src/go/doc/comment.go - go - Git at Google

 // 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.

 // Godoc comment extraction and comment -> HTML formatting.

 package doc

 import (
 	"bytes"
 	"internal/lazyregexp"
 	"io"
 	"strings"
 	"text/template" // for HTMLEscape
 	"unicode"
 	"unicode/utf8"
 )

 const (
 	ldquo = "&ldquo;"
 	rdquo = "&rdquo;"
 	ulquo = "“"
 	urquo = "”"
 )

 var (
 	htmlQuoteReplacer    = strings.NewReplacer(ulquo, ldquo, urquo, rdquo)
 	unicodeQuoteReplacer = strings.NewReplacer("``", ulquo, "''", urquo)
 )

 // Escape comment text for HTML. If nice is set,
 // also turn `` into &ldquo; and '' into &rdquo;.
 func commentEscape(w io.Writer, text string, nice bool) {
 	if nice {
 		// In the first pass, we convert `` and '' into their unicode equivalents.
 		// This prevents them from being escaped in HTMLEscape.
 		text = convertQuotes(text)
 		var buf bytes.Buffer
 		template.HTMLEscape(&buf, []byte(text))
 		// Now we convert the unicode quotes to their HTML escaped entities to maintain old behavior.
 		// We need to use a temp buffer to read the string back and do the conversion,
 		// otherwise HTMLEscape will escape & to &amp;
 		htmlQuoteReplacer.WriteString(w, buf.String())
 		return
 	}
 	template.HTMLEscape(w, []byte(text))
 }

 func convertQuotes(text string) string {
 	return unicodeQuoteReplacer.Replace(text)
 }

 const (
 	// Regexp for Go identifiers
 	identRx = `[\pL_][\pL_0-9]*`

 	// Regexp for URLs
 	// Match parens, and check later for balance - see #5043, #22285
 	// Match .,:;?! within path, but not at end - see #18139, #16565
 	// This excludes some rare yet valid urls ending in common punctuation
 	// in order to allow sentences ending in URLs.

 	// protocol (required) e.g. http
 	protoPart = `(https?|ftp|file|gopher|mailto|nntp)`
 	// host (required) e.g. www.example.com or [::1]:8080
 	hostPart = `([a-zA-Z0-9_@\-.\[\]:]+)`
 	// path+query+fragment (optional) e.g. /path/index.html?q=foo#bar
 	pathPart = `([.,:;?!]*[a-zA-Z0-9$'()*+&#=@~_/\-\[\]%])*`

 	urlRx = protoPart + `://` + hostPart + pathPart
 )

 var matchRx = lazyregexp.New(`(` + urlRx + `)|(` + identRx + `)`)

 var (
 	html_a      = []byte(`<a href="`)
 	html_aq     = []byte(`">`)
 	html_enda   = []byte("</a>")
 	html_i      = []byte("<i>")
 	html_endi   = []byte("</i>")
 	html_p      = []byte("<p>\n")
 	html_endp   = []byte("</p>\n")
 	html_pre    = []byte("<pre>")
 	html_endpre = []byte("</pre>\n")
 	html_h      = []byte(`<h3 id="`)
 	html_hq     = []byte(`">`)
 	html_endh   = []byte("</h3>\n")
 )

 // Emphasize and escape a line of text for HTML. URLs are converted into links;
 // if the URL also appears in the words map, the link is taken from the map (if
 // the corresponding map value is the empty string, the URL is not converted
 // into a link). Go identifiers that appear in the words map are italicized; if
 // the corresponding map value is not the empty string, it is considered a URL
 // and the word is converted into a link. If nice is set, the remaining text's
 // appearance is improved where it makes sense (e.g., `` is turned into &ldquo;
 // and '' into &rdquo;).
 func emphasize(w io.Writer, line string, words map[string]string, nice bool) {
 	for {
 		m := matchRx.FindStringSubmatchIndex(line)
 		if m == nil {
 			break
 		}
 		// m >= 6 (two parenthesized sub-regexps in matchRx, 1st one is urlRx)

 		// write text before match
 		commentEscape(w, line[0:m[0]], nice)

 		// adjust match for URLs
 		match := line[m[0]:m[1]]
 		if strings.Contains(match, "://") {
 			m0, m1 := m[0], m[1]
 			for _, s := range []string{"()", "{}", "[]"} {
 				open, close := s[:1], s[1:] // E.g., "(" and ")"
 				// require opening parentheses before closing parentheses (#22285)
 				if i := strings.Index(match, close); i >= 0 && i < strings.Index(match, open) {
 					m1 = m0 + i
 					match = line[m0:m1]
 				}
 				// require balanced pairs of parentheses (#5043)
 				for i := 0; strings.Count(match, open) != strings.Count(match, close) && i < 10; i++ {
 					m1 = strings.LastIndexAny(line[:m1], s)
 					match = line[m0:m1]
 				}
 			}
 			if m1 != m[1] {
 				// redo matching with shortened line for correct indices
 				m = matchRx.FindStringSubmatchIndex(line[:m[0]+len(match)])
 			}
 		}

 		// analyze match
 		url := ""
 		italics := false
 		if words != nil {
 			url, italics = words[match]
 		}
 		if m[2] >= 0 {
 			// match against first parenthesized sub-regexp; must be match against urlRx
 			if !italics {
 				// no alternative URL in words list, use match instead
 				url = match
 			}
 			italics = false // don't italicize URLs
 		}

 		// write match
 		if len(url) > 0 {
 			w.Write(html_a)
 			template.HTMLEscape(w, []byte(url))
 			w.Write(html_aq)
 		}
 		if italics {
 			w.Write(html_i)
 		}
 		commentEscape(w, match, nice)
 		if italics {
 			w.Write(html_endi)
 		}
 		if len(url) > 0 {
 			w.Write(html_enda)
 		}

 		// advance
 		line = line[m[1]:]
 	}
 	commentEscape(w, line, nice)
 }

 func indentLen(s string) int {
 	i := 0
 	for i < len(s) && (s[i] == ' ' || s[i] == '\t') {
 		i++
 	}
 	return i
 }

 func isBlank(s string) bool {
 	return len(s) == 0 || (len(s) == 1 && s[0] == '\n')
 }

 func commonPrefix(a, b string) string {
 	i := 0
 	for i < len(a) && i < len(b) && a[i] == b[i] {
 		i++
 	}
 	return a[0:i]
 }

 func unindent(block []string) {
 	if len(block) == 0 {
 		return
 	}

 	// compute maximum common white prefix
 	prefix := block[0][0:indentLen(block[0])]
 	for _, line := range block {
 		if !isBlank(line) {
 			prefix = commonPrefix(prefix, line[0:indentLen(line)])
 		}
 	}
 	n := len(prefix)

 	// remove
 	for i, line := range block {
 		if !isBlank(line) {
 			block[i] = line[n:]
 		}
 	}
 }

 // heading returns the trimmed line if it passes as a section heading;
 // otherwise it returns the empty string.
 func heading(line string) string {
 	line = strings.TrimSpace(line)
 	if len(line) == 0 {
 		return ""
 	}

 	// a heading must start with an uppercase letter
 	r, _ := utf8.DecodeRuneInString(line)
 	if !unicode.IsLetter(r) || !unicode.IsUpper(r) {
 		return ""
 	}

 	// it must end in a letter or digit:
 	r, _ = utf8.DecodeLastRuneInString(line)
 	if !unicode.IsLetter(r) && !unicode.IsDigit(r) {
 		return ""
 	}

 	// exclude lines with illegal characters. we allow "(),"
 	if strings.ContainsAny(line, ";:!?+*/=[]{}_^°&§~%#@<\">\\") {
 		return ""
 	}

 	// allow "'" for possessive "'s" only
 	for b := line; ; {
 		i := strings.IndexRune(b, '\'')
 		if i < 0 {
 			break
 		}
 		if i+1 >= len(b) || b[i+1] != 's' || (i+2 < len(b) && b[i+2] != ' ') {
 			return "" // not followed by "s "
 		}
 		b = b[i+2:]
 	}

 	// allow "." when followed by non-space
 	for b := line; ; {
 		i := strings.IndexRune(b, '.')
 		if i < 0 {
 			break
 		}
 		if i+1 >= len(b) || b[i+1] == ' ' {
 			return "" // not followed by non-space
 		}
 		b = b[i+1:]
 	}

 	return line
 }

 type op int

 const (
 	opPara op = iota
 	opHead
 	opPre
 )

 type block struct {
 	op    op
 	lines []string
 }

 var nonAlphaNumRx = lazyregexp.New(`[^a-zA-Z0-9]`)

 func anchorID(line string) string {
 	// Add a "hdr-" prefix to avoid conflicting with IDs used for package symbols.
 	return "hdr-" + nonAlphaNumRx.ReplaceAllString(line, "_")
 }

 // ToHTML converts comment text to formatted HTML.
 // The comment was prepared by DocReader,
 // so it is known not to have leading, trailing blank lines
 // nor to have trailing spaces at the end of lines.
 // The comment markers have already been removed.
 //
 // Each span of unindented non-blank lines is converted into
 // a single paragraph. There is one exception to the rule: a span that
 // consists of a single line, is followed by another paragraph span,
 // begins with a capital letter, and contains no punctuation
 // other than parentheses and commas is formatted as a heading.
 //
 // A span of indented lines is converted into a <pre> block,
 // with the common indent prefix removed.
 //
 // URLs in the comment text are converted into links; if the URL also appears
 // in the words map, the link is taken from the map (if the corresponding map
 // value is the empty string, the URL is not converted into a link).
 //
 // Go identifiers that appear in the words map are italicized; if the corresponding
 // map value is not the empty string, it is considered a URL and the word is converted
 // into a link.
 func ToHTML(w io.Writer, text string, words map[string]string) {
 	for _, b := range blocks(text) {
 		switch b.op {
 		case opPara:
 			w.Write(html_p)
 			for _, line := range b.lines {
 				emphasize(w, line, words, true)
 			}
 			w.Write(html_endp)
 		case opHead:
 			w.Write(html_h)
 			id := ""
 			for _, line := range b.lines {
 				if id == "" {
 					id = anchorID(line)
 					w.Write([]byte(id))
 					w.Write(html_hq)
 				}
 				commentEscape(w, line, true)
 			}
 			if id == "" {
 				w.Write(html_hq)
 			}
 			w.Write(html_endh)
 		case opPre:
 			w.Write(html_pre)
 			for _, line := range b.lines {
 				emphasize(w, line, nil, false)
 			}
 			w.Write(html_endpre)
 		}
 	}
 }

 func blocks(text string) []block {
 	var (
 		out  []block
 		para []string

 		lastWasBlank   = false
 		lastWasHeading = false
 	)

 	close := func() {
 		if para != nil {
 			out = append(out, block{opPara, para})
 			para = nil
 		}
 	}

 	lines := strings.SplitAfter(text, "\n")
 	unindent(lines)
 	for i := 0; i < len(lines); {
 		line := lines[i]
 		if isBlank(line) {
 			// close paragraph
 			close()
 			i++
 			lastWasBlank = true
 			continue
 		}
 		if indentLen(line) > 0 {
 			// close paragraph
 			close()

 			// count indented or blank lines
 			j := i + 1
 			for j < len(lines) && (isBlank(lines[j]) || indentLen(lines[j]) > 0) {
 				j++
 			}
 			// but not trailing blank lines
 			for j > i && isBlank(lines[j-1]) {
 				j--
 			}
 			pre := lines[i:j]
 			i = j

 			unindent(pre)

 			// put those lines in a pre block
 			out = append(out, block{opPre, pre})
 			lastWasHeading = false
 			continue
 		}

 		if lastWasBlank && !lastWasHeading && i+2 < len(lines) &&
 			isBlank(lines[i+1]) && !isBlank(lines[i+2]) && indentLen(lines[i+2]) == 0 {
 			// current line is non-blank, surrounded by blank lines
 			// and the next non-blank line is not indented: this
 			// might be a heading.
 			if head := heading(line); head != "" {
 				close()
 				out = append(out, block{opHead, []string{head}})
 				i += 2
 				lastWasHeading = true
 				continue
 			}
 		}

 		// open paragraph
 		lastWasBlank = false
 		lastWasHeading = false
 		para = append(para, lines[i])
 		i++
 	}
 	close()

 	return out
 }

 // ToText prepares comment text for presentation in textual output.
 // It wraps paragraphs of text to width or fewer Unicode code points
 // and then prefixes each line with the indent. In preformatted sections
 // (such as program text), it prefixes each non-blank line with preIndent.
 func ToText(w io.Writer, text string, indent, preIndent string, width int) {
 	l := lineWrapper{
 		out:    w,
 		width:  width,
 		indent: indent,
 	}
 	for _, b := range blocks(text) {
 		switch b.op {
 		case opPara:
 			// l.write will add leading newline if required
 			for _, line := range b.lines {
 				line = convertQuotes(line)
 				l.write(line)
 			}
 			l.flush()
 		case opHead:
 			w.Write(nl)
 			for _, line := range b.lines {
 				line = convertQuotes(line)
 				l.write(line + "\n")
 			}
 			l.flush()
 		case opPre:
 			w.Write(nl)
 			for _, line := range b.lines {
 				if isBlank(line) {
 					w.Write([]byte("\n"))
 				} else {
 					w.Write([]byte(preIndent))
 					w.Write([]byte(line))
 				}
 			}
 		}
 	}
 }

 type lineWrapper struct {
 	out       io.Writer
 	printed   bool
 	width     int
 	indent    string
 	n         int
 	pendSpace int
 }

 var nl = []byte("\n")
 var space = []byte(" ")
 var prefix = []byte("// ")

 func (l *lineWrapper) write(text string) {
 	if l.n == 0 && l.printed {
 		l.out.Write(nl) // blank line before new paragraph
 	}
 	l.printed = true

 	needsPrefix := false
 	isComment := strings.HasPrefix(text, "//")
 	for _, f := range strings.Fields(text) {
 		w := utf8.RuneCountInString(f)
 		// wrap if line is too long
 		if l.n > 0 && l.n+l.pendSpace+w > l.width {
 			l.out.Write(nl)
 			l.n = 0
 			l.pendSpace = 0
 			needsPrefix = isComment
 		}
 		if l.n == 0 {
 			l.out.Write([]byte(l.indent))
 		}
 		if needsPrefix {
 			l.out.Write(prefix)
 			needsPrefix = false
 		}
 		l.out.Write(space[:l.pendSpace])
 		l.out.Write([]byte(f))
 		l.n += l.pendSpace + w
 		l.pendSpace = 1
 	}
 }

 func (l *lineWrapper) flush() {
 	if l.n == 0 {
 		return
 	}
 	l.out.Write(nl)
 	l.pendSpace = 0
 	l.n = 0
 }
	// 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.

	// Godoc comment extraction and comment -> HTML formatting.

	package doc

	import (
	"bytes"
	"internal/lazyregexp"
	"io"
	"strings"
	"text/template" // for HTMLEscape
	"unicode"
	"unicode/utf8"
	)

	const (
	ldquo = "“"
	rdquo = "”"
	ulquo = "“"
	urquo = "”"
	)

	var (
	htmlQuoteReplacer = strings.NewReplacer(ulquo, ldquo, urquo, rdquo)
	unicodeQuoteReplacer = strings.NewReplacer("``", ulquo, "''", urquo)
	)

	// Escape comment text for HTML. If nice is set,
	// also turn `` into “ and '' into ”.
	func commentEscape(w io.Writer, text string, nice bool) {
	if nice {
	// In the first pass, we convert `` and '' into their unicode equivalents.
	// This prevents them from being escaped in HTMLEscape.
	text = convertQuotes(text)
	var buf bytes.Buffer
	template.HTMLEscape(&buf, []byte(text))
	// Now we convert the unicode quotes to their HTML escaped entities to maintain old behavior.
	// We need to use a temp buffer to read the string back and do the conversion,
	// otherwise HTMLEscape will escape & to &
	htmlQuoteReplacer.WriteString(w, buf.String())
	return
	}
	template.HTMLEscape(w, []byte(text))
	}

	func convertQuotes(text string) string {
	return unicodeQuoteReplacer.Replace(text)
	}

	const (
	// Regexp for Go identifiers
	identRx = `[\pL_][\pL_0-9]*`

	// Regexp for URLs
	// Match parens, and check later for balance - see #5043, #22285
	// Match .,:;?! within path, but not at end - see #18139, #16565
	// This excludes some rare yet valid urls ending in common punctuation
	// in order to allow sentences ending in URLs.

	// protocol (required) e.g. http
	protoPart = `(https?\|ftp\|file\|gopher\|mailto\|nntp)`
	// host (required) e.g. www.example.com or [::1]:8080
	hostPart = `([a-zA-Z0-9_@\-.\[\]:]+)`
	// path+query+fragment (optional) e.g. /path/index.html?q=foo#bar
	pathPart = `([.,:;?!][a-zA-Z0-9$'()+&#=@~_/\-\[\]%])*`

	urlRx = protoPart + `://` + hostPart + pathPart
	)

	var matchRx = lazyregexp.New(`(` + urlRx + `)\|(` + identRx + `)`)

	var (
	html_a = []byte(`<a href="`)
	html_aq = []byte(`">`)
	html_enda = []byte("</a>")
	html_i = []byte("<i>")
	html_endi = []byte("</i>")
	html_p = []byte("<p>\n")
	html_endp = []byte("</p>\n")
	html_pre = []byte("<pre>")
	html_endpre = []byte("</pre>\n")
	html_h = []byte(`<h3 id="`)
	html_hq = []byte(`">`)
	html_endh = []byte("</h3>\n")
	)

	// Emphasize and escape a line of text for HTML. URLs are converted into links;
	// if the URL also appears in the words map, the link is taken from the map (if
	// the corresponding map value is the empty string, the URL is not converted
	// into a link). Go identifiers that appear in the words map are italicized; if
	// the corresponding map value is not the empty string, it is considered a URL
	// and the word is converted into a link. If nice is set, the remaining text's
	// appearance is improved where it makes sense (e.g., `` is turned into “
	// and '' into ”).
	func emphasize(w io.Writer, line string, words map[string]string, nice bool) {
	for {
	m := matchRx.FindStringSubmatchIndex(line)
	if m == nil {
	break
	}
	// m >= 6 (two parenthesized sub-regexps in matchRx, 1st one is urlRx)

	// write text before match
	commentEscape(w, line[0:m[0]], nice)

	// adjust match for URLs
	match := line[m[0]:m[1]]
	if strings.Contains(match, "://") {
	m0, m1 := m[0], m[1]
	for _, s := range []string{"()", "{}", "[]"} {
	open, close := s[:1], s[1:] // E.g., "(" and ")"
	// require opening parentheses before closing parentheses (#22285)
	if i := strings.Index(match, close); i >= 0 && i < strings.Index(match, open) {
	m1 = m0 + i
	match = line[m0:m1]
	}
	// require balanced pairs of parentheses (#5043)
	for i := 0; strings.Count(match, open) != strings.Count(match, close) && i < 10; i++ {
	m1 = strings.LastIndexAny(line[:m1], s)
	match = line[m0:m1]
	}
	}
	if m1 != m[1] {
	// redo matching with shortened line for correct indices
	m = matchRx.FindStringSubmatchIndex(line[:m[0]+len(match)])
	}
	}

	// analyze match
	url := ""
	italics := false
	if words != nil {
	url, italics = words[match]
	}
	if m[2] >= 0 {
	// match against first parenthesized sub-regexp; must be match against urlRx
	if !italics {
	// no alternative URL in words list, use match instead
	url = match
	}
	italics = false // don't italicize URLs
	}

	// write match
	if len(url) > 0 {
	w.Write(html_a)
	template.HTMLEscape(w, []byte(url))
	w.Write(html_aq)
	}
	if italics {
	w.Write(html_i)
	}
	commentEscape(w, match, nice)
	if italics {
	w.Write(html_endi)
	}
	if len(url) > 0 {
	w.Write(html_enda)
	}

	// advance
	line = line[m[1]:]
	}
	commentEscape(w, line, nice)
	}

	func indentLen(s string) int {
	i := 0
	for i < len(s) && (s[i] == ' ' \|\| s[i] == '\t') {
	i++
	}
	return i
	}

	func isBlank(s string) bool {
	return len(s) == 0 \|\| (len(s) == 1 && s[0] == '\n')
	}

	func commonPrefix(a, b string) string {
	i := 0
	for i < len(a) && i < len(b) && a[i] == b[i] {
	i++
	}
	return a[0:i]
	}

	func unindent(block []string) {
	if len(block) == 0 {
	return
	}

	// compute maximum common white prefix
	prefix := block[0][0:indentLen(block[0])]
	for _, line := range block {
	if !isBlank(line) {
	prefix = commonPrefix(prefix, line[0:indentLen(line)])
	}
	}
	n := len(prefix)

	// remove
	for i, line := range block {
	if !isBlank(line) {
	block[i] = line[n:]
	}
	}
	}

	// heading returns the trimmed line if it passes as a section heading;
	// otherwise it returns the empty string.
	func heading(line string) string {
	line = strings.TrimSpace(line)
	if len(line) == 0 {
	return ""
	}

	// a heading must start with an uppercase letter
	r, _ := utf8.DecodeRuneInString(line)
	if !unicode.IsLetter(r) \|\| !unicode.IsUpper(r) {
	return ""
	}

	// it must end in a letter or digit:
	r, _ = utf8.DecodeLastRuneInString(line)
	if !unicode.IsLetter(r) && !unicode.IsDigit(r) {
	return ""
	}

	// exclude lines with illegal characters. we allow "(),"
	if strings.ContainsAny(line, ";:!?+*/=[]{}_^°&§~%#@<\">\\") {
	return ""
	}

	// allow "'" for possessive "'s" only
	for b := line; ; {
	i := strings.IndexRune(b, '\'')
	if i < 0 {
	break
	}
	if i+1 >= len(b) \|\| b[i+1] != 's' \|\| (i+2 < len(b) && b[i+2] != ' ') {
	return "" // not followed by "s "
	}
	b = b[i+2:]
	}

	// allow "." when followed by non-space
	for b := line; ; {
	i := strings.IndexRune(b, '.')
	if i < 0 {
	break
	}
	if i+1 >= len(b) \|\| b[i+1] == ' ' {
	return "" // not followed by non-space
	}
	b = b[i+1:]
	}

	return line
	}

	type op int

	const (
	opPara op = iota
	opHead
	opPre
	)

	type block struct {
	op op
	lines []string
	}

	var nonAlphaNumRx = lazyregexp.New(`[^a-zA-Z0-9]`)

	func anchorID(line string) string {
	// Add a "hdr-" prefix to avoid conflicting with IDs used for package symbols.
	return "hdr-" + nonAlphaNumRx.ReplaceAllString(line, "_")
	}

	// ToHTML converts comment text to formatted HTML.
	// The comment was prepared by DocReader,
	// so it is known not to have leading, trailing blank lines
	// nor to have trailing spaces at the end of lines.
	// The comment markers have already been removed.
	//
	// Each span of unindented non-blank lines is converted into
	// a single paragraph. There is one exception to the rule: a span that
	// consists of a single line, is followed by another paragraph span,
	// begins with a capital letter, and contains no punctuation
	// other than parentheses and commas is formatted as a heading.
	//
	// A span of indented lines is converted into a <pre> block,
	// with the common indent prefix removed.
	//
	// URLs in the comment text are converted into links; if the URL also appears
	// in the words map, the link is taken from the map (if the corresponding map
	// value is the empty string, the URL is not converted into a link).
	//
	// Go identifiers that appear in the words map are italicized; if the corresponding
	// map value is not the empty string, it is considered a URL and the word is converted
	// into a link.
	func ToHTML(w io.Writer, text string, words map[string]string) {
	for _, b := range blocks(text) {
	switch b.op {
	case opPara:
	w.Write(html_p)
	for _, line := range b.lines {
	emphasize(w, line, words, true)
	}
	w.Write(html_endp)
	case opHead:
	w.Write(html_h)
	id := ""
	for _, line := range b.lines {
	if id == "" {
	id = anchorID(line)
	w.Write([]byte(id))
	w.Write(html_hq)
	}
	commentEscape(w, line, true)
	}
	if id == "" {
	w.Write(html_hq)
	}
	w.Write(html_endh)
	case opPre:
	w.Write(html_pre)
	for _, line := range b.lines {
	emphasize(w, line, nil, false)
	}
	w.Write(html_endpre)
	}
	}
	}

	func blocks(text string) []block {
	var (
	out []block
	para []string

	lastWasBlank = false
	lastWasHeading = false
	)

	close := func() {
	if para != nil {
	out = append(out, block{opPara, para})
	para = nil
	}
	}

	lines := strings.SplitAfter(text, "\n")
	unindent(lines)
	for i := 0; i < len(lines); {
	line := lines[i]
	if isBlank(line) {
	// close paragraph
	close()
	i++
	lastWasBlank = true
	continue
	}
	if indentLen(line) > 0 {
	// close paragraph
	close()

	// count indented or blank lines
	j := i + 1
	for j < len(lines) && (isBlank(lines[j]) \|\| indentLen(lines[j]) > 0) {
	j++
	}
	// but not trailing blank lines
	for j > i && isBlank(lines[j-1]) {
	j--
	}
	pre := lines[i:j]
	i = j

	unindent(pre)

	// put those lines in a pre block
	out = append(out, block{opPre, pre})
	lastWasHeading = false
	continue
	}

	if lastWasBlank && !lastWasHeading && i+2 < len(lines) &&
	isBlank(lines[i+1]) && !isBlank(lines[i+2]) && indentLen(lines[i+2]) == 0 {
	// current line is non-blank, surrounded by blank lines
	// and the next non-blank line is not indented: this
	// might be a heading.
	if head := heading(line); head != "" {
	close()
	out = append(out, block{opHead, []string{head}})
	i += 2
	lastWasHeading = true
	continue
	}
	}

	// open paragraph
	lastWasBlank = false
	lastWasHeading = false
	para = append(para, lines[i])
	i++
	}
	close()

	return out
	}

	// ToText prepares comment text for presentation in textual output.
	// It wraps paragraphs of text to width or fewer Unicode code points
	// and then prefixes each line with the indent. In preformatted sections
	// (such as program text), it prefixes each non-blank line with preIndent.
	func ToText(w io.Writer, text string, indent, preIndent string, width int) {
	l := lineWrapper{
	out: w,
	width: width,
	indent: indent,
	}
	for _, b := range blocks(text) {
	switch b.op {
	case opPara:
	// l.write will add leading newline if required
	for _, line := range b.lines {
	line = convertQuotes(line)
	l.write(line)
	}
	l.flush()
	case opHead:
	w.Write(nl)
	for _, line := range b.lines {
	line = convertQuotes(line)
	l.write(line + "\n")
	}
	l.flush()
	case opPre:
	w.Write(nl)
	for _, line := range b.lines {
	if isBlank(line) {
	w.Write([]byte("\n"))
	} else {
	w.Write([]byte(preIndent))
	w.Write([]byte(line))
	}
	}
	}
	}
	}

	type lineWrapper struct {
	out io.Writer
	printed bool
	width int
	indent string
	n int
	pendSpace int
	}

	var nl = []byte("\n")
	var space = []byte(" ")
	var prefix = []byte("// ")

	func (l *lineWrapper) write(text string) {
	if l.n == 0 && l.printed {
	l.out.Write(nl) // blank line before new paragraph
	}
	l.printed = true

	needsPrefix := false
	isComment := strings.HasPrefix(text, "//")
	for _, f := range strings.Fields(text) {
	w := utf8.RuneCountInString(f)
	// wrap if line is too long
	if l.n > 0 && l.n+l.pendSpace+w > l.width {
	l.out.Write(nl)
	l.n = 0
	l.pendSpace = 0
	needsPrefix = isComment
	}
	if l.n == 0 {
	l.out.Write([]byte(l.indent))
	}
	if needsPrefix {
	l.out.Write(prefix)
	needsPrefix = false
	}
	l.out.Write(space[:l.pendSpace])
	l.out.Write([]byte(f))
	l.n += l.pendSpace + w
	l.pendSpace = 1
	}
	}

	func (l *lineWrapper) flush() {
	if l.n == 0 {
	return
	}
	l.out.Write(nl)
	l.pendSpace = 0
	l.n = 0
	}