// distance returns the column difference between from and to if both
// are on the same line; if they are on different lines (or unknown)
// the result is infinity.
func (p *printer) distance(from0 token.Pos, to token.Position) int {
	from := p.posFor(from0)
	if from.IsValid() && to.IsValid() && from.Line == to.Line {
		return to.Column - from.Column
	}
	return infinity
}

func (p *parser) parseCallOrConversion(fun ast.Expr) *ast.CallExpr {
	if p.trace {
		defer un(trace(p, "CallOrConversion"))
	}

	lparen := p.expect(token.LPAREN)
	p.exprLev++
	var list vector.Vector
	var ellipsis token.Position
	for p.tok != token.RPAREN && p.tok != token.EOF && !ellipsis.IsValid() {
		list.Push(p.parseExpr())
		if p.tok == token.ELLIPSIS {
			ellipsis = p.pos
			p.next()
		}
		if p.tok != token.COMMA {
			break
		}
		p.next()
	}
	p.exprLev--
	rparen := p.expect(token.RPAREN)

	return &ast.CallExpr{fun, lparen, makeExprList(&list), ellipsis, rparen}
}

// writeItem writes data at position pos. data is the text corresponding to
// a single lexical token, but may also be comment text. pos is the actual
// (or at least very accurately estimated) position of the data in the original
// source text. If tags are present and GenHTML is set, the tags are written
// before and after the data. writeItem updates p.last to the position
// immediately following the data.
//
func (p *printer) writeItem(pos token.Position, data []byte, tag HTMLTag) {
	fileChanged := false
	if pos.IsValid() {
		// continue with previous position if we don't have a valid pos
		if p.last.IsValid() && p.last.Filename != pos.Filename {
			// the file has changed - reset state
			// (used when printing merged ASTs of different files
			// e.g., the result of ast.MergePackageFiles)
			p.indent = 0
			p.mode = 0
			p.buffer = p.buffer[0:0]
			fileChanged = true
		}
		p.pos = pos
	}
	if debug {
		// do not update p.pos - use write0
		_, filename := path.Split(pos.Filename)
		p.write0([]byte(fmt.Sprintf("[%s:%d:%d]", filename, pos.Line, pos.Column)))
	}
	if p.Mode&GenHTML != 0 {
		// write line tag if on a new line
		// TODO(gri): should write line tags on each line at the start
		//            will be more useful (e.g. to show line numbers)
		if p.Styler != nil && (pos.Line != p.lastTaggedLine || fileChanged) {
			p.writeTaggedItem(p.Styler.LineTag(pos.Line))
			p.lastTaggedLine = pos.Line
		}
		p.writeTaggedItem(data, tag)
	} else {
		p.write(data)
	}
	p.last = p.pos
}

func error(pos token.Position, msg string, args ...interface{}) {
	nerrors++
	if pos.IsValid() {
		fmt.Fprintf(os.Stderr, "%s: ", pos)
	}
	fmt.Fprintf(os.Stderr, msg, args)
	fmt.Fprintf(os.Stderr, "\n")
}

// Obtain a (single) token position before the next comment.
// Use this function to correct a token position such that the
// token is placed before the next comment (which may be a line
// comment introducing a newline and possibly introducing a
// semicolon). Use moveCommentsAfter() to move a comment past
// more than a single token. beforeComment() is preferable if
// if can be used as it produces better results.
//
// Remove this after transitioning to new semicolon syntax and
// some reasonable grace period (12/11/09).
func (p *printer) beforeComment(pos token.Position) token.Position {
	if p.comment != nil {
		p := p.comment.List[0].Position
		if !pos.IsValid() || pos.Offset > p.Offset {
			return p
		}
	}
	return pos
}

// writeString writes the string s to p.output and updates p.pos, p.out,
// and p.last. If isLit is set, s is escaped w/ tabwriter.Escape characters
// to protect s from being interpreted by the tabwriter.
//
// Note: writeString is only used to write Go tokens, literals, and
// comments, all of which must be written literally. Thus, it is correct
// to always set isLit = true. However, setting it explicitly only when
// needed (i.e., when we don't know that s contains no tabs or line breaks)
// avoids processing extra escape characters and reduces run time of the
// printer benchmark by up to 10%.
//
func (p *printer) writeString(pos token.Position, s string, isLit bool) {
	if p.out.Column == 1 {
		p.atLineBegin(pos)
	}

	if pos.IsValid() {
		// update p.pos (if pos is invalid, continue with existing p.pos)
		// Note: Must do this after handling line beginnings because
		// atLineBegin updates p.pos if there's indentation, but p.pos
		// is the position of s.
		p.pos = pos
	}

	if isLit {
		// Protect s such that is passes through the tabwriter
		// unchanged. Note that valid Go programs cannot contain
		// tabwriter.Escape bytes since they do not appear in legal
		// UTF-8 sequences.
		p.output = append(p.output, tabwriter.Escape)
	}

	if debug {
		p.output = append(p.output, fmt.Sprintf("/*%s*/", pos)...) // do not update p.pos!
	}
	p.output = append(p.output, s...)

	// update positions
	nlines := 0
	var li int // index of last newline; valid if nlines > 0
	for i := 0; i < len(s); i++ {
		// Go tokens cannot contain '\f' - no need to look for it
		if s[i] == '\n' {
			nlines++
			li = i
		}
	}
	p.pos.Offset += len(s)
	if nlines > 0 {
		p.pos.Line += nlines
		p.out.Line += nlines
		c := len(s) - li
		p.pos.Column = c
		p.out.Column = c
	} else {
		p.pos.Column += len(s)
		p.out.Column += len(s)
	}

	if isLit {
		p.output = append(p.output, tabwriter.Escape)
	}

	p.last = p.pos
}

// Verify that calling Scan() provides the correct results.
func TestScan(t *testing.T) {
	// make source
	var src string
	for _, e := range tokens {
		src += e.lit + whitespace
	}
	src_linecount := newlineCount(src) + 1
	whitespace_linecount := newlineCount(whitespace)

	// verify scan
	var s Scanner
	s.Init(fset.AddFile("", fset.Base(), len(src)), []byte(src), &testErrorHandler{t}, ScanComments)
	index := 0
	epos := token.Position{"", 0, 1, 1} // expected position
	for {
		pos, tok, litb := s.Scan()
		e := elt{token.EOF, "", special}
		if index < len(tokens) {
			e = tokens[index]
		}
		lit := string(litb)
		if tok == token.EOF {
			lit = "<EOF>"
			epos.Line = src_linecount
			epos.Column = 1
		}
		checkPos(t, lit, pos, epos)
		if tok != e.tok {
			t.Errorf("bad token for %q: got %s, expected %s", lit, tok.String(), e.tok.String())
		}
		if e.tok.IsLiteral() && lit != e.lit {
			t.Errorf("bad literal for %q: got %q, expected %q", lit, lit, e.lit)
		}
		if tokenclass(tok) != e.class {
			t.Errorf("bad class for %q: got %d, expected %d", lit, tokenclass(tok), e.class)
		}
		epos.Offset += len(lit) + len(whitespace)
		epos.Line += newlineCount(lit) + whitespace_linecount
		if tok == token.COMMENT && litb[1] == '/' {
			// correct for unaccounted '/n' in //-style comment
			epos.Offset++
			epos.Line++
		}
		index++
		if tok == token.EOF {
			break
		}
	}
	if s.ErrorCount != 0 {
		t.Errorf("found %d errors", s.ErrorCount)
	}
}

// Verify that calling Scan() provides the correct results.
func TestScan(t *testing.T) {
	// make source
	var src string
	for _, e := range tokens {
		src += e.lit + whitespace
	}
	src_linecount := newlineCount(src)
	whitespace_linecount := newlineCount(whitespace)

	// verify scan
	index := 0
	epos := token.Position{"", 0, 1, 1} // expected position
	nerrors := Tokenize("", []byte(src), &testErrorHandler{t}, ScanComments,
		func(pos token.Position, tok token.Token, litb []byte) bool {
			e := elt{token.EOF, "", special}
			if index < len(tokens) {
				e = tokens[index]
			}
			lit := string(litb)
			if tok == token.EOF {
				lit = "<EOF>"
				epos.Line = src_linecount
				epos.Column = 1
			}
			checkPos(t, lit, pos, epos)
			if tok != e.tok {
				t.Errorf("bad token for %q: got %s, expected %s", lit, tok.String(), e.tok.String())
			}
			if e.tok.IsLiteral() && lit != e.lit {
				t.Errorf("bad literal for %q: got %q, expected %q", lit, lit, e.lit)
			}
			if tokenclass(tok) != e.class {
				t.Errorf("bad class for %q: got %d, expected %d", lit, tokenclass(tok), e.class)
			}
			epos.Offset += len(lit) + len(whitespace)
			epos.Line += newlineCount(lit) + whitespace_linecount
			if tok == token.COMMENT && litb[1] == '/' {
				// correct for unaccounted '/n' in //-style comment
				epos.Offset++
				epos.Line++
			}
			index++
			return tok != token.EOF
		})
	if nerrors != 0 {
		t.Errorf("found %d errors", nerrors)
	}
}

// FIXME: arrange to put in ast
func PositionRange(start token.Position, end token.Position) string {
	s := ""
	if start.IsValid() {
		s = start.Filename + ":" + PositionRangeSansFile(start, end)
	} else if end.IsValid() {
		s = "-"
		if end.Filename != "" {
			s += end.Filename + ":"
		}
		s += fmt.Sprintf("%d:%d", end.Line, end.Column)
	}
	if s == "" {
		s = "-"
	}
	return s
}

// writeItem writes data at position pos. data is the text corresponding to
// a single lexical token, but may also be comment text. pos is the actual
// (or at least very accurately estimated) position of the data in the original
// source text. writeItem updates p.last to the position immediately following
// the data.
//
func (p *printer) writeItem(pos token.Position, data string) {
	if pos.IsValid() {
		// continue with previous position if we don't have a valid pos
		if p.last.IsValid() && p.last.Filename != pos.Filename {
			// the file has changed - reset state
			// (used when printing merged ASTs of different files
			// e.g., the result of ast.MergePackageFiles)
			p.indent = 0
			p.mode = 0
			p.wsbuf = p.wsbuf[0:0]
		}
		p.pos = pos
	}
	if debug {
		// do not update p.pos - use write0
		_, filename := filepath.Split(pos.Filename)
		p.write0([]byte(fmt.Sprintf("[%s:%d:%d]", filename, pos.Line, pos.Column)))
	}
	p.write([]byte(data))
	p.last = p.pos
}

// Verify that calling Scan() provides the correct results.
func TestScan(t *testing.T) {
	// make source
	src_linecount := newlineCount(string(source))
	whitespace_linecount := newlineCount(whitespace)

	// verify scan
	var s Scanner
	s.Init(fset.AddFile("", fset.Base(), len(source)), source, &testErrorHandler{t}, ScanComments|dontInsertSemis)
	index := 0
	epos := token.Position{"", 0, 1, 1} // expected position
	for {
		pos, tok, lit := s.Scan()
		if lit == "" {
			// no literal value for non-literal tokens
			lit = tok.String()
		}
		e := elt{token.EOF, "", special}
		if index < len(tokens) {
			e = tokens[index]
		}
		if tok == token.EOF {
			lit = "<EOF>"
			epos.Line = src_linecount
			epos.Column = 2
		}
		checkPos(t, lit, pos, epos)
		if tok != e.tok {
			t.Errorf("bad token for %q: got %s, expected %s", lit, tok, e.tok)
		}
		if e.tok.IsLiteral() {
			// no CRs in raw string literals
			elit := e.lit
			if elit[0] == '`' {
				elit = string(stripCR([]byte(elit)))
				epos.Offset += len(e.lit) - len(lit) // correct position
			}
			if lit != elit {
				t.Errorf("bad literal for %q: got %q, expected %q", lit, lit, elit)
			}
		}
		if tokenclass(tok) != e.class {
			t.Errorf("bad class for %q: got %d, expected %d", lit, tokenclass(tok), e.class)
		}
		epos.Offset += len(lit) + len(whitespace)
		epos.Line += newlineCount(lit) + whitespace_linecount
		if tok == token.COMMENT && lit[1] == '/' {
			// correct for unaccounted '/n' in //-style comment
			epos.Offset++
			epos.Line++
		}
		index++
		if tok == token.EOF {
			break
		}
	}
	if s.ErrorCount != 0 {
		t.Errorf("found %d errors", s.ErrorCount)
	}
}

// atLineBegin emits a //line comment if necessary and prints indentation.
func (p *printer) atLineBegin(pos token.Position) {
	// write a //line comment if necessary
	if p.Config.Mode&SourcePos != 0 && pos.IsValid() && (p.out.Line != pos.Line || p.out.Filename != pos.Filename) {
		p.output = append(p.output, tabwriter.Escape) // protect '\n' in //line from tabwriter interpretation
		p.output = append(p.output, fmt.Sprintf("//line %s:%d\n", pos.Filename, pos.Line)...)
		p.output = append(p.output, tabwriter.Escape)
		// p.out must match the //line comment
		p.out.Filename = pos.Filename
		p.out.Line = pos.Line
	}

	// write indentation
	// use "hard" htabs - indentation columns
	// must not be discarded by the tabwriter
	for i := 0; i < p.indent; i++ {
		p.output = append(p.output, '\t')
	}

	// update positions
	i := p.indent
	p.pos.Offset += i
	p.pos.Column += i
	p.out.Column += i
}

func parsePattern(pos token.Position, src string, stack map[string]bool) (pattern, re, action string, bol, eol bool) {
	p := &pat{src: src, re: bytes.NewBuffer(nil), stack: stack}

	defer func() {
		if e := recover(); e != nil {
			pos.Column += p.pos
			logErr(fmt.Sprintf(`%s - "%s^%s" - %s`, pos, src[:p.pos], src[p.pos:], e.(error)))
		}
	}()

	p.parseExpr(0)
	pattern, re = src[:p.pos], p.re.String()
	bol, eol = p.bol, p.eol
	switch b := p.current(); b {
	case 0:
		return
	case ' ', '\t':
		p.move()
		action = src[p.pos:]
		return
	}
	panic(errors.New("syntax error"))
}

func PositionRangeSansFile(start token.Position, end token.Position) string {
	s := ""
	if start.IsValid() {
		s += fmt.Sprintf("%d:%d", start.Line, start.Column)
		if start.Filename == end.Filename && end.IsValid() {
			// this is what we expect
			if start.Line == end.Line {
				if start.Column != end.Column {
					s += fmt.Sprintf("-%d", end.Column)
				}
			} else {
				s += fmt.Sprintf("-%d:%d", end.Line, end.Column)
			}
		}

	} else if end.IsValid() {
		s = "-"
		s += fmt.Sprintf("%d:%d", end.Line, end.Column)
	}
	if s == "" {
		s = "-"
	}
	return s
}

// Print a list of expressions. If the list spans multiple
// source lines, the original line breaks are respected between
// expressions. Sets multiLine to true if the list spans multiple
// lines.
func (p *printer) exprList(prev token.Position, list []ast.Expr, mode exprListMode, multiLine *bool) {
	if len(list) == 0 {
		return
	}

	if mode&blankStart != 0 {
		p.print(blank)
	}

	// TODO(gri): endLine may be incorrect as it is really the beginning
	//            of the last list entry. There may be only one, very long
	//            entry in which case line == endLine.
	line := list[0].Pos().Line
	endLine := list[len(list)-1].Pos().Line

	if prev.IsValid() && prev.Line == line && line == endLine {
		// all list entries on a single line
		for i, x := range list {
			if i > 0 {
				if mode&commaSep != 0 {
					p.print(token.COMMA)
				}
				p.print(blank)
			}
			p.expr(x, multiLine)
		}
		return
	}

	// list entries span multiple lines;
	// use source code positions to guide line breaks

	// don't add extra indentation if noIndent is set;
	// i.e., pretend that the first line is already indented
	ws := ignore
	if mode&noIndent == 0 {
		ws = indent
	}

	if prev.IsValid() && prev.Line < line && p.linebreak(line, 1, 2, ws, true) {
		ws = ignore
		*multiLine = true
	}

	for i, x := range list {
		prev := line
		line = x.Pos().Line
		if i > 0 {
			if mode&commaSep != 0 {
				p.print(token.COMMA)
			}
			if prev < line {
				if p.linebreak(line, 1, 2, ws, true) {
					ws = ignore
					*multiLine = true
				}
			} else {
				p.print(blank)
			}
		}
		p.expr(x, multiLine)
	}
	if mode&commaTerm != 0 {
		p.print(token.COMMA)
		if ws == ignore && mode&noIndent == 0 {
			// should always be indented here since we have a multi-line
			// expression list - be conservative and check anyway
			p.print(unindent)
		}
		p.print(formfeed) // terminating comma needs a line break to look good
	} else if ws == ignore && mode&noIndent == 0 {
		p.print(unindent)
	}
}

// NewCommentMap creates a new comment map by associating comment groups
// of the comments list with the nodes of the AST specified by node.
//
// A comment group g is associated with a node n if:
//
//   - g starts on the same line as n ends
//   - g starts on the line immediately following n, and there is
//     at least one empty line after g and before the next node
//   - g starts before n and is not associated to the node before n
//     via the previous rules
//
// NewCommentMap tries to associate a comment group to the "largest"
// node possible: For instance, if the comment is a line comment
// trailing an assignment, the comment is associated with the entire
// assignment rather than just the last operand in the assignment.
//
func NewCommentMap(fset *token.FileSet, node Node, comments []*CommentGroup) CommentMap {
	if len(comments) == 0 {
		return nil // no comments to map
	}

	cmap := make(CommentMap)

	// set up comment reader r
	tmp := make([]*CommentGroup, len(comments))
	copy(tmp, comments) // don't change incoming comments
	sortComments(tmp)
	r := commentListReader{fset: fset, list: tmp} // !r.eol() because len(comments) > 0
	r.next()

	// create node list in lexical order
	nodes := nodeList(node)
	nodes = append(nodes, nil) // append sentinel

	// set up iteration variables
	var (
		p     Node           // previous node
		pend  token.Position // end of p
		pg    Node           // previous node group (enclosing nodes of "importance")
		pgend token.Position // end of pg
		stack nodeStack      // stack of node groups
	)

	for _, q := range nodes {
		var qpos token.Position
		if q != nil {
			qpos = fset.Position(q.Pos()) // current node position
		} else {
			// set fake sentinel position to infinity so that
			// all comments get processed before the sentinel
			const infinity = 1 << 30
			qpos.Offset = infinity
			qpos.Line = infinity
		}

		// process comments before current node
		for r.end.Offset <= qpos.Offset {
			// determine recent node group
			if top := stack.pop(r.comment.Pos()); top != nil {
				pg = top
				pgend = fset.Position(pg.End())
			}
			// Try to associate a comment first with a node group
			// (i.e., a node of "importance" such as a declaration);
			// if that fails, try to associate it with the most recent
			// node.
			// TODO(gri) try to simplify the logic below
			var assoc Node
			switch {
			case pg != nil &&
				(pgend.Line == r.pos.Line ||
					pgend.Line+1 == r.pos.Line && r.end.Line+1 < qpos.Line):
				// 1) comment starts on same line as previous node group ends, or
				// 2) comment starts on the line immediately after the
				//    previous node group and there is an empty line before
				//    the current node
				// => associate comment with previous node group
				assoc = pg
			case p != nil &&
				(pend.Line == r.pos.Line ||
					pend.Line+1 == r.pos.Line && r.end.Line+1 < qpos.Line ||
					q == nil):
				// same rules apply as above for p rather than pg,
				// but also associate with p if we are at the end (q == nil)
				assoc = p
			default:
				// otherwise, associate comment with current node
				if q == nil {
					// we can only reach here if there was no p
					// which would imply that there were no nodes
					panic("internal error: no comments should be associated with sentinel")
				}
				assoc = q
			}
			cmap.addComment(assoc, r.comment)
			if r.eol() {
				return cmap
			}
			r.next()
		}
//.........这里部分代码省略.........

// Verify that calling Scan() provides the correct results.
func TestScan(t *testing.T) {
	whitespace_linecount := newlineCount(whitespace)

	// error handler
	eh := func(_ token.Position, msg string) {
		t.Errorf("error handler called (msg = %s)", msg)
	}

	// verify scan
	var s Scanner
	s.Init(fset.AddFile("", fset.Base(), len(source)), source, eh, ScanComments|dontInsertSemis)

	// set up expected position
	epos := token.Position{
		Filename: "",
		Offset:   0,
		Line:     1,
		Column:   1,
	}

	index := 0
	for {
		pos, tok, lit := s.Scan()

		// check position
		if tok == token.EOF {
			// correction for EOF
			epos.Line = newlineCount(string(source))
			epos.Column = 2
		}
		checkPos(t, lit, pos, epos)

		// check token
		e := elt{token.EOF, "", special}
		if index < len(tokens) {
			e = tokens[index]
			index++
		}
		if tok != e.tok {
			t.Errorf("bad token for %q: got %s, expected %s", lit, tok, e.tok)
		}

		// check token class
		if tokenclass(tok) != e.class {
			t.Errorf("bad class for %q: got %d, expected %d", lit, tokenclass(tok), e.class)
		}

		// check literal
		elit := ""
		switch e.tok {
		case token.COMMENT:
			// no CRs in comments
			elit = string(stripCR([]byte(e.lit)))
			//-style comment literal doesn't contain newline
			if elit[1] == '/' {
				elit = elit[0 : len(elit)-1]
			}
		case token.IDENT:
			elit = e.lit
		case token.SEMICOLON:
			elit = ";"
		default:
			if e.tok.IsLiteral() {
				// no CRs in raw string literals
				elit = e.lit
				if elit[0] == '`' {
					elit = string(stripCR([]byte(elit)))
				}
			} else if e.tok.IsKeyword() {
				elit = e.lit
			}
		}
		if lit != elit {
			t.Errorf("bad literal for %q: got %q, expected %q", lit, lit, elit)
		}

		if tok == token.EOF {
			break
		}

		// update position
		epos.Offset += len(e.lit) + len(whitespace)
		epos.Line += newlineCount(e.lit) + whitespace_linecount

	}

	if s.ErrorCount != 0 {
		t.Errorf("found %d errors", s.ErrorCount)
	}
}

// writeCommentPrefix writes the whitespace before a comment.
// If there is any pending whitespace, it consumes as much of
// it as is likely to help position the comment nicely.
// pos is the comment position, next the position of the item
// after all pending comments, prev is the previous comment in
// a group of comments (or nil), and tok is the next token.
//
func (p *printer) writeCommentPrefix(pos, next token.Position, prev, comment *ast.Comment, tok token.Token) {
	if len(p.output) == 0 {
		// the comment is the first item to be printed - don't write any whitespace
		return
	}

	if pos.IsValid() && pos.Filename != p.last.Filename {
		// comment in a different file - separate with newlines
		p.writeByte('\f', maxNewlines)
		return
	}

	if pos.Line == p.last.Line && (prev == nil || prev.Text[1] != '/') {
		// comment on the same line as last item:
		// separate with at least one separator
		hasSep := false
		if prev == nil {
			// first comment of a comment group
			j := 0
			for i, ch := range p.wsbuf {
				switch ch {
				case blank:
					// ignore any blanks before a comment
					p.wsbuf[i] = ignore
					continue
				case vtab:
					// respect existing tabs - important
					// for proper formatting of commented structs
					hasSep = true
					continue
				case indent:
					// apply pending indentation
					continue
				}
				j = i
				break
			}
			p.writeWhitespace(j)
		}
		// make sure there is at least one separator
		if !hasSep {
			sep := byte('\t')
			if pos.Line == next.Line {
				// next item is on the same line as the comment
				// (which must be a /*-style comment): separate
				// with a blank instead of a tab
				sep = ' '
			}
			p.writeByte(sep, 1)
		}

	} else {
		// comment on a different line:
		// separate with at least one line break
		droppedLinebreak := false
		j := 0
		for i, ch := range p.wsbuf {
			switch ch {
			case blank, vtab:
				// ignore any horizontal whitespace before line breaks
				p.wsbuf[i] = ignore
				continue
			case indent:
				// apply pending indentation
				continue
			case unindent:
				// if this is not the last unindent, apply it
				// as it is (likely) belonging to the last
				// construct (e.g., a multi-line expression list)
				// and is not part of closing a block
				if i+1 < len(p.wsbuf) && p.wsbuf[i+1] == unindent {
					continue
				}
				// if the next token is not a closing }, apply the unindent
				// if it appears that the comment is aligned with the
				// token; otherwise assume the unindent is part of a
				// closing block and stop (this scenario appears with
				// comments before a case label where the comments
				// apply to the next case instead of the current one)
				if tok != token.RBRACE && pos.Column == next.Column {
					continue
				}
			case newline, formfeed:
				p.wsbuf[i] = ignore
				droppedLinebreak = prev == nil // record only if first comment of a group
			}
			j = i
			break
		}
		p.writeWhitespace(j)

		// determine number of linebreaks before the comment
		n := 0
//.........这里部分代码省略.........

func (s *byteScanner) error(pos token.Position, msg string) {
	s.ErrorCount++
	if !s.Quiet {
		fmt.Fprintf(os.Stderr, "robotstxt from %s: %s\n", pos.String(), msg)
	}
}

// writeCommentPrefix writes the whitespace before a comment.
// If there is any pending whitespace, it consumes as much of
// it as is likely to help position the comment nicely.
// pos is the comment position, next the position of the item
// after all pending comments, prev is the previous comment in
// a group of comments (or nil), and isKeyword indicates if the
// next item is a keyword.
//
func (p *printer) writeCommentPrefix(pos, next token.Position, prev *ast.Comment, isKeyword bool) {
	if p.written == 0 {
		// the comment is the first item to be printed - don't write any whitespace
		return
	}

	if pos.IsValid() && pos.Filename != p.last.Filename {
		// comment in a different file - separate with newlines (writeNewlines will limit the number)
		p.writeNewlines(10, true)
		return
	}

	if pos.Line == p.last.Line && (prev == nil || prev.Text[1] != '/') {
		// comment on the same line as last item:
		// separate with at least one separator
		hasSep := false
		if prev == nil {
			// first comment of a comment group
			j := 0
			for i, ch := range p.wsbuf {
				switch ch {
				case blank:
					// ignore any blanks before a comment
					p.wsbuf[i] = ignore
					continue
				case vtab:
					// respect existing tabs - important
					// for proper formatting of commented structs
					hasSep = true
					continue
				case indent:
					// apply pending indentation
					continue
				}
				j = i
				break
			}
			p.writeWhitespace(j)
		}
		// make sure there is at least one separator
		if !hasSep {
			if pos.Line == next.Line {
				// next item is on the same line as the comment
				// (which must be a /*-style comment): separate
				// with a blank instead of a tab
				p.write([]byte{' '})
			} else {
				p.write(htab)
			}
		}

	} else {
		// comment on a different line:
		// separate with at least one line break
		if prev == nil {
			// first comment of a comment group
			j := 0
			for i, ch := range p.wsbuf {
				switch ch {
				case blank, vtab:
					// ignore any horizontal whitespace before line breaks
					p.wsbuf[i] = ignore
					continue
				case indent:
					// apply pending indentation
					continue
				case unindent:
					// if the next token is a keyword, apply the outdent
					// if it appears that the comment is aligned with the
					// keyword; otherwise assume the outdent is part of a
					// closing block and stop (this scenario appears with
					// comments before a case label where the comments
					// apply to the next case instead of the current one)
					if isKeyword && pos.Column == next.Column {
						continue
					}
				case newline, formfeed:
					// TODO(gri): may want to keep formfeed info in some cases
					p.wsbuf[i] = ignore
				}
				j = i
				break
			}
			p.writeWhitespace(j)
		}
		// use formfeeds to break columns before a comment;
		// this is analogous to using formfeeds to separate
		// individual lines of /*-style comments - but make
		// sure there is at least one line break if the previous
		// comment was a line comment
		n := pos.Line - p.last.Line // if !pos.IsValid(), pos.Line == 0, and n will be 0
		if n <= 0 && prev != nil && prev.Text[1] == '/' {
//.........这里部分代码省略.........