src/pkg/go/scanner/scanner.go - go - Git at Google

 // 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.

 // A scanner for Go source text. Takes a []byte as source which can
 // then be tokenized through repeated calls to the Scan function.
 // Typical use:
 //
 //	var s Scanner
 //	fset := token.NewFileSet()  // position information is relative to fset
 //      file := fset.AddFile(filename, fset.Base(), len(src))  // register file
 //	s.Init(file, src, nil /* no error handler */, 0)
 //	for {
 //		pos, tok, lit := s.Scan()
 //		if tok == token.EOF {
 //			break
 //		}
 //		// do something here with pos, tok, and lit
 //	}
 //
 package scanner

 import (
 	"bytes"
 	"go/token"
 	"path/filepath"
 	"strconv"
 	"unicode"
 	"utf8"
 )


 // 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 uint         // scanning mode

 	// scanning state
 	ch         int  // 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
 }


 // 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 := int(S.src[S.rdOffset]), 1
 		switch {
 		case r == 0:
 			S.error(S.offset, "illegal character NUL")
 		case r >= 0x80:
 			// not ASCII
 			r, w = utf8.DecodeRune(S.src[S.rdOffset:])
 			if r == utf8.RuneError && w == 1 {
 				S.error(S.offset, "illegal UTF-8 encoding")
 			}
 		}
 		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
 	}
 }


 // The mode parameter to the Init function is a set of flags (or 0).
 // They control scanner behavior.
 //
 const (
 	ScanComments      = 1 << iota // return comments as COMMENT tokens
 	AllowIllegalChars             // do not report an error for illegal chars
 	InsertSemis                   // automatically insert semicolons
 )

 // 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 use 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, illegal characters, and semicolons 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 uint) {
 	// Explicitly initialize all fields since a scanner may be reused.
 	if file.Size() != len(src) {
 		panic("file size does not match src len")
 	}
 	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()
 }


 func charString(ch int) string {
 	var s string
 	switch ch {
 	case -1:
 		return `EOF`
 	case '\a':
 		s = `\a`
 	case '\b':
 		s = `\b`
 	case '\f':
 		s = `\f`
 	case '\n':
 		s = `\n`
 	case '\r':
 		s = `\r`
 	case '\t':
 		s = `\t`
 	case '\v':
 		s = `\v`
 	case '\\':
 		s = `\\`
 	case '\'':
 		s = `\'`
 	default:
 		s = string(ch)
 	}
 	return "'" + s + "' (U+" + strconv.Itob(ch, 16) + ")"
 }


 func (S *Scanner) error(offs int, msg string) {
 	if S.err != nil {
 		S.err.Error(S.file.Position(S.file.Pos(offs)), msg)
 	}
 	S.ErrorCount++
 }


 var prefix = []byte("//line ")

 func (S *Scanner) interpretLineComment(text []byte) {
 	if bytes.HasPrefix(text, prefix) {
 		// get filename and line number, if any
 		if i := bytes.LastIndex(text, []byte{':'}); i > 0 {
 			if line, err := strconv.Atoi(string(text[i+1:])); err == nil && line > 0 {
 				// valid //line filename:line comment;
 				filename := filepath.Clean(string(text[len(prefix):i]))
 				if !filepath.IsAbs(filename) {
 					// make filename relative to current directory
 					filename = filepath.Join(S.dir, filename)
 				}
 				// update scanner position
 				S.file.AddLineInfo(S.lineOffset, filename, line-1) // -1 since comment applies to next line
 			}
 		}
 	}
 }


 func (S *Scanner) scanComment() {
 	// initial '/' already consumed; S.ch == '/' || S.ch == '*'
 	offs := S.offset - 1 // position of initial '/'

 	if S.ch == '/' {
 		//-style comment
 		S.next()
 		for S.ch != '\n' && S.ch >= 0 {
 			S.next()
 		}
 		if offs == S.lineOffset {
 			// comment starts at the beginning of the current line
 			S.interpretLineComment(S.src[offs:S.offset])
 		}
 		return
 	}

 	/*-style comment */
 	S.next()
 	for S.ch >= 0 {
 		ch := S.ch
 		S.next()
 		if ch == '*' && S.ch == '/' {
 			S.next()
 			return
 		}
 	}

 	S.error(offs, "comment not terminated")
 }


 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 int) bool {
 	return 'a' <= ch && ch <= 'z' || 'A' <= ch && ch <= 'Z' || ch == '_' || ch >= 0x80 && unicode.IsLetter(ch)
 }


 func isDigit(ch int) bool {
 	return '0' <= ch && ch <= '9' || ch >= 0x80 && unicode.IsDigit(ch)
 }


 func (S *Scanner) scanIdentifier() token.Token {
 	offs := S.offset
 	for isLetter(S.ch) || isDigit(S.ch) {
 		S.next()
 	}
 	return token.Lookup(S.src[offs:S.offset])
 }


 func digitVal(ch int) int {
 	switch {
 	case '0' <= ch && ch <= '9':
 		return ch - '0'
 	case 'a' <= ch && ch <= 'f':
 		return ch - 'a' + 10
 	case 'A' <= ch && ch <= 'F':
 		return ch - 'A' + 10
 	}
 	return 16 // larger than any legal digit val
 }


 func (S *Scanner) scanMantissa(base int) {
 	for digitVal(S.ch) < base {
 		S.next()
 	}
 }


 func (S *Scanner) scanNumber(seenDecimalPoint bool) token.Token {
 	// digitVal(S.ch) < 10
 	tok := token.INT

 	if seenDecimalPoint {
 		tok = token.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)
 		} 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 = token.FLOAT
 		S.next()
 		S.scanMantissa(10)
 	}

 exponent:
 	if S.ch == 'e' || S.ch == 'E' {
 		tok = token.FLOAT
 		S.next()
 		if S.ch == '-' || S.ch == '+' {
 			S.next()
 		}
 		S.scanMantissa(10)
 	}

 	if S.ch == 'i' {
 		tok = token.IMAG
 		S.next()
 	}

 exit:
 	return tok
 }


 func (S *Scanner) scanEscape(quote int) {
 	offs := S.offset

 	var i, base, max uint32
 	switch S.ch {
 	case 'a', 'b', 'f', 'n', 'r', 't', 'v', '\\', quote:
 		S.next()
 		return
 	case '0', '1', '2', '3', '4', '5', '6', '7':
 		i, base, max = 3, 8, 255
 	case 'x':
 		S.next()
 		i, base, max = 2, 16, 255
 	case 'u':
 		S.next()
 		i, base, max = 4, 16, unicode.MaxRune
 	case 'U':
 		S.next()
 		i, base, max = 8, 16, unicode.MaxRune
 	default:
 		S.next() // always make progress
 		S.error(offs, "unknown escape sequence")
 		return
 	}

 	var x uint32
 	for ; i > 0 && S.ch != quote && S.ch >= 0; i-- {
 		d := uint32(digitVal(S.ch))
 		if d >= base {
 			S.error(S.offset, "illegal character in escape sequence")
 			break
 		}
 		x = x*base + d
 		S.next()
 	}
 	// in case of an error, consume remaining chars
 	for ; i > 0 && S.ch != quote && S.ch >= 0; i-- {
 		S.next()
 	}
 	if x > max || 0xd800 <= x && x < 0xe000 {
 		S.error(offs, "escape sequence is invalid Unicode code point")
 	}
 }


 func (S *Scanner) scanChar() {
 	// '\'' opening already consumed
 	offs := S.offset - 1

 	n := 0
 	for S.ch != '\'' {
 		ch := S.ch
 		n++
 		S.next()
 		if ch == '\n' || ch < 0 {
 			S.error(offs, "character literal not terminated")
 			n = 1
 			break
 		}
 		if ch == '\\' {
 			S.scanEscape('\'')
 		}
 	}

 	S.next()

 	if n != 1 {
 		S.error(offs, "illegal character literal")
 	}
 }


 func (S *Scanner) scanString() {
 	// '"' opening already consumed
 	offs := S.offset - 1

 	for S.ch != '"' {
 		ch := S.ch
 		S.next()
 		if ch == '\n' || ch < 0 {
 			S.error(offs, "string not terminated")
 			break
 		}
 		if ch == '\\' {
 			S.scanEscape('"')
 		}
 	}

 	S.next()
 }


 func (S *Scanner) scanRawString() {
 	// '`' opening already consumed
 	offs := S.offset - 1

 	for S.ch != '`' {
 		ch := S.ch
 		S.next()
 		if ch < 0 {
 			S.error(offs, "string not terminated")
 			break
 		}
 	}

 	S.next()
 }


 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 int, 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 int, 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
 }


 var newline = []byte{'\n'}

 // Scan scans the next token and returns the token position pos,
 // the token tok, and the literal text lit corresponding to the
 // token. The source end is indicated by token.EOF.
 //
 // If the returned token is token.SEMICOLON, the corresponding
 // literal value is ";" if the semicolon was present in the source,
 // and "\n" if the semicolon was inserted because of a newline or
 // at EOF.
 //
 // 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() (token.Pos, token.Token, []byte) {
 scanAgain:
 	S.skipWhitespace()

 	// current token start
 	insertSemi := false
 	offs := S.offset
 	tok := token.ILLEGAL

 	// determine token value
 	switch ch := S.ch; {
 	case isLetter(ch):
 		tok = S.scanIdentifier()
 		switch tok {
 		case token.IDENT, token.BREAK, token.CONTINUE, token.FALLTHROUGH, token.RETURN:
 			insertSemi = true
 		}
 	case digitVal(ch) < 10:
 		insertSemi = true
 		tok = S.scanNumber(false)
 	default:
 		S.next() // always make progress
 		switch ch {
 		case -1:
 			if S.insertSemi {
 				S.insertSemi = false // EOF consumed
 				return S.file.Pos(offs), token.SEMICOLON, newline
 			}
 			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 S.file.Pos(offs), token.SEMICOLON, newline
 		case '"':
 			insertSemi = true
 			tok = token.STRING
 			S.scanString()
 		case '\'':
 			insertSemi = true
 			tok = token.CHAR
 			S.scanChar()
 		case '`':
 			insertSemi = true
 			tok = token.STRING
 			S.scanRawString()
 		case ':':
 			tok = S.switch2(token.COLON, token.DEFINE)
 		case '.':
 			if digitVal(S.ch) < 10 {
 				insertSemi = true
 				tok = S.scanNumber(true)
 			} else if S.ch == '.' {
 				S.next()
 				if S.ch == '.' {
 					S.next()
 					tok = token.ELLIPSIS
 				}
 			} else {
 				tok = token.PERIOD
 			}
 		case ',':
 			tok = token.COMMA
 		case ';':
 			tok = token.SEMICOLON
 		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 = offs
 					S.rdOffset = offs + 1
 					S.insertSemi = false // newline consumed
 					return S.file.Pos(offs), token.SEMICOLON, newline
 				}
 				S.scanComment()
 				if S.mode&ScanComments == 0 {
 					// skip comment
 					S.insertSemi = false // newline consumed
 					goto scanAgain
 				}
 				tok = token.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:
 			if S.mode&AllowIllegalChars == 0 {
 				S.error(offs, "illegal character "+charString(ch))
 			}
 			insertSemi = S.insertSemi // preserve insertSemi info
 		}
 	}

 	if S.mode&InsertSemis != 0 {
 		S.insertSemi = insertSemi
 	}
 	return S.file.Pos(offs), tok, S.src[offs:S.offset]
 }
	// 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.

	// A scanner for Go source text. Takes a []byte as source which can
	// then be tokenized through repeated calls to the Scan function.
	// Typical use:
	//
	// var s Scanner
	// fset := token.NewFileSet() // position information is relative to fset
	// file := fset.AddFile(filename, fset.Base(), len(src)) // register file
	// s.Init(file, src, nil /* no error handler */, 0)
	// for {
	// pos, tok, lit := s.Scan()
	// if tok == token.EOF {
	// break
	// }
	// // do something here with pos, tok, and lit
	// }
	//
	package scanner

	import (
	"bytes"
	"go/token"
	"path/filepath"
	"strconv"
	"unicode"
	"utf8"
	)


	// 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 uint // scanning mode

	// scanning state
	ch int // 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
	}


	// 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 := int(S.src[S.rdOffset]), 1
	switch {
	case r == 0:
	S.error(S.offset, "illegal character NUL")
	case r >= 0x80:
	// not ASCII
	r, w = utf8.DecodeRune(S.src[S.rdOffset:])
	if r == utf8.RuneError && w == 1 {
	S.error(S.offset, "illegal UTF-8 encoding")
	}
	}
	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
	}
	}


	// The mode parameter to the Init function is a set of flags (or 0).
	// They control scanner behavior.
	//
	const (
	ScanComments = 1 << iota // return comments as COMMENT tokens
	AllowIllegalChars // do not report an error for illegal chars
	InsertSemis // automatically insert semicolons
	)

	// 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 use 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, illegal characters, and semicolons 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 uint) {
	// Explicitly initialize all fields since a scanner may be reused.
	if file.Size() != len(src) {
	panic("file size does not match src len")
	}
	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()
	}


	func charString(ch int) string {
	var s string
	switch ch {
	case -1:
	return `EOF`
	case '\a':
	s = `\a`
	case '\b':
	s = `\b`
	case '\f':
	s = `\f`
	case '\n':
	s = `\n`
	case '\r':
	s = `\r`
	case '\t':
	s = `\t`
	case '\v':
	s = `\v`
	case '\\':
	s = `\\`
	case '\'':
	s = `\'`
	default:
	s = string(ch)
	}
	return "'" + s + "' (U+" + strconv.Itob(ch, 16) + ")"
	}


	func (S *Scanner) error(offs int, msg string) {
	if S.err != nil {
	S.err.Error(S.file.Position(S.file.Pos(offs)), msg)
	}
	S.ErrorCount++
	}


	var prefix = []byte("//line ")

	func (S *Scanner) interpretLineComment(text []byte) {
	if bytes.HasPrefix(text, prefix) {
	// get filename and line number, if any
	if i := bytes.LastIndex(text, []byte{':'}); i > 0 {
	if line, err := strconv.Atoi(string(text[i+1:])); err == nil && line > 0 {
	// valid //line filename:line comment;
	filename := filepath.Clean(string(text[len(prefix):i]))
	if !filepath.IsAbs(filename) {
	// make filename relative to current directory
	filename = filepath.Join(S.dir, filename)
	}
	// update scanner position
	S.file.AddLineInfo(S.lineOffset, filename, line-1) // -1 since comment applies to next line
	}
	}
	}
	}


	func (S *Scanner) scanComment() {
	// initial '/' already consumed; S.ch == '/' \|\| S.ch == '*'
	offs := S.offset - 1 // position of initial '/'

	if S.ch == '/' {
	//-style comment
	S.next()
	for S.ch != '\n' && S.ch >= 0 {
	S.next()
	}
	if offs == S.lineOffset {
	// comment starts at the beginning of the current line
	S.interpretLineComment(S.src[offs:S.offset])
	}
	return
	}

	/-style comment /
	S.next()
	for S.ch >= 0 {
	ch := S.ch
	S.next()
	if ch == '*' && S.ch == '/' {
	S.next()
	return
	}
	}

	S.error(offs, "comment not terminated")
	}


	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 int) bool {
	return 'a' <= ch && ch <= 'z' \|\| 'A' <= ch && ch <= 'Z' \|\| ch == '_' \|\| ch >= 0x80 && unicode.IsLetter(ch)
	}


	func isDigit(ch int) bool {
	return '0' <= ch && ch <= '9' \|\| ch >= 0x80 && unicode.IsDigit(ch)
	}


	func (S *Scanner) scanIdentifier() token.Token {
	offs := S.offset
	for isLetter(S.ch) \|\| isDigit(S.ch) {
	S.next()
	}
	return token.Lookup(S.src[offs:S.offset])
	}


	func digitVal(ch int) int {
	switch {
	case '0' <= ch && ch <= '9':
	return ch - '0'
	case 'a' <= ch && ch <= 'f':
	return ch - 'a' + 10
	case 'A' <= ch && ch <= 'F':
	return ch - 'A' + 10
	}
	return 16 // larger than any legal digit val
	}


	func (S *Scanner) scanMantissa(base int) {
	for digitVal(S.ch) < base {
	S.next()
	}
	}


	func (S *Scanner) scanNumber(seenDecimalPoint bool) token.Token {
	// digitVal(S.ch) < 10
	tok := token.INT

	if seenDecimalPoint {
	tok = token.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)
	} 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 = token.FLOAT
	S.next()
	S.scanMantissa(10)
	}

	exponent:
	if S.ch == 'e' \|\| S.ch == 'E' {
	tok = token.FLOAT
	S.next()
	if S.ch == '-' \|\| S.ch == '+' {
	S.next()
	}
	S.scanMantissa(10)
	}

	if S.ch == 'i' {
	tok = token.IMAG
	S.next()
	}

	exit:
	return tok
	}


	func (S *Scanner) scanEscape(quote int) {
	offs := S.offset

	var i, base, max uint32
	switch S.ch {
	case 'a', 'b', 'f', 'n', 'r', 't', 'v', '\\', quote:
	S.next()
	return
	case '0', '1', '2', '3', '4', '5', '6', '7':
	i, base, max = 3, 8, 255
	case 'x':
	S.next()
	i, base, max = 2, 16, 255
	case 'u':
	S.next()
	i, base, max = 4, 16, unicode.MaxRune
	case 'U':
	S.next()
	i, base, max = 8, 16, unicode.MaxRune
	default:
	S.next() // always make progress
	S.error(offs, "unknown escape sequence")
	return
	}

	var x uint32
	for ; i > 0 && S.ch != quote && S.ch >= 0; i-- {
	d := uint32(digitVal(S.ch))
	if d >= base {
	S.error(S.offset, "illegal character in escape sequence")
	break
	}
	x = x*base + d
	S.next()
	}
	// in case of an error, consume remaining chars
	for ; i > 0 && S.ch != quote && S.ch >= 0; i-- {
	S.next()
	}
	if x > max \|\| 0xd800 <= x && x < 0xe000 {
	S.error(offs, "escape sequence is invalid Unicode code point")
	}
	}


	func (S *Scanner) scanChar() {
	// '\'' opening already consumed
	offs := S.offset - 1

	n := 0
	for S.ch != '\'' {
	ch := S.ch
	n++
	S.next()
	if ch == '\n' \|\| ch < 0 {
	S.error(offs, "character literal not terminated")
	n = 1
	break
	}
	if ch == '\\' {
	S.scanEscape('\'')
	}
	}

	S.next()

	if n != 1 {
	S.error(offs, "illegal character literal")
	}
	}


	func (S *Scanner) scanString() {
	// '"' opening already consumed
	offs := S.offset - 1

	for S.ch != '"' {
	ch := S.ch
	S.next()
	if ch == '\n' \|\| ch < 0 {
	S.error(offs, "string not terminated")
	break
	}
	if ch == '\\' {
	S.scanEscape('"')
	}
	}

	S.next()
	}


	func (S *Scanner) scanRawString() {
	// '`' opening already consumed
	offs := S.offset - 1

	for S.ch != '`' {
	ch := S.ch
	S.next()
	if ch < 0 {
	S.error(offs, "string not terminated")
	break
	}
	}

	S.next()
	}


	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 int, 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 int, 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
	}


	var newline = []byte{'\n'}

	// Scan scans the next token and returns the token position pos,
	// the token tok, and the literal text lit corresponding to the
	// token. The source end is indicated by token.EOF.
	//
	// If the returned token is token.SEMICOLON, the corresponding
	// literal value is ";" if the semicolon was present in the source,
	// and "\n" if the semicolon was inserted because of a newline or
	// at EOF.
	//
	// 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() (token.Pos, token.Token, []byte) {
	scanAgain:
	S.skipWhitespace()

	// current token start
	insertSemi := false
	offs := S.offset
	tok := token.ILLEGAL

	// determine token value
	switch ch := S.ch; {
	case isLetter(ch):
	tok = S.scanIdentifier()
	switch tok {
	case token.IDENT, token.BREAK, token.CONTINUE, token.FALLTHROUGH, token.RETURN:
	insertSemi = true
	}
	case digitVal(ch) < 10:
	insertSemi = true
	tok = S.scanNumber(false)
	default:
	S.next() // always make progress
	switch ch {
	case -1:
	if S.insertSemi {
	S.insertSemi = false // EOF consumed
	return S.file.Pos(offs), token.SEMICOLON, newline
	}
	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 S.file.Pos(offs), token.SEMICOLON, newline
	case '"':
	insertSemi = true
	tok = token.STRING
	S.scanString()
	case '\'':
	insertSemi = true
	tok = token.CHAR
	S.scanChar()
	case '`':
	insertSemi = true
	tok = token.STRING
	S.scanRawString()
	case ':':
	tok = S.switch2(token.COLON, token.DEFINE)
	case '.':
	if digitVal(S.ch) < 10 {
	insertSemi = true
	tok = S.scanNumber(true)
	} else if S.ch == '.' {
	S.next()
	if S.ch == '.' {
	S.next()
	tok = token.ELLIPSIS
	}
	} else {
	tok = token.PERIOD
	}
	case ',':
	tok = token.COMMA
	case ';':
	tok = token.SEMICOLON
	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 = offs
	S.rdOffset = offs + 1
	S.insertSemi = false // newline consumed
	return S.file.Pos(offs), token.SEMICOLON, newline
	}
	S.scanComment()
	if S.mode&ScanComments == 0 {
	// skip comment
	S.insertSemi = false // newline consumed
	goto scanAgain
	}
	tok = token.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:
	if S.mode&AllowIllegalChars == 0 {
	S.error(offs, "illegal character "+charString(ch))
	}
	insertSemi = S.insertSemi // preserve insertSemi info
	}
	}

	if S.mode&InsertSemis != 0 {
	S.insertSemi = insertSemi
	}
	return S.file.Pos(offs), tok, S.src[offs:S.offset]
	}