aboutsummaryrefslogtreecommitdiff
path: root/build2/file.cxx
blob: 1367b8cfe058e21c9d7da2da8febcf21828cefec (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
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
// file      : build2/file.cxx -*- C++ -*-
// copyright : Copyright (c) 2014-2018 Code Synthesis Ltd
// license   : MIT; see accompanying LICENSE file

#include <build2/file.hxx>

#include <iostream> // cin

#include <build2/scope.hxx>
#include <build2/target.hxx>
#include <build2/context.hxx>
#include <build2/filesystem.hxx>   // exists()
#include <build2/prerequisite.hxx>
#include <build2/diagnostics.hxx>

#include <build2/token.hxx>
#include <build2/lexer.hxx>
#include <build2/parser.hxx>

#include <build2/config/utility.hxx>

using namespace std;
using namespace butl;

namespace build2
{
  const dir_path build_dir ("build");
  const dir_path root_dir (dir_path (build_dir) /= "root");
  const dir_path bootstrap_dir (dir_path (build_dir) /= "bootstrap");

  const path root_file (build_dir / "root.build");
  const path bootstrap_file (build_dir / "bootstrap.build");
  const path src_root_file (bootstrap_dir / "src-root.build");
  const path out_root_file (bootstrap_dir / "out-root.build");
  const path export_file (build_dir / "export.build");

  // While strictly speaking it belongs in, say, config/module.cxx, the static
  // initialization order strikes again. If we ever make the config module
  // loadable, then we can move it there.
  //
  const path config_file (build_dir / "config.build");

  ostream&
  operator<< (ostream& os, const subprojects& sps)
  {
    for (auto b (sps.begin ()), i (b); os && i != sps.end (); ++i)
    {
      // See find_subprojects() for details.
      //
      const string& n (path::traits::is_separator (i->first.back ())
                       ? empty_string
                       : i->first);

      os << (i != b ? " " : "") << n << '@' << i->second;
    }

    return os;
  }

  bool
  is_src_root (const dir_path& d)
  {
    // We can't have root without bootstrap.
    //
    return exists (d / bootstrap_file);
  }

  bool
  is_out_root (const dir_path& d)
  {
    return exists (d / src_root_file);
  }

  dir_path
  find_src_root (const dir_path& b)
  {
    for (dir_path d (b); !d.root () && d != home; d = d.directory ())
    {
      if (is_src_root (d))
        return d;
    }

    return dir_path ();
  }

  pair<dir_path, bool>
  find_out_root (const dir_path& b)
  {
    for (dir_path d (b); !d.root () && d != home; d = d.directory ())
    {
      bool s;
      if ((s = is_src_root (d)) || is_out_root (d))
        return make_pair (move (d), s);
    }

    return make_pair (dir_path (), false);
  }

  dir_path old_src_root;
  dir_path new_src_root;

  // Remap the src_root variable value if it is inside old_src_root.
  //
  static inline void
  remap_src_root (value& v)
  {
    if (!old_src_root.empty ())
    {
      dir_path& d (cast<dir_path> (v));

      if (d.sub (old_src_root))
        d = new_src_root / d.leaf (old_src_root);
    }
  }

  static void
  source (scope& root, scope& base, const path& bf, bool boot)
  {
    tracer trace ("source");

    try
    {
      bool sin (bf.string () == "-");

      ifdstream ifs;

      if (!sin)
        ifs.open (bf);
      else
        cin.exceptions (ifdstream::failbit | ifdstream::badbit);

      istream& is (sin ? cin : ifs);

      l5 ([&]{trace << "sourcing " << bf;});

      parser p (boot);
      p.parse_buildfile (is, bf, root, base);
    }
    catch (const io_error& e)
    {
      fail << "unable to read buildfile " << bf << ": " << e;
    }
  }

  void
  source (scope& root, scope& base, const path& bf)
  {
    source (root, base, bf, false);
  }

  bool
  source_once (scope& root, scope& base, const path& bf, scope& once)
  {
    tracer trace ("source_once");

    if (!once.buildfiles.insert (bf).second)
    {
      l5 ([&]{trace << "skipping already sourced " << bf;});
      return false;
    }

    source (root, base, bf);
    return true;
  }

  // Source (once) pre-*.build (pre is true) or post-*.build (otherwise) hooks
  // from the specified subdirectory (build/bootstrap/ or build/root/) of
  // out_root/.
  //
  void
  source_hooks (scope& root, const dir_path& sd, bool pre)
  {
    dir_path d (root.out_path () / sd);

    if (!exists (d))
      return;

    // While we could have used the wildcard pattern matching functionality,
    // our needs are pretty basic and performance is quite important, so let's
    // handle this ourselves.
    //
    try
    {
      for (const dir_entry& de: dir_iterator (d, false /* ignore_dangling */))
      {
        // If this is a link, then type() will try to stat() it. And if the
        // link is dangling or points to something inaccessible, it will fail.
        // So let's first check that the name matches and only then check the
        // type.
        //
        const path& n (de.path ());

        if (n.string ().compare (0,
                                 pre ? 4 : 5,
                                 pre ? "pre-" : "post-") != 0 ||
            n.extension () != "build")
          continue;

        path f (d / n);

        try
        {
          if (de.type () != entry_type::regular)
            continue;
        }
        catch (const system_error& e)
        {
          fail << "unable to read buildfile " << f << ": " << e;
        }

        source_once (root, root, f);
      }
    }
    catch (const system_error& e)
    {
      fail << "unable to iterate over " << d << ": " << e;
    }
  }

  scope_map::iterator
  create_root (scope& l, const dir_path& out_root, const dir_path& src_root)
  {
    auto i (scopes.rw (l).insert (out_root, true));
    scope& rs (i->second);

    // Set out_path. Note that src_path is set in setup_root() below.
    //
    if (rs.out_path_ != &i->first)
    {
      assert (rs.out_path_ == nullptr);
      rs.out_path_ = &i->first;
    }

    // First time create_root() is called on this scope.
    //
    bool first (rs.meta_operations.empty ());

    // Enter built-in meta-operation and operation names. Loading of
    // modules (via the src bootstrap; see below) can result in
    // additional meta/operations being added.
    //
    if (first)
    {
      rs.meta_operations.insert (noop_id, mo_noop);
      rs.meta_operations.insert (perform_id, mo_perform);
      rs.meta_operations.insert (info_id, mo_info);

      rs.operations.insert (default_id, op_default);
      rs.operations.insert (update_id, op_update);
      rs.operations.insert (clean_id, op_clean);
    }

    // If this is already a root scope, verify that things are consistent.
    //
    {
      value& v (rs.assign (var_out_root));

      if (!v)
        v = out_root;
      else
      {
        const dir_path& p (cast<dir_path> (v));

        if (p != out_root)
          fail << "new out_root " << out_root << " does not match "
               << "existing " << p;
      }
    }

    if (!src_root.empty ())
    {
      value& v (rs.assign (var_src_root));

      if (!v)
        v = src_root;
      else
      {
        const dir_path& p (cast<dir_path> (v));

        if (p != src_root)
          fail << "new src_root " << src_root << " does not match "
               << "existing " << p;
      }
    }

    return i;
  }

  void
  setup_root (scope& s, bool forwarded)
  {
    // The caller must have made sure src_root is set on this scope.
    //
    value& v (s.assign (var_src_root));
    assert (v);
    const dir_path& d (cast<dir_path> (v));

    if (s.src_path_ == nullptr)
      s.src_path_ = &d;
    else
      assert (s.src_path_ == &d);

    s.assign (var_forwarded) = forwarded;
  }

  scope&
  setup_base (scope_map::iterator i,
              const dir_path& out_base,
              const dir_path& src_base)
  {
    scope& s (i->second);

    // Set src/out_base variables.
    //
    value& ov (s.assign (var_out_base));

    if (!ov)
      ov = out_base;
    else
      assert (cast<dir_path> (ov) == out_base);

    value& sv (s.assign (var_src_base));

    if (!sv)
      sv = src_base;
    else
      assert (cast<dir_path> (sv) == src_base);

    // Set src/out_path. The key (i->first) is out_base.
    //
    if (s.out_path_ == nullptr)
      s.out_path_ = &i->first;
    else
      assert (*s.out_path_ == out_base);

    if (s.src_path_ == nullptr)
      s.src_path_ = &cast<dir_path> (sv);
    else
      assert (*s.src_path_ == src_base);

    return s;
  }

  pair<scope&, scope*>
  switch_scope (scope& root, const dir_path& p)
  {
    // First, enter the scope into the map and see if it is in any project. If
    // it is not, then there is nothing else to do.
    //
    auto i (scopes.rw (root).insert (p, false));
    scope& base (i->second);
    scope* rs (base.root_scope ());

    if (rs != nullptr)
    {
      // Path p can be src_base or out_base. Figure out which one it is.
      //
      dir_path out_base (p.sub (rs->out_path ()) ? p : src_out (p, *rs));

      // Create and bootstrap root scope(s) of subproject(s) that this scope
      // may belong to. If any were created, load them. Note that we need to
      // do this before figuring out src_base since we may switch the root
      // project (and src_root with it).
      //
      {
        scope* nrs (&create_bootstrap_inner (*rs, out_base));

        if (rs != nrs)
          rs = nrs;
      }

      // Switch to the new root scope.
      //
      if (rs != &root)
        load_root (*rs); // Load new root(s) recursively.

      // Now we can figure out src_base and finish setting the scope.
      //
      dir_path src_base (src_out (out_base, *rs));
      setup_base (i, move (out_base), move (src_base));
    }

    return pair<scope&, scope*> (base, rs);
  }

  dir_path
  bootstrap_fwd (const dir_path& src_root)
  {
    // We cannot just source the buildfile since there is no scope to do
    // this on yet.
    //
    path bf (src_root / out_root_file);

    if (!exists (bf))
      return src_root;

    auto p (extract_variable (bf, *var_out_root));

    if (!p.second)
      fail << "variable out_root expected as first line in " << bf;

    try
    {
      return convert<dir_path> (move (p.first));
    }
    catch (const invalid_argument& e)
    {
      fail << "invalid out_root value in " << bf << ": " << e << endf;
    }
  }

  void
  bootstrap_out (scope& root)
  {
    path bf (root.out_path () / src_root_file);

    if (!exists (bf))
      return;

    //@@ TODO: if bootstrap files can source other bootstrap files
    //   (the way to express dependecies), then we need a way to
    //   prevent multiple sourcing. We handle it here but we still
    //   need something like source_once (once [scope] source) in
    //   buildfiles.
    //
    source_once (root, root, bf);
  }

  pair<value, bool>
  extract_variable (const path& bf, const variable& var)
  {
    try
    {
      ifdstream ifs (bf);

      lexer lex (ifs, bf);
      token t (lex.next ());
      token_type tt;

      if (t.type != token_type::word || t.value != var.name ||
          ((tt = lex.next ().type) != token_type::assign &&
           tt != token_type::prepend &&
           tt != token_type::append))
      {
        return make_pair (value (), false);
      }

      parser p;
      temp_scope tmp (global_scope->rw ());
      p.parse_variable (lex, tmp, var, tt);

      value* v (tmp.vars.find_to_modify (var).first);
      assert (v != nullptr);

      // Steal the value, the scope is going away.
      //
      return make_pair (move (*v), true);
    }
    catch (const io_error& e)
    {
      fail << "unable to read buildfile " << bf << ": " << e << endf;
    }
  }

  // Extract the project name from bootstrap.build.
  //
  static string
  find_project_name (const dir_path& out_root,
                     const dir_path& fallback_src_root,
                     bool* src_hint = nullptr)
  {
    tracer trace ("find_project_name");

    // First check if the root scope for this project has already been setup
    // in which case we will have src_root and maybe even the name.
    //
    const dir_path* src_root (nullptr);
    const scope& s (scopes.find (out_root));

    if (s.root_scope () == &s && s.out_path () == out_root)
    {
      if (lookup l = s.vars[var_project])
        return cast<string> (l);

      src_root = s.src_path_;
    }

    // Load the project name. If this subdirectory is the subproject's
    // src_root, then we can get directly to that. Otherwise, we first have to
    // discover its src_root.
    //
    value src_root_v; // Need it to live until the end.

    if (src_root == nullptr)
    {
      if (src_hint != nullptr ? *src_hint : is_src_root (out_root))
        src_root = &out_root;
      else
      {
        path f (out_root / src_root_file);

        if (!fallback_src_root.empty () && !exists (f))
          src_root = &fallback_src_root;
        else
        {
          auto p (extract_variable (f, *var_src_root));

          if (!p.second)
            fail << "variable src_root expected as first line in " << f;

          src_root_v = move (p.first);
          remap_src_root (src_root_v); // Remap if inside old_src_root.
          src_root = &cast<dir_path> (src_root_v);

          l5 ([&]{trace << "extracted src_root " << *src_root
                        << " for " << out_root;});
        }
      }
    }

    string name;
    {
      path f (*src_root / bootstrap_file);
      auto p (extract_variable (f, *var_project));

      if (!p.second)
        fail << "variable " << var_project->name << " expected "
             << "as a first line in " << f;

      name = cast<string> (move (p.first));
    }

    l5 ([&]{trace << "extracted project name '" << name << "' for "
                  << *src_root;});
    return name;
  }

  // Scan the specified directory for any subprojects. If a subdirectory
  // is a subproject, then enter it into the map, handling the duplicates.
  //
  static void
  find_subprojects (subprojects& sps,
                    const dir_path& d,
                    const dir_path& root,
                    bool out)
  {
    tracer trace ("find_subprojects");

    try
    {
      for (const dir_entry& de: dir_iterator (d, true /* ignore_dangling */))
      {
        if (de.type () != entry_type::directory)
          continue;

        dir_path sd (d / path_cast<dir_path> (de.path ()));

        bool src (false);
        if (!((out && is_out_root (sd)) || (src = is_src_root (sd))))
        {
          // We used to scan for subproject recursively but this is probably
          // too loose (think of some tests laying around). In the future we
          // should probably allow specifying something like extra/* or
          // extra/** in subprojects.
          //
          //find_subprojects (sps, sd, root, out);
          //
          continue;
        }

        // Calculate relative subdirectory for this subproject.
        //
        dir_path dir (sd.leaf (root));
        l5 ([&]{trace << "subproject " << sd << " as " << dir;});

        // Load its name. Note that here we don't use fallback src_root
        // since this function is used to scan both out_root and src_root.
        //
        string name (find_project_name (sd, dir_path (), &src));

        // If the name is empty, then is is an unnamed project. While the
        // 'project' variable stays empty, here we come up with a surrogate
        // name for a key. The idea is that such a key should never conflict
        // with a real project name. We ensure this by using the project's
        // sub-directory and appending a trailing directory separator to it.
        //
        if (name.empty ())
          name = dir.posix_string () + path::traits::directory_separator;

        // @@ Can't use move() because we may need the values in diagnostics
        // below. Looks like C++17 try_emplace() is what we need.
        //
        auto rp (sps.emplace (name, dir));

        // Handle duplicates.
        //
        if (!rp.second)
        {
          const dir_path& dir1 (rp.first->second);

          if (dir != dir1)
            fail << "inconsistent subproject directories for " << name <<
              info << "first alternative: " << dir1 <<
              info << "second alternative: " << dir;

          l6 ([&]{trace << "skipping duplicate";});
        }
      }
    }
    catch (const system_error& e)
    {
      fail << "unable to iterate over " << d << ": " << e;
    }
  }

  bool
  bootstrap_src (scope& root)
  {
    tracer trace ("bootstrap_src");

    bool r (false);

    const dir_path& out_root (root.out_path ());
    const dir_path& src_root (root.src_path ());

    path bf (src_root / bootstrap_file);

    if (exists (bf))
    {
      // We assume that bootstrap out cannot load this file explicitly. It
      // feels wrong to allow this since that makes the whole bootstrap
      // process hard to reason about. But we may try to bootstrap the
      // same root scope multiple time.
      //
      if (root.buildfiles.insert (bf).second)
        source (root, root, bf, true);
      else
        l5 ([&]{trace << "skipping already sourced " << bf;});

      r = true;
    }

    // See if we are a part of an amalgamation. There are two key players: the
    // outer root scope which may already be present (i.e., we were loaded as
    // part of an amalgamation) and the amalgamation variable that may or may
    // not be set by the user (in bootstrap.build) or by an earlier call to
    // this function for the same scope. When set by the user, the empty
    // special value means that the project shall not be amalgamated (and
    // which we convert to NULL below). When calculated, the NULL value
    // indicates that we are not amalgamated.
    //
    // Note: the amalgamation variable value is always a relative directory.
    //
    {
      auto rp (root.vars.insert (*var_amalgamation)); // Set NULL by default.
      value& v (rp.first);

      if (v && v.empty ()) // Convert empty to NULL.
        v = nullptr;

      if (scope* aroot = root.parent_scope ()->root_scope ())
      {
        const dir_path& ad (aroot->out_path ());
        dir_path rd (ad.relative (out_root));

        // If we already have the amalgamation variable set, verify
        // that aroot matches its value.
        //
        if (!rp.second)
        {
          if (!v)
          {
            fail << out_root << " cannot be amalgamated" <<
              info << "amalgamated by " << ad;
          }
          else
          {
            const dir_path& vd (cast<dir_path> (v));

            if (vd != rd)
            {
              fail << "inconsistent amalgamation of " << out_root <<
                info << "specified: " << vd <<
                info << "actual: " << rd << " by " << ad;
            }
          }
        }
        else
        {
          // Otherwise, use the outer root as our amalgamation.
          //
          l5 ([&]{trace << out_root << " amalgamated as " << rd;});
          v = move (rd);
        }
      }
      else if (rp.second)
      {
        // If there is no outer root and the amalgamation variable
        // hasn't been set, then we need to check if any of the
        // outer directories is a project's out_root. If so, then
        // that's our amalgamation.
        //
        const dir_path& ad (find_out_root (out_root.directory ()).first);

        if (!ad.empty ())
        {
          dir_path rd (ad.relative (out_root));
          l5 ([&]{trace << out_root << " amalgamated as " << rd;});
          v = move (rd);
        }
      }
    }

    // See if we have any subprojects. In a sense, this is the other
    // side/direction of the amalgamation logic above. Here, the subprojects
    // variable may or may not be set by the user (in bootstrap.build) or by
    // an earlier call to this function for the same scope. When set by the
    // user, the empty special value means that there are no subproject and
    // none should be searched for (and which we convert to NULL below).
    // Otherwise, it is a list of [project@]directory pairs. The directory
    // must be relative to our out_root. If the project name is not specified,
    // then we have to figure it out. When subprojects are calculated, the
    // NULL value indicates that we found no subprojects.
    //
    {
      auto rp (root.vars.insert (*var_subprojects)); // Set NULL by default.
      value& v (rp.first);

      if (rp.second)
      {
        // No subprojects set so we need to figure out if there are any.
        //
        // First we are going to scan our out_root and find all the
        // pre-configured subprojects. Then, if out_root != src_root,
        // we are going to do the same for src_root. Here, however,
        // we need to watch out for duplicates.
        //
        subprojects sps;

        if (exists (out_root))
        {
          l5 ([&]{trace << "looking for subprojects in " << out_root;});
          find_subprojects (sps, out_root, out_root, true);
        }

        if (out_root != src_root)
        {
          l5 ([&]{trace << "looking for subprojects in " << src_root;});
          find_subprojects (sps, src_root, src_root, false);
        }

        if (!sps.empty ()) // Keep it NULL if no subprojects.
          v = move (sps);
      }
      else if (v)
      {
        // Convert empty to NULL.
        //
        if (v.empty ())
          v = nullptr;
        else
        {
          // Scan the (untyped) value and convert it to the "canonical" form,
          // that is, a list of name@dir pairs.
          //
          subprojects sps;
          names& ns (cast<names> (v));

          for (auto i (ns.begin ()); i != ns.end (); ++i)
          {
            // Project name.
            //
            string n;
            if (i->pair)
            {
              if (i->pair != '@')
                fail << "unexpected pair style in variable subprojects";

              try
              {
                n = convert<string> (move (*i));

                if (n.empty ())
                  fail << "empty project name in variable subprojects";
              }
              catch (const invalid_argument&)
              {
                fail << "expected project name instead of '" << *i << "' in "
                     << "variable subprojects";
              }

              ++i; // Got to have the second half of the pair.
            }

            // Directory.
            //
            dir_path d;
            try
            {
              d = convert<dir_path> (move (*i));

              if (d.empty ())
                fail << "empty directory in variable subprojects";
            }
            catch (const invalid_argument&)
            {
              fail << "expected directory instead of '" << *i << "' in "
                   << "variable subprojects";
            }

            // Figure out the project name if the user didn't specify one.
            //
            if (n.empty ())
            {
              // Pass fallback src_root since this is a subproject that
              // was specified by the user so it is most likely in our
              // src.
              //
              n = find_project_name (out_root / d, src_root / d);

              // See find_subprojects() for details on unnamed projects.
              //
              if (n.empty ())
                n = d.posix_string () + '/';
            }

            sps.emplace (move (n), move (d));
          }

          // Change the value to the typed map.
          //
          v = move (sps);
        }
      }
    }

    return r;
  }

  bool
  bootstrapped (scope& root)
  {
    // Use the subprojects variable set by bootstrap_src() as an indicator.
    // It should either be NULL or typed (so we assume that the user will
    // never set it to NULL).
    //
    auto l (root.vars[var_subprojects]);
    return l.defined () && (l->null || l->type != nullptr);
  }

  // Return true if the inner/outer project (identified by out/src_root) of
  // the 'origin' project (identified by orig) should be forwarded.
  //
  static inline bool
  forwarded (const scope& orig,
             const dir_path& out_root,
             const dir_path& src_root)
  {
    // The conditions are:
    //
    // 1. Origin is itself forwarded.
    //
    // 2. Inner/outer src_root != out_root.
    //
    // 3. Inner/outer out-root.build exists in src_root and refers out_root.
    //
    return (out_root != src_root                        &&
            cast_false<bool> (orig.vars[var_forwarded]) &&
            bootstrap_fwd (src_root) == out_root);
  }

  void
  create_bootstrap_outer (scope& root)
  {
    auto l (root.vars[var_amalgamation]);

    if (!l)
      return;

    const dir_path& d (cast<dir_path> (l));
    dir_path out_root (root.out_path () / d);
    out_root.normalize (); // No need to actualize (d is a bunch of ..)

    // src_root is a bit more complicated. Here we have three cases:
    //
    // 1. Amalgamation's src_root is "parallel" to the sub-project's.
    // 2. Amalgamation's src_root is the same as its out_root.
    // 3. Some other pre-configured (via src-root.build) src_root.
    //
    // So we need to try all these cases in some sensible order. #3 should
    // probably be tried first since that src_root was explicitly configured
    // by the user. After that, #2 followed by #1 seems reasonable.
    //
    scope& rs (create_root (root, out_root, dir_path ())->second);

    bool bstrapped (bootstrapped (rs));

    if (!bstrapped)
    {
      bootstrap_out (rs); // #3 happens here (or it can be #1).

      value& v (rs.assign (var_src_root));

      if (!v)
      {
        if (is_src_root (out_root)) // #2
          v = out_root;
        else // #1
        {
          dir_path src_root (root.src_path () / d);
          src_root.normalize (); // No need to actualize (as above).
          v = move (src_root);
        }
      }
      else
        remap_src_root (v); // Remap if inside old_src_root.

      setup_root (rs, forwarded (root, out_root, v.as<dir_path> ()));
      bootstrap_pre (rs);
      bootstrap_src (rs);
      // bootstrap_post() delayed until after create_bootstrap_outer().
    }
    else
    {
      if (forwarded (root, rs.out_path (), rs.src_path ()))
        rs.assign (var_forwarded) = true; // Only upgrade (see main()).
    }

    create_bootstrap_outer (rs);

    if (!bstrapped)
      bootstrap_post (rs);

    // Check if we are strongly amalgamated by this outer root scope.
    //
    if (root.src_path ().sub (rs.src_path ()))
      root.strong_ = rs.strong_scope (); // Itself or some outer scope.
  }

  scope&
  create_bootstrap_inner (scope& root, const dir_path& out_base)
  {
    scope* r (&root);

    if (auto l = root.vars[var_subprojects])
    {
      for (const auto& p: cast<subprojects> (l))
      {
        dir_path out_root (root.out_path () / p.second);

        if (!out_base.empty () && !out_base.sub (out_root))
          continue;

        // The same logic to src_root as in create_bootstrap_outer().
        //
        scope& rs (create_root (root, out_root, dir_path ())->second);

        if (!bootstrapped (rs))
        {
          bootstrap_out (rs);

          value& v (rs.assign (var_src_root));

          if (!v)
          {
            v = is_src_root (out_root)
              ? out_root
              : (root.src_path () / p.second);
          }
          else
            remap_src_root (v); // Remap if inside old_src_root.

          setup_root (rs, forwarded (root, out_root, v.as<dir_path> ()));
          bootstrap_pre (rs);
          bootstrap_src (rs);
          bootstrap_post (rs);
        }
        else
        {
          if (forwarded (root, rs.out_path (), rs.src_path ()))
            rs.assign (var_forwarded) = true; // Only upgrade (see main()).
        }

        // Check if we strongly amalgamated this inner root scope.
        //
        if (rs.src_path ().sub (root.src_path ()))
          rs.strong_ = root.strong_scope (); // Itself or some outer scope.

        // See if there are more inner roots.
        //
        r = &create_bootstrap_inner (rs, out_base);

        if (!out_base.empty ())
          break; // We have found our subproject.
      }
    }

    return *r;
  }

  void
  load_root (scope& root)
  {
    tracer trace ("load_root");

    // As an optimization, check if we have already loaded root.build. If
    // that's the case, then we have already been called for this project.
    //
    path bf (root.src_path () / root_file);

    if (root.buildfiles.find (bf) != root.buildfiles.end ())
      return;

    // First load outer roots, if any.
    //
    if (scope* rs = root.parent_scope ()->root_scope ())
      load_root (*rs);

    // Finish off loading bootstrapped modules.
    //
    for (auto& p: root.modules)
    {
      module_state& s (p.second);

      if (s.boot && s.first)
        load_module (root, root, p.first, s.loc);
    }

    for (auto& p: root.modules)
    {
      module_state& s (p.second);

      if (s.boot && !s.first)
        load_module (root, root, p.first, s.loc);
    }

    // Load hooks and root.build.
    //
    // We can load the pre hooks before finishing off loading the bootstrapped
    // modules (which, in case of config would load config.build) or after and
    // one can come up with a plausible use-case for either approach. Note,
    // however, that one can probably achieve adequate pre-modules behavior
    // with a post-bootstrap hook.
    //
    source_hooks (root, root_dir, true /* pre */);
    if (exists (bf)) source_once (root, root, bf);
    source_hooks (root, root_dir, false /* pre */);
  }

  scope&
  load_project (scope& lock,
                const dir_path& out_root,
                const dir_path& src_root,
                bool forwarded,
                bool load)
  {
    assert (!forwarded || out_root != src_root);

    auto i (create_root (lock, out_root, src_root));
    scope& rs (i->second);

    if (!bootstrapped (rs))
    {
      bootstrap_out (rs);
      setup_root (rs, forwarded);
      bootstrap_pre (rs);
      bootstrap_src (rs);
      bootstrap_post (rs);
    }
    else
    {
      if (forwarded)
        rs.assign (var_forwarded) = true; // Only upgrade (see main()).
    }

    if (load)
    {
      load_root (rs);
      setup_base (i, out_root, src_root); // Setup as base.
    }

    return rs;
  }

  // Convert project name to import variable name.
  //
  static inline string
  import_name (const string& p)
  {
    // For simplicity let's assume project name is a package name and only
    // sanitize characters that we don't like from what's valid there.
    //
    auto sanitize = [] (char c)
    {
      return (c == '-' || c == '+' || c == '.') ? '_' : c;
    };

    string r;
    transform (p.begin (), p.end (), back_inserter (r), sanitize);
    return r;
  }

  names
  import (scope& ibase, name target, const location& loc)
  {
    tracer trace ("import");

    l5 ([&]{trace << target << " from " << ibase.out_path ();});

    // If there is no project specified for this target, then our run will be
    // short and sweet: we simply return it as empty-project-qualified and
    // let someone else (e.g., a rule) take a stab at it.
    //
    if (target.unqualified ())
    {
      target.proj = string ();
      return names {move (target)};
    }

    // Otherwise, get the project name and convert the target to unqualified.
    //
    string proj (move (*target.proj));
    target.proj = nullopt;

    scope& iroot (*ibase.root_scope ());

    // Figure out this project's out_root.
    //
    dir_path out_root;

    // First try the config.import.* mechanism. The idea is that if the user
    // explicitly told us the project's location, then we should prefer that
    // over anything that we may discover. In particular, we will prefer it
    // over any bundled subprojects.
    //
    auto& vp (var_pool.rw (iroot));

    for (;;) // Break-out loop.
    {
      string n ("config.import." + import_name (proj));

      // config.import.<proj>
      //
      {
        // Note: pattern-typed in context.cxx:reset() as an overridable
        // variable of type abs_dir_path (path auto-completion).
        //
        const variable& var (vp.insert (n));

        if (auto l = iroot[var])
        {
          out_root = cast<dir_path> (l);      // Normalized and actualized.
          config::save_variable (iroot, var); // Mark as part of config.

          // Empty config.import.* value means don't look in subprojects or
          // amalgamations and go straight to the rule-specific import (e.g.,
          // to use system-installed).
          //
          if (out_root.empty ())
          {
            target.proj = move (proj);
            l5 ([&]{trace << "skipping " << target;});
            return names {move (target)};
          }

          break;
        }
      }

      // config.import.<proj>.<name>.<type>
      // config.import.<proj>.<name>
      //
      // For example: config.import.build2.b.exe=/opt/build2/bin/b
      //
      if (!target.value.empty ())
      {
        auto lookup = [&iroot, &vp, &loc] (string name) -> path
        {
          // Note: pattern-typed in context.cxx:reset() as an overridable
          // variable of type path.
          //
          const variable& var (vp.insert (move (name)));

          path r;
          if (auto l = iroot[var])
          {
            r = cast<path> (l);

            if (r.empty ())
              fail (loc) << "empty path in " << var.name;

            config::save_variable (iroot, var);
          }

          return r;
        };

        // First try .<name>.<type>, then just .<name>.
        //
        path p;
        if (target.typed ())
          p = lookup (n + '.' + target.value + '.' + target.type);

        if (p.empty ())
          p = lookup (n + '.' + target.value);

        if (!p.empty ())
        {
          // If the path is relative, then keep it project-qualified assuming
          // import phase 2 knows what to do with it. Think:
          //
          // config.import.build2.b=b-boot
          //
          if (p.relative ())
            target.proj = move (proj);

          target.dir = p.directory ();
          target.value = p.leaf ().string ();

          return names {move (target)};
        }
      }

      // Otherwise search subprojects, starting with our root and then trying
      // outer roots for as long as we are inside an amalgamation.
      //
      for (scope* r (&iroot);; r = r->parent_scope ()->root_scope ())
      {
        l5 ([&]{trace << "looking in " << r->out_path ();});

        // First check the amalgamation itself.
        //
        if (r != &iroot && cast<string> (r->vars[var_project]) == proj)
        {
          out_root = r->out_path ();
          break;
        }

        if (auto l = r->vars[var_subprojects])
        {
          const auto& m (cast<subprojects> (l));
          auto i (m.find (proj));

          if (i != m.end ())
          {
            const dir_path& d ((*i).second);
            out_root = r->out_path () / d;
            break;
          }
        }

        if (!r->vars[var_amalgamation])
          break;
      }

      break;
    }

    // If we couldn't find the project, convert it back into qualified target
    // and return to let someone else (e.g., a rule) take a stab at it.
    //
    if (out_root.empty ())
    {
      target.proj = move (proj);
      l5 ([&]{trace << "postponing " << target;});
      return names {move (target)};
    }

    // Bootstrap the imported root scope. This is pretty similar to what we do
    // in main() except that here we don't try to guess src_root.
    //
    // The user can also specify the out_root of the amalgamation that contains
    // our project. For now we only consider top-level sub-projects.
    //
    scope* root;
    dir_path src_root;

    // See if this is a forwarded configuration. For top-level project we want
    // to use the same logic as in main() while for inner subprojects -- as in
    // create_bootstrap_inner().
    //
    bool fwd (false);
    if (is_src_root (out_root))
    {
      src_root = move (out_root);
      out_root = bootstrap_fwd (src_root);
      fwd = (src_root != out_root);
    }

    for (const scope* proot (nullptr); ; proot = root)
    {
      bool top (proot == nullptr);

      root = &create_root (iroot, out_root, src_root)->second;

      bool bstrapped (bootstrapped (*root));

      if (!bstrapped)
      {
        bootstrap_out (*root);

        // Check that the bootstrap process set src_root.
        //
        auto l (root->vars[*var_src_root]);
        if (l)
        {
          // Note that unlike main() here we fail hard. The idea is that if
          // the project we are importing is misconfigured, then it should be
          // fixed first.
          //
          const dir_path& p (cast<dir_path> (l));

          if (!src_root.empty () && p != src_root)
            fail (loc) << "configured src_root " << p << " does not match "
                       << "discovered " << src_root;
        }
        else
          fail (loc) << "unable to determine src_root for imported " << proj <<
            info << "consider configuring " << out_root;

        setup_root (
          *root,
          top ? fwd : forwarded (*proot, out_root, l->as<dir_path> ()));
        bootstrap_pre (*root);
        bootstrap_src (*root);
        if (!top)
          bootstrap_post (*root);
      }
      else
      {
        if (src_root.empty ())
          src_root = root->src_path ();

        if (top ? fwd : forwarded (*proot, out_root, src_root))
          root->assign (var_forwarded) = true; // Only upgrade (see main()).
      }

      if (top)
      {
        create_bootstrap_outer (*root);

        if (!bstrapped)
          bootstrap_post (*root);
      }

      // Now we know this project's name as well as all its subprojects.
      //
      if (cast<string> (root->vars[var_project]) == proj)
        break;

      if (auto l = root->vars[var_subprojects])
      {
        const auto& m (cast<subprojects> (l));
        auto i (m.find (proj));

        if (i != m.end ())
        {
          const dir_path& d ((*i).second);
          out_root = root->out_path () / d;
          src_root = is_src_root (out_root) ? out_root : dir_path ();
          continue;
        }
      }

      fail (loc) << out_root << " is not out_root for " << proj;
    }

    // Load the imported root scope.
    //
    load_root (*root);

    // Create a temporary scope so that the export stub does not mess
    // up any of our variables.
    //
    temp_scope ts (ibase);

    // "Pass" the imported project's roots to the stub.
    //
    ts.assign (var_out_root) = move (out_root);
    ts.assign (var_src_root) = move (src_root);

    // Also pass the target being imported in the import.target variable.
    //
    {
      value& v (ts.assign (var_import_target));

      if (!target.empty ()) // Otherwise leave NULL.
        v = move (target);
    }

    // Load the export stub. Note that it is loaded in the context
    // of the importing project, not the imported one. The export
    // stub will normally switch to the imported root scope at some
    // point.
    //
    path es (root->src_path () / export_file);

    try
    {
      ifdstream ifs (es);

      l5 ([&]{trace << "importing " << es;});

      // @@ Should we verify these are all unqualified names? Or maybe
      // there is a use-case for the export stub to return a qualified
      // name?
      //
      parser p;
      return p.parse_export_stub (ifs, es, iroot, ts);
    }
    catch (const io_error& e)
    {
      fail (loc) << "unable to read buildfile " << es << ": " << e;
    }

    return names (); // Never reached.
  }

  const target*
  import (const prerequisite_key& pk, bool existing)
  {
    tracer trace ("import");

    assert (pk.proj);
    const string& proj (*pk.proj);

    // Target type-specific search.
    //
    const target_key& tk (pk.tk);
    const target_type& tt (*tk.type);

    // Try to find the executable in PATH (or CWD if relative).
    //
    if (tt.is_a<exe> ())
    {
      path n (*tk.dir);
      n /= *tk.name;
      if (tk.ext)
      {
        n += '.';
        n += *tk.ext;
      }

      // Only search in PATH (or CWD).
      //
      process_path pp (process::try_path_search (n, true, dir_path (), true));

      if (!pp.empty ())
      {
        path& p (pp.effect);
        assert (!p.empty ()); // We searched for a simple name.

        const exe* t (
          !existing
          ? &targets.insert<exe> (tt,
                                  p.directory (),
                                  dir_path (),    // No out (out of project).
                                  p.leaf ().base ().string (),
                                  p.extension (), // Always specified.
                                  trace)
          : targets.find<exe> (tt,
                               p.directory (),
                               dir_path (),
                               p.leaf ().base ().string (),
                               p.extension (),
                               trace));

        if (t != nullptr)
        {
          if (!existing)
            t->path (move (p));
          else
            assert (t->path () == p);

          return t;
        }
      }
    }

    if (existing)
      return nullptr;

    // @@ We no longer have location. This is especially bad for the
    //    empty case, i.e., where do I need to specify the project
    //    name)? Looks like the only way to do this is to keep location
    //    in name and then in prerequisite. Perhaps one day...
    //
    diag_record dr;
    dr << fail << "unable to import target " << pk;

    if (proj.empty ())
      dr << info << "consider adding its installation location" <<
        info << "or explicitly specify its project name";
    else
      dr << info << "use config.import." << import_name (proj)
         << " command line variable to specifying its project out_root";

    dr << endf;
  }
}