// 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
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
p.Positions[p.pos] = p.out
}
// 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.Positions[p.pos] = p.out
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, 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 {
// 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 {
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))
}
}
}