summaryrefslogtreecommitdiff
path: root/src/pkg/regexp/syntax/parse_test.go
blob: f3089294c6aa782d2d0acb055fd0476728336988 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
// Copyright 2011 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.

package syntax

import (
	"bytes"
	"fmt"
	"testing"
	"unicode"
)

type parseTest struct {
	Regexp string
	Dump   string
}

var parseTests = []parseTest{
	// Base cases
	{`a`, `lit{a}`},
	{`a.`, `cat{lit{a}dot{}}`},
	{`a.b`, `cat{lit{a}dot{}lit{b}}`},
	{`ab`, `str{ab}`},
	{`a.b.c`, `cat{lit{a}dot{}lit{b}dot{}lit{c}}`},
	{`abc`, `str{abc}`},
	{`a|^`, `alt{lit{a}bol{}}`},
	{`a|b`, `cc{0x61-0x62}`},
	{`(a)`, `cap{lit{a}}`},
	{`(a)|b`, `alt{cap{lit{a}}lit{b}}`},
	{`a*`, `star{lit{a}}`},
	{`a+`, `plus{lit{a}}`},
	{`a?`, `que{lit{a}}`},
	{`a{2}`, `rep{2,2 lit{a}}`},
	{`a{2,3}`, `rep{2,3 lit{a}}`},
	{`a{2,}`, `rep{2,-1 lit{a}}`},
	{`a*?`, `nstar{lit{a}}`},
	{`a+?`, `nplus{lit{a}}`},
	{`a??`, `nque{lit{a}}`},
	{`a{2}?`, `nrep{2,2 lit{a}}`},
	{`a{2,3}?`, `nrep{2,3 lit{a}}`},
	{`a{2,}?`, `nrep{2,-1 lit{a}}`},
	// Malformed { } are treated as literals.
	{`x{1001`, `str{x{1001}`},
	{`x{9876543210`, `str{x{9876543210}`},
	{`x{9876543210,`, `str{x{9876543210,}`},
	{`x{2,1`, `str{x{2,1}`},
	{`x{1,9876543210`, `str{x{1,9876543210}`},
	{``, `emp{}`},
	{`|`, `emp{}`}, // alt{emp{}emp{}} but got factored
	{`|x|`, `alt{emp{}lit{x}emp{}}`},
	{`.`, `dot{}`},
	{`^`, `bol{}`},
	{`$`, `eol{}`},
	{`\|`, `lit{|}`},
	{`\(`, `lit{(}`},
	{`\)`, `lit{)}`},
	{`\*`, `lit{*}`},
	{`\+`, `lit{+}`},
	{`\?`, `lit{?}`},
	{`{`, `lit{{}`},
	{`}`, `lit{}}`},
	{`\.`, `lit{.}`},
	{`\^`, `lit{^}`},
	{`\$`, `lit{$}`},
	{`\\`, `lit{\}`},
	{`[ace]`, `cc{0x61 0x63 0x65}`},
	{`[abc]`, `cc{0x61-0x63}`},
	{`[a-z]`, `cc{0x61-0x7a}`},
	{`[a]`, `lit{a}`},
	{`\-`, `lit{-}`},
	{`-`, `lit{-}`},
	{`\_`, `lit{_}`},
	{`abc`, `str{abc}`},
	{`abc|def`, `alt{str{abc}str{def}}`},
	{`abc|def|ghi`, `alt{str{abc}str{def}str{ghi}}`},

	// Posix and Perl extensions
	{`[[:lower:]]`, `cc{0x61-0x7a}`},
	{`[a-z]`, `cc{0x61-0x7a}`},
	{`[^[:lower:]]`, `cc{0x0-0x60 0x7b-0x10ffff}`},
	{`[[:^lower:]]`, `cc{0x0-0x60 0x7b-0x10ffff}`},
	{`(?i)[[:lower:]]`, `cc{0x41-0x5a 0x61-0x7a 0x17f 0x212a}`},
	{`(?i)[a-z]`, `cc{0x41-0x5a 0x61-0x7a 0x17f 0x212a}`},
	{`(?i)[^[:lower:]]`, `cc{0x0-0x40 0x5b-0x60 0x7b-0x17e 0x180-0x2129 0x212b-0x10ffff}`},
	{`(?i)[[:^lower:]]`, `cc{0x0-0x40 0x5b-0x60 0x7b-0x17e 0x180-0x2129 0x212b-0x10ffff}`},
	{`\d`, `cc{0x30-0x39}`},
	{`\D`, `cc{0x0-0x2f 0x3a-0x10ffff}`},
	{`\s`, `cc{0x9-0xa 0xc-0xd 0x20}`},
	{`\S`, `cc{0x0-0x8 0xb 0xe-0x1f 0x21-0x10ffff}`},
	{`\w`, `cc{0x30-0x39 0x41-0x5a 0x5f 0x61-0x7a}`},
	{`\W`, `cc{0x0-0x2f 0x3a-0x40 0x5b-0x5e 0x60 0x7b-0x10ffff}`},
	{`(?i)\w`, `cc{0x30-0x39 0x41-0x5a 0x5f 0x61-0x7a 0x17f 0x212a}`},
	{`(?i)\W`, `cc{0x0-0x2f 0x3a-0x40 0x5b-0x5e 0x60 0x7b-0x17e 0x180-0x2129 0x212b-0x10ffff}`},
	{`[^\\]`, `cc{0x0-0x5b 0x5d-0x10ffff}`},
	//	{ `\C`, `byte{}` },  // probably never

	// Unicode, negatives, and a double negative.
	{`\p{Braille}`, `cc{0x2800-0x28ff}`},
	{`\P{Braille}`, `cc{0x0-0x27ff 0x2900-0x10ffff}`},
	{`\p{^Braille}`, `cc{0x0-0x27ff 0x2900-0x10ffff}`},
	{`\P{^Braille}`, `cc{0x2800-0x28ff}`},
	{`\pZ`, `cc{0x20 0xa0 0x1680 0x2000-0x200a 0x2028-0x2029 0x202f 0x205f 0x3000}`},
	{`[\p{Braille}]`, `cc{0x2800-0x28ff}`},
	{`[\P{Braille}]`, `cc{0x0-0x27ff 0x2900-0x10ffff}`},
	{`[\p{^Braille}]`, `cc{0x0-0x27ff 0x2900-0x10ffff}`},
	{`[\P{^Braille}]`, `cc{0x2800-0x28ff}`},
	{`[\pZ]`, `cc{0x20 0xa0 0x1680 0x2000-0x200a 0x2028-0x2029 0x202f 0x205f 0x3000}`},
	{`\p{Lu}`, mkCharClass(unicode.IsUpper)},
	{`[\p{Lu}]`, mkCharClass(unicode.IsUpper)},
	{`(?i)[\p{Lu}]`, mkCharClass(isUpperFold)},
	{`\p{Any}`, `dot{}`},
	{`\p{^Any}`, `cc{}`},

	// Hex, octal.
	{`[\012-\234]\141`, `cat{cc{0xa-0x9c}lit{a}}`},
	{`[\x{41}-\x7a]\x61`, `cat{cc{0x41-0x7a}lit{a}}`},

	// More interesting regular expressions.
	{`a{,2}`, `str{a{,2}}`},
	{`\.\^\$\\`, `str{.^$\}`},
	{`[a-zABC]`, `cc{0x41-0x43 0x61-0x7a}`},
	{`[^a]`, `cc{0x0-0x60 0x62-0x10ffff}`},
	{`[α-ε☺]`, `cc{0x3b1-0x3b5 0x263a}`}, // utf-8
	{`a*{`, `cat{star{lit{a}}lit{{}}`},

	// Test precedences
	{`(?:ab)*`, `star{str{ab}}`},
	{`(ab)*`, `star{cap{str{ab}}}`},
	{`ab|cd`, `alt{str{ab}str{cd}}`},
	{`a(b|c)d`, `cat{lit{a}cap{cc{0x62-0x63}}lit{d}}`},

	// Test flattening.
	{`(?:a)`, `lit{a}`},
	{`(?:ab)(?:cd)`, `str{abcd}`},
	{`(?:a+b+)(?:c+d+)`, `cat{plus{lit{a}}plus{lit{b}}plus{lit{c}}plus{lit{d}}}`},
	{`(?:a+|b+)|(?:c+|d+)`, `alt{plus{lit{a}}plus{lit{b}}plus{lit{c}}plus{lit{d}}}`},
	{`(?:a|b)|(?:c|d)`, `cc{0x61-0x64}`},
	{`a|.`, `dot{}`},
	{`.|a`, `dot{}`},
	{`(?:[abc]|A|Z|hello|world)`, `alt{cc{0x41 0x5a 0x61-0x63}str{hello}str{world}}`},
	{`(?:[abc]|A|Z)`, `cc{0x41 0x5a 0x61-0x63}`},

	// Test Perl quoted literals
	{`\Q+|*?{[\E`, `str{+|*?{[}`},
	{`\Q+\E+`, `plus{lit{+}}`},
	{`\Q\\E`, `lit{\}`},
	{`\Q\\\E`, `str{\\}`},

	// Test Perl \A and \z
	{`(?m)^`, `bol{}`},
	{`(?m)$`, `eol{}`},
	{`(?-m)^`, `bot{}`},
	{`(?-m)$`, `eot{}`},
	{`(?m)\A`, `bot{}`},
	{`(?m)\z`, `eot{\z}`},
	{`(?-m)\A`, `bot{}`},
	{`(?-m)\z`, `eot{\z}`},

	// Test named captures
	{`(?P<name>a)`, `cap{name:lit{a}}`},

	// Case-folded literals
	{`[Aa]`, `litfold{A}`},
	{`[\x{100}\x{101}]`, `litfold{Ā}`},
	{`[Δδ]`, `litfold{Δ}`},

	// Strings
	{`abcde`, `str{abcde}`},
	{`[Aa][Bb]cd`, `cat{strfold{AB}str{cd}}`},

	// Factoring.
	{`abc|abd|aef|bcx|bcy`, `alt{cat{lit{a}alt{cat{lit{b}cc{0x63-0x64}}str{ef}}}cat{str{bc}cc{0x78-0x79}}}`},
	{`ax+y|ax+z|ay+w`, `cat{lit{a}alt{cat{plus{lit{x}}cc{0x79-0x7a}}cat{plus{lit{y}}lit{w}}}}`},

	// Bug fixes.
	{`(?:.)`, `dot{}`},
	{`(?:x|(?:xa))`, `cat{lit{x}alt{emp{}lit{a}}}`},
	{`(?:.|(?:.a))`, `cat{dot{}alt{emp{}lit{a}}}`},
	{`(?:A(?:A|a))`, `cat{lit{A}litfold{A}}`},
	{`(?:A|a)`, `litfold{A}`},
	{`A|(?:A|a)`, `litfold{A}`},
	{`(?s).`, `dot{}`},
	{`(?-s).`, `dnl{}`},
	{`(?:(?:^).)`, `cat{bol{}dot{}}`},
	{`(?-s)(?:(?:^).)`, `cat{bol{}dnl{}}`},

	// RE2 prefix_tests
	{`abc|abd`, `cat{str{ab}cc{0x63-0x64}}`},
	{`a(?:b)c|abd`, `cat{str{ab}cc{0x63-0x64}}`},
	{`abc|abd|aef|bcx|bcy`,
		`alt{cat{lit{a}alt{cat{lit{b}cc{0x63-0x64}}str{ef}}}` +
			`cat{str{bc}cc{0x78-0x79}}}`},
	{`abc|x|abd`, `alt{str{abc}lit{x}str{abd}}`},
	{`(?i)abc|ABD`, `cat{strfold{AB}cc{0x43-0x44 0x63-0x64}}`},
	{`[ab]c|[ab]d`, `cat{cc{0x61-0x62}cc{0x63-0x64}}`},
	{`(?:xx|yy)c|(?:xx|yy)d`,
		`cat{alt{str{xx}str{yy}}cc{0x63-0x64}}`},
	{`x{2}|x{2}[0-9]`,
		`cat{rep{2,2 lit{x}}alt{emp{}cc{0x30-0x39}}}`},
	{`x{2}y|x{2}[0-9]y`,
		`cat{rep{2,2 lit{x}}alt{lit{y}cat{cc{0x30-0x39}lit{y}}}}`},
}

const testFlags = MatchNL | PerlX | UnicodeGroups

func TestParseSimple(t *testing.T) {
	testParseDump(t, parseTests, testFlags)
}

var foldcaseTests = []parseTest{
	{`AbCdE`, `strfold{ABCDE}`},
	{`[Aa]`, `litfold{A}`},
	{`a`, `litfold{A}`},

	// 0x17F is an old English long s (looks like an f) and folds to s.
	// 0x212A is the Kelvin symbol and folds to k.
	{`A[F-g]`, `cat{litfold{A}cc{0x41-0x7a 0x17f 0x212a}}`}, // [Aa][A-z...]
	{`[[:upper:]]`, `cc{0x41-0x5a 0x61-0x7a 0x17f 0x212a}`},
	{`[[:lower:]]`, `cc{0x41-0x5a 0x61-0x7a 0x17f 0x212a}`},
}

func TestParseFoldCase(t *testing.T) {
	testParseDump(t, foldcaseTests, FoldCase)
}

var literalTests = []parseTest{
	{"(|)^$.[*+?]{5,10},\\", "str{(|)^$.[*+?]{5,10},\\}"},
}

func TestParseLiteral(t *testing.T) {
	testParseDump(t, literalTests, Literal)
}

var matchnlTests = []parseTest{
	{`.`, `dot{}`},
	{"\n", "lit{\n}"},
	{`[^a]`, `cc{0x0-0x60 0x62-0x10ffff}`},
	{`[a\n]`, `cc{0xa 0x61}`},
}

func TestParseMatchNL(t *testing.T) {
	testParseDump(t, matchnlTests, MatchNL)
}

var nomatchnlTests = []parseTest{
	{`.`, `dnl{}`},
	{"\n", "lit{\n}"},
	{`[^a]`, `cc{0x0-0x9 0xb-0x60 0x62-0x10ffff}`},
	{`[a\n]`, `cc{0xa 0x61}`},
}

func TestParseNoMatchNL(t *testing.T) {
	testParseDump(t, nomatchnlTests, 0)
}

// Test Parse -> Dump.
func testParseDump(t *testing.T, tests []parseTest, flags Flags) {
	for _, tt := range tests {
		re, err := Parse(tt.Regexp, flags)
		if err != nil {
			t.Errorf("Parse(%#q): %v", tt.Regexp, err)
			continue
		}
		d := dump(re)
		if d != tt.Dump {
			t.Errorf("Parse(%#q).Dump() = %#q want %#q", tt.Regexp, d, tt.Dump)
		}
	}
}

// dump prints a string representation of the regexp showing
// the structure explicitly.
func dump(re *Regexp) string {
	var b bytes.Buffer
	dumpRegexp(&b, re)
	return b.String()
}

var opNames = []string{
	OpNoMatch:        "no",
	OpEmptyMatch:     "emp",
	OpLiteral:        "lit",
	OpCharClass:      "cc",
	OpAnyCharNotNL:   "dnl",
	OpAnyChar:        "dot",
	OpBeginLine:      "bol",
	OpEndLine:        "eol",
	OpBeginText:      "bot",
	OpEndText:        "eot",
	OpWordBoundary:   "wb",
	OpNoWordBoundary: "nwb",
	OpCapture:        "cap",
	OpStar:           "star",
	OpPlus:           "plus",
	OpQuest:          "que",
	OpRepeat:         "rep",
	OpConcat:         "cat",
	OpAlternate:      "alt",
}

// dumpRegexp writes an encoding of the syntax tree for the regexp re to b.
// It is used during testing to distinguish between parses that might print
// the same using re's String method.
func dumpRegexp(b *bytes.Buffer, re *Regexp) {
	if int(re.Op) >= len(opNames) || opNames[re.Op] == "" {
		fmt.Fprintf(b, "op%d", re.Op)
	} else {
		switch re.Op {
		default:
			b.WriteString(opNames[re.Op])
		case OpStar, OpPlus, OpQuest, OpRepeat:
			if re.Flags&NonGreedy != 0 {
				b.WriteByte('n')
			}
			b.WriteString(opNames[re.Op])
		case OpLiteral:
			if len(re.Rune) > 1 {
				b.WriteString("str")
			} else {
				b.WriteString("lit")
			}
			if re.Flags&FoldCase != 0 {
				for _, r := range re.Rune {
					if unicode.SimpleFold(r) != r {
						b.WriteString("fold")
						break
					}
				}
			}
		}
	}
	b.WriteByte('{')
	switch re.Op {
	case OpEndText:
		if re.Flags&WasDollar == 0 {
			b.WriteString(`\z`)
		}
	case OpLiteral:
		for _, r := range re.Rune {
			b.WriteRune(r)
		}
	case OpConcat, OpAlternate:
		for _, sub := range re.Sub {
			dumpRegexp(b, sub)
		}
	case OpStar, OpPlus, OpQuest:
		dumpRegexp(b, re.Sub[0])
	case OpRepeat:
		fmt.Fprintf(b, "%d,%d ", re.Min, re.Max)
		dumpRegexp(b, re.Sub[0])
	case OpCapture:
		if re.Name != "" {
			b.WriteString(re.Name)
			b.WriteByte(':')
		}
		dumpRegexp(b, re.Sub[0])
	case OpCharClass:
		sep := ""
		for i := 0; i < len(re.Rune); i += 2 {
			b.WriteString(sep)
			sep = " "
			lo, hi := re.Rune[i], re.Rune[i+1]
			if lo == hi {
				fmt.Fprintf(b, "%#x", lo)
			} else {
				fmt.Fprintf(b, "%#x-%#x", lo, hi)
			}
		}
	}
	b.WriteByte('}')
}

func mkCharClass(f func(rune) bool) string {
	re := &Regexp{Op: OpCharClass}
	lo := rune(-1)
	for i := rune(0); i <= unicode.MaxRune; i++ {
		if f(i) {
			if lo < 0 {
				lo = i
			}
		} else {
			if lo >= 0 {
				re.Rune = append(re.Rune, lo, i-1)
				lo = -1
			}
		}
	}
	if lo >= 0 {
		re.Rune = append(re.Rune, lo, unicode.MaxRune)
	}
	return dump(re)
}

func isUpperFold(r rune) bool {
	if unicode.IsUpper(r) {
		return true
	}
	c := unicode.SimpleFold(r)
	for c != r {
		if unicode.IsUpper(c) {
			return true
		}
		c = unicode.SimpleFold(c)
	}
	return false
}

func TestFoldConstants(t *testing.T) {
	last := rune(-1)
	for i := rune(0); i <= unicode.MaxRune; i++ {
		if unicode.SimpleFold(i) == i {
			continue
		}
		if last == -1 && minFold != i {
			t.Errorf("minFold=%#U should be %#U", minFold, i)
		}
		last = i
	}
	if maxFold != last {
		t.Errorf("maxFold=%#U should be %#U", maxFold, last)
	}
}

func TestAppendRangeCollapse(t *testing.T) {
	// AppendRange should collapse each of the new ranges
	// into the earlier ones (it looks back two ranges), so that
	// the slice never grows very large.
	// Note that we are not calling cleanClass.
	var r []rune
	for i := rune('A'); i <= 'Z'; i++ {
		r = appendRange(r, i, i)
		r = appendRange(r, i+'a'-'A', i+'a'-'A')
	}
	if string(r) != "AZaz" {
		t.Errorf("appendRange interlaced A-Z a-z = %s, want AZaz", string(r))
	}
}

var invalidRegexps = []string{
	`(`,
	`)`,
	`(a`,
	`a)`,
	`(a))`,
	`(a|b|`,
	`a|b|)`,
	`(a|b|))`,
	`(a|b`,
	`a|b)`,
	`(a|b))`,
	`[a-z`,
	`([a-z)`,
	`[a-z)`,
	`([a-z]))`,
	`x{1001}`,
	`x{9876543210}`,
	`x{2,1}`,
	`x{1,9876543210}`,
	"\xff", // Invalid UTF-8
	"[\xff]",
	"[\\\xff]",
	"\\\xff",
	`(?P<name>a`,
	`(?P<name>`,
	`(?P<name`,
	`(?P<x y>a)`,
	`(?P<>a)`,
	`[a-Z]`,
	`(?i)[a-Z]`,
	`a{100000}`,
	`a{100000,}`,
}

var onlyPerl = []string{
	`[a-b-c]`,
	`\Qabc\E`,
	`\Q*+?{[\E`,
	`\Q\\E`,
	`\Q\\\E`,
	`\Q\\\\E`,
	`\Q\\\\\E`,
	`(?:a)`,
	`(?P<name>a)`,
}

var onlyPOSIX = []string{
	"a++",
	"a**",
	"a?*",
	"a+*",
	"a{1}*",
	".{1}{2}.{3}",
}

func TestParseInvalidRegexps(t *testing.T) {
	for _, regexp := range invalidRegexps {
		if re, err := Parse(regexp, Perl); err == nil {
			t.Errorf("Parse(%#q, Perl) = %s, should have failed", regexp, dump(re))
		}
		if re, err := Parse(regexp, POSIX); err == nil {
			t.Errorf("Parse(%#q, POSIX) = %s, should have failed", regexp, dump(re))
		}
	}
	for _, regexp := range onlyPerl {
		if _, err := Parse(regexp, Perl); err != nil {
			t.Errorf("Parse(%#q, Perl): %v", regexp, err)
		}
		if re, err := Parse(regexp, POSIX); err == nil {
			t.Errorf("Parse(%#q, POSIX) = %s, should have failed", regexp, dump(re))
		}
	}
	for _, regexp := range onlyPOSIX {
		if re, err := Parse(regexp, Perl); err == nil {
			t.Errorf("Parse(%#q, Perl) = %s, should have failed", regexp, dump(re))
		}
		if _, err := Parse(regexp, POSIX); err != nil {
			t.Errorf("Parse(%#q, POSIX): %v", regexp, err)
		}
	}
}

func TestToStringEquivalentParse(t *testing.T) {
	for _, tt := range parseTests {
		re, err := Parse(tt.Regexp, testFlags)
		if err != nil {
			t.Errorf("Parse(%#q): %v", tt.Regexp, err)
			continue
		}
		d := dump(re)
		if d != tt.Dump {
			t.Errorf("Parse(%#q).Dump() = %#q want %#q", tt.Regexp, d, tt.Dump)
			continue
		}

		s := re.String()
		if s != tt.Regexp {
			// If ToString didn't return the original regexp,
			// it must have found one with fewer parens.
			// Unfortunately we can't check the length here, because
			// ToString produces "\\{" for a literal brace,
			// but "{" is a shorter equivalent in some contexts.
			nre, err := Parse(s, testFlags)
			if err != nil {
				t.Errorf("Parse(%#q.String() = %#q): %v", tt.Regexp, s, err)
				continue
			}
			nd := dump(nre)
			if d != nd {
				t.Errorf("Parse(%#q) -> %#q; %#q vs %#q", tt.Regexp, s, d, nd)
			}

			ns := nre.String()
			if s != ns {
				t.Errorf("Parse(%#q) -> %#q -> %#q", tt.Regexp, s, ns)
			}
		}
	}
}