string::npos)
-        {
-          // VC uses indentation to indicate the include nesting so there
-          // could be any number of spaces after ':'. Skip them.
-          //
-          p = l.find_first_not_of (' ', p + 1);
-        }
-
-        if (p == string::npos)
-          fail << "unable to parse /showIncludes include note line";
-
-        return string (l, p);
-      }
-      else if (l.compare (p, 4, "1083") == 0)
-      {
-        // Include error. The path is conveniently quoted with ''.
-        //
-        size_t p2 (l.rfind ('\''));
-
-        if (p2 != string::npos && p2 != 0)
-        {
-          size_t p1 (l.rfind ('\'', p2 - 1));
-
-          if (p1 != string::npos)
-          {
-            good_error = true;
-            return string (l, p1 + 1 , p2 - p1 - 1);
-          }
-        }
-
-        error << "unable to parse /showIncludes include error line";
-        throw failed ();
-      }
-      else
-      {
-        // Some other error.
-        //
-        return string ();
-      }
-    }
-
-    static void
-    inject_prerequisites (action a, target& t, lorder lo,
-                          cxx& s, scope& ds, depdb& dd)
-    {
-      tracer trace ("cxx::compile::inject_prerequisites");
-
-      l6 ([&]{trace << "target: " << t;});
-
-      // If things go wrong (and they often do in this area), give the user a
-      // bit extra context.
-      //
-      auto g (
-        make_exception_guard (
-          [&s]()
-          {
-            info << "while extracting header dependencies from " << s;
-          }));
-
-      scope& rs (t.root_scope ());
-      const string& cid (cast<string> (rs["cxx.id"]));
-
-      // Initialize lazily, only if required.
-      //
-      cstrings args;
-      string cxx_std; // Storage.
-
-      auto init_args = [&t, lo, &s, &rs, &cid, &args, &cxx_std] ()
-      {
-        const path& cxx (cast<path> (rs["config.cxx"]));
-        const string& tclass (cast<string> (rs["cxx.target.class"]));
-
-        args.push_back (cxx.string ().c_str ());
-
-        // Add cxx.export.poptions from prerequisite libraries. Note
-        // that here we don't need to see group members (see apply()).
-        //
-        for (prerequisite& p: group_prerequisites (t))
-        {
-          target* pt (p.target); // Already searched and matched.
-
-          if (lib* l = pt->is_a<lib> ())
-            pt = &link_member (*l, lo);
-
-          if (pt->is_a<liba> () || pt->is_a<libs> ())
-            append_lib_options (args, *pt, "cxx.export.poptions", lo);
-        }
-
-        append_options (args, t, "cxx.poptions");
-
-        // Some C++ options (e.g., -std, -m) affect the preprocessor.
-        //
-        append_options (args, t, "cxx.coptions");
-        append_std (args, rs, cid, t, cxx_std);
-
-        if (t.is_a<objs> ())
-        {
-          // On Darwin, Win32 -fPIC is the default.
-          //
-          if (tclass == "linux" || tclass == "freebsd")
-            args.push_back ("-fPIC");
-        }
-
-        if (cid == "msvc")
-        {
-          args.push_back ("/nologo");
-
-          // See perform_update() for details on overriding the default
-          // exceptions and runtime.
-          //
-          if (!find_option_prefix ("/EH", args))
-            args.push_back ("/EHsc");
-
-          if (!find_option_prefixes ({"/MD", "/MT"}, args))
-            args.push_back ("/MD");
-
-          args.push_back ("/EP");           // Preprocess to stdout.
-          args.push_back ("/TP");           // Preprocess as C++.
-          args.push_back ("/showIncludes"); // Goes to sterr becasue of /EP.
-        }
-        else
-        {
-          args.push_back ("-M");  // Note: -MM -MG skips missing <>-included.
-          args.push_back ("-MG"); // Treat missing headers as generated.
-
-          // Previously we used '*' as a target name but it gets expanded to
-          // the current directory file names by GCC (4.9) that comes with
-          // MSYS2 (2.4). Yes, this is the (bizarre) behavior of GCC being
-          // executed in the shell with -MQ '*' option and not just -MQ *.
-          //
-          args.push_back ("-MQ"); // Quoted target name.
-          args.push_back ("^");   // Old versions can't do empty target name.
-        }
-
-        // We are using absolute source file path in order to get absolute
-        // paths in the result. Any relative paths in the result are non-
-        // existent, potentially auto-generated headers.
-        //
-        // @@ We will also have to use absolute -I paths to guarantee
-        // that. Or just detect relative paths and error out?
-        //
-        args.push_back (s.path ().string ().c_str ());
-        args.push_back (nullptr);
-      };
-
-      // Build the prefix map lazily only if we have non-existent files.
-      // Also reuse it over restarts since it doesn't change.
-      //
-      prefix_map pm;
-
-      // If any prerequisites that we have extracted changed, then we have to
-      // redo the whole thing. The reason for this is auto-generated headers:
-      // the updated header may now include a yet-non-existent header. Unless
-      // we discover this and generate it (which, BTW, will trigger another
-      // restart since that header, in turn, can also include auto-generated
-      // headers), we will end up with an error during compilation proper.
-      //
-      // One complication with this restart logic is that we will see a
-      // "prefix" of prerequisites that we have already processed (i.e., they
-      // are already in our prerequisite_targets list) and we don't want to
-      // keep redoing this over and over again. One thing to note, however, is
-      // that the prefix that we have seen on the previous run must appear
-      // exactly the same in the subsequent run. The reason for this is that
-      // none of the files that it can possibly be based on have changed and
-      // thus it should be exactly the same. To put it another way, the
-      // presence or absence of a file in the dependency output can only
-      // depend on the previous files (assuming the compiler outputs them as
-      // it encounters them and it is hard to think of a reason why would
-      // someone do otherwise). And we have already made sure that all those
-      // files are up to date. And here is the way we are going to exploit
-      // this: we are going to keep track of how many prerequisites we have
-      // processed so far and on restart skip right to the next one.
-      //
-      // And one more thing: most of the time this list of headers would stay
-      // unchanged and extracting them by running the compiler every time is a
-      // bit wasteful. So we are going to cache them in the depdb. If the db
-      // hasn't been invalidated yet (e.g., because the compiler options have
-      // changed), then we start by reading from it. If anything is out of
-      // date then we use the same restart and skip logic to switch to the
-      // compiler run.
-      //
-
-      // Update the target "smartly". Return true if it has changed or if the
-      // passed timestamp is not timestamp_unknown and is older than the
-      // target.
-      //
-      // There would normally be a lot of headers for every source file (think
-      // all the system headers) and just calling execute_direct() on all of
-      // them can get expensive. At the same time, most of these headers are
-      // existing files that we will never be updating (again, system headers,
-      // for example) and the rule that will match them is the fallback
-      // file_rule. That rule has an optimization: it returns noop_recipe
-      // (which causes the target state to be automatically set to unchanged)
-      // if the file is known to be up to date.
-      //
-      auto update = [&trace, a] (path_target& pt, timestamp ts) -> bool
-      {
-        if (pt.state () != target_state::unchanged)
-        {
-          // We only want to restart if our call to execute() actually
-          // caused an update. In particular, the target could already
-          // have been in target_state::changed because of a dependency
-          // extraction run for some other source file.
-          //
-          target_state os (pt.state ());
-          target_state ns (execute_direct (a, pt));
-
-          if (ns != os && ns != target_state::unchanged)
-          {
-            l6 ([&]{trace << "updated " << pt
-                          << "; old state " << os
-                          << "; new state " << ns;});
-            return true;
-          }
-        }
-
-        if (ts != timestamp_unknown)
-        {
-          timestamp mt (pt.mtime ());
-
-          // See execute_prerequisites() for rationale behind the equal part.
-          //
-          return ts < mt || (ts == mt && pt.state () != target_state::changed);
-        }
-
-        return false;
-      };
-
-      // Update and add a header file to the list of prerequisite targets.
-      // Depending on the cache flag, the file is assumed to either have come
-      // from the depdb cache or from the compiler run. Return whether the
-      // extraction process should be restarted.
-      //
-      auto add = [&trace, &update, &pm, a, &t, lo, &ds, &dd]
-        (path f, bool cache) -> bool
-      {
-        if (!f.absolute ())
-        {
-          f.normalize ();
-
-          // This is probably as often an error as an auto-generated file, so
-          // trace at level 4.
-          //
-          l4 ([&]{trace << "non-existent header '" << f << "'";});
-
-          // If we already did this and build_prefix_map() returned empty,
-          // then we would have failed below.
-          //
-          if (pm.empty ())
-            pm = build_prefix_map (t, lo);
-
-          // First try the whole file. Then just the directory.
-          //
-          // @@ Has to be a separate map since the prefix can be
-          //    the same as the file name.
-          //
-          // auto i (pm.find (f));
-
-          // Find the most qualified prefix of which we are a sub-path.
-          //
-          auto i (pm.end ());
-
-          if (!pm.empty ())
-          {
-            const dir_path& d (f.directory ());
-            i = pm.upper_bound (d);
-
-            // Get the greatest less than, if any. We might still not be a
-            // sub. Note also that we still have to check the last element if
-            // upper_bound() returned end().
-            //
-            if (i == pm.begin () || !d.sub ((--i)->first))
-              i = pm.end ();
-          }
-
-          if (i == pm.end ())
-            fail << "unable to map presumably auto-generated header '"
-                 << f << "' to a project";
-
-          f = i->second / f;
-        }
-        else
-        {
-          // We used to just normalize the path but that could result in an
-          // invalid path (e.g., on CentOS 7 with Clang 3.4) because of the
-          // symlinks. So now we realize (i.e., realpath(3)) it instead. If
-          // it comes from the depdb, in which case we've already done that.
-          //
-          if (!cache)
-            f.realize ();
-        }
-
-        l6 ([&]{trace << "injecting " << f;});
-
-        // Split the name into its directory part, the name part, and
-        // extension. Here we can assume the name part is a valid filesystem
-        // name.
-        //
-        // Note that if the file has no extension, we record an empty
-        // extension rather than NULL (which would signify that the default
-        // extension should be added).
-        //
-        dir_path d (f.directory ());
-        string n (f.leaf ().base ().string ());
-        const char* es (f.extension ());
-        const string* e (&extension_pool.find (es != nullptr ? es : ""));
-
-        // Determine the target type.
-        //
-        const target_type* tt (nullptr);
-
-        // See if this directory is part of any project out_root hierarchy.
-        // Note that this will miss all the headers that come from src_root
-        // (so they will be treated as generic C headers below). Generally,
-        // we don't have the ability to determine that some file belongs to
-        // src_root of some project. But that's not a problem for our
-        // purposes: it is only important for us to accurately determine
-        // target types for headers that could be auto-generated.
-        //
-        // While at it also try to determine if this target is from the src
-        // or out tree of said project.
-        //
-        dir_path out;
-
-        scope& bs (scopes.find (d));
-        if (scope* rs = bs.root_scope ())
-        {
-          tt = map_extension (bs, n, *e);
-
-          if (bs.out_path () != bs.src_path () && d.sub (bs.src_path ()))
-            out = out_src (d, *rs);
-        }
-
-        // If it is outside any project, or the project doesn't have
-        // such an extension, assume it is a plain old C header.
-        //
-        if (tt == nullptr)
-          tt = &h::static_type;
-
-        // Find or insert target.
-        //
-        // @@ OPT: move d, out, n
-        //
-        path_target& pt (
-          static_cast<path_target&> (search (*tt, d, out, n, e, &ds)));
-
-        // Assign path.
-        //
-        if (pt.path ().empty ())
-          pt.path (move (f));
-        else
-          assert (pt.path () == f);
-
-        // Match to a rule.
-        //
-        build2::match (a, pt);
-
-        // Update.
-        //
-        // If this header came from the depdb, make sure it is no older than
-        // the db itself (if it has changed since the db was written, then
-        // chances are the cached data is stale).
-        //
-        bool restart (update (pt, cache ? dd.mtime () : timestamp_unknown));
-
-        // Verify/add it to the dependency database. We do it after update in
-        // order not to add bogus files (non-existent and without a way to
-        // update).
-        //
-        if (!cache)
-          dd.expect (pt.path ());
-
-        // Add to our prerequisite target list.
-        //
-        t.prerequisite_targets.push_back (&pt);
-
-        return restart;
-      };
-
-      // If nothing so far has invalidated the dependency database, then
-      // try the cached data before running the compiler.
-      //
-      bool cache (dd.reading ());
-
-      // But, before we do all that, make sure the source file itself if up to
-      // date.
-      //
-      if (update (s, dd.mtime ()))
-      {
-        // If the file got updated or is newer than the database, then we
-        // cannot rely on the cache any further. However, the cached data
-        // could actually still be valid so the compiler run will validate it.
-        //
-        // We do need to update the database timestamp, however. Failed that,
-        // we will keep re-validating the cached data over and over again.
-        //
-        if (cache)
-        {
-          cache = false;
-          dd.touch ();
-        }
-      }
-
-      size_t skip_count (0);
-      for (bool restart (true); restart; cache = false)
-      {
-        restart = false;
-
-        if (cache)
-        {
-          // If any, this is always the first run.
-          //
-          assert (skip_count == 0);
-
-          while (dd.more ())
-          {
-            string* l (dd.read ());
-
-            // If the line is invalid, run the compiler.
-            //
-            if (l == nullptr)
-            {
-              restart = true;
-              break;
-            }
-
-            restart = add (path (move (*l)), true);
-            skip_count++;
-
-            // The same idea as in the source file update above.
-            //
-            if (restart)
-            {
-              l6 ([&]{trace << "restarting";});
-              dd.touch ();
-              break;
-            }
-          }
-        }
-        else
-        {
-          try
-          {
-            if (args.empty ())
-              init_args ();
-
-            if (verb >= 3)
-              print_process (args);
-
-            // For VC with /EP we need a pipe to stderr and stdout should go
-            // to /dev/null.
-            //
-            process pr (args.data (),
-                        0,
-                        cid == "msvc" ? -2 : -1,
-                        cid == "msvc" ? -1 : 2);
-
-            try
-            {
-              // We may not read all the output (e.g., due to a restart).
-              // Before we used to just close the file descriptor to signal to
-              // the other end that we are not interested in the rest. This
-              // works fine with GCC but Clang (3.7.0) finds this impolite and
-              // complains, loudly (broken pipe). So now we are going to skip
-              // until the end.
-              //
-              ifdstream is (cid == "msvc" ? pr.in_efd : pr.in_ofd,
-                            fdstream_mode::text | fdstream_mode::skip,
-                            ifdstream::badbit);
-
-              // In some cases we may need to ignore the error return
-              // status. The good_error flag keeps track of that. Similarly
-              // we sometimes expect the error return status based on the
-              // output we see. The bad_error flag is for that.
-              //
-              bool good_error (false), bad_error (false);
-
-              size_t skip (skip_count);
-              for (bool first (true), second (false);
-                   !(restart || is.eof ()); )
-              {
-                string l;
-                getline (is, l);
-
-                if (is.fail ())
-                {
-                  if (is.eof ()) // Trailing newline.
-                    break;
-
-                  throw ifdstream::failure ("");
-                }
-
-                l6 ([&]{trace << "header dependency line '" << l << "'";});
-
-                // Parse different dependency output formats.
-                //
-                if (cid == "msvc")
-                {
-                  if (first)
-                  {
-                    // The first line should be the file we are compiling. If
-                    // it is not, then something went wrong even before we
-                    // could compile anything (e.g., file does not exist). In
-                    // this case the first line (and everything after it) is
-                    // presumably diagnostics.
-                    //
-                    if (l != s.path ().leaf ().string ())
-                    {
-                      text << l;
-                      bad_error = true;
-                      break;
-                    }
-
-                    first = false;
-                    continue;
-                  }
-
-                  string f (next_show (l, good_error));
-
-                  if (f.empty ()) // Some other diagnostics.
-                  {
-                    text << l;
-                    bad_error = true;
-                    break;
-                  }
-
-                  // Skip until where we left off.
-                  //
-                  if (skip != 0)
-                  {
-                    // We can't be skipping over a non-existent header.
-                    //
-                    assert (!good_error);
-                    skip--;
-                  }
-                  else
-                  {
-                    restart = add (path (move (f)), false);
-                    skip_count++;
-
-                    // If the header does not exist, we better restart.
-                    //
-                    assert (!good_error || restart);
-
-                    if (restart)
-                      l6 ([&]{trace << "restarting";});
-                  }
-                }
-                else
-                {
-                  // Make dependency declaration.
-                  //
-                  size_t pos (0);
-
-                  if (first)
-                  {
-                    // Empty output should mean the wait() call below will
-                    // return false.
-                    //
-                    if (l.empty ())
-                    {
-                      bad_error = true;
-                      break;
-                    }
-
-                    assert (l[0] == '^' && l[1] == ':' && l[2] == ' ');
-
-                    first = false;
-                    second = true;
-
-                    // While normally we would have the source file on the
-                    // first line, if too long, it will be moved to the next
-                    // line and all we will have on this line is "^: \".
-                    //
-                    if (l.size () == 4 && l[3] == '\\')
-                      continue;
-                    else
-                      pos = 3; // Skip "^: ".
-
-                    // Fall through to the 'second' block.
-                  }
-
-                  if (second)
-                  {
-                    second = false;
-                    next_make (l, pos); // Skip the source file.
-                  }
-
-                  while (pos != l.size ())
-                  {
-                    string f (next_make (l, pos));
-
-                    // Skip until where we left off.
-                    //
-                    if (skip != 0)
-                    {
-                      skip--;
-                      continue;
-                    }
-
-                    restart = add (path (move (f)), false);
-                    skip_count++;
-
-                    if (restart)
-                    {
-                      l6 ([&]{trace << "restarting";});
-                      break;
-                    }
-                  }
-                }
-              }
-
-              // In case of VC++, we are parsing stderr and if things go
-              // south, we need to copy the diagnostics for the user to see.
-              //
-              // Note that the eof check is important: if the stream is at
-              // eof, this and all subsequent writes to cerr will fail (and
-              // you won't see a thing).
-              //
-              if (is.peek () != ifdstream::traits_type::eof () &&
-                  cid == "msvc" &&
-                  bad_error)
-                cerr << is.rdbuf ();
-
-              is.close ();
-
-              // We assume the child process issued some diagnostics.
-              //
-              if (!pr.wait ())
-              {
-                if (!good_error) // Ignore expected errors (restart).
-                  throw failed ();
-              }
-              else if (bad_error)
-                fail << "expected error exist status from C++ compiler";
-            }
-            catch (const ifdstream::failure&)
-            {
-              pr.wait ();
-              fail << "unable to read C++ compiler header dependency output";
-            }
-          }
-          catch (const process_error& e)
-          {
-            error << "unable to execute " << args[0] << ": " << e.what ();
-
-            // In a multi-threaded program that fork()'ed but did not exec(),
-            // it is unwise to try to do any kind of cleanup (like unwinding
-            // the stack and running destructors).
-            //
-            if (e.child ())
-              exit (1);
-
-            throw failed ();
-          }
-        }
-      }
-    }
-
-    // Filter cl.exe noise (msvc.cxx).
-    //
-    void
-    msvc_filter_cl (ifdstream&, const path& src);
-
-    target_state compile::
-    perform_update (action a, target& xt)
-    {
-      file& t (static_cast<file&> (xt));
-      cxx* s (execute_prerequisites<cxx> (a, t, t.mtime ()));
-
-      if (s == nullptr)
-        return target_state::unchanged;
-
-      scope& bs (t.base_scope ());
-      scope& rs (*bs.root_scope ());
-
-      const path& cxx (cast<path> (rs["config.cxx"]));
-      const string& cid (cast<string> (rs["cxx.id"]));
-      const string& tclass (cast<string> (rs["cxx.target.class"]));
-
-      otype ct (compile_type (t));
-
-      cstrings args {cxx.string ().c_str ()};
-
-      // Translate paths to relative (to working directory) ones. This
-      // results in easier to read diagnostics.
-      //
-      path relo (relative (t.path ()));
-      path rels (relative (s->path ()));
-
-      // Add cxx.export.poptions from prerequisite libraries. Note that
-      // here we don't need to see group members (see apply()).
-      //
-      lorder lo (link_order (bs, ct));
-      for (prerequisite& p: group_prerequisites (t))
-      {
-        target* pt (p.target); // Already searched and matched.
-
-        if (lib* l = pt->is_a<lib> ())
-          pt = &link_member (*l, lo);
-
-        if (pt->is_a<liba> () || pt->is_a<libs> ())
-          append_lib_options (args, *pt, "cxx.export.poptions", lo);
-      }
-
-      append_options (args, t, "cxx.poptions");
-      append_options (args, t, "cxx.coptions");
-
-      string std, out, out1; // Storage.
-
-      append_std (args, rs, cid, t, std);
-
-      if (cid == "msvc")
-      {
-        // The /F*: option variants with separate names only became available
-        // in VS2013/12.0. Why do we bother? Because the command line suddenly
-        // becomes readable.
-        //
-        uint64_t cver (cast<uint64_t> (rs["cxx.version.major"]));
-
-        args.push_back ("/nologo");
-
-        // While we want to keep the low-level build as "pure" as possible,
-        // the two misguided defaults, exceptions and runtime, just have to be
-        // fixed. Otherwise the default build is pretty much unusable. But we
-        // also make sure that the user can easily disable our defaults: if we
-        // see any relevant options explicitly specified, we take our hands
-        // off.
-        //
-        if (!find_option_prefix ("/EH", args))
-          args.push_back ("/EHsc");
-
-        // The runtime is a bit more interesting. At first it may seem like a
-        // good idea to be a bit clever and use the static runtime if we are
-        // building obja{}. And for obje{} we could decide which runtime to
-        // use based on the library link order: if it is static-only, then we
-        // could assume the static runtime. But it is indeed too clever: when
-        // building liba{} we have no idea who is going to use it. It could be
-        // an exe{} that links both static and shared libraries (and is
-        // therefore built with the shared runtime). And to safely use the
-        // static runtime, everything must be built with /MT and there should
-        // be no DLLs in the picture. So we are going to play it safe and
-        // always default to the shared runtime.
-        //
-        // In a similar vein, it would seem reasonable to use the debug runtime
-        // if we are compiling with debug. But, again, there will be fireworks
-        // if we have some projects built with debug and some without and then
-        // we try to link them together (which is not an unreasonable thing to
-        // do). So by default we will always use the release runtime.
-        //
-        if (!find_option_prefixes ({"/MD", "/MT"}, args))
-          args.push_back ("/MD");
-
-        // The presence of /Zi or /ZI causes the compiler to write debug info
-        // to the .pdb file. By default it is a shared file called vcNN.pdb
-        // (where NN is the VC version) created (wait for it) in the current
-        // working directory (and not the directory of the .obj file). Also,
-        // because it is shared, there is a special Windows service that
-        // serializes access. We, of course, want none of that so we will
-        // create a .pdb per object file.
-        //
-        // Note that this also changes the name of the .idb file (used for
-        // minimal rebuild and incremental compilation): cl.exe take the /Fd
-        // value and replaces the .pdb extension with .idb.
-        //
-        // Note also that what we are doing here appears to be incompatible
-        // with PCH (/Y* options) and /Gm (minimal rebuild).
-        //
-        if (find_options ({"/Zi", "/ZI"}, args))
-        {
-          if (cver >= 18)
-            args.push_back ("/Fd:");
-          else
-            out1 = "/Fd";
-
-          out1 += relo.string ();
-          out1 += ".pdb";
-
-          args.push_back (out1.c_str ());
-        }
-
-        if (cver >= 18)
-        {
-          args.push_back ("/Fo:");
-          args.push_back (relo.string ().c_str ());
-        }
-        else
-        {
-          out = "/Fo" + relo.string ();
-          args.push_back (out.c_str ());
-        }
-
-        args.push_back ("/c");  // Compile only.
-        args.push_back ("/TP"); // Compile as C++.
-        args.push_back (rels.string ().c_str ());
-      }
-      else
-      {
-        if (ct == otype::s)
-        {
-          // On Darwin, Win32 -fPIC is the default.
-          //
-          if (tclass == "linux" || tclass == "freebsd")
-            args.push_back ("-fPIC");
-        }
-
-        args.push_back ("-o");
-        args.push_back (relo.string ().c_str ());
-
-        args.push_back ("-c");
-        args.push_back (rels.string ().c_str ());
-      }
-
-      args.push_back (nullptr);
-
-      if (verb >= 2)
-        print_process (args);
-      else if (verb)
-        text << "c++ " << *s;
-
-      try
-      {
-        // VC cl.exe sends diagnostics to stdout. It also prints the file name
-        // being compiled as the first line. So for cl.exe we redirect stdout
-        // to a pipe, filter that noise out, and send the rest to stderr.
-        //
-        // For other compilers redirect stdout to stderr, in case any of them
-        // tries to pull off something similar. For sane compilers this should
-        // be harmless.
-        //
-        bool filter (cid == "msvc");
-
-        process pr (args.data (), 0, (filter ? -1 : 2));
-
-        if (filter)
-        {
-          try
-          {
-            ifdstream is (pr.in_ofd, fdstream_mode::text, ifdstream::badbit);
-
-            msvc_filter_cl (is, rels);
-
-            // If anything remains in the stream, send it all to stderr. Note
-            // that the eof check is important: if the stream is at eof, this
-            // and all subsequent writes to cerr will fail (and you won't see
-            // a thing).
-            //
-            if (is.peek () != ifdstream::traits_type::eof ())
-              cerr << is.rdbuf ();
-
-            is.close ();
-          }
-          catch (const ifdstream::failure&) {} // Assume exits with error.
-        }
-
-        if (!pr.wait ())
-          throw failed ();
-
-        // Should we go to the filesystem and get the new mtime? We
-        // know the file has been modified, so instead just use the
-        // current clock time. It has the advantage of having the
-        // subseconds precision.
-        //
-        t.mtime (system_clock::now ());
-        return target_state::changed;
-      }
-      catch (const process_error& e)
-      {
-        error << "unable to execute " << args[0] << ": " << e.what ();
-
-        // In a multi-threaded program that fork()'ed but did not exec(),
-        // it is unwise to try to do any kind of cleanup (like unwinding
-        // the stack and running destructors).
-        //
-        if (e.child ())
-          exit (1);
-
-        throw failed ();
-      }
-    }
-
-    target_state compile::
-    perform_clean (action a, target& xt)
-    {
-      file& t (static_cast<file&> (xt));
-
-      scope& rs (t.root_scope ());
-      const string& cid (cast<string> (rs["cxx.id"]));
-
-      initializer_list<const char*> e;
-
-      if (cid == "msvc")
-        e = {".d", ".idb", ".pdb"};
-      else
-        e = {".d"};
-
-      return clean_extra (a, t, e);
-    }
-
-    compile compile::instance;
-  }
-}