Golang Position.IsValid方法代码示例

// 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
}

// 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
}

// 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.........