src/regexp/syntax/parse_test.go - go - Git at Google

 // 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 (
 	"fmt"
 	"strings"
 	"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{+}}`},
 	{`\Qab\E+`, `cat{lit{a}plus{lit{b}}}`},
 	{`\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}}lit{y}}cat{plus{lit{x}}lit{z}}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{}}`},
 	{`[\s\S]a`, `cat{cc{0x0-0x10ffff}lit{a}}`},

 	// 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}}`},
 	{`.c|.d`, `cat{dot{}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}}}}`},
 	{`a.*?c|a.*?b`,
 		`cat{lit{a}alt{cat{nstar{dot{}}lit{c}}cat{nstar{dot{}}lit{b}}}}`},

 	// Valid repetitions.
 	{`((((((((((x{2}){2}){2}){2}){2}){2}){2}){2}){2}))`, ``},
 	{`((((((((((x{1}){2}){2}){2}){2}){2}){2}){2}){2}){2})`, ``},

 	// Valid nesting.
 	{strings.Repeat("(", 999) + strings.Repeat(")", 999), ``},
 	{strings.Repeat("(?:", 999) + strings.Repeat(")*", 999), ``},
 	{"(" + strings.Repeat("|", 12345) + ")", ``}, // not nested at all
 }

 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
 		}
 		if tt.Dump == "" {
 			// It parsed. That's all we care about.
 			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 strings.Builder
 	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 *strings.Builder, 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,}`,
 	"((((((((((x{2}){2}){2}){2}){2}){2}){2}){2}){2}){2})",
 	strings.Repeat("(", 1000) + strings.Repeat(")", 1000),
 	strings.Repeat("(?:", 1000) + strings.Repeat(")*", 1000),
 	`\Q\E*`,
 }

 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
 		}
 		if tt.Dump == "" {
 			// It parsed. That's all we care about.
 			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)
 			}
 		}
 	}
 }
	// 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 (
	"fmt"
	"strings"
	"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{+}}`},
	{`\Qab\E+`, `cat{lit{a}plus{lit{b}}}`},
	{`\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}}lit{y}}cat{plus{lit{x}}lit{z}}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{}}`},
	{`[\s\S]a`, `cat{cc{0x0-0x10ffff}lit{a}}`},

	// 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}}`},
	{`.c\|.d`, `cat{dot{}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}}}}`},
	{`a.?c\|a.?b`,
	`cat{lit{a}alt{cat{nstar{dot{}}lit{c}}cat{nstar{dot{}}lit{b}}}}`},

	// Valid repetitions.
	{`((((((((((x{2}){2}){2}){2}){2}){2}){2}){2}){2}))`, ``},
	{`((((((((((x{1}){2}){2}){2}){2}){2}){2}){2}){2}){2})`, ``},

	// Valid nesting.
	{strings.Repeat("(", 999) + strings.Repeat(")", 999), ``},
	{strings.Repeat("(?:", 999) + strings.Repeat(")*", 999), ``},
	{"(" + strings.Repeat("\|", 12345) + ")", ``}, // not nested at all
	}

	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
	}
	if tt.Dump == "" {
	// It parsed. That's all we care about.
	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 strings.Builder
	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 strings.Builder, 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,}`,
	"((((((((((x{2}){2}){2}){2}){2}){2}){2}){2}){2}){2})",
	strings.Repeat("(", 1000) + strings.Repeat(")", 1000),
	strings.Repeat("(?:", 1000) + strings.Repeat(")*", 1000),
	`\Q\E*`,
	}

	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
	}
	if tt.Dump == "" {
	// It parsed. That's all we care about.
	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)
	}
	}
	}
	}