1 files changed, 169 insertions, 0 deletions
diff --git a/src/go/doc/comment/html.go b/src/go/doc/comment/html.go
new file mode 100644
index 0000000..bc076f6
--- /dev/null
+++ b/src/go/doc/comment/html.go
@@ -0,0 +1,169 @@
+// Copyright 2022 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 comment
+
+import (
+	"bytes"
+	"fmt"
+	"strconv"
+)
+
+// An htmlPrinter holds the state needed for printing a Doc as HTML.
+type htmlPrinter struct {
+	*Printer
+	tight bool
+}
+
+// HTML returns an HTML formatting of the Doc.
+// See the [Printer] documentation for ways to customize the HTML output.
+func (p *Printer) HTML(d *Doc) []byte {
+	hp := &htmlPrinter{Printer: p}
+	var out bytes.Buffer
+	for _, x := range d.Content {
+		hp.block(&out, x)
+	}
+	return out.Bytes()
+}
+
+// block prints the block x to out.
+func (p *htmlPrinter) block(out *bytes.Buffer, x Block) {
+	switch x := x.(type) {
+	default:
+		fmt.Fprintf(out, "?%T", x)
+
+	case *Paragraph:
+		if !p.tight {
+			out.WriteString("<p>")
+		}
+		p.text(out, x.Text)
+		out.WriteString("\n")
+
+	case *Heading:
+		out.WriteString("<h")
+		h := strconv.Itoa(p.headingLevel())
+		out.WriteString(h)
+		if id := p.headingID(x); id != "" {
+			out.WriteString(` id="`)
+			p.escape(out, id)
+			out.WriteString(`"`)
+		}
+		out.WriteString(">")
+		p.text(out, x.Text)
+		out.WriteString("</h")
+		out.WriteString(h)
+		out.WriteString(">\n")
+
+	case *Code:
+		out.WriteString("<pre>")
+		p.escape(out, x.Text)
+		out.WriteString("</pre>\n")
+
+	case *List:
+		kind := "ol>\n"
+		if x.Items[0].Number == "" {
+			kind = "ul>\n"
+		}
+		out.WriteString("<")
+		out.WriteString(kind)
+		next := "1"
+		for _, item := range x.Items {
+			out.WriteString("<li")
+			if n := item.Number; n != "" {
+				if n != next {
+					out.WriteString(` value="`)
+					out.WriteString(n)
+					out.WriteString(`"`)
+					next = n
+				}
+				next = inc(next)
+			}
+			out.WriteString(">")
+			p.tight = !x.BlankBetween()
+			for _, blk := range item.Content {
+				p.block(out, blk)
+			}
+			p.tight = false
+		}
+		out.WriteString("</")
+		out.WriteString(kind)
+	}
+}
+
+// inc increments the decimal string s.
+// For example, inc("1199") == "1200".
+func inc(s string) string {
+	b := []byte(s)
+	for i := len(b) - 1; i >= 0; i-- {
+		if b[i] < '9' {
+			b[i]++
+			return string(b)
+		}
+		b[i] = '0'
+	}
+	return "1" + string(b)
+}
+
+// text prints the text sequence x to out.
+func (p *htmlPrinter) text(out *bytes.Buffer, x []Text) {
+	for _, t := range x {
+		switch t := t.(type) {
+		case Plain:
+			p.escape(out, string(t))
+		case Italic:
+			out.WriteString("<i>")
+			p.escape(out, string(t))
+			out.WriteString("</i>")
+		case *Link:
+			out.WriteString(`<a href="`)
+			p.escape(out, t.URL)
+			out.WriteString(`">`)
+			p.text(out, t.Text)
+			out.WriteString("</a>")
+		case *DocLink:
+			url := p.docLinkURL(t)
+			if url != "" {
+				out.WriteString(`<a href="`)
+				p.escape(out, url)
+				out.WriteString(`">`)
+			}
+			p.text(out, t.Text)
+			if url != "" {
+				out.WriteString("</a>")
+			}
+		}
+	}
+}
+
+// escape prints s to out as plain text,
+// escaping < & " ' and > to avoid being misinterpreted
+// in larger HTML constructs.
+func (p *htmlPrinter) escape(out *bytes.Buffer, s string) {
+	start := 0
+	for i := 0; i < len(s); i++ {
+		switch s[i] {
+		case '<':
+			out.WriteString(s[start:i])
+			out.WriteString("&lt;")
+			start = i + 1
+		case '&':
+			out.WriteString(s[start:i])
+			out.WriteString("&amp;")
+			start = i + 1
+		case '"':
+			out.WriteString(s[start:i])
+			out.WriteString("&quot;")
+			start = i + 1
+		case '\'':
+			out.WriteString(s[start:i])
+			out.WriteString("&apos;")
+			start = i + 1
+		case '>':
+			out.WriteString(s[start:i])
+			out.WriteString("&gt;")
+			start = i + 1
+		}
+	}
+	out.WriteString(s[start:])
+}