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// Copyright 2019 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 source
import (
"bytes"
"io"
"regexp"
"strings"
"unicode"
"unicode/utf8"
)
// CommentToMarkdown converts comment text to formatted markdown.
// 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 line is converted into a markdown line and empty lines are just converted to
// newlines. Heading are prefixed with `### ` to make it a markdown heading.
//
// A span of indented lines retains a 4 space prefix block, with the common indent
// prefix removed unless empty, in which case it will be converted to a newline.
//
// URLs in the comment text are converted into links.
func CommentToMarkdown(text string) string {
buf := &bytes.Buffer{}
commentToMarkdown(buf, text)
return buf.String()
}
var (
mdNewline = []byte("\n")
mdHeader = []byte("### ")
mdIndent = []byte(" ")
mdLinkStart = []byte("[")
mdLinkDiv = []byte("](")
mdLinkEnd = []byte(")")
)
func commentToMarkdown(w io.Writer, text string) {
blocks := blocks(text)
for i, b := range blocks {
switch b.op {
case opPara:
for _, line := range b.lines {
emphasize(w, line, true)
}
case opHead:
// The header block can consist of only one line.
// However, check the number of lines, just in case.
if len(b.lines) == 0 {
// Skip this block.
continue
}
header := b.lines[0]
w.Write(mdHeader)
commentEscape(w, header, true)
// Header doesn't end with \n unlike the lines of other blocks.
w.Write(mdNewline)
case opPre:
for _, line := range b.lines {
if isBlank(line) {
w.Write(mdNewline)
continue
}
w.Write(mdIndent)
w.Write([]byte(line))
}
}
if i < len(blocks)-1 {
w.Write(mdNewline)
}
}
}
const (
ulquo = "“"
urquo = "”"
)
var (
markdownEscape = regexp.MustCompile(`([\\\x60*{}[\]()#+\-.!_>~|"$%&'\/:;<=?@^])`)
unicodeQuoteReplacer = strings.NewReplacer("``", ulquo, "''", urquo)
)
// commentEscape escapes comment text for markdown. If nice is set,
// also turn double ` and ' into “ and ”.
func commentEscape(w io.Writer, text string, nice bool) {
if nice {
text = convertQuotes(text)
}
text = escapeRegex(text)
w.Write([]byte(text))
}
func convertQuotes(text string) string {
return unicodeQuoteReplacer.Replace(text)
}
func escapeRegex(text string) string {
return markdownEscape.ReplaceAllString(text, `\$1`)
}
func emphasize(w io.Writer, line 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)])
}
}
// Following code has been modified from go/doc since words is always
// nil. All html formatting has also been transformed into markdown formatting
// analyze match
url := ""
if m[2] >= 0 {
url = match
}
// write match
if len(url) > 0 {
w.Write(mdLinkStart)
}
commentEscape(w, match, nice)
if len(url) > 0 {
w.Write(mdLinkDiv)
w.Write([]byte(urlReplacer.Replace(url)))
w.Write(mdLinkEnd)
}
// advance
line = line[m[1]:]
}
commentEscape(w, line, nice)
}
// Everything from here on is a copy of go/doc/comment.go
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 = regexp.MustCompile(`(` + urlRx + `)|(` + identRx + `)`)
urlReplacer = strings.NewReplacer(`(`, `\(`, `)`, `\)`)
)
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
}
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
}