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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.
// The printer package implements printing of AST nodes.
package printer
import (
"bytes"
"fmt"
"go/ast"
"go/token"
"io"
"os"
"path"
"runtime"
"tabwriter"
)
const debug = false // enable for debugging
type whiteSpace int
const (
ignore = whiteSpace(0)
blank = whiteSpace(' ')
vtab = whiteSpace('\v')
newline = whiteSpace('\n')
formfeed = whiteSpace('\f')
indent = whiteSpace('>')
unindent = whiteSpace('<')
)
const (
esc2 = '\xfe' // an escape byte that cannot occur in regular UTF-8
_ = 1 / (esc2 - tabwriter.Escape) // cause compiler error if esc2 == tabwriter.Escape
)
var (
esc = []byte{tabwriter.Escape}
htab = []byte{'\t'}
htabs = []byte("\t\t\t\t\t\t\t\t")
newlines = []byte("\n\n\n\n\n\n\n\n") // more than the max determined by nlines
formfeeds = []byte("\f\f\f\f\f\f\f\f") // more than the max determined by nlines
)
// Special positions
var noPos token.Position // use noPos when a position is needed but not known
var infinity = 1 << 30
// Use ignoreMultiLine if the multiLine information is not important.
var ignoreMultiLine = new(bool)
// A pmode value represents the current printer mode.
type pmode int
const (
inLiteral pmode = 1 << iota
noExtraLinebreak
)
type printer struct {
// Configuration (does not change after initialization)
output io.Writer
Config
fset *token.FileSet
errors chan os.Error
// Current state
nesting int // nesting level (0: top-level (package scope), >0: functions/decls.)
written int // number of bytes written
indent int // current indentation
mode pmode // current printer mode
lastTok token.Token // the last token printed (token.ILLEGAL if it's whitespace)
// Buffered whitespace
buffer []whiteSpace
// The (possibly estimated) position in the generated output;
// in AST space (i.e., pos is set whenever a token position is
// known accurately, and updated dependending on what has been
// written).
pos token.Position
// The value of pos immediately after the last item has been
// written using writeItem.
last token.Position
// HTML support
lastTaggedLine int // last line for which a line tag was written
// The list of all source comments, in order of appearance.
comments []*ast.CommentGroup // may be nil
cindex int // current comment index
useNodeComments bool // if not set, ignore lead and line comments of nodes
}
func (p *printer) init(output io.Writer, cfg *Config, fset *token.FileSet) {
p.output = output
p.Config = *cfg
p.fset = fset
p.errors = make(chan os.Error)
p.buffer = make([]whiteSpace, 0, 16) // whitespace sequences are short
}
func (p *printer) internalError(msg ...interface{}) {
if debug {
fmt.Print(p.pos.String() + ": ")
fmt.Println(msg...)
panic("go/printer")
}
}
// nlines returns the adjusted number of linebreaks given the desired number
// of breaks n such that min <= result <= max where max depends on the current
// nesting level.
//
func (p *printer) nlines(n, min int) int {
if n < min {
return min
}
max := 3 // max. number of newlines at the top level (p.nesting == 0)
if p.nesting > 0 {
max = 2 // max. number of newlines everywhere else
}
if n > max {
return max
}
return n
}
// write0 writes raw (uninterpreted) data to p.output and handles errors.
// write0 does not indent after newlines, and does not HTML-escape or update p.pos.
//
func (p *printer) write0(data []byte) {
if len(data) > 0 {
n, err := p.output.Write(data)
p.written += n
if err != nil {
p.errors <- err
runtime.Goexit()
}
}
}
// write interprets data and writes it to p.output. It inserts indentation
// after a line break unless in a tabwriter escape sequence.
// It updates p.pos as a side-effect.
//
func (p *printer) write(data []byte) {
i0 := 0
for i, b := range data {
switch b {
case '\n', '\f':
// write segment ending in b
p.write0(data[i0 : i+1])
// update p.pos
p.pos.Offset += i + 1 - i0
p.pos.Line++
p.pos.Column = 1
if p.mode&inLiteral == 0 {
// write indentation
// use "hard" htabs - indentation columns
// must not be discarded by the tabwriter
j := p.indent
for ; j > len(htabs); j -= len(htabs) {
p.write0(htabs)
}
p.write0(htabs[0:j])
// update p.pos
p.pos.Offset += p.indent
p.pos.Column += p.indent
}
// next segment start
i0 = i + 1
case tabwriter.Escape:
p.mode ^= inLiteral
// ignore escape chars introduced by printer - they are
// invisible and must not affect p.pos (was issue #1089)
p.pos.Offset--
p.pos.Column--
}
}
// write remaining segment
p.write0(data[i0:])
// update p.pos
d := len(data) - i0
p.pos.Offset += d
p.pos.Column += d
}
func (p *printer) writeNewlines(n int, useFF bool) {
if n > 0 {
n = p.nlines(n, 0)
if useFF {
p.write(formfeeds[0:n])
} else {
p.write(newlines[0:n])
}
}
}
// 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 []byte) {
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]
}
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)))
}
p.write(data)
p.last = p.pos
}
// 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.buffer {
switch ch {
case blank:
// ignore any blanks before a comment
p.buffer[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.buffer {
switch ch {
case blank, vtab:
// ignore any horizontal whitespace before line breaks
p.buffer[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.buffer[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] == '/' {
n = 1
}
p.writeNewlines(n, true)
}
}
func (p *printer) writeCommentLine(comment *ast.Comment, pos token.Position, line []byte) {
// line must pass through unchanged, bracket it with tabwriter.Escape
line = bytes.Join([][]byte{esc, line, esc}, nil)
p.writeItem(pos, line)
}
// Split comment text into lines
func split(text []byte) [][]byte {
// count lines (comment text never ends in a newline)
n := 1
for _, c := range text {
if c == '\n' {
n++
}
}
// split
lines := make([][]byte, n)
n = 0
i := 0
for j, c := range text {
if c == '\n' {
lines[n] = text[i:j] // exclude newline
i = j + 1 // discard newline
n++
}
}
lines[n] = text[i:]
return lines
}
func isBlank(s []byte) bool {
for _, b := range s {
if b > ' ' {
return false
}
}
return true
}
func commonPrefix(a, b []byte) []byte {
i := 0
for i < len(a) && i < len(b) && a[i] == b[i] && (a[i] <= ' ' || a[i] == '*') {
i++
}
return a[0:i]
}
func stripCommonPrefix(lines [][]byte) {
if len(lines) < 2 {
return // at most one line - nothing to do
}
// len(lines) >= 2
// The heuristic in this function tries to handle a few
// common patterns of /*-style comments: Comments where
// the opening /* and closing */ are aligned and the
// rest of the comment text is aligned and indented with
// blanks or tabs, cases with a vertical "line of stars"
// on the left, and cases where the closing */ is on the
// same line as the last comment text.
// Compute maximum common white prefix of all but the first,
// last, and blank lines, and replace blank lines with empty
// lines (the first line starts with /* and has no prefix).
// In case of two-line comments, consider the last line for
// the prefix computation since otherwise the prefix would
// be empty.
//
// Note that the first and last line are never empty (they
// contain the opening /* and closing */ respectively) and
// thus they can be ignored by the blank line check.
var prefix []byte
if len(lines) > 2 {
for i, line := range lines[1 : len(lines)-1] {
switch {
case isBlank(line):
lines[1+i] = nil // range starts at line 1
case prefix == nil:
prefix = commonPrefix(line, line)
default:
prefix = commonPrefix(prefix, line)
}
}
} else { // len(lines) == 2
line := lines[1]
prefix = commonPrefix(line, line)
}
/*
* Check for vertical "line of stars" and correct prefix accordingly.
*/
lineOfStars := false
if i := bytes.Index(prefix, []byte{'*'}); i >= 0 {
// Line of stars present.
if i > 0 && prefix[i-1] == ' ' {
i-- // remove trailing blank from prefix so stars remain aligned
}
prefix = prefix[0:i]
lineOfStars = true
} else {
// No line of stars present.
// Determine the white space on the first line after the /*
// and before the beginning of the comment text, assume two
// blanks instead of the /* unless the first character after
// the /* is a tab. If the first comment line is empty but
// for the opening /*, assume up to 3 blanks or a tab. This
// whitespace may be found as suffix in the common prefix.
first := lines[0]
if isBlank(first[2:]) {
// no comment text on the first line:
// reduce prefix by up to 3 blanks or a tab
// if present - this keeps comment text indented
// relative to the /* and */'s if it was indented
// in the first place
i := len(prefix)
for n := 0; n < 3 && i > 0 && prefix[i-1] == ' '; n++ {
i--
}
if i == len(prefix) && i > 0 && prefix[i-1] == '\t' {
i--
}
prefix = prefix[0:i]
} else {
// comment text on the first line
suffix := make([]byte, len(first))
n := 2 // start after opening /*
for n < len(first) && first[n] <= ' ' {
suffix[n] = first[n]
n++
}
if n > 2 && suffix[2] == '\t' {
// assume the '\t' compensates for the /*
suffix = suffix[2:n]
} else {
// otherwise assume two blanks
suffix[0], suffix[1] = ' ', ' '
suffix = suffix[0:n]
}
// Shorten the computed common prefix by the length of
// suffix, if it is found as suffix of the prefix.
if bytes.HasSuffix(prefix, suffix) {
prefix = prefix[0 : len(prefix)-len(suffix)]
}
}
}
// Handle last line: If it only contains a closing */, align it
// with the opening /*, otherwise align the text with the other
// lines.
last := lines[len(lines)-1]
closing := []byte("*/")
i := bytes.Index(last, closing)
if isBlank(last[0:i]) {
// last line only contains closing */
var sep []byte
if lineOfStars {
// insert an aligning blank
sep = []byte{' '}
}
lines[len(lines)-1] = bytes.Join([][]byte{prefix, closing}, sep)
} else {
// last line contains more comment text - assume
// it is aligned like the other lines
prefix = commonPrefix(prefix, last)
}
// Remove the common prefix from all but the first and empty lines.
for i, line := range lines[1:] {
if len(line) != 0 {
lines[1+i] = line[len(prefix):] // range starts at line 1
}
}
}
func (p *printer) writeComment(comment *ast.Comment) {
text := comment.Text
// shortcut common case of //-style comments
if text[1] == '/' {
p.writeCommentLine(comment, p.fset.Position(comment.Pos()), text)
return
}
// for /*-style comments, print line by line and let the
// write function take care of the proper indentation
lines := split(text)
stripCommonPrefix(lines)
// write comment lines, separated by formfeed,
// without a line break after the last line
linebreak := formfeeds[0:1]
pos := p.fset.Position(comment.Pos())
for i, line := range lines {
if i > 0 {
p.write(linebreak)
pos = p.pos
}
if len(line) > 0 {
p.writeCommentLine(comment, pos, line)
}
}
}
// writeCommentSuffix writes a line break after a comment if indicated
// and processes any leftover indentation information. If a line break
// is needed, the kind of break (newline vs formfeed) depends on the
// pending whitespace. writeCommentSuffix returns true if a pending
// formfeed was dropped from the whitespace buffer.
//
func (p *printer) writeCommentSuffix(needsLinebreak bool) (droppedFF bool) {
for i, ch := range p.buffer {
switch ch {
case blank, vtab:
// ignore trailing whitespace
p.buffer[i] = ignore
case indent, unindent:
// don't loose indentation information
case newline, formfeed:
// if we need a line break, keep exactly one
// but remember if we dropped any formfeeds
if needsLinebreak {
needsLinebreak = false
} else {
if ch == formfeed {
droppedFF = true
}
p.buffer[i] = ignore
}
}
}
p.writeWhitespace(len(p.buffer))
// make sure we have a line break
if needsLinebreak {
p.write([]byte{'\n'})
}
return
}
// intersperseComments consumes all comments that appear before the next token
// tok and prints it together with the buffered whitespace (i.e., the whitespace
// that needs to be written before the next token). A heuristic is used to mix
// the comments and whitespace. intersperseComments returns true if a pending
// formfeed was dropped from the whitespace buffer.
//
func (p *printer) intersperseComments(next token.Position, tok token.Token) (droppedFF bool) {
var last *ast.Comment
for ; p.commentBefore(next); p.cindex++ {
for _, c := range p.comments[p.cindex].List {
p.writeCommentPrefix(p.fset.Position(c.Pos()), next, last, tok.IsKeyword())
p.writeComment(c)
last = c
}
}
if last != nil {
if last.Text[1] == '*' && p.fset.Position(last.Pos()).Line == next.Line {
// the last comment is a /*-style comment and the next item
// follows on the same line: separate with an extra blank
p.write([]byte{' '})
}
// ensure that there is a line break after a //-style comment,
// before a closing '}' unless explicitly disabled, or at eof
needsLinebreak :=
last.Text[1] == '/' ||
tok == token.RBRACE && p.mode&noExtraLinebreak == 0 ||
tok == token.EOF
return p.writeCommentSuffix(needsLinebreak)
}
// no comment was written - we should never reach here since
// intersperseComments should not be called in that case
p.internalError("intersperseComments called without pending comments")
return false
}
// whiteWhitespace writes the first n whitespace entries.
func (p *printer) writeWhitespace(n int) {
// write entries
var data [1]byte
for i := 0; i < n; i++ {
switch ch := p.buffer[i]; ch {
case ignore:
// ignore!
case indent:
p.indent++
case unindent:
p.indent--
if p.indent < 0 {
p.internalError("negative indentation:", p.indent)
p.indent = 0
}
case newline, formfeed:
// A line break immediately followed by a "correcting"
// unindent is swapped with the unindent - this permits
// proper label positioning. If a comment is between
// the line break and the label, the unindent is not
// part of the comment whitespace prefix and the comment
// will be positioned correctly indented.
if i+1 < n && p.buffer[i+1] == unindent {
// Use a formfeed to terminate the current section.
// Otherwise, a long label name on the next line leading
// to a wide column may increase the indentation column
// of lines before the label; effectively leading to wrong
// indentation.
p.buffer[i], p.buffer[i+1] = unindent, formfeed
i-- // do it again
continue
}
fallthrough
default:
data[0] = byte(ch)
p.write(data[0:])
}
}
// shift remaining entries down
i := 0
for ; n < len(p.buffer); n++ {
p.buffer[i] = p.buffer[n]
i++
}
p.buffer = p.buffer[0:i]
}
// ----------------------------------------------------------------------------
// Printing interface
func mayCombine(prev token.Token, next byte) (b bool) {
switch prev {
case token.INT:
b = next == '.' // 1.
case token.ADD:
b = next == '+' // ++
case token.SUB:
b = next == '-' // --
case token.QUO:
b = next == '*' // /*
case token.LSS:
b = next == '-' || next == '<' // <- or <<
case token.AND:
b = next == '&' || next == '^' // && or &^
}
return
}
// print prints a list of "items" (roughly corresponding to syntactic
// tokens, but also including whitespace and formatting information).
// It is the only print function that should be called directly from
// any of the AST printing functions in nodes.go.
//
// Whitespace is accumulated until a non-whitespace token appears. Any
// comments that need to appear before that token are printed first,
// taking into account the amount and structure of any pending white-
// space for best comment placement. Then, any leftover whitespace is
// printed, followed by the actual token.
//
func (p *printer) print(args ...interface{}) {
for _, f := range args {
next := p.pos // estimated position of next item
var data []byte
var tok token.Token
switch x := f.(type) {
case pmode:
// toggle printer mode
p.mode ^= x
case whiteSpace:
if x == ignore {
// don't add ignore's to the buffer; they
// may screw up "correcting" unindents (see
// LabeledStmt)
break
}
i := len(p.buffer)
if i == cap(p.buffer) {
// Whitespace sequences are very short so this should
// never happen. Handle gracefully (but possibly with
// bad comment placement) if it does happen.
p.writeWhitespace(i)
i = 0
}
p.buffer = p.buffer[0 : i+1]
p.buffer[i] = x
case *ast.Ident:
data = []byte(x.Name)
tok = token.IDENT
case *ast.BasicLit:
// escape all literals so they pass through unchanged
// (note that valid Go programs cannot contain
// tabwriter.Escape bytes since they do not appear in
// legal UTF-8 sequences)
data = make([]byte, 0, len(x.Value)+2)
data = append(data, tabwriter.Escape)
data = append(data, x.Value...)
data = append(data, tabwriter.Escape)
tok = x.Kind
// If we have a raw string that spans multiple lines and
// the opening quote (`) is on a line preceded only by
// indentation, we don't want to write that indentation
// because the following lines of the raw string are not
// indented. It's easiest to correct the output at the end
// via the trimmer (because of the complex handling of
// white space).
// Mark multi-line raw strings by replacing the opening
// quote with esc2 and have the trimmer take care of fixing
// it up. (Do this _after_ making a copy of data!)
if data[1] == '`' && bytes.IndexByte(data, '\n') > 0 {
data[1] = esc2
}
case token.Token:
s := x.String()
if mayCombine(p.lastTok, s[0]) {
// the previous and the current token must be
// separated by a blank otherwise they combine
// into a different incorrect token sequence
// (except for token.INT followed by a '.' this
// should never happen because it is taken care
// of via binary expression formatting)
if len(p.buffer) != 0 {
p.internalError("whitespace buffer not empty")
}
p.buffer = p.buffer[0:1]
p.buffer[0] = ' '
}
data = []byte(s)
tok = x
case token.Pos:
if x.IsValid() {
next = p.fset.Position(x) // accurate position of next item
}
tok = p.lastTok
default:
fmt.Fprintf(os.Stderr, "print: unsupported argument type %T\n", f)
panic("go/printer type")
}
p.lastTok = tok
p.pos = next
if data != nil {
droppedFF := p.flush(next, tok)
// intersperse extra newlines if present in the source
// (don't do this in flush as it will cause extra newlines
// at the end of a file) - use formfeeds if we dropped one
// before
p.writeNewlines(next.Line-p.pos.Line, droppedFF)
p.writeItem(next, data)
}
}
}
// commentBefore returns true iff the current comment occurs
// before the next position in the source code.
//
func (p *printer) commentBefore(next token.Position) bool {
return p.cindex < len(p.comments) && p.fset.Position(p.comments[p.cindex].List[0].Pos()).Offset < next.Offset
}
// Flush prints any pending comments and whitespace occurring
// textually before the position of the next token tok. Flush
// returns true if a pending formfeed character was dropped
// from the whitespace buffer as a result of interspersing
// comments.
//
func (p *printer) flush(next token.Position, tok token.Token) (droppedFF bool) {
if p.commentBefore(next) {
// if there are comments before the next item, intersperse them
droppedFF = p.intersperseComments(next, tok)
} else {
// otherwise, write any leftover whitespace
p.writeWhitespace(len(p.buffer))
}
return
}
// ----------------------------------------------------------------------------
// Trimmer
// A trimmer is an io.Writer filter for stripping tabwriter.Escape
// characters, trailing blanks and tabs, and for converting formfeed
// and vtab characters into newlines and htabs (in case no tabwriter
// is used). Text bracketed by tabwriter.Escape characters is passed
// through unchanged.
//
type trimmer struct {
output io.Writer
state int
space bytes.Buffer
hasText bool
}
// trimmer is implemented as a state machine.
// It can be in one of the following states:
const (
inSpace = iota // inside space
atEscape // inside space and the last char was an opening tabwriter.Escape
inEscape // inside text bracketed by tabwriter.Escapes
inText // inside text
)
var backquote = []byte{'`'}
// Design note: It is tempting to eliminate extra blanks occurring in
// whitespace in this function as it could simplify some
// of the blanks logic in the node printing functions.
// However, this would mess up any formatting done by
// the tabwriter.
func (p *trimmer) Write(data []byte) (n int, err os.Error) {
// invariants:
// p.state == inSpace, atEscape:
// p.space is unwritten
// p.hasText indicates if there is any text on this line
// p.state == inEscape, inText:
// data[m:n] is unwritten
m := 0
var b byte
for n, b = range data {
if b == '\v' {
b = '\t' // convert to htab
}
switch p.state {
case inSpace:
switch b {
case '\t', ' ':
p.space.WriteByte(b) // WriteByte returns no errors
case '\n', '\f':
p.space.Reset() // discard trailing space
_, err = p.output.Write(newlines[0:1]) // write newline
p.hasText = false
case tabwriter.Escape:
p.state = atEscape
default:
_, err = p.output.Write(p.space.Bytes())
p.state = inText
m = n
}
case atEscape:
// discard indentation if we have a multi-line raw string
// (see printer.print for details)
if b != esc2 || p.hasText {
_, err = p.output.Write(p.space.Bytes())
}
p.state = inEscape
m = n
if b == esc2 {
_, err = p.output.Write(backquote) // convert back
m++
}
case inEscape:
if b == tabwriter.Escape {
_, err = p.output.Write(data[m:n])
p.state = inSpace
p.space.Reset()
p.hasText = true
}
case inText:
switch b {
case '\t', ' ':
_, err = p.output.Write(data[m:n])
p.state = inSpace
p.space.Reset()
p.space.WriteByte(b) // WriteByte returns no errors
p.hasText = true
case '\n', '\f':
_, err = p.output.Write(data[m:n])
p.state = inSpace
p.space.Reset()
_, err = p.output.Write(newlines[0:1]) // write newline
p.hasText = false
case tabwriter.Escape:
_, err = p.output.Write(data[m:n])
p.state = atEscape
p.space.Reset()
p.hasText = true
}
}
if err != nil {
return
}
}
n = len(data)
switch p.state {
case inEscape, inText:
_, err = p.output.Write(data[m:n])
p.state = inSpace
p.space.Reset()
p.hasText = true
}
return
}
// ----------------------------------------------------------------------------
// Public interface
// General printing is controlled with these Config.Mode flags.
const (
RawFormat uint = 1 << iota // do not use a tabwriter; if set, UseSpaces is ignored
TabIndent // use tabs for indentation independent of UseSpaces
UseSpaces // use spaces instead of tabs for alignment
)
// A Config node controls the output of Fprint.
type Config struct {
Mode uint // default: 0
Tabwidth int // default: 8
}
// Fprint "pretty-prints" an AST node to output and returns the number
// of bytes written and an error (if any) for a given configuration cfg.
// Position information is interpreted relative to the file set fset.
// The node type must be *ast.File, or assignment-compatible to ast.Expr,
// ast.Decl, ast.Spec, or ast.Stmt.
//
func (cfg *Config) Fprint(output io.Writer, fset *token.FileSet, node interface{}) (int, os.Error) {
// redirect output through a trimmer to eliminate trailing whitespace
// (Input to a tabwriter must be untrimmed since trailing tabs provide
// formatting information. The tabwriter could provide trimming
// functionality but no tabwriter is used when RawFormat is set.)
output = &trimmer{output: output}
// setup tabwriter if needed and redirect output
var tw *tabwriter.Writer
if cfg.Mode&RawFormat == 0 {
minwidth := cfg.Tabwidth
padchar := byte('\t')
if cfg.Mode&UseSpaces != 0 {
padchar = ' '
}
twmode := tabwriter.DiscardEmptyColumns
if cfg.Mode&TabIndent != 0 {
minwidth = 0
twmode |= tabwriter.TabIndent
}
tw = tabwriter.NewWriter(output, minwidth, cfg.Tabwidth, 1, padchar, twmode)
output = tw
}
// setup printer and print node
var p printer
p.init(output, cfg, fset)
go func() {
switch n := node.(type) {
case ast.Expr:
p.nesting = 1
p.useNodeComments = true
p.expr(n, ignoreMultiLine)
case ast.Stmt:
p.nesting = 1
p.useNodeComments = true
// A labeled statement will un-indent to position the
// label. Set indent to 1 so we don't get indent "underflow".
if _, labeledStmt := n.(*ast.LabeledStmt); labeledStmt {
p.indent = 1
}
p.stmt(n, false, ignoreMultiLine)
case ast.Decl:
p.nesting = 1
p.useNodeComments = true
p.decl(n, ignoreMultiLine)
case ast.Spec:
p.nesting = 1
p.useNodeComments = true
p.spec(n, 1, false, ignoreMultiLine)
case *ast.File:
p.nesting = 0
p.comments = n.Comments
p.useNodeComments = n.Comments == nil
p.file(n)
default:
p.errors <- fmt.Errorf("printer.Fprint: unsupported node type %T", n)
runtime.Goexit()
}
p.flush(token.Position{Offset: infinity, Line: infinity}, token.EOF)
p.errors <- nil // no errors
}()
err := <-p.errors // wait for completion of goroutine
// flush tabwriter, if any
if tw != nil {
tw.Flush() // ignore errors
}
return p.written, err
}
// Fprint "pretty-prints" an AST node to output.
// It calls Config.Fprint with default settings.
//
func Fprint(output io.Writer, fset *token.FileSet, node interface{}) os.Error {
_, err := (&Config{Tabwidth: 8}).Fprint(output, fset, node) // don't care about number of bytes written
return err
}