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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 parses regular expressions into syntax trees.
// WORK IN PROGRESS.
package syntax
// Note to implementers:
// In this package, re is always a *Regexp and r is always a rune.
import (
"bytes"
"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 []int // matched runes, for OpLiteral, OpCharClass
Rune0 [2]int // storage for short Rune
Min, Max int // min, max for OpRepeat
Cap int // capturing index, for OpCapture
Name string // capturing name, for OpCapture
}
// An Op is a single regular expression operator.
type Op uint8
// Operators are listed in precedence order, tightest binding to weakest.
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
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
// writeRegexp writes the Perl syntax for the regular expression re to b.
func writeRegexp(b *bytes.Buffer, 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:
for _, r := range re.Rune {
escape(b, r, false)
}
case OpCharClass:
if len(re.Rune)%2 != 0 {
b.WriteString(`[invalid char class]`)
break
}
b.WriteRune('[')
if len(re.Rune) > 0 && 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(`[^\n]`)
case OpAnyChar:
b.WriteRune('.')
case OpBeginLine:
b.WriteRune('^')
case OpEndLine:
b.WriteRune('$')
case OpBeginText:
b.WriteString(`\A`)
case OpEndText:
b.WriteString(`\z`)
case OpWordBoundary:
b.WriteString(`\b`)
case OpNoWordBoundary:
b.WriteString(`\B`)
case OpCapture:
if re.Name != "" {
b.WriteString(`(?P<`)
b.WriteString(re.Name)
b.WriteRune('>')
} else {
b.WriteRune('(')
}
writeRegexp(b, re.Sub[0])
b.WriteRune(')')
case OpStar, OpPlus, OpQuest, OpRepeat:
if sub := re.Sub[0]; sub.Op > OpCapture {
b.WriteString(`(?:`)
writeRegexp(b, sub)
b.WriteString(`)`)
} else {
writeRegexp(b, sub)
}
switch re.Op {
case OpStar:
b.WriteRune('*')
case OpPlus:
b.WriteRune('+')
case OpQuest:
b.WriteRune('?')
case OpRepeat:
b.WriteRune('{')
b.WriteString(strconv.Itoa(re.Min))
if re.Max != re.Min {
b.WriteRune(',')
if re.Max >= 0 {
b.WriteString(strconv.Itoa(re.Max))
}
}
b.WriteRune('}')
}
case OpConcat:
for _, sub := range re.Sub {
if sub.Op == OpAlternate {
b.WriteString(`(?:`)
writeRegexp(b, sub)
b.WriteString(`)`)
} else {
writeRegexp(b, sub)
}
}
case OpAlternate:
for i, sub := range re.Sub {
if i > 0 {
b.WriteRune('|')
}
writeRegexp(b, sub)
}
}
}
func (re *Regexp) String() string {
var b bytes.Buffer
writeRegexp(&b, re)
return b.String()
}
const meta = `\.+*?()|[]{}^$`
func escape(b *bytes.Buffer, r int, force bool) {
if unicode.IsPrint(r) {
if strings.IndexRune(meta, r) >= 0 || 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:
b.WriteString(`\x{`)
b.WriteString(strconv.Itob(r, 16))
b.WriteString(`}`)
}
}
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