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// 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
// Note to implementers:
// In this package, re is always a *Regexp and r is always a rune.
import (
"strconv"
"strings"
"unicode"
)
// A Regexp is a node in a regular expression syntax tree.
type Regexp struct {
Op Op // operator
Flags Flags
Sub []*Regexp // subexpressions, if any
Sub0 [1]*Regexp // storage for short Sub
Rune []rune // matched runes, for OpLiteral, OpCharClass
Rune0 [2]rune // storage for short Rune
Min, Max int // min, max for OpRepeat
Cap int // capturing index, for OpCapture
Name string // capturing name, for OpCapture
}
//go:generate stringer -type Op -trimprefix Op
// An Op is a single regular expression operator.
type Op uint8
// Operators are listed in precedence order, tightest binding to weakest.
// Character class operators are listed simplest to most complex
// (OpLiteral, OpCharClass, OpAnyCharNotNL, OpAnyChar).
const (
OpNoMatch Op = 1 + iota // matches no strings
OpEmptyMatch // matches empty string
OpLiteral // matches Runes sequence
OpCharClass // matches Runes interpreted as range pair list
OpAnyCharNotNL // matches any character except newline
OpAnyChar // matches any character
OpBeginLine // matches empty string at beginning of line
OpEndLine // matches empty string at end of line
OpBeginText // matches empty string at beginning of text
OpEndText // matches empty string at end of text
OpWordBoundary // matches word boundary `\b`
OpNoWordBoundary // matches word non-boundary `\B`
OpCapture // capturing subexpression with index Cap, optional name Name
OpStar // matches Sub[0] zero or more times
OpPlus // matches Sub[0] one or more times
OpQuest // matches Sub[0] zero or one times
OpRepeat // matches Sub[0] at least Min times, at most Max (Max == -1 is no limit)
OpConcat // matches concatenation of Subs
OpAlternate // matches alternation of Subs
)
const opPseudo Op = 128 // where pseudo-ops start
// Equal reports whether x and y have identical structure.
func (x *Regexp) Equal(y *Regexp) bool {
if x == nil || y == nil {
return x == y
}
if x.Op != y.Op {
return false
}
switch x.Op {
case OpEndText:
// The parse flags remember whether this is \z or \Z.
if x.Flags&WasDollar != y.Flags&WasDollar {
return false
}
case OpLiteral, OpCharClass:
if len(x.Rune) != len(y.Rune) {
return false
}
for i, r := range x.Rune {
if r != y.Rune[i] {
return false
}
}
case OpAlternate, OpConcat:
if len(x.Sub) != len(y.Sub) {
return false
}
for i, sub := range x.Sub {
if !sub.Equal(y.Sub[i]) {
return false
}
}
case OpStar, OpPlus, OpQuest:
if x.Flags&NonGreedy != y.Flags&NonGreedy || !x.Sub[0].Equal(y.Sub[0]) {
return false
}
case OpRepeat:
if x.Flags&NonGreedy != y.Flags&NonGreedy || x.Min != y.Min || x.Max != y.Max || !x.Sub[0].Equal(y.Sub[0]) {
return false
}
case OpCapture:
if x.Cap != y.Cap || x.Name != y.Name || !x.Sub[0].Equal(y.Sub[0]) {
return false
}
}
return true
}
// writeRegexp writes the Perl syntax for the regular expression re to b.
func writeRegexp(b *strings.Builder, re *Regexp) {
switch re.Op {
default:
b.WriteString("<invalid op" + strconv.Itoa(int(re.Op)) + ">")
case OpNoMatch:
b.WriteString(`[^\x00-\x{10FFFF}]`)
case OpEmptyMatch:
b.WriteString(`(?:)`)
case OpLiteral:
if re.Flags&FoldCase != 0 {
b.WriteString(`(?i:`)
}
for _, r := range re.Rune {
escape(b, r, false)
}
if re.Flags&FoldCase != 0 {
b.WriteString(`)`)
}
case OpCharClass:
if len(re.Rune)%2 != 0 {
b.WriteString(`[invalid char class]`)
break
}
b.WriteRune('[')
if len(re.Rune) == 0 {
b.WriteString(`^\x00-\x{10FFFF}`)
} else if re.Rune[0] == 0 && re.Rune[len(re.Rune)-1] == unicode.MaxRune {
// Contains 0 and MaxRune. Probably a negated class.
// Print the gaps.
b.WriteRune('^')
for i := 1; i < len(re.Rune)-1; i += 2 {
lo, hi := re.Rune[i]+1, re.Rune[i+1]-1
escape(b, lo, lo == '-')
if lo != hi {
b.WriteRune('-')
escape(b, hi, hi == '-')
}
}
} else {
for i := 0; i < len(re.Rune); i += 2 {
lo, hi := re.Rune[i], re.Rune[i+1]
escape(b, lo, lo == '-')
if lo != hi {
b.WriteRune('-')
escape(b, hi, hi == '-')
}
}
}
b.WriteRune(']')
case OpAnyCharNotNL:
b.WriteString(`(?-s:.)`)
case OpAnyChar:
b.WriteString(`(?s:.)`)
case OpBeginLine:
b.WriteString(`(?m:^)`)
case OpEndLine:
b.WriteString(`(?m:$)`)
case OpBeginText:
b.WriteString(`\A`)
case OpEndText:
if re.Flags&WasDollar != 0 {
b.WriteString(`(?-m:$)`)
} else {
b.WriteString(`\z`)
}
case OpWordBoundary:
b.WriteString(`\b`)
case OpNoWordBoundary:
b.WriteString(`\B`)
case OpCapture:
if re.Name != "" {
b.WriteString(`(?P<`)
b.WriteString(re.Name)
b.WriteRune('>')
} else {
b.WriteRune('(')
}
if re.Sub[0].Op != OpEmptyMatch {
writeRegexp(b, re.Sub[0])
}
b.WriteRune(')')
case OpStar, OpPlus, OpQuest, OpRepeat:
if sub := re.Sub[0]; sub.Op > OpCapture || sub.Op == OpLiteral && len(sub.Rune) > 1 {
b.WriteString(`(?:`)
writeRegexp(b, sub)
b.WriteString(`)`)
} else {
writeRegexp(b, sub)
}
switch re.Op {
case OpStar:
b.WriteRune('*')
case OpPlus:
b.WriteRune('+')
case OpQuest:
b.WriteRune('?')
case OpRepeat:
b.WriteRune('{')
b.WriteString(strconv.Itoa(re.Min))
if re.Max != re.Min {
b.WriteRune(',')
if re.Max >= 0 {
b.WriteString(strconv.Itoa(re.Max))
}
}
b.WriteRune('}')
}
if re.Flags&NonGreedy != 0 {
b.WriteRune('?')
}
case OpConcat:
for _, sub := range re.Sub {
if sub.Op == OpAlternate {
b.WriteString(`(?:`)
writeRegexp(b, sub)
b.WriteString(`)`)
} else {
writeRegexp(b, sub)
}
}
case OpAlternate:
for i, sub := range re.Sub {
if i > 0 {
b.WriteRune('|')
}
writeRegexp(b, sub)
}
}
}
func (re *Regexp) String() string {
var b strings.Builder
writeRegexp(&b, re)
return b.String()
}
const meta = `\.+*?()|[]{}^$`
func escape(b *strings.Builder, r rune, force bool) {
if unicode.IsPrint(r) {
if strings.ContainsRune(meta, r) || force {
b.WriteRune('\\')
}
b.WriteRune(r)
return
}
switch r {
case '\a':
b.WriteString(`\a`)
case '\f':
b.WriteString(`\f`)
case '\n':
b.WriteString(`\n`)
case '\r':
b.WriteString(`\r`)
case '\t':
b.WriteString(`\t`)
case '\v':
b.WriteString(`\v`)
default:
if r < 0x100 {
b.WriteString(`\x`)
s := strconv.FormatInt(int64(r), 16)
if len(s) == 1 {
b.WriteRune('0')
}
b.WriteString(s)
break
}
b.WriteString(`\x{`)
b.WriteString(strconv.FormatInt(int64(r), 16))
b.WriteString(`}`)
}
}
// MaxCap walks the regexp to find the maximum capture index.
func (re *Regexp) MaxCap() int {
m := 0
if re.Op == OpCapture {
m = re.Cap
}
for _, sub := range re.Sub {
if n := sub.MaxCap(); m < n {
m = n
}
}
return m
}
// CapNames walks the regexp to find the names of capturing groups.
func (re *Regexp) CapNames() []string {
names := make([]string, re.MaxCap()+1)
re.capNames(names)
return names
}
func (re *Regexp) capNames(names []string) {
if re.Op == OpCapture {
names[re.Cap] = re.Name
}
for _, sub := range re.Sub {
sub.capNames(names)
}
}