aboutsummaryrefslogtreecommitdiffstats
path: root/lib/AST/ASTDiagnostic.cpp
blob: 0ab1fa788603c1aa39a993d3a64e08153fcc8bdc (plain) (blame)
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
//===--- ASTDiagnostic.cpp - Diagnostic Printing Hooks for AST Nodes ------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements a diagnostic formatting hook for AST elements.
//
//===----------------------------------------------------------------------===//
#include "clang/AST/ASTDiagnostic.h"
#include "clang/AST/ASTContext.h"
#include "clang/AST/ASTLambda.h"
#include "clang/AST/Attr.h"
#include "clang/AST/DeclObjC.h"
#include "clang/AST/DeclTemplate.h"
#include "clang/AST/ExprCXX.h"
#include "clang/AST/TemplateBase.h"
#include "clang/AST/Type.h"
#include "llvm/ADT/SmallString.h"
#include "llvm/Support/raw_ostream.h"

using namespace clang;

// Returns a desugared version of the QualType, and marks ShouldAKA as true
// whenever we remove significant sugar from the type.
static QualType Desugar(ASTContext &Context, QualType QT, bool &ShouldAKA) {
  QualifierCollector QC;

  while (true) {
    const Type *Ty = QC.strip(QT);

    // Don't aka just because we saw an elaborated type...
    if (const ElaboratedType *ET = dyn_cast<ElaboratedType>(Ty)) {
      QT = ET->desugar();
      continue;
    }
    // ... or a paren type ...
    if (const ParenType *PT = dyn_cast<ParenType>(Ty)) {
      QT = PT->desugar();
      continue;
    }
    // ...or a substituted template type parameter ...
    if (const SubstTemplateTypeParmType *ST =
          dyn_cast<SubstTemplateTypeParmType>(Ty)) {
      QT = ST->desugar();
      continue;
    }
    // ...or an attributed type...
    if (const AttributedType *AT = dyn_cast<AttributedType>(Ty)) {
      QT = AT->desugar();
      continue;
    }
    // ...or an adjusted type...
    if (const AdjustedType *AT = dyn_cast<AdjustedType>(Ty)) {
      QT = AT->desugar();
      continue;
    }
    // ... or an auto type.
    if (const AutoType *AT = dyn_cast<AutoType>(Ty)) {
      if (!AT->isSugared())
        break;
      QT = AT->desugar();
      continue;
    }

    // Desugar FunctionType if return type or any parameter type should be
    // desugared. Preserve nullability attribute on desugared types.
    if (const FunctionType *FT = dyn_cast<FunctionType>(Ty)) {
      bool DesugarReturn = false;
      QualType SugarRT = FT->getReturnType();
      QualType RT = Desugar(Context, SugarRT, DesugarReturn);
      if (auto nullability = AttributedType::stripOuterNullability(SugarRT)) {
        RT = Context.getAttributedType(
            AttributedType::getNullabilityAttrKind(*nullability), RT, RT);
      }

      bool DesugarArgument = false;
      SmallVector<QualType, 4> Args;
      const FunctionProtoType *FPT = dyn_cast<FunctionProtoType>(FT);
      if (FPT) {
        for (QualType SugarPT : FPT->param_types()) {
          QualType PT = Desugar(Context, SugarPT, DesugarArgument);
          if (auto nullability =
                  AttributedType::stripOuterNullability(SugarPT)) {
            PT = Context.getAttributedType(
                AttributedType::getNullabilityAttrKind(*nullability), PT, PT);
          }
          Args.push_back(PT);
        }
      }

      if (DesugarReturn || DesugarArgument) {
        ShouldAKA = true;
        QT = FPT ? Context.getFunctionType(RT, Args, FPT->getExtProtoInfo())
                 : Context.getFunctionNoProtoType(RT, FT->getExtInfo());
        break;
      }
    }

    // Desugar template specializations if any template argument should be
    // desugared.
    if (const TemplateSpecializationType *TST =
            dyn_cast<TemplateSpecializationType>(Ty)) {
      if (!TST->isTypeAlias()) {
        bool DesugarArgument = false;
        SmallVector<TemplateArgument, 4> Args;
        for (unsigned I = 0, N = TST->getNumArgs(); I != N; ++I) {
          const TemplateArgument &Arg = TST->getArg(I);
          if (Arg.getKind() == TemplateArgument::Type)
            Args.push_back(Desugar(Context, Arg.getAsType(), DesugarArgument));
          else
            Args.push_back(Arg);
        }

        if (DesugarArgument) {
          ShouldAKA = true;
          QT = Context.getTemplateSpecializationType(
              TST->getTemplateName(), Args.data(), Args.size(), QT);
        }
        break;
      }
    }

    // Don't desugar magic Objective-C types.
    if (QualType(Ty,0) == Context.getObjCIdType() ||
        QualType(Ty,0) == Context.getObjCClassType() ||
        QualType(Ty,0) == Context.getObjCSelType() ||
        QualType(Ty,0) == Context.getObjCProtoType())
      break;

    // Don't desugar va_list.
    if (QualType(Ty, 0) == Context.getBuiltinVaListType() ||
        QualType(Ty, 0) == Context.getBuiltinMSVaListType())
      break;

    // Otherwise, do a single-step desugar.
    QualType Underlying;
    bool IsSugar = false;
    switch (Ty->getTypeClass()) {
#define ABSTRACT_TYPE(Class, Base)
#define TYPE(Class, Base) \
case Type::Class: { \
const Class##Type *CTy = cast<Class##Type>(Ty); \
if (CTy->isSugared()) { \
IsSugar = true; \
Underlying = CTy->desugar(); \
} \
break; \
}
#include "clang/AST/TypeNodes.def"
    }

    // If it wasn't sugared, we're done.
    if (!IsSugar)
      break;

    // If the desugared type is a vector type, we don't want to expand
    // it, it will turn into an attribute mess. People want their "vec4".
    if (isa<VectorType>(Underlying))
      break;

    // Don't desugar through the primary typedef of an anonymous type.
    if (const TagType *UTT = Underlying->getAs<TagType>())
      if (const TypedefType *QTT = dyn_cast<TypedefType>(QT))
        if (UTT->getDecl()->getTypedefNameForAnonDecl() == QTT->getDecl())
          break;

    // Record that we actually looked through an opaque type here.
    ShouldAKA = true;
    QT = Underlying;
  }

  // If we have a pointer-like type, desugar the pointee as well.
  // FIXME: Handle other pointer-like types.
  if (const PointerType *Ty = QT->getAs<PointerType>()) {
    QT = Context.getPointerType(Desugar(Context, Ty->getPointeeType(),
                                        ShouldAKA));
  } else if (const auto *Ty = QT->getAs<ObjCObjectPointerType>()) {
    QT = Context.getObjCObjectPointerType(Desugar(Context, Ty->getPointeeType(),
                                                  ShouldAKA));
  } else if (const LValueReferenceType *Ty = QT->getAs<LValueReferenceType>()) {
    QT = Context.getLValueReferenceType(Desugar(Context, Ty->getPointeeType(),
                                                ShouldAKA));
  } else if (const RValueReferenceType *Ty = QT->getAs<RValueReferenceType>()) {
    QT = Context.getRValueReferenceType(Desugar(Context, Ty->getPointeeType(),
                                                ShouldAKA));
  } else if (const auto *Ty = QT->getAs<ObjCObjectType>()) {
    if (Ty->getBaseType().getTypePtr() != Ty && !ShouldAKA) {
      QualType BaseType = Desugar(Context, Ty->getBaseType(), ShouldAKA);
      QT = Context.getObjCObjectType(BaseType, Ty->getTypeArgsAsWritten(),
                                     llvm::makeArrayRef(Ty->qual_begin(),
                                                        Ty->getNumProtocols()),
                                     Ty->isKindOfTypeAsWritten());
    }
  }

  return QC.apply(Context, QT);
}

/// \brief Convert the given type to a string suitable for printing as part of 
/// a diagnostic.
///
/// There are four main criteria when determining whether we should have an
/// a.k.a. clause when pretty-printing a type:
///
/// 1) Some types provide very minimal sugar that doesn't impede the
///    user's understanding --- for example, elaborated type
///    specifiers.  If this is all the sugar we see, we don't want an
///    a.k.a. clause.
/// 2) Some types are technically sugared but are much more familiar
///    when seen in their sugared form --- for example, va_list,
///    vector types, and the magic Objective C types.  We don't
///    want to desugar these, even if we do produce an a.k.a. clause.
/// 3) Some types may have already been desugared previously in this diagnostic.
///    if this is the case, doing another "aka" would just be clutter.
/// 4) Two different types within the same diagnostic have the same output
///    string.  In this case, force an a.k.a with the desugared type when
///    doing so will provide additional information.
///
/// \param Context the context in which the type was allocated
/// \param Ty the type to print
/// \param QualTypeVals pointer values to QualTypes which are used in the
/// diagnostic message
static std::string
ConvertTypeToDiagnosticString(ASTContext &Context, QualType Ty,
                            ArrayRef<DiagnosticsEngine::ArgumentValue> PrevArgs,
                            ArrayRef<intptr_t> QualTypeVals) {
  // FIXME: Playing with std::string is really slow.
  bool ForceAKA = false;
  QualType CanTy = Ty.getCanonicalType();
  std::string S = Ty.getAsString(Context.getPrintingPolicy());
  std::string CanS = CanTy.getAsString(Context.getPrintingPolicy());

  for (unsigned I = 0, E = QualTypeVals.size(); I != E; ++I) {
    QualType CompareTy =
        QualType::getFromOpaquePtr(reinterpret_cast<void*>(QualTypeVals[I]));
    if (CompareTy.isNull())
      continue;
    if (CompareTy == Ty)
      continue;  // Same types
    QualType CompareCanTy = CompareTy.getCanonicalType();
    if (CompareCanTy == CanTy)
      continue;  // Same canonical types
    std::string CompareS = CompareTy.getAsString(Context.getPrintingPolicy());
    bool ShouldAKA = false;
    QualType CompareDesugar = Desugar(Context, CompareTy, ShouldAKA);
    std::string CompareDesugarStr =
        CompareDesugar.getAsString(Context.getPrintingPolicy());
    if (CompareS != S && CompareDesugarStr != S)
      continue;  // The type string is different than the comparison string
                 // and the desugared comparison string.
    std::string CompareCanS =
        CompareCanTy.getAsString(Context.getPrintingPolicy());
    
    if (CompareCanS == CanS)
      continue;  // No new info from canonical type

    ForceAKA = true;
    break;
  }

  // Check to see if we already desugared this type in this
  // diagnostic.  If so, don't do it again.
  bool Repeated = false;
  for (unsigned i = 0, e = PrevArgs.size(); i != e; ++i) {
    // TODO: Handle ak_declcontext case.
    if (PrevArgs[i].first == DiagnosticsEngine::ak_qualtype) {
      void *Ptr = (void*)PrevArgs[i].second;
      QualType PrevTy(QualType::getFromOpaquePtr(Ptr));
      if (PrevTy == Ty) {
        Repeated = true;
        break;
      }
    }
  }

  // Consider producing an a.k.a. clause if removing all the direct
  // sugar gives us something "significantly different".
  if (!Repeated) {
    bool ShouldAKA = false;
    QualType DesugaredTy = Desugar(Context, Ty, ShouldAKA);
    if (ShouldAKA || ForceAKA) {
      if (DesugaredTy == Ty) {
        DesugaredTy = Ty.getCanonicalType();
      }
      std::string akaStr = DesugaredTy.getAsString(Context.getPrintingPolicy());
      if (akaStr != S) {
        S = "'" + S + "' (aka '" + akaStr + "')";
        return S;
      }
    }

    // Give some additional info on vector types. These are either not desugared
    // or displaying complex __attribute__ expressions so add details of the
    // type and element count.
    if (Ty->isVectorType()) {
      const VectorType *VTy = Ty->getAs<VectorType>();
      std::string DecoratedString;
      llvm::raw_string_ostream OS(DecoratedString);
      const char *Values = VTy->getNumElements() > 1 ? "values" : "value";
      OS << "'" << S << "' (vector of " << VTy->getNumElements() << " '"
         << VTy->getElementType().getAsString(Context.getPrintingPolicy())
         << "' " << Values << ")";
      return OS.str();
    }
  }

  S = "'" + S + "'";
  return S;
}

static bool FormatTemplateTypeDiff(ASTContext &Context, QualType FromType,
                                   QualType ToType, bool PrintTree,
                                   bool PrintFromType, bool ElideType,
                                   bool ShowColors, raw_ostream &OS);

void clang::FormatASTNodeDiagnosticArgument(
    DiagnosticsEngine::ArgumentKind Kind,
    intptr_t Val,
    StringRef Modifier,
    StringRef Argument,
    ArrayRef<DiagnosticsEngine::ArgumentValue> PrevArgs,
    SmallVectorImpl<char> &Output,
    void *Cookie,
    ArrayRef<intptr_t> QualTypeVals) {
  ASTContext &Context = *static_cast<ASTContext*>(Cookie);
  
  size_t OldEnd = Output.size();
  llvm::raw_svector_ostream OS(Output);
  bool NeedQuotes = true;
  
  switch (Kind) {
    default: llvm_unreachable("unknown ArgumentKind");
    case DiagnosticsEngine::ak_qualtype_pair: {
      TemplateDiffTypes &TDT = *reinterpret_cast<TemplateDiffTypes*>(Val);
      QualType FromType =
          QualType::getFromOpaquePtr(reinterpret_cast<void*>(TDT.FromType));
      QualType ToType =
          QualType::getFromOpaquePtr(reinterpret_cast<void*>(TDT.ToType));

      if (FormatTemplateTypeDiff(Context, FromType, ToType, TDT.PrintTree,
                                 TDT.PrintFromType, TDT.ElideType,
                                 TDT.ShowColors, OS)) {
        NeedQuotes = !TDT.PrintTree;
        TDT.TemplateDiffUsed = true;
        break;
      }

      // Don't fall-back during tree printing.  The caller will handle
      // this case.
      if (TDT.PrintTree)
        return;

      // Attempting to do a template diff on non-templates.  Set the variables
      // and continue with regular type printing of the appropriate type.
      Val = TDT.PrintFromType ? TDT.FromType : TDT.ToType;
      Modifier = StringRef();
      Argument = StringRef();
      // Fall through
    }
    case DiagnosticsEngine::ak_qualtype: {
      assert(Modifier.empty() && Argument.empty() &&
             "Invalid modifier for QualType argument");
      
      QualType Ty(QualType::getFromOpaquePtr(reinterpret_cast<void*>(Val)));
      OS << ConvertTypeToDiagnosticString(Context, Ty, PrevArgs, QualTypeVals);
      NeedQuotes = false;
      break;
    }
    case DiagnosticsEngine::ak_declarationname: {
      if (Modifier == "objcclass" && Argument.empty())
        OS << '+';
      else if (Modifier == "objcinstance" && Argument.empty())
        OS << '-';
      else
        assert(Modifier.empty() && Argument.empty() &&
               "Invalid modifier for DeclarationName argument");

      OS << DeclarationName::getFromOpaqueInteger(Val);
      break;
    }
    case DiagnosticsEngine::ak_nameddecl: {
      bool Qualified;
      if (Modifier == "q" && Argument.empty())
        Qualified = true;
      else {
        assert(Modifier.empty() && Argument.empty() &&
               "Invalid modifier for NamedDecl* argument");
        Qualified = false;
      }
      const NamedDecl *ND = reinterpret_cast<const NamedDecl*>(Val);
      ND->getNameForDiagnostic(OS, Context.getPrintingPolicy(), Qualified);
      break;
    }
    case DiagnosticsEngine::ak_nestednamespec: {
      NestedNameSpecifier *NNS = reinterpret_cast<NestedNameSpecifier*>(Val);
      NNS->print(OS, Context.getPrintingPolicy());
      NeedQuotes = false;
      break;
    }
    case DiagnosticsEngine::ak_declcontext: {
      DeclContext *DC = reinterpret_cast<DeclContext *> (Val);
      assert(DC && "Should never have a null declaration context");
      NeedQuotes = false;

      // FIXME: Get the strings for DeclContext from some localized place
      if (DC->isTranslationUnit()) {
        if (Context.getLangOpts().CPlusPlus)
          OS << "the global namespace";
        else
          OS << "the global scope";
      } else if (DC->isClosure()) {
        OS << "block literal";
      } else if (isLambdaCallOperator(DC)) {
        OS << "lambda expression";
      } else if (TypeDecl *Type = dyn_cast<TypeDecl>(DC)) {
        OS << ConvertTypeToDiagnosticString(Context,
                                            Context.getTypeDeclType(Type),
                                            PrevArgs, QualTypeVals);
      } else {
        assert(isa<NamedDecl>(DC) && "Expected a NamedDecl");
        NamedDecl *ND = cast<NamedDecl>(DC);
        if (isa<NamespaceDecl>(ND))
          OS << "namespace ";
        else if (isa<ObjCMethodDecl>(ND))
          OS << "method ";
        else if (isa<FunctionDecl>(ND))
          OS << "function ";

        OS << '\'';
        ND->getNameForDiagnostic(OS, Context.getPrintingPolicy(), true);
        OS << '\'';
      }
      break;
    }
    case DiagnosticsEngine::ak_attr: {
      const Attr *At = reinterpret_cast<Attr *>(Val);
      assert(At && "Received null Attr object!");
      OS << '\'' << At->getSpelling() << '\'';
      NeedQuotes = false;
      break;
    }

  }

  if (NeedQuotes) {
    Output.insert(Output.begin()+OldEnd, '\'');
    Output.push_back('\'');
  }
}

/// TemplateDiff - A class that constructs a pretty string for a pair of
/// QualTypes.  For the pair of types, a diff tree will be created containing
/// all the information about the templates and template arguments.  Afterwards,
/// the tree is transformed to a string according to the options passed in.
namespace {
class TemplateDiff {
  /// Context - The ASTContext which is used for comparing template arguments.
  ASTContext &Context;

  /// Policy - Used during expression printing.
  PrintingPolicy Policy;

  /// ElideType - Option to elide identical types.
  bool ElideType;

  /// PrintTree - Format output string as a tree.
  bool PrintTree;

  /// ShowColor - Diagnostics support color, so bolding will be used.
  bool ShowColor;

  /// FromType - When single type printing is selected, this is the type to be
  /// be printed.  When tree printing is selected, this type will show up first
  /// in the tree.
  QualType FromType;

  /// ToType - The type that FromType is compared to.  Only in tree printing
  /// will this type be outputed.
  QualType ToType;

  /// OS - The stream used to construct the output strings.
  raw_ostream &OS;

  /// IsBold - Keeps track of the bold formatting for the output string.
  bool IsBold;

  /// DiffTree - A tree representation the differences between two types.
  class DiffTree {
  public:
    /// DiffKind - The difference in a DiffNode and which fields are used.
    enum DiffKind {
      /// Incomplete or invalid node.
      Invalid,
      /// Another level of templates, uses TemplateDecl and Qualifiers
      Template,
      /// Type difference, uses QualType
      Type,
      /// Expression difference, uses Expr
      Expression,
      /// Template argument difference, uses TemplateDecl
      TemplateTemplate,
      /// Integer difference, uses APSInt and Expr
      Integer,
      /// Declaration difference, uses ValueDecl
      Declaration
    };
  private:
    /// DiffNode - The root node stores the original type.  Each child node
    /// stores template arguments of their parents.  For templated types, the
    /// template decl is also stored.
    struct DiffNode {
      DiffKind Kind;

      /// NextNode - The index of the next sibling node or 0.
      unsigned NextNode;

      /// ChildNode - The index of the first child node or 0.
      unsigned ChildNode;

      /// ParentNode - The index of the parent node.
      unsigned ParentNode;

      /// FromType, ToType - The type arguments.
      QualType FromType, ToType;

      /// FromExpr, ToExpr - The expression arguments.
      Expr *FromExpr, *ToExpr;

      /// FromNullPtr, ToNullPtr - If the template argument is a nullptr
      bool FromNullPtr, ToNullPtr;

      /// FromTD, ToTD - The template decl for template template
      /// arguments or the type arguments that are templates.
      TemplateDecl *FromTD, *ToTD;

      /// FromQual, ToQual - Qualifiers for template types.
      Qualifiers FromQual, ToQual;

      /// FromInt, ToInt - APSInt's for integral arguments.
      llvm::APSInt FromInt, ToInt;

      /// IsValidFromInt, IsValidToInt - Whether the APSInt's are valid.
      bool IsValidFromInt, IsValidToInt;

      /// FromValueDecl, ToValueDecl - Whether the argument is a decl.
      ValueDecl *FromValueDecl, *ToValueDecl;

      /// FromAddressOf, ToAddressOf - Whether the ValueDecl needs an address of
      /// operator before it.
      bool FromAddressOf, ToAddressOf;

      /// FromDefault, ToDefault - Whether the argument is a default argument.
      bool FromDefault, ToDefault;

      /// Same - Whether the two arguments evaluate to the same value.
      bool Same;

      DiffNode(unsigned ParentNode = 0)
        : Kind(Invalid), NextNode(0), ChildNode(0), ParentNode(ParentNode),
          FromType(), ToType(), FromExpr(nullptr), ToExpr(nullptr),
          FromNullPtr(false), ToNullPtr(false),
          FromTD(nullptr), ToTD(nullptr), IsValidFromInt(false),
          IsValidToInt(false), FromValueDecl(nullptr), ToValueDecl(nullptr),
          FromAddressOf(false), ToAddressOf(false), FromDefault(false),
          ToDefault(false), Same(false) {}
    };

    /// FlatTree - A flattened tree used to store the DiffNodes.
    SmallVector<DiffNode, 16> FlatTree;

    /// CurrentNode - The index of the current node being used.
    unsigned CurrentNode;

    /// NextFreeNode - The index of the next unused node.  Used when creating
    /// child nodes.
    unsigned NextFreeNode;

    /// ReadNode - The index of the current node being read.
    unsigned ReadNode;
  
  public:
    DiffTree() :
        CurrentNode(0), NextFreeNode(1) {
      FlatTree.push_back(DiffNode());
    }

    // Node writing functions.
    /// SetNode - Sets FromTD and ToTD of the current node.
    void SetNode(TemplateDecl *FromTD, TemplateDecl *ToTD) {
      FlatTree[CurrentNode].FromTD = FromTD;
      FlatTree[CurrentNode].ToTD = ToTD;
    }

    /// SetNode - Sets FromType and ToType of the current node.
    void SetNode(QualType FromType, QualType ToType) {
      FlatTree[CurrentNode].FromType = FromType;
      FlatTree[CurrentNode].ToType = ToType;
    }

    /// SetNode - Set FromExpr and ToExpr of the current node.
    void SetNode(Expr *FromExpr, Expr *ToExpr) {
      FlatTree[CurrentNode].FromExpr = FromExpr;
      FlatTree[CurrentNode].ToExpr = ToExpr;
    }

    /// SetNode - Set FromInt and ToInt of the current node.
    void SetNode(llvm::APSInt FromInt, llvm::APSInt ToInt,
                 bool IsValidFromInt, bool IsValidToInt) {
      FlatTree[CurrentNode].FromInt = FromInt;
      FlatTree[CurrentNode].ToInt = ToInt;
      FlatTree[CurrentNode].IsValidFromInt = IsValidFromInt;
      FlatTree[CurrentNode].IsValidToInt = IsValidToInt;
    }

    /// SetNode - Set FromQual and ToQual of the current node.
    void SetNode(Qualifiers FromQual, Qualifiers ToQual) {
      FlatTree[CurrentNode].FromQual = FromQual;
      FlatTree[CurrentNode].ToQual = ToQual;
    }

    /// SetNode - Set FromValueDecl and ToValueDecl of the current node.
    void SetNode(ValueDecl *FromValueDecl, ValueDecl *ToValueDecl,
                 bool FromAddressOf, bool ToAddressOf) {
      FlatTree[CurrentNode].FromValueDecl = FromValueDecl;
      FlatTree[CurrentNode].ToValueDecl = ToValueDecl;
      FlatTree[CurrentNode].FromAddressOf = FromAddressOf;
      FlatTree[CurrentNode].ToAddressOf = ToAddressOf;
    }

    /// SetSame - Sets the same flag of the current node.
    void SetSame(bool Same) {
      FlatTree[CurrentNode].Same = Same;
    }

    /// SetNullPtr - Sets the NullPtr flags of the current node.
    void SetNullPtr(bool FromNullPtr, bool ToNullPtr) {
      FlatTree[CurrentNode].FromNullPtr = FromNullPtr;
      FlatTree[CurrentNode].ToNullPtr = ToNullPtr;
    }

    /// SetDefault - Sets FromDefault and ToDefault flags of the current node.
    void SetDefault(bool FromDefault, bool ToDefault) {
      FlatTree[CurrentNode].FromDefault = FromDefault;
      FlatTree[CurrentNode].ToDefault = ToDefault;
    }

    /// SetKind - Sets the current node's type.
    void SetKind(DiffKind Kind) {
      FlatTree[CurrentNode].Kind = Kind;
    }

    /// Up - Changes the node to the parent of the current node.
    void Up() {
      CurrentNode = FlatTree[CurrentNode].ParentNode;
    }

    /// AddNode - Adds a child node to the current node, then sets that node
    /// node as the current node.
    void AddNode() {
      FlatTree.push_back(DiffNode(CurrentNode));
      DiffNode &Node = FlatTree[CurrentNode];
      if (Node.ChildNode == 0) {
        // If a child node doesn't exist, add one.
        Node.ChildNode = NextFreeNode;
      } else {
        // If a child node exists, find the last child node and add a
        // next node to it.
        unsigned i;
        for (i = Node.ChildNode; FlatTree[i].NextNode != 0;
             i = FlatTree[i].NextNode) {
        }
        FlatTree[i].NextNode = NextFreeNode;
      }
      CurrentNode = NextFreeNode;
      ++NextFreeNode;
    }

    // Node reading functions.
    /// StartTraverse - Prepares the tree for recursive traversal.
    void StartTraverse() {
      ReadNode = 0;
      CurrentNode = NextFreeNode;
      NextFreeNode = 0;
    }

    /// Parent - Move the current read node to its parent.
    void Parent() {
      ReadNode = FlatTree[ReadNode].ParentNode;
    }

    /// GetNode - Gets the FromType and ToType.
    void GetNode(QualType &FromType, QualType &ToType) {
      FromType = FlatTree[ReadNode].FromType;
      ToType = FlatTree[ReadNode].ToType;
    }

    /// GetNode - Gets the FromExpr and ToExpr.
    void GetNode(Expr *&FromExpr, Expr *&ToExpr) {
      FromExpr = FlatTree[ReadNode].FromExpr;
      ToExpr = FlatTree[ReadNode].ToExpr;
    }

    /// GetNode - Gets the FromTD and ToTD.
    void GetNode(TemplateDecl *&FromTD, TemplateDecl *&ToTD) {
      FromTD = FlatTree[ReadNode].FromTD;
      ToTD = FlatTree[ReadNode].ToTD;
    }

    /// GetNode - Gets the FromInt and ToInt.
    void GetNode(llvm::APSInt &FromInt, llvm::APSInt &ToInt,
                 bool &IsValidFromInt, bool &IsValidToInt) {
      FromInt = FlatTree[ReadNode].FromInt;
      ToInt = FlatTree[ReadNode].ToInt;
      IsValidFromInt = FlatTree[ReadNode].IsValidFromInt;
      IsValidToInt = FlatTree[ReadNode].IsValidToInt;
    }

    /// GetNode - Gets the FromQual and ToQual.
    void GetNode(Qualifiers &FromQual, Qualifiers &ToQual) {
      FromQual = FlatTree[ReadNode].FromQual;
      ToQual = FlatTree[ReadNode].ToQual;
    }

    /// GetNode - Gets the FromValueDecl and ToValueDecl.
    void GetNode(ValueDecl *&FromValueDecl, ValueDecl *&ToValueDecl,
                 bool &FromAddressOf, bool &ToAddressOf) {
      FromValueDecl = FlatTree[ReadNode].FromValueDecl;
      ToValueDecl = FlatTree[ReadNode].ToValueDecl;
      FromAddressOf = FlatTree[ReadNode].FromAddressOf;
      ToAddressOf = FlatTree[ReadNode].ToAddressOf;
    }

    /// NodeIsSame - Returns true the arguments are the same.
    bool NodeIsSame() {
      return FlatTree[ReadNode].Same;
    }

    /// HasChildrend - Returns true if the node has children.
    bool HasChildren() {
      return FlatTree[ReadNode].ChildNode != 0;
    }

    /// MoveToChild - Moves from the current node to its child.
    void MoveToChild() {
      ReadNode = FlatTree[ReadNode].ChildNode;
    }

    /// AdvanceSibling - If there is a next sibling, advance to it and return
    /// true.  Otherwise, return false.
    bool AdvanceSibling() {
      if (FlatTree[ReadNode].NextNode == 0)
        return false;

      ReadNode = FlatTree[ReadNode].NextNode;
      return true;
    }

    /// HasNextSibling - Return true if the node has a next sibling.
    bool HasNextSibling() {
      return FlatTree[ReadNode].NextNode != 0;
    }

    /// FromNullPtr - Returns true if the from argument is null.
    bool FromNullPtr() {
      return FlatTree[ReadNode].FromNullPtr;
    }

    /// ToNullPtr - Returns true if the to argument is null.
    bool ToNullPtr() {
      return FlatTree[ReadNode].ToNullPtr;
    }

    /// FromDefault - Return true if the from argument is the default.
    bool FromDefault() {
      return FlatTree[ReadNode].FromDefault;
    }

    /// ToDefault - Return true if the to argument is the default.
    bool ToDefault() {
      return FlatTree[ReadNode].ToDefault;
    }

    /// Empty - Returns true if the tree has no information.
    bool Empty() {
      return GetKind() == Invalid;
    }

    /// GetKind - Returns the current node's type.
    DiffKind GetKind() {
      return FlatTree[ReadNode].Kind;
    }
  };

  DiffTree Tree;

  /// TSTiterator - an iterator that is used to enter a
  /// TemplateSpecializationType and read TemplateArguments inside template
  /// parameter packs in order with the rest of the TemplateArguments.
  struct TSTiterator {
    typedef const TemplateArgument& reference;
    typedef const TemplateArgument* pointer;

    /// TST - the template specialization whose arguments this iterator
    /// traverse over.
    const TemplateSpecializationType *TST;

    /// DesugarTST - desugared template specialization used to extract
    /// default argument information
    const TemplateSpecializationType *DesugarTST;

    /// Index - the index of the template argument in TST.
    unsigned Index;

    /// CurrentTA - if CurrentTA is not the same as EndTA, then CurrentTA
    /// points to a TemplateArgument within a parameter pack.
    TemplateArgument::pack_iterator CurrentTA;

    /// EndTA - the end iterator of a parameter pack
    TemplateArgument::pack_iterator EndTA;

    /// TSTiterator - Constructs an iterator and sets it to the first template
    /// argument.
    TSTiterator(ASTContext &Context, const TemplateSpecializationType *TST)
        : TST(TST),
          DesugarTST(GetTemplateSpecializationType(Context, TST->desugar())),
          Index(0), CurrentTA(nullptr), EndTA(nullptr) {
      if (isEnd()) return;

      // Set to first template argument.  If not a parameter pack, done.
      TemplateArgument TA = TST->getArg(0);
      if (TA.getKind() != TemplateArgument::Pack) return;

      // Start looking into the parameter pack.
      CurrentTA = TA.pack_begin();
      EndTA = TA.pack_end();

      // Found a valid template argument.
      if (CurrentTA != EndTA) return;

      // Parameter pack is empty, use the increment to get to a valid
      // template argument.
      ++(*this);
    }

    /// isEnd - Returns true if the iterator is one past the end.
    bool isEnd() const {
      return Index >= TST->getNumArgs();
    }

    /// &operator++ - Increment the iterator to the next template argument.
    TSTiterator &operator++() {
      // After the end, Index should be the default argument position in
      // DesugarTST, if it exists.
      if (isEnd()) {
        ++Index;
        return *this;
      }

      // If in a parameter pack, advance in the parameter pack.
      if (CurrentTA != EndTA) {
        ++CurrentTA;
        if (CurrentTA != EndTA)
          return *this;
      }

      // Loop until a template argument is found, or the end is reached.
      while (true) {
        // Advance to the next template argument.  Break if reached the end.
        if (++Index == TST->getNumArgs()) break;

        // If the TemplateArgument is not a parameter pack, done.
        TemplateArgument TA = TST->getArg(Index);
        if (TA.getKind() != TemplateArgument::Pack) break;

        // Handle parameter packs.
        CurrentTA = TA.pack_begin();
        EndTA = TA.pack_end();

        // If the parameter pack is empty, try to advance again.
        if (CurrentTA != EndTA) break;
      }
      return *this;
    }

    /// operator* - Returns the appropriate TemplateArgument.
    reference operator*() const {
      assert(!isEnd() && "Index exceeds number of arguments.");
      if (CurrentTA == EndTA)
        return TST->getArg(Index);
      else
        return *CurrentTA;
    }

    /// operator-> - Allow access to the underlying TemplateArgument.
    pointer operator->() const {
      return &operator*();
    }

    /// getDesugar - Returns the deduced template argument from DesguarTST
    reference getDesugar() const {
      return DesugarTST->getArg(Index);
    }
  };

  // These functions build up the template diff tree, including functions to
  // retrieve and compare template arguments. 

  static const TemplateSpecializationType * GetTemplateSpecializationType(
      ASTContext &Context, QualType Ty) {
    if (const TemplateSpecializationType *TST =
            Ty->getAs<TemplateSpecializationType>())
      return TST;

    const RecordType *RT = Ty->getAs<RecordType>();

    if (!RT)
      return nullptr;

    const ClassTemplateSpecializationDecl *CTSD =
        dyn_cast<ClassTemplateSpecializationDecl>(RT->getDecl());

    if (!CTSD)
      return nullptr;

    Ty = Context.getTemplateSpecializationType(
             TemplateName(CTSD->getSpecializedTemplate()),
             CTSD->getTemplateArgs().data(),
             CTSD->getTemplateArgs().size(),
             Ty.getLocalUnqualifiedType().getCanonicalType());

    return Ty->getAs<TemplateSpecializationType>();
  }

  /// DiffTypes - Fills a DiffNode with information about a type difference.
  void DiffTypes(const TSTiterator &FromIter, const TSTiterator &ToIter,
                 TemplateTypeParmDecl *FromDefaultTypeDecl,
                 TemplateTypeParmDecl *ToDefaultTypeDecl) {
    QualType FromType = GetType(FromIter, FromDefaultTypeDecl);
    QualType ToType = GetType(ToIter, ToDefaultTypeDecl);

    Tree.SetNode(FromType, ToType);
    Tree.SetDefault(FromIter.isEnd() && !FromType.isNull(),
                    ToIter.isEnd() && !ToType.isNull());
    Tree.SetKind(DiffTree::Type);
    if (FromType.isNull() || ToType.isNull())
      return;

    if (Context.hasSameType(FromType, ToType)) {
      Tree.SetSame(true);
      return;
    }

    const TemplateSpecializationType *FromArgTST =
        GetTemplateSpecializationType(Context, FromType);
    if (!FromArgTST)
      return;

    const TemplateSpecializationType *ToArgTST =
        GetTemplateSpecializationType(Context, ToType);
    if (!ToArgTST)
      return;

    if (!hasSameTemplate(FromArgTST, ToArgTST))
      return;

    Qualifiers FromQual = FromType.getQualifiers(),
               ToQual = ToType.getQualifiers();
    FromQual -= QualType(FromArgTST, 0).getQualifiers();
    ToQual -= QualType(ToArgTST, 0).getQualifiers();
    Tree.SetNode(FromArgTST->getTemplateName().getAsTemplateDecl(),
                 ToArgTST->getTemplateName().getAsTemplateDecl());
    Tree.SetNode(FromQual, ToQual);
    Tree.SetKind(DiffTree::Template);
    DiffTemplate(FromArgTST, ToArgTST);
  }

  /// DiffTemplateTemplates - Fills a DiffNode with information about a
  /// template template difference.
  void DiffTemplateTemplates(const TSTiterator &FromIter,
                             const TSTiterator &ToIter,
                             TemplateTemplateParmDecl *FromDefaultTemplateDecl,
                             TemplateTemplateParmDecl *ToDefaultTemplateDecl) {
    TemplateDecl *FromDecl = GetTemplateDecl(FromIter, FromDefaultTemplateDecl);
    TemplateDecl *ToDecl = GetTemplateDecl(ToIter, ToDefaultTemplateDecl);
    Tree.SetNode(FromDecl, ToDecl);
    Tree.SetSame(FromDecl && ToDecl &&
                 FromDecl->getCanonicalDecl() == ToDecl->getCanonicalDecl());
    Tree.SetDefault(FromIter.isEnd() && FromDecl, ToIter.isEnd() && ToDecl);
    Tree.SetKind(DiffTree::TemplateTemplate);
  }

  /// InitializeNonTypeDiffVariables - Helper function for DiffNonTypes
  static void InitializeNonTypeDiffVariables(
      ASTContext &Context, const TSTiterator &Iter,
      NonTypeTemplateParmDecl *Default, bool &HasInt, bool &HasValueDecl,
      bool &IsNullPtr, Expr *&E, llvm::APSInt &Value, ValueDecl *&VD) {
    HasInt = !Iter.isEnd() && Iter->getKind() == TemplateArgument::Integral;

    HasValueDecl =
        !Iter.isEnd() && Iter->getKind() == TemplateArgument::Declaration;

    IsNullPtr = !Iter.isEnd() && Iter->getKind() == TemplateArgument::NullPtr;

    if (HasInt)
      Value = Iter->getAsIntegral();
    else if (HasValueDecl)
      VD = Iter->getAsDecl();
    else if (!IsNullPtr)
      E = GetExpr(Iter, Default);

    if (E && Default->getType()->isPointerType())
      IsNullPtr = CheckForNullPtr(Context, E);
  }

  /// NeedsAddressOf - Helper function for DiffNonTypes.  Returns true if the
  /// ValueDecl needs a '&' when printed.
  static bool NeedsAddressOf(ValueDecl *VD, Expr *E,
                             NonTypeTemplateParmDecl *Default) {
    if (!VD)
      return false;

    if (E) {
      if (UnaryOperator *UO = dyn_cast<UnaryOperator>(E->IgnoreParens())) {
        if (UO->getOpcode() == UO_AddrOf) {
          return true;
        }
      }
      return false;
    }

    if (!Default->getType()->isReferenceType()) {
      return true;
    }

    return false;
  }

  /// DiffNonTypes - Handles any template parameters not handled by DiffTypes
  /// of DiffTemplatesTemplates, such as integer and declaration parameters.
  void DiffNonTypes(const TSTiterator &FromIter, const TSTiterator &ToIter,
                    NonTypeTemplateParmDecl *FromDefaultNonTypeDecl,
                    NonTypeTemplateParmDecl *ToDefaultNonTypeDecl) {
    Expr *FromExpr = nullptr, *ToExpr = nullptr;
    llvm::APSInt FromInt, ToInt;
    ValueDecl *FromValueDecl = nullptr, *ToValueDecl = nullptr;
    bool HasFromInt = false, HasToInt = false, HasFromValueDecl = false,
         HasToValueDecl = false, FromNullPtr = false, ToNullPtr = false;
    InitializeNonTypeDiffVariables(Context, FromIter, FromDefaultNonTypeDecl,
                                     HasFromInt, HasFromValueDecl, FromNullPtr,
                                     FromExpr, FromInt, FromValueDecl);
    InitializeNonTypeDiffVariables(Context, ToIter, ToDefaultNonTypeDecl,
                                     HasToInt, HasToValueDecl, ToNullPtr,
                                     ToExpr, ToInt, ToValueDecl);

    assert(((!HasFromInt && !HasToInt) ||
            (!HasFromValueDecl && !HasToValueDecl)) &&
           "Template argument cannot be both integer and declaration");

    if (!HasFromInt && !HasToInt && !HasFromValueDecl && !HasToValueDecl) {
      Tree.SetNode(FromExpr, ToExpr);
      Tree.SetDefault(FromIter.isEnd() && FromExpr, ToIter.isEnd() && ToExpr);
      if (FromDefaultNonTypeDecl->getType()->isIntegralOrEnumerationType()) {
        if (FromExpr)
          HasFromInt = GetInt(Context, FromIter, FromExpr, FromInt,
                              FromDefaultNonTypeDecl->getType());
        if (ToExpr)
          HasToInt = GetInt(Context, ToIter, ToExpr, ToInt,
                            ToDefaultNonTypeDecl->getType());
      }
      if (HasFromInt && HasToInt) {
        Tree.SetNode(FromInt, ToInt, HasFromInt, HasToInt);
        Tree.SetSame(FromInt == ToInt);
        Tree.SetKind(DiffTree::Integer);
      } else if (HasFromInt || HasToInt) {
        Tree.SetNode(FromInt, ToInt, HasFromInt, HasToInt);
        Tree.SetSame(false);
        Tree.SetKind(DiffTree::Integer);
      } else {
        Tree.SetSame(IsEqualExpr(Context, FromExpr, ToExpr) ||
                     (FromNullPtr && ToNullPtr));
        Tree.SetNullPtr(FromNullPtr, ToNullPtr);
        Tree.SetKind(DiffTree::Expression);
      }
      return;
    }

    if (HasFromInt || HasToInt) {
      if (!HasFromInt && FromExpr)
        HasFromInt = GetInt(Context, FromIter, FromExpr, FromInt,
                            FromDefaultNonTypeDecl->getType());
      if (!HasToInt && ToExpr)
        HasToInt = GetInt(Context, ToIter, ToExpr, ToInt,
                          ToDefaultNonTypeDecl->getType());
      Tree.SetNode(FromInt, ToInt, HasFromInt, HasToInt);
      if (HasFromInt && HasToInt) {
        Tree.SetSame(FromInt == ToInt);
      } else {
        Tree.SetSame(false);
      }
      Tree.SetDefault(FromIter.isEnd() && HasFromInt,
                      ToIter.isEnd() && HasToInt);
      Tree.SetKind(DiffTree::Integer);
      return;
    }

    if (!HasFromValueDecl && FromExpr)
      FromValueDecl = GetValueDecl(FromIter, FromExpr);
    if (!HasToValueDecl && ToExpr)
      ToValueDecl = GetValueDecl(ToIter, ToExpr);

    bool FromAddressOf =
        NeedsAddressOf(FromValueDecl, FromExpr, FromDefaultNonTypeDecl);
    bool ToAddressOf =
        NeedsAddressOf(ToValueDecl, ToExpr, ToDefaultNonTypeDecl);

    Tree.SetNullPtr(FromNullPtr, ToNullPtr);
    Tree.SetNode(FromValueDecl, ToValueDecl, FromAddressOf, ToAddressOf);
    Tree.SetSame(FromValueDecl && ToValueDecl &&
                 FromValueDecl->getCanonicalDecl() ==
                     ToValueDecl->getCanonicalDecl());
    Tree.SetDefault(FromIter.isEnd() && FromValueDecl,
                    ToIter.isEnd() && ToValueDecl);
    Tree.SetKind(DiffTree::Declaration);
  }

  /// DiffTemplate - recursively visits template arguments and stores the
  /// argument info into a tree.
  void DiffTemplate(const TemplateSpecializationType *FromTST,
                    const TemplateSpecializationType *ToTST) {
    // Begin descent into diffing template tree.
    TemplateParameterList *ParamsFrom =
        FromTST->getTemplateName().getAsTemplateDecl()->getTemplateParameters();
    TemplateParameterList *ParamsTo =
        ToTST->getTemplateName().getAsTemplateDecl()->getTemplateParameters();
    unsigned TotalArgs = 0;
    for (TSTiterator FromIter(Context, FromTST), ToIter(Context, ToTST);
         !FromIter.isEnd() || !ToIter.isEnd(); ++TotalArgs) {
      Tree.AddNode();

      // Get the parameter at index TotalArgs.  If index is larger
      // than the total number of parameters, then there is an
      // argument pack, so re-use the last parameter.
      unsigned FromParamIndex = std::min(TotalArgs, ParamsFrom->size() - 1);
      unsigned ToParamIndex = std::min(TotalArgs, ParamsTo->size() - 1);
      NamedDecl *FromParamND = ParamsFrom->getParam(FromParamIndex);
      NamedDecl *ToParamND = ParamsTo->getParam(ToParamIndex);

      TemplateTypeParmDecl *FromDefaultTypeDecl =
          dyn_cast<TemplateTypeParmDecl>(FromParamND);
      TemplateTypeParmDecl *ToDefaultTypeDecl =
          dyn_cast<TemplateTypeParmDecl>(ToParamND);
      if (FromDefaultTypeDecl && ToDefaultTypeDecl)
        DiffTypes(FromIter, ToIter, FromDefaultTypeDecl, ToDefaultTypeDecl);

      TemplateTemplateParmDecl *FromDefaultTemplateDecl =
          dyn_cast<TemplateTemplateParmDecl>(FromParamND);
      TemplateTemplateParmDecl *ToDefaultTemplateDecl =
          dyn_cast<TemplateTemplateParmDecl>(ToParamND);
      if (FromDefaultTemplateDecl && ToDefaultTemplateDecl)
        DiffTemplateTemplates(FromIter, ToIter, FromDefaultTemplateDecl,
                              ToDefaultTemplateDecl);

      NonTypeTemplateParmDecl *FromDefaultNonTypeDecl =
          dyn_cast<NonTypeTemplateParmDecl>(FromParamND);
      NonTypeTemplateParmDecl *ToDefaultNonTypeDecl =
          dyn_cast<NonTypeTemplateParmDecl>(ToParamND);
      if (FromDefaultNonTypeDecl && ToDefaultNonTypeDecl)
        DiffNonTypes(FromIter, ToIter, FromDefaultNonTypeDecl,
                     ToDefaultNonTypeDecl);

      ++FromIter;
      ++ToIter;
      Tree.Up();
    }
  }

  /// makeTemplateList - Dump every template alias into the vector.
  static void makeTemplateList(
      SmallVectorImpl<const TemplateSpecializationType *> &TemplateList,
      const TemplateSpecializationType *TST) {
    while (TST) {
      TemplateList.push_back(TST);
      if (!TST->isTypeAlias())
        return;
      TST = TST->getAliasedType()->getAs<TemplateSpecializationType>();
    }
  }

  /// hasSameBaseTemplate - Returns true when the base templates are the same,
  /// even if the template arguments are not.
  static bool hasSameBaseTemplate(const TemplateSpecializationType *FromTST,
                                  const TemplateSpecializationType *ToTST) {
    return FromTST->getTemplateName().getAsTemplateDecl()->getCanonicalDecl() ==
           ToTST->getTemplateName().getAsTemplateDecl()->getCanonicalDecl();
  }

  /// hasSameTemplate - Returns true if both types are specialized from the
  /// same template declaration.  If they come from different template aliases,
  /// do a parallel ascension search to determine the highest template alias in
  /// common and set the arguments to them.
  static bool hasSameTemplate(const TemplateSpecializationType *&FromTST,
                              const TemplateSpecializationType *&ToTST) {
    // Check the top templates if they are the same.
    if (hasSameBaseTemplate(FromTST, ToTST))
      return true;

    // Create vectors of template aliases.
    SmallVector<const TemplateSpecializationType*, 1> FromTemplateList,
                                                      ToTemplateList;

    makeTemplateList(FromTemplateList, FromTST);
    makeTemplateList(ToTemplateList, ToTST);

    SmallVectorImpl<const TemplateSpecializationType *>::reverse_iterator
        FromIter = FromTemplateList.rbegin(), FromEnd = FromTemplateList.rend(),
        ToIter = ToTemplateList.rbegin(), ToEnd = ToTemplateList.rend();

    // Check if the lowest template types are the same.  If not, return.
    if (!hasSameBaseTemplate(*FromIter, *ToIter))
      return false;

    // Begin searching up the template aliases.  The bottom most template
    // matches so move up until one pair does not match.  Use the template
    // right before that one.
    for (; FromIter != FromEnd && ToIter != ToEnd; ++FromIter, ++ToIter) {
      if (!hasSameBaseTemplate(*FromIter, *ToIter))
        break;
    }

    FromTST = FromIter[-1];
    ToTST = ToIter[-1];

    return true;
  }

  /// GetType - Retrieves the template type arguments, including default
  /// arguments.
  static QualType GetType(const TSTiterator &Iter,
                          TemplateTypeParmDecl *DefaultTTPD) {
    bool isVariadic = DefaultTTPD->isParameterPack();

    if (!Iter.isEnd())
      return Iter->getAsType();
    if (isVariadic)
      return QualType();

    QualType ArgType = DefaultTTPD->getDefaultArgument();
    if (ArgType->isDependentType())
      return Iter.getDesugar().getAsType();

    return ArgType;
  }

  /// GetExpr - Retrieves the template expression argument, including default
  /// arguments.
  static Expr *GetExpr(const TSTiterator &Iter,
                       NonTypeTemplateParmDecl *DefaultNTTPD) {
    Expr *ArgExpr = nullptr;
    bool isVariadic = DefaultNTTPD->isParameterPack();

    if (!Iter.isEnd())
      ArgExpr = Iter->getAsExpr();
    else if (!isVariadic)
      ArgExpr = DefaultNTTPD->getDefaultArgument();

    if (ArgExpr)
      while (SubstNonTypeTemplateParmExpr *SNTTPE =
                 dyn_cast<SubstNonTypeTemplateParmExpr>(ArgExpr))
        ArgExpr = SNTTPE->getReplacement();

    return ArgExpr;
  }

  /// GetInt - Retrieves the template integer argument, including evaluating
  /// default arguments.  If the value comes from an expression, extend the
  /// APSInt to size of IntegerType to match the behavior in
  /// Sema::CheckTemplateArgument
  static bool GetInt(ASTContext &Context, const TSTiterator &Iter,
                     Expr *ArgExpr, llvm::APSInt &Int, QualType IntegerType) {
    // Default, value-depenedent expressions require fetching
    // from the desugared TemplateArgument, otherwise expression needs to
    // be evaluatable.
    if (Iter.isEnd() && ArgExpr->isValueDependent()) {
      switch (Iter.getDesugar().getKind()) {
        case TemplateArgument::Integral:
          Int = Iter.getDesugar().getAsIntegral();
          return true;
        case TemplateArgument::Expression:
          ArgExpr = Iter.getDesugar().getAsExpr();
          Int = ArgExpr->EvaluateKnownConstInt(Context);
          Int = Int.extOrTrunc(Context.getTypeSize(IntegerType));
          return true;
        default:
          llvm_unreachable("Unexpected template argument kind");
      }
    } else if (ArgExpr->isEvaluatable(Context)) {
      Int = ArgExpr->EvaluateKnownConstInt(Context);
      Int = Int.extOrTrunc(Context.getTypeSize(IntegerType));
      return true;
    }

    return false;
  }

  /// GetValueDecl - Retrieves the template Decl argument, including
  /// default expression argument.
  static ValueDecl *GetValueDecl(const TSTiterator &Iter, Expr *ArgExpr) {
    // Default, value-depenedent expressions require fetching
    // from the desugared TemplateArgument
    if (Iter.isEnd() && ArgExpr->isValueDependent())
      switch (Iter.getDesugar().getKind()) {
        case TemplateArgument::Declaration:
          return Iter.getDesugar().getAsDecl();
        case TemplateArgument::Expression:
          ArgExpr = Iter.getDesugar().getAsExpr();
          return cast<DeclRefExpr>(ArgExpr)->getDecl();
        default:
          llvm_unreachable("Unexpected template argument kind");
      }
    DeclRefExpr *DRE = dyn_cast<DeclRefExpr>(ArgExpr);
    if (!DRE) {
      UnaryOperator *UO = dyn_cast<UnaryOperator>(ArgExpr->IgnoreParens());
      if (!UO)
        return nullptr;
      DRE = cast<DeclRefExpr>(UO->getSubExpr());
    }

    return DRE->getDecl();
  }

  /// CheckForNullPtr - returns true if the expression can be evaluated as
  /// a null pointer
  static bool CheckForNullPtr(ASTContext &Context, Expr *E) {
    assert(E && "Expected expression");

    E = E->IgnoreParenCasts();
    if (E->isNullPointerConstant(Context, Expr::NPC_ValueDependentIsNull))
      return true;

    DeclRefExpr *DRE = dyn_cast<DeclRefExpr>(E);
    if (!DRE)
      return false;

    VarDecl *VD = dyn_cast<VarDecl>(DRE->getDecl());
    if (!VD || !VD->hasInit())
      return false;

    return VD->getInit()->IgnoreParenCasts()->isNullPointerConstant(
        Context, Expr::NPC_ValueDependentIsNull);
  }

  /// GetTemplateDecl - Retrieves the template template arguments, including
  /// default arguments.
  static TemplateDecl *GetTemplateDecl(const TSTiterator &Iter,
                                TemplateTemplateParmDecl *DefaultTTPD) {
    bool isVariadic = DefaultTTPD->isParameterPack();

    TemplateArgument TA = DefaultTTPD->getDefaultArgument().getArgument();
    TemplateDecl *DefaultTD = nullptr;
    if (TA.getKind() != TemplateArgument::Null)
      DefaultTD = TA.getAsTemplate().getAsTemplateDecl();

    if (!Iter.isEnd())
      return Iter->getAsTemplate().getAsTemplateDecl();
    if (!isVariadic)
      return DefaultTD;

    return nullptr;
  }

  /// IsEqualExpr - Returns true if the expressions evaluate to the same value.
  static bool IsEqualExpr(ASTContext &Context, Expr *FromExpr, Expr *ToExpr) {
    if (FromExpr == ToExpr)
      return true;

    if (!FromExpr || !ToExpr)
      return false;

    DeclRefExpr *FromDRE = dyn_cast<DeclRefExpr>(FromExpr->IgnoreParens()),
                *ToDRE = dyn_cast<DeclRefExpr>(ToExpr->IgnoreParens());

    if (FromDRE || ToDRE) {
      if (!FromDRE || !ToDRE)
        return false;
      return FromDRE->getDecl() == ToDRE->getDecl();
    }

    Expr::EvalResult FromResult, ToResult;
    if (!FromExpr->EvaluateAsRValue(FromResult, Context) ||
        !ToExpr->EvaluateAsRValue(ToResult, Context)) {
      llvm::FoldingSetNodeID FromID, ToID;
      FromExpr->Profile(FromID, Context, true);
      ToExpr->Profile(ToID, Context, true);
      return FromID == ToID;
    }

    APValue &FromVal = FromResult.Val;
    APValue &ToVal = ToResult.Val;

    if (FromVal.getKind() != ToVal.getKind()) return false;

    switch (FromVal.getKind()) {
      case APValue::Int:
        return FromVal.getInt() == ToVal.getInt();
      case APValue::LValue: {
        APValue::LValueBase FromBase = FromVal.getLValueBase();
        APValue::LValueBase ToBase = ToVal.getLValueBase();
        if (FromBase.isNull() && ToBase.isNull())
          return true;
        if (FromBase.isNull() || ToBase.isNull())
          return false;
        return FromBase.get<const ValueDecl*>() ==
               ToBase.get<const ValueDecl*>();
      }
      case APValue::MemberPointer:
        return FromVal.getMemberPointerDecl() == ToVal.getMemberPointerDecl();
      default:
        llvm_unreachable("Unknown template argument expression.");
    }
  }

  // These functions converts the tree representation of the template
  // differences into the internal character vector.

  /// TreeToString - Converts the Tree object into a character stream which
  /// will later be turned into the output string.
  void TreeToString(int Indent = 1) {
    if (PrintTree) {
      OS << '\n';
      OS.indent(2 * Indent);
      ++Indent;
    }

    // Handle cases where the difference is not templates with different
    // arguments.
    switch (Tree.GetKind()) {
      case DiffTree::Invalid:
        llvm_unreachable("Template diffing failed with bad DiffNode");
      case DiffTree::Type: {
        QualType FromType, ToType;
        Tree.GetNode(FromType, ToType);
        PrintTypeNames(FromType, ToType, Tree.FromDefault(), Tree.ToDefault(),
                       Tree.NodeIsSame());
        return;
      }
      case DiffTree::Expression: {
        Expr *FromExpr, *ToExpr;
        Tree.GetNode(FromExpr, ToExpr);
        PrintExpr(FromExpr, ToExpr, Tree.FromNullPtr(), Tree.ToNullPtr(),
                  Tree.FromDefault(), Tree.ToDefault(), Tree.NodeIsSame());
        return;
      }
      case DiffTree::TemplateTemplate: {
        TemplateDecl *FromTD, *ToTD;
        Tree.GetNode(FromTD, ToTD);
        PrintTemplateTemplate(FromTD, ToTD, Tree.FromDefault(),
                              Tree.ToDefault(), Tree.NodeIsSame());
        return;
      }
      case DiffTree::Integer: {
        llvm::APSInt FromInt, ToInt;
        Expr *FromExpr, *ToExpr;
        bool IsValidFromInt, IsValidToInt;
        Tree.GetNode(FromExpr, ToExpr);
        Tree.GetNode(FromInt, ToInt, IsValidFromInt, IsValidToInt);
        PrintAPSInt(FromInt, ToInt, IsValidFromInt, IsValidToInt,
                    FromExpr, ToExpr, Tree.FromDefault(), Tree.ToDefault(),
                    Tree.NodeIsSame());
        return;
      }
      case DiffTree::Declaration: {
        ValueDecl *FromValueDecl, *ToValueDecl;
        bool FromAddressOf, ToAddressOf;
        Tree.GetNode(FromValueDecl, ToValueDecl, FromAddressOf, ToAddressOf);
        PrintValueDecl(FromValueDecl, ToValueDecl, FromAddressOf, ToAddressOf,
                       Tree.FromNullPtr(), Tree.ToNullPtr(), Tree.FromDefault(),
                       Tree.ToDefault(), Tree.NodeIsSame());
        return;
      }
      case DiffTree::Template: {
        // Node is root of template.  Recurse on children.
        TemplateDecl *FromTD, *ToTD;
        Tree.GetNode(FromTD, ToTD);

        if (!Tree.HasChildren()) {
          // If we're dealing with a template specialization with zero
          // arguments, there are no children; special-case this.
          OS << FromTD->getNameAsString() << "<>";
          return;
        }

        Qualifiers FromQual, ToQual;
        Tree.GetNode(FromQual, ToQual);
        PrintQualifiers(FromQual, ToQual);

        OS << FromTD->getNameAsString() << '<'; 
        Tree.MoveToChild();
        unsigned NumElideArgs = 0;
        do {
          if (ElideType) {
            if (Tree.NodeIsSame()) {
              ++NumElideArgs;
              continue;
            }
            if (NumElideArgs > 0) {
              PrintElideArgs(NumElideArgs, Indent);
              NumElideArgs = 0;
              OS << ", ";
            }
          }
          TreeToString(Indent);
          if (Tree.HasNextSibling())
            OS << ", ";
        } while (Tree.AdvanceSibling());
        if (NumElideArgs > 0)
          PrintElideArgs(NumElideArgs, Indent);

        Tree.Parent();
        OS << ">";
        return;
      }
    }
  }

  // To signal to the text printer that a certain text needs to be bolded,
  // a special character is injected into the character stream which the
  // text printer will later strip out.

  /// Bold - Start bolding text.
  void Bold() {
    assert(!IsBold && "Attempting to bold text that is already bold.");
    IsBold = true;
    if (ShowColor)
      OS << ToggleHighlight;
  }

  /// Unbold - Stop bolding text.
  void Unbold() {
    assert(IsBold && "Attempting to remove bold from unbold text.");
    IsBold = false;
    if (ShowColor)
      OS << ToggleHighlight;
  }

  // Functions to print out the arguments and highlighting the difference.

  /// PrintTypeNames - prints the typenames, bolding differences.  Will detect
  /// typenames that are the same and attempt to disambiguate them by using
  /// canonical typenames.
  void PrintTypeNames(QualType FromType, QualType ToType,
                      bool FromDefault, bool ToDefault, bool Same) {
    assert((!FromType.isNull() || !ToType.isNull()) &&
           "Only one template argument may be missing.");

    if (Same) {
      OS << FromType.getAsString(Policy);
      return;
    }

    if (!FromType.isNull() && !ToType.isNull() &&
        FromType.getLocalUnqualifiedType() ==
        ToType.getLocalUnqualifiedType()) {
      Qualifiers FromQual = FromType.getLocalQualifiers(),
                 ToQual = ToType.getLocalQualifiers();
      PrintQualifiers(FromQual, ToQual);
      FromType.getLocalUnqualifiedType().print(OS, Policy);
      return;
    }

    std::string FromTypeStr = FromType.isNull() ? "(no argument)"
                                                : FromType.getAsString(Policy);
    std::string ToTypeStr = ToType.isNull() ? "(no argument)"
                                            : ToType.getAsString(Policy);
    // Switch to canonical typename if it is better.
    // TODO: merge this with other aka printing above.
    if (FromTypeStr == ToTypeStr) {
      std::string FromCanTypeStr =
          FromType.getCanonicalType().getAsString(Policy);
      std::string ToCanTypeStr = ToType.getCanonicalType().getAsString(Policy);
      if (FromCanTypeStr != ToCanTypeStr) {
        FromTypeStr = FromCanTypeStr;
        ToTypeStr = ToCanTypeStr;
      }
    }

    if (PrintTree) OS << '[';
    OS << (FromDefault ? "(default) " : "");
    Bold();
    OS << FromTypeStr;
    Unbold();
    if (PrintTree) {
      OS << " != " << (ToDefault ? "(default) " : "");
      Bold();
      OS << ToTypeStr;
      Unbold();
      OS << "]";
    }
    return;
  }

  /// PrintExpr - Prints out the expr template arguments, highlighting argument
  /// differences.
  void PrintExpr(const Expr *FromExpr, const Expr *ToExpr, bool FromNullPtr,
                 bool ToNullPtr, bool FromDefault, bool ToDefault, bool Same) {
    assert((FromExpr || ToExpr) &&
            "Only one template argument may be missing.");
    if (Same) {
      PrintExpr(FromExpr, FromNullPtr);
    } else if (!PrintTree) {
      OS << (FromDefault ? "(default) " : "");
      Bold();
      PrintExpr(FromExpr, FromNullPtr);
      Unbold();
    } else {
      OS << (FromDefault ? "[(default) " : "[");
      Bold();
      PrintExpr(FromExpr, FromNullPtr);
      Unbold();
      OS << " != " << (ToDefault ? "(default) " : "");
      Bold();
      PrintExpr(ToExpr, ToNullPtr);
      Unbold();
      OS << ']';
    }
  }

  /// PrintExpr - Actual formatting and printing of expressions.
  void PrintExpr(const Expr *E, bool NullPtr = false) {
    if (E) {
      E->printPretty(OS, nullptr, Policy);
      return;
    }
    if (NullPtr) {
      OS << "nullptr";
      return;
    }
    OS << "(no argument)";
  }

  /// PrintTemplateTemplate - Handles printing of template template arguments,
  /// highlighting argument differences.
  void PrintTemplateTemplate(TemplateDecl *FromTD, TemplateDecl *ToTD,
                             bool FromDefault, bool ToDefault, bool Same) {
    assert((FromTD || ToTD) && "Only one template argument may be missing.");

    std::string FromName = FromTD ? FromTD->getName() : "(no argument)";
    std::string ToName = ToTD ? ToTD->getName() : "(no argument)";
    if (FromTD && ToTD && FromName == ToName) {
      FromName = FromTD->getQualifiedNameAsString();
      ToName = ToTD->getQualifiedNameAsString();
    }

    if (Same) {
      OS << "template " << FromTD->getNameAsString();
    } else if (!PrintTree) {
      OS << (FromDefault ? "(default) template " : "template ");
      Bold();
      OS << FromName;
      Unbold();
    } else {
      OS << (FromDefault ? "[(default) template " : "[template ");
      Bold();
      OS << FromName;
      Unbold();
      OS << " != " << (ToDefault ? "(default) template " : "template ");
      Bold();
      OS << ToName;
      Unbold();
      OS << ']';
    }
  }

  /// PrintAPSInt - Handles printing of integral arguments, highlighting
  /// argument differences.
  void PrintAPSInt(llvm::APSInt FromInt, llvm::APSInt ToInt,
                   bool IsValidFromInt, bool IsValidToInt, Expr *FromExpr,
                   Expr *ToExpr, bool FromDefault, bool ToDefault, bool Same) {
    assert((IsValidFromInt || IsValidToInt) &&
           "Only one integral argument may be missing.");

    if (Same) {
      OS << FromInt.toString(10);
    } else if (!PrintTree) {
      OS << (FromDefault ? "(default) " : "");
      PrintAPSInt(FromInt, FromExpr, IsValidFromInt);
    } else {
      OS << (FromDefault ? "[(default) " : "[");
      PrintAPSInt(FromInt, FromExpr, IsValidFromInt);
      OS << " != " << (ToDefault ? "(default) " : "");
      PrintAPSInt(ToInt, ToExpr, IsValidToInt);
      OS << ']';
    }
  }

  /// PrintAPSInt - If valid, print the APSInt.  If the expression is
  /// gives more information, print it too.
  void PrintAPSInt(llvm::APSInt Val, Expr *E, bool Valid) {
    Bold();
    if (Valid) {
      if (HasExtraInfo(E)) {
        PrintExpr(E);
        Unbold();
        OS << " aka ";
        Bold();
      }
      OS << Val.toString(10);
    } else if (E) {
      PrintExpr(E);
    } else {
      OS << "(no argument)";
    }
    Unbold();
  }

  /// HasExtraInfo - Returns true if E is not an integer literal or the
  /// negation of an integer literal
  bool HasExtraInfo(Expr *E) {
    if (!E) return false;

    E = E->IgnoreImpCasts();

    if (isa<IntegerLiteral>(E)) return false;

    if (UnaryOperator *UO = dyn_cast<UnaryOperator>(E))
      if (UO->getOpcode() == UO_Minus)
        if (isa<IntegerLiteral>(UO->getSubExpr()))
          return false;

    return true;
  }

  void PrintValueDecl(ValueDecl *VD, bool AddressOf, bool NullPtr) {
    if (VD) {
      if (AddressOf)
        OS << "&";
      OS << VD->getName();
      return;
    }

    if (NullPtr) {
      OS << "nullptr";
      return;
    }

    OS << "(no argument)";
  }

  /// PrintDecl - Handles printing of Decl arguments, highlighting
  /// argument differences.
  void PrintValueDecl(ValueDecl *FromValueDecl, ValueDecl *ToValueDecl,
                      bool FromAddressOf, bool ToAddressOf, bool FromNullPtr,
                      bool ToNullPtr, bool FromDefault, bool ToDefault,
                      bool Same) {
    assert((FromValueDecl || FromNullPtr || ToValueDecl || ToNullPtr) &&
           "Only one Decl argument may be NULL");

    if (Same) {
      PrintValueDecl(FromValueDecl, FromAddressOf, FromNullPtr);
    } else if (!PrintTree) {
      OS << (FromDefault ? "(default) " : "");
      Bold();
      PrintValueDecl(FromValueDecl, FromAddressOf, FromNullPtr);
      Unbold();
    } else {
      OS << (FromDefault ? "[(default) " : "[");
      Bold();
      PrintValueDecl(FromValueDecl, FromAddressOf, FromNullPtr);
      Unbold();
      OS << " != " << (ToDefault ? "(default) " : "");
      Bold();
      PrintValueDecl(ToValueDecl, ToAddressOf, ToNullPtr);
      Unbold();
      OS << ']';
    }

  }

  // Prints the appropriate placeholder for elided template arguments.
  void PrintElideArgs(unsigned NumElideArgs, unsigned Indent) {
    if (PrintTree) {
      OS << '\n';
      for (unsigned i = 0; i < Indent; ++i)
        OS << "  ";
    }
    if (NumElideArgs == 0) return;
    if (NumElideArgs == 1)
      OS << "[...]";
    else
      OS << "[" << NumElideArgs << " * ...]";
  }

  // Prints and highlights differences in Qualifiers.
  void PrintQualifiers(Qualifiers FromQual, Qualifiers ToQual) {
    // Both types have no qualifiers
    if (FromQual.empty() && ToQual.empty())
      return;

    // Both types have same qualifiers
    if (FromQual == ToQual) {
      PrintQualifier(FromQual, /*ApplyBold*/false);
      return;
    }

    // Find common qualifiers and strip them from FromQual and ToQual.
    Qualifiers CommonQual = Qualifiers::removeCommonQualifiers(FromQual,
                                                               ToQual);

    // The qualifiers are printed before the template name.
    // Inline printing:
    // The common qualifiers are printed.  Then, qualifiers only in this type
    // are printed and highlighted.  Finally, qualifiers only in the other
    // type are printed and highlighted inside parentheses after "missing".
    // Tree printing:
    // Qualifiers are printed next to each other, inside brackets, and
    // separated by "!=".  The printing order is:
    // common qualifiers, highlighted from qualifiers, "!=",
    // common qualifiers, highlighted to qualifiers
    if (PrintTree) {
      OS << "[";
      if (CommonQual.empty() && FromQual.empty()) {
        Bold();
        OS << "(no qualifiers) ";
        Unbold();
      } else {
        PrintQualifier(CommonQual, /*ApplyBold*/false);
        PrintQualifier(FromQual, /*ApplyBold*/true);
      }
      OS << "!= ";
      if (CommonQual.empty() && ToQual.empty()) {
        Bold();
        OS << "(no qualifiers)";
        Unbold();
      } else {
        PrintQualifier(CommonQual, /*ApplyBold*/false,
                       /*appendSpaceIfNonEmpty*/!ToQual.empty());
        PrintQualifier(ToQual, /*ApplyBold*/true,
                       /*appendSpaceIfNonEmpty*/false);
      }
      OS << "] ";
    } else {
      PrintQualifier(CommonQual, /*ApplyBold*/false);
      PrintQualifier(FromQual, /*ApplyBold*/true);
    }
  }

  void PrintQualifier(Qualifiers Q, bool ApplyBold,
                      bool AppendSpaceIfNonEmpty = true) {
    if (Q.empty()) return;
    if (ApplyBold) Bold();
    Q.print(OS, Policy, AppendSpaceIfNonEmpty);
    if (ApplyBold) Unbold();
  }

public:

  TemplateDiff(raw_ostream &OS, ASTContext &Context, QualType FromType,
               QualType ToType, bool PrintTree, bool PrintFromType,
               bool ElideType, bool ShowColor)
    : Context(Context),
      Policy(Context.getLangOpts()),
      ElideType(ElideType),
      PrintTree(PrintTree),
      ShowColor(ShowColor),
      // When printing a single type, the FromType is the one printed.
      FromType(PrintFromType ? FromType : ToType),
      ToType(PrintFromType ? ToType : FromType),
      OS(OS),
      IsBold(false) {
  }

  /// DiffTemplate - Start the template type diffing.
  void DiffTemplate() {
    Qualifiers FromQual = FromType.getQualifiers(),
               ToQual = ToType.getQualifiers();

    const TemplateSpecializationType *FromOrigTST =
        GetTemplateSpecializationType(Context, FromType);
    const TemplateSpecializationType *ToOrigTST =
        GetTemplateSpecializationType(Context, ToType);

    // Only checking templates.
    if (!FromOrigTST || !ToOrigTST)
      return;

    // Different base templates.
    if (!hasSameTemplate(FromOrigTST, ToOrigTST)) {
      return;
    }

    FromQual -= QualType(FromOrigTST, 0).getQualifiers();
    ToQual -= QualType(ToOrigTST, 0).getQualifiers();
    Tree.SetNode(FromType, ToType);
    Tree.SetNode(FromQual, ToQual);
    Tree.SetKind(DiffTree::Template);

    // Same base template, but different arguments.
    Tree.SetNode(FromOrigTST->getTemplateName().getAsTemplateDecl(),
                 ToOrigTST->getTemplateName().getAsTemplateDecl());

    DiffTemplate(FromOrigTST, ToOrigTST);
  }

  /// Emit - When the two types given are templated types with the same
  /// base template, a string representation of the type difference will be
  /// emitted to the stream and return true.  Otherwise, return false.
  bool Emit() {
    Tree.StartTraverse();
    if (Tree.Empty())
      return false;

    TreeToString();
    assert(!IsBold && "Bold is applied to end of string.");
    return true;
  }
}; // end class TemplateDiff
}  // end namespace

/// FormatTemplateTypeDiff - A helper static function to start the template
/// diff and return the properly formatted string.  Returns true if the diff
/// is successful.
static bool FormatTemplateTypeDiff(ASTContext &Context, QualType FromType,
                                   QualType ToType, bool PrintTree,
                                   bool PrintFromType, bool ElideType, 
                                   bool ShowColors, raw_ostream &OS) {
  if (PrintTree)
    PrintFromType = true;
  TemplateDiff TD(OS, Context, FromType, ToType, PrintTree, PrintFromType,
                  ElideType, ShowColors);
  TD.DiffTemplate();
  return TD.Emit();
}