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
  
1714
  
1715
  
1716
  
1717
  
1718
  
1719
  
1720
  
1721
  
1722
  
1723
  
1724
  
1725
  
1726
  
1727
  
1728
  
1729
  
1730
  
1731
  
1732
  
1733
  
1734
  
1735
  
1736
  
1737
  
1738
  
1739
  
1740
  
1741
  
1742
  
1743
  
1744
  
1745
  
1746
  
1747
  
1748
  
1749
  
1750
  
1751
  
1752
  
1753
  
1754
  
1755
  
1756
  
1757
  
1758
  
1759
  
1760
  
1761
  
1762
  
1763
  
1764
  
1765
  
1766
  
1767
  
1768
  
1769
  
1770
  
1771
  
1772
  
1773
  
1774
  
1775
  
1776
  
1777
  
1778
  
1779
  
1780
  
1781
  
1782
  
1783
  
1784
  
1785
  
1786
  
1787
  
1788
  
1789
  
1790
  
1791
  
1792
  
1793
  
1794
  
1795
  
1796
  
1797
  
1798
  
1799
  
1800
  
1801
  
1802
  
1803
  
1804
  
1805
  
1806
  
1807
  
1808
  
1809
  
1810
  
1811
  
1812
  
1813
  
1814
  
1815
  
1816
  
1817
  
1818
  
1819
  
1820
  
1821
  
1822
  
1823
  
1824
  
1825
  
1826
  
1827
  
1828
  
1829
  
1830
  
1831
  
1832
  
1833
  
1834
  
1835
  
1836
  
1837
  
1838
  
1839
  
1840
  
1841
  
1842
  
1843
  
1844
  
1845
  
1846
  
1847
  
1848
  
1849
  
1850
  
1851
  
1852
  
1853
  
1854
  
1855
  
1856
  
1857
  
1858
  
1859
  
1860
  
1861
  
1862
  
1863
  
1864
  
1865
  
1866
  
1867
  
1868
  
1869
  
1870
  
1871
  
1872
  
1873
  
1874
  
1875
  
1876
  
1877
  
1878
  
1879
  
1880
  
1881
  
1882
  
1883
  
1884
  
1885
  
1886
  
1887
  
1888
  
1889
  
1890
  
1891
  
1892
  
1893
  
1894
  
1895
  
1896
  
1897
  
1898
  
1899
  
1900
  
1901
  
1902
  
1903
  
1904
  
1905
  
1906
  
1907
  
1908
  
1909
  
1910
  
1911
  
1912
  
1913
  
1914
  
1915
  
1916
  
1917
  
1918
  
1919
  
1920
  
1921
  
1922
  
1923
  
1924
  
1925
  
1926
  
1927
  
1928
  
1929
  
1930
  
1931
  
1932
  
1933
  
1934
  
1935
  
1936
  
1937
  
1938
  
1939
  
1940
  
1941
  
1942
  
1943
  
1944
  
1945
  
1946
  
1947
  
1948
  
1949
  
1950
  
1951
  
1952
  
1953
  
1954
  
1955
  
1956
  
1957
  
1958
  
1959
  
1960
  
1961
  
1962
  
1963
  
1964
  
1965
  
1966
  
1967
  
1968
  
1969
  
1970
  
1971
  
1972
  
1973
  
1974
  
1975
  
1976
  
1977
  
1978
  
1979
  
1980
  
1981
  
1982
  
1983
  
1984
  
1985
  
1986
  
1987
  
1988
  
1989
  
1990
  
1991
  
1992
  
1993
  
1994
  
1995
  
1996
  
1997
  
1998
  
1999
  
2000
  
2001
  
2002
  
2003
  
2004
  
2005
  
2006
  
2007
  
2008
  
2009
  
2010
  
2011
  
2012
  
2013
  
2014
  
2015
  
2016
  
2017
  
2018
  
2019
  
2020
  
2021
  
2022
  
2023
  
2024
  
2025
  
2026
  
2027
  
2028
  
2029
  
2030
  
2031
  
2032
  
2033
  
2034
  
2035
  
2036
  
2037
  
2038
  
2039
  
2040
  
2041
  
2042
  
2043
  
2044
  
2045
  
2046
  
2047
  
2048
  
2049
  
2050
  
2051
  
2052
  
2053
  
2054
  
2055
  
2056
  
2057
  
2058
  
2059
  
2060
  
2061
  
2062
  
2063
  
2064
  
2065
  
2066
  
2067
  
2068
  
2069
  
2070
  
2071
  
2072
  
2073
  
2074
  
2075
  
2076
  
2077
  
2078
  
2079
  
2080
  
2081
  
2082
  
2083
  
2084
  
2085
  
2086
  
2087
  
2088
  
2089
  
2090
  
2091
  
2092
  
2093
  
2094
  
2095
  
2096
  
2097
  
2098
  
2099
  
2100
  
2101
  
2102
  
2103
  
2104
  
2105
  
2106
  
2107
  
2108
  
2109
  
2110
  
2111
  
2112
  
2113
  
2114
  
2115
  
2116
  
2117
  
2118
  
2119
  
2120
  
2121
  
2122
  
2123
  
2124
  
2125
  
2126
  
2127
  
2128
  
2129
  
2130
  
2131
  
2132
  
#include "sass.hpp" 
#include "extend.hpp" 
#include "context.hpp" 
#include "backtrace.hpp" 
#include "paths.hpp" 
#include "parser.hpp" 
#include "expand.hpp" 
#include "node.hpp" 
#include "sass_util.hpp" 
#include "remove_placeholders.hpp" 
#include "debug.hpp" 
#include <iostream> 
#include <deque> 
#include <set> 
 
/* 
 NOTES: 
 
 - The print* functions print to cerr. This allows our testing frameworks (like sass-spec) to ignore the output, which 
   is very helpful when debugging. The format of the output is mainly to wrap things in square brackets to match what 
   ruby already outputs (to make comparisons easier). 
 
 - For the direct porting effort, we're trying to port method-for-method until we get all the tests passing. 
   Where applicable, I've tried to include the ruby code above the function for reference until all our tests pass. 
   The ruby code isn't always directly portable, so I've tried to include any modified ruby code that was actually 
   used for the porting. 
 
 - DO NOT try to optimize yet. We get a tremendous benefit out of comparing the output of each stage of the extend to the ruby 
   output at the same stage. This makes it much easier to determine where problems are. Try to keep as close to 
   the ruby code as you can until we have all the sass-spec tests passing. Then, we should optimize. However, if you see 
   something that could probably be optimized, let's not forget it. Add a // TODO: or // IMPROVEMENT: comment. 
 
 - Coding conventions in this file (these may need to be changed before merging back into master) 
   - Very basic hungarian notation: 
     p prefix for pointers (pSelector) 
     no prefix for value types and references (selector) 
   - Use STL iterators where possible 
   - prefer verbose naming over terse naming 
   - use typedefs for STL container types for make maintenance easier 
 
 - You may see a lot of comments that say "// TODO: is this the correct combinator?". See the comment referring to combinators 
   in extendCompoundSelector for a more extensive explanation of my confusion. I think our divergence in data model from ruby 
   sass causes this to be necessary. 
 
 
 GLOBAL TODOS: 
 
 - wrap the contents of the print functions in DEBUG preprocesser conditionals so they will be optimized away in non-debug mode. 
 
 - consider making the extend* functions member functions to avoid passing around ctx and subset_map map around. This has the 
   drawback that the implementation details of the operator are then exposed to the outside world, which is not ideal and 
   can cause additional compile time dependencies. 
 
 - mark the helper methods in this file static to given them compilation unit linkage. 
 
 - implement parent directive matching 
 
 - fix compilation warnings for unused Extend members if we really don't need those references anymore. 
 */ 
 
 
namespace Sass { 
 
 
 
#ifdef DEBUG 
 
  // TODO: move the ast specific ostream operators into ast.hpp/ast.cpp 
  std::ostream& operator<<(std::ostream& os, const Complex_Selector::Combinator combinator) { 
    switch (combinator) { 
      case Complex_Selector::ANCESTOR_OF: os << "\" \""; break; 
      case Complex_Selector::PARENT_OF:   os << "\">\""; break; 
      case Complex_Selector::PRECEDES:    os << "\"~\""; break; 
      case Complex_Selector::ADJACENT_TO: os << "\"+\""; break; 
      case Complex_Selector::REFERENCE:   os << "\"/\""; break; 
    } 
 
    return os; 
  } 
 
 
  std::ostream& operator<<(std::ostream& os, Compound_Selector& compoundSelector) { 
    for (size_t i = 0, L = compoundSelector.length(); i < L; ++i) { 
      if (i > 0) os << ", "; 
      os << compoundSelector[i]->to_string(); 
    } 
    return os; 
  } 
 
  std::ostream& operator<<(std::ostream& os, Simple_Selector& simpleSelector) { 
    os << simpleSelector.to_string(); 
    return os; 
  } 
 
  // Print a string representation of a Compound_Selector 
  static void printSimpleSelector(Simple_Selector* pSimpleSelector, const char* message=NULL, bool newline=true) { 
 
    if (message) { 
      std::cerr << message; 
    } 
 
    if (pSimpleSelector) { 
      std::cerr << "[" << *pSimpleSelector << "]"; 
    } else { 
      std::cerr << "NULL"; 
    } 
 
    if (newline) { 
      std::cerr << std::endl; 
    } 
  } 
 
  // Print a string representation of a Compound_Selector 
  static void printCompoundSelector(Compound_Selector_Ptr pCompoundSelector, const char* message=NULL, bool newline=true) { 
 
    if (message) { 
      std::cerr << message; 
    } 
 
    if (pCompoundSelector) { 
      std::cerr << "[" << *pCompoundSelector << "]"; 
    } else { 
      std::cerr << "NULL"; 
    } 
 
    if (newline) { 
      std::cerr << std::endl; 
    } 
  } 
 
 
  std::ostream& operator<<(std::ostream& os, Complex_Selector& complexSelector) { 
 
    os << "["; 
    Complex_Selector_Ptr pIter = &complexSelector; 
    bool first = true; 
    while (pIter) { 
      if (pIter->combinator() != Complex_Selector::ANCESTOR_OF) { 
        if (!first) { 
          os << ", "; 
        } 
        first = false; 
        os << pIter->combinator(); 
      } 
 
      if (!first) { 
        os << ", "; 
      } 
      first = false; 
 
      if (pIter->head()) { 
        os << pIter->head()->to_string(); 
      } else { 
        os << "NULL_HEAD"; 
      } 
 
      pIter = pIter->tail(); 
    } 
    os << "]"; 
 
    return os; 
  } 
 
 
  // Print a string representation of a Complex_Selector 
  static void printComplexSelector(Complex_Selector_Ptr pComplexSelector, const char* message=NULL, bool newline=true) { 
 
    if (message) { 
      std::cerr << message; 
    } 
 
    if (pComplexSelector) { 
      std::cerr << *pComplexSelector; 
    } else { 
      std::cerr << "NULL"; 
    } 
 
    if (newline) { 
      std::cerr << std::endl; 
    } 
  } 
 
  static void printSelsNewSeqPairCollection(SubSetMapLookups& collection, const char* message=NULL, bool newline=true) { 
 
    if (message) { 
      std::cerr << message; 
    } 
    bool first = true; 
    std::cerr << "["; 
    for(SubSetMapLookup& pair : collection) { 
      if (first) { 
        first = false; 
      } else { 
        std::cerr << ", "; 
      } 
      std::cerr << "["; 
      Compound_Selector_Ptr pSels = pair.first; 
      Complex_Selector_Ptr pNewSelector = pair.second; 
      std::cerr << "[" << *pSels << "], "; 
      printComplexSelector(pNewSelector, NULL, false); 
    } 
    std::cerr << "]"; 
 
    if (newline) { 
      std::cerr << std::endl; 
    } 
  } 
 
  // Print a string representation of a ComplexSelectorSet 
  static void printSourcesSet(ComplexSelectorSet& sources, const char* message=NULL, bool newline=true) { 
 
    if (message) { 
      std::cerr << message; 
    } 
 
    // Convert to a deque of strings so we can sort since order doesn't matter in a set. This should cut down on 
    // the differences we see when debug printing. 
    typedef std::deque<std::string> SourceStrings; 
    SourceStrings sourceStrings; 
    for (ComplexSelectorSet::iterator iterator = sources.begin(), iteratorEnd = sources.end(); iterator != iteratorEnd; ++iterator) { 
      Complex_Selector_Ptr pSource = *iterator; 
      std::stringstream sstream; 
      sstream << complexSelectorToNode(pSource); 
      sourceStrings.push_back(sstream.str()); 
    } 
 
    // Sort to get consistent output 
    std::sort(sourceStrings.begin(), sourceStrings.end()); 
 
    std::cerr << "ComplexSelectorSet["; 
    for (SourceStrings::iterator iterator = sourceStrings.begin(), iteratorEnd = sourceStrings.end(); iterator != iteratorEnd; ++iterator) { 
      std::string source = *iterator; 
      if (iterator != sourceStrings.begin()) { 
        std::cerr << ", "; 
      } 
      std::cerr << source; 
    } 
    std::cerr << "]"; 
 
    if (newline) { 
      std::cerr << std::endl; 
    } 
  } 
 
 
  std::ostream& operator<<(std::ostream& os, SubSetMapPairs& entries) { 
    os << "SUBSET_MAP_ENTRIES["; 
 
    for (SubSetMapPairs::iterator iterator = entries.begin(), endIterator = entries.end(); iterator != endIterator; ++iterator) { 
      Complex_Selector_Obj pExtComplexSelector = iterator->first;    // The selector up to where the @extend is (ie, the thing to merge) 
      Compound_Selector_Obj pExtCompoundSelector = iterator->second; // The stuff after the @extend 
 
      if (iterator != entries.begin()) { 
        os << ", "; 
      } 
 
      os << "("; 
 
      if (pExtComplexSelector) { 
        std::cerr << *pExtComplexSelector; 
      } else { 
        std::cerr << "NULL"; 
      } 
 
      os << " -> "; 
 
      if (pExtCompoundSelector) { 
        std::cerr << *pExtCompoundSelector; 
      } else { 
        std::cerr << "NULL"; 
      } 
 
      os << ")"; 
 
    } 
 
    os << "]"; 
 
    return os; 
  } 
#endif 
 
  static bool parentSuperselector(Complex_Selector_Ptr pOne, Complex_Selector_Ptr pTwo) { 
    // TODO: figure out a better way to create a Complex_Selector from scratch 
    // TODO: There's got to be a better way. This got ugly quick... 
    Element_Selector_Obj fakeParent = SASS_MEMORY_NEW(Element_Selector, ParserState("[FAKE]"), "temp"); 
    Compound_Selector_Obj fakeHead = SASS_MEMORY_NEW(Compound_Selector, ParserState("[FAKE]"), 1 /*size*/); 
    fakeHead->elements().push_back(fakeParent); 
    Complex_Selector_Obj fakeParentContainer = SASS_MEMORY_NEW(Complex_Selector, ParserState("[FAKE]"), Complex_Selector::ANCESTOR_OF, fakeHead /*head*/, NULL /*tail*/); 
 
    pOne->set_innermost(fakeParentContainer, Complex_Selector::ANCESTOR_OF); 
    pTwo->set_innermost(fakeParentContainer, Complex_Selector::ANCESTOR_OF); 
 
    bool isSuperselector = pOne->is_superselector_of(pTwo); 
 
    pOne->clear_innermost(); 
    pTwo->clear_innermost(); 
 
    return isSuperselector; 
  } 
 
  void nodeToComplexSelectorDeque(const Node& node, ComplexSelectorDeque& out) { 
    for (NodeDeque::iterator iter = node.collection()->begin(), iterEnd = node.collection()->end(); iter != iterEnd; iter++) { 
      Node& child = *iter; 
      out.push_back(nodeToComplexSelector(child)); 
    } 
  } 
 
  Node complexSelectorDequeToNode(const ComplexSelectorDeque& deque) { 
    Node result = Node::createCollection(); 
 
    for (ComplexSelectorDeque::const_iterator iter = deque.begin(), iterEnd = deque.end(); iter != iterEnd; iter++) { 
      Complex_Selector_Obj pChild = *iter; 
      result.collection()->push_back(complexSelectorToNode(pChild)); 
    } 
 
    return result; 
  } 
 
  class LcsCollectionComparator { 
  public: 
    LcsCollectionComparator() {} 
 
    bool operator()(Complex_Selector_Obj pOne, Complex_Selector_Obj pTwo, Complex_Selector_Obj& pOut) const { 
      /* 
      This code is based on the following block from ruby sass' subweave 
        do |s1, s2| 
          next s1 if s1 == s2 
          next unless s1.first.is_a?(SimpleSequence) && s2.first.is_a?(SimpleSequence) 
          next s2 if parent_superselector?(s1, s2) 
          next s1 if parent_superselector?(s2, s1) 
        end 
      */ 
 
      if (*pOne == *pTwo) { 
        pOut = pOne; 
        return true; 
      } 
 
      if (pOne->combinator() != Complex_Selector::ANCESTOR_OF || pTwo->combinator() != Complex_Selector::ANCESTOR_OF) { 
        return false; 
      } 
 
      if (parentSuperselector(pOne, pTwo)) { 
        pOut = pTwo; 
        return true; 
      } 
 
      if (parentSuperselector(pTwo, pOne)) { 
        pOut = pOne; 
        return true; 
      } 
 
      return false; 
    } 
  }; 
 
 
  /* 
  This is the equivalent of ruby's Sass::Util.lcs_backtrace. 
 
  # Computes a single longest common subsequence for arrays x and y. 
  # Algorithm from http://en.wikipedia.org/wiki/Longest_common_subsequence_problem#Reading_out_an_LCS 
  */ 
  void lcs_backtrace(const LCSTable& c, ComplexSelectorDeque& x, ComplexSelectorDeque& y, int i, int j, const LcsCollectionComparator& comparator, ComplexSelectorDeque& out) { 
    //DEBUG_PRINTLN(LCS, "LCSBACK: X=" << x << " Y=" << y << " I=" << i << " J=" << j) 
    // TODO: make printComplexSelectorDeque and use DEBUG_EXEC AND DEBUG_PRINTLN HERE to get equivalent output 
 
    if (i == 0 || j == 0) { 
      DEBUG_PRINTLN(LCS, "RETURNING EMPTY") 
      return; 
    } 
 
 
    Complex_Selector_Obj pCompareOut; 
    if (comparator(x[i], y[j], pCompareOut)) { 
      DEBUG_PRINTLN(LCS, "RETURNING AFTER ELEM COMPARE") 
      lcs_backtrace(c, x, y, i - 1, j - 1, comparator, out); 
      out.push_back(pCompareOut); 
      return; 
    } 
 
    if (c[i][j - 1] > c[i - 1][j]) { 
      DEBUG_PRINTLN(LCS, "RETURNING AFTER TABLE COMPARE") 
      lcs_backtrace(c, x, y, i, j - 1, comparator, out); 
      return; 
    } 
 
    DEBUG_PRINTLN(LCS, "FINAL RETURN") 
    lcs_backtrace(c, x, y, i - 1, j, comparator, out); 
    return; 
  } 
 
  /* 
  This is the equivalent of ruby's Sass::Util.lcs_table. 
 
  # Calculates the memoization table for the Least Common Subsequence algorithm. 
  # Algorithm from http://en.wikipedia.org/wiki/Longest_common_subsequence_problem#Computing_the_length_of_the_LCS 
  */ 
  void lcs_table(const ComplexSelectorDeque& x, const ComplexSelectorDeque& y, const LcsCollectionComparator& comparator, LCSTable& out) { 
    //DEBUG_PRINTLN(LCS, "LCSTABLE: X=" << x << " Y=" << y) 
    // TODO: make printComplexSelectorDeque and use DEBUG_EXEC AND DEBUG_PRINTLN HERE to get equivalent output 
 
    LCSTable c(x.size(), std::vector<int>(y.size())); 
 
    // These shouldn't be necessary since the vector will be initialized to 0 already. 
    // x.size.times {|i| c[i][0] = 0} 
    // y.size.times {|j| c[0][j] = 0} 
 
    for (size_t i = 1; i < x.size(); i++) { 
      for (size_t j = 1; j < y.size(); j++) { 
        Complex_Selector_Obj pCompareOut; 
 
        if (comparator(x[i], y[j], pCompareOut)) { 
          c[i][j] = c[i - 1][j - 1] + 1; 
        } else { 
          c[i][j] = std::max(c[i][j - 1], c[i - 1][j]); 
        } 
      } 
    } 
 
    out = c; 
  } 
 
  /* 
  This is the equivalent of ruby's Sass::Util.lcs. 
 
  # Computes a single longest common subsequence for `x` and `y`. 
  # If there are more than one longest common subsequences, 
  # the one returned is that which starts first in `x`. 
 
  # @param x [NodeCollection] 
  # @param y [NodeCollection] 
  # @comparator An equality check between elements of `x` and `y`. 
  # @return [NodeCollection] The LCS 
 
  http://en.wikipedia.org/wiki/Longest_common_subsequence_problem 
  */ 
  void lcs(ComplexSelectorDeque& x, ComplexSelectorDeque& y, const LcsCollectionComparator& comparator, ComplexSelectorDeque& out) { 
    //DEBUG_PRINTLN(LCS, "LCS: X=" << x << " Y=" << y) 
    // TODO: make printComplexSelectorDeque and use DEBUG_EXEC AND DEBUG_PRINTLN HERE to get equivalent output 
 
    x.push_front(NULL); 
    y.push_front(NULL); 
 
    LCSTable table; 
    lcs_table(x, y, comparator, table); 
 
    return lcs_backtrace(table, x, y, static_cast<int>(x.size()) - 1, static_cast<int>(y.size()) - 1, comparator, out); 
  } 
 
 
  /* 
   This is the equivalent of ruby's Sequence.trim. 
 
   The following is the modified version of the ruby code that was more portable to C++. You 
   should be able to drop it into ruby 3.2.19 and get the same results from ruby sass. 
 
        # Avoid truly horrific quadratic behavior. TODO: I think there 
        # may be a way to get perfect trimming without going quadratic. 
        return seqses if seqses.size > 100 
 
        # Keep the results in a separate array so we can be sure we aren't 
        # comparing against an already-trimmed selector. This ensures that two 
        # identical selectors don't mutually trim one another. 
        result = seqses.dup 
 
        # This is n^2 on the sequences, but only comparing between 
        # separate sequences should limit the quadratic behavior. 
        seqses.each_with_index do |seqs1, i| 
          tempResult = [] 
 
          for seq1 in seqs1 do 
            max_spec = 0 
            for seq in _sources(seq1) do 
              max_spec = [max_spec, seq.specificity].max 
            end 
 
 
            isMoreSpecificOuter = false 
            for seqs2 in result do 
              if seqs1.equal?(seqs2) then 
                next 
              end 
 
              # Second Law of Extend: the specificity of a generated selector 
              # should never be less than the specificity of the extending 
              # selector. 
              # 
              # See https://github.com/nex3/sass/issues/324. 
              isMoreSpecificInner = false 
              for seq2 in seqs2 do 
                isMoreSpecificInner = _specificity(seq2) >= max_spec && _superselector?(seq2, seq1) 
                if isMoreSpecificInner then 
                  break 
                end 
              end 
 
              if isMoreSpecificInner then 
                isMoreSpecificOuter = true 
                break 
              end 
            end 
 
            if !isMoreSpecificOuter then 
              tempResult.push(seq1) 
            end 
          end 
 
          result[i] = tempResult 
 
        end 
 
        result 
   */ 
  /* 
   - IMPROVEMENT: We could probably work directly in the output trimmed deque. 
   */ 
  Node Extend::trim(Node& seqses, bool isReplace) { 
    // See the comments in the above ruby code before embarking on understanding this function. 
 
    // Avoid poor performance in extreme cases. 
    if (seqses.collection()->size() > 100) { 
      return seqses; 
    } 
 
 
    DEBUG_PRINTLN(TRIM, "TRIM: " << seqses) 
 
 
    Node result = Node::createCollection(); 
    result.plus(seqses); 
 
    DEBUG_PRINTLN(TRIM, "RESULT INITIAL: " << result) 
 
    // Normally we use the standard STL iterators, but in this case, we need to access the result collection by index since we're 
    // iterating the input collection, computing a value, and then setting the result in the output collection. We have to keep track 
    // of the index manually. 
    int toTrimIndex = 0; 
 
    for (NodeDeque::iterator seqsesIter = seqses.collection()->begin(), seqsesIterEnd = seqses.collection()->end(); seqsesIter != seqsesIterEnd; ++seqsesIter) { 
      Node& seqs1 = *seqsesIter; 
 
      DEBUG_PRINTLN(TRIM, "SEQS1: " << seqs1 << " " << toTrimIndex) 
 
      Node tempResult = Node::createCollection(); 
      tempResult.got_line_feed = seqs1.got_line_feed; 
 
      for (NodeDeque::iterator seqs1Iter = seqs1.collection()->begin(), seqs1EndIter = seqs1.collection()->end(); seqs1Iter != seqs1EndIter; ++seqs1Iter) { 
        Node& seq1 = *seqs1Iter; 
 
        Complex_Selector_Obj pSeq1 = nodeToComplexSelector(seq1); 
 
        // Compute the maximum specificity. This requires looking at the "sources" of the sequence. See SimpleSequence.sources in the ruby code 
        // for a good description of sources. 
        // 
        // TODO: I'm pretty sure there's a bug in the sources code. It was implemented for sass-spec's 182_test_nested_extend_loop test. 
        // While the test passes, I compared the state of each trim call to verify correctness. The last trim call had incorrect sources. We 
        // had an extra source that the ruby version did not have. Without a failing test case, this is going to be extra hard to find. My 
        // best guess at this point is that we're cloning an object somewhere and maintaining the sources when we shouldn't be. This is purely 
        // a guess though. 
        unsigned long maxSpecificity = isReplace ? pSeq1->specificity() : 0; 
        ComplexSelectorSet sources = pSeq1->sources(); 
 
        DEBUG_PRINTLN(TRIM, "TRIM SEQ1: " << seq1) 
        DEBUG_EXEC(TRIM, printSourcesSet(sources, "TRIM SOURCES: ")) 
 
        for (ComplexSelectorSet::iterator sourcesSetIterator = sources.begin(), sourcesSetIteratorEnd = sources.end(); sourcesSetIterator != sourcesSetIteratorEnd; ++sourcesSetIterator) { 
          const Complex_Selector_Obj& pCurrentSelector = *sourcesSetIterator; 
          maxSpecificity = std::max(maxSpecificity, pCurrentSelector->specificity()); 
        } 
 
        DEBUG_PRINTLN(TRIM, "MAX SPECIFICITY: " << maxSpecificity) 
 
        bool isMoreSpecificOuter = false; 
 
        int resultIndex = 0; 
 
        for (NodeDeque::iterator resultIter = result.collection()->begin(), resultIterEnd = result.collection()->end(); resultIter != resultIterEnd; ++resultIter) { 
          Node& seqs2 = *resultIter; 
 
          DEBUG_PRINTLN(TRIM, "SEQS1: " << seqs1) 
          DEBUG_PRINTLN(TRIM, "SEQS2: " << seqs2) 
 
          // Do not compare the same sequence to itself. The ruby call we're trying to 
          // emulate is: seqs1.equal?(seqs2). equal? is an object comparison, not an equivalency comparision. 
          // Since we have the same pointers in seqes and results, we can do a pointer comparision. seqs1 is 
          // derived from seqses and seqs2 is derived from result. 
          if (seqs1.collection() == seqs2.collection()) { 
            DEBUG_PRINTLN(TRIM, "CONTINUE") 
            continue; 
          } 
 
          bool isMoreSpecificInner = false; 
 
          for (NodeDeque::iterator seqs2Iter = seqs2.collection()->begin(), seqs2IterEnd = seqs2.collection()->end(); seqs2Iter != seqs2IterEnd; ++seqs2Iter) { 
            Node& seq2 = *seqs2Iter; 
 
            Complex_Selector_Obj pSeq2 = nodeToComplexSelector(seq2); 
 
            DEBUG_PRINTLN(TRIM, "SEQ2 SPEC: " << pSeq2->specificity()) 
            DEBUG_PRINTLN(TRIM, "IS SPEC: " << pSeq2->specificity() << " >= " << maxSpecificity << " " << (pSeq2->specificity() >= maxSpecificity ? "true" : "false")) 
            DEBUG_PRINTLN(TRIM, "IS SUPER: " << (pSeq2->is_superselector_of(pSeq1) ? "true" : "false")) 
 
            isMoreSpecificInner = pSeq2->specificity() >= maxSpecificity && pSeq2->is_superselector_of(pSeq1); 
 
            if (isMoreSpecificInner) { 
              DEBUG_PRINTLN(TRIM, "FOUND MORE SPECIFIC") 
              break; 
            } 
          } 
 
          // If we found something more specific, we're done. Let the outer loop know and stop iterating. 
          if (isMoreSpecificInner) { 
            isMoreSpecificOuter = true; 
            break; 
          } 
 
          resultIndex++; 
        } 
 
        if (!isMoreSpecificOuter) { 
          DEBUG_PRINTLN(TRIM, "PUSHING: " << seq1) 
          tempResult.collection()->push_back(seq1); 
        } 
 
      } 
 
      DEBUG_PRINTLN(TRIM, "RESULT BEFORE ASSIGN: " << result) 
      DEBUG_PRINTLN(TRIM, "TEMP RESULT: " << toTrimIndex << " " << tempResult) 
      (*result.collection())[toTrimIndex] = tempResult; 
 
      toTrimIndex++; 
 
      DEBUG_PRINTLN(TRIM, "RESULT: " << result) 
    } 
 
    return result; 
  } 
 
 
 
  static bool parentSuperselector(const Node& one, const Node& two) { 
    // TODO: figure out a better way to create a Complex_Selector from scratch 
    // TODO: There's got to be a better way. This got ugly quick... 
    Element_Selector_Obj fakeParent = SASS_MEMORY_NEW(Element_Selector, ParserState("[FAKE]"), "temp"); 
    Compound_Selector_Obj fakeHead = SASS_MEMORY_NEW(Compound_Selector, ParserState("[FAKE]"), 1 /*size*/); 
    fakeHead->elements().push_back(fakeParent); 
    Complex_Selector_Obj fakeParentContainer = SASS_MEMORY_NEW(Complex_Selector, ParserState("[FAKE]"), Complex_Selector::ANCESTOR_OF, fakeHead /*head*/, NULL /*tail*/); 
 
    Complex_Selector_Obj pOneWithFakeParent = nodeToComplexSelector(one); 
    pOneWithFakeParent->set_innermost(fakeParentContainer, Complex_Selector::ANCESTOR_OF); 
    Complex_Selector_Obj pTwoWithFakeParent = nodeToComplexSelector(two); 
    pTwoWithFakeParent->set_innermost(fakeParentContainer, Complex_Selector::ANCESTOR_OF); 
 
    return pOneWithFakeParent->is_superselector_of(pTwoWithFakeParent); 
  } 
 
 
  class ParentSuperselectorChunker { 
  public: 
    ParentSuperselectorChunker(Node& lcs) : mLcs(lcs) {} 
    Node& mLcs; 
 
    bool operator()(const Node& seq) const { 
      // {|s| parent_superselector?(s.first, lcs.first)} 
      if (seq.collection()->size() == 0) return false; 
      return parentSuperselector(seq.collection()->front(), mLcs.collection()->front()); 
    } 
  }; 
 
  class SubweaveEmptyChunker { 
  public: 
    bool operator()(const Node& seq) const { 
      // {|s| s.empty?} 
 
      return seq.collection()->empty(); 
    } 
  }; 
 
  /* 
  # Takes initial subsequences of `seq1` and `seq2` and returns all 
  # orderings of those subsequences. The initial subsequences are determined 
  # by a block. 
  # 
  # Destructively removes the initial subsequences of `seq1` and `seq2`. 
  # 
  # For example, given `(A B C | D E)` and `(1 2 | 3 4 5)` (with `|` 
  # denoting the boundary of the initial subsequence), this would return 
  # `[(A B C 1 2), (1 2 A B C)]`. The sequences would then be `(D E)` and 
  # `(3 4 5)`. 
  # 
  # @param seq1 [Array] 
  # @param seq2 [Array] 
  # @yield [a] Used to determine when to cut off the initial subsequences. 
  #   Called repeatedly for each sequence until it returns true. 
  # @yieldparam a [Array] A final subsequence of one input sequence after 
  #   cutting off some initial subsequence. 
  # @yieldreturn [Boolean] Whether or not to cut off the initial subsequence 
  #   here. 
  # @return [Array<Array>] All possible orderings of the initial subsequences. 
  def chunks(seq1, seq2) 
    chunk1 = [] 
    chunk1 << seq1.shift until yield seq1 
    chunk2 = [] 
    chunk2 << seq2.shift until yield seq2 
    return [] if chunk1.empty? && chunk2.empty? 
    return [chunk2] if chunk1.empty? 
    return [chunk1] if chunk2.empty? 
    [chunk1 + chunk2, chunk2 + chunk1] 
  end 
  */ 
  template<typename ChunkerType> 
  static Node chunks(Node& seq1, Node& seq2, const ChunkerType& chunker) { 
    Node chunk1 = Node::createCollection(); 
    while (seq1.collection()->size() && !chunker(seq1)) { 
      chunk1.collection()->push_back(seq1.collection()->front()); 
      seq1.collection()->pop_front(); 
    } 
 
    Node chunk2 = Node::createCollection(); 
    while (!seq2.collection()->empty() && !chunker(seq2)) { 
      chunk2.collection()->push_back(seq2.collection()->front()); 
      seq2.collection()->pop_front(); 
    } 
 
    if (chunk1.collection()->empty() && chunk2.collection()->empty()) { 
      DEBUG_PRINTLN(CHUNKS, "RETURNING BOTH EMPTY") 
      return Node::createCollection(); 
    } 
 
    if (chunk1.collection()->empty()) { 
      Node chunk2Wrapper = Node::createCollection(); 
      chunk2Wrapper.collection()->push_back(chunk2); 
      DEBUG_PRINTLN(CHUNKS, "RETURNING ONE EMPTY") 
      return chunk2Wrapper; 
    } 
 
    if (chunk2.collection()->empty()) { 
      Node chunk1Wrapper = Node::createCollection(); 
      chunk1Wrapper.collection()->push_back(chunk1); 
      DEBUG_PRINTLN(CHUNKS, "RETURNING TWO EMPTY") 
      return chunk1Wrapper; 
    } 
 
    Node perms = Node::createCollection(); 
 
    Node firstPermutation = Node::createCollection(); 
    firstPermutation.collection()->insert(firstPermutation.collection()->end(), chunk1.collection()->begin(), chunk1.collection()->end()); 
    firstPermutation.collection()->insert(firstPermutation.collection()->end(), chunk2.collection()->begin(), chunk2.collection()->end()); 
    perms.collection()->push_back(firstPermutation); 
 
    Node secondPermutation = Node::createCollection(); 
    secondPermutation.collection()->insert(secondPermutation.collection()->end(), chunk2.collection()->begin(), chunk2.collection()->end()); 
    secondPermutation.collection()->insert(secondPermutation.collection()->end(), chunk1.collection()->begin(), chunk1.collection()->end()); 
    perms.collection()->push_back(secondPermutation); 
 
    DEBUG_PRINTLN(CHUNKS, "RETURNING PERM") 
 
    return perms; 
  } 
 
 
  static Node groupSelectors(Node& seq) { 
    Node newSeq = Node::createCollection(); 
 
    Node tail = Node::createCollection(); 
    tail.plus(seq); 
 
    while (!tail.collection()->empty()) { 
      Node head = Node::createCollection(); 
 
      do { 
        head.collection()->push_back(tail.collection()->front()); 
        tail.collection()->pop_front(); 
      } while (!tail.collection()->empty() && (head.collection()->back().isCombinator() || tail.collection()->front().isCombinator())); 
 
      newSeq.collection()->push_back(head); 
    } 
 
    return newSeq; 
  } 
 
 
  static void getAndRemoveInitialOps(Node& seq, Node& ops) { 
    NodeDeque& seqCollection = *(seq.collection()); 
    NodeDeque& opsCollection = *(ops.collection()); 
 
    while (seqCollection.size() > 0 && seqCollection.front().isCombinator()) { 
      opsCollection.push_back(seqCollection.front()); 
      seqCollection.pop_front(); 
    } 
  } 
 
 
  static void getAndRemoveFinalOps(Node& seq, Node& ops) { 
    NodeDeque& seqCollection = *(seq.collection()); 
    NodeDeque& opsCollection = *(ops.collection()); 
 
    while (seqCollection.size() > 0 && seqCollection.back().isCombinator()) { 
      opsCollection.push_back(seqCollection.back()); // Purposefully reversed to match ruby code 
      seqCollection.pop_back(); 
    } 
  } 
 
 
  /* 
      def merge_initial_ops(seq1, seq2) 
        ops1, ops2 = [], [] 
        ops1 << seq1.shift while seq1.first.is_a?(String) 
        ops2 << seq2.shift while seq2.first.is_a?(String) 
 
        newline = false 
        newline ||= !!ops1.shift if ops1.first == "\n" 
        newline ||= !!ops2.shift if ops2.first == "\n" 
 
        # If neither sequence is a subsequence of the other, they cannot be 
        # merged successfully 
        lcs = Sass::Util.lcs(ops1, ops2) 
        return unless lcs == ops1 || lcs == ops2 
        return (newline ? ["\n"] : []) + (ops1.size > ops2.size ? ops1 : ops2) 
      end 
  */ 
  static Node mergeInitialOps(Node& seq1, Node& seq2) { 
    Node ops1 = Node::createCollection(); 
    Node ops2 = Node::createCollection(); 
 
    getAndRemoveInitialOps(seq1, ops1); 
    getAndRemoveInitialOps(seq2, ops2); 
 
    // TODO: Do we have this information available to us? 
    // newline = false 
    // newline ||= !!ops1.shift if ops1.first == "\n" 
    // newline ||= !!ops2.shift if ops2.first == "\n" 
 
    // If neither sequence is a subsequence of the other, they cannot be merged successfully 
    DefaultLcsComparator lcsDefaultComparator; 
    Node opsLcs = lcs(ops1, ops2, lcsDefaultComparator); 
 
    if (!(opsLcs == ops1 || opsLcs == ops2)) { 
      return Node::createNil(); 
    } 
 
    // TODO: more newline logic 
    // return (newline ? ["\n"] : []) + (ops1.size > ops2.size ? ops1 : ops2) 
 
    return (ops1.collection()->size() > ops2.collection()->size() ? ops1 : ops2); 
  } 
 
 
  /* 
      def merge_final_ops(seq1, seq2, res = []) 
 
 
        # This code looks complicated, but it's actually just a bunch of special 
        # cases for interactions between different combinators. 
        op1, op2 = ops1.first, ops2.first 
        if op1 && op2 
          sel1 = seq1.pop 
          sel2 = seq2.pop 
          if op1 == '~' && op2 == '~' 
            if sel1.superselector?(sel2) 
              res.unshift sel2, '~' 
            elsif sel2.superselector?(sel1) 
              res.unshift sel1, '~' 
            else 
              merged = sel1.unify(sel2.members, sel2.subject?) 
              res.unshift [ 
                [sel1, '~', sel2, '~'], 
                [sel2, '~', sel1, '~'], 
                ([merged, '~'] if merged) 
              ].compact 
            end 
          elsif (op1 == '~' && op2 == '+') || (op1 == '+' && op2 == '~') 
            if op1 == '~' 
              tilde_sel, plus_sel = sel1, sel2 
            else 
              tilde_sel, plus_sel = sel2, sel1 
            end 
 
            if tilde_sel.superselector?(plus_sel) 
              res.unshift plus_sel, '+' 
            else 
              merged = plus_sel.unify(tilde_sel.members, tilde_sel.subject?) 
              res.unshift [ 
                [tilde_sel, '~', plus_sel, '+'], 
                ([merged, '+'] if merged) 
              ].compact 
            end 
          elsif op1 == '>' && %w[~ +].include?(op2) 
            res.unshift sel2, op2 
            seq1.push sel1, op1 
          elsif op2 == '>' && %w[~ +].include?(op1) 
            res.unshift sel1, op1 
            seq2.push sel2, op2 
          elsif op1 == op2 
            return unless merged = sel1.unify(sel2.members, sel2.subject?) 
            res.unshift merged, op1 
          else 
            # Unknown selector combinators can't be unified 
            return 
          end 
          return merge_final_ops(seq1, seq2, res) 
        elsif op1 
          seq2.pop if op1 == '>' && seq2.last && seq2.last.superselector?(seq1.last) 
          res.unshift seq1.pop, op1 
          return merge_final_ops(seq1, seq2, res) 
        else # op2 
          seq1.pop if op2 == '>' && seq1.last && seq1.last.superselector?(seq2.last) 
          res.unshift seq2.pop, op2 
          return merge_final_ops(seq1, seq2, res) 
        end 
      end 
  */ 
  static Node mergeFinalOps(Node& seq1, Node& seq2, Node& res) { 
 
    Node ops1 = Node::createCollection(); 
    Node ops2 = Node::createCollection(); 
 
    getAndRemoveFinalOps(seq1, ops1); 
    getAndRemoveFinalOps(seq2, ops2); 
 
    // TODO: do we have newlines to remove? 
    // ops1.reject! {|o| o == "\n"} 
    // ops2.reject! {|o| o == "\n"} 
 
    if (ops1.collection()->empty() && ops2.collection()->empty()) { 
      return res; 
    } 
 
    if (ops1.collection()->size() > 1 || ops2.collection()->size() > 1) { 
      DefaultLcsComparator lcsDefaultComparator; 
      Node opsLcs = lcs(ops1, ops2, lcsDefaultComparator); 
 
      // If there are multiple operators, something hacky's going on. If one is a supersequence of the other, use that, otherwise give up. 
 
      if (!(opsLcs == ops1 || opsLcs == ops2)) { 
        return Node::createNil(); 
      } 
 
      if (ops1.collection()->size() > ops2.collection()->size()) { 
        res.collection()->insert(res.collection()->begin(), ops1.collection()->rbegin(), ops1.collection()->rend()); 
      } else { 
        res.collection()->insert(res.collection()->begin(), ops2.collection()->rbegin(), ops2.collection()->rend()); 
      } 
 
      return res; 
    } 
 
    if (!ops1.collection()->empty() && !ops2.collection()->empty()) { 
 
      Node op1 = ops1.collection()->front(); 
      Node op2 = ops2.collection()->front(); 
 
      Node sel1 = seq1.collection()->back(); 
      seq1.collection()->pop_back(); 
 
      Node sel2 = seq2.collection()->back(); 
      seq2.collection()->pop_back(); 
 
      if (op1.combinator() == Complex_Selector::PRECEDES && op2.combinator() == Complex_Selector::PRECEDES) { 
 
        if (sel1.selector()->is_superselector_of(sel2.selector())) { 
 
          res.collection()->push_front(op1 /*PRECEDES - could have been op2 as well*/); 
          res.collection()->push_front(sel2); 
 
        } else if (sel2.selector()->is_superselector_of(sel1.selector())) { 
 
          res.collection()->push_front(op1 /*PRECEDES - could have been op2 as well*/); 
          res.collection()->push_front(sel1); 
 
        } else { 
 
          DEBUG_PRINTLN(ALL, "sel1: " << sel1) 
          DEBUG_PRINTLN(ALL, "sel2: " << sel2) 
 
          Complex_Selector_Obj pMergedWrapper = SASS_MEMORY_CLONE(sel1.selector()); // Clone the Complex_Selector to get back to something we can transform to a node once we replace the head with the unification result 
          // TODO: does subject matter? Ruby: return unless merged = sel1.unify(sel2.members, sel2.subject?) 
          Compound_Selector_Ptr pMerged = sel1.selector()->head()->unify_with(sel2.selector()->head()); 
          pMergedWrapper->head(pMerged); 
 
          DEBUG_EXEC(ALL, printCompoundSelector(pMerged, "MERGED: ")) 
 
          Node newRes = Node::createCollection(); 
 
          Node firstPerm = Node::createCollection(); 
          firstPerm.collection()->push_back(sel1); 
          firstPerm.collection()->push_back(Node::createCombinator(Complex_Selector::PRECEDES)); 
          firstPerm.collection()->push_back(sel2); 
          firstPerm.collection()->push_back(Node::createCombinator(Complex_Selector::PRECEDES)); 
          newRes.collection()->push_back(firstPerm); 
 
          Node secondPerm = Node::createCollection(); 
          secondPerm.collection()->push_back(sel2); 
          secondPerm.collection()->push_back(Node::createCombinator(Complex_Selector::PRECEDES)); 
          secondPerm.collection()->push_back(sel1); 
          secondPerm.collection()->push_back(Node::createCombinator(Complex_Selector::PRECEDES)); 
          newRes.collection()->push_back(secondPerm); 
 
          if (pMerged) { 
            Node mergedPerm = Node::createCollection(); 
            mergedPerm.collection()->push_back(Node::createSelector(pMergedWrapper)); 
            mergedPerm.collection()->push_back(Node::createCombinator(Complex_Selector::PRECEDES)); 
            newRes.collection()->push_back(mergedPerm); 
          } 
 
          res.collection()->push_front(newRes); 
 
          DEBUG_PRINTLN(ALL, "RESULT: " << res) 
 
        } 
 
      } else if (((op1.combinator() == Complex_Selector::PRECEDES && op2.combinator() == Complex_Selector::ADJACENT_TO)) || ((op1.combinator() == Complex_Selector::ADJACENT_TO && op2.combinator() == Complex_Selector::PRECEDES))) { 
 
          Node tildeSel = sel1; 
          Node plusSel = sel2; 
          Node plusOp = op2; 
          if (op1.combinator() != Complex_Selector::PRECEDES) { 
            tildeSel = sel2; 
            plusSel = sel1; 
            plusOp = op1; 
          } 
 
          if (tildeSel.selector()->is_superselector_of(plusSel.selector())) { 
 
            res.collection()->push_front(plusOp); 
            res.collection()->push_front(plusSel); 
 
          } else { 
 
            DEBUG_PRINTLN(ALL, "PLUS SEL: " << plusSel) 
            DEBUG_PRINTLN(ALL, "TILDE SEL: " << tildeSel) 
 
            Complex_Selector_Obj pMergedWrapper = SASS_MEMORY_CLONE(plusSel.selector()); // Clone the Complex_Selector to get back to something we can transform to a node once we replace the head with the unification result 
            // TODO: does subject matter? Ruby: merged = plus_sel.unify(tilde_sel.members, tilde_sel.subject?) 
            Compound_Selector_Ptr pMerged = plusSel.selector()->head()->unify_with(tildeSel.selector()->head()); 
            pMergedWrapper->head(pMerged); 
 
            DEBUG_EXEC(ALL, printCompoundSelector(pMerged, "MERGED: ")) 
 
            Node newRes = Node::createCollection(); 
 
            Node firstPerm = Node::createCollection(); 
            firstPerm.collection()->push_back(tildeSel); 
            firstPerm.collection()->push_back(Node::createCombinator(Complex_Selector::PRECEDES)); 
            firstPerm.collection()->push_back(plusSel); 
            firstPerm.collection()->push_back(Node::createCombinator(Complex_Selector::ADJACENT_TO)); 
            newRes.collection()->push_back(firstPerm); 
 
            if (pMerged) { 
              Node mergedPerm = Node::createCollection(); 
              mergedPerm.collection()->push_back(Node::createSelector(pMergedWrapper)); 
              mergedPerm.collection()->push_back(Node::createCombinator(Complex_Selector::ADJACENT_TO)); 
              newRes.collection()->push_back(mergedPerm); 
            } 
 
            res.collection()->push_front(newRes); 
 
            DEBUG_PRINTLN(ALL, "RESULT: " << res) 
 
          } 
      } else if (op1.combinator() == Complex_Selector::PARENT_OF && (op2.combinator() == Complex_Selector::PRECEDES || op2.combinator() == Complex_Selector::ADJACENT_TO)) { 
 
        res.collection()->push_front(op2); 
        res.collection()->push_front(sel2); 
 
        seq1.collection()->push_back(sel1); 
        seq1.collection()->push_back(op1); 
 
      } else if (op2.combinator() == Complex_Selector::PARENT_OF && (op1.combinator() == Complex_Selector::PRECEDES || op1.combinator() == Complex_Selector::ADJACENT_TO)) { 
 
        res.collection()->push_front(op1); 
        res.collection()->push_front(sel1); 
 
        seq2.collection()->push_back(sel2); 
        seq2.collection()->push_back(op2); 
 
      } else if (op1.combinator() == op2.combinator()) { 
 
        DEBUG_PRINTLN(ALL, "sel1: " << sel1) 
        DEBUG_PRINTLN(ALL, "sel2: " << sel2) 
 
        Complex_Selector_Obj pMergedWrapper = SASS_MEMORY_CLONE(sel1.selector()); // Clone the Complex_Selector to get back to something we can transform to a node once we replace the head with the unification result 
        // TODO: does subject matter? Ruby: return unless merged = sel1.unify(sel2.members, sel2.subject?) 
        Compound_Selector_Ptr pMerged = sel1.selector()->head()->unify_with(sel2.selector()->head()); 
        pMergedWrapper->head(pMerged); 
 
        DEBUG_EXEC(ALL, printCompoundSelector(pMerged, "MERGED: ")) 
 
        if (!pMerged) { 
          return Node::createNil(); 
        } 
 
        res.collection()->push_front(op1); 
        res.collection()->push_front(Node::createSelector(pMergedWrapper)); 
 
        DEBUG_PRINTLN(ALL, "RESULT: " << res) 
 
      } else { 
        return Node::createNil(); 
      } 
 
      return mergeFinalOps(seq1, seq2, res); 
 
    } else if (!ops1.collection()->empty()) { 
 
      Node op1 = ops1.collection()->front(); 
 
      if (op1.combinator() == Complex_Selector::PARENT_OF && !seq2.collection()->empty() && seq2.collection()->back().selector()->is_superselector_of(seq1.collection()->back().selector())) { 
        seq2.collection()->pop_back(); 
      } 
 
      // TODO: consider unshift(NodeCollection, Node) 
      res.collection()->push_front(op1); 
      res.collection()->push_front(seq1.collection()->back()); 
      seq1.collection()->pop_back(); 
 
      return mergeFinalOps(seq1, seq2, res); 
 
    } else { // !ops2.collection()->empty() 
 
      Node op2 = ops2.collection()->front(); 
 
      if (op2.combinator() == Complex_Selector::PARENT_OF && !seq1.collection()->empty() && seq1.collection()->back().selector()->is_superselector_of(seq2.collection()->back().selector())) { 
        seq1.collection()->pop_back(); 
      } 
 
      res.collection()->push_front(op2); 
      res.collection()->push_front(seq2.collection()->back()); 
      seq2.collection()->pop_back(); 
 
      return mergeFinalOps(seq1, seq2, res); 
 
    } 
 
  } 
 
 
  /* 
    This is the equivalent of ruby's Sequence.subweave. 
 
    Here is the original subweave code for reference during porting. 
 
      def subweave(seq1, seq2) 
        return [seq2] if seq1.empty? 
        return [seq1] if seq2.empty? 
 
        seq1, seq2 = seq1.dup, seq2.dup 
        return unless init = merge_initial_ops(seq1, seq2) 
        return unless fin = merge_final_ops(seq1, seq2) 
        seq1 = group_selectors(seq1) 
        seq2 = group_selectors(seq2) 
        lcs = Sass::Util.lcs(seq2, seq1) do |s1, s2| 
          next s1 if s1 == s2 
          next unless s1.first.is_a?(SimpleSequence) && s2.first.is_a?(SimpleSequence) 
          next s2 if parent_superselector?(s1, s2) 
          next s1 if parent_superselector?(s2, s1) 
        end 
 
        diff = [[init]] 
        until lcs.empty? 
          diff << chunks(seq1, seq2) {|s| parent_superselector?(s.first, lcs.first)} << [lcs.shift] 
          seq1.shift 
          seq2.shift 
        end 
        diff << chunks(seq1, seq2) {|s| s.empty?} 
        diff += fin.map {|sel| sel.is_a?(Array) ? sel : [sel]} 
        diff.reject! {|c| c.empty?} 
 
        result = Sass::Util.paths(diff).map {|p| p.flatten}.reject {|p| path_has_two_subjects?(p)} 
 
        result 
      end 
  */ 
  Node subweave(Node& one, Node& two) { 
    // Check for the simple cases 
    if (one.collection()->size() == 0) { 
      Node out = Node::createCollection(); 
      out.collection()->push_back(two); 
      return out; 
    } 
    if (two.collection()->size() == 0) { 
      Node out = Node::createCollection(); 
      out.collection()->push_back(one); 
      return out; 
    } 
 
    Node seq1 = Node::createCollection(); 
    seq1.plus(one); 
    Node seq2 = Node::createCollection(); 
    seq2.plus(two); 
 
    DEBUG_PRINTLN(SUBWEAVE, "SUBWEAVE ONE: " << seq1) 
    DEBUG_PRINTLN(SUBWEAVE, "SUBWEAVE TWO: " << seq2) 
 
    Node init = mergeInitialOps(seq1, seq2); 
    if (init.isNil()) { 
      return Node::createNil(); 
    } 
 
    DEBUG_PRINTLN(SUBWEAVE, "INIT: " << init) 
 
    Node res = Node::createCollection(); 
    Node fin = mergeFinalOps(seq1, seq2, res); 
    if (fin.isNil()) { 
      return Node::createNil(); 
    } 
 
    DEBUG_PRINTLN(SUBWEAVE, "FIN: " << fin) 
 
 
    // Moving this line up since fin isn't modified between now and when it happened before 
    // fin.map {|sel| sel.is_a?(Array) ? sel : [sel]} 
 
    for (NodeDeque::iterator finIter = fin.collection()->begin(), finEndIter = fin.collection()->end(); 
           finIter != finEndIter; ++finIter) { 
 
      Node& childNode = *finIter; 
 
      if (!childNode.isCollection()) { 
        Node wrapper = Node::createCollection(); 
        wrapper.collection()->push_back(childNode); 
        childNode = wrapper; 
      } 
 
    } 
 
    DEBUG_PRINTLN(SUBWEAVE, "FIN MAPPED: " << fin) 
 
 
 
    Node groupSeq1 = groupSelectors(seq1); 
    DEBUG_PRINTLN(SUBWEAVE, "SEQ1: " << groupSeq1) 
 
    Node groupSeq2 = groupSelectors(seq2); 
    DEBUG_PRINTLN(SUBWEAVE, "SEQ2: " << groupSeq2) 
 
 
    ComplexSelectorDeque groupSeq1Converted; 
    nodeToComplexSelectorDeque(groupSeq1, groupSeq1Converted); 
 
    ComplexSelectorDeque groupSeq2Converted; 
    nodeToComplexSelectorDeque(groupSeq2, groupSeq2Converted); 
 
    ComplexSelectorDeque out; 
    LcsCollectionComparator collectionComparator; 
    lcs(groupSeq2Converted, groupSeq1Converted, collectionComparator, out); 
    Node seqLcs = complexSelectorDequeToNode(out); 
 
    DEBUG_PRINTLN(SUBWEAVE, "SEQLCS: " << seqLcs) 
 
 
    Node initWrapper = Node::createCollection(); 
    initWrapper.collection()->push_back(init); 
    Node diff = Node::createCollection(); 
    diff.collection()->push_back(initWrapper); 
 
    DEBUG_PRINTLN(SUBWEAVE, "DIFF INIT: " << diff) 
 
 
    while (!seqLcs.collection()->empty()) { 
      ParentSuperselectorChunker superselectorChunker(seqLcs); 
      Node chunksResult = chunks(groupSeq1, groupSeq2, superselectorChunker); 
      diff.collection()->push_back(chunksResult); 
 
      Node lcsWrapper = Node::createCollection(); 
      lcsWrapper.collection()->push_back(seqLcs.collection()->front()); 
      seqLcs.collection()->pop_front(); 
      diff.collection()->push_back(lcsWrapper); 
 
      if (groupSeq1.collection()->size()) groupSeq1.collection()->pop_front(); 
      if (groupSeq2.collection()->size()) groupSeq2.collection()->pop_front(); 
    } 
 
    DEBUG_PRINTLN(SUBWEAVE, "DIFF POST LCS: " << diff) 
 
 
    DEBUG_PRINTLN(SUBWEAVE, "CHUNKS: ONE=" << groupSeq1 << " TWO=" << groupSeq2) 
 
 
    SubweaveEmptyChunker emptyChunker; 
    Node chunksResult = chunks(groupSeq1, groupSeq2, emptyChunker); 
    diff.collection()->push_back(chunksResult); 
 
 
    DEBUG_PRINTLN(SUBWEAVE, "DIFF POST CHUNKS: " << diff) 
 
 
    diff.collection()->insert(diff.collection()->end(), fin.collection()->begin(), fin.collection()->end()); 
 
    DEBUG_PRINTLN(SUBWEAVE, "DIFF POST FIN MAPPED: " << diff) 
 
    // JMA - filter out the empty nodes (use a new collection, since iterator erase() invalidates the old collection) 
    Node diffFiltered = Node::createCollection(); 
    for (NodeDeque::iterator diffIter = diff.collection()->begin(), diffEndIter = diff.collection()->end(); 
           diffIter != diffEndIter; ++diffIter) { 
      Node& node = *diffIter; 
      if (node.collection() && !node.collection()->empty()) { 
        diffFiltered.collection()->push_back(node); 
      } 
    } 
    diff = diffFiltered; 
 
    DEBUG_PRINTLN(SUBWEAVE, "DIFF POST REJECT: " << diff) 
 
 
    Node pathsResult = paths(diff); 
 
    DEBUG_PRINTLN(SUBWEAVE, "PATHS: " << pathsResult) 
 
 
    // We're flattening in place 
    for (NodeDeque::iterator pathsIter = pathsResult.collection()->begin(), pathsEndIter = pathsResult.collection()->end(); 
      pathsIter != pathsEndIter; ++pathsIter) { 
 
      Node& child = *pathsIter; 
      child = flatten(child); 
    } 
 
    DEBUG_PRINTLN(SUBWEAVE, "FLATTENED: " << pathsResult) 
 
 
    /* 
      TODO: implement 
      rejected = mapped.reject {|p| path_has_two_subjects?(p)} 
      $stderr.puts "REJECTED: #{rejected}" 
     */ 
 
 
    return pathsResult; 
 
  } 
  /* 
  // disabled to avoid clang warning [-Wunused-function] 
  static Node subweaveNaive(const Node& one, const Node& two) { 
    Node out = Node::createCollection(); 
 
    // Check for the simple cases 
    if (one.isNil()) { 
      out.collection()->push_back(two.klone()); 
    } else if (two.isNil()) { 
      out.collection()->push_back(one.klone()); 
    } else { 
      // Do the naive implementation. pOne = A B and pTwo = C D ...yields...  A B C D and C D A B 
      // See https://gist.github.com/nex3/7609394 for details. 
 
      Node firstPerm = one.klone(); 
      Node twoCloned = two.klone(); 
      firstPerm.plus(twoCloned); 
      out.collection()->push_back(firstPerm); 
 
      Node secondPerm = two.klone(); 
      Node oneCloned = one.klone(); 
      secondPerm.plus(oneCloned ); 
      out.collection()->push_back(secondPerm); 
    } 
 
    return out; 
  } 
  */ 
 
 
  /* 
   This is the equivalent of ruby's Sequence.weave. 
 
   The following is the modified version of the ruby code that was more portable to C++. You 
   should be able to drop it into ruby 3.2.19 and get the same results from ruby sass. 
 
      def weave(path) 
        # This function works by moving through the selector path left-to-right, 
        # building all possible prefixes simultaneously. These prefixes are 
        # `befores`, while the remaining parenthesized suffixes is `afters`. 
        befores = [[]] 
        afters = path.dup 
 
        until afters.empty? 
          current = afters.shift.dup 
          last_current = [current.pop] 
 
          tempResult = [] 
 
          for before in befores do 
            sub = subweave(before, current) 
            if sub.nil? 
              next 
            end 
 
            for seqs in sub do 
              tempResult.push(seqs + last_current) 
            end 
          end 
 
          befores = tempResult 
 
        end 
 
        return befores 
      end 
   */ 
  /* 
      def weave(path) 
        befores = [[]] 
        afters = path.dup 
 
        until afters.empty? 
          current = afters.shift.dup 
 
          last_current = [current.pop] 
 
 
          tempResult = [] 
 
          for before in befores do 
            sub = subweave(before, current) 
 
            if sub.nil? 
              next [] 
            end 
 
 
            for seqs in sub do 
              toPush = seqs + last_current 
 
              tempResult.push(seqs + last_current) 
            end 
 
          end 
 
          befores = tempResult 
 
        end 
 
        return befores 
      end 
  */ 
  Node Extend::weave(Node& path) { 
 
    DEBUG_PRINTLN(WEAVE, "WEAVE: " << path) 
 
    Node befores = Node::createCollection(); 
    befores.collection()->push_back(Node::createCollection()); 
 
    Node afters = Node::createCollection(); 
    afters.plus(path); 
 
    while (!afters.collection()->empty()) { 
      Node current = afters.collection()->front().klone(); 
      afters.collection()->pop_front(); 
      DEBUG_PRINTLN(WEAVE, "CURRENT: " << current) 
      if (current.collection()->size() == 0) continue; 
 
      Node last_current = Node::createCollection(); 
      last_current.collection()->push_back(current.collection()->back()); 
      current.collection()->pop_back(); 
      DEBUG_PRINTLN(WEAVE, "CURRENT POST POP: " << current) 
      DEBUG_PRINTLN(WEAVE, "LAST CURRENT: " << last_current) 
 
      Node tempResult = Node::createCollection(); 
 
      for (NodeDeque::iterator beforesIter = befores.collection()->begin(), beforesEndIter = befores.collection()->end(); beforesIter != beforesEndIter; beforesIter++) { 
        Node& before = *beforesIter; 
 
        Node sub = subweave(before, current); 
 
        DEBUG_PRINTLN(WEAVE, "SUB: " << sub) 
 
        if (sub.isNil()) { 
          return Node::createCollection(); 
        } 
 
        for (NodeDeque::iterator subIter = sub.collection()->begin(), subEndIter = sub.collection()->end(); subIter != subEndIter; subIter++) { 
          Node& seqs = *subIter; 
 
          Node toPush = Node::createCollection(); 
          toPush.plus(seqs); 
          toPush.plus(last_current); 
 
          // move line feed from inner to outer selector (very hacky indeed) 
          if (last_current.collection() && last_current.collection()->front().selector()) { 
            toPush.got_line_feed = last_current.collection()->front().got_line_feed; 
            last_current.collection()->front().selector()->has_line_feed(false); 
            last_current.collection()->front().got_line_feed = false; 
          } 
 
          tempResult.collection()->push_back(toPush); 
 
        } 
      } 
 
      befores = tempResult; 
 
    } 
 
    return befores; 
  } 
 
 
 
  /* 
   This is the equivalent of ruby's SimpleSequence.do_extend. 
 
    // TODO: I think I have some modified ruby code to put here. Check. 
  */ 
  /* 
   ISSUES: 
   - Previous TODO: Do we need to group the results by extender? 
   - What does subject do in?: next unless unified = seq.members.last.unify(self_without_sel, subject?) 
   - IMPROVEMENT: The search for uniqueness at the end is not ideal since it's has to loop over everything... 
   - IMPROVEMENT: Check if the final search for uniqueness is doing anything that extendComplexSelector isn't already doing... 
   */ 
  template<typename KeyType> 
  class GroupByToAFunctor { 
  public: 
    KeyType operator()(SubSetMapPair& extPair) const { 
      Complex_Selector_Obj pSelector = extPair.first; 
      return pSelector; 
    } 
  }; 
  Node Extend::extendCompoundSelector(Compound_Selector_Ptr pSelector, CompoundSelectorSet& seen, bool isReplace) { 
 
    /* this turned out to be too much overhead 
       probably due to holding a "Node" object 
    // check if we already extended this selector 
    // we can do this since subset_map is "static" 
    auto memoized = memoizeCompound.find(pSelector); 
    if (memoized != memoizeCompound.end()) { 
      return memoized->second.klone(); 
    } 
    */ 
 
    DEBUG_EXEC(EXTEND_COMPOUND, printCompoundSelector(pSelector, "EXTEND COMPOUND: ")) 
    // TODO: Ruby has another loop here to skip certain members? 
 
    // let RESULTS be an empty list of complex selectors 
    Node results = Node::createCollection(); 
    // extendedSelectors.got_line_feed = true; 
 
    SubSetMapPairs entries = subset_map.get_v(pSelector); 
 
    GroupByToAFunctor<Complex_Selector_Obj> extPairKeyFunctor; 
    SubSetMapResults arr; 
    group_by_to_a(entries, extPairKeyFunctor, arr); 
 
    SubSetMapLookups holder; 
 
    // for each (EXTENDER, TARGET) in MAP.get(COMPOUND): 
    for (SubSetMapResult& groupedPair : arr) { 
 
      Complex_Selector_Obj seq = groupedPair.first; 
      SubSetMapPairs& group = groupedPair.second; 
 
      DEBUG_EXEC(EXTEND_COMPOUND, printComplexSelector(seq, "SEQ: ")) 
 
      Compound_Selector_Obj pSels = SASS_MEMORY_NEW(Compound_Selector, pSelector->pstate()); 
      for (SubSetMapPair& pair : group) { 
        pair.second->extended(true); 
        pSels->concat(pair.second); 
      } 
 
      DEBUG_EXEC(EXTEND_COMPOUND, printCompoundSelector(pSels, "SELS: ")) 
 
      // The selector up to where the @extend is (ie, the thing to merge) 
      Complex_Selector_Ptr pExtComplexSelector = seq; 
 
      // TODO: This can return a Compound_Selector with no elements. Should that just be returning NULL? 
      // RUBY: self_without_sel = Sass::Util.array_minus(members, sels) 
      Compound_Selector_Obj pSelectorWithoutExtendSelectors = pSelector->minus(pSels); 
 
      DEBUG_EXEC(EXTEND_COMPOUND, printCompoundSelector(pSelector, "MEMBERS: ")) 
      DEBUG_EXEC(EXTEND_COMPOUND, printCompoundSelector(pSelectorWithoutExtendSelectors, "SELF_WO_SEL: ")) 
 
      Compound_Selector_Obj pInnermostCompoundSelector = pExtComplexSelector->last()->head(); 
 
      if (!pInnermostCompoundSelector) { 
        pInnermostCompoundSelector = SASS_MEMORY_NEW(Compound_Selector, pSelector->pstate()); 
      } 
      Compound_Selector_Obj pUnifiedSelector = pInnermostCompoundSelector->unify_with(pSelectorWithoutExtendSelectors); 
 
      DEBUG_EXEC(EXTEND_COMPOUND, printCompoundSelector(pInnermostCompoundSelector, "LHS: ")) 
      DEBUG_EXEC(EXTEND_COMPOUND, printCompoundSelector(pSelectorWithoutExtendSelectors, "RHS: ")) 
      DEBUG_EXEC(EXTEND_COMPOUND, printCompoundSelector(pUnifiedSelector, "UNIFIED: ")) 
 
      // RUBY: next unless unified 
      if (!pUnifiedSelector || pUnifiedSelector->length() == 0) { 
        continue; 
      } 
 
      // TODO: implement the parent directive match (if necessary based on test failures) 
      // next if group.map {|e, _| check_directives_match!(e, parent_directives)}.none? 
 
      // TODO: This seems a little fishy to me. See if it causes any problems. From the ruby, we should be able to just 
      // get rid of the last Compound_Selector and replace it with this one. I think the reason this code is more 
      // complex is that Complex_Selector contains a combinator, but in ruby combinators have already been filtered 
      // out and aren't operated on. 
      Complex_Selector_Obj pNewSelector = SASS_MEMORY_CLONE(pExtComplexSelector); // ->first(); 
 
      Complex_Selector_Obj pNewInnerMost = SASS_MEMORY_NEW(Complex_Selector, pSelector->pstate(), Complex_Selector::ANCESTOR_OF, pUnifiedSelector, NULL); 
 
      Complex_Selector::Combinator combinator = pNewSelector->clear_innermost(); 
      pNewSelector->set_innermost(pNewInnerMost, combinator); 
 
#ifdef DEBUG 
      ComplexSelectorSet debugSet; 
      debugSet = pNewSelector->sources(); 
      if (debugSet.size() > 0) { 
        throw std::runtime_error("The new selector should start with no sources. Something needs to be cloned to fix this."); 
      } 
      debugSet = pExtComplexSelector->sources(); 
      if (debugSet.size() > 0) { 
        throw std::runtime_error("The extension selector from our subset map should not have sources. These will bleed to the new selector. Something needs to be cloned to fix this."); 
      } 
#endif 
 
 
      // if (pSelector && pSelector->has_line_feed()) pNewInnerMost->has_line_feed(true); 
      // Set the sources on our new Complex_Selector to the sources of this simple sequence plus the thing we're extending. 
      DEBUG_PRINTLN(EXTEND_COMPOUND, "SOURCES SETTING ON NEW SEQ: " << complexSelectorToNode(pNewSelector)) 
 
      DEBUG_EXEC(EXTEND_COMPOUND, ComplexSelectorSet oldSet = pNewSelector->sources(); printSourcesSet(oldSet, "SOURCES NEW SEQ BEGIN: ")) 
 
      // I actually want to create a copy here (performance!) 
      ComplexSelectorSet newSourcesSet = pSelector->sources(); // XXX 
      DEBUG_EXEC(EXTEND_COMPOUND, printSourcesSet(newSourcesSet, "SOURCES THIS EXTEND: ")) 
 
      newSourcesSet.insert(pExtComplexSelector); 
      DEBUG_EXEC(EXTEND_COMPOUND, printSourcesSet(newSourcesSet, "SOURCES WITH NEW SOURCE: ")) 
 
      // RUBY: new_seq.add_sources!(sources + [seq]) 
      pNewSelector->addSources(newSourcesSet); 
 
      DEBUG_EXEC(EXTEND_COMPOUND, ComplexSelectorSet newSet = pNewSelector->sources(); printSourcesSet(newSet, "SOURCES ON NEW SELECTOR AFTER ADD: ")) 
      DEBUG_EXEC(EXTEND_COMPOUND, printSourcesSet(pSelector->sources(), "SOURCES THIS EXTEND WHICH SHOULD BE SAME STILL: ")) 
 
 
      if (pSels->has_line_feed()) pNewSelector->has_line_feed(true); 
 
      holder.push_back(std::make_pair(pSels, pNewSelector)); 
    } 
 
 
    for (SubSetMapLookup& pair : holder) { 
 
      Compound_Selector_Obj pSels = pair.first; 
      Complex_Selector_Obj pNewSelector = pair.second; 
 
 
      // RUBY??: next [] if seen.include?(sels) 
      if (seen.find(pSels) != seen.end()) { 
        continue; 
      } 
 
 
      CompoundSelectorSet recurseSeen(seen); 
      recurseSeen.insert(pSels); 
 
 
      DEBUG_PRINTLN(EXTEND_COMPOUND, "RECURSING DO EXTEND: " << complexSelectorToNode(pNewSelector)) 
      Node recurseExtendedSelectors = extendComplexSelector(pNewSelector, recurseSeen, isReplace, false); // !:isOriginal 
 
      DEBUG_PRINTLN(EXTEND_COMPOUND, "RECURSING DO EXTEND RETURN: " << recurseExtendedSelectors) 
 
      for (NodeDeque::iterator iterator = recurseExtendedSelectors.collection()->begin(), endIterator = recurseExtendedSelectors.collection()->end(); 
           iterator != endIterator; ++iterator) { 
        Node newSelector = *iterator; 
 
//        DEBUG_PRINTLN(EXTEND_COMPOUND, "EXTENDED AT THIS POINT: " << results) 
//        DEBUG_PRINTLN(EXTEND_COMPOUND, "SELECTOR EXISTS ALREADY: " << newSelector << " " << results.contains(newSelector, false /*simpleSelectorOrderDependent*/)); 
 
        if (!results.contains(newSelector)) { 
//          DEBUG_PRINTLN(EXTEND_COMPOUND, "ADDING NEW SELECTOR") 
          results.collection()->push_back(newSelector); 
        } 
      } 
    } 
 
    DEBUG_EXEC(EXTEND_COMPOUND, printCompoundSelector(pSelector, "EXTEND COMPOUND END: ")) 
 
    // this turned out to be too much overhead 
    // memory results in a map table - since extending is very expensive 
    // memoizeCompound.insert(std::pair<Compound_Selector_Obj, Node>(pSelector, results)); 
 
    return results; 
  } 
 
 
  // check if selector has something to be extended by subset_map 
  bool Extend::complexSelectorHasExtension(Complex_Selector_Ptr selector, CompoundSelectorSet& seen) { 
 
    bool hasExtension = false; 
 
    Complex_Selector_Obj pIter = selector; 
 
    while (!hasExtension && pIter) { 
      Compound_Selector_Obj pHead = pIter->head(); 
 
      if (pHead) { 
        SubSetMapPairs entries = subset_map.get_v(pHead); 
        for (SubSetMapPair ext : entries) { 
          // check if both selectors have the same media block parent 
          // if (ext.first->media_block() == pComplexSelector->media_block()) continue; 
          if (ext.second->media_block() == 0) continue; 
          if (pHead->media_block() && 
              ext.second->media_block()->media_queries() && 
              pHead->media_block()->media_queries() 
          ) { 
            std::string query_left(ext.second->media_block()->media_queries()->to_string()); 
            std::string query_right(pHead->media_block()->media_queries()->to_string()); 
            if (query_left == query_right) continue; 
          } 
 
          // fail if one goes across media block boundaries 
          std::stringstream err; 
          std::string cwd(Sass::File::get_cwd()); 
          ParserState pstate(ext.second->pstate()); 
          std::string rel_path(Sass::File::abs2rel(pstate.path, cwd, cwd)); 
          err << "You may not @extend an outer selector from within @media.\n"; 
          err << "You may only @extend selectors within the same directive.\n"; 
          err << "From \"@extend " << ext.second->to_string() << "\""; 
          err << " on line " << pstate.line+1 << " of " << rel_path << "\n"; 
          error(err.str(), selector->pstate()); 
        } 
        if (entries.size() > 0) hasExtension = true; 
      } 
 
      pIter = pIter->tail(); 
    } 
 
    return hasExtension; 
  } 
 
 
  /* 
   This is the equivalent of ruby's Sequence.do_extend. 
 
   // TODO: I think I have some modified ruby code to put here. Check. 
   */ 
  /* 
   ISSUES: 
   - check to automatically include combinators doesn't transfer over to libsass' data model where 
     the combinator and compound selector are one unit 
     next [[sseq_or_op]] unless sseq_or_op.is_a?(SimpleSequence) 
   */ 
  Node Extend::extendComplexSelector(Complex_Selector_Ptr selector, CompoundSelectorSet& seen, bool isReplace, bool isOriginal) { 
 
    // check if we already extended this selector 
    // we can do this since subset_map is "static" 
    auto memoized = memoizeComplex.find(selector); 
    if (memoized != memoizeComplex.end()) { 
      return memoized->second; 
    } 
 
    // convert the input selector to extend node format 
    Node complexSelector = complexSelectorToNode(selector); 
    DEBUG_PRINTLN(EXTEND_COMPLEX, "EXTEND COMPLEX: " << complexSelector) 
 
    // let CHOICES be an empty list of selector-lists 
    // create new collection to hold the results 
    Node choices = Node::createCollection(); 
 
    // for each compound selector COMPOUND in COMPLEX: 
    for (Node& sseqOrOp : *complexSelector.collection()) { 
 
      DEBUG_PRINTLN(EXTEND_COMPLEX, "LOOP: " << sseqOrOp) 
 
      // If it's not a selector (meaning it's a combinator), just include it automatically 
      // RUBY: next [[sseq_or_op]] unless sseq_or_op.is_a?(SimpleSequence) 
      if (!sseqOrOp.isSelector()) { 
        // Wrap our Combinator in two collections to match ruby. This is essentially making a collection Node 
        // with one collection child. The collection child represents a Complex_Selector that is only a combinator. 
        Node outer = Node::createCollection(); 
        Node inner = Node::createCollection(); 
        outer.collection()->push_back(inner); 
        inner.collection()->push_back(sseqOrOp); 
        choices.collection()->push_back(outer); 
        continue; 
      } 
 
      // verified now that node is a valid selector 
      Complex_Selector_Obj sseqSel = sseqOrOp.selector(); 
      Compound_Selector_Obj sseqHead = sseqSel->head(); 
 
      // let EXTENDED be extend_compound(COMPOUND, SEEN) 
      // extend the compound selector against the given subset_map 
      // RUBY: extended = sseq_or_op.do_extend(extends, parent_directives, replace, seen) 
      Node extended = extendCompoundSelector(sseqHead, seen, isReplace); // slow(17%)! 
      if (sseqOrOp.got_line_feed) extended.got_line_feed = true; 
      DEBUG_PRINTLN(EXTEND_COMPLEX, "EXTENDED: " << extended) 
 
      // Prepend the Compound_Selector based on the choices logic; choices seems to be extend but with a ruby 
      // Array instead of a Sequence due to the member mapping: choices = extended.map {|seq| seq.members} 
      // RUBY: extended.first.add_sources!([self]) if original && !has_placeholder? 
      if (isOriginal && !selector->has_placeholder()) { 
        ComplexSelectorSet srcset; 
        srcset.insert(selector); 
        sseqSel->addSources(srcset); 
        // DEBUG_PRINTLN(EXTEND_COMPLEX, "ADD SOURCES: " << *pComplexSelector) 
      } 
 
      bool isSuperselector = false; 
      // if no complex selector in EXTENDED is a superselector of COMPOUND: 
      for (Node& childNode : *extended.collection()) { 
        Complex_Selector_Obj pExtensionSelector = nodeToComplexSelector(childNode); 
        if (pExtensionSelector->is_superselector_of(sseqSel)) { 
          isSuperselector = true; 
          break; 
        } 
      } 
 
      if (!isSuperselector) { 
        // add a complex selector composed only of COMPOUND to EXTENDED 
        if (sseqOrOp.got_line_feed) sseqSel->has_line_feed(sseqOrOp.got_line_feed); 
        extended.collection()->push_front(complexSelectorToNode(sseqSel)); 
      } 
 
      DEBUG_PRINTLN(EXTEND_COMPLEX, "CHOICES UNSHIFTED: " << extended) 
 
      // add EXTENDED to CHOICES 
      // Aggregate our current extensions 
      choices.collection()->push_back(extended); 
    } 
 
 
    DEBUG_PRINTLN(EXTEND_COMPLEX, "EXTENDED NOT EXPANDED: " << choices) 
 
 
 
    // Ruby Equivalent: paths 
    Node paths = Sass::paths(choices); 
 
    DEBUG_PRINTLN(EXTEND_COMPLEX, "PATHS: " << paths) 
 
    // let WEAVES be an empty list of selector lists 
    Node weaves = Node::createCollection(); 
 
    // for each list of complex selectors PATH in paths(CHOICES): 
    for (Node& path : *paths.collection()) { 
      // add weave(PATH) to WEAVES 
      Node weaved = weave(path); // slow(12%)! 
      weaved.got_line_feed = path.got_line_feed; 
      weaves.collection()->push_back(weaved); 
    } 
 
    DEBUG_PRINTLN(EXTEND_COMPLEX, "WEAVES: " << weaves) 
 
    // Ruby Equivalent: trim 
    Node trimmed(trim(weaves, isReplace)); // slow(19%)! 
 
    DEBUG_PRINTLN(EXTEND_COMPLEX, "TRIMMED: " << trimmed) 
 
    // Ruby Equivalent: flatten 
    Node flattened(flatten(trimmed, 1)); 
 
    DEBUG_PRINTLN(EXTEND_COMPLEX, ">>>>> EXTENDED: " << extendedSelectors) 
    DEBUG_PRINTLN(EXTEND_COMPLEX, "EXTEND COMPLEX END: " << complexSelector) 
 
    // memory results in a map table - since extending is very expensive 
    memoizeComplex.insert(std::pair<Complex_Selector_Obj, Node>(selector, flattened)); 
 
    // return trim(WEAVES) 
    return flattened; 
  } 
 
 
 
  /* 
   This is the equivalent of ruby's CommaSequence.do_extend. 
  */ 
  // We get a selector list with has something to extend and a subset_map with 
  // all extenders. Pick the ones that match our selectors in the list. 
  Selector_List_Ptr Extend::extendSelectorList(Selector_List_Obj pSelectorList, bool isReplace, bool& extendedSomething, CompoundSelectorSet& seen) { 
 
    Selector_List_Obj pNewSelectors = SASS_MEMORY_NEW(Selector_List, pSelectorList->pstate(), pSelectorList->length()); 
 
    // check if we already extended this selector 
    // we can do this since subset_map is "static" 
    auto memoized = memoizeList.find(pSelectorList); 
    if (memoized != memoizeList.end()) { 
      extendedSomething = true; 
      return memoized->second; 
    } 
 
    extendedSomething = false; 
    // process each comlplex selector in the selector list. 
    // Find the ones that can be extended by given subset_map. 
    for (size_t index = 0, length = pSelectorList->length(); index < length; index++) { 
      Complex_Selector_Obj pSelector = (*pSelectorList)[index]; 
 
      // ruby sass seems to keep a list of things that have extensions and then only extend those. We don't currently do that. 
      // Since it's not that expensive to check if an extension exists in the subset map and since it can be relatively expensive to 
      // run through the extend code (which does a data model transformation), check if there is anything to extend before doing 
      // the extend. We might be able to optimize extendComplexSelector, but this approach keeps us closer to ruby sass (which helps 
      // when debugging). 
      if (!complexSelectorHasExtension(pSelector, seen)) { 
        pNewSelectors->append(pSelector); 
        continue; 
      } 
 
      // complexSelectorHasExtension was true! 
      extendedSomething = true; 
 
      // now do the actual extension of the complex selector 
      Node extendedSelectors = extendComplexSelector(pSelector, seen, isReplace, true); 
 
      if (!pSelector->has_placeholder()) { 
        Node nSelector(complexSelectorToNode(pSelector)); 
        if (!extendedSelectors.contains(nSelector)) { 
          pNewSelectors->append(pSelector); 
          continue; 
        } 
      } 
 
      bool doReplace = isReplace; 
      for (Node& childNode : *extendedSelectors.collection()) { 
        // When it is a replace, skip the first one, unless there is only one 
        if(doReplace && extendedSelectors.collection()->size() > 1 ) { 
          doReplace = false; 
          continue; 
        } 
        pNewSelectors->append(nodeToComplexSelector(childNode)); 
      } 
    } 
 
    Remove_Placeholders remove_placeholders; 
    // it seems that we have to remove the place holders early here 
    // normally we do this as the very last step (compare to ruby sass) 
    pNewSelectors = remove_placeholders.remove_placeholders(pNewSelectors); 
 
    // unwrap all wrapped selectors with inner lists 
    for (Complex_Selector_Obj cur : pNewSelectors->elements()) { 
      // process tails 
      while (cur) { 
        // process header 
        if (cur->head() && seen.find(cur->head()) == seen.end()) { 
          CompoundSelectorSet recseen(seen); 
          recseen.insert(cur->head()); 
          // create a copy since we add multiple items if stuff get unwrapped 
          Compound_Selector_Obj cpy_head = SASS_MEMORY_NEW(Compound_Selector, cur->pstate()); 
          for (Simple_Selector_Obj hs : *cur->head()) { 
            if (Wrapped_Selector_Obj ws = Cast<Wrapped_Selector>(hs)) { 
              ws->selector(SASS_MEMORY_CLONE(ws->selector())); 
              if (Selector_List_Obj sl = Cast<Selector_List>(ws->selector())) { 
                // special case for ruby ass 
                if (sl->empty()) { 
                  // this seems inconsistent but it is how ruby sass seems to remove parentheses 
                  cpy_head->append(SASS_MEMORY_NEW(Element_Selector, hs->pstate(), ws->name())); 
                } 
                // has wrapped not selectors 
                else if (ws->name() == ":not") { 
                  // extend the inner list of wrapped selector 
                  bool extended = false; 
                  Selector_List_Obj ext_sl = extendSelectorList(sl, false, extended, recseen); 
                  for (size_t i = 0; i < ext_sl->length(); i += 1) { 
                    if (Complex_Selector_Obj ext_cs = ext_sl->at(i)) { 
                      // create clones for wrapped selector and the inner list 
                      Wrapped_Selector_Obj cpy_ws = SASS_MEMORY_COPY(ws); 
                      Selector_List_Obj cpy_ws_sl = SASS_MEMORY_NEW(Selector_List, sl->pstate()); 
                      // remove parent selectors from inner selector 
                      Compound_Selector_Obj ext_head = NULL; 
                      if (ext_cs->first()) ext_head = ext_cs->first()->head(); 
                      if (ext_head && ext_head && ext_head->length() > 0) { 
                        cpy_ws_sl->append(ext_cs->first()); 
                      } 
                      // assign list to clone 
                      cpy_ws->selector(cpy_ws_sl); 
                      // append the clone 
                      cpy_head->append(cpy_ws); 
                    } 
                  } 
                  if (eval && extended) { 
                    eval->exp.selector_stack.push_back(pNewSelectors); 
                    cpy_head->perform(eval); 
                    eval->exp.selector_stack.pop_back(); 
                  } 
                } 
                // has wrapped selectors 
                else { 
                  Wrapped_Selector_Obj cpy_ws = SASS_MEMORY_COPY(ws); 
                  Selector_List_Obj ext_sl = extendSelectorList(sl, recseen); 
                  cpy_ws->selector(ext_sl); 
                  cpy_head->append(cpy_ws); 
                } 
              } else { 
                cpy_head->append(hs); 
              } 
            } else { 
              cpy_head->append(hs); 
            } 
          } 
          // replace header 
          cur->head(cpy_head); 
        } 
        // process tail 
        cur = cur->tail(); 
      } 
    } 
 
    // memory results in a map table - since extending is very expensive 
    memoizeList.insert(std::pair<Selector_List_Obj, Selector_List_Obj>(pSelectorList, pNewSelectors)); 
 
    return pNewSelectors.detach(); 
 
  } 
 
 
  bool shouldExtendBlock(Block_Obj b) { 
 
    // If a block is empty, there's no reason to extend it since any rules placed on this block 
    // won't have any output. The main benefit of this is for structures like: 
    // 
    //    .a { 
    //      .b { 
    //        x: y; 
    //      } 
    //    } 
    // 
    // We end up visiting two rulesets (one with the selector .a and the other with the selector .a .b). 
    // In this case, we don't want to try to pull rules onto .a since they won't get output anyway since 
    // there are no child statements. However .a .b should have extensions applied. 
 
    for (size_t i = 0, L = b->length(); i < L; ++i) { 
      Statement_Obj stm = b->at(i); 
 
      if (Cast<Ruleset>(stm)) { 
        // Do nothing. This doesn't count as a statement that causes extension since we'll 
        // iterate over this rule set in a future visit and try to extend it. 
      } 
      else { 
        return true; 
      } 
    } 
 
    return false; 
 
  } 
 
 
  // Extend a ruleset by extending the selectors and updating them on the ruleset. The block's rules don't need to change. 
  // Every Ruleset in the whole tree is calling this function. We decide if there 
  // was is @extend that matches our selector. If we find one, we will go further 
  // and call the extend magic for our selector. The subset_map contains all blocks 
  // where @extend was found. Pick the ones that match our selector! 
  void Extend::extendObjectWithSelectorAndBlock(Ruleset_Ptr pObject) { 
 
    DEBUG_PRINTLN(EXTEND_OBJECT, "FOUND SELECTOR: " << Cast<Selector_List>(pObject->selector())->to_string()) 
 
    // Ruby sass seems to filter nodes that don't have any content well before we get here. 
    // I'm not sure the repercussions of doing so, so for now, let's just not extend things 
    // that won't be output later. Profiling shows this may us 0.2% or so. 
    if (!shouldExtendBlock(pObject->block())) { 
      DEBUG_PRINTLN(EXTEND_OBJECT, "RETURNING WITHOUT EXTEND ATTEMPT") 
      return; 
    } 
 
    bool extendedSomething = false; 
 
    CompoundSelectorSet seen; 
    Selector_List_Obj pNewSelectorList = extendSelectorList(pObject->selector(), false, extendedSomething, seen); 
 
    if (extendedSomething && pNewSelectorList) { 
      DEBUG_PRINTLN(EXTEND_OBJECT, "EXTEND ORIGINAL SELECTORS: " << pObject->selector()->to_string()) 
      DEBUG_PRINTLN(EXTEND_OBJECT, "EXTEND SETTING NEW SELECTORS: " << pNewSelectorList->to_string()) 
      pNewSelectorList->remove_parent_selectors(); 
      pObject->selector(pNewSelectorList); 
    } else { 
      DEBUG_PRINTLN(EXTEND_OBJECT, "EXTEND DID NOT TRY TO EXTEND ANYTHING") 
    } 
  } 
 
  Extend::Extend(Subset_Map& ssm) 
  : subset_map(ssm), eval(NULL) 
  { } 
 
  void Extend::setEval(Eval& e) { 
    eval = &e; 
  } 
 
  void Extend::operator()(Block_Ptr b) 
  { 
    for (size_t i = 0, L = b->length(); i < L; ++i) { 
      Statement_Obj stm = b->at(i); 
      stm->perform(this); 
    } 
    // do final check if everything was extended 
    // we set `extended` flag on extended selectors 
    if (b->is_root()) { 
      // debug_subset_map(subset_map); 
      for(auto const &it : subset_map.values()) { 
        Complex_Selector_Ptr sel = NULL; 
        Compound_Selector_Ptr ext = NULL; 
        if (it.first) sel = it.first->first(); 
        if (it.second) ext = it.second; 
        if (ext && (ext->extended() || ext->is_optional())) continue; 
        std::string str_sel(sel ? sel->to_string({ NESTED, 5 }) : "NULL"); 
        std::string str_ext(ext ? ext->to_string({ NESTED, 5 }) : "NULL"); 
        // debug_ast(sel, "sel: "); 
        // debug_ast(ext, "ext: "); 
        error("\"" + str_sel + "\" failed to @extend \"" + str_ext + "\".\n" 
              "The selector \"" + str_ext + "\" was not found.\n" 
              "Use \"@extend " + str_ext + " !optional\" if the" 
              " extend should be able to fail.", (ext ? ext->pstate() : NULL)); 
      } 
    } 
 
  } 
 
  void Extend::operator()(Ruleset_Ptr pRuleset) 
  { 
    extendObjectWithSelectorAndBlock( pRuleset ); 
    pRuleset->block()->perform(this); 
  } 
 
  void Extend::operator()(Supports_Block_Ptr pFeatureBlock) 
  { 
    pFeatureBlock->block()->perform(this); 
  } 
 
  void Extend::operator()(Media_Block_Ptr pMediaBlock) 
  { 
    pMediaBlock->block()->perform(this); 
  } 
 
  void Extend::operator()(Directive_Ptr a) 
  { 
    // Selector_List_Ptr ls = Cast<Selector_List>(a->selector()); 
    // selector_stack.push_back(ls); 
    if (a->block()) a->block()->perform(this); 
    // exp.selector_stack.pop_back(); 
  } 
}