aboutsummaryrefslogtreecommitdiff
path: root/libbuild2/cc/common.cxx
blob: c7ca7bc8ffbb4ae20f890ded2547195c6171b600 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
// file      : libbuild2/cc/common.cxx -*- C++ -*-
// license   : MIT; see accompanying LICENSE file

#include <libbuild2/cc/common.hxx>

#include <libbuild2/file.hxx>        // import()
#include <libbuild2/scope.hxx>
#include <libbuild2/variable.hxx>
#include <libbuild2/algorithm.hxx>
#include <libbuild2/filesystem.hxx>
#include <libbuild2/diagnostics.hxx>

#include <libbuild2/cc/utility.hxx>

using namespace std;
using namespace butl;

namespace build2
{
  namespace cc
  {
    using namespace bin;

    // Recursively process prerequisite libraries of the specified library. If
    // proc_impl returns false, then only process interface (*.export.libs),
    // otherwise -- interface and implementation (prerequisite and from
    // *.libs, unless overriden with *.export.imp_libs).
    //
    // Note that here we assume that an interface library is also always an
    // implementation (since we don't use *.export.libs for static linking).
    // We currently have this restriction to make sure the target in
    // *.export.libs is up-to-date (which will happen automatically if it is
    // listed as a prerequisite of this library).
    //
    // Storing a reference to library path in proc_lib is legal (it comes
    // either from the target's path or from one of the *.libs variables
    // neither of which should change on this run).
    //
    // Note that the order of processing is:
    //
    // 1. options (x.* then cc.* to be consistent with poptions/loptions)
    // 2. lib itself (if self is true)
    // 3. dependency libs (prerequisite_targets, left to right, depth-first)
    // 4. dependency libs (*.libs variables).
    //
    // The first argument to proc_lib is a pointer to the last element of an
    // array that contains the current library dependency chain all the way to
    // the library passed to process_libraries(). The first element of this
    // array is NULL.
    //
    void common::
    process_libraries (
      action a,
      const scope& top_bs,
      linfo top_li,
      const dir_paths& top_sysd,
      const file& l,
      bool la,
      lflags lf,
      const function<bool (const file&,
                           bool la)>& proc_impl, // Implementation?
      const function<void (const file* const*,   // Can be NULL.
                           const string& path,   // Library path.
                           lflags,               // Link flags.
                           bool sys)>& proc_lib, // True if system library.
      const function<void (const file&,
                           const string& type,   // cc.type
                           bool com,             // cc. or x.
                           bool exp)>& proc_opt, // *.export.
      bool self /*= false*/,                     // Call proc_lib on l?
      small_vector<const file*, 16>* chain) const
    {
      small_vector<const file*, 16> chain_storage;
      if (chain == nullptr)
      {
        chain = &chain_storage;
        chain->push_back (nullptr);
      }

      // See what type of library this is (C, C++, etc). Use it do decide
      // which x.libs variable name to use. If it's unknown, then we only
      // look into prerequisites. Note: lookup starting from rule-specific
      // variables (target should already be matched).
      //
      const string* t (cast_null<string> (l.state[a][c_type]));

      bool impl (proc_impl && proc_impl (l, la));
      bool cc (false), same (false);

      auto& vp (top_bs.ctx.var_pool);
      lookup c_e_libs;
      lookup x_e_libs;

      if (t != nullptr)
      {
        cc   = (*t == "cc");
        same = (!cc && *t == x);

        // Note that we used to treat *.export.libs set on the liba/libs{}
        // members as *.libs overrides rather than as member-specific
        // interface dependencies. This difference in semantics proved to be
        // surprising so now we have separate *.export.imp_libs for that.
        // Note that in this case options come from *.export.* variables.
        //
        // Note also that we only check for *.*libs. If one doesn't have any
        // libraries but needs to set, say, *.loptions, then *.*libs should be
        // set to NULL or empty (this is why we check for the result being
        // defined).
        //
        c_e_libs = l[impl ? c_export_imp_libs : c_export_libs];

        if (!cc)
          x_e_libs = l[same
                       ? (impl ? x_export_imp_libs : x_export_libs)
                       : vp[*t + (impl ? ".export.imp_libs" : ".export.libs")]];

        // Process options first.
        //
        if (proc_opt)
        {
          // If all we know is it's a C-common library, then in both cases we
          // only look for cc.export.*.
          //
          if (cc)
            proc_opt (l, *t, true, true);
          else
          {
            if (impl)
            {
              // Interface and implementation: as discussed above, we can have
              // two situations: overriden export or default export.
              //
              if (c_e_libs.defined () || x_e_libs.defined ())
              {
                // NOTE: should this not be from l.vars rather than l? Or
                // perhaps we can assume non-common values will be set on
                // libs{}/liba{}.
                //
                // Note: options come from *.export.* variables.
                //
                proc_opt (l, *t, false, true);
                proc_opt (l, *t, true, true);
              }
              else
              {
                // For default export we use the same options as were used to
                // build the library.
                //
                proc_opt (l, *t, false, false);
                proc_opt (l, *t, true, false);
              }
            }
            else
            {
              // Interface: only add *.export.* (interface dependencies).
              //
              proc_opt (l, *t, false, true);
              proc_opt (l, *t, true, true);
            }
          }
        }
      }

      // Determine if an absolute path is to a system library. Note that
      // we assume both paths to be normalized.
      //
      auto sys = [] (const dir_paths& sysd, const string& p) -> bool
      {
        size_t pn (p.size ());

        for (const dir_path& d: sysd)
        {
          const string& ds (d.string ()); // Can be "/", otherwise no slash.
          size_t dn (ds.size ());

          if (pn > dn &&
              p.compare (0, dn, ds) == 0 &&
              (path::traits_type::is_separator (ds[dn - 1]) ||
               path::traits_type::is_separator (p[dn])))
            return true;
        }

        return false;
      };

      // Next process the library itself if requested.
      //
      if (self && proc_lib)
      {
        chain->push_back (&l);

        // Note that while normally the path is assigned, in case of an import
        // stub the path to the DLL may not be known and so the path will be
        // empty (but proc_lib() will use the import stub).
        //
        const path& p (l.path ());

        bool s (t != nullptr // If cc library (matched or imported).
                ? cast_false<bool> (l.vars[c_system])
                : !p.empty () && sys (top_sysd, p.string ()));

        proc_lib (&chain->back (), p.string (), lf, s);
      }

      const scope& bs (t == nullptr || cc ? top_bs : l.base_scope ());
      optional<linfo> li;                        // Calculate lazily.
      const dir_paths* sysd (nullptr);           // Resolve lazily.

      // Find system search directories corresponding to this library, i.e.,
      // from its project and for its type (C, C++, etc).
      //
      auto find_sysd = [&top_sysd, t, cc, same, &bs, &sysd, this] ()
      {
        // Use the search dirs corresponding to this library scope/type.
        //
        sysd = (t == nullptr || cc)
        ? &top_sysd // Imported library, use importer's sysd.
        : &cast<dir_paths> (
          bs.root_scope ()->vars[same
                                 ? x_sys_lib_dirs
                                 : bs.ctx.var_pool[*t + ".sys_lib_dirs"]]);
      };

      auto find_linfo = [top_li, t, cc, &bs, &l, &li] ()
      {
        li = (t == nullptr || cc)
        ? top_li
        : link_info (bs, link_type (l).type);
      };

      // Only go into prerequisites (implementation) if instructed and we are
      // not using explicit export. Otherwise, interface dependencies come
      // from the lib{}:*.export.imp_libs below.
      //
      if (impl && !c_e_libs.defined () && !x_e_libs.defined ())
      {
        for (const prerequisite_target& pt: l.prerequisite_targets[a])
        {
          // Note: adhoc prerequisites are not part of the library metadata
          // protocol (and we should check for adhoc first to avoid races).
          //
          if (pt.adhoc || pt == nullptr)
            continue;

          bool la;
          const file* f;

          if ((la = (f = pt->is_a<liba>  ())) ||
              (la = (f = pt->is_a<libux> ())) ||
              (      f = pt->is_a<libs>  ()))
          {
            if (sysd == nullptr) find_sysd ();
            if (!li) find_linfo ();

            process_libraries (a, bs, *li, *sysd,
                               *f, la, pt.data,
                               proc_impl, proc_lib, proc_opt, true, chain);
          }
        }
      }

      // Process libraries (recursively) from *.export.*libs (of type names)
      // handling import, etc.
      //
      // If it is not a C-common library, then it probably doesn't have any of
      // the *.libs.
      //
      if (t != nullptr)
      {
        optional<dir_paths> usrd; // Extract lazily.

        // Determine if a "simple path" is a system library.
        //
        auto sys_simple = [&sysd, &sys, &find_sysd] (const string& p) -> bool
        {
          bool s (!path::traits_type::absolute (p));

          if (!s)
          {
            if (sysd == nullptr) find_sysd ();

            s = sys (*sysd, p);
          }

          return s;
        };

        auto proc_int = [&l,
                         &proc_impl, &proc_lib, &proc_opt, chain,
                         &sysd, &usrd,
                         &find_sysd, &find_linfo, &sys_simple,
                         &bs, a, &li, impl, this] (const lookup& lu)
        {
          const vector<name>* ns (cast_null<vector<name>> (lu));
          if (ns == nullptr || ns->empty ())
            return;

          for (auto i (ns->begin ()), e (ns->end ()); i != e; ++i)
          {
            const name& n (*i);

            if (n.simple ())
            {
              // This is something like -lpthread or shell32.lib so should be
              // a valid path. But it can also be an absolute library path
              // (e.g., something that may come from our .static/shared.pc
              // files).
              //
              if (proc_lib)
                proc_lib (nullptr, n.value, 0, sys_simple (n.value));
            }
            else
            {
              // This is a potentially project-qualified target.
              //
              if (sysd == nullptr) find_sysd ();
              if (!li) find_linfo ();

              const file& t (
                resolve_library (a,
                                 bs,
                                 n,
                                 (n.pair ? (++i)->dir : dir_path ()),
                                 *li,
                                 *sysd, usrd));

              if (proc_lib)
              {
                // This can happen if the target is mentioned in *.export.libs
                // (i.e., it is an interface dependency) but not in the
                // library's prerequisites (i.e., it is not an implementation
                // dependency).
                //
                // Note that we used to just check for path being assigned but
                // on Windows import-installed DLLs may legally have empty
                // paths.
                //
                if (t.mtime () == timestamp_unknown)
                  fail   << (impl ? "implementation" : "interface")
                         << " dependency " << t << " is out of date" <<
                    info << "mentioned in *.export." << (impl ? "imp_" : "")
                         << "libs of target " << l <<
                    info << "is it a prerequisite of " << l << "?";
              }

              // Process it recursively.
              //
              // @@ Where can we get the link flags? Should we try to find
              //    them in the library's prerequisites? What about installed
              //    stuff?
              //
              process_libraries (a, bs, *li, *sysd,
                                 t, t.is_a<liba> () || t.is_a<libux> (), 0,
                                 proc_impl, proc_lib, proc_opt, true, chain);
            }
          }
        };

        // Process libraries from *.libs (of type strings).
        //
        auto proc_imp = [&proc_lib, &sys_simple] (const lookup& lu)
        {
          const strings* ns (cast_null<strings> (lu));
          if (ns == nullptr || ns->empty ())
            return;

          for (const string& n: *ns)
          {
            // This is something like -lpthread or shell32.lib so should be a
            // valid path.
            //
            proc_lib (nullptr, n, 0, sys_simple (n));
          }
        };

        // Note: the same structure as when processing options above.
        //
        // If all we know is it's a C-common library, then in both cases we
        // only look for cc.export.*libs.
        //
        if (cc)
        {
          if (c_e_libs) proc_int (c_e_libs);
        }
        else
        {
          if (impl)
          {
            // Interface and implementation: as discussed above, we can have
            // two situations: overriden export or default export.
            //
            if (c_e_libs.defined () || x_e_libs.defined ())
            {
              if (c_e_libs) proc_int (c_e_libs);
              if (x_e_libs) proc_int (x_e_libs);
            }
            else
            {
              // For default export we use the same options/libs as were used
              // to build the library. Since libraries in (non-export) *.libs
              // are not targets, we don't need to recurse.
              //
              if (proc_lib)
              {
                proc_imp (l[c_libs]);
                proc_imp (l[same ? x_libs : vp[*t + ".libs"]]);
              }
            }
          }
          else
          {
            // Interface: only add *.export.* (interface dependencies).
            //
            if (c_e_libs) proc_int (c_e_libs);
            if (x_e_libs) proc_int (x_e_libs);
          }
        }
      }

      // Remove this library from the chain.
      //
      if (self && proc_lib)
        chain->pop_back ();
    }

    // The name can be an absolute or relative target name (for example,
    // /tmp/libfoo/lib{foo} or ../libfoo/lib{foo}) or a project-qualified
    // relative target name (e.g., libfoo%lib{foo}).
    //
    // Note that in case of the relative target that comes from export.*libs,
    // the resolution happens relative to the base scope of the target from
    // which this export.*libs came, which is exactly what we want.
    //
    // Note that the scope, search paths, and the link order should all be
    // derived from the library target that mentioned this name. This way we
    // will select exactly the same target as the library's matched rule and
    // that's the only way to guarantee it will be up-to-date.
    //
    const file& common::
    resolve_library (action a,
                     const scope& s,
                     const name& cn,
                     const dir_path& out,
                     linfo li,
                     const dir_paths& sysd,
                     optional<dir_paths>& usrd) const
    {
      if (cn.type != "lib" && cn.type != "liba" && cn.type != "libs")
        fail << "target name " << cn << " is not a library";

      const target* xt (nullptr);

      if (!cn.qualified ())
      {
        // Search for an existing target with this name "as if" it was a
        // prerequisite.
        //
        xt = search_existing (cn, s, out);

        if (xt == nullptr)
          fail << "unable to find library " << cn;
      }
      else
      {
        // This is import.
        //
        name n (cn), o; // Note: find_prerequisite_key() changes name.
        prerequisite_key pk (s.find_prerequisite_key (n, o, location ()));
        xt = search_library_existing (a, sysd, usrd, pk);

        if (xt == nullptr)
        {
          if (n.qualified ())
            xt = import_existing (s.ctx, pk);
        }

        if (xt == nullptr)
          fail << "unable to find library " << pk;
      }

      // If this is lib{}/libu*{}, pick appropriate member.
      //
      if (const libx* l = xt->is_a<libx> ())
        xt = link_member (*l, a, li); // Pick lib*{e,a,s}{}.

      return xt->as<file> ();
    }

    // Note that pk's scope should not be NULL (even if dir is absolute).
    //
    target* common::
    search_library (action act,
                    const dir_paths& sysd,
                    optional<dir_paths>& usrd,
                    const prerequisite_key& p,
                    bool exist) const
    {
      tracer trace (x, "search_library");

      assert (p.scope != nullptr);

      context& ctx (p.scope->ctx);
      const scope& rs (*p.scope->root_scope ());

      // Here is the problem: we may be building for two different toolchains
      // simultaneously that use the same installed library. But our search is
      // toolchain-specific. To make sure we end up with different targets for
      // each toolchain we are going to "tag" each target with the linker path
      // as its out directory.
      //
      const process_path& ld (tsys != "win32-msvc"
                              ? cpath
                              : cast<process_path> (rs["bin.ld.path"]));

      // @@ This is hairy enough to warrant a separate implementation for
      //    Windows.

      // Note: since we are searching for a (presumably) installed library,
      // utility libraries do not apply.
      //
      bool l (p.is_a<lib> ());
      const optional<string>& ext (l ? nullopt : p.tk.ext); // Only liba/libs.

      // First figure out what we need to search for.
      //
      const string& name (*p.tk.name);

      // liba
      //
      path an;
      optional<string> ae;

      if (l || p.is_a<liba> ())
      {
        // We are trying to find a library in the search paths extracted from
        // the compiler. It would only be natural if we used the library
        // prefix/extension that correspond to this compiler and/or its
        // target.
        //
        // Unlike MinGW, VC's .lib/.dll.lib naming is by no means standard and
        // we might need to search for other names. In fact, there is no
        // reliable way to guess from the file name what kind of library it
        // is, static or import and we will have to do deep inspection of such
        // alternative names. However, if we did find .dll.lib, then we can
        // assume that .lib is the static library without any deep inspection
        // overhead.
        //
        const char* e ("");

        if (tsys == "win32-msvc")
        {
          an = path (name);
          e = "lib";
        }
        else
        {
          an = path ("lib" + name);
          e = "a";
        }

        ae = ext ? ext : string (e);
        if (!ae->empty ())
        {
          an += '.';
          an += *ae;
        }
      }

      // libs
      //
      path sn;
      optional<string> se;

      if (l || p.is_a<libs> ())
      {
        const char* e ("");

        if (tsys == "win32-msvc")
        {
          sn = path (name);
          e = "dll.lib";
        }
        else
        {
          sn = path ("lib" + name);

          if      (tsys == "darwin")  e = "dylib";
          else if (tsys == "mingw32") e = "dll.a"; // See search code below.
          else                        e = "so";
        }

        se = ext ? ext : string (e);
        if (!se->empty ())
        {
          sn += '.';
          sn += *se;
        }
      }

      // Now search.
      //
      liba* a (nullptr);
      libs* s (nullptr);

      pair<path, path> pc; // pkg-config .pc file paths.
      path f;              // Reuse the buffer.

      auto search =[&a, &s, &pc,
                    &an, &ae,
                    &sn, &se,
                    &name, ext,
                    &ld, &f,
                    &p, exist, &trace, this] (const dir_path& d) -> bool
      {
        context& ctx (p.scope->ctx);

        timestamp mt;

        // libs
        //
        // Look for the shared library first. The order is important for VC:
        // only if we found .dll.lib can we safely assumy that just .lib is a
        // static library.
        //
        if (!sn.empty ())
        {
          f = d;
          f /= sn;
          mt = mtime (f);

          if (mt != timestamp_nonexistent)
          {
            // On Windows what we found is the import library which we need
            // to make the first ad hoc member of libs{}.
            //
            if (tclass == "windows")
            {
              libi* i (nullptr);
              insert_library (ctx, i, name, d, ld, se, exist, trace);

              ulock l (
                insert_library (ctx, s, name, d, ld, nullopt, exist, trace));

              if (!exist)
              {
                if (l.owns_lock ())
                {
                  s->adhoc_member = i; // We are first.
                  l.unlock ();
                }
                else
                  assert (find_adhoc_member<libi> (*s) == i);

                // Presumably there is a DLL somewhere, we just don't know
                // where (and its possible we might have to look for one if we
                // decide we need to do rpath emulation for installed
                // libraries as well). We will represent this as empty path
                // but valid timestamp (aka "trust me, it's there").
                //
                i->path_mtime (move (f), mt);
                s->path_mtime (path (), mt);
              }
            }
            else
            {
              insert_library (ctx, s, name, d, ld, se, exist, trace);
              s->path_mtime (move (f), mt);
            }
          }
          else if (!ext && tsys == "mingw32")
          {
            // Above we searched for the import library (.dll.a) but if it's
            // not found, then we also search for the .dll (unless the
            // extension was specified explicitly) since we can link to it
            // directly. Note also that the resulting libs{} would end up
            // being the .dll.
            //
            se = string ("dll");
            f = f.base (); // Remove .a from .dll.a.
            mt = mtime (f);

            if (mt != timestamp_nonexistent)
            {
              insert_library (ctx, s, name, d, ld, se, exist, trace);
              s->path_mtime (move (f), mt);
            }
          }
        }

        // liba
        //
        // If we didn't find .dll.lib then we cannot assume .lib is static.
        //
        if (!an.empty () && (s != nullptr || tsys != "win32-msvc"))
        {
          f = d;
          f /= an;

          if ((mt = mtime (f)) != timestamp_nonexistent)
          {
            // Enter the target. Note that because the search paths are
            // normalized, the result is automatically normalized as well.
            //
            // Note that this target is outside any project which we treat
            // as out trees.
            //
            insert_library (ctx, a, name, d, ld, ae, exist, trace);
            a->path_mtime (move (f), mt);
          }
        }

        // Alternative search for VC.
        //
        if (tsys == "win32-msvc")
        {
          if (s == nullptr && !sn.empty ())
            s = msvc_search_shared (ld, d, p, exist);

          if (a == nullptr && !an.empty ())
            a = msvc_search_static (ld, d, p, exist);
        }

        // Look for binary-less libraries via pkg-config .pc files. Note that
        // it is possible we have already found one of them as binfull but the
        // other is binless.
        //
        {
          bool na (a == nullptr && !an.empty ()); // Need static.
          bool ns (s == nullptr && !sn.empty ()); // Need shared.

          if (na || ns)
          {
            // Only consider the common .pc file if we can be sure there
            // is no binfull variant.
            //
            pair<path, path> r (
              pkgconfig_search (d, p.proj, name, na && ns /* common */));

            if (na && !r.first.empty ())
            {
              insert_library (ctx, a, name, d, ld, nullopt, exist, trace);
              a->path_mtime (path (), timestamp_unreal);
            }

            if (ns && !r.second.empty ())
            {
              insert_library (ctx, s, name, d, ld, nullopt, exist, trace);
              s->path_mtime (path (), timestamp_unreal);
            }

            // Only keep these .pc paths if we found anything via them.
            //
            if ((na && a != nullptr) || (ns && s != nullptr))
              pc = move (r);
          }
        }

        return a != nullptr || s != nullptr;
      };

      // First try user directories (i.e., -L or /LIBPATH).
      //
      bool sys (false);

      if (!usrd)
      {
        usrd = extract_library_search_dirs (*p.scope);

        // Handle automatic importing of installed build2 libraries. This is a
        // mirror side of the uninstalled case that is handled via the special
        // import.build2 value in import_search().
        //
        if (build_installed && p.proj && *p.proj == "build2")
        {
          // Check if import.build2 is set to NULL to disable relying on the
          // built-in path. We use this in our tests to make sure we are
          // importing and testing the build system being built and not the
          // one doing the building.
          //
          // Note that for the installed case this value is undefined by
          // default.
          //
          lookup l (rs[ctx.var_import_build2]);
          if (!(l.defined () && l->null))
          {
            // Note that we prepend it to other user directories instead of
            // making it the only one to allow things to be overriden (e.g.,
            // if build2 was moved or some such).
            //
            usrd->insert (usrd->begin (), build_install_lib);
          }
        }
      }

      const dir_path* pd (nullptr);
      for (const dir_path& d: *usrd)
      {
        if (search (d))
        {
          pd = &d;
          break;
        }
      }

      // Next try system directories (i.e., those extracted from the compiler).
      //
      if (pd == nullptr)
      {
        for (const dir_path& d: sysd)
        {
          if (search (d))
          {
            pd = &d;
            break;
          }
        }

        sys = true;
      }

      if (pd == nullptr)
      {
        l5 ([&]{trace << "no library found for " << p;});
        return nullptr;
      }

      // Enter (or find) the lib{} target group.
      //
      lib* lt;
      insert_library (
        ctx, lt, name, *pd, ld, l ? p.tk.ext : nullopt, exist, trace);

      // Result.
      //
      target* r (l ? lt : (p.is_a<liba> () ? static_cast<target*> (a) : s));

      // Assume the rest is already done if existing.
      //
      if (exist)
        return r;

      // If we cannot acquire the lock then this mean the target has already
      // been matched (though not clear by whom) and we assume all of this
      // has already been done.
      //
      target_lock ll (lock (act, *lt));

      // Set lib{} group members to indicate what's available. Note that we
      // must be careful here since its possible we have already imported some
      // of its members.
      //
      if (ll)
      {
        if (a != nullptr) lt->a = a;
        if (s != nullptr) lt->s = s;
      }

      target_lock al (a != nullptr ? lock (act, *a, true) : target_lock ());
      target_lock sl (s != nullptr ? lock (act, *s, true) : target_lock ());

      if (al && al.offset == target::offset_matched)
      {
        assert ((*a)[act].rule == &file_rule::rule_match);
        al.unlock ();
      }

      if (sl && sl.offset == target::offset_matched)
      {
        assert ((*s)[act].rule == &file_rule::rule_match);
        sl.unlock ();
      }

      if (!al) a = nullptr;
      if (!sl) s = nullptr;

      if (a != nullptr) a->group = lt;
      if (s != nullptr) s->group = lt;

      // Mark as a "cc" library (unless already marked) and set the system
      // flag.
      //
      auto mark_cc = [sys, this] (target& t) -> bool
      {
        auto p (t.vars.insert (c_type));

        if (p.second)
        {
          p.first.get () = string ("cc");

          if (sys)
            t.vars.assign (c_system) = true;
        }

        return p.second;
      };

      // If the library already has cc.type, then assume it was either
      // already imported or was matched by a rule.
      //
      if (a != nullptr && !mark_cc (*a)) a = nullptr;
      if (s != nullptr && !mark_cc (*s)) s = nullptr;

      // Add the "using static/shared library" macro (used, for example, to
      // handle DLL export). The absence of either of these macros would
      // mean some other build system that cannot distinguish between the
      // two (and no pkg-config information).
      //
      auto add_macro = [this] (target& t, const char* suffix)
      {
        // If there is already a value (either in cc.export or x.export),
        // don't add anything: we don't want to be accumulating defines nor
        // messing with custom values. And if we are adding, then use the
        // generic cc.export.
        //
        // 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 (!t.vars[x_export_poptions])
        {
          auto p (t.vars.insert (c_export_poptions));

          if (p.second)
          {
            // The "standard" macro name will be LIB<NAME>_{STATIC,SHARED},
            // where <name> is the target name. Here we want to strike a
            // balance between being unique and not too noisy.
            //
            string d ("-DLIB");

            d += sanitize_identifier (
              ucase (const_cast<const string&> (t.name)));

            d += '_';
            d += suffix;

            strings o;
            o.push_back (move (d));
            p.first.get () = move (o);
          }
        }
      };

      if (ll && (a != nullptr || s != nullptr))
      {
        // Try to extract library information from pkg-config. We only add the
        // default macro if we could not extract more precise information. The
        // idea is that in .pc files that we generate, we copy those macros
        // (or custom ones) from *.export.poptions.
        //
        if (pc.first.empty () && pc.second.empty ())
        {
          if (!pkgconfig_load (act, *p.scope,
                               *lt, a, s,
                               p.proj, name,
                               *pd, sysd, *usrd))
          {
            if (a != nullptr) add_macro (*a, "STATIC");
            if (s != nullptr) add_macro (*s, "SHARED");
          }
        }
        else
          pkgconfig_load (act, *p.scope, *lt, a, s, pc, *pd, sysd, *usrd);
      }

      // If we have the lock (meaning this is the first time), set the
      // traget's rule/recipe. Failed that we will keep re-locking it,
      // updating its members, etc.
      //
      // For members, use the fallback file rule instead of noop since we may
      // need their prerequisites matched (used for modules support; see
      // pkgconfig_load(), search_modules() for details).
      //
      // Note also that these calls clear target data.
      //
      if (al) match_rule (al, file_rule::rule_match);
      if (sl) match_rule (sl, file_rule::rule_match);
      if (ll) match_recipe (ll, noop_recipe);

      return r;
    }

    void
    gcc_extract_library_search_dirs (const strings&, dir_paths&); // gcc.cxx

    void
    msvc_extract_library_search_dirs (const strings&, dir_paths&); // msvc.cxx

    dir_paths common::
    extract_library_search_dirs (const scope& bs) const
    {
      dir_paths r;

      // Extract user-supplied search paths (i.e., -L, /LIBPATH).
      //
      auto extract = [&bs, &r, this] (const value& val, const variable& var)
      {
        const auto& v (cast<strings> (val));

        auto df = make_diag_frame (
          [&var, &bs](const diag_record& dr)
          {
            dr << info << "in variable " << var << " for scope " << bs;
          });

        if (tsys == "win32-msvc")
          msvc_extract_library_search_dirs (v, r);
        else
          gcc_extract_library_search_dirs (v, r);
      };

      // Note that the compiler mode options are in sys_lib_dirs.
      //
      if (auto l = bs[c_loptions]) extract (*l, c_loptions);
      if (auto l = bs[x_loptions]) extract (*l, x_loptions);

      return r;
    }
  }
}