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// Copyright 2009 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 scanner implements a scanner for Go source text.
// It takes a []byte as source which can then be tokenized
// through repeated calls to the Scan method.
//
package scanner
import (
"bytes"
"fmt"
"go/token"
"path/filepath"
"strconv"
"unicode"
"unicode/utf8"
)
// An ErrorHandler may be provided to Scanner.Init. If a syntax error is
// encountered and a handler was installed, the handler is called with a
// position and an error message. The position points to the beginning of
// the offending token.
//
type ErrorHandler func(pos token.Position, msg string)
// A Scanner holds the scanner's internal state while processing
// a given text. It can be allocated as part of another data
// structure but must be initialized via Init before use.
//
type Scanner struct {
// immutable state
file *token.File // source file handle
dir string // directory portion of file.Name()
src []byte // source
err ErrorHandler // error reporting; or nil
mode Mode // scanning mode
// scanning state
ch rune // current character
offset int // character offset
rdOffset int // reading offset (position after current character)
lineOffset int // current line offset
insertSemi bool // insert a semicolon before next newline
// public state - ok to modify
ErrorCount int // number of errors encountered
}
const bom = 0xFEFF // byte order mark, only permitted as very first character
// Read the next Unicode char into s.ch.
// s.ch < 0 means end-of-file.
//
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 >= utf8.RuneSelf:
// not ASCII
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 // eof
}
}
// peek returns the byte following the most recently read character without
// advancing the scanner. If the scanner is at EOF, peek returns 0.
func (s *Scanner) peek() byte {
if s.rdOffset < len(s.src) {
return s.src[s.rdOffset]
}
return 0
}
// A mode value is a set of flags (or 0).
// They control scanner behavior.
//
type Mode uint
const (
ScanComments Mode = 1 << iota // return comments as COMMENT tokens
dontInsertSemis // do not automatically insert semicolons - for testing only
)
// 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, mode Mode) {
// 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.mode = mode
s.ch = ' '
s.offset = 0
s.rdOffset = 0
s.lineOffset = 0
s.insertSemi = false
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.Position(s.file.Pos(offs)), msg)
}
s.ErrorCount++
}
func (s *Scanner) errorf(offs int, format string, args ...interface{}) {
s.error(offs, fmt.Sprintf(format, args...))
}
func (s *Scanner) scanComment() string {
// initial '/' already consumed; s.ch == '/' || s.ch == '*'
offs := s.offset - 1 // position of initial '/'
next := -1 // position immediately following the comment; < 0 means invalid comment
numCR := 0
if s.ch == '/' {
//-style comment
// (the final '\n' is not considered part of the comment)
s.next()
for s.ch != '\n' && s.ch >= 0 {
if s.ch == '\r' {
numCR++
}
s.next()
}
// if we are at '\n', the position following the comment is afterwards
next = s.offset
if s.ch == '\n' {
next++
}
goto exit
}
/*-style comment */
s.next()
for s.ch >= 0 {
ch := s.ch
if ch == '\r' {
numCR++
}
s.next()
if ch == '*' && s.ch == '/' {
s.next()
next = s.offset
goto exit
}
}
s.error(offs, "comment not terminated")
exit:
lit := s.src[offs:s.offset]
// On Windows, a (//-comment) line may end in "\r\n".
// Remove the final '\r' before analyzing the text for
// line directives (matching the compiler). Remove any
// other '\r' afterwards (matching the pre-existing be-
// havior of the scanner).
if numCR > 0 && len(lit) >= 2 && lit[1] == '/' && lit[len(lit)-1] == '\r' {
lit = lit[:len(lit)-1]
numCR--
}
// interpret line directives
// (//line directives must start at the beginning of the current line)
if next >= 0 /* implies valid comment */ && (lit[1] == '*' || offs == s.lineOffset) && bytes.HasPrefix(lit[2:], prefix) {
s.updateLineInfo(next, offs, lit)
}
if numCR > 0 {
lit = stripCR(lit, lit[1] == '*')
}
return string(lit)
}
var prefix = []byte("line ")
// updateLineInfo parses the incoming comment text at offset offs
// as a line directive. If successful, it updates the line info table
// for the position next per the line directive.
func (s *Scanner) updateLineInfo(next, offs int, text []byte) {
// extract comment text
if text[1] == '*' {
text = text[:len(text)-2] // lop off trailing "*/"
}
text = text[7:] // lop off leading "//line " or "/*line "
offs += 7
i, n, ok := trailingDigits(text)
if i == 0 {
return // ignore (not a line directive)
}
// i > 0
if !ok {
// text has a suffix :xxx but xxx is not a number
s.error(offs+i, "invalid line number: "+string(text[i:]))
return
}
var line, col int
i2, n2, ok2 := trailingDigits(text[:i-1])
if ok2 {
//line filename:line:col
i, i2 = i2, i
line, col = n2, n
if col == 0 {
s.error(offs+i2, "invalid column number: "+string(text[i2:]))
return
}
text = text[:i2-1] // lop off ":col"
} else {
//line filename:line
line = n
}
if line == 0 {
s.error(offs+i, "invalid line number: "+string(text[i:]))
return
}
// If we have a column (//line filename:line:col form),
// an empty filename means to use the previous filename.
filename := string(text[:i-1]) // lop off ":line", and trim white space
if filename == "" && ok2 {
filename = s.file.Position(s.file.Pos(offs)).Filename
} else if filename != "" {
// Put a relative filename in the current directory.
// This is for compatibility with earlier releases.
// See issue 26671.
filename = filepath.Clean(filename)
if !filepath.IsAbs(filename) {
filename = filepath.Join(s.dir, filename)
}
}
s.file.AddLineColumnInfo(next, filename, line, col)
}
func trailingDigits(text []byte) (int, int, bool) {
i := bytes.LastIndexByte(text, ':') // look from right (Windows filenames may contain ':')
if i < 0 {
return 0, 0, false // no ":"
}
// i >= 0
n, err := strconv.ParseUint(string(text[i+1:]), 10, 0)
return i + 1, int(n), err == nil
}
func (s *Scanner) findLineEnd() bool {
// initial '/' already consumed
defer func(offs int) {
// reset scanner state to where it was upon calling findLineEnd
s.ch = '/'
s.offset = offs
s.rdOffset = offs + 1
s.next() // consume initial '/' again
}(s.offset - 1)
// read ahead until a newline, EOF, or non-comment token is found
for s.ch == '/' || s.ch == '*' {
if s.ch == '/' {
//-style comment always contains a newline
return true
}
/*-style comment: look for newline */
s.next()
for s.ch >= 0 {
ch := s.ch
if ch == '\n' {
return true
}
s.next()
if ch == '*' && s.ch == '/' {
s.next()
break
}
}
s.skipWhitespace() // s.insertSemi is set
if s.ch < 0 || s.ch == '\n' {
return true
}
if s.ch != '/' {
// non-comment token
return false
}
s.next() // consume '/'
}
return false
}
func isLetter(ch rune) bool {
return 'a' <= lower(ch) && lower(ch) <= 'z' || ch == '_' || ch >= utf8.RuneSelf && unicode.IsLetter(ch)
}
func isDigit(ch rune) bool {
return isDecimal(ch) || ch >= utf8.RuneSelf && 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 digitVal(ch rune) int {
switch {
case '0' <= ch && ch <= '9':
return int(ch - '0')
case 'a' <= lower(ch) && lower(ch) <= 'f':
return int(lower(ch) - 'a' + 10)
}
return 16 // larger than any legal digit val
}
func lower(ch rune) rune { return ('a' - 'A') | ch } // returns lower-case ch iff ch is ASCII letter
func isDecimal(ch rune) bool { return '0' <= ch && ch <= '9' }
func isHex(ch rune) bool { return '0' <= ch && ch <= '9' || 'a' <= lower(ch) && lower(ch) <= 'f' }
// digits accepts the sequence { digit | '_' }.
// If base <= 10, digits accepts any decimal digit but records
// the offset (relative to the source start) of a digit >= base
// in *invalid, if *invalid < 0.
// digits returns a bitset describing whether the sequence contained
// digits (bit 0 is set), or separators '_' (bit 1 is set).
func (s *Scanner) digits(base int, invalid *int) (digsep int) {
if base <= 10 {
max := rune('0' + base)
for isDecimal(s.ch) || s.ch == '_' {
ds := 1
if s.ch == '_' {
ds = 2
} else if s.ch >= max && *invalid < 0 {
*invalid = int(s.offset) // record invalid rune offset
}
digsep |= ds
s.next()
}
} else {
for isHex(s.ch) || s.ch == '_' {
ds := 1
if s.ch == '_' {
ds = 2
}
digsep |= ds
s.next()
}
}
return
}
func (s *Scanner) scanNumber() (token.Token, string) {
offs := s.offset
tok := token.ILLEGAL
base := 10 // number base
prefix := rune(0) // one of 0 (decimal), '0' (0-octal), 'x', 'o', or 'b'
digsep := 0 // bit 0: digit present, bit 1: '_' present
invalid := -1 // index of invalid digit in literal, or < 0
// integer part
if s.ch != '.' {
tok = token.INT
if s.ch == '0' {
s.next()
switch lower(s.ch) {
case 'x':
s.next()
base, prefix = 16, 'x'
case 'o':
s.next()
base, prefix = 8, 'o'
case 'b':
s.next()
base, prefix = 2, 'b'
default:
base, prefix = 8, '0'
digsep = 1 // leading 0
}
}
digsep |= s.digits(base, &invalid)
}
// fractional part
if s.ch == '.' {
tok = token.FLOAT
if prefix == 'o' || prefix == 'b' {
s.error(s.offset, "invalid radix point in "+litname(prefix))
}
s.next()
digsep |= s.digits(base, &invalid)
}
if digsep&1 == 0 {
s.error(s.offset, litname(prefix)+" has no digits")
}
// exponent
if e := lower(s.ch); e == 'e' || e == 'p' {
switch {
case e == 'e' && prefix != 0 && prefix != '0':
s.errorf(s.offset, "%q exponent requires decimal mantissa", s.ch)
case e == 'p' && prefix != 'x':
s.errorf(s.offset, "%q exponent requires hexadecimal mantissa", s.ch)
}
s.next()
tok = token.FLOAT
if s.ch == '+' || s.ch == '-' {
s.next()
}
ds := s.digits(10, nil)
digsep |= ds
if ds&1 == 0 {
s.error(s.offset, "exponent has no digits")
}
} else if prefix == 'x' && tok == token.FLOAT {
s.error(s.offset, "hexadecimal mantissa requires a 'p' exponent")
}
// suffix 'i'
if s.ch == 'i' {
tok = token.IMAG
s.next()
}
lit := string(s.src[offs:s.offset])
if tok == token.INT && invalid >= 0 {
s.errorf(invalid, "invalid digit %q in %s", lit[invalid-offs], litname(prefix))
}
if digsep&2 != 0 {
if i := invalidSep(lit); i >= 0 {
s.error(offs+i, "'_' must separate successive digits")
}
}
return tok, lit
}
func litname(prefix rune) string {
switch prefix {
case 'x':
return "hexadecimal literal"
case 'o', '0':
return "octal literal"
case 'b':
return "binary literal"
}
return "decimal literal"
}
// invalidSep returns the index of the first invalid separator in x, or -1.
func invalidSep(x string) int {
x1 := ' ' // prefix char, we only care if it's 'x'
d := '.' // digit, one of '_', '0' (a digit), or '.' (anything else)
i := 0
// a prefix counts as a digit
if len(x) >= 2 && x[0] == '0' {
x1 = lower(rune(x[1]))
if x1 == 'x' || x1 == 'o' || x1 == 'b' {
d = '0'
i = 2
}
}
// mantissa and exponent
for ; i < len(x); i++ {
p := d // previous digit
d = rune(x[i])
switch {
case d == '_':
if p != '0' {
return i
}
case isDecimal(d) || x1 == 'x' && isHex(d):
d = '0'
default:
if p == '_' {
return i - 1
}
d = '.'
}
}
if d == '_' {
return len(x) - 1
}
return -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 (s *Scanner) scanRune() string {
// '\'' opening already consumed
offs := s.offset - 1
valid := true
n := 0
for {
ch := s.ch
if ch == '\n' || ch < 0 {
// only report error if we don't have one already
if valid {
s.error(offs, "rune literal not terminated")
valid = false
}
break
}
s.next()
if ch == '\'' {
break
}
n++
if ch == '\\' {
if !s.scanEscape('\'') {
valid = false
}
// continue to read to closing quote
}
}
if valid && n != 1 {
s.error(offs, "illegal rune literal")
}
return string(s.src[offs:s.offset])
}
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:s.offset])
}
func stripCR(b []byte, comment bool) []byte {
c := make([]byte, len(b))
i := 0
for j, ch := range b {
// In a /*-style comment, don't strip \r from *\r/ (incl.
// sequences of \r from *\r\r...\r/) since the resulting
// */ would terminate the comment too early unless the \r
// is immediately following the opening /* in which case
// it's ok because /*/ is not closed yet (issue #11151).
if ch != '\r' || comment && i > len("/*") && c[i-1] == '*' && j+1 < len(b) && b[j+1] == '/' {
c[i] = ch
i++
}
}
return c[:i]
}
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:s.offset]
if hasCR {
lit = stripCR(lit, false)
}
return string(lit)
}
func (s *Scanner) skipWhitespace() {
for s.ch == ' ' || s.ch == '\t' || s.ch == '\n' && !s.insertSemi || s.ch == '\r' {
s.next()
}
}
// Helper functions for scanning multi-byte tokens such as >> += >>= .
// Different routines recognize different length tok_i based on matches
// of ch_i. If a token ends in '=', the result is tok1 or tok3
// respectively. Otherwise, the result is tok0 if there was no other
// matching character, or tok2 if the matching character was ch2.
func (s *Scanner) switch2(tok0, tok1 token.Token) token.Token {
if s.ch == '=' {
s.next()
return tok1
}
return tok0
}
func (s *Scanner) switch3(tok0, tok1 token.Token, ch2 rune, tok2 token.Token) token.Token {
if s.ch == '=' {
s.next()
return tok1
}
if s.ch == ch2 {
s.next()
return tok2
}
return tok0
}
func (s *Scanner) switch4(tok0, tok1 token.Token, ch2 rune, tok2, tok3 token.Token) token.Token {
if s.ch == '=' {
s.next()
return tok1
}
if s.ch == ch2 {
s.next()
if s.ch == '=' {
s.next()
return tok3
}
return tok2
}
return tok0
}
// Scan scans the next token and returns the token position, the token,
// and its literal string if applicable. The source end is indicated by
// token.EOF.
//
// If the returned token is a literal (token.IDENT, token.INT, token.FLOAT,
// token.IMAG, token.CHAR, token.STRING) or token.COMMENT, the literal string
// has the corresponding value.
//
// If the returned token is a keyword, the literal string is the keyword.
//
// If the returned token is token.SEMICOLON, the corresponding
// literal string is ";" if the semicolon was present in the source,
// and "\n" if the semicolon was inserted because of a newline or
// at EOF.
//
// If the returned token is token.ILLEGAL, the literal string is the
// offending character.
//
// In all other cases, Scan returns an empty literal string.
//
// For more tolerant parsing, Scan will return a valid token if
// possible even if a syntax error was encountered. Thus, even
// if the resulting token sequence contains no illegal tokens,
// a client may not assume that no error occurred. Instead it
// must check the scanner's ErrorCount or the number of calls
// of the error handler, if there was one installed.
//
// Scan adds line information to the file added to the file
// set with Init. Token positions are relative to that file
// and thus relative to the file set.
//
func (s *Scanner) Scan() (pos token.Pos, tok token.Token, lit string) {
scanAgain:
s.skipWhitespace()
// current token start
pos = s.file.Pos(s.offset)
// determine token value
insertSemi := false
switch ch := s.ch; {
case isLetter(ch):
lit = s.scanIdentifier()
if len(lit) > 1 {
// keywords are longer than one letter - avoid lookup otherwise
tok = token.Lookup(lit)
switch tok {
case token.IDENT, token.BREAK, token.CONTINUE, token.FALLTHROUGH, token.RETURN:
insertSemi = true
}
} else {
insertSemi = true
tok = token.IDENT
}
case isDecimal(ch) || ch == '.' && isDecimal(rune(s.peek())):
insertSemi = true
tok, lit = s.scanNumber()
default:
s.next() // always make progress
switch ch {
case -1:
if s.insertSemi {
s.insertSemi = false // EOF consumed
return pos, token.SEMICOLON, "\n"
}
tok = token.EOF
case '\n':
// we only reach here if s.insertSemi was
// set in the first place and exited early
// from s.skipWhitespace()
s.insertSemi = false // newline consumed
return pos, token.SEMICOLON, "\n"
case '"':
insertSemi = true
tok = token.STRING
lit = s.scanString()
case '\'':
insertSemi = true
tok = token.CHAR
lit = s.scanRune()
case '`':
insertSemi = true
tok = token.STRING
lit = s.scanRawString()
case ':':
tok = s.switch2(token.COLON, token.DEFINE)
case '.':
// fractions starting with a '.' are handled by outer switch
tok = token.PERIOD
if s.ch == '.' && s.peek() == '.' {
s.next()
s.next() // consume last '.'
tok = token.ELLIPSIS
}
case ',':
tok = token.COMMA
case ';':
tok = token.SEMICOLON
lit = ";"
case '(':
tok = token.LPAREN
case ')':
insertSemi = true
tok = token.RPAREN
case '[':
tok = token.LBRACK
case ']':
insertSemi = true
tok = token.RBRACK
case '{':
tok = token.LBRACE
case '}':
insertSemi = true
tok = token.RBRACE
case '+':
tok = s.switch3(token.ADD, token.ADD_ASSIGN, '+', token.INC)
if tok == token.INC {
insertSemi = true
}
case '-':
tok = s.switch3(token.SUB, token.SUB_ASSIGN, '-', token.DEC)
if tok == token.DEC {
insertSemi = true
}
case '*':
tok = s.switch2(token.MUL, token.MUL_ASSIGN)
case '/':
if s.ch == '/' || s.ch == '*' {
// comment
if s.insertSemi && s.findLineEnd() {
// reset position to the beginning of the comment
s.ch = '/'
s.offset = s.file.Offset(pos)
s.rdOffset = s.offset + 1
s.insertSemi = false // newline consumed
return pos, token.SEMICOLON, "\n"
}
comment := s.scanComment()
if s.mode&ScanComments == 0 {
// skip comment
s.insertSemi = false // newline consumed
goto scanAgain
}
tok = token.COMMENT
lit = comment
} else {
tok = s.switch2(token.QUO, token.QUO_ASSIGN)
}
case '%':
tok = s.switch2(token.REM, token.REM_ASSIGN)
case '^':
tok = s.switch2(token.XOR, token.XOR_ASSIGN)
case '<':
if s.ch == '-' {
s.next()
tok = token.ARROW
} else {
tok = s.switch4(token.LSS, token.LEQ, '<', token.SHL, token.SHL_ASSIGN)
}
case '>':
tok = s.switch4(token.GTR, token.GEQ, '>', token.SHR, token.SHR_ASSIGN)
case '=':
tok = s.switch2(token.ASSIGN, token.EQL)
case '!':
tok = s.switch2(token.NOT, token.NEQ)
case '&':
if s.ch == '^' {
s.next()
tok = s.switch2(token.AND_NOT, token.AND_NOT_ASSIGN)
} else {
tok = s.switch3(token.AND, token.AND_ASSIGN, '&', token.LAND)
}
case '|':
tok = s.switch3(token.OR, token.OR_ASSIGN, '|', token.LOR)
default:
// next reports unexpected BOMs - don't repeat
if ch != bom {
s.errorf(s.file.Offset(pos), "illegal character %#U", ch)
}
insertSemi = s.insertSemi // preserve insertSemi info
tok = token.ILLEGAL
lit = string(ch)
}
}
if s.mode&dontInsertSemis == 0 {
s.insertSemi = insertSemi
}
return
}
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