// 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.fset.Position(from0)
if from.IsValid() && to.IsValid() && from.Line == to.Line {
return to.Column - from.Column
}
return infinity
}
// 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 := filepath.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)
}
}