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scanner.go
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scanner.go
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// Copyright (c) 2019 The BFE Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// scanner for condition expression
package parser
import (
"fmt"
"go/token"
"path/filepath"
"unicode"
"unicode/utf8"
)
type Scanner struct {
file *token.File
dir string
src []byte
err ErrorHandler // error reporting; or nil
ch rune
offset int
rdOffset int
lineOffset int
ErrorCount int
}
const bom = 0xFEFF // byte order mark, only permitted as very first character
// Init prepares the scanner s to tokenize the text src by setting the
// scanner at the beginning of src. The scanner uses the file set file
// for position information and it adds line information for each line.
// It is ok to re-use the same file when re-scanning the same file as
// line information which is already present is ignored. Init causes a
// panic if the file size does not match the src size.
//
// Calls to Scan will invoke the error handler err if they encounter a
// syntax error and err is not nil. Also, for each error encountered,
// the Scanner field ErrorCount is incremented by one. The mode parameter
// determines how comments are handled.
//
// Note that Init may call err if there is an error in the first character
// of the file.
//
func (s *Scanner) Init(file *token.File, src []byte, err ErrorHandler) {
// Explicitly initialize all fields since a scanner may be reused.
if file.Size() != len(src) {
panic(fmt.Sprintf("file size (%d) does not match src len (%d)", file.Size(), len(src)))
}
s.file = file
s.dir, _ = filepath.Split(file.Name())
s.src = src
s.err = err
s.ch = ' '
s.offset = 0
s.rdOffset = 0
s.lineOffset = 0
s.ErrorCount = 0
s.next()
if s.ch == bom {
s.next() // ignore BOM at file beginning
}
}
func (s *Scanner) error(offs int, msg string) {
if s.err != nil {
s.err(s.file.Pos(offs), msg)
}
s.ErrorCount++
}
func (s *Scanner) next() {
if s.rdOffset < len(s.src) {
s.offset = s.rdOffset
if s.ch == '\n' {
s.lineOffset = s.offset
s.file.AddLine(s.offset)
}
r, w := rune(s.src[s.rdOffset]), 1
switch {
case r == 0:
s.error(s.offset, "illegal character NUL")
case r >= 0x80:
r, w = utf8.DecodeRune(s.src[s.rdOffset:])
if r == utf8.RuneError && w == 1 {
s.error(s.offset, "illegal UTF-8 encoding")
} else if r == bom && s.offset > 0 {
s.error(s.offset, "illegal byte order mark")
}
}
s.rdOffset += w
s.ch = r
} else {
s.offset = len(s.src)
if s.ch == '\n' {
s.lineOffset = s.offset
s.file.AddLine(s.offset)
}
s.ch = -1
}
}
func (s *Scanner) skipWhitespace() {
for s.ch == ' ' || s.ch == '\t' || s.ch == '\r' || s.ch == '\n' {
s.next()
}
}
func isLetter(ch rune) bool {
return 'a' <= ch && ch <= 'z' || 'A' <= ch && ch <= 'Z' || ch == '_' || ch == '-' || ch >= 0x80 && unicode.IsLetter(ch)
}
func isDigit(ch rune) bool {
return '0' <= ch && ch <= '9' || ch >= 0x80 && unicode.IsDigit(ch)
}
func (s *Scanner) scanIdentifier() string {
offs := s.offset
for isLetter(s.ch) || isDigit(s.ch) {
s.next()
}
return string(s.src[offs:s.offset])
}
func stripCR(b []byte) []byte {
c := make([]byte, len(b))
i := 0
for _, ch := range b {
if ch != '\r' {
c[i] = ch
i++
}
}
return c[:i]
}
func (s *Scanner) scanString() string {
// '"' opening already consumed
offs := s.offset - 1
for {
ch := s.ch
if ch == '\n' || ch < 0 {
s.error(offs, "string literal not terminated")
break
}
s.next()
if ch == '"' {
break
}
if ch == '\\' {
s.scanEscape('"')
}
}
return string(s.src[offs+1 : s.offset-1])
}
// scanEscape parses an escape sequence where rune is the accepted
// escaped quote. In case of a syntax error, it stops at the offending
// character (without consuming it) and returns false. Otherwise
// it returns true.
func (s *Scanner) scanEscape(quote rune) bool {
offs := s.offset
var n int
var base, max uint32
switch s.ch {
case 'a', 'b', 'f', 'n', 'r', 't', 'v', '\\', quote:
s.next()
return true
case '0', '1', '2', '3', '4', '5', '6', '7':
n, base, max = 3, 8, 255
case 'x':
s.next()
n, base, max = 2, 16, 255
case 'u':
s.next()
n, base, max = 4, 16, unicode.MaxRune
case 'U':
s.next()
n, base, max = 8, 16, unicode.MaxRune
default:
msg := "unknown escape sequence"
if s.ch < 0 {
msg = "escape sequence not terminated"
}
s.error(offs, msg)
return false
}
var x uint32
for n > 0 {
d := uint32(digitVal(s.ch))
if d >= base {
msg := fmt.Sprintf("illegal character %#U in escape sequence", s.ch)
if s.ch < 0 {
msg = "escape sequence not terminated"
}
s.error(s.offset, msg)
return false
}
x = x*base + d
s.next()
n--
}
if x > max || 0xD800 <= x && x < 0xE000 {
s.error(offs, "escape sequence is invalid Unicode code point")
return false
}
return true
}
func digitVal(ch rune) int {
switch {
case '0' <= ch && ch <= '9':
return int(ch - '0')
case 'a' <= ch && ch <= 'f':
return int(ch - 'a' + 10)
case 'A' <= ch && ch <= 'F':
return int(ch - 'A' + 10)
}
return 16 // larger than any legal digit val
}
func (s *Scanner) scanRawString() string {
// '`' opening already consumed
offs := s.offset - 1
hasCR := false
for {
ch := s.ch
if ch < 0 {
s.error(offs, "raw string literal not terminated")
break
}
s.next()
if ch == '`' {
break
}
if ch == '\r' {
hasCR = true
}
}
lit := s.src[offs+1 : s.offset-1]
if hasCR {
lit = stripCR(lit)
}
return string(lit)
}
func (s *Scanner) scanComment() string {
offs := s.offset - 1
hasCR := false
s.next()
for s.ch != '\n' && s.ch >= 0 {
if s.ch == '\r' {
hasCR = true
}
s.next()
}
lit := s.src[offs:s.offset]
if hasCR {
lit = stripCR(lit)
}
return string(lit)
}
func (s *Scanner) scanMantissa(base int) {
for digitVal(s.ch) < base {
s.next()
}
}
func (s *Scanner) scanNumber(seenDecimalPoint bool) (Token, string) {
// digitVal(s.ch) < 10
offs := s.offset
tok := INT
if seenDecimalPoint {
offs--
tok = FLOAT
s.scanMantissa(10)
goto exponent
}
if s.ch == '0' {
// int or float
offs := s.offset
s.next()
if s.ch == 'x' || s.ch == 'X' {
// hexadecimal int
s.next()
s.scanMantissa(16)
if s.offset-offs <= 2 {
// only scanned "0x" or "0X"
s.error(offs, "illegal hexadecimal number")
}
} else {
// octal int or float
seenDecimalDigit := false
s.scanMantissa(8)
if s.ch == '8' || s.ch == '9' {
// illegal octal int or float
seenDecimalDigit = true
s.scanMantissa(10)
}
if s.ch == '.' || s.ch == 'e' || s.ch == 'E' || s.ch == 'i' {
goto fraction
}
// octal int
if seenDecimalDigit {
s.error(offs, "illegal octal number")
}
}
goto exit
}
// decimal int or float
s.scanMantissa(10)
fraction:
if s.ch == '.' {
tok = FLOAT
s.next()
s.scanMantissa(10)
}
exponent:
if s.ch == 'e' || s.ch == 'E' {
tok = FLOAT
s.next()
if s.ch == '-' || s.ch == '+' {
s.next()
}
s.scanMantissa(10)
}
if s.ch == 'i' {
tok = IMAG
s.next()
}
exit:
return Token(tok), string(s.src[offs:s.offset])
}
func (s *Scanner) Scan() (pos token.Pos, tok Token, lit string) {
scanAgain:
s.skipWhitespace()
// current token start
pos = s.file.Pos(s.offset)
// determine token value
switch ch := s.ch; {
case isLetter(ch):
lit = s.scanIdentifier()
if len(lit) > 1 {
// keywords are longer than one letter - avoid lookup otherwise
tok = Lookup(lit)
if tok != IDENT {
// go keyword can't be used
tok = ILLEGAL
s.error(s.offset, "keyword can't be used")
}
if lit == "true" || lit == "false" {
tok = BOOL
}
} else {
tok = IDENT
}
case '0' <= ch && ch <= '9':
tok, lit = s.scanNumber(false)
default:
s.next() // always make progress
switch ch {
case -1:
tok = EOF
case ';':
tok = SEMICOLON
lit = ";"
case '"':
tok = STRING
lit = s.scanString()
case '`':
tok = STRING
lit = s.scanRawString()
case '(':
tok = LPAREN
lit = "("
case ')':
tok = RPAREN
lit = ")"
case '!':
tok = NOT
lit = "!"
case ',':
tok = COMMA
lit = ","
case '&':
if s.ch == '&' {
s.next()
tok = LAND
lit = "&&"
} else {
tok = ILLEGAL
lit = string(ch)
}
case '|':
if s.ch == '|' {
s.next()
tok = LOR
lit = "||"
} else {
tok = ILLEGAL
lit = string(ch)
}
case '/':
if s.ch == '/' {
tok = COMMENT
lit = s.scanComment()
goto scanAgain
} else {
tok = ILLEGAL
lit = string(ch)
}
default:
tok = ILLEGAL
lit = string(ch)
}
}
return
}