aboutsummaryrefslogtreecommitdiff
path: root/libbuild2/scope.cxx
blob: c1c5ed7b19d4fe983edb48438818c171f664f544 (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
// file      : libbuild2/scope.cxx -*- C++ -*-
// license   : MIT; see accompanying LICENSE file

#include <libbuild2/scope.hxx>

#include <libbuild2/rule.hxx>
#include <libbuild2/target.hxx>
#include <libbuild2/context.hxx>

using namespace std;

namespace build2
{
  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 project_name& n (
        path::traits_type::is_separator (i->first.string ().back ())
        ? empty_project_name
        : i->first);

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

    return os;
  }

  // scope
  //
  scope::
  scope (context& c, bool shared)
      : ctx (c), vars (*this, shared), target_vars (c, shared)
  {
  }

  scope::
  ~scope ()
  {
    // Definition of adhoc_rule_pattern.
  }

  pair<lookup, size_t> scope::
  lookup_original (const variable& var,
                   const target_key* tk,
                   const target_key* g1k,
                   const target_key* g2k,
                   size_t start_d) const
  {
    assert (tk != nullptr || var.visibility != variable_visibility::target);
    assert (g2k == nullptr || g1k != nullptr);

    size_t d (0);

    if (var.visibility == variable_visibility::prereq)
      return make_pair (lookup_type (), d);

    // Process target type/pattern-specific prepend/append values.
    //
    auto pre_app = [&var, this] (lookup_type& l,
                                 const scope* s,
                                 const target_key* tk,
                                 const target_key* g1k,
                                 const target_key* g2k,
                                 string n)
    {
      const value& v (*l);
      assert ((v.extra == 1 || v.extra == 2) && v.type == nullptr);

      // First we need to look for the stem value starting from the "next
      // lookup point". That is, if we have the group, then from the
      // s->target_vars (for the group), otherwise from s->vars, and then
      // continuing looking in the outer scopes (for both target and group).
      // Note that this may have to be repeated recursively, i.e., we may have
      // prepents/appends in outer scopes. Also, if the value is for the
      // group, then we shouldn't be looking for stem in the target's
      // variables. In other words, once we "jump" to group, we stay there.
      //
      lookup_type stem (s->lookup_original (var, tk, g1k, g2k, 2).first);

      // Check the cache.
      //
      pair<value&, ulock> entry (
        s->target_vars.cache.insert (
          ctx,
          make_tuple (&v, tk->type, !n.empty () ? move (n) : *tk->name),
          stem,
          static_cast<const variable_map::value_data&> (v).version,
          var));

      value& cv (entry.first);

      // If cache miss/invalidation, update the value.
      //
      if (entry.second.owns_lock ())
      {
        // Un-typify the cache. This can be necessary, for example, if we are
        // changing from one value-typed stem to another.
        //
        // Note: very similar logic as in the override cache population code
        // below.
        //
        if (!stem.defined () || cv.type != stem->type)
        {
          cv = nullptr;
          cv.type = nullptr; // Un-typify.
        }

        // Copy the stem.
        //
        if (stem.defined ())
          cv = *stem;

        // Typify the cache value in case there is no stem (we still want to
        // prepend/append things in type-aware way).
        //
        if (cv.type == nullptr && var.type != nullptr)
          typify (cv, *var.type, &var);

        // Now prepend/append the value, unless it is NULL.
        //
        if (v)
        {
          if (v.extra == 1)
            cv.prepend (names (cast<names> (v)), &var);
          else
            cv.append (names (cast<names> (v)), &var);
        }
      }

      // Return cache as the resulting value but retain l.var/vars, so it
      // looks as if the value came from s->target_vars.
      //
      l.value = &cv;
    };

    // Most of the time we match against the target name directly but
    // sometimes we may need to match against the directory leaf (dir{} or
    // fsdir{}) or incorporate the extension. We therefore try hard to avoid
    // the copy.
    //
    optional<string> tn;
    optional<string> g1n;
    optional<string> g2n;

    for (const scope* s (this); s != nullptr; )
    {
      if (tk != nullptr) // This started from the target.
      {
        bool f (!s->target_vars.empty ());

        // Target.
        //
        if (++d >= start_d)
        {
          if (f)
          {
            lookup_type l (s->target_vars.find (*tk, var, tn));

            if (l.defined ())
            {
              if (l->extra != 0) // Prepend/append?
                pre_app (l, s, tk, g1k, g2k, move (*tn));

              return make_pair (move (l), d);
            }
          }
        }

        // Group.
        //
        if (++d >= start_d)
        {
          if (f && g1k != nullptr)
          {
            lookup_type l (s->target_vars.find (*g1k, var, g1n));

            if (l.defined ())
            {
              if (l->extra != 0) // Prepend/append?
                pre_app (l, s, g1k, g2k, nullptr, move (*g1n));

              return make_pair (move (l), d);
            }

            if (g2k != nullptr)
            {
              l = s->target_vars.find (*g2k, var, g2n);

              if (l.defined ())
              {
                if (l->extra != 0) // Prepend/append?
                  pre_app (l, s, g2k, nullptr, nullptr, move (*g2n));

                return make_pair (move (l), d);
              }
            }
          }
        }
      }

      // Note that we still increment the lookup depth so that we can compare
      // depths of variables with different visibilities.
      //
      if (++d >= start_d && var.visibility != variable_visibility::target)
      {
        auto p (s->vars.lookup (var));
        if (p.first != nullptr)
          return make_pair (lookup_type (*p.first, p.second, s->vars), d);
      }

      switch (var.visibility)
      {
      case variable_visibility::scope:
        s = nullptr;
        break;
      case variable_visibility::target:
      case variable_visibility::project:
        s = s->root () ? nullptr : s->parent_scope ();
        break;
      case variable_visibility::global:
        s = s->parent_scope ();
        break;
      case variable_visibility::prereq:
        assert (false);
      }
    }

    return make_pair (lookup_type (), size_t (~0));
  }

  auto scope::
  lookup_override_info (const variable& var,
                        const pair<lookup_type, size_t> original,
                        bool target,
                        bool rule) const -> override_info
  {
    assert (!rule || target); // Rule-specific is target-specific.

    // Normally there would be no overrides and if there are, there will only
    // be a few of them. As a result, here we concentrate on keeping the logic
    // as straightforward as possible without trying to optimize anything.
    //
    // Note also that we rely (e.g., in the config module) on the fact that if
    // no overrides apply, then we return the original value and not its copy
    // in the cache (this is used to detect if the value was overriden).
    //
    assert (var.overrides != nullptr);

    const lookup_type& orig (original.first);
    size_t orig_depth (original.second);

    // The first step is to find out where our cache will reside. After some
    // meditation you will see it should be next to the innermost (scope-wise)
    // value of this variable (override or original).
    //
    // We also keep track of the root scope of the project from which this
    // innermost value comes. This is used to decide whether a non-recursive
    // project-wise override applies. And also where our variable cache is.
    //
    const variable_map* inner_vars (nullptr);
    const scope* inner_proj (nullptr);

    // One special case is if the original is target/rule-specific, which is
    // the most innermost. Or is it innermostest?
    //
    bool targetspec (false);
    if (target)
    {
      targetspec = orig.defined () && (orig_depth == 1 ||
                                       orig_depth == 2 ||
                                       (rule && orig_depth == 3));
      if (targetspec)
      {
        inner_vars = orig.vars;
        inner_proj = root_scope ();
      }
    }

    const scope* s;

    // Return true if the override applies to a value from vars/proj. Note
    // that it expects vars and proj to be not NULL; if there is nothing "more
    // inner", then any override will still be "visible".
    //
    auto applies = [&s] (const variable* o,
                         const variable_map* vars,
                         const scope* proj) -> bool
    {
      switch (o->visibility)
      {
      case variable_visibility::scope:
      {
        // Does not apply if in a different scope.
        //
        if (vars != &s->vars)
          return false;

        break;
      }
      case variable_visibility::project:
      {
        // Does not apply if in a subproject.
        //
        // Note that before we used to require the same project but that
        // missed values that are "visible" from the outer projects.
        //
        // If root scope is NULL, then we are looking at the global scope.
        //
        const scope* rs (s->root_scope ());
        if (rs != nullptr && rs->sub_root (*proj))
          return false;

        break;
      }
      case variable_visibility::global:
        break;
      case variable_visibility::target:
      case variable_visibility::prereq:
        assert (false);
      }

      return true;
    };

    // Return the override value if present in scope s and (optionally) of
    // the specified kind (__override, __prefix, etc).
    //
    auto lookup = [&s, &var] (const variable* o,
                              const char* k = nullptr) -> lookup_type
    {
      if (k != nullptr && !o->override (k))
        return lookup_type ();

      // Note: using the original as storage variable.
      // Note: have to suppress aliases since used for something else.
      //
      return lookup_type (
        s->vars.lookup (*o, true /* typed */, false /* aliased */).first,
        &var,
        &s->vars);
    };

    // Return true if a value is from this scope (either target type/pattern-
    // specific or ordinary).
    //
    auto belongs = [&s, target] (const lookup_type& l) -> bool
    {
      if (target)
      {
        for (auto& p1: s->target_vars)
          for (auto& p2: p1.second)
            if (l.vars == &p2.second)
              return true;
      }

      return l.vars == &s->vars;
    };

    // While looking for the cache we also detect if none of the overrides
    // apply. In this case the result is simply the original value (if any).
    //
    bool apply (false);

    for (s = this; s != nullptr; s = s->parent_scope ())
    {
      // If we are still looking for the cache, see if the original comes from
      // this scope. We check this before the overrides since it can come from
      // the target type/patter-specific variables, which is "more inner" than
      // normal scope variables (see lookup_original()).
      //
      if (inner_vars == nullptr && orig.defined () && belongs (orig))
      {
        inner_vars = orig.vars;
        inner_proj = s->root_scope ();
      }

      for (const variable* o (var.overrides.get ());
           o != nullptr;
           o = o->overrides.get ())
      {
        if (inner_vars != nullptr && !applies (o, inner_vars, inner_proj))
          continue;

        auto l (lookup (o));

        if (l.defined ())
        {
          if (inner_vars == nullptr)
          {
            inner_vars = l.vars;
            inner_proj = s->root_scope ();
          }

          apply = true;
          break;
        }
      }

      // We can stop if we found the cache and at least one override applies.
      //
      if (inner_vars != nullptr && apply)
        break;
    }

    if (!apply)
      return override_info {original, orig.defined ()};

    assert (inner_vars != nullptr);

    // If for some reason we are not in a project, use the cache from the
    // global scope.
    //
    if (inner_proj == nullptr)
      inner_proj = &ctx.global_scope;

    // Now find our "stem", that is, the value to which we will be appending
    // suffixes and prepending prefixes. This is either the original or the
    // __override, provided it applies. We may also not have either.
    //
    lookup_type stem;
    size_t stem_depth (0);
    const scope* stem_proj (nullptr);
    const variable* stem_ovr (nullptr); // __override if found and applies.

    // Again the special case of a target/rule-specific variable.
    //
    if (targetspec)
    {
      stem = orig;
      stem_depth = orig_depth;
      stem_proj = root_scope ();
    }

    // Depth at which we found the override (with implied target/rule-specific
    // lookup counts).
    //
    size_t ovr_depth (target ? (rule ? 3 : 2) : 0);

    for (s = this; s != nullptr; s = s->parent_scope ())
    {
      bool done (false);

      // First check if the original is from this scope.
      //
      if (orig.defined () && belongs (orig))
      {
        stem = orig;
        stem_depth = orig_depth;
        stem_proj = s->root_scope ();
        // Keep searching.
      }

      ++ovr_depth;

      // Then look for an __override that applies.
      //
      // Note that the override list is in the reverse order of appearance and
      // so we will naturally see the most recent override first.
      //
      for (const variable* o (var.overrides.get ());
           o != nullptr;
           o = o->overrides.get ())
      {
        // If we haven't yet found anything, then any override will still be
        // "visible" even if it doesn't apply.
        //
        if (stem.defined () && !applies (o, stem.vars, stem_proj))
          continue;

        auto l (lookup (o, "__override"));

        if (l.defined ())
        {
          stem = move (l);
          stem_depth = ovr_depth;
          stem_proj = s->root_scope ();
          stem_ovr = o;
          done = true;
          break;
        }
      }

      if (done)
        break;
    }

    // Check the cache.
    //
    variable_override_cache& cache (
      inner_proj == &ctx.global_scope
      ? ctx.global_override_cache
      : inner_proj->root_extra->override_cache);

    pair<value&, ulock> entry (
      cache.insert (
        ctx,
        make_pair (&var, inner_vars),
        stem,
        0, // Overrides are immutable.
        var));

    value& cv (entry.first);
    bool cl (entry.second.owns_lock ());

    // If cache miss/invalidation, update the value.
    //
    if (cl)
    {
      // Note: very similar logic as in the target type/pattern specific cache
      // population code above.
      //

      // Un-typify the cache. This can be necessary, for example, if we are
      // changing from one value-typed stem to another.
      //
      if (!stem.defined () || cv.type != stem->type)
      {
        cv = nullptr;
        cv.type = nullptr; // Un-typify.
      }

      if (stem.defined ())
        cv = *stem;

      // Typify the cache value. If the stem is the original, then the type
      // would get propagated automatically. But the stem could also be the
      // override, which is kept untyped. Or the stem might not be there at
      // all while we still need to apply prefixes/suffixes in the type-aware
      // way.
      //
      if (cv.type == nullptr && var.type != nullptr)
        typify (cv, *var.type, &var);
    }

    // Now apply override prefixes and suffixes (if updating the cache). Also
    // calculate the vars and depth of the result, which will be those of the
    // stem or prefix/suffix that applies, whichever is the innermost.
    //
    // Note: we could probably cache this information instead of recalculating
    // it every time.
    //
    size_t depth (stem_depth);
    const variable_map* vars (stem.vars);
    const scope* proj (stem_proj);

    ovr_depth = target ? (rule ? 3 : 2) : 0;

    for (s = this; s != nullptr; s = s->parent_scope ())
    {
      ++ovr_depth;

      // The override list is in the reverse order of appearance so we need to
      // iterate backwards in order to apply things in the correct order.
      //
      // We also need to skip any append/prepend overrides that appear before
      // __override (in the command line order), provided it is from this
      // scope.
      //
      bool skip (stem_ovr != nullptr && stem_depth == ovr_depth);

      for (const variable* o (var.overrides->aliases); // Last override.
           o != nullptr;
           o = (o->aliases != var.overrides->aliases ? o->aliases : nullptr))
      {
        if (skip)
        {
          if (stem_ovr == o) // Keep skipping until after we see __override.
            skip = false;

          continue;
        }

        // First see if this override applies. This is tricky: what if the
        // stem is a "visible" override from an outer project?  Shouldn't its
        // overrides apply? Sure sounds logical. So we use the project of the
        // stem's scope.
        //
        if (vars != nullptr && !applies (o, vars, proj))
          continue;

        // Note that we keep override values as untyped names even if the
        // variable itself is typed. We also pass the original variable for
        // diagnostics.
        //
        auto lp (lookup (o, "__prefix"));
        auto ls (lookup (o, "__suffix"));

        if (cl)
        {
          // Note: if we have both, then one is already in the stem.
          //
          if (lp) // No sense to prepend/append if NULL.
          {
            cv.prepend (names (cast<names> (lp)), &var);
          }
          else if (ls)
          {
            cv.append (names (cast<names> (ls)), &var);
          }
        }

        if (lp.defined () || ls.defined ())
        {
          // If we had no stem, use the first override as a surrogate stem.
          //
          if (vars == nullptr)
          {
            depth = ovr_depth;
            vars = &s->vars;
            proj = s->root_scope ();
          }
          // Otherwise, pick the innermost location between the stem and
          // prefix/suffix.
          //
          else if (ovr_depth < depth)
          {
            depth = ovr_depth;
            vars = &s->vars;
          }
        }
      }
    }

    // Use the location of the innermost value that contributed as the
    // location of the result.
    //
    return override_info {
      make_pair (lookup_type (&cv, &var, vars), depth),
      orig.defined () && stem == orig};
  }

  value& scope::
  append (const variable& var)
  {
    // Note that here we want the original value without any overrides
    // applied.
    //
    auto l (lookup_original (var).first);

    if (l.defined () && l.belongs (*this)) // Existing var in this scope.
      return vars.modify (l); // Ok since this is original.

    value& r (assign (var)); // NULL.

    if (l.defined ())
      r = *l; // Copy value (and type) from the outer scope.

    return r;
  }

  const target_type* scope::
  find_target_type (const string& tt) const
  {
    // Search the project's root scope then the global scope.
    //
    if (const scope* rs = root_scope ())
    {
      if (const target_type* r = rs->root_extra->target_types.find (tt))
        return r;
    }

    return ctx.global_target_types.find (tt);
  }

  // Find target type from file name.
  //
  static const target_type*
  find_target_type_file (const scope& s, const string& n)
  {
    // Pretty much the same logic as in find_target_type() above.
    //
    if (const scope* rs = s.root_scope ())
    {
      if (const target_type* r = rs->root_extra->target_types.find_file (n))
        return r;
    }

    return s.ctx.global_target_types.find_file (n);
  }

  pair<const target_type*, optional<string>> scope::
  find_target_type (name& n, const location& loc, const target_type* tt) const
  {
    // NOTE: see also functions-name.cxx:filter() if changing anything here.

    optional<string> ext;

    string& v (n.value);

    // If the name is typed, resolve the target type it and bail out if not
    // found. Otherwise, we know in the end it will resolve to something (if
    // nothing else, either dir{} or file{}), so we can go ahead and process
    // the name.
    //
    if (tt == nullptr)
    {
      if (n.typed ())
      {
        tt = find_target_type (n.type);

        if (tt == nullptr)
          return make_pair (tt, move (ext));
      }
      else
      {
        // Empty name as well as '.' and '..' signify a directory. Note that
        // this logic must be consistent with other places (grep for "..").
        //
        if (v.empty () || v == "." || v == "..")
          tt = &dir::static_type;
      }
    }

    // Directories require special name processing. If we find that more
    // targets deviate, then we should make this target type-specific.
    //
    if (tt != nullptr && (tt->is_a<dir> () || tt->is_a<fsdir> ()))
    {
      // The canonical representation of a directory name is with empty
      // value.
      //
      if (!v.empty ())
      {
        n.dir /= dir_path (v); // Move name value to dir.
        v.clear ();
      }
    }
    else if (!v.empty ())
    {
      // Split the path into its directory part (if any) the name part, and
      // the extension (if any).
      //
      // See also parser::expand_name_pattern() if changing anything here.
      //
      try
      {
        n.canonicalize ();
      }
      catch (const invalid_path& e)
      {
        fail (loc) << "invalid path '" << e.path << "'";
      }
      catch (const invalid_argument&)
      {
        // This is probably too general of a place to ignore multiple
        // trailing slashes and treat it as a directory (e.g., we don't want
        // to encourage this sloppiness in buildfiles). We could, however,
        // do it for certain contexts, such as buildspec. Maybe a lax flag?
        //
        fail (loc) << "invalid name '" << v << "'";
      }

      // Extract the extension.
      //
      ext = target::split_name (v, loc);
    }

    // If the target type is still unknown, map it using the name/extension,
    // falling back to file{}.
    //
    if (tt == nullptr)
    {
      // We only consider files without extension for file name mapping.
      //
      if (!ext)
        tt = find_target_type_file (*this, v);

      //@@ TODO: derive type from extension.

      if (tt == nullptr)
        tt = &file::static_type;
    }

    // If the target type does not use extensions but one was specified,
    // factor it back into the name (this way we won't assert when printing
    // diagnostics; see to_stream(target_key) for details).
    //
    if (ext                              &&
        tt->fixed_extension   == nullptr &&
        tt->default_extension == nullptr)
    {
      v += '.';
      v += *ext;
      ext = nullopt;
    }

    return make_pair (tt, move (ext));
  }

  pair<const target_type&, optional<string>> scope::
  find_target_type (name& n, name& o, const location& loc) const
  {
    auto r (find_target_type (n, loc));

    if (r.first == nullptr)
      fail (loc) << "unknown target type " << n.type << " in " << n;

    bool src (n.pair); // If out-qualified, then it is from src.
    if (src)
    {
      assert (n.pair == '@');

      if (!o.directory ())
        fail (loc) << "expected directory after '@'";
    }

    dir_path& dir (n.dir);

    const dir_path& sd (src_path ());
    const dir_path& od (out_path ());

    bool nabs (false);

    if (dir.empty ())
      dir = src ? sd : od; // Already normalized.
    else
    {
      if (dir.relative ())
        dir = (src ? sd : od) / dir;
      else if (src)
        nabs = true;

      dir.normalize ();
    }

    dir_path out;
    if (src)
    {
      bool oabs (o.dir.absolute ());

      out = oabs ? move (o.dir) : od / o.dir;
      out.normalize ();

      // Make sure out and src are parallel unless both were specified as
      // absolute. We make an exception for this case because out may be used
      // to "tag" imported targets (see cc::search_library()). So it's sort of
      // the "I know what I am doing" escape hatch (it would have been even
      // better to verify such a target is outside any project but that won't
      // be cheap).
      //
      // See similar code for prerequisites in parser::parse_dependency().
      //
      if (nabs && oabs)
        ;
      else if (root_->out_eq_src ()
               ? out == dir
               //
               // @@ PERF: could just compare leafs in place.
               //
               : (out.sub (root_->out_path ()) &&
                  dir.sub (root_->src_path ()) &&
                  out.leaf (root_->out_path ()) == dir.leaf (root_->src_path ())))
        ;
      else
        // @@ TMP change warn to fail after 0.16.0 release.
        //
        warn (loc) << "target output directory " << out
                   << " must be parallel to source directory " << dir;

      // If this target is in this project, then out must be empty if this is
      // in source build. We assume that if either src or out are relative,
      // then it belongs to this project.
      //
      if (root_->out_eq_src ())
      {
        if (!nabs || !oabs || out.sub (root_->out_path ()))
          out.clear ();
      }
    }
    o.dir = move (out); // Result.

    return pair<const target_type&, optional<string>> (
      *r.first, move (r.second));
  }

  target_key scope::
  find_target_key (names& ns, const location& loc) const
  {
    if (size_t n = ns.size ())
    {
      if (n == (ns[0].pair ? 2 : 1))
      {
        name dummy;
        return find_target_key (ns[0], n == 1 ? dummy : ns[1], loc);
      }
    }

    fail (loc) << "invalid target name: " << ns << endf;
  }

  pair<const target_type&, optional<string>> scope::
  find_prerequisite_type (name& n, name& o, const location& loc) const
  {
    auto r (find_target_type (n, loc));

    if (r.first == nullptr)
      fail (loc) << "unknown target type " << n.type << " in " << n;

    if (n.pair) // If out-qualified, then it is from src.
    {
      assert (n.pair == '@');

      if (!o.directory ())
        fail (loc) << "expected directory after '@'";
    }

    if (!n.dir.empty ())
      n.dir.normalize (false, true); // Current dir collapses to an empty one.

    if (!o.dir.empty ())
      o.dir.normalize (false, true); // Ditto.

    return pair<const target_type&, optional<string>> (
      *r.first, move (r.second));
  }

  prerequisite_key scope::
  find_prerequisite_key (names& ns, const location& loc) const
  {
    if (size_t n = ns.size ())
    {
      if (n == (ns[0].pair ? 2 : 1))
      {
        name dummy;
        return find_prerequisite_key (ns[0], n == 1 ? dummy : ns[1], loc);
      }
    }

    fail (loc) << "invalid prerequisite name: " << ns << endf;
  }

  static target*
  derived_tt_factory (context& c,
                      const target_type& t, dir_path d, dir_path o, string n)
  {
    // Pass our type to the base factory so that it can detect that it is
    // being called to construct a derived target. This can be used, for
    // example, to decide whether to "link up" to the group.
    //
    // One exception: if we are derived from a derived target type, then this
    // logic would lead to infinite recursion. So in this case get the
    // ultimate base.
    //
    const target_type* bt (t.base);
    for (; bt->factory == &derived_tt_factory; bt = bt->base) ;

    target* r (bt->factory (c, t, move (d), move (o), move (n)));
    r->derived_type = &t;
    return r;
  }

  pair<reference_wrapper<const target_type>, bool> scope::
  derive_target_type (const string& name,
                      const target_type& base,
                      target_type::flag flags)
  {
    assert (root_scope () == this);

    // Base target type uses extensions.
    //
    bool ext (base.fixed_extension   != nullptr ||
              base.default_extension != nullptr);

    // @@ Looks like we may need the ability to specify a fixed extension
    //    (which will be used to compare existing targets and not just
    //    search for existing files that is handled by the target_type::
    //    extension hook). See the file_factory() for details. We will
    //    probably need to specify it as part of the define directive (and
    //    have the ability to specify empty and NULL).
    //
    //    Currently, if we define myfile{}: file{}, then myfile{foo} and
    //    myfile{foo.x} are the same target.

    // Note: copies flags.
    //
    unique_ptr<target_type> dt (new target_type (base));
    dt->base = &base;
    dt->factory = &derived_tt_factory;
    dt->flags |= flags;

#if 0
    // @@ We should probably inherit the fixed extension unless overriden with
    // another fixed? But then any derivation from file{} will have to specify
    // (or override) the fixed extension? But what is the use of deriving from
    // a fixed extension target and not overriding its extension? Some kind of
    // alias. Fuzzy.
    //
    dt->fixed_extension = nullptr /*&target_extension_fix<???>*/; // @@ TODO

    // Override default extension/pattern derivation function: we most likely
    // don't want to use the same default as our base (think cli: file). But,
    // if our base doesn't use extensions, then most likely neither do we
    // (think foo: alias).
    //
    dt->default_extension =
      ext && dt->fixed_extension == nullptr
      ? &target_extension_var<nullptr>
      : nullptr;

    dt->pattern =
      dt->fixed_extension != nullptr ? nullptr /*&target_pattern_fix<???>*/ :
      dt->default_extension != nullptr ? &target_pattern_var<nullptr> :
      nullptr;

    // There is actually a difference between "fixed fixed" (like man1{}) and
    // "fixed but overridable" (like file{}). Fuzzy: feels like there are
    // different kinds of "fixed" (file{} vs man{} vs man1{}).
    //
    dt->print =
      dt->fixed_extension != nullptr
      ? &target_print_0_ext_verb  // Fixed extension, no use printing.
      : nullptr;                  // Normal.
#endif

    // An attempt to clarify the above mess:
    //
    // 1. If we have a "really fixed" extension (like man1{}) then we keep
    //    it (including pattern and print functions).
    //
    // 2. Otherwise, we make it target_extension_var.
    //
    // Note that this still mis-fires for the following scenarios:
    //
    // file{} -- What if the user does not set the default extension expecting
    //           similar semantics as file{} or man{} itself. Maybe explicit
    //           via attribute (i.e., inherit from base)?
    //
    // @@ Get the fallback extension from base target_extension_var
    //    somehow (we know the base target type so could just call it)?
    //
    if (ext)
    {
      if (dt->fixed_extension == nullptr                ||
          dt->fixed_extension == &target_extension_none ||
          dt->fixed_extension == &target_extension_must)
      {
        dt->fixed_extension = nullptr;
        dt->default_extension = &target_extension_var<nullptr>;
        dt->pattern = &target_pattern_var<nullptr>;
        dt->print = nullptr;
      }
    }
    else
    {
      dt->fixed_extension = nullptr;
      dt->default_extension = nullptr;
      dt->pattern = nullptr;
      dt->print = nullptr;
    }

    return root_extra->target_types.insert (name, move (dt));
  }

  const target_type& scope::
  derive_target_type (const target_type& et)
  {
    assert (root_scope () == this);
    unique_ptr<target_type> dt (new target_type (et));
    dt->factory = &derived_tt_factory;
    return root_extra->target_types.insert (et.name, move (dt)).first;
  }

  // scope_map
  //

  auto scope_map::
  insert_out (const dir_path& k, bool root) -> iterator
  {
    auto er (map_.emplace (k, scopes ()));

    if (er.second)
      er.first->second.push_back (nullptr);

    if (er.first->second.front () == nullptr)
    {
      er.first->second.front () = new scope (ctx, true /* shared */);
      er.second = true;
    }

    scope& s (*er.first->second.front ());

    // If this is a new scope, update the parent chain.
    //
    if (er.second)
    {
      scope* p (nullptr);

      // Update scopes of which we are a new parent/root (unless this is the
      // global scope). Also find our parent while at it.
      //
      if (map_.size () > 1)
      {
        // The first entry is ourselves.
        //
        auto r (map_.find_sub (k));
        for (++r.first; r.first != r.second; ++r.first)
        {
          if (scope* c = r.first->second.front ())
          {
            // The first scope of which we are a parent is the least
            // (shortest) one which means there is no other scope between it
            // and our parent.
            //
            if (p == nullptr)
              p = c->parent_;

            if (root && c->root_ == p->root_) // No intermediate root.
              c->root_ = &s;

            if (p == c->parent_) // No intermediate parent.
              c->parent_ = &s;
          }
        }

        // We couldn't get the parent from one of its old children so we have
        // to find it ourselves.
        //
        if (p == nullptr)
          p = &find_out (k.directory ());
      }

      s.parent_ = p;
      s.root_ = root ? &s : (p != nullptr ? p->root_ : nullptr);
    }
    else if (root && !s.root ())
    {
      // Upgrade to root scope.
      //
      auto r (map_.find_sub (k));
      for (++r.first; r.first != r.second; ++r.first)
      {
        if (scope* c = r.first->second.front ())
        {
          if (c->root_ == s.root_) // No intermediate root.
            c->root_ = &s;
        }
      }

      s.root_ = &s;
    }

    return er.first;
  }

  auto scope_map::
  insert_src (scope& s, const dir_path& k) -> iterator
  {
    auto er (map_.emplace (k, scopes ()));

    if (er.second)
      er.first->second.push_back (nullptr); // Owning out path entry.

    // It doesn't feel like this function can possibly be called multiple
    // times for the same scope and path so we skip the duplicate check.
    //
    er.first->second.push_back (&s);

    return er.first;
  }

  scope& scope_map::
  find_out (const dir_path& k)
  {
    assert (k.normalized (false)); // Allow non-canonical dir separators.

    // This one is tricky: if we found an entry that doesn't contain the
    // out path scope, then we need to consider outer scopes.
    //
    auto i (map_.find_sup_if (k,
                              [] (const pair<const dir_path, scopes>& v)
                              {
                                return v.second.front () != nullptr;
                              }));

    assert (i != map_.end ()); // Should have at least global scope.
    return *i->second.front ();
  }

  auto scope_map::
  find (const dir_path& k) const -> pair<scopes::const_iterator,
                                         scopes::const_iterator>
  {
    assert (k.normalized (false));
    auto i (map_.find_sup (k));
    assert (i != map_.end ());

    auto b (i->second.begin ());
    auto e (i->second.end ());

    // Skip NULL first element.
    //
    if (*b == nullptr)
      ++b;

    assert (b != e);
    return make_pair (b, e);
  }
}