Move cc build system module to separate library

1 files changed, 1550 insertions, 0 deletions

diff --git a/libbuild2/cc/pkgconfig.cxx b/libbuild2/cc/pkgconfig.cxx
new file mode 100644
index 0000000..0669b02
--- /dev/null
+++ b/libbuild2/cc/pkgconfig.cxx
@@ -0,0 +1,1550 @@
+// file      : libbuild2/cc/pkgconfig.cxx -*- C++ -*-
+// copyright : Copyright (c) 2014-2019 Code Synthesis Ltd
+// license   : MIT; see accompanying LICENSE file
+
+// In order not to complicate the bootstrap procedure with libpkgconf building
+// exclude functionality that involves reading of .pc files.
+//
+#ifndef BUILD2_BOOTSTRAP
+#  include <libpkgconf/libpkgconf.h>
+#endif
+
+#include <libbuild2/scope.hxx>
+#include <libbuild2/target.hxx>
+#include <libbuild2/context.hxx>
+#include <libbuild2/variable.hxx>
+#include <libbuild2/algorithm.hxx>
+#include <libbuild2/filesystem.hxx>
+#include <libbuild2/diagnostics.hxx>
+
+#include <libbuild2/install/utility.hxx>
+
+#include <libbuild2/bin/target.hxx>
+
+#include <libbuild2/cc/types.hxx>
+#include <libbuild2/cc/target.hxx>  // pc
+#include <libbuild2/cc/utility.hxx>
+
+#include <libbuild2/cc/common.hxx>
+#include <libbuild2/cc/compile-rule.hxx>
+#include <libbuild2/cc/link-rule.hxx>
+
+#ifndef BUILD2_BOOTSTRAP
+
+// Note that the libpkgconf library doesn't provide the version macro that we
+// could use to compile the code conditionally against different API versions.
+// Thus, we need to sense the pkgconf_client_new() function signature
+// ourselves to call it properly.
+//
+namespace details
+{
+  void*
+  pkgconf_cross_personality_default (); // Never called.
+}
+
+using namespace details;
+
+template <typename H>
+static inline pkgconf_client_t*
+call_pkgconf_client_new (pkgconf_client_t* (*f) (H, void*),
+                         H error_handler,
+                         void* error_handler_data)
+{
+  return f (error_handler, error_handler_data);
+}
+
+template <typename H, typename P>
+static inline pkgconf_client_t*
+call_pkgconf_client_new (pkgconf_client_t* (*f) (H, void*, P),
+                         H error_handler,
+                         void* error_handler_data)
+{
+  return f (error_handler,
+            error_handler_data,
+            ::pkgconf_cross_personality_default ());
+}
+
+#endif
+
+using namespace std;
+using namespace butl;
+
+namespace build2
+{
+#ifndef BUILD2_BOOTSTRAP
+
+  // Load package information from a .pc file. Filter out the -I/-L options
+  // that refer to system directories.
+  //
+  // Note that the prerequisite package .pc files search order is as follows:
+  //
+  // - in directory of the specified file
+  // - in pc_dirs directories (in the natural order)
+  //
+  class pkgconf
+  {
+  public:
+    using path_type = build2::path;
+
+    path_type path;
+
+  public:
+    explicit
+    pkgconf (path_type,
+             const dir_paths& pc_dirs,
+             const dir_paths& sys_inc_dirs,
+             const dir_paths& sys_lib_dirs);
+
+    // Create a special empty object. Querying package information on such
+    // an object is illegal.
+    //
+    pkgconf () = default;
+
+    ~pkgconf ();
+
+    // Movable-only type.
+    //
+    pkgconf (pkgconf&& p)
+        : path (move (p.path)),
+          client_ (p.client_),
+          pkg_ (p.pkg_)
+    {
+      p.client_ = nullptr;
+      p.pkg_ = nullptr;
+    }
+
+    pkgconf&
+    operator= (pkgconf&& p)
+    {
+      if (this != &p)
+      {
+        this->~pkgconf ();
+        new (this) pkgconf (move (p)); // Assume noexcept move-construction.
+      }
+      return *this;
+    }
+
+    pkgconf (const pkgconf&) = delete;
+    pkgconf& operator= (const pkgconf&) = delete;
+
+    strings
+    cflags (bool stat) const;
+
+    strings
+    libs (bool stat) const;
+
+    string
+    variable (const char*) const;
+
+    string
+    variable (const string& s) const {return variable (s.c_str ());}
+
+  private:
+    // Keep them as raw pointers not to deal with API thread-unsafety in
+    // deleters and introducing additional mutex locks.
+    //
+    pkgconf_client_t* client_ = nullptr;
+    pkgconf_pkg_t* pkg_ = nullptr;
+  };
+
+  // Currently the library is not thread-safe, even on the pkgconf_client_t
+  // level (see issue #128 for details).
+  //
+  // @@ An update: seems that the obvious thread-safety issues are fixed.
+  //    However, let's keep mutex locking for now not to introduce potential
+  //    issues before we make sure that there are no other ones.
+  //
+  static mutex pkgconf_mutex;
+
+  // The package dependency traversal depth limit.
+  //
+  static const int pkgconf_max_depth = 100;
+
+  // Normally the error_handler() callback can be called multiple times to
+  // report a single error (once per message line), to produce a multi-line
+  // message like this:
+  //
+  //   Package foo was not found in the pkg-config search path.\n
+  //   Perhaps you should add the directory containing `foo.pc'\n
+  //   to the PKG_CONFIG_PATH environment variable\n
+  //   Package 'foo', required by 'bar', not found\n
+  //
+  // For the above example callback will be called 4 times. To suppress all the
+  // junk we will use PKGCONF_PKG_PKGF_SIMPLIFY_ERRORS to get just:
+  //
+  //   Package 'foo', required by 'bar', not found\n
+  //
+  static const int pkgconf_flags = PKGCONF_PKG_PKGF_SIMPLIFY_ERRORS;
+
+  static bool
+  pkgconf_error_handler (const char* msg, const pkgconf_client_t*, const void*)
+  {
+    error << runtime_error (msg); // Sanitize the message.
+    return true;
+  }
+
+  // Deleters. Note that they are thread-safe.
+  //
+  struct fragments_deleter
+  {
+    void operator() (pkgconf_list_t* f) const {pkgconf_fragment_free (f);}
+  };
+
+  // Convert fragments to strings. Skip the -I/-L options that refer to system
+  // directories.
+  //
+  static strings
+  to_strings (const pkgconf_list_t& frags,
+              char type,
+              const pkgconf_list_t& sysdirs)
+  {
+    assert (type == 'I' || type == 'L');
+
+    strings r;
+
+    auto add = [&r] (const pkgconf_fragment_t* frag)
+    {
+      string s;
+      if (frag->type != '\0')
+      {
+        s += '-';
+        s += frag->type;
+      }
+
+      s += frag->data;
+      r.push_back (move (s));
+    };
+
+    // Option that is separated from its value, for example:
+    //
+    // -I /usr/lib
+    //
+    const pkgconf_fragment_t* opt (nullptr);
+
+    pkgconf_node_t *node;
+    PKGCONF_FOREACH_LIST_ENTRY(frags.head, node)
+    {
+      auto frag (static_cast<const pkgconf_fragment_t*> (node->data));
+
+      // Add the separated option and directory, unless the latest is a system
+      // one.
+      //
+      if (opt != nullptr)
+      {
+        // Note that we should restore the directory path that was
+        // (mis)interpreted as an option, for example:
+        //
+        // -I -Ifoo
+        //
+        // In the above example option '-I' is followed by directory '-Ifoo',
+        // which is represented by libpkgconf library as fragment 'foo' with
+        // type 'I'.
+        //
+        if (!pkgconf_path_match_list (
+              frag->type == '\0'
+              ? frag->data
+              : (string ({'-', frag->type}) + frag->data).c_str (),
+              &sysdirs))
+        {
+          add (opt);
+          add (frag);
+        }
+
+        opt = nullptr;
+        continue;
+      }
+
+      // Skip the -I/-L option if it refers to a system directory.
+      //
+      if (frag->type == type)
+      {
+        // The option is separated from a value, that will (presumably) follow.
+        //
+        if (*frag->data == '\0')
+        {
+          opt = frag;
+          continue;
+        }
+
+        if (pkgconf_path_match_list (frag->data, &sysdirs))
+          continue;
+      }
+
+      add (frag);
+    }
+
+    if (opt != nullptr) // Add the dangling option.
+      add (opt);
+
+    return r;
+  }
+
+  // Note that some libpkgconf functions can potentially return NULL, failing
+  // to allocate the required memory block. However, we will not check the
+  // returned value for NULL as the library doesn't do so, prior to filling the
+  // allocated structures. So such a code complication on our side would be
+  // useless. Also, for some functions the NULL result has a special semantics,
+  // for example "not found".
+  //
+  pkgconf::
+  pkgconf (path_type p,
+           const dir_paths& pc_dirs,
+           const dir_paths& sys_lib_dirs,
+           const dir_paths& sys_inc_dirs)
+      : path (move (p))
+  {
+    auto add_dirs = [] (pkgconf_list_t& dir_list,
+                        const dir_paths& dirs,
+                        bool suppress_dups,
+                        bool cleanup = false)
+    {
+      if (cleanup)
+      {
+        pkgconf_path_free (&dir_list);
+        dir_list = PKGCONF_LIST_INITIALIZER;
+      }
+
+      for (const auto& d: dirs)
+        pkgconf_path_add (d.string ().c_str (), &dir_list, suppress_dups);
+    };
+
+    mlock l (pkgconf_mutex);
+
+    // Initialize the client handle.
+    //
+    unique_ptr<pkgconf_client_t, void (*) (pkgconf_client_t*)> c (
+      call_pkgconf_client_new (&pkgconf_client_new,
+                               pkgconf_error_handler,
+                               nullptr /* handler_data */),
+      [] (pkgconf_client_t* c) {pkgconf_client_free (c);});
+
+    pkgconf_client_set_flags (c.get (), pkgconf_flags);
+
+    // Note that the system header and library directory lists are
+    // automatically pre-filled by the pkgconf_client_new() call (see above).
+    // We will re-create these lists from scratch.
+    //
+    add_dirs (c->filter_libdirs,
+              sys_lib_dirs,
+              false /* suppress_dups */,
+              true  /* cleanup */);
+
+    add_dirs (c->filter_includedirs,
+              sys_inc_dirs,
+              false /* suppress_dups */,
+              true  /* cleanup */);
+
+    // Note that the loaded file directory is added to the (yet empty) search
+    // list. Also note that loading of the prerequisite packages is delayed
+    // until flags retrieval, and their file directories are not added to the
+    // search list.
+    //
+    pkg_ = pkgconf_pkg_find (c.get (), path.string ().c_str ());
+
+    if (pkg_ == nullptr)
+      fail << "package '" << path << "' not found or invalid";
+
+    // Add the .pc file search directories.
+    //
+    assert (c->dir_list.length == 1); // Package file directory (see above).
+    add_dirs (c->dir_list, pc_dirs, true /* suppress_dups */);
+
+    client_ = c.release ();
+  }
+
+  pkgconf::
+  ~pkgconf ()
+  {
+    if (client_ != nullptr) // Not empty.
+    {
+      assert (pkg_ != nullptr);
+
+      mlock l (pkgconf_mutex);
+      pkgconf_pkg_unref (client_, pkg_);
+      pkgconf_client_free (client_);
+    }
+  }
+
+  strings pkgconf::
+  cflags (bool stat) const
+  {
+    assert (client_ != nullptr); // Must not be empty.
+
+    mlock l (pkgconf_mutex);
+
+    pkgconf_client_set_flags (
+      client_,
+      pkgconf_flags |
+
+      // Walk through the private package dependencies (Requires.private)
+      // besides the public ones while collecting the flags. Note that we do
+      // this for both static and shared linking.
+      //
+      PKGCONF_PKG_PKGF_SEARCH_PRIVATE |
+
+      // Collect flags from Cflags.private besides those from Cflags for the
+      // static linking.
+      //
+      (stat
+       ? PKGCONF_PKG_PKGF_MERGE_PRIVATE_FRAGMENTS
+       : 0));
+
+    pkgconf_list_t f = PKGCONF_LIST_INITIALIZER; // Aggregate initialization.
+    int e (pkgconf_pkg_cflags (client_, pkg_, &f, pkgconf_max_depth));
+
+    if (e != PKGCONF_PKG_ERRF_OK)
+      throw failed (); // Assume the diagnostics is issued.
+
+    unique_ptr<pkgconf_list_t, fragments_deleter> fd (&f); // Auto-deleter.
+    return to_strings (f, 'I', client_->filter_includedirs);
+  }
+
+  strings pkgconf::
+  libs (bool stat) const
+  {
+    assert (client_ != nullptr); // Must not be empty.
+
+    mlock l (pkgconf_mutex);
+
+    pkgconf_client_set_flags (
+      client_,
+      pkgconf_flags |
+
+      // Additionally collect flags from the private dependency packages
+      // (see above) and from the Libs.private value for the static linking.
+      //
+      (stat
+       ? PKGCONF_PKG_PKGF_SEARCH_PRIVATE |
+         PKGCONF_PKG_PKGF_MERGE_PRIVATE_FRAGMENTS
+       : 0));
+
+    pkgconf_list_t f = PKGCONF_LIST_INITIALIZER; // Aggregate initialization.
+    int e (pkgconf_pkg_libs (client_, pkg_, &f, pkgconf_max_depth));
+
+    if (e != PKGCONF_PKG_ERRF_OK)
+      throw failed (); // Assume the diagnostics is issued.
+
+    unique_ptr<pkgconf_list_t, fragments_deleter> fd (&f); // Auto-deleter.
+    return to_strings (f, 'L', client_->filter_libdirs);
+  }
+
+  string pkgconf::
+  variable (const char* name) const
+  {
+    assert (client_ != nullptr); // Must not be empty.
+
+    mlock l (pkgconf_mutex);
+    const char* r (pkgconf_tuple_find (client_, &pkg_->vars, name));
+    return r != nullptr ? string (r) : string ();
+  }
+
+#endif
+
+  namespace cc
+  {
+    using namespace bin;
+
+    // In pkg-config backslashes, spaces, etc are escaped with a backslash.
+    //
+    static string
+    escape (const string& s)
+    {
+      string r;
+
+      for (size_t p (0);;)
+      {
+        size_t sp (s.find_first_of ("\\ ", p));
+
+        if (sp != string::npos)
+        {
+          r.append (s, p, sp - p);
+          r += '\\';
+          r += s[sp];
+          p = sp + 1;
+        }
+        else
+        {
+          r.append (s, p, sp);
+          break;
+        }
+      }
+
+      return r;
+    }
+
+    // Try to find a .pc file in the pkgconfig/ subdirectory of libd, trying
+    // several names derived from stem. If not found, return false. If found,
+    // load poptions, loptions, libs, and modules, set the corresponding
+    // *.export.* variables and add prerequisites on targets, and return true.
+    // Note that we assume the targets are locked so that all of this is
+    // MT-safe.
+    //
+    // System library search paths (those extracted from the compiler) are
+    // passed in top_sysd while the user-provided (via -L) in top_usrd.
+    //
+    // Note that scope and link order should be "top-level" from the
+    // search_library() POV.
+    //
+    // Also note that the bootstrapped version of build2 will not search for
+    // .pc files, always returning false (see above for the reasoning).
+    //
+#ifndef BUILD2_BOOTSTRAP
+
+    // Iterate over pkgconf directories that correspond to the specified
+    // library directory, passing them to the callback function for as long as
+    // it returns false (not found). Return true if the callback returned
+    // true.
+    //
+    bool common::
+    pkgconfig_search (const dir_path& d, const pkgconfig_callback& f) const
+    {
+      dir_path pd (d);
+
+      // First always check the pkgconfig/ subdirectory in this library
+      // directory. Even on platforms where this is not the canonical place,
+      // .pc files of autotools-based packages installed by the user often
+      // still end up there.
+      //
+      if (exists (pd /= "pkgconfig") && f (move (pd)))
+        return true;
+
+      // Platform-specific locations.
+      //
+      if (tsys == "freebsd")
+      {
+        // On FreeBSD .pc files go to libdata/pkgconfig/, not lib/pkgconfig/.
+        //
+        (((pd = d) /= "..") /= "libdata") /= "pkgconfig";
+
+        if (exists (pd) && f (move (pd)))
+          return true;
+      }
+
+      return false;
+    }
+
+    // Search for the .pc files in the pkgconf directories that correspond to
+    // the specified library directory. If found, return static (first) and
+    // shared (second) library .pc files. If common is false, then only
+    // consider our .static/.shared files.
+    //
+    pair<path, path> common::
+    pkgconfig_search (const dir_path& libd,
+                      const optional<project_name>& proj,
+                      const string& stem,
+                      bool common) const
+    {
+      // When it comes to looking for .pc files we have to decide where to
+      // search (which directory(ies)) as well as what to search for (which
+      // names). Suffix is our ".shared" or ".static" extension.
+      //
+      auto search_dir = [&proj, &stem] (const dir_path& dir,
+                                        const string& sfx) -> path
+      {
+        path f;
+
+        // See if there is a corresponding .pc file. About half of them are
+        // called foo.pc and half libfoo.pc (and one of the pkg-config's
+        // authors suggests that some of you should call yours foolib.pc, just
+        // to keep things interesting, you know).
+        //
+        // Given the (general) import in the form <proj>%lib{<stem>}, we will
+        // first try lib<stem>.pc, then <stem>.pc. Maybe it also makes sense
+        // to try <proj>.pc, just in case. Though, according to pkg-config
+        // docs, the .pc file should correspond to a library, not project. But
+        // then you get something like zlib which calls it zlib.pc. So let's
+        // just do it.
+        //
+        f = dir;
+        f /= "lib";
+        f += stem;
+        f += sfx;
+        f += ".pc";
+        if (exists (f))
+          return f;
+
+        f = dir;
+        f /= stem;
+        f += sfx;
+        f += ".pc";
+        if (exists (f))
+          return f;
+
+        if (proj)
+        {
+          f = dir;
+          f /= proj->string ();
+          f += sfx;
+          f += ".pc";
+          if (exists (f))
+            return f;
+        }
+
+        return path ();
+      };
+
+      // Return false (and so stop the iteration) if a .pc file is found.
+      //
+      // Note that we rely on the "small function object" optimization here.
+      //
+      struct data
+      {
+        path a;
+        path s;
+        bool common;
+      } d {path (), path (), common};
+
+      auto check = [&d, &search_dir] (dir_path&& p) -> bool
+      {
+        // First look for static/shared-specific files.
+        //
+        d.a = search_dir (p, ".static");
+        d.s = search_dir (p, ".shared");
+
+        if (!d.a.empty () || !d.s.empty ())
+          return true;
+
+        // Then the common.
+        //
+        if (d.common)
+          d.a = d.s = search_dir (p, "");
+
+        return !d.a.empty ();
+      };
+
+      pair<path, path> r;
+
+      if (pkgconfig_search (libd, check))
+      {
+        r.first  = move (d.a);
+        r.second = move (d.s);
+      }
+
+      return r;
+    };
+
+    bool common::
+    pkgconfig_load (action a,
+                    const scope& s,
+                    lib& lt,
+                    liba* at,
+                    libs* st,
+                    const optional<project_name>& proj,
+                    const string& stem,
+                    const dir_path& libd,
+                    const dir_paths& top_sysd,
+                    const dir_paths& top_usrd) const
+    {
+      assert (at != nullptr || st != nullptr);
+
+      pair<path, path> p (
+        pkgconfig_search (libd, proj, stem, true /* common */));
+
+      if (p.first.empty () && p.second.empty ())
+        return false;
+
+      pkgconfig_load (a, s, lt, at, st, p, libd, top_sysd, top_usrd);
+      return true;
+    }
+
+    void common::
+    pkgconfig_load (action a,
+                    const scope& s,
+                    lib& lt,
+                    liba* at,
+                    libs* st,
+                    const pair<path, path>& paths,
+                    const dir_path& libd,
+                    const dir_paths& top_sysd,
+                    const dir_paths& top_usrd) const
+    {
+      tracer trace (x, "pkgconfig_load");
+
+      assert (at != nullptr || st != nullptr);
+
+      const path& ap (paths.first);
+      const path& sp (paths.second);
+
+      assert (!ap.empty () || !sp.empty ());
+
+      // Extract --cflags and set them as lib?{}:export.poptions. Note that we
+      // still pass --static in case this is pkgconf which has Cflags.private.
+      //
+      auto parse_cflags = [&trace, this] (target& t,
+                                          const pkgconf& pc,
+                                          bool la)
+      {
+        strings pops;
+
+        bool arg (false);
+        for (auto& o: pc.cflags (la))
+        {
+          if (arg)
+          {
+            // Can only be an argument for -I, -D, -U options.
+            //
+            pops.push_back (move (o));
+            arg = false;
+            continue;
+          }
+
+          size_t n (o.size ());
+
+          // We only keep -I, -D and -U.
+          //
+          if (n >= 2 &&
+              o[0] == '-' &&
+              (o[1] == 'I' || o[1] == 'D' || o[1] == 'U'))
+          {
+            pops.push_back (move (o));
+            arg = (n == 2);
+            continue;
+          }
+
+          l4 ([&]{trace << "ignoring " << pc.path << " --cflags option "
+                        << o;});
+        }
+
+        if (arg)
+          fail << "argument expected after " << pops.back () <<
+            info << "while parsing pkg-config --cflags " << pc.path;
+
+        if (!pops.empty ())
+        {
+          auto p (t.vars.insert (c_export_poptions));
+
+          // The only way we could already have this value is if this same
+          // library was also imported as a project (as opposed to installed).
+          // Unlikely but possible. In this case the values were set by the
+          // export stub and we shouldn't touch them.
+          //
+          if (p.second)
+            p.first.get () = move (pops);
+        }
+      };
+
+      // Parse --libs into loptions/libs (interface and implementation). If
+      // ps is not NULL, add each resolves library target as a prerequisite.
+      //
+      auto parse_libs = [a, &s, top_sysd, this] (target& t,
+                                                 bool binless,
+                                                 const pkgconf& pc,
+                                                 bool la,
+                                                 prerequisites* ps)
+      {
+        strings lops;
+        vector<name> libs;
+
+        // Normally we will have zero or more -L's followed by one or more
+        // -l's, with the first one being the library itself, unless the
+        // library is binless. But sometimes we may have other linker options,
+        // for example, -Wl,... or -pthread. It's probably a bad idea to
+        // ignore them. Also, theoretically, we could have just the library
+        // name/path.
+        //
+        // The tricky part, of course, is to know whether what follows after
+        // an option we don't recognize is its argument or another option or
+        // library. What we do at the moment is stop recognizing just library
+        // names (without -l) after seeing an unknown option.
+        //
+        bool arg (false), first (true), known (true), have_L;
+        for (auto& o: pc.libs (la))
+        {
+          if (arg)
+          {
+            // Can only be an argument for an loption.
+            //
+            lops.push_back (move (o));
+            arg = false;
+            continue;
+          }
+
+          size_t n (o.size ());
+
+          // See if this is -L.
+          //
+          if (n >= 2 && o[0] == '-' && o[1] == 'L')
+          {
+            have_L = true;
+            lops.push_back (move (o));
+            arg = (n == 2);
+            continue;
+          }
+
+          // See if that's -l or just the library name/path.
+          //
+          if ((known && o[0] != '-') ||
+              (n > 2 && o[0] == '-' && o[1] == 'l'))
+          {
+            // Unless binless, the first one is the library itself, which we
+            // skip. Note that we don't verify this and theoretically it could
+            // be some other library, but we haven't encountered such a beast
+            // yet.
+            //
+            if (first)
+            {
+              first = false;
+
+              if (!binless)
+                continue;
+            }
+
+            // @@ If by some reason this is the library itself (doesn't go
+            //    first or libpkgconf parsed libs in some bizarre way) we will
+            //    hang trying to lock it's target inside search_library() (or
+            //    fail an assertion if run serially) as by now it is already
+            //    locked. To be safe we probably shouldn't rely on the position
+            //    and filter out all occurrences of the library itself (by
+            //    name?) and complain if none were encountered.
+            //
+            libs.push_back (name (move (o)));
+            continue;
+          }
+
+          // Otherwise we assume it is some other loption.
+          //
+          known = false;
+          lops.push_back (move (o));
+        }
+
+        if (arg)
+          fail << "argument expected after " << lops.back () <<
+            info << "while parsing pkg-config --libs " << pc.path;
+
+        // Space-separated list of escaped library flags.
+        //
+        auto lflags = [&pc, la] () -> string
+        {
+          string r;
+          for (const auto& o: pc.libs (la))
+          {
+            if (!r.empty ())
+              r += ' ';
+            r += escape (o);
+          }
+          return r;
+        };
+
+        if (first && !binless)
+          fail << "library expected in '" << lflags () << "'" <<
+            info << "while parsing pkg-config --libs " << pc.path;
+
+        // Resolve -lfoo into the library file path using our import installed
+        // machinery (i.e., we are going to call search_library() that will
+        // probably call us again, and so on).
+        //
+        // The reason we do it is the link order. For general libraries it
+        // shouldn't matter if we imported them via an export stub, direct
+        // import installed, or via a .pc file (which we could have generated
+        // from the export stub). The exception is "runtime libraries" (which
+        // are really the extension of libc) such as -lm, -ldl, -lpthread,
+        // etc. Those we will detect and leave as -l*.
+        //
+        // If we managed to resolve all the -l's (sans runtime), then we can
+        // omit -L's for nice and tidy command line.
+        //
+        bool all (true);
+        optional<dir_paths> usrd; // Populate lazily.
+
+        for (name& n: libs)
+        {
+          string& l (n.value);
+
+          // These ones are common/standard/POSIX.
+          //
+          if (l[0] != '-'      || // e.g., shell32.lib
+              l == "-lm"       ||
+              l == "-ldl"      ||
+              l == "-lrt"      ||
+              l == "-lpthread")
+            continue;
+
+          // Note: these list are most likely incomplete.
+          //
+          if (tclass == "linux")
+          {
+            // Some extras from libc (see libc6-dev) and other places.
+            //
+            if (l == "-lanl"     ||
+                l == "-lcrypt"   ||
+                l == "-lnsl"     ||
+                l == "-lresolv"  ||
+                l == "-lgcc")
+            continue;
+          }
+          else if (tclass == "macos")
+          {
+            if (l == "-lSystem")
+              continue;
+          }
+
+          // Prepare user search paths by entering the -L paths from the .pc
+          // file.
+          //
+          if (have_L && !usrd)
+          {
+            usrd = dir_paths ();
+
+            for (auto i (lops.begin ()); i != lops.end (); ++i)
+            {
+              const string& o (*i);
+
+              if (o.size () >= 2 && o[0] == '-' && o[1] == 'L')
+              {
+                string p;
+
+                if (o.size () == 2)
+                  p = *++i; // We've verified it's there.
+                else
+                  p = string (o, 2);
+
+                dir_path d (move (p));
+
+                if (d.relative ())
+                  fail << "relative -L directory in '" << lflags () << "'" <<
+                    info << "while parsing pkg-config --libs " << pc.path;
+
+                usrd->push_back (move (d));
+              }
+            }
+          }
+
+          // @@ OUT: for now we assume out is undetermined, just like in
+          // resolve_library().
+          //
+          dir_path out;
+          string name (l, 2); // Sans -l.
+
+          prerequisite_key pk {
+            nullopt, {&lib::static_type, &out, &out, &name, nullopt}, &s};
+
+          if (const target* lt = search_library (a, top_sysd, usrd, pk))
+          {
+            // We used to pick a member but that doesn't seem right since the
+            // same target could be used with different link orders.
+            //
+            n.dir = lt->dir;
+            n.type = lib::static_type.name;
+            n.value = lt->name;
+
+            if (ps != nullptr)
+              ps->push_back (prerequisite (*lt));
+          }
+          else
+            // If we couldn't find the library, then leave it as -l.
+            //
+            all = false;
+        }
+
+        // If all the -l's resolved and there were no other options, then drop
+        // all the -L's. If we have unknown options, then leave them in to be
+        // safe.
+        //
+        if (all && known)
+          lops.clear ();
+
+        if (!lops.empty ())
+        {
+          if (cclass == compiler_class::msvc)
+          {
+            // Translate -L to /LIBPATH.
+            //
+            for (auto i (lops.begin ()); i != lops.end (); )
+            {
+              string& o (*i);
+              size_t n (o.size ());
+
+              if (n >= 2 && o[0] == '-' && o[1] == 'L')
+              {
+                o.replace (0, 2, "/LIBPATH:");
+
+                if (n == 2)
+                {
+                  o += *++i; // We've verified it's there.
+                  i = lops.erase (i);
+                  continue;
+                }
+              }
+
+              ++i;
+            }
+          }
+
+          auto p (t.vars.insert (c_export_loptions));
+
+          if (p.second)
+            p.first.get () = move (lops);
+        }
+
+        // Set even if empty (export override).
+        //
+        {
+          auto p (t.vars.insert (c_export_libs));
+
+          if (p.second)
+            p.first.get () = move (libs);
+        }
+      };
+
+      // On Windows pkg-config will escape backslahses in paths. In fact, it
+      // may escape things even on non-Windows platforms, for example,
+      // spaces. So we use a slightly modified version of next_word().
+      //
+      auto next = [] (const string& s, size_t& b, size_t& e) -> string
+      {
+        string r;
+        size_t n (s.size ());
+
+        if (b != e)
+          b = e;
+
+        // Skip leading delimiters.
+        //
+        for (; b != n && s[b] == ' '; ++b) ;
+
+        if (b == n)
+        {
+          e = n;
+          return r;
+        }
+
+        // Find first trailing delimiter while taking care of escapes.
+        //
+        r = s[b];
+        for (e = b + 1; e != n && s[e] != ' '; ++e)
+        {
+          if (s[e] == '\\')
+          {
+            if (++e == n)
+              fail << "dangling escape in pkg-config output '" << s << "'";
+          }
+
+          r += s[e];
+        }
+
+        return r;
+      };
+
+      // Parse modules and add them to the prerequisites.
+      //
+      auto parse_modules = [&trace, &next, &s, this]
+        (const pkgconf& pc, prerequisites& ps)
+      {
+        string mstr (pc.variable ("cxx_modules"));
+
+        string m;
+        for (size_t b (0), e (0); !(m = next (mstr, b, e)).empty (); )
+        {
+          // The format is <name>=<path>.
+          //
+          size_t p (m.find ('='));
+          if (p == string::npos ||
+              p == 0            || // Empty name.
+              p == m.size () - 1)  // Empty path.
+            fail << "invalid module information in '" << mstr << "'" <<
+              info << "while parsing pkg-config --variable=cxx_modules "
+                   << pc.path;
+
+          string mn (m, 0, p);
+          path mp (m, p + 1, string::npos);
+          path mf (mp.leaf ());
+
+          // Extract module properties, if any.
+          //
+          string pp (pc.variable ("cxx_module_preprocessed." + mn));
+          string se (pc.variable ("cxx_module_symexport." + mn));
+
+          // For now there are only C++ modules.
+          //
+          auto tl (
+            s.ctx.targets.insert_locked (
+              *x_mod,
+              mp.directory (),
+              dir_path (),
+              mf.base ().string (),
+              mf.extension (),
+              true, // Implied.
+              trace));
+
+          target& mt (tl.first);
+
+          // If the target already exists, then setting its variables is not
+          // MT-safe. So currently we only do it if we have the lock (and thus
+          // nobody can see this target yet) assuming that this has already
+          // been done otherwise.
+          //
+          // @@ This is not quite correct, though: this target could already
+          //    exist but for a "different purpose" (e.g., it could be used as
+          //    a header).
+          //
+          // @@ Could setting it in the rule-specific vars help? (But we
+          //    are not matching a rule for it.) Note that we are setting
+          //    it on the module source, not bmi*{}! So rule-specific vars
+          //    don't seem to the answer here.
+          //
+          if (tl.second.owns_lock ())
+          {
+            mt.vars.assign (c_module_name) = move (mn);
+
+            // Set module properties. Note that if unspecified we should still
+            // set them to their default values since the hosting project may
+            // have them set to incompatible value.
+            //
+            {
+              value& v (mt.vars.assign (x_preprocessed)); // NULL
+              if (!pp.empty ()) v = move (pp);
+            }
+
+            {
+              mt.vars.assign (x_symexport) = (se == "true");
+            }
+
+            tl.second.unlock ();
+          }
+
+          ps.push_back (prerequisite (mt));
+        }
+      };
+
+      // For now we only populate prerequisites for lib{}. To do it for
+      // liba{} would require weeding out duplicates that are already in
+      // lib{}.
+      //
+      prerequisites prs;
+
+      pkgconf apc;
+      pkgconf spc;
+
+      // Create the .pc files search directory list.
+      //
+      dir_paths pc_dirs;
+
+      // Note that we rely on the "small function object" optimization here.
+      //
+      auto add_pc_dir = [&pc_dirs] (dir_path&& d) -> bool
+      {
+        pc_dirs.emplace_back (move (d));
+        return false;
+      };
+
+      pkgconfig_search (libd, add_pc_dir);
+      for (const dir_path& d: top_usrd) pkgconfig_search (d, add_pc_dir);
+      for (const dir_path& d: top_sysd) pkgconfig_search (d, add_pc_dir);
+
+      bool pa (at != nullptr && !ap.empty ());
+      if (pa || sp.empty ())
+        apc = pkgconf (ap, pc_dirs, sys_lib_dirs, sys_inc_dirs);
+
+      bool ps (st != nullptr && !sp.empty ());
+      if (ps || ap.empty ())
+        spc = pkgconf (sp, pc_dirs, sys_lib_dirs, sys_inc_dirs);
+
+      // Sort out the interface dependencies (which we are setting on lib{}).
+      // If we have the shared .pc variant, then we use that.  Otherwise --
+      // static but extract without the --static option (see also the saving
+      // logic).
+      //
+      pkgconf& ipc (ps ? spc : apc); // Interface package info.
+
+      parse_libs (
+        lt,
+        (ps ? st->mtime () : at->mtime ()) == timestamp_unreal /* binless */,
+        ipc,
+        false,
+        &prs);
+
+      if (pa)
+      {
+        parse_cflags (*at, apc, true);
+        parse_libs (*at, at->path ().empty (), apc, true, nullptr);
+      }
+
+      if (ps)
+        parse_cflags (*st, spc, false);
+
+      // For now we assume static and shared variants export the same set of
+      // modules. While technically possible, having a different set will
+      // most likely lead to all sorts of trouble (at least for installed
+      // libraries) and life is short.
+      //
+      if (modules)
+        parse_modules (ipc, prs);
+
+      assert (!lt.has_prerequisites ());
+      if (!prs.empty ())
+        lt.prerequisites (move (prs));
+
+      // Bless the library group with a "trust me it exists" timestamp. Failed
+      // that, if we add it as a prerequisite (like we do above), the fallback
+      // file rule won't match.
+      //
+      lt.mtime (mtime (ipc.path));
+    }
+
+#else
+
+    pair<path, path> common::
+    pkgconfig_search (const dir_path&,
+                      const optional<project_name>&,
+                      const string&,
+                      bool) const
+    {
+      return pair<path, path> ();
+    }
+
+    bool common::
+    pkgconfig_load (action,
+                    const scope&,
+                    lib&,
+                    liba*,
+                    libs*,
+                    const optional<project_name>&,
+                    const string&,
+                    const dir_path&,
+                    const dir_paths&,
+                    const dir_paths&) const
+    {
+      return false;
+    }
+
+    void common::
+    pkgconfig_load (action,
+                    const scope&,
+                    lib&,
+                    liba*,
+                    libs*,
+                    const pair<path, path>&,
+                    const dir_path&,
+                    const dir_paths&,
+                    const dir_paths&) const
+    {
+      assert (false); // Should never be called.
+    }
+
+#endif
+
+    void link_rule::
+    pkgconfig_save (action a, const file& l, bool la, bool binless) const
+    {
+      tracer trace (x, "pkgconfig_save");
+
+      context& ctx (l.ctx);
+
+      const scope& bs (l.base_scope ());
+      const scope& rs (*bs.root_scope ());
+
+      auto* t (find_adhoc_member<pc> (l));
+      assert (t != nullptr);
+
+      // By default we assume things go into install.{include, lib}.
+      //
+      using install::resolve_dir;
+
+      dir_path idir (resolve_dir (l, cast<dir_path> (l["install.include"])));
+      dir_path ldir (resolve_dir (l, cast<dir_path> (l["install.lib"])));
+
+      const path& p (t->path ());
+
+      if (verb >= 2)
+        text << "cat >" << p;
+
+      if (ctx.dry_run)
+        return;
+
+      auto_rmfile arm (p);
+
+      try
+      {
+        ofdstream os (p);
+
+        {
+          const project_name& n (project (rs));
+
+          if (n.empty ())
+            fail << "no project name in " <<  rs;
+
+          lookup vl (rs.vars[ctx.var_version]);
+          if (!vl)
+            fail << "no version variable in project " << n <<
+              info << "while generating " << p;
+
+          const string& v (cast<string> (vl));
+
+          os << "Name: " << n << endl;
+          os << "Version: " << v << endl;
+
+          // This one is required so make something up if unspecified.
+          //
+          os << "Description: ";
+          if (const string* s = cast_null<string> (rs[ctx.var_project_summary]))
+            os << *s << endl;
+          else
+            os << n << ' ' << v << endl;
+
+          if (const string* u = cast_null<string> (rs[ctx.var_project_url]))
+            os << "URL: " << *u << endl;
+        }
+
+        auto save_poptions = [&l, &os] (const variable& var)
+        {
+          if (const strings* v = cast_null<strings> (l[var]))
+          {
+            for (auto i (v->begin ()); i != v->end (); ++i)
+            {
+              const string& o (*i);
+              size_t n (o.size ());
+
+              // Filter out -I (both -I<dir> and -I <dir> forms).
+              //
+              if (n >= 2 && o[0] == '-' && o[1] == 'I')
+              {
+                if (n == 2)
+                  ++i;
+
+                continue;
+              }
+
+              os << ' ' << escape (o);
+            }
+          }
+        };
+
+        // Given a library save its -l-style library name.
+        //
+        auto save_library = [&os, this] (const file& l)
+        {
+          // If available (it may not, in case of import-installed libraris),
+          // use the .pc file name to derive the -l library name (in case of
+          // the shared library, l.path() may contain version).
+          //
+          string n;
+
+          auto strip_lib = [&n] ()
+          {
+            if (n.size () > 3 &&
+                path::traits_type::compare (n.c_str (), 3, "lib", 3) == 0)
+              n.erase (0, 3);
+          };
+
+          if (auto* t = find_adhoc_member<pc> (l))
+          {
+            // We also want to strip the lib prefix unless it is part of the
+            // target name while keeping custom library prefix/suffix, if any.
+            //
+            n = t->path ().leaf ().base ().base ().string ();
+
+            if (path::traits_type::compare (n.c_str (), n.size (),
+                                       l.name.c_str (), l.name.size ()) != 0)
+              strip_lib ();
+          }
+          else
+          {
+            // Derive -l-name from the file name in a fuzzy, platform-specific
+            // manner.
+            //
+            n = l.path ().leaf ().base ().string ();
+
+            if (cclass != compiler_class::msvc)
+              strip_lib ();
+          }
+
+          os << " -l" << n;
+        };
+
+        // @@ TODO: support whole archive?
+        //
+
+        // Cflags.
+        //
+        os << "Cflags:";
+        os << " -I" << escape (idir.string ());
+        save_poptions (c_export_poptions);
+        save_poptions (x_export_poptions);
+        os << endl;
+
+        // Libs.
+        //
+        // While we generate split shared/static .pc files, in case of static
+        // we still want to sort things out into Libs/Libs.private. This is
+        // necessary to distinguish between interface and implementation
+        // dependencies if we don't have the shared variant (see the load
+        // logic for details).
+        //
+        //@@ TODO: would be nice to weed out duplicates. But is it always
+        //   safe? Think linking archives: will have to keep duplicates in
+        //   the second position, not first. Gets even trickier with
+        //   Libs.private split.
+        //
+        {
+          os << "Libs:";
+
+          // While we don't need it for a binless library itselt, it may be
+          // necessary to resolve its binfull dependencies.
+          //
+          os << " -L" << escape (ldir.string ());
+
+          // Now process ourselves as if we were being linked to something (so
+          // pretty similar to link_rule::append_libraries()).
+          //
+          bool priv (false);
+          auto imp = [&priv] (const file&, bool la) {return priv && la;};
+
+          auto lib = [&os, &save_library] (const file* const* c,
+                                           const string& p,
+                                           lflags,
+                                           bool)
+          {
+            const file* l (c != nullptr ? *c : nullptr);
+
+            if (l != nullptr)
+            {
+              if (l->is_a<libs> () || l->is_a<liba> ()) // See through libux.
+                save_library (*l);
+            }
+            else
+              os << ' ' << p; // Something "system'y", pass as is.
+          };
+
+          auto opt = [] (const file&,
+                         const string&,
+                         bool, bool)
+          {
+            //@@ TODO: should we filter -L similar to -I?
+            //@@ TODO: how will the Libs/Libs.private work?
+            //@@ TODO: remember to use escape()
+
+            /*
+            // If we need an interface value, then use the group (lib{}).
+            //
+            if (const target* g = exp && l.is_a<libs> () ? l.group : &l)
+            {
+              const variable& var (
+                com
+                ? (exp ? c_export_loptions : c_loptions)
+                : (t == x
+                   ? (exp ? x_export_loptions : x_loptions)
+                   : var_pool[t + (exp ? ".export.loptions" : ".loptions")]));
+
+              append_options (args, *g, var);
+            }
+            */
+          };
+
+          // Pretend we are linking an executable using what would be normal,
+          // system-default link order.
+          //
+          linfo li {otype::e, la ? lorder::a_s : lorder::s_a};
+
+          process_libraries (a, bs, li, sys_lib_dirs,
+                             l, la, 0, // Link flags.
+                             imp, lib, opt, !binless);
+          os << endl;
+
+          if (la)
+          {
+            os << "Libs.private:";
+
+            priv = true;
+            process_libraries (a, bs, li, sys_lib_dirs,
+                               l, la, 0, // Link flags.
+                               imp, lib, opt, false);
+            os << endl;
+          }
+        }
+
+        // If we have modules, list them in the modules variable. We also save
+        // some extra info about them (yes, the rabbit hole runs deep). This
+        // code is pretty similar to compiler::search_modules().
+        //
+        if (modules)
+        {
+          struct module
+          {
+            string name;
+            path file;
+
+            string pp;
+            bool symexport;
+          };
+          vector<module> modules;
+
+          for (const target* pt: l.prerequisite_targets[a])
+          {
+            // @@ UTL: we need to (recursively) see through libu*{} (and
+            //    also in search_modules()).
+            //
+            if (pt != nullptr && pt->is_a<bmix> ())
+            {
+              // What we have is a binary module interface. What we need is
+              // a module interface source it was built from. We assume it's
+              // the first mxx{} target that we see.
+              //
+              const target* mt (nullptr);
+              for (const target* t: pt->prerequisite_targets[a])
+              {
+                if ((mt = t->is_a (*x_mod)))
+                  break;
+              }
+
+              // Can/should there be a bmi{} without mxx{}? Can't think of a
+              // reason.
+              //
+              assert (mt != nullptr);
+
+              path p (install::resolve_file (mt->as<file> ()));
+
+              if (p.empty ()) // Not installed.
+                continue;
+
+              string pp;
+              if (const string* v = cast_null<string> ((*mt)[x_preprocessed]))
+                pp = *v;
+
+              modules.push_back (
+                module {
+                  cast<string> (pt->state[a].vars[c_module_name]),
+                  move (p),
+                  move (pp),
+                  symexport
+                });
+            }
+          }
+
+          if (!modules.empty ())
+          {
+            os << endl
+               << "cxx_modules =";
+
+            // Module names shouldn't require escaping.
+            //
+            for (const module& m: modules)
+              os << ' ' << m.name << '=' << escape (m.file.string ());
+
+            os << endl;
+
+            // Module-specific properties. The format is:
+            //
+            // <lang>_module_<property>.<module> = <value>
+            //
+            for (const module& m: modules)
+            {
+              if (!m.pp.empty ())
+                os << "cxx_module_preprocessed." << m.name << " = " << m.pp
+                   << endl;
+
+              if (m.symexport)
+                os << "cxx_module_symexport." << m.name << " = true" << endl;
+            }
+          }
+        }
+
+        os.close ();
+        arm.cancel ();
+      }
+      catch (const io_error& e)
+      {
+        fail << "unable to write " << p << ": " << e;
+      }
+    }
+  }
+}