go printer 源码
golang printer 代码
文件路径：/src/go/printer/printer.go
// 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 printer implements printing of AST nodes.
package printer
import (
"fmt"
"go/ast"
"go/build/constraint"
"go/token"
"io"
"os"
"strings"
"text/tabwriter"
"unicode"
)
const (
maxNewlines = 2 // max. number of newlines between source text
debug = false // enable for debugging
infinity = 1 << 30
)
type whiteSpace byte
const (
ignore = whiteSpace(0)
blank = whiteSpace(' ')
vtab = whiteSpace('\v')
newline = whiteSpace('\n')
formfeed = whiteSpace('\f')
indent = whiteSpace('>')
unindent = whiteSpace('<')
)
// A pmode value represents the current printer mode.
type pmode int
const (
noExtraBlank pmode = 1 << iota // disables extra blank after /*-style comment
noExtraLinebreak // disables extra line break after /*-style comment
)
type commentInfo struct {
cindex int // current comment index
comment *ast.CommentGroup // = printer.comments[cindex]; or nil
commentOffset int // = printer.posFor(printer.comments[cindex].List[0].Pos()).Offset; or infinity
commentNewline bool // true if the comment group contains newlines
}
type printer struct {
// Configuration (does not change after initialization)
Config
fset *token.FileSet
// Current state
output []byte // raw printer result
indent int // current indentation
level int // level == 0: outside composite literal; level > 0: inside composite literal
mode pmode // current printer mode
endAlignment bool // if set, terminate alignment immediately
impliedSemi bool // if set, a linebreak implies a semicolon
lastTok token.Token // last token printed (token.ILLEGAL if it's whitespace)
prevOpen token.Token // previous non-brace "open" token (, [, or token.ILLEGAL
wsbuf []whiteSpace // delayed white space
goBuild []int // start index of all //go:build comments in output
plusBuild []int // start index of all // +build comments in output
// Positions
// The out position differs from the pos position when the result
// formatting differs from the source formatting (in the amount of
// white space). If there's a difference and SourcePos is set in
// ConfigMode, //line directives are used in the output to restore
// original source positions for a reader.
pos token.Position // current position in AST (source) space
out token.Position // current position in output space
last token.Position // value of pos after calling writeString
linePtr *int // if set, record out.Line for the next token in *linePtr
// The list of all source comments, in order of appearance.
comments []*ast.CommentGroup // may be nil
useNodeComments bool // if not set, ignore lead and line comments of nodes
// Information about p.comments[p.cindex]; set up by nextComment.
commentInfo
// Cache of already computed node sizes.
nodeSizes map[ast.Node]int
// Cache of most recently computed line position.
cachedPos token.Pos
cachedLine int // line corresponding to cachedPos
}
func (p *printer) init(cfg *Config, fset *token.FileSet, nodeSizes map[ast.Node]int) {
p.Config = *cfg
p.fset = fset
p.pos = token.Position{Line: 1, Column: 1}
p.out = token.Position{Line: 1, Column: 1}
p.wsbuf = make([]whiteSpace, 0, 16) // whitespace sequences are short
p.nodeSizes = nodeSizes
p.cachedPos = -1
}
func (p *printer) internalError(msg ...any) {
if debug {
fmt.Print(p.pos.String() + ": ")
fmt.Println(msg...)
panic("go/printer")
}
}
// commentsHaveNewline reports whether a list of comments belonging to
// an *ast.CommentGroup contains newlines. Because the position information
// may only be partially correct, we also have to read the comment text.
func (p *printer) commentsHaveNewline(list []*ast.Comment) bool {
// len(list) > 0
line := p.lineFor(list[0].Pos())
for i, c := range list {
if i > 0 && p.lineFor(list[i].Pos()) != line {
// not all comments on the same line
return true
}
if t := c.Text; len(t) >= 2 && (t[1] == '/' || strings.Contains(t, "\n")) {
return true
}
}
_ = line
return false
}
func (p *printer) nextComment() {
for p.cindex < len(p.comments) {
c := p.comments[p.cindex]
p.cindex++
if list := c.List; len(list) > 0 {
p.comment = c
p.commentOffset = p.posFor(list[0].Pos()).Offset
p.commentNewline = p.commentsHaveNewline(list)
return
}
// we should not reach here (correct ASTs don't have empty
// ast.CommentGroup nodes), but be conservative and try again
}
// no more comments
p.commentOffset = infinity
}
// commentBefore reports whether the current comment group occurs
// before the next position in the source code and printing it does
// not introduce implicit semicolons.
func (p *printer) commentBefore(next token.Position) bool {
return p.commentOffset < next.Offset && (!p.impliedSemi || !p.commentNewline)
}
// commentSizeBefore returns the estimated size of the
// comments on the same line before the next position.
func (p *printer) commentSizeBefore(next token.Position) int {
// save/restore current p.commentInfo (p.nextComment() modifies it)
defer func(info commentInfo) {
p.commentInfo = info
}(p.commentInfo)
size := 0
for p.commentBefore(next) {
for _, c := range p.comment.List {
size += len(c.Text)
}
p.nextComment()
}
return size
}
// recordLine records the output line number for the next non-whitespace
// token in *linePtr. It is used to compute an accurate line number for a
// formatted construct, independent of pending (not yet emitted) whitespace
// or comments.
func (p *printer) recordLine(linePtr *int) {
p.linePtr = linePtr
}
// linesFrom returns the number of output lines between the current
// output line and the line argument, ignoring any pending (not yet
// emitted) whitespace or comments. It is used to compute an accurate
// size (in number of lines) for a formatted construct.
func (p *printer) linesFrom(line int) int {
return p.out.Line - line
}
func (p *printer) posFor(pos token.Pos) token.Position {
// not used frequently enough to cache entire token.Position
return p.fset.PositionFor(pos, false /* absolute position */)
}
func (p *printer) lineFor(pos token.Pos) int {
if pos != p.cachedPos {
p.cachedPos = pos
p.cachedLine = p.fset.PositionFor(pos, false /* absolute position */).Line
}
return p.cachedLine
}
// writeLineDirective writes a //line directive if necessary.
func (p *printer) writeLineDirective(pos token.Position) {
if 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 directive
p.out.Filename = pos.Filename
p.out.Line = pos.Line
}
}
// writeIndent writes indentation.
func (p *printer) writeIndent() {
// use "hard" htabs - indentation columns
// must not be discarded by the tabwriter
n := p.Config.Indent + p.indent // include base indentation
for i := 0; i < n; i++ {
p.output = append(p.output, '\t')
}
// update positions
p.pos.Offset += n
p.pos.Column += n
p.out.Column += n
}
// writeByte writes ch n times to p.output and updates p.pos.
// Only used to write formatting (white space) characters.
func (p *printer) writeByte(ch byte, n int) {
if p.endAlignment {
// Ignore any alignment control character;
// and at the end of the line, break with
// a formfeed to indicate termination of
// existing columns.
switch ch {
case '\t', '\v':
ch = ' '
case '\n', '\f':
ch = '\f'
p.endAlignment = false
}
}
if p.out.Column == 1 {
// no need to write line directives before white space
p.writeIndent()
}
for i := 0; i < n; i++ {
p.output = append(p.output, ch)
}
// update positions
p.pos.Offset += n
if ch == '\n' || ch == '\f' {
p.pos.Line += n
p.out.Line += n
p.pos.Column = 1
p.out.Column = 1
return
}
p.pos.Column += n
p.out.Column += n
}
// 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 {
if p.Config.Mode&SourcePos != 0 {
p.writeLineDirective(pos)
}
p.writeIndent()
}
if pos.IsValid() {
// update p.pos (if pos is invalid, continue with existing p.pos)
// Note: Must do this after handling line beginnings because
// writeIndent 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++ {
// Raw string literals may contain any character except back quote (`).
if ch := s[i]; ch == '\n' || ch == '\f' {
// account for line break
nlines++
li = i
// A line break inside a literal will break whatever column
// formatting is in place; ignore any further alignment through
// the end of the line.
p.endAlignment = true
}
}
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
}
// 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 *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
if pos.IsValid() && p.last.IsValid() {
n = pos.Line - p.last.Line
if n < 0 { // should never happen
n = 0
}
}
// at the package scope level only (p.indent == 0),
// add an extra newline if we dropped one before:
// this preserves a blank line before documentation
// comments at the package scope level (issue 2570)
if p.indent == 0 && droppedLinebreak {
n++
}
// make sure there is at least one line break
// if the previous comment was a line comment
if n == 0 && prev != nil && prev.Text[1] == '/' {
n = 1
}
if n > 0 {
// use formfeeds to break columns before a comment;
// this is analogous to using formfeeds to separate
// individual lines of /*-style comments
p.writeByte('\f', nlimit(n))
}
}
}
// Returns true if s contains only white space
// (only tabs and blanks can appear in the printer's context).
func isBlank(s string) bool {
for i := 0; i < len(s); i++ {
if s[i] > ' ' {
return false
}
}
return true
}
// commonPrefix returns the common prefix of a and b.
func commonPrefix(a, b string) string {
i := 0
for i < len(a) && i < len(b) && a[i] == b[i] && (a[i] <= ' ' || a[i] == '*') {
i++
}
return a[0:i]
}
// trimRight returns s with trailing whitespace removed.
func trimRight(s string) string {
return strings.TrimRightFunc(s, unicode.IsSpace)
}
// stripCommonPrefix removes a common prefix from /*-style comment lines (unless no
// comment line is indented, all but the first line have some form of space prefix).
// The prefix is computed using heuristics such that is likely that the comment
// contents are nicely laid out after re-printing each line using the printer's
// current indentation.
func stripCommonPrefix(lines []string) {
if len(lines) <= 1 {
return // at most one line - nothing to do
}
// len(lines) > 1
// 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 cases where only the first and last lines are not blank,
// such as two-line comments, or comments where all inner lines
// are blank, 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.
prefix := ""
prefixSet := false
if len(lines) > 2 {
for i, line := range lines[1 : len(lines)-1] {
if isBlank(line) {
lines[1+i] = "" // range starts with lines[1]
} else {
if !prefixSet {
prefix = line
prefixSet = true
}
prefix = commonPrefix(prefix, line)
}
}
}
// If we don't have a prefix yet, consider the last line.
if !prefixSet {
line := lines[len(lines)-1]
prefix = commonPrefix(line, line)
}
/*
* Check for vertical "line of stars" and correct prefix accordingly.
*/
lineOfStars := false
if p, _, ok := strings.Cut(prefix, "*"); ok {
// remove trailing blank from prefix so stars remain aligned
prefix = strings.TrimSuffix(p, " ")
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.
prefix = strings.TrimSuffix(prefix, string(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 := "*/"
before, _, _ := strings.Cut(last, closing) // closing always present
if isBlank(before) {
// last line only contains closing */
if lineOfStars {
closing = " */" // add blank to align final star
}
lines[len(lines)-1] = prefix + closing
} else {
// last line contains more comment text - assume
// it is aligned like the other lines and include
// in prefix computation
prefix = commonPrefix(prefix, last)
}
// Remove the common prefix from all but the first and empty lines.
for i, line := range lines {
if i > 0 && line != "" {
lines[i] = line[len(prefix):]
}
}
}
func (p *printer) writeComment(comment *ast.Comment) {
text := comment.Text
pos := p.posFor(comment.Pos())
const linePrefix = "//line "
if strings.HasPrefix(text, linePrefix) && (!pos.IsValid() || pos.Column == 1) {
// Possibly a //-style line directive.
// Suspend indentation temporarily to keep line directive valid.
defer func(indent int) { p.indent = indent }(p.indent)
p.indent = 0
}
// shortcut common case of //-style comments
if text[1] == '/' {
if constraint.IsGoBuild(text) {
p.goBuild = append(p.goBuild, len(p.output))
} else if constraint.IsPlusBuild(text) {
p.plusBuild = append(p.plusBuild, len(p.output))
}
p.writeString(pos, trimRight(text), true)
return
}
// for /*-style comments, print line by line and let the
// write function take care of the proper indentation
lines := strings.Split(text, "\n")
// The comment started in the first column but is going
// to be indented. For an idempotent result, add indentation
// to all lines such that they look like they were indented
// before - this will make sure the common prefix computation
// is the same independent of how many times formatting is
// applied (was issue 1835).
if pos.IsValid() && pos.Column == 1 && p.indent > 0 {
for i, line := range lines[1:] {
lines[1+i] = " " + line
}
}
stripCommonPrefix(lines)
// write comment lines, separated by formfeed,
// without a line break after the last line
for i, line := range lines {
if i > 0 {
p.writeByte('\f', 1)
pos = p.pos
}
if len(line) > 0 {
p.writeString(pos, trimRight(line), true)
}
}
}
// 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. The writeCommentSuffix result indicates if a
// newline was written or if a formfeed was dropped from the whitespace
// buffer.
func (p *printer) writeCommentSuffix(needsLinebreak bool) (wroteNewline, droppedFF bool) {
for i, ch := range p.wsbuf {
switch ch {
case blank, vtab:
// ignore trailing whitespace
p.wsbuf[i] = ignore
case indent, unindent:
// don't lose 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
wroteNewline = true
} else {
if ch == formfeed {
droppedFF = true
}
p.wsbuf[i] = ignore
}
}
}
p.writeWhitespace(len(p.wsbuf))
// make sure we have a line break
if needsLinebreak {
p.writeByte('\n', 1)
wroteNewline = true
}
return
}
// containsLinebreak reports whether the whitespace buffer contains any line breaks.
func (p *printer) containsLinebreak() bool {
for _, ch := range p.wsbuf {
if ch == newline || ch == formfeed {
return true
}
}
return false
}
// 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. The intersperseComments result indicates if a
// newline was written or if a formfeed was dropped from the whitespace buffer.
func (p *printer) intersperseComments(next token.Position, tok token.Token) (wroteNewline, droppedFF bool) {
var last *ast.Comment
for p.commentBefore(next) {
list := p.comment.List
changed := false
if p.lastTok != token.IMPORT && // do not rewrite cgo's import "C" comments
p.posFor(p.comment.Pos()).Column == 1 &&
p.posFor(p.comment.End()+1) == next {
// Unindented comment abutting next token position:
// a top-level doc comment.
list = formatDocComment(list)
changed = true
if len(p.comment.List) > 0 && len(list) == 0 {
// The doc comment was removed entirely.
// Keep preceding whitespace.
p.writeCommentPrefix(p.posFor(p.comment.Pos()), next, last, tok)
// Change print state to continue at next.
p.pos = next
p.last = next
// There can't be any more comments.
p.nextComment()
return p.writeCommentSuffix(false)
}
}
for _, c := range list {
p.writeCommentPrefix(p.posFor(c.Pos()), next, last, tok)
p.writeComment(c)
last = c
}
// In case list was rewritten, change print state to where
// the original list would have ended.
if len(p.comment.List) > 0 && changed {
last = p.comment.List[len(p.comment.List)-1]
p.pos = p.posFor(last.End())
p.last = p.pos
}
p.nextComment()
}
if last != nil {
// If the last comment is a /*-style comment and the next item
// follows on the same line but is not a comma, and not a "closing"
// token immediately following its corresponding "opening" token,
// add an extra separator unless explicitly disabled. Use a blank
// as separator unless we have pending linebreaks, they are not
// disabled, and we are outside a composite literal, in which case
// we want a linebreak (issue 15137).
// TODO(gri) This has become overly complicated. We should be able
// to track whether we're inside an expression or statement and
// use that information to decide more directly.
needsLinebreak := false
if p.mode&noExtraBlank == 0 &&
last.Text[1] == '*' && p.lineFor(last.Pos()) == next.Line &&
tok != token.COMMA &&
(tok != token.RPAREN || p.prevOpen == token.LPAREN) &&
(tok != token.RBRACK || p.prevOpen == token.LBRACK) {
if p.containsLinebreak() && p.mode&noExtraLinebreak == 0 && p.level == 0 {
needsLinebreak = true
} else {
p.writeByte(' ', 1)
}
}
// Ensure that there is a line break after a //-style comment,
// before EOF, and before a closing '}' unless explicitly disabled.
if last.Text[1] == '/' ||
tok == token.EOF ||
tok == token.RBRACE && p.mode&noExtraLinebreak == 0 {
needsLinebreak = true
}
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
}
// whiteWhitespace writes the first n whitespace entries.
func (p *printer) writeWhitespace(n int) {
// write entries
for i := 0; i < n; i++ {
switch ch := p.wsbuf[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.wsbuf[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.wsbuf[i], p.wsbuf[i+1] = unindent, formfeed
i-- // do it again
continue
}
fallthrough
default:
p.writeByte(byte(ch), 1)
}
}
// shift remaining entries down
l := copy(p.wsbuf, p.wsbuf[n:])
p.wsbuf = p.wsbuf[:l]
}
// ----------------------------------------------------------------------------
// Printing interface
// nlimit limits n to maxNewlines.
func nlimit(n int) int {
if n > maxNewlines {
n = maxNewlines
}
return n
}
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 ...any) {
for _, arg := range args {
// information about the current arg
var data string
var isLit bool
var impliedSemi bool // value for p.impliedSemi after this arg
// record previous opening token, if any
switch p.lastTok {
case token.ILLEGAL:
// ignore (white space)
case token.LPAREN, token.LBRACK:
p.prevOpen = p.lastTok
default:
// other tokens followed any opening token
p.prevOpen = token.ILLEGAL
}
switch x := arg.(type) {
case pmode:
// toggle printer mode
p.mode ^= x
continue
case whiteSpace:
if x == ignore {
// don't add ignore's to the buffer; they
// may screw up "correcting" unindents (see
// LabeledStmt)
continue
}
i := len(p.wsbuf)
if i == cap(p.wsbuf) {
// 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.wsbuf = p.wsbuf[0 : i+1]
p.wsbuf[i] = x
if x == newline || x == formfeed {
// newlines affect the current state (p.impliedSemi)
// and not the state after printing arg (impliedSemi)
// because comments can be interspersed before the arg
// in this case
p.impliedSemi = false
}
p.lastTok = token.ILLEGAL
continue
case *ast.Ident:
data = x.Name
impliedSemi = true
p.lastTok = token.IDENT
case *ast.BasicLit:
data = x.Value
isLit = true
impliedSemi = true
p.lastTok = x.Kind
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.wsbuf) != 0 {
p.internalError("whitespace buffer not empty")
}
p.wsbuf = p.wsbuf[0:1]
p.wsbuf[0] = ' '
}
data = s
// some keywords followed by a newline imply a semicolon
switch x {
case token.BREAK, token.CONTINUE, token.FALLTHROUGH, token.RETURN,
token.INC, token.DEC, token.RPAREN, token.RBRACK, token.RBRACE:
impliedSemi = true
}
p.lastTok = x
case token.Pos:
if x.IsValid() {
p.pos = p.posFor(x) // accurate position of next item
}
continue
case string:
// incorrect AST - print error message
data = x
isLit = true
impliedSemi = true
p.lastTok = token.STRING
default:
fmt.Fprintf(os.Stderr, "print: unsupported argument %v (%T)\n", arg, arg)
panic("go/printer type")
}
// data != ""
next := p.pos // estimated/accurate position of next item
wroteNewline, droppedFF := p.flush(next, p.lastTok)
// intersperse extra newlines if present in the source and
// if they don't cause extra semicolons (don't do this in
// flush as it will cause extra newlines at the end of a file)
if !p.impliedSemi {
n := nlimit(next.Line - p.pos.Line)
// don't exceed maxNewlines if we already wrote one
if wroteNewline && n == maxNewlines {
n = maxNewlines - 1
}
if n > 0 {
ch := byte('\n')
if droppedFF {
ch = '\f' // use formfeed since we dropped one before
}
p.writeByte(ch, n)
impliedSemi = false
}
}
// the next token starts now - record its line number if requested
if p.linePtr != nil {
*p.linePtr = p.out.Line
p.linePtr = nil
}
p.writeString(next, data, isLit)
p.impliedSemi = impliedSemi
}
}
// flush prints any pending comments and whitespace occurring textually
// before the position of the next token tok. The flush result indicates
// if a newline was written or if a formfeed was dropped from the whitespace
// buffer.
func (p *printer) flush(next token.Position, tok token.Token) (wroteNewline, droppedFF bool) {
if p.commentBefore(next) {
// if there are comments before the next item, intersperse them
wroteNewline, droppedFF = p.intersperseComments(next, tok)
} else {
// otherwise, write any leftover whitespace
p.writeWhitespace(len(p.wsbuf))
}
return
}
// getNode returns the ast.CommentGroup associated with n, if any.
func getDoc(n ast.Node) *ast.CommentGroup {
switch n := n.(type) {
case *ast.Field:
return n.Doc
case *ast.ImportSpec:
return n.Doc
case *ast.ValueSpec:
return n.Doc
case *ast.TypeSpec:
return n.Doc
case *ast.GenDecl:
return n.Doc
case *ast.FuncDecl:
return n.Doc
case *ast.File:
return n.Doc
}
return nil
}
func getLastComment(n ast.Node) *ast.CommentGroup {
switch n := n.(type) {
case *ast.Field:
return n.Comment
case *ast.ImportSpec:
return n.Comment
case *ast.ValueSpec:
return n.Comment
case *ast.TypeSpec:
return n.Comment
case *ast.GenDecl:
if len(n.Specs) > 0 {
return getLastComment(n.Specs[len(n.Specs)-1])
}
case *ast.File:
if len(n.Comments) > 0 {
return n.Comments[len(n.Comments)-1]
}
}
return nil
}
func (p *printer) printNode(node any) error {
// unpack *CommentedNode, if any
var comments []*ast.CommentGroup
if cnode, ok := node.(*CommentedNode); ok {
node = cnode.Node
comments = cnode.Comments
}
if comments != nil {
// commented node - restrict comment list to relevant range
n, ok := node.(ast.Node)
if !ok {
goto unsupported
}
beg := n.Pos()
end := n.End()
// if the node has associated documentation,
// include that commentgroup in the range
// (the comment list is sorted in the order
// of the comment appearance in the source code)
if doc := getDoc(n); doc != nil {
beg = doc.Pos()
}
if com := getLastComment(n); com != nil {
if e := com.End(); e > end {
end = e
}
}
// token.Pos values are global offsets, we can
// compare them directly
i := 0
for i < len(comments) && comments[i].End() < beg {
i++
}
j := i
for j < len(comments) && comments[j].Pos() < end {
j++
}
if i < j {
p.comments = comments[i:j]
}
} else if n, ok := node.(*ast.File); ok {
// use ast.File comments, if any
p.comments = n.Comments
}
// if there are no comments, use node comments
p.useNodeComments = p.comments == nil
// get comments ready for use
p.nextComment()
p.print(pmode(0))
// format node
switch n := node.(type) {
case ast.Expr:
p.expr(n)
case ast.Stmt:
// A labeled statement will un-indent to position the label.
// Set p.indent to 1 so we don't get indent "underflow".
if _, ok := n.(*ast.LabeledStmt); ok {
p.indent = 1
}
p.stmt(n, false)
case ast.Decl:
p.decl(n)
case ast.Spec:
p.spec(n, 1, false)
case []ast.Stmt:
// A labeled statement will un-indent to position the label.
// Set p.indent to 1 so we don't get indent "underflow".
for _, s := range n {
if _, ok := s.(*ast.LabeledStmt); ok {
p.indent = 1
}
}
p.stmtList(n, 0, false)
case []ast.Decl:
p.declList(n)
case *ast.File:
p.file(n)
default:
goto unsupported
}
return nil
unsupported:
return fmt.Errorf("go/printer: unsupported node type %T", node)
}
// ----------------------------------------------------------------------------
// 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 []byte
}
// trimmer is implemented as a state machine.
// It can be in one of the following states:
const (
inSpace = iota // inside space
inEscape // inside text bracketed by tabwriter.Escapes
inText // inside text
)
func (p *trimmer) resetSpace() {
p.state = inSpace
p.space = p.space[0:0]
}
// 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.
var aNewline = []byte("\n")
func (p *trimmer) Write(data []byte) (n int, err error) {
// invariants:
// p.state == inSpace:
// p.space is unwritten
// 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 = append(p.space, b)
case '\n', '\f':
p.resetSpace() // discard trailing space
_, err = p.output.Write(aNewline)
case tabwriter.Escape:
_, err = p.output.Write(p.space)
p.state = inEscape
m = n + 1 // +1: skip tabwriter.Escape
default:
_, err = p.output.Write(p.space)
p.state = inText
m = n
}
case inEscape:
if b == tabwriter.Escape {
_, err = p.output.Write(data[m:n])
p.resetSpace()
}
case inText:
switch b {
case '\t', ' ':
_, err = p.output.Write(data[m:n])
p.resetSpace()
p.space = append(p.space, b)
case '\n', '\f':
_, err = p.output.Write(data[m:n])
p.resetSpace()
if err == nil {
_, err = p.output.Write(aNewline)
}
case tabwriter.Escape:
_, err = p.output.Write(data[m:n])
p.state = inEscape
m = n + 1 // +1: skip tabwriter.Escape
}
default:
panic("unreachable")
}
if err != nil {
return
}
}
n = len(data)
switch p.state {
case inEscape, inText:
_, err = p.output.Write(data[m:n])
p.resetSpace()
}
return
}
// ----------------------------------------------------------------------------
// Public interface
// A Mode value is a set of flags (or 0). They control printing.
type Mode uint
const (
RawFormat Mode = 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
SourcePos // emit //line directives to preserve original source positions
)
// The mode below is not included in printer's public API because
// editing code text is deemed out of scope. Because this mode is
// unexported, it's also possible to modify or remove it based on
// the evolving needs of go/format and cmd/gofmt without breaking
// users. See discussion in CL 240683.
const (
// normalizeNumbers means to canonicalize number
// literal prefixes and exponents while printing.
//
// This value is known in and used by go/format and cmd/gofmt.
// It is currently more convenient and performant for those
// packages to apply number normalization during printing,
// rather than by modifying the AST in advance.
normalizeNumbers Mode = 1 << 30
)
// A Config node controls the output of Fprint.
type Config struct {
Mode Mode // default: 0
Tabwidth int // default: 8
Indent int // default: 0 (all code is indented at least by this much)
}
// fprint implements Fprint and takes a nodesSizes map for setting up the printer state.
func (cfg *Config) fprint(output io.Writer, fset *token.FileSet, node any, nodeSizes map[ast.Node]int) (err error) {
// print node
var p printer
p.init(cfg, fset, nodeSizes)
if err = p.printNode(node); err != nil {
return
}
// print outstanding comments
p.impliedSemi = false // EOF acts like a newline
p.flush(token.Position{Offset: infinity, Line: infinity}, token.EOF)
// output is buffered in p.output now.
// fix //go:build and // +build comments if needed.
p.fixGoBuildLines()
// 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}
// redirect output through a tabwriter if necessary
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
}
output = tabwriter.NewWriter(output, minwidth, cfg.Tabwidth, 1, padchar, twmode)
}
// write printer result via tabwriter/trimmer to output
if _, err = output.Write(p.output); err != nil {
return
}
// flush tabwriter, if any
if tw, _ := output.(*tabwriter.Writer); tw != nil {
err = tw.Flush()
}
return
}
// A CommentedNode bundles an AST node and corresponding comments.
// It may be provided as argument to any of the Fprint functions.
type CommentedNode struct {
Node any // *ast.File, or ast.Expr, ast.Decl, ast.Spec, or ast.Stmt
Comments []*ast.CommentGroup
}
// Fprint "pretty-prints" an AST node to output for a given configuration cfg.
// Position information is interpreted relative to the file set fset.
// The node type must be *ast.File, *CommentedNode, []ast.Decl, []ast.Stmt,
// or assignment-compatible to ast.Expr, ast.Decl, ast.Spec, or ast.Stmt.
func (cfg *Config) Fprint(output io.Writer, fset *token.FileSet, node any) error {
return cfg.fprint(output, fset, node, make(map[ast.Node]int))
}
// Fprint "pretty-prints" an AST node to output.
// It calls Config.Fprint with default settings.
// Note that gofmt uses tabs for indentation but spaces for alignment;
// use format.Node (package go/format) for output that matches gofmt.
func Fprint(output io.Writer, fset *token.FileSet, node any) error {
return (&Config{Tabwidth: 8}).Fprint(output, fset, node)
}
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