summaryrefslogtreecommitdiff
path: root/src/buildstream/node.pyx
blob: 58fd0f33dd445eda2e345cd3200f18879d336f8c (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
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
#
#  Copyright (C) 2018 Codethink Limited
#  Copyright (C) 2019 Bloomberg LLP
#
#  This program is free software; you can redistribute it and/or
#  modify it under the terms of the GNU Lesser General Public
#  License as published by the Free Software Foundation; either
#  version 2 of the License, or (at your option) any later version.
#
#  This library is distributed in the hope that it will be useful,
#  but WITHOUT ANY WARRANTY; without even the implied warranty of
#  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.	 See the GNU
#  Lesser General Public License for more details.
#
#  You should have received a copy of the GNU Lesser General Public
#  License along with this library. If not, see <http://www.gnu.org/licenses/>.
#
#  Authors:
#        Tristan Van Berkom <tristan.vanberkom@codethink.co.uk>
#        Daniel Silverstone <daniel.silverstone@codethink.co.uk>
#        James Ennis <james.ennis@codethink.co.uk>
#        Benjamin Schubert <bschubert@bloomberg.net>

"""
Node - Parsed YAML configuration
================================

This module contains the building blocks for handling YAML configuration.

Everything that is loaded from YAML is encapsulated in such nodes, which
provide helper methods to validate configuration on access.

Using node methods when reading configuration will ensure that errors
are always coherently notified to the user.


Node types
----------

The most important classes defined here are:

* :class:`.MappingNode`: represents a YAML Mapping (dictionary)
* :class:`.ScalarNode`: represents a YAML Scalar (string, boolean, integer)
* :class:`.SequenceNode`: represents a YAML Sequence (list)


Class Reference
---------------
"""

import string

from ._exceptions import LoadError, LoadErrorReason


# A sentinel to be used as a default argument for functions that need
# to distinguish between a kwarg set to None and an unset kwarg.
_sentinel = object()


cdef class Node:
    """This is the base class for YAML document nodes.

    YAML Nodes contain information to describe the provenance of the YAML
    which resulted in the Node, allowing mapping back from a Node to the place
    in the file it came from.

    .. note:: You should never need to create a :class:`.Node` manually.
              If you do, you can create :class:`.Node` from dictionaries with
              :func:`Node.from_dict() <buildstream.node.Node.from_dict>`.
              If something else is needed, please open an issue.
    """

    def __init__(self):
        raise NotImplementedError("Please do not construct nodes like this. Use Node.from_dict(dict) instead.")

    def __cinit__(self, int file_index, int line, int column, *args):
        self.file_index = file_index
        self.line = line
        self.column = column

    # This is in order to ensure we never add a `Node` to a cache key
    # as ujson will try to convert objects if they have a `__json__`
    # attribute.
    def __json__(self):
        raise ValueError("Nodes should not be allowed when jsonify-ing data", self)

    #############################################################
    #                  Abstract Public Methods                  #
    #############################################################

    cpdef Node clone(self):
        """Clone the node and return the copy.

        Returns:
            :class:`.Node`: a clone of the current node
        """
        raise NotImplementedError()

    cpdef object strip_node_info(self):
        """ Remove all the node information (provenance) and return the underlying data as plain python objects 

        Returns:
            (list, dict, str, None): the underlying data that was held in the node structure.
        """
        raise NotImplementedError()

    #############################################################
    #                       Public Methods                      #
    #############################################################

    @classmethod
    def from_dict(cls, dict value):
        """from_dict(value)

        Create a new node from the given dictionary.

        This is a recursive operation, and will transform every value in the
        dictionary to a :class:`.Node` instance

        Valid values for keys are `str`
        Valid values for values are `list`, `dict`, `str`, `int`, `bool` or None.
        `list` and `dict` can also only contain such types.

        Args:
            value (dict): dictionary from which to create a node.

        Raises:
            :class:`TypeError`: when the value cannot be converted to a :class:`Node`

        Returns:
            :class:`.MappingNode`: a new mapping containing the value
        """
        if value:
            return __new_node_from_dict(value, MappingNode.__new__(
                MappingNode, _SYNTHETIC_FILE_INDEX, 0, __next_synthetic_counter(), {}))
        else:
            # We got an empty dict, we can shortcut
            return MappingNode.__new__(MappingNode, _SYNTHETIC_FILE_INDEX, 0, __next_synthetic_counter(), {})

    cpdef ProvenanceInformation get_provenance(self):
        """A convenience accessor to obtain the node's :class:`.ProvenanceInformation`

        The provenance information allows you to inform the user of where
        a node came. Transforming the information to a string will show the file, line and column
        in the file where the node is.

        An example usage would be:

        .. code-block:: python

            # With `config` being your node
            max_jobs_node = config.get_node('max-jobs')
            max_jobs = max_jobs_node.as_int()

            if max_jobs < 1:  # We can't get a negative number of jobs
                raise LoadError("Error at {}: Max jobs needs to be >= 1".format(
                    max_jobs_node.get_provenance()
                )

            # Will print something like:
            # element.bst [line 4, col 7]: Max jobs needs to be >= 1

        Returns:
            :class:`.ProvenanceInformation`: the provenance information for the node.
        """
        return ProvenanceInformation(self)

    #############################################################
    #        Abstract Private Methods used in BuildStream       #
    #############################################################

    # _assert_fully_composited()
    #
    # This must be called on a fully loaded and composited node,
    # after all composition has completed.
    #
    # This checks that no more composition directives are present
    # in the data.
    #
    # Raises:
    #    (LoadError): If any assertions fail
    #
    cpdef void _assert_fully_composited(self) except *:
        raise NotImplementedError()

    #############################################################
    #                Abstract Protected Methods                 #
    #############################################################

    # _compose_on(key, target, path)
    #
    # Compose the current node on the given target.
    #
    # Args:
    #   key (str): key on the target on which to compose the current value
    #   target (.Node): target node on which to compose
    #   path (list): path from the root of the target when composing recursively
    #         in order to give accurate error reporting.
    #
    # Raises:
    #   (_CompositeError): if an error is encountered during composition
    #
    cdef void _compose_on(self, str key, MappingNode target, list path) except *:
        raise NotImplementedError()

    # _is_composite_list
    #
    # Checks if the node is a Mapping with array composition
    # directives.
    #
    # Returns:
    #    (bool): True if node was a Mapping containing only
    #            list composition directives
    #
    # Raises:
    #    (LoadError): If node was a mapping and contained a mix of
    #                 list composition directives and other keys
    #
    cdef bint _is_composite_list(self) except *:
        raise NotImplementedError()

    # _walk_find(target, path)
    #
    # Walk the node to search for `target`.
    #
    # When this returns `True`, the `path` argument will contain the full path
    # to the target from the root node.
    #
    # Args:
    #   target (.Node): target to find in the node tree
    #   path (list): current path from the root
    #
    # Returns:
    #   (bool): whether the target was found in the tree or not
    #
    cdef bint _walk_find(self, Node target, list path) except *:
        raise NotImplementedError()

    #############################################################
    #                     Protected Methods                     #
    #############################################################

    # _shares_position_with(target)
    #
    # Check whether the current node is at the same position in its tree as the target.
    #
    # This is useful when we want to know if two nodes are 'identical', that is they
    # are at the exact same position in each respective tree, but do not necessarily
    # have the same content.
    #
    # Args:
    #   target (.Node): the target to compare with the current node.
    #
    # Returns:
    #   (bool): whether the two nodes share the same position
    #
    cdef bint _shares_position_with(self, Node target):
        return (self.file_index == target.file_index and
                self.line == target.line and
                self.column == target.column)


cdef class ScalarNode(Node):
    """This class represents a Scalar (int, str, bool, None) in a YAML document.

    .. note:: If you need to store another type of scalars, please open an issue
              on the project.

    .. note:: You should never have to create a :class:`.ScalarNode` directly
    """

    def __cinit__(self, int file_index, int line, int column, object value):
        cdef value_type = type(value)

        if value_type is str:
            value = value.strip()
        elif value_type is bool:
            if value:
                value = "True"
            else:
                value = "False"
        elif value_type is int:
            value = str(value)
        elif value is None:
            pass
        else:
            raise ValueError("ScalarNode can only hold str, int, bool or None objects")

        self.value = value

    def __reduce__(self):
        return (
            ScalarNode.__new__,
            (ScalarNode, self.file_index, self.line, self.column, self.value),
        )

    #############################################################
    #                       Public Methods                      #
    #############################################################

    cpdef bint as_bool(self) except *:
        """Get the value of the node as a boolean.

        .. note:: BuildStream treats the values 'True' and 'true' as True,
                  and the values 'False' and 'false' as False.  Any other
                  string values (such as the valid YAML 'TRUE' or 'FALSE'
                  will be considered as an error)

        Raises:
            :class:`buildstream._exceptions.LoadError`: if the value cannot be coerced to
                                                        a bool correctly.

        Returns:
            :class:`bool`: the value contained in the node, as a boolean
        """
        if type(self.value) is bool:
            return self.value

        # Don't coerce strings to booleans, this makes "False" strings evaluate to True
        if self.value in ('True', 'true'):
            return True
        elif self.value in ('False', 'false'):
            return False
        else:
            provenance = self.get_provenance()
            path = provenance._toplevel._find(self)[-1]
            raise LoadError("{}: Value of '{}' is not of the expected type '{}'"
                            .format(provenance, path, bool.__name__, self.value),
                            LoadErrorReason.INVALID_DATA)

    cpdef object as_enum(self, object constraint):
        """Get the value of the node as an enum member from `constraint`

        The constraint must be a :class:`buildstream.types.FastEnum` or a plain python Enum.

        For example you could do:

        .. code-block:: python

            from buildstream.types import FastEnum

            class SupportedCompressions(FastEnum):
              NONE = "none"
              GZIP = "gzip"
              XZ = "xz"


            x = config.get_scalar('compress').as_enum(SupportedCompressions)

            if x == SupportedCompressions.GZIP:
                print("Using GZIP")

        Args:
            constraint (:class:`buildstream.types.FastEnum` or :class:`Enum`): an enum from which to extract the value
                                                                               for the current node.

        Returns:
            :class:`FastEnum` or :class:`Enum`: the value contained in the node, as a member of `constraint`
        """
        try:
            return constraint(self.value)
        except ValueError:
            provenance = self.get_provenance()
            path = provenance._toplevel._find(self)[-1]
            valid_values = [str(v.value) for v in constraint]
            raise LoadError("{}: Value of '{}' should be one of '{}'".format(
                                provenance, path, ", ".join(valid_values)),
                            LoadErrorReason.INVALID_DATA)

    cpdef int as_int(self) except *:
        """Get the value of the node as an integer.

        Raises:
            :class:`buildstream._exceptions.LoadError`: if the value cannot be coerced to
                                                        an integer correctly.

        Returns:
            :class:`int`: the value contained in the node, as a integer
        """
        try:
            return int(self.value)
        except ValueError:
            provenance = self.get_provenance()
            path = provenance._toplevel._find(self)[-1]
            raise LoadError("{}: Value of '{}' is not of the expected type '{}'"
                            .format(provenance, path, int.__name__),
                            LoadErrorReason.INVALID_DATA)

    cpdef str as_str(self):
        """Get the value of the node as a string.

        Returns:
            :class:`str`: the value contained in the node, as a string, or `None` if the content
                          is `None`.
        """
        # We keep 'None' as 'None' to simplify the API's usage and allow chaining for users
        if self.value is None:
            return None
        return str(self.value)

    cpdef bint is_none(self):
        """Determine whether the current scalar is `None`.

        Returns:
            :class:`bool`: `True` if the value of the scalar is `None`, else `False`
        """
        return self.value is None

    #############################################################
    #               Public Methods implementations              #
    #############################################################

    cpdef ScalarNode clone(self):
        return self

    cpdef object strip_node_info(self):
        return self.value

    #############################################################
    #              Private Methods implementations              #
    #############################################################

    cpdef void _assert_fully_composited(self) except *:
        pass

    #############################################################
    #                     Protected Methods                     #
    #############################################################

    cdef void _compose_on(self, str key, MappingNode target, list path) except *:
        cdef Node target_value = target.value.get(key)

        if target_value is not None and type(target_value) is not ScalarNode:
            raise __CompositeError(path,
                                   "{}: Cannot compose scalar on non-scalar at {}".format(
                                       self.get_provenance(),
                                       target_value.get_provenance()))

        target.value[key] = self

    cdef bint _is_composite_list(self) except *:
        return False

    cdef bint _walk_find(self, Node target, list path) except *:
        return self._shares_position_with(target)


cdef class MappingNode(Node):
    """This class represents a Mapping (dict) in a YAML document.

    It behaves mostly like a :class:`dict`, but doesn't allow untyped value access
    (Nothing of the form :code:`my_dict[my_value]`.

    It also doesn't allow anything else than :class:`str` as keys, to align with YAML.

    You can however use common dict operations in it:

    .. code-block:: python

        # Assign a new value to a key
        my_mapping[key] = my_value

        # Delete an entry
        del my_mapping[key]

    When assigning a key/value pair, the key must be a string,
    and the value can be any of:

    * a :class:`Node`, in which case the node is just assigned like normally
    * a :class:`list`, :class:`dict`, :class:`int`, :class:`str`, :class:`bool` or :class:`None`.
      In which case, the value will be converted to a :class:`Node` for you.

    Therefore, all values in a :class:`.MappingNode` will be :class:`Node`.

    .. note:: You should never create an instance directly. Use :func:`Node.from_dict() <buildstream.node.Node.from_dict>`
              instead, which will ensure your node is correctly formatted.
    """

    def __cinit__(self, int file_index, int line, int column, dict value):
        self.value = value

    def __reduce__(self):
        return (
            MappingNode.__new__,
            (MappingNode, self.file_index, self.line, self.column, self.value),
        )

    def __contains__(self, what):
        return what in self.value

    def __delitem__(self, str key):
        del self.value[key]

    def __setitem__(self, str key, object value):
        cdef Node old_value

        if type(value) in [MappingNode, ScalarNode, SequenceNode]:
            self.value[key] = value
        else:
            node = __create_node_recursive(value, self)

            # FIXME: Do we really want to override provenance?
            #
            # Related to https://gitlab.com/BuildStream/buildstream/issues/1058
            #
            # There are only two cases were nodes are set in the code (hence without provenance):
            #   - When automatic variables are set by the core (e-g: max-jobs)
            #   - when plugins call Element.set_public_data
            #
            # The first case should never throw errors, so it is of limited interests.
            #
            # The second is more important. What should probably be done here is to have 'set_public_data'
            # able of creating a fake provenance with the name of the plugin, the project and probably the
            # element name.
            #
            # We would therefore have much better error messages, and would be able to get rid of most synthetic
            # nodes.
            old_value = self.value.get(key)
            if old_value:
                node.file_index = old_value.file_index
                node.line = old_value.line
                node.column = old_value.column

            self.value[key] = node

    #############################################################
    #                       Public Methods                      #
    #############################################################

    cpdef bint get_bool(self, str key, object default=_sentinel) except *:
        """get_bool(key, default=sentinel)

        Get the value of the node for `key` as a boolean.

        This is equivalent to: :code:`mapping.get_scalar(my_key, my_default).as_bool()`.

        Args:
            key (str): key for which to get the value
            default (bool): default value to return if `key` is not in the mapping

        Raises:
           :class:`buildstream._exceptions.LoadError`: if the value at `key` is not a
                                                       :class:`.ScalarNode` or isn't a
                                                       valid `boolean`

        Returns:
            :class:`bool`: the value at `key` or the default
        """
        cdef ScalarNode scalar = self.get_scalar(key, default)
        return scalar.as_bool()

    cpdef object get_enum(self, str key, object constraint, object default=_sentinel):
        """Get the value of the node as an enum member from `constraint`

        Args:
            key (str): key for which to get the value
            constraint (:class:`buildstream.types.FastEnum` or :class:`Enum`): an enum from which to extract the value
                                                                               for the current node.
            default (object): default value to return if `key` is not in the mapping

        Raises:
            :class:`buildstream._exceptions.LoadError`: if the value is not is not found or not part of the
                                                        provided enum.

        Returns:
            :class:`buildstream.types.Enum` or :class:`Enum`: the value contained in the node, as a member of
                                                              `constraint`
        """
        cdef object value = self.value.get(key, _sentinel)

        if value is _sentinel:
            if default is _sentinel:
                provenance = self.get_provenance()
                raise LoadError("{}: Dictionary did not contain expected key '{}'".format(provenance, key),
                                LoadErrorReason.INVALID_DATA)

            if default is None:
                return None
            else:
                return constraint(default)

        if type(value) is not ScalarNode:
            provenance = value.get_provenance()
            raise LoadError("{}: Value of '{}' is not of the expected type 'scalar'"
                                .format(provenance, key),
                            LoadErrorReason.INVALID_DATA)

        return (<ScalarNode> value).as_enum(constraint)

    cpdef int get_int(self, str key, object default=_sentinel) except *:
        """get_int(key, default=sentinel)

        Get the value of the node for `key` as an integer.

        This is equivalent to: :code:`mapping.get_scalar(my_key, my_default).as_int()`.

        Args:
            key (str): key for which to get the value
            default (int): default value to return if `key` is not in the mapping

        Raises:
           :class:`buildstream._exceptions.LoadError`: if the value at `key` is not a
                                                       :class:`.ScalarNode` or isn't a
                                                       valid `integer`

        Returns:
            :class:`int`: the value at `key` or the default
        """
        cdef ScalarNode scalar = self.get_scalar(key, default)
        return scalar.as_int()

    cpdef MappingNode get_mapping(self, str key, object default=_sentinel):
        """get_mapping(key, default=sentinel)

        Get the value of the node for `key` as a :class:`.MappingNode`.

        Args:
            key (str): key for which to get the value
            default (dict): default value to return if `key` is not in the mapping. It will be converted
                            to a :class:`.MappingNode` before being returned

        Raises:
           :class:`buildstream._exceptions.LoadError`: if the value at `key` is not a
                                                       :class:`.MappingNode`

        Returns:
            :class:`.MappingNode`: the value at `key` or the default
        """
        value = self._get(key, default, MappingNode)

        if type(value) is not MappingNode and value is not None:
            provenance = value.get_provenance()
            raise LoadError("{}: Value of '{}' is not of the expected type 'dict'"
                            .format(provenance, key), LoadErrorReason.INVALID_DATA)

        return value

    cpdef Node get_node(self, str key, list allowed_types = None, bint allow_none = False):
        """get_node(key, allowed_types=None, allow_none=False)

        Get the value of the node for `key` as a :class:`.Node`.

        This is useful if you have configuration that can be either a :class:`.ScalarNode` or
        a :class:`.MappingNode` for example.

        This method will validate that the value is indeed exactly one of those types (not a subclass)
        and raise an exception accordingly.

        Args:
            key (str): key for which to get the value
            allowed_types (list): list of valid subtypes of :class:`.Node` that are valid return values.
                                  If this is `None`, no checks are done on the return value.
            allow_none (bool): whether to allow the return value to be `None` or not

        Raises:
           :class:`buildstream._exceptions.LoadError`: if the value at `key` is not one
                                                       of the expected types or if it doesn't
                                                       exist.

        Returns:
            :class:`.Node`: the value at `key` or `None`
        """
        cdef value = self.value.get(key, _sentinel)

        if value is _sentinel:
            if allow_none:
                return None

            provenance = self.get_provenance()
            raise LoadError("{}: Dictionary did not contain expected key '{}'".format(provenance, key),
                            LoadErrorReason.INVALID_DATA)

        if allowed_types and type(value) not in allowed_types:
            provenance = self.get_provenance()
            human_types = []
            if MappingNode in allowed_types:
                human_types.append("dict")
            if SequenceNode in allowed_types:
                human_types.append('list')
            if ScalarNode in allowed_types:
                human_types.append('scalar')

            raise LoadError("{}: Value of '{}' is not one of the following: {}.".format(
                            provenance, key, ", ".join(human_types)), LoadErrorReason.INVALID_DATA)

        return value

    cpdef ScalarNode get_scalar(self, str key, object default=_sentinel):
        """get_scalar(key, default=sentinel)

        Get the value of the node for `key` as a :class:`.ScalarNode`.

        Args:
            key (str): key for which to get the value
            default (str, int, bool, None): default value to return if `key` is not in the mapping.
                                            It will be converted to a :class:`.ScalarNode` before being
                                            returned.

        Raises:
           :class:`buildstream._exceptions.LoadError`: if the value at `key` is not a
                                                       :class:`.MappingNode`

        Returns:
            :class:`.ScalarNode`: the value at `key` or the default
        """
        value = self._get(key, default, ScalarNode)

        if type(value) is not ScalarNode:
            if value is None:
                value = ScalarNode.__new__(ScalarNode, self.file_index, 0, __next_synthetic_counter(), None)
            else:
                provenance = value.get_provenance()
                raise LoadError("{}: Value of '{}' is not of the expected type 'scalar'"
                                .format(provenance, key), LoadErrorReason.INVALID_DATA)

        return value

    cpdef SequenceNode get_sequence(self, str key, object default=_sentinel):
        """get_sequence(key, default=sentinel)

        Get the value of the node for `key` as a :class:`.SequenceNode`.

        Args:
            key (str): key for which to get the value
            default (list): default value to return if `key` is not in the mapping. It will be converted
                            to a :class:`.SequenceNode` before being returned

        Raises:
           :class:`buildstream._exceptions.LoadError`: if the value at `key` is not a
                                                       :class:`.SequenceNode`

        Returns:
            :class:`.SequenceNode`: the value at `key` or the default
        """
        value = self._get(key, default, SequenceNode)

        if type(value) is not SequenceNode and value is not None:
            provenance = value.get_provenance()
            raise LoadError("{}: Value of '{}' is not of the expected type 'list'"
                            .format(provenance, key), LoadErrorReason.INVALID_DATA)

        return value

    cpdef str get_str(self, str key, object default=_sentinel):
        """get_str(key, default=sentinel)

        Get the value of the node for `key` as an string.

        This is equivalent to: :code:`mapping.get_scalar(my_key, my_default).as_str()`.

        Args:
            key (str): key for which to get the value
            default (str): default value to return if `key` is not in the mapping

        Raises:
           :class:`buildstream._exceptions.LoadError`: if the value at `key` is not a
                                                       :class:`.ScalarNode` or isn't a
                                                       valid `str`

        Returns:
            :class:`str`: the value at `key` or the default
        """
        cdef ScalarNode scalar = self.get_scalar(key, default)
        return scalar.as_str()

    cpdef list get_str_list(self, str key, object default=_sentinel):
        """get_str_list(key, default=sentinel)

        Get the value of the node for `key` as a list of strings.

        This is equivalent to: :code:`mapping.get_sequence(my_key, my_default).as_str_list()`.

        Args:
            key (str): key for which to get the value
            default (str): default value to return if `key` is not in the mapping

        Raises:
           :class:`buildstream._exceptions.LoadError`: if the value at `key` is not a
                                                       :class:`.SequenceNode` or if any
                                                       of its internal values is not a ScalarNode.

        Returns:
            :class:`list`: the value at `key` or the default
        """
        cdef SequenceNode sequence = self.get_sequence(key, default)
        return sequence.as_str_list()

    cpdef object items(self):
        """Get a new view of the mapping items ((key, value) pairs).

        This is equivalent to running :code:`my_dict.item()` on a `dict`.

        Returns:
             :class:`dict_items`: a view on the underlying dictionary
        """
        return self.value.items()

    cpdef list keys(self):
        """Get the list of all keys in the mapping.

        This is equivalent to running :code:`my_dict.keys()` on a `dict`.

        Returns:
             :class:`list`: a list of all keys in the mapping
        """
        return list(self.value.keys())

    cpdef void safe_del(self, str key):
        """safe_del(key)

        Remove the entry at `key` in the dictionary if it exists.

        This method is a safe equivalent to :code:`del mapping[key]`, that doesn't
        throw anything if the key doesn't exist.

        Args:
            key (str): key to remove from the mapping
        """
        self.value.pop(key, None)

    cpdef void validate_keys(self, list valid_keys) except *:
        """validate_keys(valid_keys)

        Validate that the node doesn't contain extra keys

        This validates the node so as to ensure the user has not specified
        any keys which are unrecognized by BuildStream (usually this
        means a typo which would otherwise not trigger an error).

        Args:
           valid_keys (list): A list of valid keys for the specified node

        Raises:
            :class:`buildstream._exceptions.LoadError`: In the case that the specified node contained
                                                        one or more invalid keys
        """

        # Probably the fastest way to do this: https://stackoverflow.com/a/23062482
        cdef set valid_keys_set = set(valid_keys)
        cdef str key

        for key in self.value:
            if key not in valid_keys_set:
                provenance = self.get_node(key).get_provenance()
                raise LoadError("{}: Unexpected key: {}".format(provenance, key),
                                LoadErrorReason.INVALID_DATA)

    cpdef object values(self):
        """Get the values in the mapping.

        This is equivalent to running :code:`my_dict.values()` on a `dict`.

        Returns:
             :class:`dict_values`: a list of all values in the mapping
        """
        return self.value.values()

    #############################################################
    #               Public Methods implementations              #
    #############################################################

    cpdef MappingNode clone(self):
        cdef dict copy = {}
        cdef str key
        cdef Node value

        for key, value in self.value.items():
            copy[key] = value.clone()

        return MappingNode.__new__(MappingNode, self.file_index, self.line, self.column, copy)

    cpdef object strip_node_info(self):
        cdef str key
        cdef Node value

        return {key: value.strip_node_info() for key, value in self.value.items()}

    #############################################################
    #            Private Methods used in BuildStream            #
    #############################################################

    # _composite()
    #
    # Compose one mapping node onto another
    #
    # Args:
    #    target (Node): The target to compose into
    #
    # Raises: LoadError
    #
    cpdef void _composite(self, MappingNode target) except *:
        try:
            self.__composite(target, [])
        except __CompositeError as e:
            source_provenance = self.get_provenance()
            error_prefix = ""
            if source_provenance:
                error_prefix = "{}: ".format(source_provenance)
            raise LoadError("{}Failure composing {}: {}"
                            .format(error_prefix,
                                    e.path,
                                    e.message),
                            LoadErrorReason.ILLEGAL_COMPOSITE) from e

    # Like self._composite(target), but where values in the target don't get overridden by values in self.
    #
    cpdef void _composite_under(self, MappingNode target) except *:
        target._composite(self)

        cdef str key
        cdef Node value
        cdef list to_delete = [key for key in target.value.keys() if key not in self.value]

        for key, value in self.value.items():
            target.value[key] = value
        for key in to_delete:
            del target.value[key]

    # _find()
    #
    # Searches the given node tree for the given target node.
    #
    # This is typically used when trying to walk a path to a given node
    # for the purpose of then modifying a similar tree of objects elsewhere
    #
    # Args:
    #    target (Node): The node you are looking for in that tree
    #
    # Returns:
    #    (list): A path from `node` to `target` or None if `target` is not in the subtree
    cpdef list _find(self, Node target):
        cdef list path = []
        if self._walk_find(target, path):
            return path
        return None

    #############################################################
    #              Private Methods implementations              #
    #############################################################

    cpdef void _assert_fully_composited(self) except *:
        cdef str key
        cdef Node value

        for key, value in self.value.items():
            # Assert that list composition directives dont remain, this
            # indicates that the user intended to override a list which
            # never existed in the underlying data
            #
            if key in ('(>)', '(<)', '(=)'):
                provenance = value.get_provenance()
                raise LoadError("{}: Attempt to override non-existing list".format(provenance),
                                LoadErrorReason.TRAILING_LIST_DIRECTIVE)

            value._assert_fully_composited()

    #############################################################
    #                     Protected Methods                     #
    #############################################################

    cdef void _compose_on(self, str key, MappingNode target, list path) except *:
        cdef Node target_value

        if self._is_composite_list():
            if key not in target.value:
                # Composite list clobbers empty space
                target.value[key] = self
            else:
                target_value = target.value[key]

                if type(target_value) is SequenceNode:
                    # Composite list composes into a list
                    self._compose_on_list(target_value)
                elif target_value._is_composite_list():
                    # Composite list merges into composite list
                    self._compose_on_composite_dict(target_value)
                else:
                    # Else composing on top of normal dict or a scalar, so raise...
                    raise __CompositeError(path,
                                           "{}: Cannot compose lists onto {}".format(
                                                self.get_provenance(),
                                                target_value.get_provenance()))
        else:
            # We're composing a dict into target now
            if key not in target.value:
                # Target lacks a dict at that point, make a fresh one with
                # the same provenance as the incoming dict
                target.value[key] = MappingNode.__new__(MappingNode, self.file_index, self.line, self.column, {})

            self.__composite(target.value[key], path)

    # _compose_on_list(target)
    #
    # Compose the current node on the given sequence.
    #
    # Args:
    #   target (.SequenceNode): sequence on which to compose the current composite dict
    #
    cdef void _compose_on_list(self, SequenceNode target):
        cdef SequenceNode clobber = self.value.get("(=)")
        cdef SequenceNode prefix = self.value.get("(<)")
        cdef SequenceNode suffix = self.value.get("(>)")

        if clobber is not None:
            target.value.clear()
            target.value.extend(clobber.value)
        if prefix is not None:
            for v in reversed(prefix.value):
                target.value.insert(0, v)
        if suffix is not None:
            target.value.extend(suffix.value)

    # _compose_on_composite_dict(target)
    #
    # Compose the current node on the given composite dict.
    #
    # A composite dict is a dict that contains composition directives.
    #
    # Args:
    #   target (.MappingNode): sequence on which to compose the current composite dict
    #
    cdef void _compose_on_composite_dict(self, MappingNode target):
        cdef SequenceNode clobber = self.value.get("(=)")
        cdef SequenceNode prefix = self.value.get("(<)")
        cdef SequenceNode suffix = self.value.get("(>)")

        if clobber is not None:
            # We want to clobber the target list
            # which basically means replacing the target list
            # with ourselves
            target.value["(=)"] = clobber
            if prefix is not None:
                target.value["(<)"] = prefix
            elif "(<)" in target.value:
                (<SequenceNode> target.value["(<)"]).value.clear()
            if suffix is not None:
                target.value["(>)"] = suffix
            elif "(>)" in target.value:
                (<SequenceNode> target.value["(>)"]).value.clear()
        else:
            # Not clobbering, so prefix the prefix and suffix the suffix
            if prefix is not None:
                if "(<)" in target.value:
                    for v in reversed(prefix.value):
                        (<SequenceNode> target.value["(<)"]).value.insert(0, v)
                else:
                    target.value["(<)"] = prefix
            if suffix is not None:
                if "(>)" in target.value:
                    (<SequenceNode> target.value["(>)"]).value.extend(suffix.value)
                else:
                    target.value["(>)"] = suffix

    cdef bint _is_composite_list(self) except *:
        cdef bint has_directives = False
        cdef bint has_keys = False
        cdef str key

        for key in self.value.keys():
            if key in ['(>)', '(<)', '(=)']:
                has_directives = True
            else:
                has_keys = True

        if has_keys and has_directives:
            provenance = self.get_provenance()
            raise LoadError("{}: Dictionary contains array composition directives and arbitrary keys"
                            .format(provenance), LoadErrorReason.INVALID_DATA)

        return has_directives

    cdef bint _walk_find(self, Node target, list path) except *:
        cdef str k
        cdef Node v

        if self._shares_position_with(target):
            return True

        for k, v in self.value.items():
            path.append(k)
            if v._walk_find(target, path):
                return True
            del path[-1]

        return False

    #############################################################
    #                      Private Methods                      #
    #############################################################

    # __composite(target, path)
    #
    # Helper method to compose the current node on another.
    #
    # Args:
    #   target (.MappingNode): target on which to compose the current node
    #   path (list): path from the root of the target when composing recursively
    #                in order to give accurate error reporting.
    #
    cdef void __composite(self, MappingNode target, list path) except *:
        cdef str key
        cdef Node value

        for key, value in self.value.items():
            path.append(key)
            value._compose_on(key, target, path)
            path.pop()

        # Clobber the provenance of the target mapping node if we're not
        # synthetic.
        if self.file_index != _SYNTHETIC_FILE_INDEX:
            target.file_index = self.file_index
            target.line = self.line
            target.column = self.column

    # _get(key, default, default_constructor)
    #
    # Internal helper method to get an entry from the underlying dictionary.
    #
    # Args:
    #   key (str): the key for which to retrieve the entry
    #   default (object): default value if the entry is not present
    #   default_constructor (object): method to transform the `default` into a Node
    #                                 if the entry is not present
    #
    # Raises:
    #   (LoadError): if the key is not present and no default has been given.
    #
    cdef Node _get(self, str key, object default, object default_constructor):
        value = self.value.get(key, _sentinel)

        if value is _sentinel:
            if default is _sentinel:
                provenance = self.get_provenance()
                raise LoadError("{}: Dictionary did not contain expected key '{}'".format(provenance, key),
                                LoadErrorReason.INVALID_DATA)

            if default is None:
                value = None
            else:
                value = default_constructor.__new__(
                    default_constructor, _SYNTHETIC_FILE_INDEX, 0, __next_synthetic_counter(), default)

        return value


cdef class SequenceNode(Node):
    """This class represents a Sequence (list) in a YAML document.

    It behaves mostly like a :class:`list`, but doesn't allow untyped value access
    (Nothing of the form :code:`my_list[my_value]`).

    You can however perform common list operations on it:

    .. code-block:: python

        # Assign a value
        my_sequence[key] = value

        # Get the length
        len(my_sequence)

        # Reverse it
        reversed(my_sequence)

        # And iter over it
        for value in my_sequence:
            print(value)

    All values in a :class:`SequenceNode` will be :class:`Node`.
    """

    def __cinit__(self, int file_index, int line, int column, list value):
        self.value = value

    def __reduce__(self):
        return (
            SequenceNode.__new__,
            (SequenceNode, self.file_index, self.line, self.column, self.value),
        )

    def __iter__(self):
        return iter(self.value)

    def __len__(self):
        return len(self.value)

    def __reversed__(self):
        return reversed(self.value)

    def __setitem__(self, int key, object value):
        cdef Node old_value

        if type(value) in [MappingNode, ScalarNode, SequenceNode]:
            self.value[key] = value
        else:
            node = __create_node_recursive(value, self)

            # FIXME: Do we really want to override provenance?
            # See __setitem__ on 'MappingNode' for more context
            old_value = self.value[key]
            if old_value:
                node.file_index = old_value.file_index
                node.line = old_value.line
                node.column = old_value.column

            self.value[key] = node

    #############################################################
    #                       Public Methods                      #
    #############################################################

    cpdef void append(self, object value):
        """append(value)

        Append the given object to the sequence.

        Args:
            value (object): the value to append to the list. This can either be:

                                - a :class:`Node`
                                - a :class:`int`, :class:`bool`, :class:`str`, :class:`None`,
                                  :class:`dict` or :class:`list`. In which case, this will be
                                  converted into a :class:`Node` beforehand

        Raises:
            :class:`TypeError`: when the value cannot be converted to a :class:`Node`
        """
        if type(value) in [MappingNode, ScalarNode, SequenceNode]:
            self.value.append(value)
        else:
            node = __create_node_recursive(value, self)
            self.value.append(node)

    cpdef list as_str_list(self):
        """Get the values of the sequence as a list of strings.

        Raises:
            :class:`buildstream._exceptions.LoadError`: if the sequence contains more than
                                                        :class:`ScalarNode`

        Returns:
            :class:`list`: the content of the sequence as a list of strings
        """
        return [node.as_str() for node in self.value]

    cpdef MappingNode mapping_at(self, int index):
        """mapping_at(index)

        Retrieve the entry at `index` as a :class:`.MappingNode`.

        Args:
            index (int): index for which to get the value

        Raises:
           :class:`buildstream._exceptions.LoadError`: if the value at `key` is not a
                                                       :class:`.MappingNode`
           :class:`IndexError`: if no value exists at this index

        Returns:
            :class:`.MappingNode`: the value at `index`
        """
        value = self.value[index]

        if type(value) is not MappingNode:
            provenance = self.get_provenance()
            path = ["[{}]".format(p) for p in provenance._toplevel._find(self)] + ["[{}]".format(index)]
            raise LoadError("{}: Value of '{}' is not of the expected type '{}'"
                            .format(provenance, path, MappingNode.__name__),
                            LoadErrorReason.INVALID_DATA)
        return value

    cpdef Node node_at(self, int index, list allowed_types = None):
        """node_at(index, allowed_types=None)

        Retrieve the entry at `index` as a :class:`.Node`.

        This is useful if you have configuration that can be either a :class:`.ScalarNode` or
        a :class:`.MappingNode` for example.

        This method will validate that the value is indeed exactly one of those types (not a subclass)
        and raise an exception accordingly.

        Args:
            index (int): index for which to get the value
            allowed_types (list): list of valid subtypes of :class:`.Node` that are valid return values.
                                  If this is `None`, no checks are done on the return value.

        Raises:
           :class:`buildstream._exceptions.LoadError`: if the value at `index` is not of one of the
                                                       expected types
           :class:`IndexError`: if no value exists at this index

        Returns:
            :class:`.Node`: the value at `index`
        """
        cdef value = self.value[index]

        if allowed_types and type(value) not in allowed_types:
            provenance = self.get_provenance()
            raise LoadError("{}: Value of '{}' is not one of the following: {}.".format(
                            provenance, index, ", ".join(allowed_types)),
                            LoadErrorReason.INVALID_DATA)

        return value

    cpdef ScalarNode scalar_at(self, int index):
        """scalar_at(index)

        Retrieve the entry at `index` as a :class:`.ScalarNode`.

        Args:
            index (int): index for which to get the value

        Raises:
           :class:`buildstream._exceptions.LoadError`: if the value at `key` is not a
                                                       :class:`.ScalarNode`
           :class:`IndexError`: if no value exists at this index

        Returns:
            :class:`.ScalarNode`: the value at `index`
        """
        value = self.value[index]

        if type(value) is not ScalarNode:
            provenance = self.get_provenance()
            path = ["[{}]".format(p) for p in provenance._toplevel._find(self)] + ["[{}]".format(index)]
            raise LoadError("{}: Value of '{}' is not of the expected type '{}'"
                            .format(provenance, path, ScalarNode.__name__),
                            LoadErrorReason.INVALID_DATA)
        return value

    cpdef SequenceNode sequence_at(self, int index):
        """sequence_at(index)

        Retrieve the entry at `index` as a :class:`.SequenceNode`.

        Args:
            index (int): index for which to get the value

        Raises:
           :class:`buildstream._exceptions.LoadError`: if the value at `key` is not a
                                                       :class:`.SequenceNode`
           :class:`IndexError`: if no value exists at this index

        Returns:
            :class:`.SequenceNode`: the value at `index`
        """
        value = self.value[index]

        if type(value) is not SequenceNode:
            provenance = self.get_provenance()
            path = ["[{}]".format(p) for p in provenance.toplevel._find(self)] + ["[{}]".format(index)]
            raise LoadError("{}: Value of '{}' is not of the expected type '{}'"
                            .format(provenance, path, SequenceNode.__name__),
                            LoadErrorReason.INVALID_DATA)

        return value

    #############################################################
    #               Public Methods implementations              #
    #############################################################

    cpdef SequenceNode clone(self):
        cdef list copy = []
        cdef Node entry

        for entry in self.value:
            copy.append(entry.clone())

        return SequenceNode.__new__(SequenceNode, self.file_index, self.line, self.column, copy)

    cpdef object strip_node_info(self):
        cdef Node value
        return [value.strip_node_info() for value in self.value]

    #############################################################
    #              Private Methods implementations              #
    #############################################################

    cpdef void _assert_fully_composited(self) except *:
        cdef Node value
        for value in self.value:
            value._assert_fully_composited()

    #############################################################
    #                     Protected Methods                     #
    #############################################################

    cdef void _compose_on(self, str key, MappingNode target, list path) except *:
        # List clobbers anything list-like
        cdef Node target_value = target.value.get(key)

        if not (target_value is None or
                type(target_value) is SequenceNode or
                target_value._is_composite_list()):
            raise __CompositeError(path,
                                  "{}: List cannot overwrite {} at: {}"
                                  .format(self.get_provenance(),
                                          key,
                                          target_value.get_provenance()))
        # Looks good, clobber it
        target.value[key] = self

    cdef bint _is_composite_list(self) except *:
        return False

    cdef bint _walk_find(self, Node target, list path) except *:
        cdef int i
        cdef Node v

        if self._shares_position_with(target):
            return True

        for i, v in enumerate(self.value):
            path.append(i)
            if v._walk_find(target, path):
                return True
            del path[-1]

        return False


# Returned from Node.get_provenance
cdef class ProvenanceInformation:
    """Represents the location of a YAML node in a file.

    This can effectively be used as a pretty print to display those information in
    errors consistently.

    You can retrieve this information for a :class:`Node` with
    :func:`Node.get_provenance() <buildstream.node.Node.get_provenance()>`
    """

    def __init__(self, Node nodeish):
        cdef __FileInfo fileinfo

        self._node = nodeish
        if (nodeish is None) or (nodeish.file_index == _SYNTHETIC_FILE_INDEX):
            self._filename = ""
            self._shortname = ""
            self._displayname = ""
            self._line = 1
            self._col = 0
            self._toplevel = None
            self._project = None
        else:
            fileinfo = <__FileInfo> __FILE_LIST[nodeish.file_index]
            self._filename = fileinfo.filename
            self._shortname = fileinfo.shortname
            self._displayname = fileinfo.displayname
            # We add 1 here to convert from computerish to humanish
            self._line = nodeish.line + 1
            self._col = nodeish.column
            self._toplevel = fileinfo.toplevel
            self._project = fileinfo.project
        self._is_synthetic = (self._filename == '') or (self._col < 0)

    # Convert a Provenance to a string for error reporting
    def __str__(self):
        if self._is_synthetic:
            return "{} [synthetic node]".format(self._displayname)
        else:
            return "{} [line {:d} column {:d}]".format(self._displayname, self._line, self._col)


#############################################################
#                BuildStream Private methods                #
#############################################################

# Purely synthetic nodes will have _SYNTHETIC_FILE_INDEX for the file number, have line number
# zero, and a negative column number which comes from inverting the next value
# out of this counter.  Synthetic nodes created with a reference node will
# have a file number from the reference node, some unknown line number, and
# a negative column number from this counter.
cdef int _SYNTHETIC_FILE_INDEX = -1

# _assert_symbol_name()
#
# A helper function to check if a loaded string is a valid symbol
# name and to raise a consistent LoadError if not. For strings which
# are required to be symbols.
#
# Args:
#    symbol_name (str): The loaded symbol name
#    purpose (str): The purpose of the string, for an error message
#    ref_node (Node): The node of the loaded symbol, or None
#    allow_dashes (bool): Whether dashes are allowed for this symbol
#
# Raises:
#    LoadError: If the symbol_name is invalid
#
# Note that dashes are generally preferred for variable names and
# usage in YAML, but things such as option names which will be
# evaluated with jinja2 cannot use dashes.
def _assert_symbol_name(str symbol_name, str purpose, *, Node ref_node=None, bint allow_dashes=True):
    cdef str valid_chars = string.digits + string.ascii_letters + '_'
    if allow_dashes:
        valid_chars += '-'

    cdef bint valid = True
    if not symbol_name:
        valid = False
    elif any(x not in valid_chars for x in symbol_name):
        valid = False
    elif symbol_name[0] in string.digits:
        valid = False

    if not valid:
        detail = "Symbol names must contain only alphanumeric characters, " + \
                 "may not start with a digit, and may contain underscores"
        if allow_dashes:
            detail += " or dashes"

        message = "Invalid symbol name for {}: '{}'".format(purpose, symbol_name)
        if ref_node:
            provenance = ref_node.get_provenance()
            if provenance is not None:
                message = "{}: {}".format(provenance, message)

        raise LoadError(message, LoadErrorReason.INVALID_SYMBOL_NAME, detail=detail)


# _create_new_file(filename, shortname, displayname, toplevel, project)
#
# Create a new synthetic file and return it's index in the `._FILE_LIST`.
#
# Args:
#   filename (str): the name to give to the file
#   shortname (str): a shorter name used when showing information on the screen
#   displayname (str): the name to give when reporting errors
#   project (object): project with which to associate the current file (when dealing with junctions)
#
# Returns:
#   (int): the index in the `._FILE_LIST` that identifies the new file
#
cdef Py_ssize_t _create_new_file(str filename, str shortname, str displayname, object project):
    cdef Py_ssize_t file_number = len(__FILE_LIST)
    __FILE_LIST.append(__FileInfo(filename, shortname, displayname, None, project))

    return file_number


# _set_root_node_for_file(file_index, contents)
#
# Set the root node for the given file
#
# Args:
#   file_index (int): the index in the `._FILE_LIST` for the file for which to set the root
#   contents (.MappingNode): node that should be the root for the file
#
cdef void _set_root_node_for_file(Py_ssize_t file_index, MappingNode contents) except *:
    cdef __FileInfo f_info

    if file_index != _SYNTHETIC_FILE_INDEX:
        f_info = <__FileInfo> __FILE_LIST[file_index]
        f_info.toplevel = contents


# _new_synthetic_file()
#
# Create a new synthetic mapping node, with an associated file entry
# (in _FILE_LIST) such that later tracking can correctly determine which
# file needs writing to in order to persist the changes.
#
# Args:
#    filename (str): The name of the synthetic file to create
#    project (Project): The optional project to associate this synthetic file with
#
# Returns:
#    (Node): An empty YAML mapping node, whose provenance is to this new
#            synthetic file
#
def _new_synthetic_file(str filename, object project=None):
    cdef Py_ssize_t file_index = len(__FILE_LIST)
    cdef Node node = MappingNode.__new__(MappingNode, file_index, 0, 0, {})

    __FILE_LIST.append(__FileInfo(filename,
                                  filename,
                                  "<synthetic {}>".format(filename),
                                  node,
                                  project))
    return node


# _reset_global_state()
#
# This resets the global variables __FILE_LIST and __counter to their initial
# state. This is used by the test suite to improve isolation between tests
# running in the same process.
#
def _reset_global_state():
    global __FILE_LIST, __counter
    __FILE_LIST = []
    __counter = 0


# _get_state_for_pickling()
#
# This gets the global variables necessary to preserve in a child process when
# e.g. running a ChildJob. Things that are pickled from the parent process to
# the child process will expect this module to be in the same state as in the
# parent.
#
# Returns:
#    (object): The state to supply to a call of _get_state_for_pickling().
#
def _get_state_for_pickling():
    return __FILE_LIST, __counter


# _set_state_from_pickling()
#
# This restores the global variables saved from _get_state_for_pickling(). See
# that function for more details.
#
# Args:
#    state (object): The result of calling _get_state_for_pickling().
#
def _set_state_from_pickling(state):
    global __FILE_LIST, __counter
    __FILE_LIST, __counter = state


#############################################################
#                 Module local helper Methods               #
#############################################################

# File name handling
cdef list __FILE_LIST = []

# synthetic counter for synthetic nodes
cdef int __counter = 0


class __CompositeError(Exception):
    def __init__(self, path, message):
        super().__init__(message)
        self.path = path
        self.message = message


# Metadata container for a yaml toplevel node.
#
# This class contains metadata around a yaml node in order to be able
# to trace back the provenance of a node to the file.
#
cdef class __FileInfo:

    cdef str filename, shortname, displayname
    cdef MappingNode toplevel,
    cdef object project

    def __init__(self, str filename, str shortname, str displayname, MappingNode toplevel, object project):
        self.filename = filename
        self.shortname = shortname
        self.displayname = displayname
        self.toplevel = toplevel
        self.project = project


cdef int __next_synthetic_counter():
    global __counter
    __counter -= 1
    return __counter


cdef Node __create_node_recursive(object value, Node ref_node):
    cdef value_type = type(value)

    if value_type is list:
        node = __new_node_from_list(value, ref_node)
    elif value_type in [int, str, bool]:
        node = ScalarNode.__new__(ScalarNode, ref_node.file_index, ref_node.line, __next_synthetic_counter(), value)
    elif value_type is dict:
        node = __new_node_from_dict(value, ref_node)
    else:
        raise TypeError(
            "Unable to assign a value of type {} to a Node.".format(value_type))

    return node


# _new_node_from_dict()
#
# Args:
#   indict (dict): The input dictionary
#   ref_node (Node): The dictionary to take as reference for position
#
# Returns:
#   (Node): A new synthetic YAML tree which represents this dictionary
#
cdef Node __new_node_from_dict(dict indict, Node ref_node):
    cdef MappingNode ret = MappingNode.__new__(
        MappingNode, ref_node.file_index, ref_node.line, __next_synthetic_counter(), {})
    cdef str k

    for k, v in indict.items():
        ret.value[k] = __create_node_recursive(v, ref_node)

    return ret


# Internal function to help new_node_from_dict() to handle lists
cdef Node __new_node_from_list(list inlist, Node ref_node):
    cdef SequenceNode ret = SequenceNode.__new__(
        SequenceNode, ref_node.file_index, ref_node.line, __next_synthetic_counter(), [])

    for v in inlist:
        ret.value.append(__create_node_recursive(v, ref_node))

    return ret