Codebase list golint / fresh-snapshots/main lint.go
fresh-snapshots/main

Tree @fresh-snapshots/main (Download .tar.gz)

lint.go @fresh-snapshots/mainraw · history · 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
// Copyright (c) 2013 The Go Authors. All rights reserved.
//
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file or at
// https://developers.google.com/open-source/licenses/bsd.

// Package lint contains a linter for Go source code.
package lint // import "golang.org/x/lint"

import (
	"bufio"
	"bytes"
	"fmt"
	"go/ast"
	"go/parser"
	"go/printer"
	"go/token"
	"go/types"
	"regexp"
	"sort"
	"strconv"
	"strings"
	"unicode"
	"unicode/utf8"

	"golang.org/x/tools/go/ast/astutil"
	"golang.org/x/tools/go/gcexportdata"
)

const styleGuideBase = "https://golang.org/wiki/CodeReviewComments"

// A Linter lints Go source code.
type Linter struct {
}

// Problem represents a problem in some source code.
type Problem struct {
	Position   token.Position // position in source file
	Text       string         // the prose that describes the problem
	Link       string         // (optional) the link to the style guide for the problem
	Confidence float64        // a value in (0,1] estimating the confidence in this problem's correctness
	LineText   string         // the source line
	Category   string         // a short name for the general category of the problem

	// If the problem has a suggested fix (the minority case),
	// ReplacementLine is a full replacement for the relevant line of the source file.
	ReplacementLine string
}

func (p *Problem) String() string {
	if p.Link != "" {
		return p.Text + "\n\n" + p.Link
	}
	return p.Text
}

type byPosition []Problem

func (p byPosition) Len() int      { return len(p) }
func (p byPosition) Swap(i, j int) { p[i], p[j] = p[j], p[i] }

func (p byPosition) Less(i, j int) bool {
	pi, pj := p[i].Position, p[j].Position

	if pi.Filename != pj.Filename {
		return pi.Filename < pj.Filename
	}
	if pi.Line != pj.Line {
		return pi.Line < pj.Line
	}
	if pi.Column != pj.Column {
		return pi.Column < pj.Column
	}

	return p[i].Text < p[j].Text
}

// Lint lints src.
func (l *Linter) Lint(filename string, src []byte) ([]Problem, error) {
	return l.LintFiles(map[string][]byte{filename: src})
}

// LintFiles lints a set of files of a single package.
// The argument is a map of filename to source.
func (l *Linter) LintFiles(files map[string][]byte) ([]Problem, error) {
	pkg := &pkg{
		fset:  token.NewFileSet(),
		files: make(map[string]*file),
	}
	var pkgName string
	for filename, src := range files {
		if isGenerated(src) {
			continue // See issue #239
		}
		f, err := parser.ParseFile(pkg.fset, filename, src, parser.ParseComments)
		if err != nil {
			return nil, err
		}
		if pkgName == "" {
			pkgName = f.Name.Name
		} else if f.Name.Name != pkgName {
			return nil, fmt.Errorf("%s is in package %s, not %s", filename, f.Name.Name, pkgName)
		}
		pkg.files[filename] = &file{
			pkg:      pkg,
			f:        f,
			fset:     pkg.fset,
			src:      src,
			filename: filename,
		}
	}
	if len(pkg.files) == 0 {
		return nil, nil
	}
	return pkg.lint(), nil
}

var (
	genHdr = []byte("// Code generated ")
	genFtr = []byte(" DO NOT EDIT.")
)

// isGenerated reports whether the source file is generated code
// according the rules from https://golang.org/s/generatedcode.
func isGenerated(src []byte) bool {
	sc := bufio.NewScanner(bytes.NewReader(src))
	for sc.Scan() {
		b := sc.Bytes()
		if bytes.HasPrefix(b, genHdr) && bytes.HasSuffix(b, genFtr) && len(b) >= len(genHdr)+len(genFtr) {
			return true
		}
	}
	return false
}

// pkg represents a package being linted.
type pkg struct {
	fset  *token.FileSet
	files map[string]*file

	typesPkg  *types.Package
	typesInfo *types.Info

	// sortable is the set of types in the package that implement sort.Interface.
	sortable map[string]bool
	// main is whether this is a "main" package.
	main bool

	problems []Problem
}

func (p *pkg) lint() []Problem {
	if err := p.typeCheck(); err != nil {
		/* TODO(dsymonds): Consider reporting these errors when golint operates on entire packages.
		if e, ok := err.(types.Error); ok {
			pos := p.fset.Position(e.Pos)
			conf := 1.0
			if strings.Contains(e.Msg, "can't find import: ") {
				// Golint is probably being run in a context that doesn't support
				// typechecking (e.g. package files aren't found), so don't warn about it.
				conf = 0
			}
			if conf > 0 {
				p.errorfAt(pos, conf, category("typechecking"), e.Msg)
			}

			// TODO(dsymonds): Abort if !e.Soft?
		}
		*/
	}

	p.scanSortable()
	p.main = p.isMain()

	for _, f := range p.files {
		f.lint()
	}

	sort.Sort(byPosition(p.problems))

	return p.problems
}

// file represents a file being linted.
type file struct {
	pkg      *pkg
	f        *ast.File
	fset     *token.FileSet
	src      []byte
	filename string
}

func (f *file) isTest() bool { return strings.HasSuffix(f.filename, "_test.go") }

func (f *file) lint() {
	f.lintPackageComment()
	f.lintImports()
	f.lintBlankImports()
	f.lintExported()
	f.lintNames()
	f.lintElses()
	f.lintRanges()
	f.lintErrorf()
	f.lintErrors()
	f.lintErrorStrings()
	f.lintReceiverNames()
	f.lintIncDec()
	f.lintErrorReturn()
	f.lintUnexportedReturn()
	f.lintTimeNames()
	f.lintContextKeyTypes()
	f.lintContextArgs()
}

type link string
type category string

// The variadic arguments may start with link and category types,
// and must end with a format string and any arguments.
// It returns the new Problem.
func (f *file) errorf(n ast.Node, confidence float64, args ...interface{}) *Problem {
	pos := f.fset.Position(n.Pos())
	if pos.Filename == "" {
		pos.Filename = f.filename
	}
	return f.pkg.errorfAt(pos, confidence, args...)
}

func (p *pkg) errorfAt(pos token.Position, confidence float64, args ...interface{}) *Problem {
	problem := Problem{
		Position:   pos,
		Confidence: confidence,
	}
	if pos.Filename != "" {
		// The file might not exist in our mapping if a //line directive was encountered.
		if f, ok := p.files[pos.Filename]; ok {
			problem.LineText = srcLine(f.src, pos)
		}
	}

argLoop:
	for len(args) > 1 { // always leave at least the format string in args
		switch v := args[0].(type) {
		case link:
			problem.Link = string(v)
		case category:
			problem.Category = string(v)
		default:
			break argLoop
		}
		args = args[1:]
	}

	problem.Text = fmt.Sprintf(args[0].(string), args[1:]...)

	p.problems = append(p.problems, problem)
	return &p.problems[len(p.problems)-1]
}

var newImporter = func(fset *token.FileSet) types.ImporterFrom {
	return gcexportdata.NewImporter(fset, make(map[string]*types.Package))
}

func (p *pkg) typeCheck() error {
	config := &types.Config{
		// By setting a no-op error reporter, the type checker does as much work as possible.
		Error:    func(error) {},
		Importer: newImporter(p.fset),
	}
	info := &types.Info{
		Types:  make(map[ast.Expr]types.TypeAndValue),
		Defs:   make(map[*ast.Ident]types.Object),
		Uses:   make(map[*ast.Ident]types.Object),
		Scopes: make(map[ast.Node]*types.Scope),
	}
	var anyFile *file
	var astFiles []*ast.File
	for _, f := range p.files {
		anyFile = f
		astFiles = append(astFiles, f.f)
	}
	pkg, err := config.Check(anyFile.f.Name.Name, p.fset, astFiles, info)
	// Remember the typechecking info, even if config.Check failed,
	// since we will get partial information.
	p.typesPkg = pkg
	p.typesInfo = info
	return err
}

func (p *pkg) typeOf(expr ast.Expr) types.Type {
	if p.typesInfo == nil {
		return nil
	}
	return p.typesInfo.TypeOf(expr)
}

func (p *pkg) isNamedType(typ types.Type, importPath, name string) bool {
	n, ok := typ.(*types.Named)
	if !ok {
		return false
	}
	tn := n.Obj()
	return tn != nil && tn.Pkg() != nil && tn.Pkg().Path() == importPath && tn.Name() == name
}

// scopeOf returns the tightest scope encompassing id.
func (p *pkg) scopeOf(id *ast.Ident) *types.Scope {
	var scope *types.Scope
	if obj := p.typesInfo.ObjectOf(id); obj != nil {
		scope = obj.Parent()
	}
	if scope == p.typesPkg.Scope() {
		// We were given a top-level identifier.
		// Use the file-level scope instead of the package-level scope.
		pos := id.Pos()
		for _, f := range p.files {
			if f.f.Pos() <= pos && pos < f.f.End() {
				scope = p.typesInfo.Scopes[f.f]
				break
			}
		}
	}
	return scope
}

func (p *pkg) scanSortable() {
	p.sortable = make(map[string]bool)

	// bitfield for which methods exist on each type.
	const (
		Len = 1 << iota
		Less
		Swap
	)
	nmap := map[string]int{"Len": Len, "Less": Less, "Swap": Swap}
	has := make(map[string]int)
	for _, f := range p.files {
		f.walk(func(n ast.Node) bool {
			fn, ok := n.(*ast.FuncDecl)
			if !ok || fn.Recv == nil || len(fn.Recv.List) == 0 {
				return true
			}
			// TODO(dsymonds): We could check the signature to be more precise.
			recv := receiverType(fn)
			if i, ok := nmap[fn.Name.Name]; ok {
				has[recv] |= i
			}
			return false
		})
	}
	for typ, ms := range has {
		if ms == Len|Less|Swap {
			p.sortable[typ] = true
		}
	}
}

func (p *pkg) isMain() bool {
	for _, f := range p.files {
		if f.isMain() {
			return true
		}
	}
	return false
}

func (f *file) isMain() bool {
	if f.f.Name.Name == "main" {
		return true
	}
	return false
}

// lintPackageComment checks package comments. It complains if
// there is no package comment, or if it is not of the right form.
// This has a notable false positive in that a package comment
// could rightfully appear in a different file of the same package,
// but that's not easy to fix since this linter is file-oriented.
func (f *file) lintPackageComment() {
	if f.isTest() {
		return
	}

	const ref = styleGuideBase + "#package-comments"
	prefix := "Package " + f.f.Name.Name + " "

	// Look for a detached package comment.
	// First, scan for the last comment that occurs before the "package" keyword.
	var lastCG *ast.CommentGroup
	for _, cg := range f.f.Comments {
		if cg.Pos() > f.f.Package {
			// Gone past "package" keyword.
			break
		}
		lastCG = cg
	}
	if lastCG != nil && strings.HasPrefix(lastCG.Text(), prefix) {
		endPos := f.fset.Position(lastCG.End())
		pkgPos := f.fset.Position(f.f.Package)
		if endPos.Line+1 < pkgPos.Line {
			// There isn't a great place to anchor this error;
			// the start of the blank lines between the doc and the package statement
			// is at least pointing at the location of the problem.
			pos := token.Position{
				Filename: endPos.Filename,
				// Offset not set; it is non-trivial, and doesn't appear to be needed.
				Line:   endPos.Line + 1,
				Column: 1,
			}
			f.pkg.errorfAt(pos, 0.9, link(ref), category("comments"), "package comment is detached; there should be no blank lines between it and the package statement")
			return
		}
	}

	if f.f.Doc == nil {
		f.errorf(f.f, 0.2, link(ref), category("comments"), "should have a package comment, unless it's in another file for this package")
		return
	}
	s := f.f.Doc.Text()
	if ts := strings.TrimLeft(s, " \t"); ts != s {
		f.errorf(f.f.Doc, 1, link(ref), category("comments"), "package comment should not have leading space")
		s = ts
	}
	// Only non-main packages need to keep to this form.
	if !f.pkg.main && !strings.HasPrefix(s, prefix) {
		f.errorf(f.f.Doc, 1, link(ref), category("comments"), `package comment should be of the form "%s..."`, prefix)
	}
}

// lintBlankImports complains if a non-main package has blank imports that are
// not documented.
func (f *file) lintBlankImports() {
	// In package main and in tests, we don't complain about blank imports.
	if f.pkg.main || f.isTest() {
		return
	}

	// The first element of each contiguous group of blank imports should have
	// an explanatory comment of some kind.
	for i, imp := range f.f.Imports {
		pos := f.fset.Position(imp.Pos())

		if !isBlank(imp.Name) {
			continue // Ignore non-blank imports.
		}
		if i > 0 {
			prev := f.f.Imports[i-1]
			prevPos := f.fset.Position(prev.Pos())
			if isBlank(prev.Name) && prevPos.Line+1 == pos.Line {
				continue // A subsequent blank in a group.
			}
		}

		// This is the first blank import of a group.
		if imp.Doc == nil && imp.Comment == nil {
			ref := ""
			f.errorf(imp, 1, link(ref), category("imports"), "a blank import should be only in a main or test package, or have a comment justifying it")
		}
	}
}

// lintImports examines import blocks.
func (f *file) lintImports() {
	for i, is := range f.f.Imports {
		_ = i
		if is.Name != nil && is.Name.Name == "." && !f.isTest() {
			f.errorf(is, 1, link(styleGuideBase+"#import-dot"), category("imports"), "should not use dot imports")
		}

	}
}

const docCommentsLink = styleGuideBase + "#doc-comments"

// lintExported examines the exported names.
// It complains if any required doc comments are missing,
// or if they are not of the right form. The exact rules are in
// lintFuncDoc, lintTypeDoc and lintValueSpecDoc; this function
// also tracks the GenDecl structure being traversed to permit
// doc comments for constants to be on top of the const block.
// It also complains if the names stutter when combined with
// the package name.
func (f *file) lintExported() {
	if f.isTest() {
		return
	}

	var lastGen *ast.GenDecl // last GenDecl entered.

	// Set of GenDecls that have already had missing comments flagged.
	genDeclMissingComments := make(map[*ast.GenDecl]bool)

	f.walk(func(node ast.Node) bool {
		switch v := node.(type) {
		case *ast.GenDecl:
			if v.Tok == token.IMPORT {
				return false
			}
			// token.CONST, token.TYPE or token.VAR
			lastGen = v
			return true
		case *ast.FuncDecl:
			f.lintFuncDoc(v)
			if v.Recv == nil {
				// Only check for stutter on functions, not methods.
				// Method names are not used package-qualified.
				f.checkStutter(v.Name, "func")
			}
			// Don't proceed inside funcs.
			return false
		case *ast.TypeSpec:
			// inside a GenDecl, which usually has the doc
			doc := v.Doc
			if doc == nil {
				doc = lastGen.Doc
			}
			f.lintTypeDoc(v, doc)
			f.checkStutter(v.Name, "type")
			// Don't proceed inside types.
			return false
		case *ast.ValueSpec:
			f.lintValueSpecDoc(v, lastGen, genDeclMissingComments)
			return false
		}
		return true
	})
}

var (
	allCapsRE = regexp.MustCompile(`^[A-Z0-9_]+$`)
	anyCapsRE = regexp.MustCompile(`[A-Z]`)
)

// knownNameExceptions is a set of names that are known to be exempt from naming checks.
// This is usually because they are constrained by having to match names in the
// standard library.
var knownNameExceptions = map[string]bool{
	"LastInsertId": true, // must match database/sql
	"kWh":          true,
}

func isInTopLevel(f *ast.File, ident *ast.Ident) bool {
	path, _ := astutil.PathEnclosingInterval(f, ident.Pos(), ident.End())
	for _, f := range path {
		switch f.(type) {
		case *ast.File, *ast.GenDecl, *ast.ValueSpec, *ast.Ident:
			continue
		}
		return false
	}
	return true
}

// lintNames examines all names in the file.
// It complains if any use underscores or incorrect known initialisms.
func (f *file) lintNames() {
	// Package names need slightly different handling than other names.
	if strings.Contains(f.f.Name.Name, "_") && !strings.HasSuffix(f.f.Name.Name, "_test") {
		f.errorf(f.f, 1, link("http://golang.org/doc/effective_go.html#package-names"), category("naming"), "don't use an underscore in package name")
	}
	if anyCapsRE.MatchString(f.f.Name.Name) {
		f.errorf(f.f, 1, link("http://golang.org/doc/effective_go.html#package-names"), category("mixed-caps"), "don't use MixedCaps in package name; %s should be %s", f.f.Name.Name, strings.ToLower(f.f.Name.Name))
	}

	check := func(id *ast.Ident, thing string) {
		if id.Name == "_" {
			return
		}
		if knownNameExceptions[id.Name] {
			return
		}

		// Handle two common styles from other languages that don't belong in Go.
		if len(id.Name) >= 5 && allCapsRE.MatchString(id.Name) && strings.Contains(id.Name, "_") {
			capCount := 0
			for _, c := range id.Name {
				if 'A' <= c && c <= 'Z' {
					capCount++
				}
			}
			if capCount >= 2 {
				f.errorf(id, 0.8, link(styleGuideBase+"#mixed-caps"), category("naming"), "don't use ALL_CAPS in Go names; use CamelCase")
				return
			}
		}
		if thing == "const" || (thing == "var" && isInTopLevel(f.f, id)) {
			if len(id.Name) > 2 && id.Name[0] == 'k' && id.Name[1] >= 'A' && id.Name[1] <= 'Z' {
				should := string(id.Name[1]+'a'-'A') + id.Name[2:]
				f.errorf(id, 0.8, link(styleGuideBase+"#mixed-caps"), category("naming"), "don't use leading k in Go names; %s %s should be %s", thing, id.Name, should)
			}
		}

		should := lintName(id.Name)
		if id.Name == should {
			return
		}

		if len(id.Name) > 2 && strings.Contains(id.Name[1:], "_") {
			f.errorf(id, 0.9, link("http://golang.org/doc/effective_go.html#mixed-caps"), category("naming"), "don't use underscores in Go names; %s %s should be %s", thing, id.Name, should)
			return
		}
		f.errorf(id, 0.8, link(styleGuideBase+"#initialisms"), category("naming"), "%s %s should be %s", thing, id.Name, should)
	}
	checkList := func(fl *ast.FieldList, thing string) {
		if fl == nil {
			return
		}
		for _, f := range fl.List {
			for _, id := range f.Names {
				check(id, thing)
			}
		}
	}
	f.walk(func(node ast.Node) bool {
		switch v := node.(type) {
		case *ast.AssignStmt:
			if v.Tok == token.ASSIGN {
				return true
			}
			for _, exp := range v.Lhs {
				if id, ok := exp.(*ast.Ident); ok {
					check(id, "var")
				}
			}
		case *ast.FuncDecl:
			if f.isTest() && (strings.HasPrefix(v.Name.Name, "Example") || strings.HasPrefix(v.Name.Name, "Test") || strings.HasPrefix(v.Name.Name, "Benchmark")) {
				return true
			}

			thing := "func"
			if v.Recv != nil {
				thing = "method"
			}

			// Exclude naming warnings for functions that are exported to C but
			// not exported in the Go API.
			// See https://github.com/golang/lint/issues/144.
			if ast.IsExported(v.Name.Name) || !isCgoExported(v) {
				check(v.Name, thing)
			}

			checkList(v.Type.Params, thing+" parameter")
			checkList(v.Type.Results, thing+" result")
		case *ast.GenDecl:
			if v.Tok == token.IMPORT {
				return true
			}
			var thing string
			switch v.Tok {
			case token.CONST:
				thing = "const"
			case token.TYPE:
				thing = "type"
			case token.VAR:
				thing = "var"
			}
			for _, spec := range v.Specs {
				switch s := spec.(type) {
				case *ast.TypeSpec:
					check(s.Name, thing)
				case *ast.ValueSpec:
					for _, id := range s.Names {
						check(id, thing)
					}
				}
			}
		case *ast.InterfaceType:
			// Do not check interface method names.
			// They are often constrainted by the method names of concrete types.
			for _, x := range v.Methods.List {
				ft, ok := x.Type.(*ast.FuncType)
				if !ok { // might be an embedded interface name
					continue
				}
				checkList(ft.Params, "interface method parameter")
				checkList(ft.Results, "interface method result")
			}
		case *ast.RangeStmt:
			if v.Tok == token.ASSIGN {
				return true
			}
			if id, ok := v.Key.(*ast.Ident); ok {
				check(id, "range var")
			}
			if id, ok := v.Value.(*ast.Ident); ok {
				check(id, "range var")
			}
		case *ast.StructType:
			for _, f := range v.Fields.List {
				for _, id := range f.Names {
					check(id, "struct field")
				}
			}
		}
		return true
	})
}

// lintName returns a different name if it should be different.
func lintName(name string) (should string) {
	// Fast path for simple cases: "_" and all lowercase.
	if name == "_" {
		return name
	}
	allLower := true
	for _, r := range name {
		if !unicode.IsLower(r) {
			allLower = false
			break
		}
	}
	if allLower {
		return name
	}

	// Split camelCase at any lower->upper transition, and split on underscores.
	// Check each word for common initialisms.
	runes := []rune(name)
	w, i := 0, 0 // index of start of word, scan
	for i+1 <= len(runes) {
		eow := false // whether we hit the end of a word
		if i+1 == len(runes) {
			eow = true
		} else if runes[i+1] == '_' {
			// underscore; shift the remainder forward over any run of underscores
			eow = true
			n := 1
			for i+n+1 < len(runes) && runes[i+n+1] == '_' {
				n++
			}

			// Leave at most one underscore if the underscore is between two digits
			if i+n+1 < len(runes) && unicode.IsDigit(runes[i]) && unicode.IsDigit(runes[i+n+1]) {
				n--
			}

			copy(runes[i+1:], runes[i+n+1:])
			runes = runes[:len(runes)-n]
		} else if unicode.IsLower(runes[i]) && !unicode.IsLower(runes[i+1]) {
			// lower->non-lower
			eow = true
		}
		i++
		if !eow {
			continue
		}

		// [w,i) is a word.
		word := string(runes[w:i])
		if u := strings.ToUpper(word); commonInitialisms[u] {
			// Keep consistent case, which is lowercase only at the start.
			if w == 0 && unicode.IsLower(runes[w]) {
				u = strings.ToLower(u)
			}
			// All the common initialisms are ASCII,
			// so we can replace the bytes exactly.
			copy(runes[w:], []rune(u))
		} else if w > 0 && strings.ToLower(word) == word {
			// already all lowercase, and not the first word, so uppercase the first character.
			runes[w] = unicode.ToUpper(runes[w])
		}
		w = i
	}
	return string(runes)
}

// commonInitialisms is a set of common initialisms.
// Only add entries that are highly unlikely to be non-initialisms.
// For instance, "ID" is fine (Freudian code is rare), but "AND" is not.
var commonInitialisms = map[string]bool{
	"ACL":   true,
	"API":   true,
	"ASCII": true,
	"CPU":   true,
	"CSS":   true,
	"DNS":   true,
	"EOF":   true,
	"GUID":  true,
	"HTML":  true,
	"HTTP":  true,
	"HTTPS": true,
	"ID":    true,
	"IP":    true,
	"JSON":  true,
	"LHS":   true,
	"QPS":   true,
	"RAM":   true,
	"RHS":   true,
	"RPC":   true,
	"SLA":   true,
	"SMTP":  true,
	"SQL":   true,
	"SSH":   true,
	"TCP":   true,
	"TLS":   true,
	"TTL":   true,
	"UDP":   true,
	"UI":    true,
	"UID":   true,
	"UUID":  true,
	"URI":   true,
	"URL":   true,
	"UTF8":  true,
	"VM":    true,
	"XML":   true,
	"XMPP":  true,
	"XSRF":  true,
	"XSS":   true,
}

// lintTypeDoc examines the doc comment on a type.
// It complains if they are missing from an exported type,
// or if they are not of the standard form.
func (f *file) lintTypeDoc(t *ast.TypeSpec, doc *ast.CommentGroup) {
	if !ast.IsExported(t.Name.Name) {
		return
	}
	if doc == nil {
		f.errorf(t, 1, link(docCommentsLink), category("comments"), "exported type %v should have comment or be unexported", t.Name)
		return
	}

	s := doc.Text()
	articles := [...]string{"A", "An", "The"}
	for _, a := range articles {
		if strings.HasPrefix(s, a+" ") {
			s = s[len(a)+1:]
			break
		}
	}
	if !strings.HasPrefix(s, t.Name.Name+" ") {
		f.errorf(doc, 1, link(docCommentsLink), category("comments"), `comment on exported type %v should be of the form "%v ..." (with optional leading article)`, t.Name, t.Name)
	}
}

var commonMethods = map[string]bool{
	"Error":     true,
	"Read":      true,
	"ServeHTTP": true,
	"String":    true,
	"Write":     true,
	"Unwrap":    true,
}

// lintFuncDoc examines doc comments on functions and methods.
// It complains if they are missing, or not of the right form.
// It has specific exclusions for well-known methods (see commonMethods above).
func (f *file) lintFuncDoc(fn *ast.FuncDecl) {
	if !ast.IsExported(fn.Name.Name) {
		// func is unexported
		return
	}
	kind := "function"
	name := fn.Name.Name
	if fn.Recv != nil && len(fn.Recv.List) > 0 {
		// method
		kind = "method"
		recv := receiverType(fn)
		if !ast.IsExported(recv) {
			// receiver is unexported
			return
		}
		if commonMethods[name] {
			return
		}
		switch name {
		case "Len", "Less", "Swap":
			if f.pkg.sortable[recv] {
				return
			}
		}
		name = recv + "." + name
	}
	if fn.Doc == nil {
		f.errorf(fn, 1, link(docCommentsLink), category("comments"), "exported %s %s should have comment or be unexported", kind, name)
		return
	}
	s := fn.Doc.Text()
	prefix := fn.Name.Name + " "
	if !strings.HasPrefix(s, prefix) {
		f.errorf(fn.Doc, 1, link(docCommentsLink), category("comments"), `comment on exported %s %s should be of the form "%s..."`, kind, name, prefix)
	}
}

// lintValueSpecDoc examines package-global variables and constants.
// It complains if they are not individually declared,
// or if they are not suitably documented in the right form (unless they are in a block that is commented).
func (f *file) lintValueSpecDoc(vs *ast.ValueSpec, gd *ast.GenDecl, genDeclMissingComments map[*ast.GenDecl]bool) {
	kind := "var"
	if gd.Tok == token.CONST {
		kind = "const"
	}

	if len(vs.Names) > 1 {
		// Check that none are exported except for the first.
		for _, n := range vs.Names[1:] {
			if ast.IsExported(n.Name) {
				f.errorf(vs, 1, category("comments"), "exported %s %s should have its own declaration", kind, n.Name)
				return
			}
		}
	}

	// Only one name.
	name := vs.Names[0].Name
	if !ast.IsExported(name) {
		return
	}

	if vs.Doc == nil && gd.Doc == nil {
		if genDeclMissingComments[gd] {
			return
		}
		block := ""
		if kind == "const" && gd.Lparen.IsValid() {
			block = " (or a comment on this block)"
		}
		f.errorf(vs, 1, link(docCommentsLink), category("comments"), "exported %s %s should have comment%s or be unexported", kind, name, block)
		genDeclMissingComments[gd] = true
		return
	}
	// If this GenDecl has parens and a comment, we don't check its comment form.
	if gd.Lparen.IsValid() && gd.Doc != nil {
		return
	}
	// The relevant text to check will be on either vs.Doc or gd.Doc.
	// Use vs.Doc preferentially.
	doc := vs.Doc
	if doc == nil {
		doc = gd.Doc
	}
	prefix := name + " "
	if !strings.HasPrefix(doc.Text(), prefix) {
		f.errorf(doc, 1, link(docCommentsLink), category("comments"), `comment on exported %s %s should be of the form "%s..."`, kind, name, prefix)
	}
}

func (f *file) checkStutter(id *ast.Ident, thing string) {
	pkg, name := f.f.Name.Name, id.Name
	if !ast.IsExported(name) {
		// unexported name
		return
	}
	// A name stutters if the package name is a strict prefix
	// and the next character of the name starts a new word.
	if len(name) <= len(pkg) {
		// name is too short to stutter.
		// This permits the name to be the same as the package name.
		return
	}
	if !strings.EqualFold(pkg, name[:len(pkg)]) {
		return
	}
	// We can assume the name is well-formed UTF-8.
	// If the next rune after the package name is uppercase or an underscore
	// the it's starting a new word and thus this name stutters.
	rem := name[len(pkg):]
	if next, _ := utf8.DecodeRuneInString(rem); next == '_' || unicode.IsUpper(next) {
		f.errorf(id, 0.8, link(styleGuideBase+"#package-names"), category("naming"), "%s name will be used as %s.%s by other packages, and that stutters; consider calling this %s", thing, pkg, name, rem)
	}
}

// zeroLiteral is a set of ast.BasicLit values that are zero values.
// It is not exhaustive.
var zeroLiteral = map[string]bool{
	"false": true, // bool
	// runes
	`'\x00'`: true,
	`'\000'`: true,
	// strings
	`""`: true,
	"``": true,
	// numerics
	"0":   true,
	"0.":  true,
	"0.0": true,
	"0i":  true,
}

// lintElses examines else blocks. It complains about any else block whose if block ends in a return.
func (f *file) lintElses() {
	// We don't want to flag if { } else if { } else { } constructions.
	// They will appear as an IfStmt whose Else field is also an IfStmt.
	// Record such a node so we ignore it when we visit it.
	ignore := make(map[*ast.IfStmt]bool)

	f.walk(func(node ast.Node) bool {
		ifStmt, ok := node.(*ast.IfStmt)
		if !ok || ifStmt.Else == nil {
			return true
		}
		if elseif, ok := ifStmt.Else.(*ast.IfStmt); ok {
			ignore[elseif] = true
			return true
		}
		if ignore[ifStmt] {
			return true
		}
		if _, ok := ifStmt.Else.(*ast.BlockStmt); !ok {
			// only care about elses without conditions
			return true
		}
		if len(ifStmt.Body.List) == 0 {
			return true
		}
		shortDecl := false // does the if statement have a ":=" initialization statement?
		if ifStmt.Init != nil {
			if as, ok := ifStmt.Init.(*ast.AssignStmt); ok && as.Tok == token.DEFINE {
				shortDecl = true
			}
		}
		lastStmt := ifStmt.Body.List[len(ifStmt.Body.List)-1]
		if _, ok := lastStmt.(*ast.ReturnStmt); ok {
			extra := ""
			if shortDecl {
				extra = " (move short variable declaration to its own line if necessary)"
			}
			f.errorf(ifStmt.Else, 1, link(styleGuideBase+"#indent-error-flow"), category("indent"), "if block ends with a return statement, so drop this else and outdent its block"+extra)
		}
		return true
	})
}

// lintRanges examines range clauses. It complains about redundant constructions.
func (f *file) lintRanges() {
	f.walk(func(node ast.Node) bool {
		rs, ok := node.(*ast.RangeStmt)
		if !ok {
			return true
		}

		if isIdent(rs.Key, "_") && (rs.Value == nil || isIdent(rs.Value, "_")) {
			p := f.errorf(rs.Key, 1, category("range-loop"), "should omit values from range; this loop is equivalent to `for range ...`")

			newRS := *rs // shallow copy
			newRS.Value = nil
			newRS.Key = nil
			p.ReplacementLine = f.firstLineOf(&newRS, rs)

			return true
		}

		if isIdent(rs.Value, "_") {
			p := f.errorf(rs.Value, 1, category("range-loop"), "should omit 2nd value from range; this loop is equivalent to `for %s %s range ...`", f.render(rs.Key), rs.Tok)

			newRS := *rs // shallow copy
			newRS.Value = nil
			p.ReplacementLine = f.firstLineOf(&newRS, rs)
		}

		return true
	})
}

// lintErrorf examines errors.New and testing.Error calls. It complains if its only argument is an fmt.Sprintf invocation.
func (f *file) lintErrorf() {
	f.walk(func(node ast.Node) bool {
		ce, ok := node.(*ast.CallExpr)
		if !ok || len(ce.Args) != 1 {
			return true
		}
		isErrorsNew := isPkgDot(ce.Fun, "errors", "New")
		var isTestingError bool
		se, ok := ce.Fun.(*ast.SelectorExpr)
		if ok && se.Sel.Name == "Error" {
			if typ := f.pkg.typeOf(se.X); typ != nil {
				isTestingError = typ.String() == "*testing.T"
			}
		}
		if !isErrorsNew && !isTestingError {
			return true
		}
		if !f.imports("errors") {
			return true
		}
		arg := ce.Args[0]
		ce, ok = arg.(*ast.CallExpr)
		if !ok || !isPkgDot(ce.Fun, "fmt", "Sprintf") {
			return true
		}
		errorfPrefix := "fmt"
		if isTestingError {
			errorfPrefix = f.render(se.X)
		}
		p := f.errorf(node, 1, category("errors"), "should replace %s(fmt.Sprintf(...)) with %s.Errorf(...)", f.render(se), errorfPrefix)

		m := f.srcLineWithMatch(ce, `^(.*)`+f.render(se)+`\(fmt\.Sprintf\((.*)\)\)(.*)$`)
		if m != nil {
			p.ReplacementLine = m[1] + errorfPrefix + ".Errorf(" + m[2] + ")" + m[3]
		}

		return true
	})
}

// lintErrors examines global error vars. It complains if they aren't named in the standard way.
func (f *file) lintErrors() {
	for _, decl := range f.f.Decls {
		gd, ok := decl.(*ast.GenDecl)
		if !ok || gd.Tok != token.VAR {
			continue
		}
		for _, spec := range gd.Specs {
			spec := spec.(*ast.ValueSpec)
			if len(spec.Names) != 1 || len(spec.Values) != 1 {
				continue
			}
			ce, ok := spec.Values[0].(*ast.CallExpr)
			if !ok {
				continue
			}
			if !isPkgDot(ce.Fun, "errors", "New") && !isPkgDot(ce.Fun, "fmt", "Errorf") {
				continue
			}

			id := spec.Names[0]
			prefix := "err"
			if id.IsExported() {
				prefix = "Err"
			}
			if !strings.HasPrefix(id.Name, prefix) {
				f.errorf(id, 0.9, category("naming"), "error var %s should have name of the form %sFoo", id.Name, prefix)
			}
		}
	}
}

func lintErrorString(s string) (isClean bool, conf float64) {
	const basicConfidence = 0.8
	const capConfidence = basicConfidence - 0.2
	first, firstN := utf8.DecodeRuneInString(s)
	last, _ := utf8.DecodeLastRuneInString(s)
	if last == '.' || last == ':' || last == '!' || last == '\n' {
		return false, basicConfidence
	}
	if unicode.IsUpper(first) {
		// People use proper nouns and exported Go identifiers in error strings,
		// so decrease the confidence of warnings for capitalization.
		if len(s) <= firstN {
			return false, capConfidence
		}
		// Flag strings starting with something that doesn't look like an initialism.
		if second, _ := utf8.DecodeRuneInString(s[firstN:]); !unicode.IsUpper(second) {
			return false, capConfidence
		}
	}
	return true, 0
}

// lintErrorStrings examines error strings.
// It complains if they are capitalized or end in punctuation or a newline.
func (f *file) lintErrorStrings() {
	f.walk(func(node ast.Node) bool {
		ce, ok := node.(*ast.CallExpr)
		if !ok {
			return true
		}
		if !isPkgDot(ce.Fun, "errors", "New") && !isPkgDot(ce.Fun, "fmt", "Errorf") {
			return true
		}
		if len(ce.Args) < 1 {
			return true
		}
		str, ok := ce.Args[0].(*ast.BasicLit)
		if !ok || str.Kind != token.STRING {
			return true
		}
		s, _ := strconv.Unquote(str.Value) // can assume well-formed Go
		if s == "" {
			return true
		}
		clean, conf := lintErrorString(s)
		if clean {
			return true
		}

		f.errorf(str, conf, link(styleGuideBase+"#error-strings"), category("errors"),
			"error strings should not be capitalized or end with punctuation or a newline")
		return true
	})
}

// lintReceiverNames examines receiver names. It complains about inconsistent
// names used for the same type and names such as "this".
func (f *file) lintReceiverNames() {
	typeReceiver := map[string]string{}
	f.walk(func(n ast.Node) bool {
		fn, ok := n.(*ast.FuncDecl)
		if !ok || fn.Recv == nil || len(fn.Recv.List) == 0 {
			return true
		}
		names := fn.Recv.List[0].Names
		if len(names) < 1 {
			return true
		}
		name := names[0].Name
		const ref = styleGuideBase + "#receiver-names"
		if name == "_" {
			f.errorf(n, 1, link(ref), category("naming"), `receiver name should not be an underscore, omit the name if it is unused`)
			return true
		}
		if name == "this" || name == "self" {
			f.errorf(n, 1, link(ref), category("naming"), `receiver name should be a reflection of its identity; don't use generic names such as "this" or "self"`)
			return true
		}
		recv := receiverType(fn)
		if prev, ok := typeReceiver[recv]; ok && prev != name {
			f.errorf(n, 1, link(ref), category("naming"), "receiver name %s should be consistent with previous receiver name %s for %s", name, prev, recv)
			return true
		}
		typeReceiver[recv] = name
		return true
	})
}

// lintIncDec examines statements that increment or decrement a variable.
// It complains if they don't use x++ or x--.
func (f *file) lintIncDec() {
	f.walk(func(n ast.Node) bool {
		as, ok := n.(*ast.AssignStmt)
		if !ok {
			return true
		}
		if len(as.Lhs) != 1 {
			return true
		}
		if !isOne(as.Rhs[0]) {
			return true
		}
		var suffix string
		switch as.Tok {
		case token.ADD_ASSIGN:
			suffix = "++"
		case token.SUB_ASSIGN:
			suffix = "--"
		default:
			return true
		}
		f.errorf(as, 0.8, category("unary-op"), "should replace %s with %s%s", f.render(as), f.render(as.Lhs[0]), suffix)
		return true
	})
}

// lintErrorReturn examines function declarations that return an error.
// It complains if the error isn't the last parameter.
func (f *file) lintErrorReturn() {
	f.walk(func(n ast.Node) bool {
		fn, ok := n.(*ast.FuncDecl)
		if !ok || fn.Type.Results == nil {
			return true
		}
		ret := fn.Type.Results.List
		if len(ret) <= 1 {
			return true
		}
		if isIdent(ret[len(ret)-1].Type, "error") {
			return true
		}
		// An error return parameter should be the last parameter.
		// Flag any error parameters found before the last.
		for _, r := range ret[:len(ret)-1] {
			if isIdent(r.Type, "error") {
				f.errorf(fn, 0.9, category("arg-order"), "error should be the last type when returning multiple items")
				break // only flag one
			}
		}
		return true
	})
}

// lintUnexportedReturn examines exported function declarations.
// It complains if any return an unexported type.
func (f *file) lintUnexportedReturn() {
	f.walk(func(n ast.Node) bool {
		fn, ok := n.(*ast.FuncDecl)
		if !ok {
			return true
		}
		if fn.Type.Results == nil {
			return false
		}
		if !fn.Name.IsExported() {
			return false
		}
		thing := "func"
		if fn.Recv != nil && len(fn.Recv.List) > 0 {
			thing = "method"
			if !ast.IsExported(receiverType(fn)) {
				// Don't report exported methods of unexported types,
				// such as private implementations of sort.Interface.
				return false
			}
		}
		for _, ret := range fn.Type.Results.List {
			typ := f.pkg.typeOf(ret.Type)
			if exportedType(typ) {
				continue
			}
			f.errorf(ret.Type, 0.8, category("unexported-type-in-api"),
				"exported %s %s returns unexported type %s, which can be annoying to use",
				thing, fn.Name.Name, typ)
			break // only flag one
		}
		return false
	})
}

// exportedType reports whether typ is an exported type.
// It is imprecise, and will err on the side of returning true,
// such as for composite types.
func exportedType(typ types.Type) bool {
	switch T := typ.(type) {
	case *types.Named:
		// Builtin types have no package.
		return T.Obj().Pkg() == nil || T.Obj().Exported()
	case *types.Map:
		return exportedType(T.Key()) && exportedType(T.Elem())
	case interface {
		Elem() types.Type
	}: // array, slice, pointer, chan
		return exportedType(T.Elem())
	}
	// Be conservative about other types, such as struct, interface, etc.
	return true
}

// timeSuffixes is a list of name suffixes that imply a time unit.
// This is not an exhaustive list.
var timeSuffixes = []string{
	"Sec", "Secs", "Seconds",
	"Msec", "Msecs",
	"Milli", "Millis", "Milliseconds",
	"Usec", "Usecs", "Microseconds",
	"MS", "Ms",
}

func (f *file) lintTimeNames() {
	f.walk(func(node ast.Node) bool {
		v, ok := node.(*ast.ValueSpec)
		if !ok {
			return true
		}
		for _, name := range v.Names {
			origTyp := f.pkg.typeOf(name)
			// Look for time.Duration or *time.Duration;
			// the latter is common when using flag.Duration.
			typ := origTyp
			if pt, ok := typ.(*types.Pointer); ok {
				typ = pt.Elem()
			}
			if !f.pkg.isNamedType(typ, "time", "Duration") {
				continue
			}
			suffix := ""
			for _, suf := range timeSuffixes {
				if strings.HasSuffix(name.Name, suf) {
					suffix = suf
					break
				}
			}
			if suffix == "" {
				continue
			}
			f.errorf(v, 0.9, category("time"), "var %s is of type %v; don't use unit-specific suffix %q", name.Name, origTyp, suffix)
		}
		return true
	})
}

// lintContextKeyTypes checks for call expressions to context.WithValue with
// basic types used for the key argument.
// See: https://golang.org/issue/17293
func (f *file) lintContextKeyTypes() {
	f.walk(func(node ast.Node) bool {
		switch node := node.(type) {
		case *ast.CallExpr:
			f.checkContextKeyType(node)
		}

		return true
	})
}

// checkContextKeyType reports an error if the call expression calls
// context.WithValue with a key argument of basic type.
func (f *file) checkContextKeyType(x *ast.CallExpr) {
	sel, ok := x.Fun.(*ast.SelectorExpr)
	if !ok {
		return
	}
	pkg, ok := sel.X.(*ast.Ident)
	if !ok || pkg.Name != "context" {
		return
	}
	if sel.Sel.Name != "WithValue" {
		return
	}

	// key is second argument to context.WithValue
	if len(x.Args) != 3 {
		return
	}
	key := f.pkg.typesInfo.Types[x.Args[1]]

	if ktyp, ok := key.Type.(*types.Basic); ok && ktyp.Kind() != types.Invalid {
		f.errorf(x, 1.0, category("context"), fmt.Sprintf("should not use basic type %s as key in context.WithValue", key.Type))
	}
}

// lintContextArgs examines function declarations that contain an
// argument with a type of context.Context
// It complains if that argument isn't the first parameter.
func (f *file) lintContextArgs() {
	f.walk(func(n ast.Node) bool {
		fn, ok := n.(*ast.FuncDecl)
		if !ok || len(fn.Type.Params.List) <= 1 {
			return true
		}
		// A context.Context should be the first parameter of a function.
		// Flag any that show up after the first.
		for _, arg := range fn.Type.Params.List[1:] {
			if isPkgDot(arg.Type, "context", "Context") {
				f.errorf(fn, 0.9, link("https://golang.org/pkg/context/"), category("arg-order"), "context.Context should be the first parameter of a function")
				break // only flag one
			}
		}
		return true
	})
}

// containsComments returns whether the interval [start, end) contains any
// comments without "// MATCH " prefix.
func (f *file) containsComments(start, end token.Pos) bool {
	for _, cgroup := range f.f.Comments {
		comments := cgroup.List
		if comments[0].Slash >= end {
			// All comments starting with this group are after end pos.
			return false
		}
		if comments[len(comments)-1].Slash < start {
			// Comments group ends before start pos.
			continue
		}
		for _, c := range comments {
			if start <= c.Slash && c.Slash < end && !strings.HasPrefix(c.Text, "// MATCH ") {
				return true
			}
		}
	}
	return false
}

// receiverType returns the named type of the method receiver, sans "*",
// or "invalid-type" if fn.Recv is ill formed.
func receiverType(fn *ast.FuncDecl) string {
	switch e := fn.Recv.List[0].Type.(type) {
	case *ast.Ident:
		return e.Name
	case *ast.StarExpr:
		if id, ok := e.X.(*ast.Ident); ok {
			return id.Name
		}
	}
	// The parser accepts much more than just the legal forms.
	return "invalid-type"
}

func (f *file) walk(fn func(ast.Node) bool) {
	ast.Walk(walker(fn), f.f)
}

func (f *file) render(x interface{}) string {
	var buf bytes.Buffer
	if err := printer.Fprint(&buf, f.fset, x); err != nil {
		panic(err)
	}
	return buf.String()
}

func (f *file) debugRender(x interface{}) string {
	var buf bytes.Buffer
	if err := ast.Fprint(&buf, f.fset, x, nil); err != nil {
		panic(err)
	}
	return buf.String()
}

// walker adapts a function to satisfy the ast.Visitor interface.
// The function return whether the walk should proceed into the node's children.
type walker func(ast.Node) bool

func (w walker) Visit(node ast.Node) ast.Visitor {
	if w(node) {
		return w
	}
	return nil
}

func isIdent(expr ast.Expr, ident string) bool {
	id, ok := expr.(*ast.Ident)
	return ok && id.Name == ident
}

// isBlank returns whether id is the blank identifier "_".
// If id == nil, the answer is false.
func isBlank(id *ast.Ident) bool { return id != nil && id.Name == "_" }

func isPkgDot(expr ast.Expr, pkg, name string) bool {
	sel, ok := expr.(*ast.SelectorExpr)
	return ok && isIdent(sel.X, pkg) && isIdent(sel.Sel, name)
}

func isOne(expr ast.Expr) bool {
	lit, ok := expr.(*ast.BasicLit)
	return ok && lit.Kind == token.INT && lit.Value == "1"
}

func isCgoExported(f *ast.FuncDecl) bool {
	if f.Recv != nil || f.Doc == nil {
		return false
	}

	cgoExport := regexp.MustCompile(fmt.Sprintf("(?m)^//export %s$", regexp.QuoteMeta(f.Name.Name)))
	for _, c := range f.Doc.List {
		if cgoExport.MatchString(c.Text) {
			return true
		}
	}
	return false
}

var basicTypeKinds = map[types.BasicKind]string{
	types.UntypedBool:    "bool",
	types.UntypedInt:     "int",
	types.UntypedRune:    "rune",
	types.UntypedFloat:   "float64",
	types.UntypedComplex: "complex128",
	types.UntypedString:  "string",
}

// isUntypedConst reports whether expr is an untyped constant,
// and indicates what its default type is.
// scope may be nil.
func (f *file) isUntypedConst(expr ast.Expr) (defType string, ok bool) {
	// Re-evaluate expr outside of its context to see if it's untyped.
	// (An expr evaluated within, for example, an assignment context will get the type of the LHS.)
	exprStr := f.render(expr)
	tv, err := types.Eval(f.fset, f.pkg.typesPkg, expr.Pos(), exprStr)
	if err != nil {
		return "", false
	}
	if b, ok := tv.Type.(*types.Basic); ok {
		if dt, ok := basicTypeKinds[b.Kind()]; ok {
			return dt, true
		}
	}

	return "", false
}

// firstLineOf renders the given node and returns its first line.
// It will also match the indentation of another node.
func (f *file) firstLineOf(node, match ast.Node) string {
	line := f.render(node)
	if i := strings.Index(line, "\n"); i >= 0 {
		line = line[:i]
	}
	return f.indentOf(match) + line
}

func (f *file) indentOf(node ast.Node) string {
	line := srcLine(f.src, f.fset.Position(node.Pos()))
	for i, r := range line {
		switch r {
		case ' ', '\t':
		default:
			return line[:i]
		}
	}
	return line // unusual or empty line
}

func (f *file) srcLineWithMatch(node ast.Node, pattern string) (m []string) {
	line := srcLine(f.src, f.fset.Position(node.Pos()))
	line = strings.TrimSuffix(line, "\n")
	rx := regexp.MustCompile(pattern)
	return rx.FindStringSubmatch(line)
}

// imports returns true if the current file imports the specified package path.
func (f *file) imports(importPath string) bool {
	all := astutil.Imports(f.fset, f.f)
	for _, p := range all {
		for _, i := range p {
			uq, err := strconv.Unquote(i.Path.Value)
			if err == nil && importPath == uq {
				return true
			}
		}
	}
	return false
}

// srcLine returns the complete line at p, including the terminating newline.
func srcLine(src []byte, p token.Position) string {
	// Run to end of line in both directions if not at line start/end.
	lo, hi := p.Offset, p.Offset+1
	for lo > 0 && src[lo-1] != '\n' {
		lo--
	}
	for hi < len(src) && src[hi-1] != '\n' {
		hi++
	}
	return string(src[lo:hi])
}