Adding upstream version 1.21.8.upstream/1.21.8

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

188 files changed, 14293 insertions, 0 deletions

diff --git a/src/go/doc/Makefile b/src/go/doc/Makefile
new file mode 100644
index 0000000..ca4948f
--- /dev/null
+++ b/src/go/doc/Makefile
@@ -0,0 +1,7 @@
+# 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.
+
+# Script to test heading detection heuristic
+headscan: headscan.go
+	go build headscan.go
diff --git a/src/go/doc/comment.go b/src/go/doc/comment.go
new file mode 100644
index 0000000..4f73664
--- /dev/null
+++ b/src/go/doc/comment.go
@@ -0,0 +1,71 @@
+// 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.
+
+package doc
+
+import (
+	"go/doc/comment"
+	"io"
+)
+
+// ToHTML converts comment text to formatted HTML.
+//
+// Deprecated: ToHTML cannot identify documentation links
+// in the doc comment, because they depend on knowing what
+// package the text came from, which is not included in this API.
+//
+// Given the *[doc.Package] p where text was found,
+// ToHTML(w, text, nil) can be replaced by:
+//
+//	w.Write(p.HTML(text))
+//
+// which is in turn shorthand for:
+//
+//	w.Write(p.Printer().HTML(p.Parser().Parse(text)))
+//
+// If words may be non-nil, the longer replacement is:
+//
+//	parser := p.Parser()
+//	parser.Words = words
+//	w.Write(p.Printer().HTML(parser.Parse(d)))
+func ToHTML(w io.Writer, text string, words map[string]string) {
+	p := new(Package).Parser()
+	p.Words = words
+	d := p.Parse(text)
+	pr := new(comment.Printer)
+	w.Write(pr.HTML(d))
+}
+
+// ToText converts comment text to formatted text.
+//
+// Deprecated: ToText cannot identify documentation links
+// in the doc comment, because they depend on knowing what
+// package the text came from, which is not included in this API.
+//
+// Given the *[doc.Package] p where text was found,
+// ToText(w, text, "", "\t", 80) can be replaced by:
+//
+//	w.Write(p.Text(text))
+//
+// In the general case, ToText(w, text, prefix, codePrefix, width)
+// can be replaced by:
+//
+//	d := p.Parser().Parse(text)
+//	pr := p.Printer()
+//	pr.TextPrefix = prefix
+//	pr.TextCodePrefix = codePrefix
+//	pr.TextWidth = width
+//	w.Write(pr.Text(d))
+//
+// See the documentation for [Package.Text] and [comment.Printer.Text]
+// for more details.
+func ToText(w io.Writer, text string, prefix, codePrefix string, width int) {
+	d := new(Package).Parser().Parse(text)
+	pr := &comment.Printer{
+		TextPrefix:     prefix,
+		TextCodePrefix: codePrefix,
+		TextWidth:      width,
+	}
+	w.Write(pr.Text(d))
+}
diff --git a/src/go/doc/comment/doc.go b/src/go/doc/comment/doc.go
new file mode 100644
index 0000000..45a476a
--- /dev/null
+++ b/src/go/doc/comment/doc.go
@@ -0,0 +1,36 @@
+// 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 implements parsing and reformatting of Go doc comments,
+(documentation comments), which are comments that immediately precede
+a top-level declaration of a package, const, func, type, or var.
+
+Go doc comment syntax is a simplified subset of Markdown that supports
+links, headings, paragraphs, lists (without nesting), and preformatted text blocks.
+The details of the syntax are documented at https://go.dev/doc/comment.
+
+To parse the text associated with a doc comment (after removing comment markers),
+use a [Parser]:
+
+	var p comment.Parser
+	doc := p.Parse(text)
+
+The result is a [*Doc].
+To reformat it as a doc comment, HTML, Markdown, or plain text,
+use a [Printer]:
+
+	var pr comment.Printer
+	os.Stdout.Write(pr.Text(doc))
+
+The [Parser] and [Printer] types are structs whose fields can be
+modified to customize the operations.
+For details, see the documentation for those types.
+
+Use cases that need additional control over reformatting can
+implement their own logic by inspecting the parsed syntax itself.
+See the documentation for [Doc], [Block], [Text] for an overview
+and links to additional types.
+*/
+package comment
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:])
+}
diff --git a/src/go/doc/comment/markdown.go b/src/go/doc/comment/markdown.go
new file mode 100644
index 0000000..d8550f2
--- /dev/null
+++ b/src/go/doc/comment/markdown.go
@@ -0,0 +1,188 @@
+// 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"
+	"strings"
+)
+
+// An mdPrinter holds the state needed for printing a Doc as Markdown.
+type mdPrinter struct {
+	*Printer
+	headingPrefix string
+	raw           bytes.Buffer
+}
+
+// Markdown returns a Markdown formatting of the Doc.
+// See the [Printer] documentation for ways to customize the Markdown output.
+func (p *Printer) Markdown(d *Doc) []byte {
+	mp := &mdPrinter{
+		Printer:       p,
+		headingPrefix: strings.Repeat("#", p.headingLevel()) + " ",
+	}
+
+	var out bytes.Buffer
+	for i, x := range d.Content {
+		if i > 0 {
+			out.WriteByte('\n')
+		}
+		mp.block(&out, x)
+	}
+	return out.Bytes()
+}
+
+// block prints the block x to out.
+func (p *mdPrinter) block(out *bytes.Buffer, x Block) {
+	switch x := x.(type) {
+	default:
+		fmt.Fprintf(out, "?%T", x)
+
+	case *Paragraph:
+		p.text(out, x.Text)
+		out.WriteString("\n")
+
+	case *Heading:
+		out.WriteString(p.headingPrefix)
+		p.text(out, x.Text)
+		if id := p.headingID(x); id != "" {
+			out.WriteString(" {#")
+			out.WriteString(id)
+			out.WriteString("}")
+		}
+		out.WriteString("\n")
+
+	case *Code:
+		md := x.Text
+		for md != "" {
+			var line string
+			line, md, _ = strings.Cut(md, "\n")
+			if line != "" {
+				out.WriteString("\t")
+				out.WriteString(line)
+			}
+			out.WriteString("\n")
+		}
+
+	case *List:
+		loose := x.BlankBetween()
+		for i, item := range x.Items {
+			if i > 0 && loose {
+				out.WriteString("\n")
+			}
+			if n := item.Number; n != "" {
+				out.WriteString(" ")
+				out.WriteString(n)
+				out.WriteString(". ")
+			} else {
+				out.WriteString("  - ") // SP SP - SP
+			}
+			for i, blk := range item.Content {
+				const fourSpace = "    "
+				if i > 0 {
+					out.WriteString("\n" + fourSpace)
+				}
+				p.text(out, blk.(*Paragraph).Text)
+				out.WriteString("\n")
+			}
+		}
+	}
+}
+
+// text prints the text sequence x to out.
+func (p *mdPrinter) text(out *bytes.Buffer, x []Text) {
+	p.raw.Reset()
+	p.rawText(&p.raw, x)
+	line := bytes.TrimSpace(p.raw.Bytes())
+	if len(line) == 0 {
+		return
+	}
+	switch line[0] {
+	case '+', '-', '*', '#':
+		// Escape what would be the start of an unordered list or heading.
+		out.WriteByte('\\')
+	case '0', '1', '2', '3', '4', '5', '6', '7', '8', '9':
+		i := 1
+		for i < len(line) && '0' <= line[i] && line[i] <= '9' {
+			i++
+		}
+		if i < len(line) && (line[i] == '.' || line[i] == ')') {
+			// Escape what would be the start of an ordered list.
+			out.Write(line[:i])
+			out.WriteByte('\\')
+			line = line[i:]
+		}
+	}
+	out.Write(line)
+}
+
+// rawText prints the text sequence x to out,
+// without worrying about escaping characters
+// that have special meaning at the start of a Markdown line.
+func (p *mdPrinter) rawText(out *bytes.Buffer, x []Text) {
+	for _, t := range x {
+		switch t := t.(type) {
+		case Plain:
+			p.escape(out, string(t))
+		case Italic:
+			out.WriteString("*")
+			p.escape(out, string(t))
+			out.WriteString("*")
+		case *Link:
+			out.WriteString("[")
+			p.rawText(out, t.Text)
+			out.WriteString("](")
+			out.WriteString(t.URL)
+			out.WriteString(")")
+		case *DocLink:
+			url := p.docLinkURL(t)
+			if url != "" {
+				out.WriteString("[")
+			}
+			p.rawText(out, t.Text)
+			if url != "" {
+				out.WriteString("](")
+				url = strings.ReplaceAll(url, "(", "%28")
+				url = strings.ReplaceAll(url, ")", "%29")
+				out.WriteString(url)
+				out.WriteString(")")
+			}
+		}
+	}
+}
+
+// escape prints s to out as plain text,
+// escaping special characters to avoid being misinterpreted
+// as Markdown markup sequences.
+func (p *mdPrinter) escape(out *bytes.Buffer, s string) {
+	start := 0
+	for i := 0; i < len(s); i++ {
+		switch s[i] {
+		case '\n':
+			// Turn all \n into spaces, for a few reasons:
+			//   - Avoid introducing paragraph breaks accidentally.
+			//   - Avoid the need to reindent after the newline.
+			//   - Avoid problems with Markdown renderers treating
+			//     every mid-paragraph newline as a <br>.
+			out.WriteString(s[start:i])
+			out.WriteByte(' ')
+			start = i + 1
+			continue
+		case '`', '_', '*', '[', '<', '\\':
+			// Not all of these need to be escaped all the time,
+			// but is valid and easy to do so.
+			// We assume the Markdown is being passed to a
+			// Markdown renderer, not edited by a person,
+			// so it's fine to have escapes that are not strictly
+			// necessary in some cases.
+			out.WriteString(s[start:i])
+			out.WriteByte('\\')
+			out.WriteByte(s[i])
+			start = i + 1
+		}
+	}
+	out.WriteString(s[start:])
+}
diff --git a/src/go/doc/comment/mkstd.sh b/src/go/doc/comment/mkstd.sh
new file mode 100755
index 0000000..c9dee8c
--- /dev/null
+++ b/src/go/doc/comment/mkstd.sh
@@ -0,0 +1,24 @@
+#!/bin/bash
+# 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.
+
+# This could be a good use for embed but go/doc/comment
+# is built into the bootstrap go command, so it can't use embed.
+# Also not using embed lets us emit a string array directly
+# and avoid init-time work.
+
+(
+echo "// 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.
+
+// Code generated by 'go generate' DO NOT EDIT.
+//go:generate ./mkstd.sh
+
+package comment
+
+var stdPkgs = []string{"
+go list std | grep -v / | sort | sed 's/.*/"&",/'
+echo "}"
+) | gofmt >std.go.tmp && mv std.go.tmp std.go
diff --git a/src/go/doc/comment/old_test.go b/src/go/doc/comment/old_test.go
new file mode 100644
index 0000000..944f94d
--- /dev/null
+++ b/src/go/doc/comment/old_test.go
@@ -0,0 +1,80 @@
+// Copyright 2011 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.
+
+// These tests are carried forward from the old go/doc implementation.
+
+package comment
+
+import "testing"
+
+var oldHeadingTests = []struct {
+	line string
+	ok   bool
+}{
+	{"Section", true},
+	{"A typical usage", true},
+	{"ΔΛΞ is Greek", true},
+	{"Foo 42", true},
+	{"", false},
+	{"section", false},
+	{"A typical usage:", false},
+	{"This code:", false},
+	{"δ is Greek", false},
+	{"Foo §", false},
+	{"Fermat's Last Sentence", true},
+	{"Fermat's", true},
+	{"'sX", false},
+	{"Ted 'Too' Bar", false},
+	{"Use n+m", false},
+	{"Scanning:", false},
+	{"N:M", false},
+}
+
+func TestIsOldHeading(t *testing.T) {
+	for _, tt := range oldHeadingTests {
+		if isOldHeading(tt.line, []string{"Text.", "", tt.line, "", "Text."}, 2) != tt.ok {
+			t.Errorf("isOldHeading(%q) = %v, want %v", tt.line, !tt.ok, tt.ok)
+		}
+	}
+}
+
+var autoURLTests = []struct {
+	in, out string
+}{
+	{"", ""},
+	{"http://[::1]:8080/foo.txt", "http://[::1]:8080/foo.txt"},
+	{"https://www.google.com) after", "https://www.google.com"},
+	{"https://www.google.com:30/x/y/z:b::c. After", "https://www.google.com:30/x/y/z:b::c"},
+	{"http://www.google.com/path/:;!-/?query=%34b#093124", "http://www.google.com/path/:;!-/?query=%34b#093124"},
+	{"http://www.google.com/path/:;!-/?query=%34bar#093124", "http://www.google.com/path/:;!-/?query=%34bar#093124"},
+	{"http://www.google.com/index.html! After", "http://www.google.com/index.html"},
+	{"http://www.google.com/", "http://www.google.com/"},
+	{"https://www.google.com/", "https://www.google.com/"},
+	{"http://www.google.com/path.", "http://www.google.com/path"},
+	{"http://en.wikipedia.org/wiki/Camellia_(cipher)", "http://en.wikipedia.org/wiki/Camellia_(cipher)"},
+	{"http://www.google.com/)", "http://www.google.com/"},
+	{"http://gmail.com)", "http://gmail.com"},
+	{"http://gmail.com))", "http://gmail.com"},
+	{"http://gmail.com ((http://gmail.com)) ()", "http://gmail.com"},
+	{"http://example.com/ quux!", "http://example.com/"},
+	{"http://example.com/%2f/ /world.", "http://example.com/%2f/"},
+	{"http: ipsum //host/path", ""},
+	{"javascript://is/not/linked", ""},
+	{"http://foo", "http://foo"},
+	{"https://www.example.com/person/][Person Name]]", "https://www.example.com/person/"},
+	{"http://golang.org/)", "http://golang.org/"},
+	{"http://golang.org/hello())", "http://golang.org/hello()"},
+	{"http://git.qemu.org/?p=qemu.git;a=blob;f=qapi-schema.json;hb=HEAD", "http://git.qemu.org/?p=qemu.git;a=blob;f=qapi-schema.json;hb=HEAD"},
+	{"https://foo.bar/bal/x(])", "https://foo.bar/bal/x"}, // inner ] causes (]) to be cut off from URL
+	{"http://bar(])", "http://bar"},                       // same
+}
+
+func TestAutoURL(t *testing.T) {
+	for _, tt := range autoURLTests {
+		url, ok := autoURL(tt.in)
+		if url != tt.out || ok != (tt.out != "") {
+			t.Errorf("autoURL(%q) = %q, %v, want %q, %v", tt.in, url, ok, tt.out, tt.out != "")
+		}
+	}
+}
diff --git a/src/go/doc/comment/parse.go b/src/go/doc/comment/parse.go
new file mode 100644
index 0000000..62a0f8f
--- /dev/null
+++ b/src/go/doc/comment/parse.go
@@ -0,0 +1,1262 @@
+// 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 (
+	"sort"
+	"strings"
+	"unicode"
+	"unicode/utf8"
+)
+
+// A Doc is a parsed Go doc comment.
+type Doc struct {
+	// Content is the sequence of content blocks in the comment.
+	Content []Block
+
+	// Links is the link definitions in the comment.
+	Links []*LinkDef
+}
+
+// A LinkDef is a single link definition.
+type LinkDef struct {
+	Text string // the link text
+	URL  string // the link URL
+	Used bool   // whether the comment uses the definition
+}
+
+// A Block is block-level content in a doc comment,
+// one of [*Code], [*Heading], [*List], or [*Paragraph].
+type Block interface {
+	block()
+}
+
+// A Heading is a doc comment heading.
+type Heading struct {
+	Text []Text // the heading text
+}
+
+func (*Heading) block() {}
+
+// A List is a numbered or bullet list.
+// Lists are always non-empty: len(Items) > 0.
+// In a numbered list, every Items[i].Number is a non-empty string.
+// In a bullet list, every Items[i].Number is an empty string.
+type List struct {
+	// Items is the list items.
+	Items []*ListItem
+
+	// ForceBlankBefore indicates that the list must be
+	// preceded by a blank line when reformatting the comment,
+	// overriding the usual conditions. See the BlankBefore method.
+	//
+	// The comment parser sets ForceBlankBefore for any list
+	// that is preceded by a blank line, to make sure
+	// the blank line is preserved when printing.
+	ForceBlankBefore bool
+
+	// ForceBlankBetween indicates that list items must be
+	// separated by blank lines when reformatting the comment,
+	// overriding the usual conditions. See the BlankBetween method.
+	//
+	// The comment parser sets ForceBlankBetween for any list
+	// that has a blank line between any two of its items, to make sure
+	// the blank lines are preserved when printing.
+	ForceBlankBetween bool
+}
+
+func (*List) block() {}
+
+// BlankBefore reports whether a reformatting of the comment
+// should include a blank line before the list.
+// The default rule is the same as for [BlankBetween]:
+// if the list item content contains any blank lines
+// (meaning at least one item has multiple paragraphs)
+// then the list itself must be preceded by a blank line.
+// A preceding blank line can be forced by setting [List].ForceBlankBefore.
+func (l *List) BlankBefore() bool {
+	return l.ForceBlankBefore || l.BlankBetween()
+}
+
+// BlankBetween reports whether a reformatting of the comment
+// should include a blank line between each pair of list items.
+// The default rule is that if the list item content contains any blank lines
+// (meaning at least one item has multiple paragraphs)
+// then list items must themselves be separated by blank lines.
+// Blank line separators can be forced by setting [List].ForceBlankBetween.
+func (l *List) BlankBetween() bool {
+	if l.ForceBlankBetween {
+		return true
+	}
+	for _, item := range l.Items {
+		if len(item.Content) != 1 {
+			// Unreachable for parsed comments today,
+			// since the only way to get multiple item.Content
+			// is multiple paragraphs, which must have been
+			// separated by a blank line.
+			return true
+		}
+	}
+	return false
+}
+
+// A ListItem is a single item in a numbered or bullet list.
+type ListItem struct {
+	// Number is a decimal string in a numbered list
+	// or an empty string in a bullet list.
+	Number string // "1", "2", ...; "" for bullet list
+
+	// Content is the list content.
+	// Currently, restrictions in the parser and printer
+	// require every element of Content to be a *Paragraph.
+	Content []Block // Content of this item.
+}
+
+// A Paragraph is a paragraph of text.
+type Paragraph struct {
+	Text []Text
+}
+
+func (*Paragraph) block() {}
+
+// A Code is a preformatted code block.
+type Code struct {
+	// Text is the preformatted text, ending with a newline character.
+	// It may be multiple lines, each of which ends with a newline character.
+	// It is never empty, nor does it start or end with a blank line.
+	Text string
+}
+
+func (*Code) block() {}
+
+// A Text is text-level content in a doc comment,
+// one of [Plain], [Italic], [*Link], or [*DocLink].
+type Text interface {
+	text()
+}
+
+// A Plain is a string rendered as plain text (not italicized).
+type Plain string
+
+func (Plain) text() {}
+
+// An Italic is a string rendered as italicized text.
+type Italic string
+
+func (Italic) text() {}
+
+// A Link is a link to a specific URL.
+type Link struct {
+	Auto bool   // is this an automatic (implicit) link of a literal URL?
+	Text []Text // text of link
+	URL  string // target URL of link
+}
+
+func (*Link) text() {}
+
+// A DocLink is a link to documentation for a Go package or symbol.
+type DocLink struct {
+	Text []Text // text of link
+
+	// ImportPath, Recv, and Name identify the Go package or symbol
+	// that is the link target. The potential combinations of
+	// non-empty fields are:
+	//  - ImportPath: a link to another package
+	//  - ImportPath, Name: a link to a const, func, type, or var in another package
+	//  - ImportPath, Recv, Name: a link to a method in another package
+	//  - Name: a link to a const, func, type, or var in this package
+	//  - Recv, Name: a link to a method in this package
+	ImportPath string // import path
+	Recv       string // receiver type, without any pointer star, for methods
+	Name       string // const, func, type, var, or method name
+}
+
+func (*DocLink) text() {}
+
+// A Parser is a doc comment parser.
+// The fields in the struct can be filled in before calling Parse
+// in order to customize the details of the parsing process.
+type Parser struct {
+	// Words is a map of Go identifier words that
+	// should be italicized and potentially linked.
+	// If Words[w] is the empty string, then the word w
+	// is only italicized. Otherwise it is linked, using
+	// Words[w] as the link target.
+	// Words corresponds to the [go/doc.ToHTML] words parameter.
+	Words map[string]string
+
+	// LookupPackage resolves a package name to an import path.
+	//
+	// If LookupPackage(name) returns ok == true, then [name]
+	// (or [name.Sym] or [name.Sym.Method])
+	// is considered a documentation link to importPath's package docs.
+	// It is valid to return "", true, in which case name is considered
+	// to refer to the current package.
+	//
+	// If LookupPackage(name) returns ok == false,
+	// then [name] (or [name.Sym] or [name.Sym.Method])
+	// will not be considered a documentation link,
+	// except in the case where name is the full (but single-element) import path
+	// of a package in the standard library, such as in [math] or [io.Reader].
+	// LookupPackage is still called for such names,
+	// in order to permit references to imports of other packages
+	// with the same package names.
+	//
+	// Setting LookupPackage to nil is equivalent to setting it to
+	// a function that always returns "", false.
+	LookupPackage func(name string) (importPath string, ok bool)
+
+	// LookupSym reports whether a symbol name or method name
+	// exists in the current package.
+	//
+	// If LookupSym("", "Name") returns true, then [Name]
+	// is considered a documentation link for a const, func, type, or var.
+	//
+	// Similarly, if LookupSym("Recv", "Name") returns true,
+	// then [Recv.Name] is considered a documentation link for
+	// type Recv's method Name.
+	//
+	// Setting LookupSym to nil is equivalent to setting it to a function
+	// that always returns false.
+	LookupSym func(recv, name string) (ok bool)
+}
+
+// parseDoc is parsing state for a single doc comment.
+type parseDoc struct {
+	*Parser
+	*Doc
+	links     map[string]*LinkDef
+	lines     []string
+	lookupSym func(recv, name string) bool
+}
+
+// lookupPkg is called to look up the pkg in [pkg], [pkg.Name], and [pkg.Name.Recv].
+// If pkg has a slash, it is assumed to be the full import path and is returned with ok = true.
+//
+// Otherwise, pkg is probably a simple package name like "rand" (not "crypto/rand" or "math/rand").
+// d.LookupPackage provides a way for the caller to allow resolving such names with reference
+// to the imports in the surrounding package.
+//
+// There is one collision between these two cases: single-element standard library names
+// like "math" are full import paths but don't contain slashes. We let d.LookupPackage have
+// the first chance to resolve it, in case there's a different package imported as math,
+// and otherwise we refer to a built-in list of single-element standard library package names.
+func (d *parseDoc) lookupPkg(pkg string) (importPath string, ok bool) {
+	if strings.Contains(pkg, "/") { // assume a full import path
+		if validImportPath(pkg) {
+			return pkg, true
+		}
+		return "", false
+	}
+	if d.LookupPackage != nil {
+		// Give LookupPackage a chance.
+		if path, ok := d.LookupPackage(pkg); ok {
+			return path, true
+		}
+	}
+	return DefaultLookupPackage(pkg)
+}
+
+func isStdPkg(path string) bool {
+	// TODO(rsc): Use sort.Find once we don't have to worry about
+	// copying this code into older Go environments.
+	i := sort.Search(len(stdPkgs), func(i int) bool { return stdPkgs[i] >= path })
+	return i < len(stdPkgs) && stdPkgs[i] == path
+}
+
+// DefaultLookupPackage is the default package lookup
+// function, used when [Parser].LookupPackage is nil.
+// It recognizes names of the packages from the standard
+// library with single-element import paths, such as math,
+// which would otherwise be impossible to name.
+//
+// Note that the go/doc package provides a more sophisticated
+// lookup based on the imports used in the current package.
+func DefaultLookupPackage(name string) (importPath string, ok bool) {
+	if isStdPkg(name) {
+		return name, true
+	}
+	return "", false
+}
+
+// Parse parses the doc comment text and returns the *Doc form.
+// Comment markers (/* // and */) in the text must have already been removed.
+func (p *Parser) Parse(text string) *Doc {
+	lines := unindent(strings.Split(text, "\n"))
+	d := &parseDoc{
+		Parser:    p,
+		Doc:       new(Doc),
+		links:     make(map[string]*LinkDef),
+		lines:     lines,
+		lookupSym: func(recv, name string) bool { return false },
+	}
+	if p.LookupSym != nil {
+		d.lookupSym = p.LookupSym
+	}
+
+	// First pass: break into block structure and collect known links.
+	// The text is all recorded as Plain for now.
+	var prev span
+	for _, s := range parseSpans(lines) {
+		var b Block
+		switch s.kind {
+		default:
+			panic("go/doc/comment: internal error: unknown span kind")
+		case spanList:
+			b = d.list(lines[s.start:s.end], prev.end < s.start)
+		case spanCode:
+			b = d.code(lines[s.start:s.end])
+		case spanOldHeading:
+			b = d.oldHeading(lines[s.start])
+		case spanHeading:
+			b = d.heading(lines[s.start])
+		case spanPara:
+			b = d.paragraph(lines[s.start:s.end])
+		}
+		if b != nil {
+			d.Content = append(d.Content, b)
+		}
+		prev = s
+	}
+
+	// Second pass: interpret all the Plain text now that we know the links.
+	for _, b := range d.Content {
+		switch b := b.(type) {
+		case *Paragraph:
+			b.Text = d.parseLinkedText(string(b.Text[0].(Plain)))
+		case *List:
+			for _, i := range b.Items {
+				for _, c := range i.Content {
+					p := c.(*Paragraph)
+					p.Text = d.parseLinkedText(string(p.Text[0].(Plain)))
+				}
+			}
+		}
+	}
+
+	return d.Doc
+}
+
+// A span represents a single span of comment lines (lines[start:end])
+// of an identified kind (code, heading, paragraph, and so on).
+type span struct {
+	start int
+	end   int
+	kind  spanKind
+}
+
+// A spanKind describes the kind of span.
+type spanKind int
+
+const (
+	_ spanKind = iota
+	spanCode
+	spanHeading
+	spanList
+	spanOldHeading
+	spanPara
+)
+
+func parseSpans(lines []string) []span {
+	var spans []span
+
+	// The loop may process a line twice: once as unindented
+	// and again forced indented. So the maximum expected
+	// number of iterations is 2*len(lines). The repeating logic
+	// can be subtle, though, and to protect against introduction
+	// of infinite loops in future changes, we watch to see that
+	// we are not looping too much. A panic is better than a
+	// quiet infinite loop.
+	watchdog := 2 * len(lines)
+
+	i := 0
+	forceIndent := 0
+Spans:
+	for {
+		// Skip blank lines.
+		for i < len(lines) && lines[i] == "" {
+			i++
+		}
+		if i >= len(lines) {
+			break
+		}
+		if watchdog--; watchdog < 0 {
+			panic("go/doc/comment: internal error: not making progress")
+		}
+
+		var kind spanKind
+		start := i
+		end := i
+		if i < forceIndent || indented(lines[i]) {
+			// Indented (or force indented).
+			// Ends before next unindented. (Blank lines are OK.)
+			// If this is an unindented list that we are heuristically treating as indented,
+			// then accept unindented list item lines up to the first blank lines.
+			// The heuristic is disabled at blank lines to contain its effect
+			// to non-gofmt'ed sections of the comment.
+			unindentedListOK := isList(lines[i]) && i < forceIndent
+			i++
+			for i < len(lines) && (lines[i] == "" || i < forceIndent || indented(lines[i]) || (unindentedListOK && isList(lines[i]))) {
+				if lines[i] == "" {
+					unindentedListOK = false
+				}
+				i++
+			}
+
+			// Drop trailing blank lines.
+			end = i
+			for end > start && lines[end-1] == "" {
+				end--
+			}
+
+			// If indented lines are followed (without a blank line)
+			// by an unindented line ending in a brace,
+			// take that one line too. This fixes the common mistake
+			// of pasting in something like
+			//
+			// func main() {
+			//	fmt.Println("hello, world")
+			// }
+			//
+			// and forgetting to indent it.
+			// The heuristic will never trigger on a gofmt'ed comment,
+			// because any gofmt'ed code block or list would be
+			// followed by a blank line or end of comment.
+			if end < len(lines) && strings.HasPrefix(lines[end], "}") {
+				end++
+			}
+
+			if isList(lines[start]) {
+				kind = spanList
+			} else {
+				kind = spanCode
+			}
+		} else {
+			// Unindented. Ends at next blank or indented line.
+			i++
+			for i < len(lines) && lines[i] != "" && !indented(lines[i]) {
+				i++
+			}
+			end = i
+
+			// If unindented lines are followed (without a blank line)
+			// by an indented line that would start a code block,
+			// check whether the final unindented lines
+			// should be left for the indented section.
+			// This can happen for the common mistakes of
+			// unindented code or unindented lists.
+			// The heuristic will never trigger on a gofmt'ed comment,
+			// because any gofmt'ed code block would have a blank line
+			// preceding it after the unindented lines.
+			if i < len(lines) && lines[i] != "" && !isList(lines[i]) {
+				switch {
+				case isList(lines[i-1]):
+					// If the final unindented line looks like a list item,
+					// this may be the first indented line wrap of
+					// a mistakenly unindented list.
+					// Leave all the unindented list items.
+					forceIndent = end
+					end--
+					for end > start && isList(lines[end-1]) {
+						end--
+					}
+
+				case strings.HasSuffix(lines[i-1], "{") || strings.HasSuffix(lines[i-1], `\`):
+					// If the final unindented line ended in { or \
+					// it is probably the start of a misindented code block.
+					// Give the user a single line fix.
+					// Often that's enough; if not, the user can fix the others themselves.
+					forceIndent = end
+					end--
+				}
+
+				if start == end && forceIndent > start {
+					i = start
+					continue Spans
+				}
+			}
+
+			// Span is either paragraph or heading.
+			if end-start == 1 && isHeading(lines[start]) {
+				kind = spanHeading
+			} else if end-start == 1 && isOldHeading(lines[start], lines, start) {
+				kind = spanOldHeading
+			} else {
+				kind = spanPara
+			}
+		}
+
+		spans = append(spans, span{start, end, kind})
+		i = end
+	}
+
+	return spans
+}
+
+// indented reports whether line is indented
+// (starts with a leading space or tab).
+func indented(line string) bool {
+	return line != "" && (line[0] == ' ' || line[0] == '\t')
+}
+
+// unindent removes any common space/tab prefix
+// from each line in lines, returning a copy of lines in which
+// those prefixes have been trimmed from each line.
+// It also replaces any lines containing only spaces with blank lines (empty strings).
+func unindent(lines []string) []string {
+	// Trim leading and trailing blank lines.
+	for len(lines) > 0 && isBlank(lines[0]) {
+		lines = lines[1:]
+	}
+	for len(lines) > 0 && isBlank(lines[len(lines)-1]) {
+		lines = lines[:len(lines)-1]
+	}
+	if len(lines) == 0 {
+		return nil
+	}
+
+	// Compute and remove common indentation.
+	prefix := leadingSpace(lines[0])
+	for _, line := range lines[1:] {
+		if !isBlank(line) {
+			prefix = commonPrefix(prefix, leadingSpace(line))
+		}
+	}
+
+	out := make([]string, len(lines))
+	for i, line := range lines {
+		line = strings.TrimPrefix(line, prefix)
+		if strings.TrimSpace(line) == "" {
+			line = ""
+		}
+		out[i] = line
+	}
+	for len(out) > 0 && out[0] == "" {
+		out = out[1:]
+	}
+	for len(out) > 0 && out[len(out)-1] == "" {
+		out = out[:len(out)-1]
+	}
+	return out
+}
+
+// isBlank reports whether s is a blank line.
+func isBlank(s string) bool {
+	return len(s) == 0 || (len(s) == 1 && s[0] == '\n')
+}
+
+// commonPrefix returns the longest common prefix of a and b.
+func commonPrefix(a, b string) string {
+	i := 0
+	for i < len(a) && i < len(b) && a[i] == b[i] {
+		i++
+	}
+	return a[0:i]
+}
+
+// leadingSpace returns the longest prefix of s consisting of spaces and tabs.
+func leadingSpace(s string) string {
+	i := 0
+	for i < len(s) && (s[i] == ' ' || s[i] == '\t') {
+		i++
+	}
+	return s[:i]
+}
+
+// isOldHeading reports whether line is an old-style section heading.
+// line is all[off].
+func isOldHeading(line string, all []string, off int) bool {
+	if off <= 0 || all[off-1] != "" || off+2 >= len(all) || all[off+1] != "" || leadingSpace(all[off+2]) != "" {
+		return false
+	}
+
+	line = strings.TrimSpace(line)
+
+	// a heading must start with an uppercase letter
+	r, _ := utf8.DecodeRuneInString(line)
+	if !unicode.IsLetter(r) || !unicode.IsUpper(r) {
+		return false
+	}
+
+	// it must end in a letter or digit:
+	r, _ = utf8.DecodeLastRuneInString(line)
+	if !unicode.IsLetter(r) && !unicode.IsDigit(r) {
+		return false
+	}
+
+	// exclude lines with illegal characters. we allow "(),"
+	if strings.ContainsAny(line, ";:!?+*/=[]{}_^°&§~%#@<\">\\") {
+		return false
+	}
+
+	// allow "'" for possessive "'s" only
+	for b := line; ; {
+		var ok bool
+		if _, b, ok = strings.Cut(b, "'"); !ok {
+			break
+		}
+		if b != "s" && !strings.HasPrefix(b, "s ") {
+			return false // ' not followed by s and then end-of-word
+		}
+	}
+
+	// allow "." when followed by non-space
+	for b := line; ; {
+		var ok bool
+		if _, b, ok = strings.Cut(b, "."); !ok {
+			break
+		}
+		if b == "" || strings.HasPrefix(b, " ") {
+			return false // not followed by non-space
+		}
+	}
+
+	return true
+}
+
+// oldHeading returns the *Heading for the given old-style section heading line.
+func (d *parseDoc) oldHeading(line string) Block {
+	return &Heading{Text: []Text{Plain(strings.TrimSpace(line))}}
+}
+
+// isHeading reports whether line is a new-style section heading.
+func isHeading(line string) bool {
+	return len(line) >= 2 &&
+		line[0] == '#' &&
+		(line[1] == ' ' || line[1] == '\t') &&
+		strings.TrimSpace(line) != "#"
+}
+
+// heading returns the *Heading for the given new-style section heading line.
+func (d *parseDoc) heading(line string) Block {
+	return &Heading{Text: []Text{Plain(strings.TrimSpace(line[1:]))}}
+}
+
+// code returns a code block built from the lines.
+func (d *parseDoc) code(lines []string) *Code {
+	body := unindent(lines)
+	body = append(body, "") // to get final \n from Join
+	return &Code{Text: strings.Join(body, "\n")}
+}
+
+// paragraph returns a paragraph block built from the lines.
+// If the lines are link definitions, paragraph adds them to d and returns nil.
+func (d *parseDoc) paragraph(lines []string) Block {
+	// Is this a block of known links? Handle.
+	var defs []*LinkDef
+	for _, line := range lines {
+		def, ok := parseLink(line)
+		if !ok {
+			goto NoDefs
+		}
+		defs = append(defs, def)
+	}
+	for _, def := range defs {
+		d.Links = append(d.Links, def)
+		if d.links[def.Text] == nil {
+			d.links[def.Text] = def
+		}
+	}
+	return nil
+NoDefs:
+
+	return &Paragraph{Text: []Text{Plain(strings.Join(lines, "\n"))}}
+}
+
+// parseLink parses a single link definition line:
+//
+//	[text]: url
+//
+// It returns the link definition and whether the line was well formed.
+func parseLink(line string) (*LinkDef, bool) {
+	if line == "" || line[0] != '[' {
+		return nil, false
+	}
+	i := strings.Index(line, "]:")
+	if i < 0 || i+3 >= len(line) || (line[i+2] != ' ' && line[i+2] != '\t') {
+		return nil, false
+	}
+
+	text := line[1:i]
+	url := strings.TrimSpace(line[i+3:])
+	j := strings.Index(url, "://")
+	if j < 0 || !isScheme(url[:j]) {
+		return nil, false
+	}
+
+	// Line has right form and has valid scheme://.
+	// That's good enough for us - we are not as picky
+	// about the characters beyond the :// as we are
+	// when extracting inline URLs from text.
+	return &LinkDef{Text: text, URL: url}, true
+}
+
+// list returns a list built from the indented lines,
+// using forceBlankBefore as the value of the List's ForceBlankBefore field.
+func (d *parseDoc) list(lines []string, forceBlankBefore bool) *List {
+	num, _, _ := listMarker(lines[0])
+	var (
+		list *List = &List{ForceBlankBefore: forceBlankBefore}
+		item *ListItem
+		text []string
+	)
+	flush := func() {
+		if item != nil {
+			if para := d.paragraph(text); para != nil {
+				item.Content = append(item.Content, para)
+			}
+		}
+		text = nil
+	}
+
+	for _, line := range lines {
+		if n, after, ok := listMarker(line); ok && (n != "") == (num != "") {
+			// start new list item
+			flush()
+
+			item = &ListItem{Number: n}
+			list.Items = append(list.Items, item)
+			line = after
+		}
+		line = strings.TrimSpace(line)
+		if line == "" {
+			list.ForceBlankBetween = true
+			flush()
+			continue
+		}
+		text = append(text, strings.TrimSpace(line))
+	}
+	flush()
+	return list
+}
+
+// listMarker parses the line as beginning with a list marker.
+// If it can do that, it returns the numeric marker ("" for a bullet list),
+// the rest of the line, and ok == true.
+// Otherwise, it returns "", "", false.
+func listMarker(line string) (num, rest string, ok bool) {
+	line = strings.TrimSpace(line)
+	if line == "" {
+		return "", "", false
+	}
+
+	// Can we find a marker?
+	if r, n := utf8.DecodeRuneInString(line); r == '•' || r == '*' || r == '+' || r == '-' {
+		num, rest = "", line[n:]
+	} else if '0' <= line[0] && line[0] <= '9' {
+		n := 1
+		for n < len(line) && '0' <= line[n] && line[n] <= '9' {
+			n++
+		}
+		if n >= len(line) || (line[n] != '.' && line[n] != ')') {
+			return "", "", false
+		}
+		num, rest = line[:n], line[n+1:]
+	} else {
+		return "", "", false
+	}
+
+	if !indented(rest) || strings.TrimSpace(rest) == "" {
+		return "", "", false
+	}
+
+	return num, rest, true
+}
+
+// isList reports whether the line is the first line of a list,
+// meaning starts with a list marker after any indentation.
+// (The caller is responsible for checking the line is indented, as appropriate.)
+func isList(line string) bool {
+	_, _, ok := listMarker(line)
+	return ok
+}
+
+// parseLinkedText parses text that is allowed to contain explicit links,
+// such as [math.Sin] or [Go home page], into a slice of Text items.
+//
+// A “pkg” is only assumed to be a full import path if it starts with
+// a domain name (a path element with a dot) or is one of the packages
+// from the standard library (“[os]”, “[encoding/json]”, and so on).
+// To avoid problems with maps, generics, and array types, doc links
+// must be both preceded and followed by punctuation, spaces, tabs,
+// or the start or end of a line. An example problem would be treating
+// map[ast.Expr]TypeAndValue as containing a link.
+func (d *parseDoc) parseLinkedText(text string) []Text {
+	var out []Text
+	wrote := 0
+	flush := func(i int) {
+		if wrote < i {
+			out = d.parseText(out, text[wrote:i], true)
+			wrote = i
+		}
+	}
+
+	start := -1
+	var buf []byte
+	for i := 0; i < len(text); i++ {
+		c := text[i]
+		if c == '\n' || c == '\t' {
+			c = ' '
+		}
+		switch c {
+		case '[':
+			start = i
+		case ']':
+			if start >= 0 {
+				if def, ok := d.links[string(buf)]; ok {
+					def.Used = true
+					flush(start)
+					out = append(out, &Link{
+						Text: d.parseText(nil, text[start+1:i], false),
+						URL:  def.URL,
+					})
+					wrote = i + 1
+				} else if link, ok := d.docLink(text[start+1:i], text[:start], text[i+1:]); ok {
+					flush(start)
+					link.Text = d.parseText(nil, text[start+1:i], false)
+					out = append(out, link)
+					wrote = i + 1
+				}
+			}
+			start = -1
+			buf = buf[:0]
+		}
+		if start >= 0 && i != start {
+			buf = append(buf, c)
+		}
+	}
+
+	flush(len(text))
+	return out
+}
+
+// docLink parses text, which was found inside [ ] brackets,
+// as a doc link if possible, returning the DocLink and ok == true
+// or else nil, false.
+// The before and after strings are the text before the [ and after the ]
+// on the same line. Doc links must be preceded and followed by
+// punctuation, spaces, tabs, or the start or end of a line.
+func (d *parseDoc) docLink(text, before, after string) (link *DocLink, ok bool) {
+	if before != "" {
+		r, _ := utf8.DecodeLastRuneInString(before)
+		if !unicode.IsPunct(r) && r != ' ' && r != '\t' && r != '\n' {
+			return nil, false
+		}
+	}
+	if after != "" {
+		r, _ := utf8.DecodeRuneInString(after)
+		if !unicode.IsPunct(r) && r != ' ' && r != '\t' && r != '\n' {
+			return nil, false
+		}
+	}
+	text = strings.TrimPrefix(text, "*")
+	pkg, name, ok := splitDocName(text)
+	var recv string
+	if ok {
+		pkg, recv, _ = splitDocName(pkg)
+	}
+	if pkg != "" {
+		if pkg, ok = d.lookupPkg(pkg); !ok {
+			return nil, false
+		}
+	} else {
+		if ok = d.lookupSym(recv, name); !ok {
+			return nil, false
+		}
+	}
+	link = &DocLink{
+		ImportPath: pkg,
+		Recv:       recv,
+		Name:       name,
+	}
+	return link, true
+}
+
+// If text is of the form before.Name, where Name is a capitalized Go identifier,
+// then splitDocName returns before, name, true.
+// Otherwise it returns text, "", false.
+func splitDocName(text string) (before, name string, foundDot bool) {
+	i := strings.LastIndex(text, ".")
+	name = text[i+1:]
+	if !isName(name) {
+		return text, "", false
+	}
+	if i >= 0 {
+		before = text[:i]
+	}
+	return before, name, true
+}
+
+// parseText parses s as text and returns the result of appending
+// those parsed Text elements to out.
+// parseText does not handle explicit links like [math.Sin] or [Go home page]:
+// those are handled by parseLinkedText.
+// If autoLink is true, then parseText recognizes URLs and words from d.Words
+// and converts those to links as appropriate.
+func (d *parseDoc) parseText(out []Text, s string, autoLink bool) []Text {
+	var w strings.Builder
+	wrote := 0
+	writeUntil := func(i int) {
+		w.WriteString(s[wrote:i])
+		wrote = i
+	}
+	flush := func(i int) {
+		writeUntil(i)
+		if w.Len() > 0 {
+			out = append(out, Plain(w.String()))
+			w.Reset()
+		}
+	}
+	for i := 0; i < len(s); {
+		t := s[i:]
+		if autoLink {
+			if url, ok := autoURL(t); ok {
+				flush(i)
+				// Note: The old comment parser would look up the URL in words
+				// and replace the target with words[URL] if it was non-empty.
+				// That would allow creating links that display as one URL but
+				// when clicked go to a different URL. Not sure what the point
+				// of that is, so we're not doing that lookup here.
+				out = append(out, &Link{Auto: true, Text: []Text{Plain(url)}, URL: url})
+				i += len(url)
+				wrote = i
+				continue
+			}
+			if id, ok := ident(t); ok {
+				url, italics := d.Words[id]
+				if !italics {
+					i += len(id)
+					continue
+				}
+				flush(i)
+				if url == "" {
+					out = append(out, Italic(id))
+				} else {
+					out = append(out, &Link{Auto: true, Text: []Text{Italic(id)}, URL: url})
+				}
+				i += len(id)
+				wrote = i
+				continue
+			}
+		}
+		switch {
+		case strings.HasPrefix(t, "``"):
+			if len(t) >= 3 && t[2] == '`' {
+				// Do not convert `` inside ```, in case people are mistakenly writing Markdown.
+				i += 3
+				for i < len(t) && t[i] == '`' {
+					i++
+				}
+				break
+			}
+			writeUntil(i)
+			w.WriteRune('“')
+			i += 2
+			wrote = i
+		case strings.HasPrefix(t, "''"):
+			writeUntil(i)
+			w.WriteRune('”')
+			i += 2
+			wrote = i
+		default:
+			i++
+		}
+	}
+	flush(len(s))
+	return out
+}
+
+// autoURL checks whether s begins with a URL that should be hyperlinked.
+// If so, it returns the URL, which is a prefix of s, and ok == true.
+// Otherwise it returns "", false.
+// The caller should skip over the first len(url) bytes of s
+// before further processing.
+func autoURL(s string) (url string, ok bool) {
+	// Find the ://. Fast path to pick off non-URL,
+	// since we call this at every position in the string.
+	// The shortest possible URL is ftp://x, 7 bytes.
+	var i int
+	switch {
+	case len(s) < 7:
+		return "", false
+	case s[3] == ':':
+		i = 3
+	case s[4] == ':':
+		i = 4
+	case s[5] == ':':
+		i = 5
+	case s[6] == ':':
+		i = 6
+	default:
+		return "", false
+	}
+	if i+3 > len(s) || s[i:i+3] != "://" {
+		return "", false
+	}
+
+	// Check valid scheme.
+	if !isScheme(s[:i]) {
+		return "", false
+	}
+
+	// Scan host part. Must have at least one byte,
+	// and must start and end in non-punctuation.
+	i += 3
+	if i >= len(s) || !isHost(s[i]) || isPunct(s[i]) {
+		return "", false
+	}
+	i++
+	end := i
+	for i < len(s) && isHost(s[i]) {
+		if !isPunct(s[i]) {
+			end = i + 1
+		}
+		i++
+	}
+	i = end
+
+	// At this point we are definitely returning a URL (scheme://host).
+	// We just have to find the longest path we can add to it.
+	// Heuristics abound.
+	// We allow parens, braces, and brackets,
+	// but only if they match (#5043, #22285).
+	// We allow .,:;?! in the path but not at the end,
+	// to avoid end-of-sentence punctuation (#18139, #16565).
+	stk := []byte{}
+	end = i
+Path:
+	for ; i < len(s); i++ {
+		if isPunct(s[i]) {
+			continue
+		}
+		if !isPath(s[i]) {
+			break
+		}
+		switch s[i] {
+		case '(':
+			stk = append(stk, ')')
+		case '{':
+			stk = append(stk, '}')
+		case '[':
+			stk = append(stk, ']')
+		case ')', '}', ']':
+			if len(stk) == 0 || stk[len(stk)-1] != s[i] {
+				break Path
+			}
+			stk = stk[:len(stk)-1]
+		}
+		if len(stk) == 0 {
+			end = i + 1
+		}
+	}
+
+	return s[:end], true
+}
+
+// isScheme reports whether s is a recognized URL scheme.
+// Note that if strings of new length (beyond 3-7)
+// are added here, the fast path at the top of autoURL will need updating.
+func isScheme(s string) bool {
+	switch s {
+	case "file",
+		"ftp",
+		"gopher",
+		"http",
+		"https",
+		"mailto",
+		"nntp":
+		return true
+	}
+	return false
+}
+
+// isHost reports whether c is a byte that can appear in a URL host,
+// like www.example.com or user@[::1]:8080
+func isHost(c byte) bool {
+	// mask is a 128-bit bitmap with 1s for allowed bytes,
+	// so that the byte c can be tested with a shift and an and.
+	// If c > 128, then 1<<c and 1<<(c-64) will both be zero,
+	// and this function will return false.
+	const mask = 0 |
+		(1<<26-1)<<'A' |
+		(1<<26-1)<<'a' |
+		(1<<10-1)<<'0' |
+		1<<'_' |
+		1<<'@' |
+		1<<'-' |
+		1<<'.' |
+		1<<'[' |
+		1<<']' |
+		1<<':'
+
+	return ((uint64(1)<<c)&(mask&(1<<64-1)) |
+		(uint64(1)<<(c-64))&(mask>>64)) != 0
+}
+
+// isPunct reports whether c is a punctuation byte that can appear
+// inside a path but not at the end.
+func isPunct(c byte) bool {
+	// mask is a 128-bit bitmap with 1s for allowed bytes,
+	// so that the byte c can be tested with a shift and an and.
+	// If c > 128, then 1<<c and 1<<(c-64) will both be zero,
+	// and this function will return false.
+	const mask = 0 |
+		1<<'.' |
+		1<<',' |
+		1<<':' |
+		1<<';' |
+		1<<'?' |
+		1<<'!'
+
+	return ((uint64(1)<<c)&(mask&(1<<64-1)) |
+		(uint64(1)<<(c-64))&(mask>>64)) != 0
+}
+
+// isPath reports whether c is a (non-punctuation) path byte.
+func isPath(c byte) bool {
+	// mask is a 128-bit bitmap with 1s for allowed bytes,
+	// so that the byte c can be tested with a shift and an and.
+	// If c > 128, then 1<<c and 1<<(c-64) will both be zero,
+	// and this function will return false.
+	const mask = 0 |
+		(1<<26-1)<<'A' |
+		(1<<26-1)<<'a' |
+		(1<<10-1)<<'0' |
+		1<<'$' |
+		1<<'\'' |
+		1<<'(' |
+		1<<')' |
+		1<<'*' |
+		1<<'+' |
+		1<<'&' |
+		1<<'#' |
+		1<<'=' |
+		1<<'@' |
+		1<<'~' |
+		1<<'_' |
+		1<<'/' |
+		1<<'-' |
+		1<<'[' |
+		1<<']' |
+		1<<'{' |
+		1<<'}' |
+		1<<'%'
+
+	return ((uint64(1)<<c)&(mask&(1<<64-1)) |
+		(uint64(1)<<(c-64))&(mask>>64)) != 0
+}
+
+// isName reports whether s is a capitalized Go identifier (like Name).
+func isName(s string) bool {
+	t, ok := ident(s)
+	if !ok || t != s {
+		return false
+	}
+	r, _ := utf8.DecodeRuneInString(s)
+	return unicode.IsUpper(r)
+}
+
+// ident checks whether s begins with a Go identifier.
+// If so, it returns the identifier, which is a prefix of s, and ok == true.
+// Otherwise it returns "", false.
+// The caller should skip over the first len(id) bytes of s
+// before further processing.
+func ident(s string) (id string, ok bool) {
+	// Scan [\pL_][\pL_0-9]*
+	n := 0
+	for n < len(s) {
+		if c := s[n]; c < utf8.RuneSelf {
+			if isIdentASCII(c) && (n > 0 || c < '0' || c > '9') {
+				n++
+				continue
+			}
+			break
+		}
+		r, nr := utf8.DecodeRuneInString(s[n:])
+		if unicode.IsLetter(r) {
+			n += nr
+			continue
+		}
+		break
+	}
+	return s[:n], n > 0
+}
+
+// isIdentASCII reports whether c is an ASCII identifier byte.
+func isIdentASCII(c byte) bool {
+	// mask is a 128-bit bitmap with 1s for allowed bytes,
+	// so that the byte c can be tested with a shift and an and.
+	// If c > 128, then 1<<c and 1<<(c-64) will both be zero,
+	// and this function will return false.
+	const mask = 0 |
+		(1<<26-1)<<'A' |
+		(1<<26-1)<<'a' |
+		(1<<10-1)<<'0' |
+		1<<'_'
+
+	return ((uint64(1)<<c)&(mask&(1<<64-1)) |
+		(uint64(1)<<(c-64))&(mask>>64)) != 0
+}
+
+// validImportPath reports whether path is a valid import path.
+// It is a lightly edited copy of golang.org/x/mod/module.CheckImportPath.
+func validImportPath(path string) bool {
+	if !utf8.ValidString(path) {
+		return false
+	}
+	if path == "" {
+		return false
+	}
+	if path[0] == '-' {
+		return false
+	}
+	if strings.Contains(path, "//") {
+		return false
+	}
+	if path[len(path)-1] == '/' {
+		return false
+	}
+	elemStart := 0
+	for i, r := range path {
+		if r == '/' {
+			if !validImportPathElem(path[elemStart:i]) {
+				return false
+			}
+			elemStart = i + 1
+		}
+	}
+	return validImportPathElem(path[elemStart:])
+}
+
+func validImportPathElem(elem string) bool {
+	if elem == "" || elem[0] == '.' || elem[len(elem)-1] == '.' {
+		return false
+	}
+	for i := 0; i < len(elem); i++ {
+		if !importPathOK(elem[i]) {
+			return false
+		}
+	}
+	return true
+}
+
+func importPathOK(c byte) bool {
+	// mask is a 128-bit bitmap with 1s for allowed bytes,
+	// so that the byte c can be tested with a shift and an and.
+	// If c > 128, then 1<<c and 1<<(c-64) will both be zero,
+	// and this function will return false.
+	const mask = 0 |
+		(1<<26-1)<<'A' |
+		(1<<26-1)<<'a' |
+		(1<<10-1)<<'0' |
+		1<<'-' |
+		1<<'.' |
+		1<<'~' |
+		1<<'_' |
+		1<<'+'
+
+	return ((uint64(1)<<c)&(mask&(1<<64-1)) |
+		(uint64(1)<<(c-64))&(mask>>64)) != 0
+}
diff --git a/src/go/doc/comment/parse_test.go b/src/go/doc/comment/parse_test.go
new file mode 100644
index 0000000..bce733e
--- /dev/null
+++ b/src/go/doc/comment/parse_test.go
@@ -0,0 +1,12 @@
+// 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 "testing"
+
+// See https://golang.org/issue/52353
+func Test52353(t *testing.T) {
+	ident("𫕐ﯯ")
+}
diff --git a/src/go/doc/comment/print.go b/src/go/doc/comment/print.go
new file mode 100644
index 0000000..e1c070d
--- /dev/null
+++ b/src/go/doc/comment/print.go
@@ -0,0 +1,288 @@
+// 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"
+	"strings"
+)
+
+// A Printer is a doc comment printer.
+// The fields in the struct can be filled in before calling
+// any of the printing methods
+// in order to customize the details of the printing process.
+type Printer struct {
+	// HeadingLevel is the nesting level used for
+	// HTML and Markdown headings.
+	// If HeadingLevel is zero, it defaults to level 3,
+	// meaning to use <h3> and ###.
+	HeadingLevel int
+
+	// HeadingID is a function that computes the heading ID
+	// (anchor tag) to use for the heading h when generating
+	// HTML and Markdown. If HeadingID returns an empty string,
+	// then the heading ID is omitted.
+	// If HeadingID is nil, h.DefaultID is used.
+	HeadingID func(h *Heading) string
+
+	// DocLinkURL is a function that computes the URL for the given DocLink.
+	// If DocLinkURL is nil, then link.DefaultURL(p.DocLinkBaseURL) is used.
+	DocLinkURL func(link *DocLink) string
+
+	// DocLinkBaseURL is used when DocLinkURL is nil,
+	// passed to [DocLink.DefaultURL] to construct a DocLink's URL.
+	// See that method's documentation for details.
+	DocLinkBaseURL string
+
+	// TextPrefix is a prefix to print at the start of every line
+	// when generating text output using the Text method.
+	TextPrefix string
+
+	// TextCodePrefix is the prefix to print at the start of each
+	// preformatted (code block) line when generating text output,
+	// instead of (not in addition to) TextPrefix.
+	// If TextCodePrefix is the empty string, it defaults to TextPrefix+"\t".
+	TextCodePrefix string
+
+	// TextWidth is the maximum width text line to generate,
+	// measured in Unicode code points,
+	// excluding TextPrefix and the newline character.
+	// If TextWidth is zero, it defaults to 80 minus the number of code points in TextPrefix.
+	// If TextWidth is negative, there is no limit.
+	TextWidth int
+}
+
+func (p *Printer) headingLevel() int {
+	if p.HeadingLevel <= 0 {
+		return 3
+	}
+	return p.HeadingLevel
+}
+
+func (p *Printer) headingID(h *Heading) string {
+	if p.HeadingID == nil {
+		return h.DefaultID()
+	}
+	return p.HeadingID(h)
+}
+
+func (p *Printer) docLinkURL(link *DocLink) string {
+	if p.DocLinkURL != nil {
+		return p.DocLinkURL(link)
+	}
+	return link.DefaultURL(p.DocLinkBaseURL)
+}
+
+// DefaultURL constructs and returns the documentation URL for l,
+// using baseURL as a prefix for links to other packages.
+//
+// The possible forms returned by DefaultURL are:
+//   - baseURL/ImportPath, for a link to another package
+//   - baseURL/ImportPath#Name, for a link to a const, func, type, or var in another package
+//   - baseURL/ImportPath#Recv.Name, for a link to a method in another package
+//   - #Name, for a link to a const, func, type, or var in this package
+//   - #Recv.Name, for a link to a method in this package
+//
+// If baseURL ends in a trailing slash, then DefaultURL inserts
+// a slash between ImportPath and # in the anchored forms.
+// For example, here are some baseURL values and URLs they can generate:
+//
+//	"/pkg/" → "/pkg/math/#Sqrt"
+//	"/pkg"  → "/pkg/math#Sqrt"
+//	"/"     → "/math/#Sqrt"
+//	""      → "/math#Sqrt"
+func (l *DocLink) DefaultURL(baseURL string) string {
+	if l.ImportPath != "" {
+		slash := ""
+		if strings.HasSuffix(baseURL, "/") {
+			slash = "/"
+		} else {
+			baseURL += "/"
+		}
+		switch {
+		case l.Name == "":
+			return baseURL + l.ImportPath + slash
+		case l.Recv != "":
+			return baseURL + l.ImportPath + slash + "#" + l.Recv + "." + l.Name
+		default:
+			return baseURL + l.ImportPath + slash + "#" + l.Name
+		}
+	}
+	if l.Recv != "" {
+		return "#" + l.Recv + "." + l.Name
+	}
+	return "#" + l.Name
+}
+
+// DefaultID returns the default anchor ID for the heading h.
+//
+// The default anchor ID is constructed by converting every
+// rune that is not alphanumeric ASCII to an underscore
+// and then adding the prefix “hdr-”.
+// For example, if the heading text is “Go Doc Comments”,
+// the default ID is “hdr-Go_Doc_Comments”.
+func (h *Heading) DefaultID() string {
+	// Note: The “hdr-” prefix is important to avoid DOM clobbering attacks.
+	// See https://pkg.go.dev/github.com/google/safehtml#Identifier.
+	var out strings.Builder
+	var p textPrinter
+	p.oneLongLine(&out, h.Text)
+	s := strings.TrimSpace(out.String())
+	if s == "" {
+		return ""
+	}
+	out.Reset()
+	out.WriteString("hdr-")
+	for _, r := range s {
+		if r < 0x80 && isIdentASCII(byte(r)) {
+			out.WriteByte(byte(r))
+		} else {
+			out.WriteByte('_')
+		}
+	}
+	return out.String()
+}
+
+type commentPrinter struct {
+	*Printer
+}
+
+// Comment returns the standard Go formatting of the Doc,
+// without any comment markers.
+func (p *Printer) Comment(d *Doc) []byte {
+	cp := &commentPrinter{Printer: p}
+	var out bytes.Buffer
+	for i, x := range d.Content {
+		if i > 0 && blankBefore(x) {
+			out.WriteString("\n")
+		}
+		cp.block(&out, x)
+	}
+
+	// Print one block containing all the link definitions that were used,
+	// and then a second block containing all the unused ones.
+	// This makes it easy to clean up the unused ones: gofmt and
+	// delete the final block. And it's a nice visual signal without
+	// affecting the way the comment formats for users.
+	for i := 0; i < 2; i++ {
+		used := i == 0
+		first := true
+		for _, def := range d.Links {
+			if def.Used == used {
+				if first {
+					out.WriteString("\n")
+					first = false
+				}
+				out.WriteString("[")
+				out.WriteString(def.Text)
+				out.WriteString("]: ")
+				out.WriteString(def.URL)
+				out.WriteString("\n")
+			}
+		}
+	}
+
+	return out.Bytes()
+}
+
+// blankBefore reports whether the block x requires a blank line before it.
+// All blocks do, except for Lists that return false from x.BlankBefore().
+func blankBefore(x Block) bool {
+	if x, ok := x.(*List); ok {
+		return x.BlankBefore()
+	}
+	return true
+}
+
+// block prints the block x to out.
+func (p *commentPrinter) block(out *bytes.Buffer, x Block) {
+	switch x := x.(type) {
+	default:
+		fmt.Fprintf(out, "?%T", x)
+
+	case *Paragraph:
+		p.text(out, "", x.Text)
+		out.WriteString("\n")
+
+	case *Heading:
+		out.WriteString("# ")
+		p.text(out, "", x.Text)
+		out.WriteString("\n")
+
+	case *Code:
+		md := x.Text
+		for md != "" {
+			var line string
+			line, md, _ = strings.Cut(md, "\n")
+			if line != "" {
+				out.WriteString("\t")
+				out.WriteString(line)
+			}
+			out.WriteString("\n")
+		}
+
+	case *List:
+		loose := x.BlankBetween()
+		for i, item := range x.Items {
+			if i > 0 && loose {
+				out.WriteString("\n")
+			}
+			out.WriteString(" ")
+			if item.Number == "" {
+				out.WriteString(" - ")
+			} else {
+				out.WriteString(item.Number)
+				out.WriteString(". ")
+			}
+			for i, blk := range item.Content {
+				const fourSpace = "    "
+				if i > 0 {
+					out.WriteString("\n" + fourSpace)
+				}
+				p.text(out, fourSpace, blk.(*Paragraph).Text)
+				out.WriteString("\n")
+			}
+		}
+	}
+}
+
+// text prints the text sequence x to out.
+func (p *commentPrinter) text(out *bytes.Buffer, indent string, x []Text) {
+	for _, t := range x {
+		switch t := t.(type) {
+		case Plain:
+			p.indent(out, indent, string(t))
+		case Italic:
+			p.indent(out, indent, string(t))
+		case *Link:
+			if t.Auto {
+				p.text(out, indent, t.Text)
+			} else {
+				out.WriteString("[")
+				p.text(out, indent, t.Text)
+				out.WriteString("]")
+			}
+		case *DocLink:
+			out.WriteString("[")
+			p.text(out, indent, t.Text)
+			out.WriteString("]")
+		}
+	}
+}
+
+// indent prints s to out, indenting with the indent string
+// after each newline in s.
+func (p *commentPrinter) indent(out *bytes.Buffer, indent, s string) {
+	for s != "" {
+		line, rest, ok := strings.Cut(s, "\n")
+		out.WriteString(line)
+		if ok {
+			out.WriteString("\n")
+			out.WriteString(indent)
+		}
+		s = rest
+	}
+}
diff --git a/src/go/doc/comment/std.go b/src/go/doc/comment/std.go
new file mode 100644
index 0000000..fd8c8ce
--- /dev/null
+++ b/src/go/doc/comment/std.go
@@ -0,0 +1,47 @@
+// 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.
+
+// Code generated by 'go generate' DO NOT EDIT.
+//go:generate ./mkstd.sh
+
+package comment
+
+var stdPkgs = []string{
+	"bufio",
+	"bytes",
+	"cmp",
+	"context",
+	"crypto",
+	"embed",
+	"encoding",
+	"errors",
+	"expvar",
+	"flag",
+	"fmt",
+	"hash",
+	"html",
+	"image",
+	"io",
+	"log",
+	"maps",
+	"math",
+	"mime",
+	"net",
+	"os",
+	"path",
+	"plugin",
+	"reflect",
+	"regexp",
+	"runtime",
+	"slices",
+	"sort",
+	"strconv",
+	"strings",
+	"sync",
+	"syscall",
+	"testing",
+	"time",
+	"unicode",
+	"unsafe",
+}
diff --git a/src/go/doc/comment/std_test.go b/src/go/doc/comment/std_test.go
new file mode 100644
index 0000000..89206e6
--- /dev/null
+++ b/src/go/doc/comment/std_test.go
@@ -0,0 +1,34 @@
+// 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 (
+	"internal/diff"
+	"internal/testenv"
+	"sort"
+	"strings"
+	"testing"
+)
+
+func TestStd(t *testing.T) {
+	out, err := testenv.Command(t, testenv.GoToolPath(t), "list", "std").CombinedOutput()
+	if err != nil {
+		t.Fatalf("%v\n%s", err, out)
+	}
+
+	var list []string
+	for _, pkg := range strings.Fields(string(out)) {
+		if !strings.Contains(pkg, "/") {
+			list = append(list, pkg)
+		}
+	}
+	sort.Strings(list)
+
+	have := strings.Join(stdPkgs, "\n") + "\n"
+	want := strings.Join(list, "\n") + "\n"
+	if have != want {
+		t.Errorf("stdPkgs is out of date: regenerate with 'go generate'\n%s", diff.Diff("stdPkgs", []byte(have), "want", []byte(want)))
+	}
+}
diff --git a/src/go/doc/comment/testdata/README.md b/src/go/doc/comment/testdata/README.md
new file mode 100644
index 0000000..d6f2c54
--- /dev/null
+++ b/src/go/doc/comment/testdata/README.md
@@ -0,0 +1,42 @@
+This directory contains test files (*.txt) for the comment parser.
+
+The files are in [txtar format](https://pkg.go.dev/golang.org/x/tools/txtar).
+Consider this example:
+
+	-- input --
+	Hello.
+	-- gofmt --
+	Hello.
+	-- html --
+	<p>Hello.
+	-- markdown --
+	Hello.
+	-- text --
+	Hello.
+
+Each `-- name --` line introduces a new file with the given name.
+The file named “input” must be first and contains the input to
+[comment.Parser](https://pkg.go.dev/go/doc/comment/#Parser).
+
+The remaining files contain the expected output for the named format generated by
+[comment.Printer](https://pkg.go.dev/go/doc/comment/#Printer):
+“gofmt” for Printer.Comment (Go comment format, as used by gofmt),
+“html” for Printer.HTML, “markdown” for Printer.Markdown, and “text” for Printer.Text.
+The format can also be “dump” for a textual dump of the raw data structures.
+
+The text before the `-- input --` line, if present, is JSON to be unmarshalled
+to initialize a comment.Printer. For example, this test case sets the Printer's
+TextWidth field to 20:
+
+	{"TextWidth": 20}
+	-- input --
+	Package gob manages streams of gobs - binary values exchanged between an
+	Encoder (transmitter) and a Decoder (receiver).
+	-- text --
+	Package gob
+	manages streams
+	of gobs - binary
+	values exchanged
+	between an Encoder
+	(transmitter) and a
+	Decoder (receiver).
diff --git a/src/go/doc/comment/testdata/blank.txt b/src/go/doc/comment/testdata/blank.txt
new file mode 100644
index 0000000..9049fde
--- /dev/null
+++ b/src/go/doc/comment/testdata/blank.txt
@@ -0,0 +1,12 @@
+-- input --
+	$
+	Blank line at start and end.
+	$
+-- gofmt --
+Blank line at start and end.
+-- text --
+Blank line at start and end.
+-- markdown --
+Blank line at start and end.
+-- html --
+<p>Blank line at start and end.
diff --git a/src/go/doc/comment/testdata/code.txt b/src/go/doc/comment/testdata/code.txt
new file mode 100644
index 0000000..06b1519
--- /dev/null
+++ b/src/go/doc/comment/testdata/code.txt
@@ -0,0 +1,94 @@
+-- input --
+Text.
+	A tab-indented
+	(no, not eight-space indented)
+	code block and haiku.
+More text.
+ One space
+  is
+   enough
+    to
+     start
+      a
+       block.
+More text.
+
+      Blocks
+    can
+
+  have
+    blank
+      lines.
+-- gofmt --
+Text.
+
+	A tab-indented
+	(no, not eight-space indented)
+	code block and haiku.
+
+More text.
+
+	One space
+	 is
+	  enough
+	   to
+	    start
+	     a
+	      block.
+
+More text.
+
+	    Blocks
+	  can
+
+	have
+	  blank
+	    lines.
+-- markdown --
+Text.
+
+	A tab-indented
+	(no, not eight-space indented)
+	code block and haiku.
+
+More text.
+
+	One space
+	 is
+	  enough
+	   to
+	    start
+	     a
+	      block.
+
+More text.
+
+	    Blocks
+	  can
+
+	have
+	  blank
+	    lines.
+-- html --
+<p>Text.
+<pre>A tab-indented
+(no, not eight-space indented)
+code block and haiku.
+</pre>
+<p>More text.
+<pre>One space
+ is
+  enough
+   to
+    start
+     a
+      block.
+</pre>
+<p>More text.
+<pre>    Blocks
+  can
+
+have
+  blank
+    lines.
+</pre>
diff --git a/src/go/doc/comment/testdata/code2.txt b/src/go/doc/comment/testdata/code2.txt
new file mode 100644
index 0000000..0810bed
--- /dev/null
+++ b/src/go/doc/comment/testdata/code2.txt
@@ -0,0 +1,31 @@
+-- input --
+Text.
+
+	A tab-indented
+	(no, not eight-space indented)
+	code block and haiku.
+
+More text.
+-- gofmt --
+Text.
+
+	A tab-indented
+	(no, not eight-space indented)
+	code block and haiku.
+
+More text.
+-- markdown --
+Text.
+
+	A tab-indented
+	(no, not eight-space indented)
+	code block and haiku.
+
+More text.
+-- html --
+<p>Text.
+<pre>A tab-indented
+(no, not eight-space indented)
+code block and haiku.
+</pre>
+<p>More text.
diff --git a/src/go/doc/comment/testdata/code3.txt b/src/go/doc/comment/testdata/code3.txt
new file mode 100644
index 0000000..4a96a0e
--- /dev/null
+++ b/src/go/doc/comment/testdata/code3.txt
@@ -0,0 +1,33 @@
+-- input --
+Text.
+
+	$
+	A tab-indented
+	(surrounded by more blank lines)
+	code block and haiku.
+	$
+
+More text.
+-- gofmt --
+Text.
+
+	A tab-indented
+	(surrounded by more blank lines)
+	code block and haiku.
+
+More text.
+-- markdown --
+Text.
+
+	A tab-indented
+	(surrounded by more blank lines)
+	code block and haiku.
+
+More text.
+-- html --
+<p>Text.
+<pre>A tab-indented
+(surrounded by more blank lines)
+code block and haiku.
+</pre>
+<p>More text.
diff --git a/src/go/doc/comment/testdata/code4.txt b/src/go/doc/comment/testdata/code4.txt
new file mode 100644
index 0000000..f128c9a
--- /dev/null
+++ b/src/go/doc/comment/testdata/code4.txt
@@ -0,0 +1,38 @@
+-- input --
+To test, run this command:
+  go test -more
+
+Or, to test specific things, run this command:
+
+go test -more \
+  -pkg first/package \
+  -pkg second/package \
+  -pkg third/package
+
+Happy testing!
+-- gofmt --
+To test, run this command:
+
+	go test -more
+
+Or, to test specific things, run this command:
+
+	go test -more \
+	  -pkg first/package \
+	  -pkg second/package \
+	  -pkg third/package
+
+Happy testing!
+-- markdown --
+To test, run this command:
+
+	go test -more
+
+Or, to test specific things, run this command:
+
+	go test -more \
+	  -pkg first/package \
+	  -pkg second/package \
+	  -pkg third/package
+
+Happy testing!
diff --git a/src/go/doc/comment/testdata/code5.txt b/src/go/doc/comment/testdata/code5.txt
new file mode 100644
index 0000000..0e340dd
--- /dev/null
+++ b/src/go/doc/comment/testdata/code5.txt
@@ -0,0 +1,21 @@
+-- input --
+L1
+L2
+L3
+L4
+L5
+- L6 {
+	L7
+}
+L8
+-- gofmt --
+L1
+L2
+L3
+L4
+L5
+  - L6 {
+    L7
+    }
+
+L8
diff --git a/src/go/doc/comment/testdata/code6.txt b/src/go/doc/comment/testdata/code6.txt
new file mode 100644
index 0000000..d2915d1
--- /dev/null
+++ b/src/go/doc/comment/testdata/code6.txt
@@ -0,0 +1,24 @@
+-- input --
+Run this program:
+
+func main() {
+	fmt.Println("hello, world")
+}
+
+Or this:
+
+go func() {
+	fmt.Println("hello, world")
+}()
+-- gofmt --
+Run this program:
+
+	func main() {
+		fmt.Println("hello, world")
+	}
+
+Or this:
+
+	go func() {
+		fmt.Println("hello, world")
+	}()
diff --git a/src/go/doc/comment/testdata/crash1.txt b/src/go/doc/comment/testdata/crash1.txt
new file mode 100644
index 0000000..6bb2f6f
--- /dev/null
+++ b/src/go/doc/comment/testdata/crash1.txt
@@ -0,0 +1,16 @@
+-- input --
+[]
+
+[]: http://
+-- gofmt --
+[]
+
+[]: http://
+-- html --
+<p><a href="http://"></a>
+-- markdown --
+[](http://)
+-- text --
+
+
+[]: http://
diff --git a/src/go/doc/comment/testdata/doclink.txt b/src/go/doc/comment/testdata/doclink.txt
new file mode 100644
index 0000000..a932347
--- /dev/null
+++ b/src/go/doc/comment/testdata/doclink.txt
@@ -0,0 +1,21 @@
+-- input --
+In this package, see [Doc] and [Parser.Parse].
+There is no [Undef] or [Undef.Method].
+See also the [comment] package,
+especially [comment.Doc] and [comment.Parser.Parse].
+-- gofmt --
+In this package, see [Doc] and [Parser.Parse].
+There is no [Undef] or [Undef.Method].
+See also the [comment] package,
+especially [comment.Doc] and [comment.Parser.Parse].
+-- text --
+In this package, see Doc and Parser.Parse. There is no [Undef] or
+[Undef.Method]. See also the comment package, especially comment.Doc and
+comment.Parser.Parse.
+-- markdown --
+In this package, see [Doc](#Doc) and [Parser.Parse](#Parser.Parse). There is no \[Undef] or \[Undef.Method]. See also the [comment](/go/doc/comment) package, especially [comment.Doc](/go/doc/comment#Doc) and [comment.Parser.Parse](/go/doc/comment#Parser.Parse).
+-- html --
+<p>In this package, see <a href="#Doc">Doc</a> and <a href="#Parser.Parse">Parser.Parse</a>.
+There is no [Undef] or [Undef.Method].
+See also the <a href="/go/doc/comment">comment</a> package,
+especially <a href="/go/doc/comment#Doc">comment.Doc</a> and <a href="/go/doc/comment#Parser.Parse">comment.Parser.Parse</a>.
diff --git a/src/go/doc/comment/testdata/doclink2.txt b/src/go/doc/comment/testdata/doclink2.txt
new file mode 100644
index 0000000..ecd8e4e
--- /dev/null
+++ b/src/go/doc/comment/testdata/doclink2.txt
@@ -0,0 +1,8 @@
+-- input --
+We use [io.Reader] a lot, and also a few map[io.Reader]string.
+
+Never [io.Reader]int or Slice[io.Reader] though.
+-- markdown --
+We use [io.Reader](/io#Reader) a lot, and also a few map\[io.Reader]string.
+
+Never \[io.Reader]int or Slice\[io.Reader] though.
diff --git a/src/go/doc/comment/testdata/doclink3.txt b/src/go/doc/comment/testdata/doclink3.txt
new file mode 100644
index 0000000..0ccfb3d
--- /dev/null
+++ b/src/go/doc/comment/testdata/doclink3.txt
@@ -0,0 +1,8 @@
+-- input --
+[encoding/json.Marshal] is a doc link.
+
+[rot13.Marshal] is not.
+-- markdown --
+[encoding/json.Marshal](/encoding/json#Marshal) is a doc link.
+
+\[rot13.Marshal] is not.
diff --git a/src/go/doc/comment/testdata/doclink4.txt b/src/go/doc/comment/testdata/doclink4.txt
new file mode 100644
index 0000000..c709527
--- /dev/null
+++ b/src/go/doc/comment/testdata/doclink4.txt
@@ -0,0 +1,7 @@
+-- input --
+[io] at start of comment.
+[io] at start of line.
+At end of line: [io]
+At end of comment: [io]
+-- markdown --
+[io](/io) at start of comment. [io](/io) at start of line. At end of line: [io](/io) At end of comment: [io](/io)
diff --git a/src/go/doc/comment/testdata/doclink5.txt b/src/go/doc/comment/testdata/doclink5.txt
new file mode 100644
index 0000000..ac7b3ae
--- /dev/null
+++ b/src/go/doc/comment/testdata/doclink5.txt
@@ -0,0 +1,5 @@
+{"DocLinkBaseURL": "https://pkg.go.dev"}
+-- input --
+[encoding/json.Marshal] is a doc link.
+-- markdown --
+[encoding/json.Marshal](https://pkg.go.dev/encoding/json#Marshal) is a doc link.
diff --git a/src/go/doc/comment/testdata/doclink6.txt b/src/go/doc/comment/testdata/doclink6.txt
new file mode 100644
index 0000000..1acd03b
--- /dev/null
+++ b/src/go/doc/comment/testdata/doclink6.txt
@@ -0,0 +1,5 @@
+{"DocLinkBaseURL": "https://go.dev/pkg/"}
+-- input --
+[encoding/json.Marshal] is a doc link, and so is [rsc.io/quote.NonExist].
+-- markdown --
+[encoding/json.Marshal](https://go.dev/pkg/encoding/json/#Marshal) is a doc link, and so is [rsc.io/quote.NonExist](https://go.dev/pkg/rsc.io/quote/#NonExist).
diff --git a/src/go/doc/comment/testdata/doclink7.txt b/src/go/doc/comment/testdata/doclink7.txt
new file mode 100644
index 0000000..d34979a
--- /dev/null
+++ b/src/go/doc/comment/testdata/doclink7.txt
@@ -0,0 +1,4 @@
+-- input --
+You see more [*bytes.Buffer] than [bytes.Buffer].
+-- markdown --
+You see more [\*bytes.Buffer](/bytes#Buffer) than [bytes.Buffer](/bytes#Buffer).
diff --git a/src/go/doc/comment/testdata/escape.txt b/src/go/doc/comment/testdata/escape.txt
new file mode 100644
index 0000000..f54663f
--- /dev/null
+++ b/src/go/doc/comment/testdata/escape.txt
@@ -0,0 +1,55 @@
+-- input --
+What the ~!@#$%^&*()_+-=`{}|[]\:";',./<>?
+
++ Line
+
+- Line
+
+* Line
+
+999. Line
+
+## Line
+-- gofmt --
+What the ~!@#$%^&*()_+-=`{}|[]\:";',./<>?
+
++ Line
+
+- Line
+
+* Line
+
+999. Line
+
+## Line
+-- text --
+What the ~!@#$%^&*()_+-=`{}|[]\:";',./<>?
+
++ Line
+
+- Line
+
+* Line
+
+999. Line
+
+## Line
+-- markdown --
+What the ~!@#$%^&\*()\_+-=\`{}|\[]\\:";',./\<>?
+
+\+ Line
+
+\- Line
+
+\* Line
+
+999\. Line
+
+\## Line
+-- html --
+<p>What the ~!@#$%^&amp;*()_+-=`{}|[]\:&quot;;&apos;,./&lt;&gt;?
+<p>+ Line
+<p>- Line
+<p>* Line
+<p>999. Line
+<p>## Line
diff --git a/src/go/doc/comment/testdata/head.txt b/src/go/doc/comment/testdata/head.txt
new file mode 100644
index 0000000..b99a8c5
--- /dev/null
+++ b/src/go/doc/comment/testdata/head.txt
@@ -0,0 +1,92 @@
+-- input --
+Some text.
+
+An Old Heading
+
+Not An Old Heading.
+
+And some text.
+
+# A New Heading.
+
+And some more text.
+
+# Not a heading,
+because text follows it.
+
+Because text precedes it,
+# not a heading.
+
+## Not a heading either.
+
+-- gofmt --
+Some text.
+
+# An Old Heading
+
+Not An Old Heading.
+
+And some text.
+
+# A New Heading.
+
+And some more text.
+
+# Not a heading,
+because text follows it.
+
+Because text precedes it,
+# not a heading.
+
+## Not a heading either.
+
+-- text --
+Some text.
+
+# An Old Heading
+
+Not An Old Heading.
+
+And some text.
+
+# A New Heading.
+
+And some more text.
+
+# Not a heading, because text follows it.
+
+Because text precedes it, # not a heading.
+
+## Not a heading either.
+
+-- markdown --
+Some text.
+
+### An Old Heading {#hdr-An_Old_Heading}
+
+Not An Old Heading.
+
+And some text.
+
+### A New Heading. {#hdr-A_New_Heading_}
+
+And some more text.
+
+\# Not a heading, because text follows it.
+
+Because text precedes it, # not a heading.
+
+\## Not a heading either.
+
+-- html --
+<p>Some text.
+<h3 id="hdr-An_Old_Heading">An Old Heading</h3>
+<p>Not An Old Heading.
+<p>And some text.
+<h3 id="hdr-A_New_Heading_">A New Heading.</h3>
+<p>And some more text.
+<p># Not a heading,
+because text follows it.
+<p>Because text precedes it,
+# not a heading.
+<p>## Not a heading either.
diff --git a/src/go/doc/comment/testdata/head2.txt b/src/go/doc/comment/testdata/head2.txt
new file mode 100644
index 0000000..d357632
--- /dev/null
+++ b/src/go/doc/comment/testdata/head2.txt
@@ -0,0 +1,36 @@
+-- input --
+✦
+
+Almost a+heading
+
+✦
+
+Don't be a heading
+
+✦
+
+A.b is a heading
+
+✦
+
+A. b is not a heading
+
+✦
+-- gofmt --
+✦
+
+Almost a+heading
+
+✦
+
+Don't be a heading
+
+✦
+
+# A.b is a heading
+
+✦
+
+A. b is not a heading
+
+✦
diff --git a/src/go/doc/comment/testdata/head3.txt b/src/go/doc/comment/testdata/head3.txt
new file mode 100644
index 0000000..dbb7cb3
--- /dev/null
+++ b/src/go/doc/comment/testdata/head3.txt
@@ -0,0 +1,7 @@
+{"HeadingLevel": 5}
+-- input --
+# Heading
+-- markdown --
+##### Heading {#hdr-Heading}
+-- html --
+<h5 id="hdr-Heading">Heading</h5>
diff --git a/src/go/doc/comment/testdata/hello.txt b/src/go/doc/comment/testdata/hello.txt
new file mode 100644
index 0000000..fb07f1e
--- /dev/null
+++ b/src/go/doc/comment/testdata/hello.txt
@@ -0,0 +1,35 @@
+-- input --
+	Hello,
+	world
+
+	This is
+	a test.
+-- dump --
+Doc
+	Paragraph
+		Plain
+			"Hello,\n"
+			"world"
+	Paragraph
+		Plain
+			"This is\n"
+			"a test."
+-- gofmt --
+Hello,
+world
+
+This is
+a test.
+-- html --
+<p>Hello,
+world
+<p>This is
+a test.
+-- markdown --
+Hello, world
+
+This is a test.
+-- text --
+Hello, world
+
+This is a test.
diff --git a/src/go/doc/comment/testdata/link.txt b/src/go/doc/comment/testdata/link.txt
new file mode 100644
index 0000000..551e306
--- /dev/null
+++ b/src/go/doc/comment/testdata/link.txt
@@ -0,0 +1,17 @@
+-- input --
+The Go home page is https://go.dev/.
+It used to be https://golang.org.
+
+-- gofmt --
+The Go home page is https://go.dev/.
+It used to be https://golang.org.
+
+-- text --
+The Go home page is https://go.dev/. It used to be https://golang.org.
+
+-- markdown --
+The Go home page is [https://go.dev/](https://go.dev/). It used to be [https://golang.org](https://golang.org).
+
+-- html --
+<p>The Go home page is <a href="https://go.dev/">https://go.dev/</a>.
+It used to be <a href="https://golang.org">https://golang.org</a>.
diff --git a/src/go/doc/comment/testdata/link2.txt b/src/go/doc/comment/testdata/link2.txt
new file mode 100644
index 0000000..8637a32
--- /dev/null
+++ b/src/go/doc/comment/testdata/link2.txt
@@ -0,0 +1,31 @@
+-- input --
+The Go home page is https://go.dev/.
+It used to be https://golang.org.
+https:// is not a link.
+Nor is https://
+https://☺ is not a link.
+https://:80 is not a link.
+
+-- gofmt --
+The Go home page is https://go.dev/.
+It used to be https://golang.org.
+https:// is not a link.
+Nor is https://
+https://☺ is not a link.
+https://:80 is not a link.
+
+-- text --
+The Go home page is https://go.dev/. It used to be https://golang.org. https://
+is not a link. Nor is https:// https://☺ is not a link. https://:80 is not a
+link.
+
+-- markdown --
+The Go home page is [https://go.dev/](https://go.dev/). It used to be [https://golang.org](https://golang.org). https:// is not a link. Nor is https:// https://☺ is not a link. https://:80 is not a link.
+
+-- html --
+<p>The Go home page is <a href="https://go.dev/">https://go.dev/</a>.
+It used to be <a href="https://golang.org">https://golang.org</a>.
+https:// is not a link.
+Nor is https://
+https://☺ is not a link.
+https://:80 is not a link.
diff --git a/src/go/doc/comment/testdata/link3.txt b/src/go/doc/comment/testdata/link3.txt
new file mode 100644
index 0000000..5a115b5
--- /dev/null
+++ b/src/go/doc/comment/testdata/link3.txt
@@ -0,0 +1,14 @@
+-- input --
+Doc text.
+
+[Go home page]: https://go.dev
+-- gofmt --
+Doc text.
+
+[Go home page]: https://go.dev
+-- text --
+Doc text.
+-- markdown --
+Doc text.
+-- html --
+<p>Doc text.
diff --git a/src/go/doc/comment/testdata/link4.txt b/src/go/doc/comment/testdata/link4.txt
new file mode 100644
index 0000000..75f194c
--- /dev/null
+++ b/src/go/doc/comment/testdata/link4.txt
@@ -0,0 +1,77 @@
+-- input --
+These are not links.
+
+[x
+
+[x]:
+
+[x]:https://go.dev
+
+[x]https://go.dev
+
+[x]: surprise://go.dev
+
+[x]: surprise!
+
+But this is, with a tab (although it's unused).
+
+[z]:	https://go.dev
+-- gofmt --
+These are not links.
+
+[x
+
+[x]:
+
+[x]:https://go.dev
+
+[x]https://go.dev
+
+[x]: surprise://go.dev
+
+[x]: surprise!
+
+But this is, with a tab (although it's unused).
+
+[z]: https://go.dev
+-- text --
+These are not links.
+
+[x
+
+[x]:
+
+[x]:https://go.dev
+
+[x]https://go.dev
+
+[x]: surprise://go.dev
+
+[x]: surprise!
+
+But this is, with a tab (although it's unused).
+-- markdown --
+These are not links.
+
+\[x
+
+\[x]:
+
+\[x]:[https://go.dev](https://go.dev)
+
+\[x][https://go.dev](https://go.dev)
+
+\[x]: surprise://go.dev
+
+\[x]: surprise!
+
+But this is, with a tab (although it's unused).
+-- html --
+<p>These are not links.
+<p>[x
+<p>[x]:
+<p>[x]:<a href="https://go.dev">https://go.dev</a>
+<p>[x]<a href="https://go.dev">https://go.dev</a>
+<p>[x]: surprise://go.dev
+<p>[x]: surprise!
+<p>But this is, with a tab (although it&apos;s unused).
diff --git a/src/go/doc/comment/testdata/link5.txt b/src/go/doc/comment/testdata/link5.txt
new file mode 100644
index 0000000..b4fb588
--- /dev/null
+++ b/src/go/doc/comment/testdata/link5.txt
@@ -0,0 +1,36 @@
+-- input --
+See the [Go home page] and the [pkg
+site].
+
+[Go home page]: https://go.dev/
+[pkg site]: https://pkg.go.dev
+[Go home page]: https://duplicate.ignored
+
+They're really great!
+
+-- gofmt --
+See the [Go home page] and the [pkg
+site].
+
+They're really great!
+
+[Go home page]: https://go.dev/
+[pkg site]: https://pkg.go.dev
+
+[Go home page]: https://duplicate.ignored
+
+-- text --
+See the Go home page and the pkg site.
+
+They're really great!
+
+[Go home page]: https://go.dev/
+[pkg site]: https://pkg.go.dev
+-- markdown --
+See the [Go home page](https://go.dev/) and the [pkg site](https://pkg.go.dev).
+
+They're really great!
+-- html --
+<p>See the <a href="https://go.dev/">Go home page</a> and the <a href="https://pkg.go.dev">pkg
+site</a>.
+<p>They&apos;re really great!
diff --git a/src/go/doc/comment/testdata/link6.txt b/src/go/doc/comment/testdata/link6.txt
new file mode 100644
index 0000000..ff629b4
--- /dev/null
+++ b/src/go/doc/comment/testdata/link6.txt
@@ -0,0 +1,50 @@
+-- input --
+URLs with punctuation are hard.
+We don't want to consume the end-of-sentence punctuation.
+
+For example, https://en.wikipedia.org/wiki/John_Adams_(miniseries).
+And https://example.com/[foo]/bar{.
+And https://example.com/(foo)/bar!
+And https://example.com/{foo}/bar{.
+And https://example.com/)baz{foo}.
+
+[And https://example.com/].
+
+-- gofmt --
+URLs with punctuation are hard.
+We don't want to consume the end-of-sentence punctuation.
+
+For example, https://en.wikipedia.org/wiki/John_Adams_(miniseries).
+And https://example.com/[foo]/bar{.
+And https://example.com/(foo)/bar!
+And https://example.com/{foo}/bar{.
+And https://example.com/)baz{foo}.
+
+[And https://example.com/].
+
+-- text --
+URLs with punctuation are hard. We don't want to consume the end-of-sentence
+punctuation.
+
+For example, https://en.wikipedia.org/wiki/John_Adams_(miniseries).
+And https://example.com/[foo]/bar{. And https://example.com/(foo)/bar! And
+https://example.com/{foo}/bar{. And https://example.com/)baz{foo}.
+
+[And https://example.com/].
+
+-- markdown --
+URLs with punctuation are hard. We don't want to consume the end-of-sentence punctuation.
+
+For example, [https://en.wikipedia.org/wiki/John\_Adams\_(miniseries)](https://en.wikipedia.org/wiki/John_Adams_(miniseries)). And [https://example.com/\[foo]/bar](https://example.com/[foo]/bar){. And [https://example.com/(foo)/bar](https://example.com/(foo)/bar)! And [https://example.com/{foo}/bar](https://example.com/{foo}/bar){. And [https://example.com/](https://example.com/))baz{foo}.
+
+\[And [https://example.com/](https://example.com/)].
+
+-- html --
+<p>URLs with punctuation are hard.
+We don&apos;t want to consume the end-of-sentence punctuation.
+<p>For example, <a href="https://en.wikipedia.org/wiki/John_Adams_(miniseries)">https://en.wikipedia.org/wiki/John_Adams_(miniseries)</a>.
+And <a href="https://example.com/[foo]/bar">https://example.com/[foo]/bar</a>{.
+And <a href="https://example.com/(foo)/bar">https://example.com/(foo)/bar</a>!
+And <a href="https://example.com/{foo}/bar">https://example.com/{foo}/bar</a>{.
+And <a href="https://example.com/">https://example.com/</a>)baz{foo}.
+<p>[And <a href="https://example.com/">https://example.com/</a>].
diff --git a/src/go/doc/comment/testdata/link7.txt b/src/go/doc/comment/testdata/link7.txt
new file mode 100644
index 0000000..89a8b31
--- /dev/null
+++ b/src/go/doc/comment/testdata/link7.txt
@@ -0,0 +1,25 @@
+-- input --
+[math] is a package but this is not a doc link.
+
+[io] is a doc link.
+
+[math]: https://example.com
+-- gofmt --
+[math] is a package but this is not a doc link.
+
+[io] is a doc link.
+
+[math]: https://example.com
+-- text --
+math is a package but this is not a doc link.
+
+io is a doc link.
+
+[math]: https://example.com
+-- markdown --
+[math](https://example.com) is a package but this is not a doc link.
+
+[io](/io) is a doc link.
+-- html --
+<p><a href="https://example.com">math</a> is a package but this is not a doc link.
+<p><a href="/io">io</a> is a doc link.
diff --git a/src/go/doc/comment/testdata/linklist.txt b/src/go/doc/comment/testdata/linklist.txt
new file mode 100644
index 0000000..baf4062
--- /dev/null
+++ b/src/go/doc/comment/testdata/linklist.txt
@@ -0,0 +1,18 @@
+{"DocLinkBaseURL": "https://pkg.go.dev"}
+-- input --
+Did you know?
+
+  - [encoding/json.Marshal] is a doc link. So is [encoding/json.Unmarshal].
+-- text --
+Did you know?
+
+  - encoding/json.Marshal is a doc link. So is encoding/json.Unmarshal.
+-- markdown --
+Did you know?
+
+  - [encoding/json.Marshal](https://pkg.go.dev/encoding/json#Marshal) is a doc link. So is [encoding/json.Unmarshal](https://pkg.go.dev/encoding/json#Unmarshal).
+-- html --
+<p>Did you know?
+<ul>
+<li><a href="https://pkg.go.dev/encoding/json#Marshal">encoding/json.Marshal</a> is a doc link. So is <a href="https://pkg.go.dev/encoding/json#Unmarshal">encoding/json.Unmarshal</a>.
+</ul>
diff --git a/src/go/doc/comment/testdata/linklist2.txt b/src/go/doc/comment/testdata/linklist2.txt
new file mode 100644
index 0000000..81b3061
--- /dev/null
+++ b/src/go/doc/comment/testdata/linklist2.txt
@@ -0,0 +1,39 @@
+{"DocLinkBaseURL": "https://pkg.go.dev"}
+-- input --
+Did you know?
+
+  - [testing.T] is one doc link.
+  - So is [testing.M].
+  - So is [testing.B].
+    This is the same list paragraph.
+
+    There is [testing.PB] in this list item, too!
+-- text --
+Did you know?
+
+  - testing.T is one doc link.
+
+  - So is testing.M.
+
+  - So is testing.B. This is the same list paragraph.
+
+    There is testing.PB in this list item, too!
+-- markdown --
+Did you know?
+
+  - [testing.T](https://pkg.go.dev/testing#T) is one doc link.
+
+  - So is [testing.M](https://pkg.go.dev/testing#M).
+
+  - So is [testing.B](https://pkg.go.dev/testing#B). This is the same list paragraph.
+
+    There is [testing.PB](https://pkg.go.dev/testing#PB) in this list item, too!
+-- html --
+<p>Did you know?
+<ul>
+<li><p><a href="https://pkg.go.dev/testing#T">testing.T</a> is one doc link.
+<li><p>So is <a href="https://pkg.go.dev/testing#M">testing.M</a>.
+<li><p>So is <a href="https://pkg.go.dev/testing#B">testing.B</a>.
+This is the same list paragraph.
+<p>There is <a href="https://pkg.go.dev/testing#PB">testing.PB</a> in this list item, too!
+</ul>
diff --git a/src/go/doc/comment/testdata/linklist3.txt b/src/go/doc/comment/testdata/linklist3.txt
new file mode 100644
index 0000000..701a54e
--- /dev/null
+++ b/src/go/doc/comment/testdata/linklist3.txt
@@ -0,0 +1,31 @@
+{"DocLinkBaseURL": "https://pkg.go.dev"}
+-- input --
+Cool things:
+
+  - Foo
+  - [Go]
+  - Bar
+
+[Go]: https://go.dev/
+-- text --
+Cool things:
+
+  - Foo
+  - Go
+  - Bar
+
+[Go]: https://go.dev/
+-- markdown --
+Cool things:
+
+  - Foo
+  - [Go](https://go.dev/)
+  - Bar
+
+-- html --
+<p>Cool things:
+<ul>
+<li>Foo
+<li><a href="https://go.dev/">Go</a>
+<li>Bar
+</ul>
diff --git a/src/go/doc/comment/testdata/linklist4.txt b/src/go/doc/comment/testdata/linklist4.txt
new file mode 100644
index 0000000..db39ec4
--- /dev/null
+++ b/src/go/doc/comment/testdata/linklist4.txt
@@ -0,0 +1,36 @@
+{"DocLinkBaseURL": "https://pkg.go.dev"}
+-- input --
+Cool things:
+
+  - Foo
+  - [Go] is great
+    
+    [Go]: https://go.dev/
+  - Bar
+
+-- text --
+Cool things:
+
+  - Foo
+
+  - Go is great
+
+  - Bar
+
+[Go]: https://go.dev/
+-- markdown --
+Cool things:
+
+  - Foo
+
+  - [Go](https://go.dev/) is great
+
+  - Bar
+
+-- html --
+<p>Cool things:
+<ul>
+<li><p>Foo
+<li><p><a href="https://go.dev/">Go</a> is great
+<li><p>Bar
+</ul>
diff --git a/src/go/doc/comment/testdata/list.txt b/src/go/doc/comment/testdata/list.txt
new file mode 100644
index 0000000..455782f
--- /dev/null
+++ b/src/go/doc/comment/testdata/list.txt
@@ -0,0 +1,48 @@
+-- input --
+Text.
+- Not a list.
+ - Here is the list.
+     • Using multiple bullets.
+          * Indentation does not matter.
+     + Lots of bullets.
+More text.
+
+-- gofmt --
+Text.
+- Not a list.
+  - Here is the list.
+  - Using multiple bullets.
+  - Indentation does not matter.
+  - Lots of bullets.
+
+More text.
+
+-- text --
+Text. - Not a list.
+  - Here is the list.
+  - Using multiple bullets.
+  - Indentation does not matter.
+  - Lots of bullets.
+
+More text.
+
+-- markdown --
+Text. - Not a list.
+
+  - Here is the list.
+  - Using multiple bullets.
+  - Indentation does not matter.
+  - Lots of bullets.
+
+More text.
+
+-- html --
+<p>Text.
+- Not a list.
+<ul>
+<li>Here is the list.
+<li>Using multiple bullets.
+<li>Indentation does not matter.
+<li>Lots of bullets.
+</ul>
+<p>More text.
diff --git a/src/go/doc/comment/testdata/list10.txt b/src/go/doc/comment/testdata/list10.txt
new file mode 100644
index 0000000..9c49083
--- /dev/null
+++ b/src/go/doc/comment/testdata/list10.txt
@@ -0,0 +1,13 @@
+-- input --
+
+	1. This list
+	2. Starts the comment
+	3. And also has a blank line before it.
+
+All of which is a little weird.
+-- gofmt --
+ 1. This list
+ 2. Starts the comment
+ 3. And also has a blank line before it.
+
+All of which is a little weird.
diff --git a/src/go/doc/comment/testdata/list2.txt b/src/go/doc/comment/testdata/list2.txt
new file mode 100644
index 0000000..c390b3d
--- /dev/null
+++ b/src/go/doc/comment/testdata/list2.txt
@@ -0,0 +1,57 @@
+-- input --
+Text.
+ 1. Uno
+   2) Dos
+ 3. Tres
+   5. Cinco
+ 7. Siete
+   11. Once
+ 12. Doce
+ 13. Trece.
+
+-- gofmt --
+Text.
+ 1. Uno
+ 2. Dos
+ 3. Tres
+ 5. Cinco
+ 7. Siete
+ 11. Once
+ 12. Doce
+ 13. Trece.
+
+-- text --
+Text.
+ 1. Uno
+ 2. Dos
+ 3. Tres
+ 5. Cinco
+ 7. Siete
+ 11. Once
+ 12. Doce
+ 13. Trece.
+
+-- markdown --
+Text.
+
+ 1. Uno
+ 2. Dos
+ 3. Tres
+ 5. Cinco
+ 7. Siete
+ 11. Once
+ 12. Doce
+ 13. Trece.
+
+-- html --
+<p>Text.
+<ol>
+<li>Uno
+<li>Dos
+<li>Tres
+<li value="5">Cinco
+<li value="7">Siete
+<li value="11">Once
+<li>Doce
+<li>Trece.
+</ol>
diff --git a/src/go/doc/comment/testdata/list3.txt b/src/go/doc/comment/testdata/list3.txt
new file mode 100644
index 0000000..d7d345d
--- /dev/null
+++ b/src/go/doc/comment/testdata/list3.txt
@@ -0,0 +1,32 @@
+-- input --
+Text.
+
+ 1. Uno
+ 1. Dos
+ 1. Tres
+ 1. Quatro
+
+-- gofmt --
+Text.
+
+ 1. Uno
+ 1. Dos
+ 1. Tres
+ 1. Quatro
+
+-- markdown --
+Text.
+
+ 1. Uno
+ 1. Dos
+ 1. Tres
+ 1. Quatro
+
+-- html --
+<p>Text.
+<ol>
+<li>Uno
+<li value="1">Dos
+<li value="1">Tres
+<li value="1">Quatro
+</ol>
diff --git a/src/go/doc/comment/testdata/list4.txt b/src/go/doc/comment/testdata/list4.txt
new file mode 100644
index 0000000..9c28d65
--- /dev/null
+++ b/src/go/doc/comment/testdata/list4.txt
@@ -0,0 +1,38 @@
+-- input --
+Text.
+  1. List
+2. Not indented, not a list.
+  3. Another list.
+
+-- gofmt --
+Text.
+ 1. List
+
+2. Not indented, not a list.
+ 3. Another list.
+
+-- text --
+Text.
+ 1. List
+
+2. Not indented, not a list.
+ 3. Another list.
+
+-- markdown --
+Text.
+
+ 1. List
+
+2\. Not indented, not a list.
+
+ 3. Another list.
+
+-- html --
+<p>Text.
+<ol>
+<li>List
+</ol>
+<p>2. Not indented, not a list.
+<ol>
+<li value="3">Another list.
+</ol>
diff --git a/src/go/doc/comment/testdata/list5.txt b/src/go/doc/comment/testdata/list5.txt
new file mode 100644
index 0000000..a5128e5
--- /dev/null
+++ b/src/go/doc/comment/testdata/list5.txt
@@ -0,0 +1,40 @@
+-- input --
+Text.
+
+  1. One
+  999999999999999999999. Big
+  1000000000000000000000. Bigger
+  1000000000000000000001. Biggest
+
+-- gofmt --
+Text.
+
+ 1. One
+ 999999999999999999999. Big
+ 1000000000000000000000. Bigger
+ 1000000000000000000001. Biggest
+
+-- text --
+Text.
+
+ 1. One
+ 999999999999999999999. Big
+ 1000000000000000000000. Bigger
+ 1000000000000000000001. Biggest
+
+-- markdown --
+Text.
+
+ 1. One
+ 999999999999999999999. Big
+ 1000000000000000000000. Bigger
+ 1000000000000000000001. Biggest
+
+-- html --
+<p>Text.
+<ol>
+<li>One
+<li value="999999999999999999999">Big
+<li>Bigger
+<li>Biggest
+</ol>
diff --git a/src/go/doc/comment/testdata/list6.txt b/src/go/doc/comment/testdata/list6.txt
new file mode 100644
index 0000000..ffc0122
--- /dev/null
+++ b/src/go/doc/comment/testdata/list6.txt
@@ -0,0 +1,129 @@
+-- input --
+Text.
+ - List immediately after.
+ - Another.
+
+More text.
+
+ - List after blank line.
+ - Another.
+
+Even more text.
+ - List immediately after.
+
+ - Blank line between items.
+
+Yet more text.
+
+ - Another list after blank line.
+
+ - Blank line between items.
+
+Still more text.
+ - One list item.
+
+   Multiple paragraphs.
+-- dump --
+Doc
+	Paragraph
+		Plain "Text."
+	List ForceBlankBefore=false ForceBlankBetween=false
+		Item Number=""
+			Paragraph
+				Plain "List immediately after."
+		Item Number=""
+			Paragraph
+				Plain "Another."
+	Paragraph
+		Plain "More text."
+	List ForceBlankBefore=true ForceBlankBetween=false
+		Item Number=""
+			Paragraph
+				Plain "List after blank line."
+		Item Number=""
+			Paragraph
+				Plain "Another."
+	Paragraph
+		Plain "Even more text."
+	List ForceBlankBefore=false ForceBlankBetween=true
+		Item Number=""
+			Paragraph
+				Plain "List immediately after."
+		Item Number=""
+			Paragraph
+				Plain "Blank line between items."
+	Paragraph
+		Plain "Yet more text."
+	List ForceBlankBefore=true ForceBlankBetween=true
+		Item Number=""
+			Paragraph
+				Plain "Another list after blank line."
+		Item Number=""
+			Paragraph
+				Plain "Blank line between items."
+	Paragraph
+		Plain "Still more text."
+	List ForceBlankBefore=false ForceBlankBetween=true
+		Item Number=""
+			Paragraph
+				Plain "One list item."
+			Paragraph
+				Plain "Multiple paragraphs."
+
+-- gofmt --
+Text.
+  - List immediately after.
+  - Another.
+
+More text.
+
+  - List after blank line.
+  - Another.
+
+Even more text.
+
+  - List immediately after.
+
+  - Blank line between items.
+
+Yet more text.
+
+  - Another list after blank line.
+
+  - Blank line between items.
+
+Still more text.
+
+  - One list item.
+
+    Multiple paragraphs.
+
+-- markdown --
+Text.
+
+  - List immediately after.
+  - Another.
+
+More text.
+
+  - List after blank line.
+  - Another.
+
+Even more text.
+
+  - List immediately after.
+
+  - Blank line between items.
+
+Yet more text.
+
+  - Another list after blank line.
+
+  - Blank line between items.
+
+Still more text.
+
+  - One list item.
+
+    Multiple paragraphs.
+
diff --git a/src/go/doc/comment/testdata/list7.txt b/src/go/doc/comment/testdata/list7.txt
new file mode 100644
index 0000000..4466050
--- /dev/null
+++ b/src/go/doc/comment/testdata/list7.txt
@@ -0,0 +1,98 @@
+-- input --
+Almost list markers (but not quite):
+
+ -
+
+❦
+
+ - $
+
+❦
+
+ - $
+
+❦
+
+  $
+   $
+
+❦
+
+ 1! List.
+
+❦
+-- gofmt --
+Almost list markers (but not quite):
+
+	-
+
+❦
+
+	- $
+
+❦
+
+	- $
+
+❦
+
+❦
+
+	1! List.
+
+❦
+-- text --
+Almost list markers (but not quite):
+
+	-
+
+❦
+
+	-
+
+❦
+
+	-
+
+❦
+
+❦
+
+	1! List.
+
+❦
+-- markdown --
+Almost list markers (but not quite):
+
+	-
+
+❦
+
+	- $
+
+❦
+
+	- $
+
+❦
+
+❦
+
+	1! List.
+
+❦
+-- html --
+<p>Almost list markers (but not quite):
+<pre>-
+</pre>
+<p>❦
+<pre>- $
+</pre>
+<p>❦
+<pre>- $
+</pre>
+<p>❦
+<p>❦
+<pre>1! List.
+</pre>
+<p>❦
diff --git a/src/go/doc/comment/testdata/list8.txt b/src/go/doc/comment/testdata/list8.txt
new file mode 100644
index 0000000..fc46b0d
--- /dev/null
+++ b/src/go/doc/comment/testdata/list8.txt
@@ -0,0 +1,56 @@
+-- input --
+Loose lists.
+  - A
+
+    B
+  - C
+    D
+  - E
+  - F
+-- gofmt --
+Loose lists.
+
+  - A
+
+    B
+
+  - C
+    D
+
+  - E
+
+  - F
+-- text --
+Loose lists.
+
+  - A
+
+    B
+
+  - C D
+
+  - E
+
+  - F
+-- markdown --
+Loose lists.
+
+  - A
+
+    B
+
+  - C D
+
+  - E
+
+  - F
+-- html --
+<p>Loose lists.
+<ul>
+<li><p>A
+<p>B
+<li><p>C
+D
+<li><p>E
+<li><p>F
+</ul>
diff --git a/src/go/doc/comment/testdata/list9.txt b/src/go/doc/comment/testdata/list9.txt
new file mode 100644
index 0000000..48e4673
--- /dev/null
+++ b/src/go/doc/comment/testdata/list9.txt
@@ -0,0 +1,30 @@
+-- input --
+Text.
+
+1. Not a list
+2. because it is
+3. unindented.
+
+4. This one
+  is a list
+  because of the indented text.
+5. More wrapped
+  items.
+6. And unwrapped.
+
+7. The blank line stops the heuristic.
+-- gofmt --
+Text.
+
+1. Not a list
+2. because it is
+3. unindented.
+
+ 4. This one
+    is a list
+    because of the indented text.
+ 5. More wrapped
+    items.
+ 6. And unwrapped.
+
+7. The blank line stops the heuristic.
diff --git a/src/go/doc/comment/testdata/para.txt b/src/go/doc/comment/testdata/para.txt
new file mode 100644
index 0000000..2355fa8
--- /dev/null
+++ b/src/go/doc/comment/testdata/para.txt
@@ -0,0 +1,17 @@
+-- input --
+Hello, world.
+This is a paragraph.
+
+-- gofmt --
+Hello, world.
+This is a paragraph.
+
+-- text --
+Hello, world. This is a paragraph.
+
+-- markdown --
+Hello, world. This is a paragraph.
+
+-- html --
+<p>Hello, world.
+This is a paragraph.
diff --git a/src/go/doc/comment/testdata/quote.txt b/src/go/doc/comment/testdata/quote.txt
new file mode 100644
index 0000000..b64adae
--- /dev/null
+++ b/src/go/doc/comment/testdata/quote.txt
@@ -0,0 +1,15 @@
+-- input --
+Doubled single quotes like `` and '' turn into Unicode double quotes,
+but single quotes ` and ' do not.
+Misplaced markdown fences ``` do not either.
+-- gofmt --
+Doubled single quotes like “ and ” turn into Unicode double quotes,
+but single quotes ` and ' do not.
+Misplaced markdown fences ``` do not either.
+-- text --
+Doubled single quotes like “ and ” turn into Unicode double quotes, but single
+quotes ` and ' do not. Misplaced markdown fences ``` do not either.
+-- html --
+<p>Doubled single quotes like “ and ” turn into Unicode double quotes,
+but single quotes ` and &apos; do not.
+Misplaced markdown fences ``` do not either.
diff --git a/src/go/doc/comment/testdata/text.txt b/src/go/doc/comment/testdata/text.txt
new file mode 100644
index 0000000..c4de6e2
--- /dev/null
+++ b/src/go/doc/comment/testdata/text.txt
@@ -0,0 +1,62 @@
+{"TextPrefix":"|", "TextCodePrefix": "@"}
+-- input --
+Hello, world
+ Code block here.
+More text.
+Tight list
+ - one
+ - two
+ - three
+Loose list
+ - one
+
+ - two
+
+ - three
+
+# Heading
+
+More text.
+-- gofmt --
+Hello, world
+
+	Code block here.
+
+More text.
+Tight list
+  - one
+  - two
+  - three
+
+Loose list
+
+  - one
+
+  - two
+
+  - three
+
+# Heading
+
+More text.
+-- text --
+|Hello, world
+|
+@Code block here.
+|
+|More text. Tight list
+|  - one
+|  - two
+|  - three
+|
+|Loose list
+|
+|  - one
+|
+|  - two
+|
+|  - three
+|
+|# Heading
+|
+|More text.
diff --git a/src/go/doc/comment/testdata/text2.txt b/src/go/doc/comment/testdata/text2.txt
new file mode 100644
index 0000000..a099d0b
--- /dev/null
+++ b/src/go/doc/comment/testdata/text2.txt
@@ -0,0 +1,14 @@
+{"TextWidth": -1}
+-- input --
+Package gob manages streams of gobs - binary values exchanged between an
+Encoder (transmitter) and a Decoder (receiver). A typical use is
+transporting arguments and results of remote procedure calls (RPCs) such as
+those provided by package "net/rpc".
+
+The implementation compiles a custom codec for each data type in the stream
+and is most efficient when a single Encoder is used to transmit a stream of
+values, amortizing the cost of compilation.
+-- text --
+Package gob manages streams of gobs - binary values exchanged between an Encoder (transmitter) and a Decoder (receiver). A typical use is transporting arguments and results of remote procedure calls (RPCs) such as those provided by package "net/rpc".
+
+The implementation compiles a custom codec for each data type in the stream and is most efficient when a single Encoder is used to transmit a stream of values, amortizing the cost of compilation.
diff --git a/src/go/doc/comment/testdata/text3.txt b/src/go/doc/comment/testdata/text3.txt
new file mode 100644
index 0000000..75d2c37
--- /dev/null
+++ b/src/go/doc/comment/testdata/text3.txt
@@ -0,0 +1,28 @@
+{"TextWidth": 30}
+-- input --
+Package gob manages streams of gobs - binary values exchanged between an
+Encoder (transmitter) and a Decoder (receiver). A typical use is
+transporting arguments and results of remote procedure calls (RPCs) such as
+those provided by package "net/rpc".
+
+The implementation compiles a custom codec for each data type in the stream
+and is most efficient when a single Encoder is used to transmit a stream of
+values, amortizing the cost of compilation.
+-- text --
+Package gob manages streams
+of gobs - binary values
+exchanged between an Encoder
+(transmitter) and a Decoder
+(receiver). A typical use is
+transporting arguments and
+results of remote procedure
+calls (RPCs) such as those
+provided by package "net/rpc".
+
+The implementation compiles
+a custom codec for each data
+type in the stream and is
+most efficient when a single
+Encoder is used to transmit a
+stream of values, amortizing
+the cost of compilation.
diff --git a/src/go/doc/comment/testdata/text4.txt b/src/go/doc/comment/testdata/text4.txt
new file mode 100644
index 0000000..e429985
--- /dev/null
+++ b/src/go/doc/comment/testdata/text4.txt
@@ -0,0 +1,29 @@
+{"TextWidth": 29}
+-- input --
+Package gob manages streams of gobs - binary values exchanged between an
+Encoder (transmitter) and a Decoder (receiver). A typical use is
+transporting arguments and results of remote procedure calls (RPCs) such as
+those provided by package "net/rpc".
+
+The implementation compiles a custom codec for each data type in the stream
+and is most efficient when a single Encoder is used to transmit a stream of
+values, amortizing the cost of compilation.
+-- text --
+Package gob manages streams
+of gobs - binary values
+exchanged between an Encoder
+(transmitter) and a Decoder
+(receiver). A typical use
+is transporting arguments
+and results of remote
+procedure calls (RPCs) such
+as those provided by package
+"net/rpc".
+
+The implementation compiles
+a custom codec for each data
+type in the stream and is
+most efficient when a single
+Encoder is used to transmit a
+stream of values, amortizing
+the cost of compilation.
diff --git a/src/go/doc/comment/testdata/text5.txt b/src/go/doc/comment/testdata/text5.txt
new file mode 100644
index 0000000..2408fc5
--- /dev/null
+++ b/src/go/doc/comment/testdata/text5.txt
@@ -0,0 +1,38 @@
+{"TextWidth": 20}
+-- input --
+Package gob manages streams of gobs - binary values exchanged between an
+Encoder (transmitter) and a Decoder (receiver). A typical use is
+transporting arguments and results of remote procedure calls (RPCs) such as
+those provided by package "net/rpc".
+
+The implementation compiles a custom codec for each data type in the stream
+and is most efficient when a single Encoder is used to transmit a stream of
+values, amortizing the cost of compilation.
+-- text --
+Package gob
+manages streams
+of gobs - binary
+values exchanged
+between an Encoder
+(transmitter) and a
+Decoder (receiver).
+A typical use
+is transporting
+arguments and
+results of remote
+procedure calls
+(RPCs) such as those
+provided by package
+"net/rpc".
+
+The implementation
+compiles a custom
+codec for each
+data type in the
+stream and is most
+efficient when a
+single Encoder is
+used to transmit a
+stream of values,
+amortizing the cost
+of compilation.
diff --git a/src/go/doc/comment/testdata/text6.txt b/src/go/doc/comment/testdata/text6.txt
new file mode 100644
index 0000000..d6deff5
--- /dev/null
+++ b/src/go/doc/comment/testdata/text6.txt
@@ -0,0 +1,18 @@
+-- input --
+Package gob manages streams of gobs - binary values exchanged between an
+Encoder (transmitter) and a Decoder (receiver). A typical use is
+transporting arguments and results of remote procedure calls (RPCs) such as
+those provided by package "net/rpc".
+
+The implementation compiles a custom codec for each data type in the stream
+and is most efficient when a single Encoder is used to transmit a stream of
+values, amortizing the cost of compilation.
+-- text --
+Package gob manages streams of gobs - binary values exchanged between an Encoder
+(transmitter) and a Decoder (receiver). A typical use is transporting arguments
+and results of remote procedure calls (RPCs) such as those provided by package
+"net/rpc".
+
+The implementation compiles a custom codec for each data type in the stream and
+is most efficient when a single Encoder is used to transmit a stream of values,
+amortizing the cost of compilation.
diff --git a/src/go/doc/comment/testdata/text7.txt b/src/go/doc/comment/testdata/text7.txt
new file mode 100644
index 0000000..c9fb6d3
--- /dev/null
+++ b/src/go/doc/comment/testdata/text7.txt
@@ -0,0 +1,21 @@
+{"TextPrefix": "                    "}
+-- input --
+Package gob manages streams of gobs - binary values exchanged between an
+Encoder (transmitter) and a Decoder (receiver). A typical use is
+transporting arguments and results of remote procedure calls (RPCs) such as
+those provided by package "net/rpc".
+
+The implementation compiles a custom codec for each data type in the stream
+and is most efficient when a single Encoder is used to transmit a stream of
+values, amortizing the cost of compilation.
+-- text --
+                    Package gob manages streams of gobs - binary values
+                    exchanged between an Encoder (transmitter) and a Decoder
+                    (receiver). A typical use is transporting arguments and
+                    results of remote procedure calls (RPCs) such as those
+                    provided by package "net/rpc".
+
+                    The implementation compiles a custom codec for each data
+                    type in the stream and is most efficient when a single
+                    Encoder is used to transmit a stream of values, amortizing
+                    the cost of compilation.
diff --git a/src/go/doc/comment/testdata/text8.txt b/src/go/doc/comment/testdata/text8.txt
new file mode 100644
index 0000000..560ac95
--- /dev/null
+++ b/src/go/doc/comment/testdata/text8.txt
@@ -0,0 +1,94 @@
+{"TextWidth": 40}
+-- input --
+If the arguments have version suffixes (like @latest or @v1.0.0), "go install"
+builds packages in module-aware mode, ignoring the go.mod file in the current
+directory or any parent directory, if there is one. This is useful for
+installing executables without affecting the dependencies of the main module.
+To eliminate ambiguity about which module versions are used in the build, the
+arguments must satisfy the following constraints:
+
+ - Arguments must be package paths or package patterns (with "..." wildcards).
+ They must not be standard packages (like fmt), meta-patterns (std, cmd,
+ all), or relative or absolute file paths.
+
+ - All arguments must have the same version suffix. Different queries are not
+ allowed, even if they refer to the same version.
+
+ - All arguments must refer to packages in the same module at the same version.
+
+ - Package path arguments must refer to main packages. Pattern arguments
+ will only match main packages.
+
+ - No module is considered the "main" module. If the module containing
+ packages named on the command line has a go.mod file, it must not contain
+ directives (replace and exclude) that would cause it to be interpreted
+ differently than if it were the main module. The module must not require
+ a higher version of itself.
+
+ - Vendor directories are not used in any module. (Vendor directories are not
+ included in the module zip files downloaded by 'go install'.)
+
+If the arguments don't have version suffixes, "go install" may run in
+module-aware mode or GOPATH mode, depending on the GO111MODULE environment
+variable and the presence of a go.mod file. See 'go help modules' for details.
+If module-aware mode is enabled, "go install" runs in the context of the main
+module.
+-- text --
+If the arguments have version suffixes
+(like @latest or @v1.0.0), "go install"
+builds packages in module-aware mode,
+ignoring the go.mod file in the current
+directory or any parent directory,
+if there is one. This is useful for
+installing executables without affecting
+the dependencies of the main module.
+To eliminate ambiguity about which
+module versions are used in the build,
+the arguments must satisfy the following
+constraints:
+
+  - Arguments must be package paths
+    or package patterns (with "..."
+    wildcards). They must not be
+    standard packages (like fmt),
+    meta-patterns (std, cmd, all),
+    or relative or absolute file paths.
+
+  - All arguments must have the same
+    version suffix. Different queries
+    are not allowed, even if they refer
+    to the same version.
+
+  - All arguments must refer to packages
+    in the same module at the same
+    version.
+
+  - Package path arguments must refer
+    to main packages. Pattern arguments
+    will only match main packages.
+
+  - No module is considered the "main"
+    module. If the module containing
+    packages named on the command line
+    has a go.mod file, it must not
+    contain directives (replace and
+    exclude) that would cause it to be
+    interpreted differently than if it
+    were the main module. The module
+    must not require a higher version of
+    itself.
+
+  - Vendor directories are not used in
+    any module. (Vendor directories are
+    not included in the module zip files
+    downloaded by 'go install'.)
+
+If the arguments don't have version
+suffixes, "go install" may run in
+module-aware mode or GOPATH mode,
+depending on the GO111MODULE environment
+variable and the presence of a go.mod
+file. See 'go help modules' for details.
+If module-aware mode is enabled,
+"go install" runs in the context of the
+main module.
diff --git a/src/go/doc/comment/testdata/text9.txt b/src/go/doc/comment/testdata/text9.txt
new file mode 100644
index 0000000..07a64aa
--- /dev/null
+++ b/src/go/doc/comment/testdata/text9.txt
@@ -0,0 +1,12 @@
+{"TextPrefix":"|", "TextCodePrefix": "@"}
+-- input --
+Hello, world
+ Code block here.
+-- gofmt --
+Hello, world
+
+	Code block here.
+-- text --
+|Hello, world
+|
+@Code block here.
diff --git a/src/go/doc/comment/testdata/words.txt b/src/go/doc/comment/testdata/words.txt
new file mode 100644
index 0000000..63c7e1a
--- /dev/null
+++ b/src/go/doc/comment/testdata/words.txt
@@ -0,0 +1,10 @@
+-- input --
+This is an italicword and a linkedword and Unicöde.
+-- gofmt --
+This is an italicword and a linkedword and Unicöde.
+-- text --
+This is an italicword and a linkedword and Unicöde.
+-- markdown --
+This is an *italicword* and a [*linkedword*](https://example.com/linkedword) and Unicöde.
+-- html --
+<p>This is an <i>italicword</i> and a <a href="https://example.com/linkedword"><i>linkedword</i></a> and Unicöde.
diff --git a/src/go/doc/comment/testdata_test.go b/src/go/doc/comment/testdata_test.go
new file mode 100644
index 0000000..0676d86
--- /dev/null
+++ b/src/go/doc/comment/testdata_test.go
@@ -0,0 +1,202 @@
+// 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"
+	"encoding/json"
+	"fmt"
+	"internal/diff"
+	"internal/txtar"
+	"path/filepath"
+	"strings"
+	"testing"
+)
+
+func TestTestdata(t *testing.T) {
+	files, _ := filepath.Glob("testdata/*.txt")
+	if len(files) == 0 {
+		t.Fatalf("no testdata")
+	}
+	var p Parser
+	p.Words = map[string]string{
+		"italicword": "",
+		"linkedword": "https://example.com/linkedword",
+	}
+	p.LookupPackage = func(name string) (importPath string, ok bool) {
+		if name == "comment" {
+			return "go/doc/comment", true
+		}
+		return DefaultLookupPackage(name)
+	}
+	p.LookupSym = func(recv, name string) (ok bool) {
+		if recv == "Parser" && name == "Parse" ||
+			recv == "" && name == "Doc" ||
+			recv == "" && name == "NoURL" {
+			return true
+		}
+		return false
+	}
+
+	stripDollars := func(b []byte) []byte {
+		// Remove trailing $ on lines.
+		// They make it easier to see lines with trailing spaces,
+		// as well as turning them into lines without trailing spaces,
+		// in case editors remove trailing spaces.
+		return bytes.ReplaceAll(b, []byte("$\n"), []byte("\n"))
+	}
+	for _, file := range files {
+		t.Run(filepath.Base(file), func(t *testing.T) {
+			var pr Printer
+			a, err := txtar.ParseFile(file)
+			if err != nil {
+				t.Fatal(err)
+			}
+			if len(a.Comment) > 0 {
+				err := json.Unmarshal(a.Comment, &pr)
+				if err != nil {
+					t.Fatalf("unmarshalling top json: %v", err)
+				}
+			}
+			if len(a.Files) < 1 || a.Files[0].Name != "input" {
+				t.Fatalf("first file is not %q", "input")
+			}
+			d := p.Parse(string(stripDollars(a.Files[0].Data)))
+			for _, f := range a.Files[1:] {
+				want := stripDollars(f.Data)
+				for len(want) >= 2 && want[len(want)-1] == '\n' && want[len(want)-2] == '\n' {
+					want = want[:len(want)-1]
+				}
+				var out []byte
+				switch f.Name {
+				default:
+					t.Fatalf("unknown output file %q", f.Name)
+				case "dump":
+					out = dump(d)
+				case "gofmt":
+					out = pr.Comment(d)
+				case "html":
+					out = pr.HTML(d)
+				case "markdown":
+					out = pr.Markdown(d)
+				case "text":
+					out = pr.Text(d)
+				}
+				if string(out) != string(want) {
+					t.Errorf("%s: %s", file, diff.Diff(f.Name, want, "have", out))
+				}
+			}
+		})
+	}
+}
+
+func dump(d *Doc) []byte {
+	var out bytes.Buffer
+	dumpTo(&out, 0, d)
+	return out.Bytes()
+}
+
+func dumpTo(out *bytes.Buffer, indent int, x any) {
+	switch x := x.(type) {
+	default:
+		fmt.Fprintf(out, "?%T", x)
+
+	case *Doc:
+		fmt.Fprintf(out, "Doc")
+		dumpTo(out, indent+1, x.Content)
+		if len(x.Links) > 0 {
+			dumpNL(out, indent+1)
+			fmt.Fprintf(out, "Links")
+			dumpTo(out, indent+2, x.Links)
+		}
+		fmt.Fprintf(out, "\n")
+
+	case []*LinkDef:
+		for _, def := range x {
+			dumpNL(out, indent)
+			dumpTo(out, indent, def)
+		}
+
+	case *LinkDef:
+		fmt.Fprintf(out, "LinkDef Used:%v Text:%q URL:%s", x.Used, x.Text, x.URL)
+
+	case []Block:
+		for _, blk := range x {
+			dumpNL(out, indent)
+			dumpTo(out, indent, blk)
+		}
+
+	case *Heading:
+		fmt.Fprintf(out, "Heading")
+		dumpTo(out, indent+1, x.Text)
+
+	case *List:
+		fmt.Fprintf(out, "List ForceBlankBefore=%v ForceBlankBetween=%v", x.ForceBlankBefore, x.ForceBlankBetween)
+		dumpTo(out, indent+1, x.Items)
+
+	case []*ListItem:
+		for _, item := range x {
+			dumpNL(out, indent)
+			dumpTo(out, indent, item)
+		}
+
+	case *ListItem:
+		fmt.Fprintf(out, "Item Number=%q", x.Number)
+		dumpTo(out, indent+1, x.Content)
+
+	case *Paragraph:
+		fmt.Fprintf(out, "Paragraph")
+		dumpTo(out, indent+1, x.Text)
+
+	case *Code:
+		fmt.Fprintf(out, "Code")
+		dumpTo(out, indent+1, x.Text)
+
+	case []Text:
+		for _, t := range x {
+			dumpNL(out, indent)
+			dumpTo(out, indent, t)
+		}
+
+	case Plain:
+		if !strings.Contains(string(x), "\n") {
+			fmt.Fprintf(out, "Plain %q", string(x))
+		} else {
+			fmt.Fprintf(out, "Plain")
+			dumpTo(out, indent+1, string(x))
+		}
+
+	case Italic:
+		if !strings.Contains(string(x), "\n") {
+			fmt.Fprintf(out, "Italic %q", string(x))
+		} else {
+			fmt.Fprintf(out, "Italic")
+			dumpTo(out, indent+1, string(x))
+		}
+
+	case string:
+		for _, line := range strings.SplitAfter(x, "\n") {
+			if line != "" {
+				dumpNL(out, indent)
+				fmt.Fprintf(out, "%q", line)
+			}
+		}
+
+	case *Link:
+		fmt.Fprintf(out, "Link %q", x.URL)
+		dumpTo(out, indent+1, x.Text)
+
+	case *DocLink:
+		fmt.Fprintf(out, "DocLink pkg:%q, recv:%q, name:%q", x.ImportPath, x.Recv, x.Name)
+		dumpTo(out, indent+1, x.Text)
+	}
+}
+
+func dumpNL(out *bytes.Buffer, n int) {
+	out.WriteByte('\n')
+	for i := 0; i < n; i++ {
+		out.WriteByte('\t')
+	}
+}
diff --git a/src/go/doc/comment/text.go b/src/go/doc/comment/text.go
new file mode 100644
index 0000000..6f9c2e2
--- /dev/null
+++ b/src/go/doc/comment/text.go
@@ -0,0 +1,337 @@
+// 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"
+	"sort"
+	"strings"
+	"unicode/utf8"
+)
+
+// A textPrinter holds the state needed for printing a Doc as plain text.
+type textPrinter struct {
+	*Printer
+	long       strings.Builder
+	prefix     string
+	codePrefix string
+	width      int
+}
+
+// Text returns a textual formatting of the Doc.
+// See the [Printer] documentation for ways to customize the text output.
+func (p *Printer) Text(d *Doc) []byte {
+	tp := &textPrinter{
+		Printer:    p,
+		prefix:     p.TextPrefix,
+		codePrefix: p.TextCodePrefix,
+		width:      p.TextWidth,
+	}
+	if tp.codePrefix == "" {
+		tp.codePrefix = p.TextPrefix + "\t"
+	}
+	if tp.width == 0 {
+		tp.width = 80 - utf8.RuneCountInString(tp.prefix)
+	}
+
+	var out bytes.Buffer
+	for i, x := range d.Content {
+		if i > 0 && blankBefore(x) {
+			out.WriteString(tp.prefix)
+			writeNL(&out)
+		}
+		tp.block(&out, x)
+	}
+	anyUsed := false
+	for _, def := range d.Links {
+		if def.Used {
+			anyUsed = true
+			break
+		}
+	}
+	if anyUsed {
+		writeNL(&out)
+		for _, def := range d.Links {
+			if def.Used {
+				fmt.Fprintf(&out, "[%s]: %s\n", def.Text, def.URL)
+			}
+		}
+	}
+	return out.Bytes()
+}
+
+// writeNL calls out.WriteByte('\n')
+// but first trims trailing spaces on the previous line.
+func writeNL(out *bytes.Buffer) {
+	// Trim trailing spaces.
+	data := out.Bytes()
+	n := 0
+	for n < len(data) && (data[len(data)-n-1] == ' ' || data[len(data)-n-1] == '\t') {
+		n++
+	}
+	if n > 0 {
+		out.Truncate(len(data) - n)
+	}
+	out.WriteByte('\n')
+}
+
+// block prints the block x to out.
+func (p *textPrinter) block(out *bytes.Buffer, x Block) {
+	switch x := x.(type) {
+	default:
+		fmt.Fprintf(out, "?%T\n", x)
+
+	case *Paragraph:
+		out.WriteString(p.prefix)
+		p.text(out, "", x.Text)
+
+	case *Heading:
+		out.WriteString(p.prefix)
+		out.WriteString("# ")
+		p.text(out, "", x.Text)
+
+	case *Code:
+		text := x.Text
+		for text != "" {
+			var line string
+			line, text, _ = strings.Cut(text, "\n")
+			if line != "" {
+				out.WriteString(p.codePrefix)
+				out.WriteString(line)
+			}
+			writeNL(out)
+		}
+
+	case *List:
+		loose := x.BlankBetween()
+		for i, item := range x.Items {
+			if i > 0 && loose {
+				out.WriteString(p.prefix)
+				writeNL(out)
+			}
+			out.WriteString(p.prefix)
+			out.WriteString(" ")
+			if item.Number == "" {
+				out.WriteString(" - ")
+			} else {
+				out.WriteString(item.Number)
+				out.WriteString(". ")
+			}
+			for i, blk := range item.Content {
+				const fourSpace = "    "
+				if i > 0 {
+					writeNL(out)
+					out.WriteString(p.prefix)
+					out.WriteString(fourSpace)
+				}
+				p.text(out, fourSpace, blk.(*Paragraph).Text)
+			}
+		}
+	}
+}
+
+// text prints the text sequence x to out.
+func (p *textPrinter) text(out *bytes.Buffer, indent string, x []Text) {
+	p.oneLongLine(&p.long, x)
+	words := strings.Fields(p.long.String())
+	p.long.Reset()
+
+	var seq []int
+	if p.width < 0 || len(words) == 0 {
+		seq = []int{0, len(words)} // one long line
+	} else {
+		seq = wrap(words, p.width-utf8.RuneCountInString(indent))
+	}
+	for i := 0; i+1 < len(seq); i++ {
+		if i > 0 {
+			out.WriteString(p.prefix)
+			out.WriteString(indent)
+		}
+		for j, w := range words[seq[i]:seq[i+1]] {
+			if j > 0 {
+				out.WriteString(" ")
+			}
+			out.WriteString(w)
+		}
+		writeNL(out)
+	}
+}
+
+// oneLongLine prints the text sequence x to out as one long line,
+// without worrying about line wrapping.
+// Explicit links have the [ ] dropped to improve readability.
+func (p *textPrinter) oneLongLine(out *strings.Builder, x []Text) {
+	for _, t := range x {
+		switch t := t.(type) {
+		case Plain:
+			out.WriteString(string(t))
+		case Italic:
+			out.WriteString(string(t))
+		case *Link:
+			p.oneLongLine(out, t.Text)
+		case *DocLink:
+			p.oneLongLine(out, t.Text)
+		}
+	}
+}
+
+// wrap wraps words into lines of at most max runes,
+// minimizing the sum of the squares of the leftover lengths
+// at the end of each line (except the last, of course),
+// with a preference for ending lines at punctuation (.,:;).
+//
+// The returned slice gives the indexes of the first words
+// on each line in the wrapped text with a final entry of len(words).
+// Thus the lines are words[seq[0]:seq[1]], words[seq[1]:seq[2]],
+// ..., words[seq[len(seq)-2]:seq[len(seq)-1]].
+//
+// The implementation runs in O(n log n) time, where n = len(words),
+// using the algorithm described in D. S. Hirschberg and L. L. Larmore,
+// “[The least weight subsequence problem],” FOCS 1985, pp. 137-143.
+//
+// [The least weight subsequence problem]: https://doi.org/10.1109/SFCS.1985.60
+func wrap(words []string, max int) (seq []int) {
+	// The algorithm requires that our scoring function be concave,
+	// meaning that for all i₀ ≤ i₁ < j₀ ≤ j₁,
+	// weight(i₀, j₀) + weight(i₁, j₁) ≤ weight(i₀, j₁) + weight(i₁, j₀).
+	//
+	// Our weights are two-element pairs [hi, lo]
+	// ordered by elementwise comparison.
+	// The hi entry counts the weight for lines that are longer than max,
+	// and the lo entry counts the weight for lines that are not.
+	// This forces the algorithm to first minimize the number of lines
+	// that are longer than max, which correspond to lines with
+	// single very long words. Having done that, it can move on to
+	// minimizing the lo score, which is more interesting.
+	//
+	// The lo score is the sum for each line of the square of the
+	// number of spaces remaining at the end of the line and a
+	// penalty of 64 given out for not ending the line in a
+	// punctuation character (.,:;).
+	// The penalty is somewhat arbitrarily chosen by trying
+	// different amounts and judging how nice the wrapped text looks.
+	// Roughly speaking, using 64 means that we are willing to
+	// end a line with eight blank spaces in order to end at a
+	// punctuation character, even if the next word would fit in
+	// those spaces.
+	//
+	// We care about ending in punctuation characters because
+	// it makes the text easier to skim if not too many sentences
+	// or phrases begin with a single word on the previous line.
+
+	// A score is the score (also called weight) for a given line.
+	// add and cmp add and compare scores.
+	type score struct {
+		hi int64
+		lo int64
+	}
+	add := func(s, t score) score { return score{s.hi + t.hi, s.lo + t.lo} }
+	cmp := func(s, t score) int {
+		switch {
+		case s.hi < t.hi:
+			return -1
+		case s.hi > t.hi:
+			return +1
+		case s.lo < t.lo:
+			return -1
+		case s.lo > t.lo:
+			return +1
+		}
+		return 0
+	}
+
+	// total[j] is the total number of runes
+	// (including separating spaces) in words[:j].
+	total := make([]int, len(words)+1)
+	total[0] = 0
+	for i, s := range words {
+		total[1+i] = total[i] + utf8.RuneCountInString(s) + 1
+	}
+
+	// weight returns weight(i, j).
+	weight := func(i, j int) score {
+		// On the last line, there is zero weight for being too short.
+		n := total[j] - 1 - total[i]
+		if j == len(words) && n <= max {
+			return score{0, 0}
+		}
+
+		// Otherwise the weight is the penalty plus the square of the number of
+		// characters remaining on the line or by which the line goes over.
+		// In the latter case, that value goes in the hi part of the score.
+		// (See note above.)
+		p := wrapPenalty(words[j-1])
+		v := int64(max-n) * int64(max-n)
+		if n > max {
+			return score{v, p}
+		}
+		return score{0, v + p}
+	}
+
+	// The rest of this function is “The Basic Algorithm” from
+	// Hirschberg and Larmore's conference paper,
+	// using the same names as in the paper.
+	f := []score{{0, 0}}
+	g := func(i, j int) score { return add(f[i], weight(i, j)) }
+
+	bridge := func(a, b, c int) bool {
+		k := c + sort.Search(len(words)+1-c, func(k int) bool {
+			k += c
+			return cmp(g(a, k), g(b, k)) > 0
+		})
+		if k > len(words) {
+			return true
+		}
+		return cmp(g(c, k), g(b, k)) <= 0
+	}
+
+	// d is a one-ended deque implemented as a slice.
+	d := make([]int, 1, len(words))
+	d[0] = 0
+	bestleft := make([]int, 1, len(words))
+	bestleft[0] = -1
+	for m := 1; m < len(words); m++ {
+		f = append(f, g(d[0], m))
+		bestleft = append(bestleft, d[0])
+		for len(d) > 1 && cmp(g(d[1], m+1), g(d[0], m+1)) <= 0 {
+			d = d[1:] // “Retire”
+		}
+		for len(d) > 1 && bridge(d[len(d)-2], d[len(d)-1], m) {
+			d = d[:len(d)-1] // “Fire”
+		}
+		if cmp(g(m, len(words)), g(d[len(d)-1], len(words))) < 0 {
+			d = append(d, m) // “Hire”
+			// The next few lines are not in the paper but are necessary
+			// to handle two-word inputs correctly. It appears to be
+			// just a bug in the paper's pseudocode.
+			if len(d) == 2 && cmp(g(d[1], m+1), g(d[0], m+1)) <= 0 {
+				d = d[1:]
+			}
+		}
+	}
+	bestleft = append(bestleft, d[0])
+
+	// Recover least weight sequence from bestleft.
+	n := 1
+	for m := len(words); m > 0; m = bestleft[m] {
+		n++
+	}
+	seq = make([]int, n)
+	for m := len(words); m > 0; m = bestleft[m] {
+		n--
+		seq[n] = m
+	}
+	return seq
+}
+
+// wrapPenalty is the penalty for inserting a line break after word s.
+func wrapPenalty(s string) int64 {
+	switch s[len(s)-1] {
+	case '.', ',', ':', ';':
+		return 0
+	}
+	return 64
+}
diff --git a/src/go/doc/comment/wrap_test.go b/src/go/doc/comment/wrap_test.go
new file mode 100644
index 0000000..f9802c9
--- /dev/null
+++ b/src/go/doc/comment/wrap_test.go
@@ -0,0 +1,141 @@
+// 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 (
+	"flag"
+	"fmt"
+	"math/rand"
+	"testing"
+	"time"
+	"unicode/utf8"
+)
+
+var wrapSeed = flag.Int64("wrapseed", 0, "use `seed` for wrap test (default auto-seeds)")
+
+func TestWrap(t *testing.T) {
+	if *wrapSeed == 0 {
+		*wrapSeed = time.Now().UnixNano()
+	}
+	t.Logf("-wrapseed=%#x\n", *wrapSeed)
+	r := rand.New(rand.NewSource(*wrapSeed))
+
+	// Generate words of random length.
+	s := "1234567890αβcdefghijklmnopqrstuvwxyz"
+	sN := utf8.RuneCountInString(s)
+	var words []string
+	for i := 0; i < 100; i++ {
+		n := 1 + r.Intn(sN-1)
+		if n >= 12 {
+			n++ // extra byte for β
+		}
+		if n >= 11 {
+			n++ // extra byte for α
+		}
+		words = append(words, s[:n])
+	}
+
+	for n := 1; n <= len(words) && !t.Failed(); n++ {
+		t.Run(fmt.Sprint("n=", n), func(t *testing.T) {
+			words := words[:n]
+			t.Logf("words: %v", words)
+			for max := 1; max < 100 && !t.Failed(); max++ {
+				t.Run(fmt.Sprint("max=", max), func(t *testing.T) {
+					seq := wrap(words, max)
+
+					// Compute score for seq.
+					start := 0
+					score := int64(0)
+					if len(seq) == 0 {
+						t.Fatalf("wrap seq is empty")
+					}
+					if seq[0] != 0 {
+						t.Fatalf("wrap seq does not start with 0")
+					}
+					for _, n := range seq[1:] {
+						if n <= start {
+							t.Fatalf("wrap seq is non-increasing: %v", seq)
+						}
+						if n > len(words) {
+							t.Fatalf("wrap seq contains %d > %d: %v", n, len(words), seq)
+						}
+						size := -1
+						for _, s := range words[start:n] {
+							size += 1 + utf8.RuneCountInString(s)
+						}
+						if n-start == 1 && size >= max {
+							// no score
+						} else if size > max {
+							t.Fatalf("wrap used overlong line %d:%d: %v", start, n, words[start:n])
+						} else if n != len(words) {
+							score += int64(max-size)*int64(max-size) + wrapPenalty(words[n-1])
+						}
+						start = n
+					}
+					if start != len(words) {
+						t.Fatalf("wrap seq does not use all words (%d < %d): %v", start, len(words), seq)
+					}
+
+					// Check that score matches slow reference implementation.
+					slowSeq, slowScore := wrapSlow(words, max)
+					if score != slowScore {
+						t.Fatalf("wrap score = %d != wrapSlow score %d\nwrap: %v\nslow: %v", score, slowScore, seq, slowSeq)
+					}
+				})
+			}
+		})
+	}
+}
+
+// wrapSlow is an O(n²) reference implementation for wrap.
+// It returns a minimal-score sequence along with the score.
+// It is OK if wrap returns a different sequence as long as that
+// sequence has the same score.
+func wrapSlow(words []string, max int) (seq []int, score int64) {
+	// Quadratic dynamic programming algorithm for line wrapping problem.
+	// best[i] tracks the best score possible for words[:i],
+	// assuming that for i < len(words) the line breaks after those words.
+	// bestleft[i] tracks the previous line break for best[i].
+	best := make([]int64, len(words)+1)
+	bestleft := make([]int, len(words)+1)
+	best[0] = 0
+	for i, w := range words {
+		if utf8.RuneCountInString(w) >= max {
+			// Overlong word must appear on line by itself. No effect on score.
+			best[i+1] = best[i]
+			continue
+		}
+		best[i+1] = 1e18
+		p := wrapPenalty(w)
+		n := -1
+		for j := i; j >= 0; j-- {
+			n += 1 + utf8.RuneCountInString(words[j])
+			if n > max {
+				break
+			}
+			line := int64(n-max)*int64(n-max) + p
+			if i == len(words)-1 {
+				line = 0 // no score for final line being too short
+			}
+			s := best[j] + line
+			if best[i+1] > s {
+				best[i+1] = s
+				bestleft[i+1] = j
+			}
+		}
+	}
+
+	// Recover least weight sequence from bestleft.
+	n := 1
+	for m := len(words); m > 0; m = bestleft[m] {
+		n++
+	}
+	seq = make([]int, n)
+	for m := len(words); m > 0; m = bestleft[m] {
+		n--
+		seq[n] = m
+	}
+	return seq, best[len(words)]
+}
diff --git a/src/go/doc/comment_test.go b/src/go/doc/comment_test.go
new file mode 100644
index 0000000..004ae9d
--- /dev/null
+++ b/src/go/doc/comment_test.go
@@ -0,0 +1,67 @@
+// 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 doc
+
+import (
+	"bytes"
+	"go/parser"
+	"go/token"
+	"internal/diff"
+	"testing"
+)
+
+func TestComment(t *testing.T) {
+	fset := token.NewFileSet()
+	pkgs, err := parser.ParseDir(fset, "testdata/pkgdoc", nil, parser.ParseComments)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if pkgs["pkgdoc"] == nil {
+		t.Fatal("missing package pkgdoc")
+	}
+	pkg := New(pkgs["pkgdoc"], "testdata/pkgdoc", 0)
+
+	var (
+		input           = "[T] and [U] are types, and [T.M] is a method, but [V] is a broken link. [rand.Int] and [crand.Reader] are things. [G.M1] and [G.M2] are generic methods.\n"
+		wantHTML        = `<p><a href="#T">T</a> and <a href="#U">U</a> are types, and <a href="#T.M">T.M</a> is a method, but [V] is a broken link. <a href="/math/rand#Int">rand.Int</a> and <a href="/crypto/rand#Reader">crand.Reader</a> are things. <a href="#G.M1">G.M1</a> and <a href="#G.M2">G.M2</a> are generic methods.` + "\n"
+		wantOldHTML     = "<p>[T] and [U] are <i>types</i>, and [T.M] is a method, but [V] is a broken link. [rand.Int] and [crand.Reader] are things. [G.M1] and [G.M2] are generic methods.\n"
+		wantMarkdown    = "[T](#T) and [U](#U) are types, and [T.M](#T.M) is a method, but \\[V] is a broken link. [rand.Int](/math/rand#Int) and [crand.Reader](/crypto/rand#Reader) are things. [G.M1](#G.M1) and [G.M2](#G.M2) are generic methods.\n"
+		wantText        = "T and U are types, and T.M is a method, but [V] is a broken link. rand.Int and\ncrand.Reader are things. G.M1 and G.M2 are generic methods.\n"
+		wantOldText     = "[T] and [U] are types, and [T.M] is a method, but [V] is a broken link.\n[rand.Int] and [crand.Reader] are things. [G.M1] and [G.M2] are generic methods.\n"
+		wantSynopsis    = "T and U are types, and T.M is a method, but [V] is a broken link."
+		wantOldSynopsis = "[T] and [U] are types, and [T.M] is a method, but [V] is a broken link."
+	)
+
+	if b := pkg.HTML(input); string(b) != wantHTML {
+		t.Errorf("%s", diff.Diff("pkg.HTML", b, "want", []byte(wantHTML)))
+	}
+	if b := pkg.Markdown(input); string(b) != wantMarkdown {
+		t.Errorf("%s", diff.Diff("pkg.Markdown", b, "want", []byte(wantMarkdown)))
+	}
+	if b := pkg.Text(input); string(b) != wantText {
+		t.Errorf("%s", diff.Diff("pkg.Text", b, "want", []byte(wantText)))
+	}
+	if b := pkg.Synopsis(input); b != wantSynopsis {
+		t.Errorf("%s", diff.Diff("pkg.Synopsis", []byte(b), "want", []byte(wantText)))
+	}
+
+	var buf bytes.Buffer
+
+	buf.Reset()
+	ToHTML(&buf, input, map[string]string{"types": ""})
+	if b := buf.Bytes(); string(b) != wantOldHTML {
+		t.Errorf("%s", diff.Diff("ToHTML", b, "want", []byte(wantOldHTML)))
+	}
+
+	buf.Reset()
+	ToText(&buf, input, "", "\t", 80)
+	if b := buf.Bytes(); string(b) != wantOldText {
+		t.Errorf("%s", diff.Diff("ToText", b, "want", []byte(wantOldText)))
+	}
+
+	if b := Synopsis(input); b != wantOldSynopsis {
+		t.Errorf("%s", diff.Diff("Synopsis", []byte(b), "want", []byte(wantOldText)))
+	}
+}
diff --git a/src/go/doc/doc.go b/src/go/doc/doc.go
new file mode 100644
index 0000000..eefadfa
--- /dev/null
+++ b/src/go/doc/doc.go
@@ -0,0 +1,354 @@
+// 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.
+
+// Package doc extracts source code documentation from a Go AST.
+package doc
+
+import (
+	"fmt"
+	"go/ast"
+	"go/doc/comment"
+	"go/token"
+	"strings"
+)
+
+// Package is the documentation for an entire package.
+type Package struct {
+	Doc        string
+	Name       string
+	ImportPath string
+	Imports    []string
+	Filenames  []string
+	Notes      map[string][]*Note
+
+	// Deprecated: For backward compatibility Bugs is still populated,
+	// but all new code should use Notes instead.
+	Bugs []string
+
+	// declarations
+	Consts []*Value
+	Types  []*Type
+	Vars   []*Value
+	Funcs  []*Func
+
+	// Examples is a sorted list of examples associated with
+	// the package. Examples are extracted from _test.go files
+	// provided to NewFromFiles.
+	Examples []*Example
+
+	importByName map[string]string
+	syms         map[string]bool
+}
+
+// Value is the documentation for a (possibly grouped) var or const declaration.
+type Value struct {
+	Doc   string
+	Names []string // var or const names in declaration order
+	Decl  *ast.GenDecl
+
+	order int
+}
+
+// Type is the documentation for a type declaration.
+type Type struct {
+	Doc  string
+	Name string
+	Decl *ast.GenDecl
+
+	// associated declarations
+	Consts  []*Value // sorted list of constants of (mostly) this type
+	Vars    []*Value // sorted list of variables of (mostly) this type
+	Funcs   []*Func  // sorted list of functions returning this type
+	Methods []*Func  // sorted list of methods (including embedded ones) of this type
+
+	// Examples is a sorted list of examples associated with
+	// this type. Examples are extracted from _test.go files
+	// provided to NewFromFiles.
+	Examples []*Example
+}
+
+// Func is the documentation for a func declaration.
+type Func struct {
+	Doc  string
+	Name string
+	Decl *ast.FuncDecl
+
+	// methods
+	// (for functions, these fields have the respective zero value)
+	Recv  string // actual   receiver "T" or "*T" possibly followed by type parameters [P1, ..., Pn]
+	Orig  string // original receiver "T" or "*T"
+	Level int    // embedding level; 0 means not embedded
+
+	// Examples is a sorted list of examples associated with this
+	// function or method. Examples are extracted from _test.go files
+	// provided to NewFromFiles.
+	Examples []*Example
+}
+
+// A Note represents a marked comment starting with "MARKER(uid): note body".
+// Any note with a marker of 2 or more upper case [A-Z] letters and a uid of
+// at least one character is recognized. The ":" following the uid is optional.
+// Notes are collected in the Package.Notes map indexed by the notes marker.
+type Note struct {
+	Pos, End token.Pos // position range of the comment containing the marker
+	UID      string    // uid found with the marker
+	Body     string    // note body text
+}
+
+// Mode values control the operation of New and NewFromFiles.
+type Mode int
+
+const (
+	// AllDecls says to extract documentation for all package-level
+	// declarations, not just exported ones.
+	AllDecls Mode = 1 << iota
+
+	// AllMethods says to show all embedded methods, not just the ones of
+	// invisible (unexported) anonymous fields.
+	AllMethods
+
+	// PreserveAST says to leave the AST unmodified. Originally, pieces of
+	// the AST such as function bodies were nil-ed out to save memory in
+	// godoc, but not all programs want that behavior.
+	PreserveAST
+)
+
+// New computes the package documentation for the given package AST.
+// New takes ownership of the AST pkg and may edit or overwrite it.
+// To have the Examples fields populated, use NewFromFiles and include
+// the package's _test.go files.
+func New(pkg *ast.Package, importPath string, mode Mode) *Package {
+	var r reader
+	r.readPackage(pkg, mode)
+	r.computeMethodSets()
+	r.cleanupTypes()
+	p := &Package{
+		Doc:        r.doc,
+		Name:       pkg.Name,
+		ImportPath: importPath,
+		Imports:    sortedKeys(r.imports),
+		Filenames:  r.filenames,
+		Notes:      r.notes,
+		Bugs:       noteBodies(r.notes["BUG"]),
+		Consts:     sortedValues(r.values, token.CONST),
+		Types:      sortedTypes(r.types, mode&AllMethods != 0),
+		Vars:       sortedValues(r.values, token.VAR),
+		Funcs:      sortedFuncs(r.funcs, true),
+
+		importByName: r.importByName,
+		syms:         make(map[string]bool),
+	}
+
+	p.collectValues(p.Consts)
+	p.collectValues(p.Vars)
+	p.collectTypes(p.Types)
+	p.collectFuncs(p.Funcs)
+
+	return p
+}
+
+func (p *Package) collectValues(values []*Value) {
+	for _, v := range values {
+		for _, name := range v.Names {
+			p.syms[name] = true
+		}
+	}
+}
+
+func (p *Package) collectTypes(types []*Type) {
+	for _, t := range types {
+		if p.syms[t.Name] {
+			// Shouldn't be any cycles but stop just in case.
+			continue
+		}
+		p.syms[t.Name] = true
+		p.collectValues(t.Consts)
+		p.collectValues(t.Vars)
+		p.collectFuncs(t.Funcs)
+		p.collectFuncs(t.Methods)
+	}
+}
+
+func (p *Package) collectFuncs(funcs []*Func) {
+	for _, f := range funcs {
+		if f.Recv != "" {
+			r := strings.TrimPrefix(f.Recv, "*")
+			if i := strings.IndexByte(r, '['); i >= 0 {
+				r = r[:i] // remove type parameters
+			}
+			p.syms[r+"."+f.Name] = true
+		} else {
+			p.syms[f.Name] = true
+		}
+	}
+}
+
+// NewFromFiles computes documentation for a package.
+//
+// The package is specified by a list of *ast.Files and corresponding
+// file set, which must not be nil.
+// NewFromFiles uses all provided files when computing documentation,
+// so it is the caller's responsibility to provide only the files that
+// match the desired build context. "go/build".Context.MatchFile can
+// be used for determining whether a file matches a build context with
+// the desired GOOS and GOARCH values, and other build constraints.
+// The import path of the package is specified by importPath.
+//
+// Examples found in _test.go files are associated with the corresponding
+// type, function, method, or the package, based on their name.
+// If the example has a suffix in its name, it is set in the
+// Example.Suffix field. Examples with malformed names are skipped.
+//
+// Optionally, a single extra argument of type Mode can be provided to
+// control low-level aspects of the documentation extraction behavior.
+//
+// NewFromFiles takes ownership of the AST files and may edit them,
+// unless the PreserveAST Mode bit is on.
+func NewFromFiles(fset *token.FileSet, files []*ast.File, importPath string, opts ...any) (*Package, error) {
+	// Check for invalid API usage.
+	if fset == nil {
+		panic(fmt.Errorf("doc.NewFromFiles: no token.FileSet provided (fset == nil)"))
+	}
+	var mode Mode
+	switch len(opts) { // There can only be 0 or 1 options, so a simple switch works for now.
+	case 0:
+		// Nothing to do.
+	case 1:
+		m, ok := opts[0].(Mode)
+		if !ok {
+			panic(fmt.Errorf("doc.NewFromFiles: option argument type must be doc.Mode"))
+		}
+		mode = m
+	default:
+		panic(fmt.Errorf("doc.NewFromFiles: there must not be more than 1 option argument"))
+	}
+
+	// Collect .go and _test.go files.
+	var (
+		goFiles     = make(map[string]*ast.File)
+		testGoFiles []*ast.File
+	)
+	for i := range files {
+		f := fset.File(files[i].Pos())
+		if f == nil {
+			return nil, fmt.Errorf("file files[%d] is not found in the provided file set", i)
+		}
+		switch name := f.Name(); {
+		case strings.HasSuffix(name, ".go") && !strings.HasSuffix(name, "_test.go"):
+			goFiles[name] = files[i]
+		case strings.HasSuffix(name, "_test.go"):
+			testGoFiles = append(testGoFiles, files[i])
+		default:
+			return nil, fmt.Errorf("file files[%d] filename %q does not have a .go extension", i, name)
+		}
+	}
+
+	// TODO(dmitshur,gri): A relatively high level call to ast.NewPackage with a simpleImporter
+	// ast.Importer implementation is made below. It might be possible to short-circuit and simplify.
+
+	// Compute package documentation.
+	pkg, _ := ast.NewPackage(fset, goFiles, simpleImporter, nil) // Ignore errors that can happen due to unresolved identifiers.
+	p := New(pkg, importPath, mode)
+	classifyExamples(p, Examples(testGoFiles...))
+	return p, nil
+}
+
+// simpleImporter returns a (dummy) package object named by the last path
+// component of the provided package path (as is the convention for packages).
+// This is sufficient to resolve package identifiers without doing an actual
+// import. It never returns an error.
+func simpleImporter(imports map[string]*ast.Object, path string) (*ast.Object, error) {
+	pkg := imports[path]
+	if pkg == nil {
+		// note that strings.LastIndex returns -1 if there is no "/"
+		pkg = ast.NewObj(ast.Pkg, path[strings.LastIndex(path, "/")+1:])
+		pkg.Data = ast.NewScope(nil) // required by ast.NewPackage for dot-import
+		imports[path] = pkg
+	}
+	return pkg, nil
+}
+
+// lookupSym reports whether the package has a given symbol or method.
+//
+// If recv == "", HasSym reports whether the package has a top-level
+// const, func, type, or var named name.
+//
+// If recv != "", HasSym reports whether the package has a type
+// named recv with a method named name.
+func (p *Package) lookupSym(recv, name string) bool {
+	if recv != "" {
+		return p.syms[recv+"."+name]
+	}
+	return p.syms[name]
+}
+
+// lookupPackage returns the import path identified by name
+// in the given package. If name uniquely identifies a single import,
+// then lookupPackage returns that import.
+// If multiple packages are imported as name, importPath returns "", false.
+// Otherwise, if name is the name of p itself, importPath returns "", true,
+// to signal a reference to p.
+// Otherwise, importPath returns "", false.
+func (p *Package) lookupPackage(name string) (importPath string, ok bool) {
+	if path, ok := p.importByName[name]; ok {
+		if path == "" {
+			return "", false // multiple imports used the name
+		}
+		return path, true // found import
+	}
+	if p.Name == name {
+		return "", true // allow reference to this package
+	}
+	return "", false // unknown name
+}
+
+// Parser returns a doc comment parser configured
+// for parsing doc comments from package p.
+// Each call returns a new parser, so that the caller may
+// customize it before use.
+func (p *Package) Parser() *comment.Parser {
+	return &comment.Parser{
+		LookupPackage: p.lookupPackage,
+		LookupSym:     p.lookupSym,
+	}
+}
+
+// Printer returns a doc comment printer configured
+// for printing doc comments from package p.
+// Each call returns a new printer, so that the caller may
+// customize it before use.
+func (p *Package) Printer() *comment.Printer {
+	// No customization today, but having p.Printer()
+	// gives us flexibility in the future, and it is convenient for callers.
+	return &comment.Printer{}
+}
+
+// HTML returns formatted HTML for the doc comment text.
+//
+// To customize details of the HTML, use [Package.Printer]
+// to obtain a [comment.Printer], and configure it
+// before calling its HTML method.
+func (p *Package) HTML(text string) []byte {
+	return p.Printer().HTML(p.Parser().Parse(text))
+}
+
+// Markdown returns formatted Markdown for the doc comment text.
+//
+// To customize details of the Markdown, use [Package.Printer]
+// to obtain a [comment.Printer], and configure it
+// before calling its Markdown method.
+func (p *Package) Markdown(text string) []byte {
+	return p.Printer().Markdown(p.Parser().Parse(text))
+}
+
+// Text returns formatted text for the doc comment text,
+// wrapped to 80 Unicode code points and using tabs for
+// code block indentation.
+//
+// To customize details of the formatting, use [Package.Printer]
+// to obtain a [comment.Printer], and configure it
+// before calling its Text method.
+func (p *Package) Text(text string) []byte {
+	return p.Printer().Text(p.Parser().Parse(text))
+}
diff --git a/src/go/doc/doc_test.go b/src/go/doc/doc_test.go
new file mode 100644
index 0000000..b79087e
--- /dev/null
+++ b/src/go/doc/doc_test.go
@@ -0,0 +1,292 @@
+// Copyright 2012 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 doc
+
+import (
+	"bytes"
+	"flag"
+	"fmt"
+	"go/ast"
+	"go/parser"
+	"go/printer"
+	"go/token"
+	"io/fs"
+	"os"
+	"path/filepath"
+	"regexp"
+	"strings"
+	"testing"
+	"text/template"
+)
+
+var update = flag.Bool("update", false, "update golden (.out) files")
+var files = flag.String("files", "", "consider only Go test files matching this regular expression")
+
+const dataDir = "testdata"
+
+var templateTxt = readTemplate("template.txt")
+
+func readTemplate(filename string) *template.Template {
+	t := template.New(filename)
+	t.Funcs(template.FuncMap{
+		"node":     nodeFmt,
+		"synopsis": synopsisFmt,
+		"indent":   indentFmt,
+	})
+	return template.Must(t.ParseFiles(filepath.Join(dataDir, filename)))
+}
+
+func nodeFmt(node any, fset *token.FileSet) string {
+	var buf bytes.Buffer
+	printer.Fprint(&buf, fset, node)
+	return strings.ReplaceAll(strings.TrimSpace(buf.String()), "\n", "\n\t")
+}
+
+func synopsisFmt(s string) string {
+	const n = 64
+	if len(s) > n {
+		// cut off excess text and go back to a word boundary
+		s = s[0:n]
+		if i := strings.LastIndexAny(s, "\t\n "); i >= 0 {
+			s = s[0:i]
+		}
+		s = strings.TrimSpace(s) + " ..."
+	}
+	return "// " + strings.ReplaceAll(s, "\n", " ")
+}
+
+func indentFmt(indent, s string) string {
+	end := ""
+	if strings.HasSuffix(s, "\n") {
+		end = "\n"
+		s = s[:len(s)-1]
+	}
+	return indent + strings.ReplaceAll(s, "\n", "\n"+indent) + end
+}
+
+func isGoFile(fi fs.FileInfo) bool {
+	name := fi.Name()
+	return !fi.IsDir() &&
+		len(name) > 0 && name[0] != '.' && // ignore .files
+		filepath.Ext(name) == ".go"
+}
+
+type bundle struct {
+	*Package
+	FSet *token.FileSet
+}
+
+func test(t *testing.T, mode Mode) {
+	// determine file filter
+	filter := isGoFile
+	if *files != "" {
+		rx, err := regexp.Compile(*files)
+		if err != nil {
+			t.Fatal(err)
+		}
+		filter = func(fi fs.FileInfo) bool {
+			return isGoFile(fi) && rx.MatchString(fi.Name())
+		}
+	}
+
+	// get packages
+	fset := token.NewFileSet()
+	pkgs, err := parser.ParseDir(fset, dataDir, filter, parser.ParseComments)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// test packages
+	for _, pkg := range pkgs {
+		t.Run(pkg.Name, func(t *testing.T) {
+			importPath := dataDir + "/" + pkg.Name
+			var files []*ast.File
+			for _, f := range pkg.Files {
+				files = append(files, f)
+			}
+			doc, err := NewFromFiles(fset, files, importPath, mode)
+			if err != nil {
+				t.Fatal(err)
+			}
+
+			// golden files always use / in filenames - canonicalize them
+			for i, filename := range doc.Filenames {
+				doc.Filenames[i] = filepath.ToSlash(filename)
+			}
+
+			// print documentation
+			var buf bytes.Buffer
+			if err := templateTxt.Execute(&buf, bundle{doc, fset}); err != nil {
+				t.Fatal(err)
+			}
+			got := buf.Bytes()
+
+			// update golden file if necessary
+			golden := filepath.Join(dataDir, fmt.Sprintf("%s.%d.golden", pkg.Name, mode))
+			if *update {
+				err := os.WriteFile(golden, got, 0644)
+				if err != nil {
+					t.Fatal(err)
+				}
+			}
+
+			// get golden file
+			want, err := os.ReadFile(golden)
+			if err != nil {
+				t.Fatal(err)
+			}
+
+			// compare
+			if !bytes.Equal(got, want) {
+				t.Errorf("package %s\n\tgot:\n%s\n\twant:\n%s", pkg.Name, got, want)
+			}
+		})
+	}
+}
+
+func Test(t *testing.T) {
+	t.Run("default", func(t *testing.T) { test(t, 0) })
+	t.Run("AllDecls", func(t *testing.T) { test(t, AllDecls) })
+	t.Run("AllMethods", func(t *testing.T) { test(t, AllMethods) })
+}
+
+func TestFuncs(t *testing.T) {
+	fset := token.NewFileSet()
+	file, err := parser.ParseFile(fset, "funcs.go", strings.NewReader(funcsTestFile), parser.ParseComments)
+	if err != nil {
+		t.Fatal(err)
+	}
+	doc, err := NewFromFiles(fset, []*ast.File{file}, "importPath", Mode(0))
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	for _, f := range doc.Funcs {
+		f.Decl = nil
+	}
+	for _, ty := range doc.Types {
+		for _, f := range ty.Funcs {
+			f.Decl = nil
+		}
+		for _, m := range ty.Methods {
+			m.Decl = nil
+		}
+	}
+
+	compareFuncs := func(t *testing.T, msg string, got, want *Func) {
+		// ignore Decl and Examples
+		got.Decl = nil
+		got.Examples = nil
+		if !(got.Doc == want.Doc &&
+			got.Name == want.Name &&
+			got.Recv == want.Recv &&
+			got.Orig == want.Orig &&
+			got.Level == want.Level) {
+			t.Errorf("%s:\ngot  %+v\nwant %+v", msg, got, want)
+		}
+	}
+
+	compareSlices(t, "Funcs", doc.Funcs, funcsPackage.Funcs, compareFuncs)
+	compareSlices(t, "Types", doc.Types, funcsPackage.Types, func(t *testing.T, msg string, got, want *Type) {
+		if got.Name != want.Name {
+			t.Errorf("%s.Name: got %q, want %q", msg, got.Name, want.Name)
+		} else {
+			compareSlices(t, got.Name+".Funcs", got.Funcs, want.Funcs, compareFuncs)
+			compareSlices(t, got.Name+".Methods", got.Methods, want.Methods, compareFuncs)
+		}
+	})
+}
+
+func compareSlices[E any](t *testing.T, name string, got, want []E, compareElem func(*testing.T, string, E, E)) {
+	if len(got) != len(want) {
+		t.Errorf("%s: got %d, want %d", name, len(got), len(want))
+	}
+	for i := 0; i < len(got) && i < len(want); i++ {
+		compareElem(t, fmt.Sprintf("%s[%d]", name, i), got[i], want[i])
+	}
+}
+
+const funcsTestFile = `
+package funcs
+
+func F() {}
+
+type S1 struct {
+	S2  // embedded, exported
+	s3  // embedded, unexported
+}
+
+func NewS1()  S1 {return S1{} }
+func NewS1p() *S1 { return &S1{} }
+
+func (S1) M1() {}
+func (r S1) M2() {}
+func(S1) m3() {}		// unexported not shown
+func (*S1) P1() {}		// pointer receiver
+
+type S2 int
+func (S2) M3() {}		// shown on S2
+
+type s3 int
+func (s3) M4() {}		// shown on S1
+
+type G1[T any] struct {
+	*s3
+}
+
+func NewG1[T any]() G1[T] { return G1[T]{} }
+
+func (G1[T]) MG1() {}
+func (*G1[U]) MG2() {}
+
+type G2[T, U any] struct {}
+
+func NewG2[T, U any]() G2[T, U] { return G2[T, U]{} }
+
+func (G2[T, U]) MG3() {}
+func (*G2[A, B]) MG4() {}
+
+
+`
+
+var funcsPackage = &Package{
+	Funcs: []*Func{{Name: "F"}},
+	Types: []*Type{
+		{
+			Name:  "G1",
+			Funcs: []*Func{{Name: "NewG1"}},
+			Methods: []*Func{
+				{Name: "M4", Recv: "G1", // TODO: synthesize a param for G1?
+					Orig: "s3", Level: 1},
+				{Name: "MG1", Recv: "G1[T]", Orig: "G1[T]", Level: 0},
+				{Name: "MG2", Recv: "*G1[U]", Orig: "*G1[U]", Level: 0},
+			},
+		},
+		{
+			Name:  "G2",
+			Funcs: []*Func{{Name: "NewG2"}},
+			Methods: []*Func{
+				{Name: "MG3", Recv: "G2[T, U]", Orig: "G2[T, U]", Level: 0},
+				{Name: "MG4", Recv: "*G2[A, B]", Orig: "*G2[A, B]", Level: 0},
+			},
+		},
+		{
+			Name:  "S1",
+			Funcs: []*Func{{Name: "NewS1"}, {Name: "NewS1p"}},
+			Methods: []*Func{
+				{Name: "M1", Recv: "S1", Orig: "S1", Level: 0},
+				{Name: "M2", Recv: "S1", Orig: "S1", Level: 0},
+				{Name: "M4", Recv: "S1", Orig: "s3", Level: 1},
+				{Name: "P1", Recv: "*S1", Orig: "*S1", Level: 0},
+			},
+		},
+		{
+			Name: "S2",
+			Methods: []*Func{
+				{Name: "M3", Recv: "S2", Orig: "S2", Level: 0},
+			},
+		},
+	},
+}
diff --git a/src/go/doc/example.go b/src/go/doc/example.go
new file mode 100644
index 0000000..65ca885
--- /dev/null
+++ b/src/go/doc/example.go
@@ -0,0 +1,722 @@
+// Copyright 2011 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.
+
+// Extract example functions from file ASTs.
+
+package doc
+
+import (
+	"go/ast"
+	"go/token"
+	"internal/lazyregexp"
+	"path"
+	"sort"
+	"strconv"
+	"strings"
+	"unicode"
+	"unicode/utf8"
+)
+
+// An Example represents an example function found in a test source file.
+type Example struct {
+	Name        string // name of the item being exemplified (including optional suffix)
+	Suffix      string // example suffix, without leading '_' (only populated by NewFromFiles)
+	Doc         string // example function doc string
+	Code        ast.Node
+	Play        *ast.File // a whole program version of the example
+	Comments    []*ast.CommentGroup
+	Output      string // expected output
+	Unordered   bool
+	EmptyOutput bool // expect empty output
+	Order       int  // original source code order
+}
+
+// Examples returns the examples found in testFiles, sorted by Name field.
+// The Order fields record the order in which the examples were encountered.
+// The Suffix field is not populated when Examples is called directly, it is
+// only populated by NewFromFiles for examples it finds in _test.go files.
+//
+// Playable Examples must be in a package whose name ends in "_test".
+// An Example is "playable" (the Play field is non-nil) in either of these
+// circumstances:
+//   - The example function is self-contained: the function references only
+//     identifiers from other packages (or predeclared identifiers, such as
+//     "int") and the test file does not include a dot import.
+//   - The entire test file is the example: the file contains exactly one
+//     example function, zero test, fuzz test, or benchmark function, and at
+//     least one top-level function, type, variable, or constant declaration
+//     other than the example function.
+func Examples(testFiles ...*ast.File) []*Example {
+	var list []*Example
+	for _, file := range testFiles {
+		hasTests := false // file contains tests, fuzz test, or benchmarks
+		numDecl := 0      // number of non-import declarations in the file
+		var flist []*Example
+		for _, decl := range file.Decls {
+			if g, ok := decl.(*ast.GenDecl); ok && g.Tok != token.IMPORT {
+				numDecl++
+				continue
+			}
+			f, ok := decl.(*ast.FuncDecl)
+			if !ok || f.Recv != nil {
+				continue
+			}
+			numDecl++
+			name := f.Name.Name
+			if isTest(name, "Test") || isTest(name, "Benchmark") || isTest(name, "Fuzz") {
+				hasTests = true
+				continue
+			}
+			if !isTest(name, "Example") {
+				continue
+			}
+			if params := f.Type.Params; len(params.List) != 0 {
+				continue // function has params; not a valid example
+			}
+			if f.Body == nil { // ast.File.Body nil dereference (see issue 28044)
+				continue
+			}
+			var doc string
+			if f.Doc != nil {
+				doc = f.Doc.Text()
+			}
+			output, unordered, hasOutput := exampleOutput(f.Body, file.Comments)
+			flist = append(flist, &Example{
+				Name:        name[len("Example"):],
+				Doc:         doc,
+				Code:        f.Body,
+				Play:        playExample(file, f),
+				Comments:    file.Comments,
+				Output:      output,
+				Unordered:   unordered,
+				EmptyOutput: output == "" && hasOutput,
+				Order:       len(flist),
+			})
+		}
+		if !hasTests && numDecl > 1 && len(flist) == 1 {
+			// If this file only has one example function, some
+			// other top-level declarations, and no tests or
+			// benchmarks, use the whole file as the example.
+			flist[0].Code = file
+			flist[0].Play = playExampleFile(file)
+		}
+		list = append(list, flist...)
+	}
+	// sort by name
+	sort.Slice(list, func(i, j int) bool {
+		return list[i].Name < list[j].Name
+	})
+	return list
+}
+
+var outputPrefix = lazyregexp.New(`(?i)^[[:space:]]*(unordered )?output:`)
+
+// Extracts the expected output and whether there was a valid output comment.
+func exampleOutput(b *ast.BlockStmt, comments []*ast.CommentGroup) (output string, unordered, ok bool) {
+	if _, last := lastComment(b, comments); last != nil {
+		// test that it begins with the correct prefix
+		text := last.Text()
+		if loc := outputPrefix.FindStringSubmatchIndex(text); loc != nil {
+			if loc[2] != -1 {
+				unordered = true
+			}
+			text = text[loc[1]:]
+			// Strip zero or more spaces followed by \n or a single space.
+			text = strings.TrimLeft(text, " ")
+			if len(text) > 0 && text[0] == '\n' {
+				text = text[1:]
+			}
+			return text, unordered, true
+		}
+	}
+	return "", false, false // no suitable comment found
+}
+
+// isTest tells whether name looks like a test, example, fuzz test, or
+// benchmark. It is a Test (say) if there is a character after Test that is not
+// a lower-case letter. (We don't want Testiness.)
+func isTest(name, prefix string) bool {
+	if !strings.HasPrefix(name, prefix) {
+		return false
+	}
+	if len(name) == len(prefix) { // "Test" is ok
+		return true
+	}
+	rune, _ := utf8.DecodeRuneInString(name[len(prefix):])
+	return !unicode.IsLower(rune)
+}
+
+// playExample synthesizes a new *ast.File based on the provided
+// file with the provided function body as the body of main.
+func playExample(file *ast.File, f *ast.FuncDecl) *ast.File {
+	body := f.Body
+
+	if !strings.HasSuffix(file.Name.Name, "_test") {
+		// We don't support examples that are part of the
+		// greater package (yet).
+		return nil
+	}
+
+	// Collect top-level declarations in the file.
+	topDecls := make(map[*ast.Object]ast.Decl)
+	typMethods := make(map[string][]ast.Decl)
+
+	for _, decl := range file.Decls {
+		switch d := decl.(type) {
+		case *ast.FuncDecl:
+			if d.Recv == nil {
+				topDecls[d.Name.Obj] = d
+			} else {
+				if len(d.Recv.List) == 1 {
+					t := d.Recv.List[0].Type
+					tname, _ := baseTypeName(t)
+					typMethods[tname] = append(typMethods[tname], d)
+				}
+			}
+		case *ast.GenDecl:
+			for _, spec := range d.Specs {
+				switch s := spec.(type) {
+				case *ast.TypeSpec:
+					topDecls[s.Name.Obj] = d
+				case *ast.ValueSpec:
+					for _, name := range s.Names {
+						topDecls[name.Obj] = d
+					}
+				}
+			}
+		}
+	}
+
+	// Find unresolved identifiers and uses of top-level declarations.
+	depDecls, unresolved := findDeclsAndUnresolved(body, topDecls, typMethods)
+
+	// Remove predeclared identifiers from unresolved list.
+	for n := range unresolved {
+		if predeclaredTypes[n] || predeclaredConstants[n] || predeclaredFuncs[n] {
+			delete(unresolved, n)
+		}
+	}
+
+	// Use unresolved identifiers to determine the imports used by this
+	// example. The heuristic assumes package names match base import
+	// paths for imports w/o renames (should be good enough most of the time).
+	var namedImports []ast.Spec
+	var blankImports []ast.Spec // _ imports
+
+	// To preserve the blank lines between groups of imports, find the
+	// start position of each group, and assign that position to all
+	// imports from that group.
+	groupStarts := findImportGroupStarts(file.Imports)
+	groupStart := func(s *ast.ImportSpec) token.Pos {
+		for i, start := range groupStarts {
+			if s.Path.ValuePos < start {
+				return groupStarts[i-1]
+			}
+		}
+		return groupStarts[len(groupStarts)-1]
+	}
+
+	for _, s := range file.Imports {
+		p, err := strconv.Unquote(s.Path.Value)
+		if err != nil {
+			continue
+		}
+		if p == "syscall/js" {
+			// We don't support examples that import syscall/js,
+			// because the package syscall/js is not available in the playground.
+			return nil
+		}
+		n := path.Base(p)
+		if s.Name != nil {
+			n = s.Name.Name
+			switch n {
+			case "_":
+				blankImports = append(blankImports, s)
+				continue
+			case ".":
+				// We can't resolve dot imports (yet).
+				return nil
+			}
+		}
+		if unresolved[n] {
+			// Copy the spec and its path to avoid modifying the original.
+			spec := *s
+			path := *s.Path
+			spec.Path = &path
+			spec.Path.ValuePos = groupStart(&spec)
+			namedImports = append(namedImports, &spec)
+			delete(unresolved, n)
+		}
+	}
+
+	// If there are other unresolved identifiers, give up because this
+	// synthesized file is not going to build.
+	if len(unresolved) > 0 {
+		return nil
+	}
+
+	// Include documentation belonging to blank imports.
+	var comments []*ast.CommentGroup
+	for _, s := range blankImports {
+		if c := s.(*ast.ImportSpec).Doc; c != nil {
+			comments = append(comments, c)
+		}
+	}
+
+	// Include comments that are inside the function body.
+	for _, c := range file.Comments {
+		if body.Pos() <= c.Pos() && c.End() <= body.End() {
+			comments = append(comments, c)
+		}
+	}
+
+	// Strip the "Output:" or "Unordered output:" comment and adjust body
+	// end position.
+	body, comments = stripOutputComment(body, comments)
+
+	// Include documentation belonging to dependent declarations.
+	for _, d := range depDecls {
+		switch d := d.(type) {
+		case *ast.GenDecl:
+			if d.Doc != nil {
+				comments = append(comments, d.Doc)
+			}
+		case *ast.FuncDecl:
+			if d.Doc != nil {
+				comments = append(comments, d.Doc)
+			}
+		}
+	}
+
+	// Synthesize import declaration.
+	importDecl := &ast.GenDecl{
+		Tok:    token.IMPORT,
+		Lparen: 1, // Need non-zero Lparen and Rparen so that printer
+		Rparen: 1, // treats this as a factored import.
+	}
+	importDecl.Specs = append(namedImports, blankImports...)
+
+	// Synthesize main function.
+	funcDecl := &ast.FuncDecl{
+		Name: ast.NewIdent("main"),
+		Type: f.Type,
+		Body: body,
+	}
+
+	decls := make([]ast.Decl, 0, 2+len(depDecls))
+	decls = append(decls, importDecl)
+	decls = append(decls, depDecls...)
+	decls = append(decls, funcDecl)
+
+	sort.Slice(decls, func(i, j int) bool {
+		return decls[i].Pos() < decls[j].Pos()
+	})
+	sort.Slice(comments, func(i, j int) bool {
+		return comments[i].Pos() < comments[j].Pos()
+	})
+
+	// Synthesize file.
+	return &ast.File{
+		Name:     ast.NewIdent("main"),
+		Decls:    decls,
+		Comments: comments,
+	}
+}
+
+// findDeclsAndUnresolved returns all the top-level declarations mentioned in
+// the body, and a set of unresolved symbols (those that appear in the body but
+// have no declaration in the program).
+//
+// topDecls maps objects to the top-level declaration declaring them (not
+// necessarily obj.Decl, as obj.Decl will be a Spec for GenDecls, but
+// topDecls[obj] will be the GenDecl itself).
+func findDeclsAndUnresolved(body ast.Node, topDecls map[*ast.Object]ast.Decl, typMethods map[string][]ast.Decl) ([]ast.Decl, map[string]bool) {
+	// This function recursively finds every top-level declaration used
+	// transitively by the body, populating usedDecls and usedObjs. Then it
+	// trims down the declarations to include only the symbols actually
+	// referenced by the body.
+
+	unresolved := make(map[string]bool)
+	var depDecls []ast.Decl
+	usedDecls := make(map[ast.Decl]bool)   // set of top-level decls reachable from the body
+	usedObjs := make(map[*ast.Object]bool) // set of objects reachable from the body (each declared by a usedDecl)
+
+	var inspectFunc func(ast.Node) bool
+	inspectFunc = func(n ast.Node) bool {
+		switch e := n.(type) {
+		case *ast.Ident:
+			if e.Obj == nil && e.Name != "_" {
+				unresolved[e.Name] = true
+			} else if d := topDecls[e.Obj]; d != nil {
+
+				usedObjs[e.Obj] = true
+				if !usedDecls[d] {
+					usedDecls[d] = true
+					depDecls = append(depDecls, d)
+				}
+			}
+			return true
+		case *ast.SelectorExpr:
+			// For selector expressions, only inspect the left hand side.
+			// (For an expression like fmt.Println, only add "fmt" to the
+			// set of unresolved names, not "Println".)
+			ast.Inspect(e.X, inspectFunc)
+			return false
+		case *ast.KeyValueExpr:
+			// For key value expressions, only inspect the value
+			// as the key should be resolved by the type of the
+			// composite literal.
+			ast.Inspect(e.Value, inspectFunc)
+			return false
+		}
+		return true
+	}
+
+	inspectFieldList := func(fl *ast.FieldList) {
+		if fl != nil {
+			for _, f := range fl.List {
+				ast.Inspect(f.Type, inspectFunc)
+			}
+		}
+	}
+
+	// Find the decls immediately referenced by body.
+	ast.Inspect(body, inspectFunc)
+	// Now loop over them, adding to the list when we find a new decl that the
+	// body depends on. Keep going until we don't find anything new.
+	for i := 0; i < len(depDecls); i++ {
+		switch d := depDecls[i].(type) {
+		case *ast.FuncDecl:
+			// Inpect type parameters.
+			inspectFieldList(d.Type.TypeParams)
+			// Inspect types of parameters and results. See #28492.
+			inspectFieldList(d.Type.Params)
+			inspectFieldList(d.Type.Results)
+
+			// Functions might not have a body. See #42706.
+			if d.Body != nil {
+				ast.Inspect(d.Body, inspectFunc)
+			}
+		case *ast.GenDecl:
+			for _, spec := range d.Specs {
+				switch s := spec.(type) {
+				case *ast.TypeSpec:
+					inspectFieldList(s.TypeParams)
+					ast.Inspect(s.Type, inspectFunc)
+					depDecls = append(depDecls, typMethods[s.Name.Name]...)
+				case *ast.ValueSpec:
+					if s.Type != nil {
+						ast.Inspect(s.Type, inspectFunc)
+					}
+					for _, val := range s.Values {
+						ast.Inspect(val, inspectFunc)
+					}
+				}
+			}
+		}
+	}
+
+	// Some decls include multiple specs, such as a variable declaration with
+	// multiple variables on the same line, or a parenthesized declaration. Trim
+	// the declarations to include only the specs that are actually mentioned.
+	// However, if there is a constant group with iota, leave it all: later
+	// constant declarations in the group may have no value and so cannot stand
+	// on their own, and removing any constant from the group could change the
+	// values of subsequent ones.
+	// See testdata/examples/iota.go for a minimal example.
+	var ds []ast.Decl
+	for _, d := range depDecls {
+		switch d := d.(type) {
+		case *ast.FuncDecl:
+			ds = append(ds, d)
+		case *ast.GenDecl:
+			containsIota := false // does any spec have iota?
+			// Collect all Specs that were mentioned in the example.
+			var specs []ast.Spec
+			for _, s := range d.Specs {
+				switch s := s.(type) {
+				case *ast.TypeSpec:
+					if usedObjs[s.Name.Obj] {
+						specs = append(specs, s)
+					}
+				case *ast.ValueSpec:
+					if !containsIota {
+						containsIota = hasIota(s)
+					}
+					// A ValueSpec may have multiple names (e.g. "var a, b int").
+					// Keep only the names that were mentioned in the example.
+					// Exception: the multiple names have a single initializer (which
+					// would be a function call with multiple return values). In that
+					// case, keep everything.
+					if len(s.Names) > 1 && len(s.Values) == 1 {
+						specs = append(specs, s)
+						continue
+					}
+					ns := *s
+					ns.Names = nil
+					ns.Values = nil
+					for i, n := range s.Names {
+						if usedObjs[n.Obj] {
+							ns.Names = append(ns.Names, n)
+							if s.Values != nil {
+								ns.Values = append(ns.Values, s.Values[i])
+							}
+						}
+					}
+					if len(ns.Names) > 0 {
+						specs = append(specs, &ns)
+					}
+				}
+			}
+			if len(specs) > 0 {
+				// Constant with iota? Keep it all.
+				if d.Tok == token.CONST && containsIota {
+					ds = append(ds, d)
+				} else {
+					// Synthesize a GenDecl with just the Specs we need.
+					nd := *d // copy the GenDecl
+					nd.Specs = specs
+					if len(specs) == 1 {
+						// Remove grouping parens if there is only one spec.
+						nd.Lparen = 0
+					}
+					ds = append(ds, &nd)
+				}
+			}
+		}
+	}
+	return ds, unresolved
+}
+
+func hasIota(s ast.Spec) bool {
+	has := false
+	ast.Inspect(s, func(n ast.Node) bool {
+		// Check that this is the special built-in "iota" identifier, not
+		// a user-defined shadow.
+		if id, ok := n.(*ast.Ident); ok && id.Name == "iota" && id.Obj == nil {
+			has = true
+			return false
+		}
+		return true
+	})
+	return has
+}
+
+// findImportGroupStarts finds the start positions of each sequence of import
+// specs that are not separated by a blank line.
+func findImportGroupStarts(imps []*ast.ImportSpec) []token.Pos {
+	startImps := findImportGroupStarts1(imps)
+	groupStarts := make([]token.Pos, len(startImps))
+	for i, imp := range startImps {
+		groupStarts[i] = imp.Pos()
+	}
+	return groupStarts
+}
+
+// Helper for findImportGroupStarts to ease testing.
+func findImportGroupStarts1(origImps []*ast.ImportSpec) []*ast.ImportSpec {
+	// Copy to avoid mutation.
+	imps := make([]*ast.ImportSpec, len(origImps))
+	copy(imps, origImps)
+	// Assume the imports are sorted by position.
+	sort.Slice(imps, func(i, j int) bool { return imps[i].Pos() < imps[j].Pos() })
+	// Assume gofmt has been applied, so there is a blank line between adjacent imps
+	// if and only if they are more than 2 positions apart (newline, tab).
+	var groupStarts []*ast.ImportSpec
+	prevEnd := token.Pos(-2)
+	for _, imp := range imps {
+		if imp.Pos()-prevEnd > 2 {
+			groupStarts = append(groupStarts, imp)
+		}
+		prevEnd = imp.End()
+		// Account for end-of-line comments.
+		if imp.Comment != nil {
+			prevEnd = imp.Comment.End()
+		}
+	}
+	return groupStarts
+}
+
+// playExampleFile takes a whole file example and synthesizes a new *ast.File
+// such that the example is function main in package main.
+func playExampleFile(file *ast.File) *ast.File {
+	// Strip copyright comment if present.
+	comments := file.Comments
+	if len(comments) > 0 && strings.HasPrefix(comments[0].Text(), "Copyright") {
+		comments = comments[1:]
+	}
+
+	// Copy declaration slice, rewriting the ExampleX function to main.
+	var decls []ast.Decl
+	for _, d := range file.Decls {
+		if f, ok := d.(*ast.FuncDecl); ok && isTest(f.Name.Name, "Example") {
+			// Copy the FuncDecl, as it may be used elsewhere.
+			newF := *f
+			newF.Name = ast.NewIdent("main")
+			newF.Body, comments = stripOutputComment(f.Body, comments)
+			d = &newF
+		}
+		decls = append(decls, d)
+	}
+
+	// Copy the File, as it may be used elsewhere.
+	f := *file
+	f.Name = ast.NewIdent("main")
+	f.Decls = decls
+	f.Comments = comments
+	return &f
+}
+
+// stripOutputComment finds and removes the "Output:" or "Unordered output:"
+// comment from body and comments, and adjusts the body block's end position.
+func stripOutputComment(body *ast.BlockStmt, comments []*ast.CommentGroup) (*ast.BlockStmt, []*ast.CommentGroup) {
+	// Do nothing if there is no "Output:" or "Unordered output:" comment.
+	i, last := lastComment(body, comments)
+	if last == nil || !outputPrefix.MatchString(last.Text()) {
+		return body, comments
+	}
+
+	// Copy body and comments, as the originals may be used elsewhere.
+	newBody := &ast.BlockStmt{
+		Lbrace: body.Lbrace,
+		List:   body.List,
+		Rbrace: last.Pos(),
+	}
+	newComments := make([]*ast.CommentGroup, len(comments)-1)
+	copy(newComments, comments[:i])
+	copy(newComments[i:], comments[i+1:])
+	return newBody, newComments
+}
+
+// lastComment returns the last comment inside the provided block.
+func lastComment(b *ast.BlockStmt, c []*ast.CommentGroup) (i int, last *ast.CommentGroup) {
+	if b == nil {
+		return
+	}
+	pos, end := b.Pos(), b.End()
+	for j, cg := range c {
+		if cg.Pos() < pos {
+			continue
+		}
+		if cg.End() > end {
+			break
+		}
+		i, last = j, cg
+	}
+	return
+}
+
+// classifyExamples classifies examples and assigns them to the Examples field
+// of the relevant Func, Type, or Package that the example is associated with.
+//
+// The classification process is ambiguous in some cases:
+//
+//   - ExampleFoo_Bar matches a type named Foo_Bar
+//     or a method named Foo.Bar.
+//   - ExampleFoo_bar matches a type named Foo_bar
+//     or Foo (with a "bar" suffix).
+//
+// Examples with malformed names are not associated with anything.
+func classifyExamples(p *Package, examples []*Example) {
+	if len(examples) == 0 {
+		return
+	}
+	// Mapping of names for funcs, types, and methods to the example listing.
+	ids := make(map[string]*[]*Example)
+	ids[""] = &p.Examples // package-level examples have an empty name
+	for _, f := range p.Funcs {
+		if !token.IsExported(f.Name) {
+			continue
+		}
+		ids[f.Name] = &f.Examples
+	}
+	for _, t := range p.Types {
+		if !token.IsExported(t.Name) {
+			continue
+		}
+		ids[t.Name] = &t.Examples
+		for _, f := range t.Funcs {
+			if !token.IsExported(f.Name) {
+				continue
+			}
+			ids[f.Name] = &f.Examples
+		}
+		for _, m := range t.Methods {
+			if !token.IsExported(m.Name) {
+				continue
+			}
+			ids[strings.TrimPrefix(nameWithoutInst(m.Recv), "*")+"_"+m.Name] = &m.Examples
+		}
+	}
+
+	// Group each example with the associated func, type, or method.
+	for _, ex := range examples {
+		// Consider all possible split points for the suffix
+		// by starting at the end of string (no suffix case),
+		// then trying all positions that contain a '_' character.
+		//
+		// An association is made on the first successful match.
+		// Examples with malformed names that match nothing are skipped.
+		for i := len(ex.Name); i >= 0; i = strings.LastIndexByte(ex.Name[:i], '_') {
+			prefix, suffix, ok := splitExampleName(ex.Name, i)
+			if !ok {
+				continue
+			}
+			exs, ok := ids[prefix]
+			if !ok {
+				continue
+			}
+			ex.Suffix = suffix
+			*exs = append(*exs, ex)
+			break
+		}
+	}
+
+	// Sort list of example according to the user-specified suffix name.
+	for _, exs := range ids {
+		sort.Slice((*exs), func(i, j int) bool {
+			return (*exs)[i].Suffix < (*exs)[j].Suffix
+		})
+	}
+}
+
+// nameWithoutInst returns name if name has no brackets. If name contains
+// brackets, then it returns name with all the contents between (and including)
+// the outermost left and right bracket removed.
+//
+// Adapted from debug/gosym/symtab.go:Sym.nameWithoutInst.
+func nameWithoutInst(name string) string {
+	start := strings.Index(name, "[")
+	if start < 0 {
+		return name
+	}
+	end := strings.LastIndex(name, "]")
+	if end < 0 {
+		// Malformed name, should contain closing bracket too.
+		return name
+	}
+	return name[0:start] + name[end+1:]
+}
+
+// splitExampleName attempts to split example name s at index i,
+// and reports if that produces a valid split. The suffix may be
+// absent. Otherwise, it must start with a lower-case letter and
+// be preceded by '_'.
+//
+// One of i == len(s) or s[i] == '_' must be true.
+func splitExampleName(s string, i int) (prefix, suffix string, ok bool) {
+	if i == len(s) {
+		return s, "", true
+	}
+	if i == len(s)-1 {
+		return "", "", false
+	}
+	prefix, suffix = s[:i], s[i+1:]
+	return prefix, suffix, isExampleSuffix(suffix)
+}
+
+func isExampleSuffix(s string) bool {
+	r, size := utf8.DecodeRuneInString(s)
+	return size > 0 && unicode.IsLower(r)
+}
diff --git a/src/go/doc/example_internal_test.go b/src/go/doc/example_internal_test.go
new file mode 100644
index 0000000..08ddfaf
--- /dev/null
+++ b/src/go/doc/example_internal_test.go
@@ -0,0 +1,121 @@
+// 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 doc
+
+import (
+	"go/parser"
+	"go/token"
+	"reflect"
+	"strconv"
+	"strings"
+	"testing"
+)
+
+func TestImportGroupStarts(t *testing.T) {
+	for _, test := range []struct {
+		name string
+		in   string
+		want []string // paths of group-starting imports
+	}{
+		{
+			name: "one group",
+			in: `package p
+import (
+	"a"
+	"b"
+	"c"
+	"d"
+)
+`,
+			want: []string{"a"},
+		},
+		{
+			name: "several groups",
+			in: `package p
+import (
+	"a"
+
+	"b"
+	"c"
+
+	"d"
+)
+`,
+			want: []string{"a", "b", "d"},
+		},
+		{
+			name: "extra space",
+			in: `package p
+import (
+	"a"
+
+
+	"b"
+	"c"
+
+
+	"d"
+)
+`,
+			want: []string{"a", "b", "d"},
+		},
+		{
+			name: "line comment",
+			in: `package p
+import (
+	"a" // comment
+	"b" // comment
+
+	"c"
+)`,
+			want: []string{"a", "c"},
+		},
+		{
+			name: "named import",
+			in: `package p
+import (
+	"a"
+	n "b"
+
+	m "c"
+	"d"
+)`,
+			want: []string{"a", "c"},
+		},
+		{
+			name: "blank import",
+			in: `package p
+import (
+	"a"
+
+	_ "b"
+
+	_ "c"
+	"d"
+)`,
+			want: []string{"a", "b", "c"},
+		},
+	} {
+		t.Run(test.name, func(t *testing.T) {
+			fset := token.NewFileSet()
+			file, err := parser.ParseFile(fset, "test.go", strings.NewReader(test.in), parser.ParseComments)
+			if err != nil {
+				t.Fatal(err)
+			}
+			imps := findImportGroupStarts1(file.Imports)
+			got := make([]string, len(imps))
+			for i, imp := range imps {
+				got[i], err = strconv.Unquote(imp.Path.Value)
+				if err != nil {
+					t.Fatal(err)
+				}
+			}
+			if !reflect.DeepEqual(got, test.want) {
+				t.Errorf("got %v, want %v", got, test.want)
+			}
+		})
+	}
+
+}
diff --git a/src/go/doc/example_test.go b/src/go/doc/example_test.go
new file mode 100644
index 0000000..7919c3a
--- /dev/null
+++ b/src/go/doc/example_test.go
@@ -0,0 +1,336 @@
+// Copyright 2013 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 doc_test
+
+import (
+	"bytes"
+	"fmt"
+	"go/ast"
+	"go/doc"
+	"go/format"
+	"go/parser"
+	"go/token"
+	"internal/diff"
+	"internal/txtar"
+	"path/filepath"
+	"reflect"
+	"strings"
+	"testing"
+)
+
+func TestExamples(t *testing.T) {
+	dir := filepath.Join("testdata", "examples")
+	filenames, err := filepath.Glob(filepath.Join(dir, "*.go"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	for _, filename := range filenames {
+		t.Run(strings.TrimSuffix(filepath.Base(filename), ".go"), func(t *testing.T) {
+			fset := token.NewFileSet()
+			astFile, err := parser.ParseFile(fset, filename, nil, parser.ParseComments)
+			if err != nil {
+				t.Fatal(err)
+			}
+			goldenFilename := strings.TrimSuffix(filename, ".go") + ".golden"
+			archive, err := txtar.ParseFile(goldenFilename)
+			if err != nil {
+				t.Fatal(err)
+			}
+			golden := map[string]string{}
+			for _, f := range archive.Files {
+				golden[f.Name] = strings.TrimSpace(string(f.Data))
+			}
+
+			// Collect the results of doc.Examples in a map keyed by example name.
+			examples := map[string]*doc.Example{}
+			for _, e := range doc.Examples(astFile) {
+				examples[e.Name] = e
+				// Treat missing sections in the golden as empty.
+				for _, kind := range []string{"Play", "Output"} {
+					key := e.Name + "." + kind
+					if _, ok := golden[key]; !ok {
+						golden[key] = ""
+					}
+				}
+			}
+
+			// Each section in the golden file corresponds to an example we expect
+			// to see.
+			for sectionName, want := range golden {
+				name, kind, found := strings.Cut(sectionName, ".")
+				if !found {
+					t.Fatalf("bad section name %q, want EXAMPLE_NAME.KIND", sectionName)
+				}
+				ex := examples[name]
+				if ex == nil {
+					t.Fatalf("no example named %q", name)
+				}
+
+				var got string
+				switch kind {
+				case "Play":
+					got = strings.TrimSpace(formatFile(t, fset, ex.Play))
+
+				case "Output":
+					got = strings.TrimSpace(ex.Output)
+				default:
+					t.Fatalf("bad section kind %q", kind)
+				}
+
+				if got != want {
+					t.Errorf("%s mismatch:\n%s", sectionName,
+						diff.Diff("want", []byte(want), "got", []byte(got)))
+				}
+			}
+		})
+	}
+}
+
+func formatFile(t *testing.T, fset *token.FileSet, n *ast.File) string {
+	t.Helper()
+	if n == nil {
+		return "<nil>"
+	}
+	var buf bytes.Buffer
+	if err := format.Node(&buf, fset, n); err != nil {
+		t.Fatal(err)
+	}
+	return buf.String()
+}
+
+// This example illustrates how to use NewFromFiles
+// to compute package documentation with examples.
+func ExampleNewFromFiles() {
+	// src and test are two source files that make up
+	// a package whose documentation will be computed.
+	const src = `
+// This is the package comment.
+package p
+
+import "fmt"
+
+// This comment is associated with the Greet function.
+func Greet(who string) {
+	fmt.Printf("Hello, %s!\n", who)
+}
+`
+	const test = `
+package p_test
+
+// This comment is associated with the ExampleGreet_world example.
+func ExampleGreet_world() {
+	Greet("world")
+}
+`
+
+	// Create the AST by parsing src and test.
+	fset := token.NewFileSet()
+	files := []*ast.File{
+		mustParse(fset, "src.go", src),
+		mustParse(fset, "src_test.go", test),
+	}
+
+	// Compute package documentation with examples.
+	p, err := doc.NewFromFiles(fset, files, "example.com/p")
+	if err != nil {
+		panic(err)
+	}
+
+	fmt.Printf("package %s - %s", p.Name, p.Doc)
+	fmt.Printf("func %s - %s", p.Funcs[0].Name, p.Funcs[0].Doc)
+	fmt.Printf(" ⤷ example with suffix %q - %s", p.Funcs[0].Examples[0].Suffix, p.Funcs[0].Examples[0].Doc)
+
+	// Output:
+	// package p - This is the package comment.
+	// func Greet - This comment is associated with the Greet function.
+	//  ⤷ example with suffix "world" - This comment is associated with the ExampleGreet_world example.
+}
+
+func TestClassifyExamples(t *testing.T) {
+	const src = `
+package p
+
+const Const1 = 0
+var   Var1   = 0
+
+type (
+	Type1     int
+	Type1_Foo int
+	Type1_foo int
+	type2     int
+
+	Embed struct { Type1 }
+	Uembed struct { type2 }
+)
+
+func Func1()     {}
+func Func1_Foo() {}
+func Func1_foo() {}
+func func2()     {}
+
+func (Type1) Func1() {}
+func (Type1) Func1_Foo() {}
+func (Type1) Func1_foo() {}
+func (Type1) func2() {}
+
+func (type2) Func1() {}
+
+type (
+	Conflict          int
+	Conflict_Conflict int
+	Conflict_conflict int
+)
+
+func (Conflict) Conflict() {}
+
+func GFunc[T any]() {}
+
+type GType[T any] int
+
+func (GType[T]) M() {}
+`
+	const test = `
+package p_test
+
+func ExampleConst1() {} // invalid - no support for consts and vars
+func ExampleVar1()   {} // invalid - no support for consts and vars
+
+func Example()               {}
+func Example_()              {} // invalid - suffix must start with a lower-case letter
+func Example_suffix()        {}
+func Example_suffix_xX_X_x() {}
+func Example_世界()           {} // invalid - suffix must start with a lower-case letter
+func Example_123()           {} // invalid - suffix must start with a lower-case letter
+func Example_BadSuffix()     {} // invalid - suffix must start with a lower-case letter
+
+func ExampleType1()               {}
+func ExampleType1_()              {} // invalid - suffix must start with a lower-case letter
+func ExampleType1_suffix()        {}
+func ExampleType1_BadSuffix()     {} // invalid - suffix must start with a lower-case letter
+func ExampleType1_Foo()           {}
+func ExampleType1_Foo_suffix()    {}
+func ExampleType1_Foo_BadSuffix() {} // invalid - suffix must start with a lower-case letter
+func ExampleType1_foo()           {}
+func ExampleType1_foo_suffix()    {}
+func ExampleType1_foo_Suffix()    {} // matches Type1, instead of Type1_foo
+func Exampletype2()               {} // invalid - cannot match unexported
+
+func ExampleFunc1()               {}
+func ExampleFunc1_()              {} // invalid - suffix must start with a lower-case letter
+func ExampleFunc1_suffix()        {}
+func ExampleFunc1_BadSuffix()     {} // invalid - suffix must start with a lower-case letter
+func ExampleFunc1_Foo()           {}
+func ExampleFunc1_Foo_suffix()    {}
+func ExampleFunc1_Foo_BadSuffix() {} // invalid - suffix must start with a lower-case letter
+func ExampleFunc1_foo()           {}
+func ExampleFunc1_foo_suffix()    {}
+func ExampleFunc1_foo_Suffix()    {} // matches Func1, instead of Func1_foo
+func Examplefunc1()               {} // invalid - cannot match unexported
+
+func ExampleType1_Func1()               {}
+func ExampleType1_Func1_()              {} // invalid - suffix must start with a lower-case letter
+func ExampleType1_Func1_suffix()        {}
+func ExampleType1_Func1_BadSuffix()     {} // invalid - suffix must start with a lower-case letter
+func ExampleType1_Func1_Foo()           {}
+func ExampleType1_Func1_Foo_suffix()    {}
+func ExampleType1_Func1_Foo_BadSuffix() {} // invalid - suffix must start with a lower-case letter
+func ExampleType1_Func1_foo()           {}
+func ExampleType1_Func1_foo_suffix()    {}
+func ExampleType1_Func1_foo_Suffix()    {} // matches Type1.Func1, instead of Type1.Func1_foo
+func ExampleType1_func2()               {} // matches Type1, instead of Type1.func2
+
+func ExampleEmbed_Func1()         {} // invalid - no support for forwarded methods from embedding exported type
+func ExampleUembed_Func1()        {} // methods from embedding unexported types are OK
+func ExampleUembed_Func1_suffix() {}
+
+func ExampleConflict_Conflict()        {} // ambiguous with either Conflict or Conflict_Conflict type
+func ExampleConflict_conflict()        {} // ambiguous with either Conflict or Conflict_conflict type
+func ExampleConflict_Conflict_suffix() {} // ambiguous with either Conflict or Conflict_Conflict type
+func ExampleConflict_conflict_suffix() {} // ambiguous with either Conflict or Conflict_conflict type
+
+func ExampleGFunc() {}
+func ExampleGFunc_suffix() {}
+
+func ExampleGType_M() {}
+func ExampleGType_M_suffix() {}
+`
+
+	// Parse literal source code as a *doc.Package.
+	fset := token.NewFileSet()
+	files := []*ast.File{
+		mustParse(fset, "src.go", src),
+		mustParse(fset, "src_test.go", test),
+	}
+	p, err := doc.NewFromFiles(fset, files, "example.com/p")
+	if err != nil {
+		t.Fatalf("doc.NewFromFiles: %v", err)
+	}
+
+	// Collect the association of examples to top-level identifiers.
+	got := map[string][]string{}
+	got[""] = exampleNames(p.Examples)
+	for _, f := range p.Funcs {
+		got[f.Name] = exampleNames(f.Examples)
+	}
+	for _, t := range p.Types {
+		got[t.Name] = exampleNames(t.Examples)
+		for _, f := range t.Funcs {
+			got[f.Name] = exampleNames(f.Examples)
+		}
+		for _, m := range t.Methods {
+			got[t.Name+"."+m.Name] = exampleNames(m.Examples)
+		}
+	}
+
+	want := map[string][]string{
+		"": {"", "suffix", "suffix_xX_X_x"}, // Package-level examples.
+
+		"Type1":     {"", "foo_Suffix", "func2", "suffix"},
+		"Type1_Foo": {"", "suffix"},
+		"Type1_foo": {"", "suffix"},
+
+		"Func1":     {"", "foo_Suffix", "suffix"},
+		"Func1_Foo": {"", "suffix"},
+		"Func1_foo": {"", "suffix"},
+
+		"Type1.Func1":     {"", "foo_Suffix", "suffix"},
+		"Type1.Func1_Foo": {"", "suffix"},
+		"Type1.Func1_foo": {"", "suffix"},
+
+		"Uembed.Func1": {"", "suffix"},
+
+		// These are implementation dependent due to the ambiguous parsing.
+		"Conflict_Conflict": {"", "suffix"},
+		"Conflict_conflict": {"", "suffix"},
+
+		"GFunc":   {"", "suffix"},
+		"GType.M": {"", "suffix"},
+	}
+
+	for id := range got {
+		if !reflect.DeepEqual(got[id], want[id]) {
+			t.Errorf("classification mismatch for %q:\ngot  %q\nwant %q", id, got[id], want[id])
+		}
+		delete(want, id)
+	}
+	if len(want) > 0 {
+		t.Errorf("did not find:\n%q", want)
+	}
+}
+
+func exampleNames(exs []*doc.Example) (out []string) {
+	for _, ex := range exs {
+		out = append(out, ex.Suffix)
+	}
+	return out
+}
+
+func mustParse(fset *token.FileSet, filename, src string) *ast.File {
+	f, err := parser.ParseFile(fset, filename, src, parser.ParseComments)
+	if err != nil {
+		panic(err)
+	}
+	return f
+}
diff --git a/src/go/doc/exports.go b/src/go/doc/exports.go
new file mode 100644
index 0000000..655e889
--- /dev/null
+++ b/src/go/doc/exports.go
@@ -0,0 +1,324 @@
+// Copyright 2011 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.
+
+// This file implements export filtering of an AST.
+
+package doc
+
+import (
+	"go/ast"
+	"go/token"
+)
+
+// filterIdentList removes unexported names from list in place
+// and returns the resulting list.
+func filterIdentList(list []*ast.Ident) []*ast.Ident {
+	j := 0
+	for _, x := range list {
+		if token.IsExported(x.Name) {
+			list[j] = x
+			j++
+		}
+	}
+	return list[0:j]
+}
+
+var underscore = ast.NewIdent("_")
+
+func filterCompositeLit(lit *ast.CompositeLit, filter Filter, export bool) {
+	n := len(lit.Elts)
+	lit.Elts = filterExprList(lit.Elts, filter, export)
+	if len(lit.Elts) < n {
+		lit.Incomplete = true
+	}
+}
+
+func filterExprList(list []ast.Expr, filter Filter, export bool) []ast.Expr {
+	j := 0
+	for _, exp := range list {
+		switch x := exp.(type) {
+		case *ast.CompositeLit:
+			filterCompositeLit(x, filter, export)
+		case *ast.KeyValueExpr:
+			if x, ok := x.Key.(*ast.Ident); ok && !filter(x.Name) {
+				continue
+			}
+			if x, ok := x.Value.(*ast.CompositeLit); ok {
+				filterCompositeLit(x, filter, export)
+			}
+		}
+		list[j] = exp
+		j++
+	}
+	return list[0:j]
+}
+
+// updateIdentList replaces all unexported identifiers with underscore
+// and reports whether at least one exported name exists.
+func updateIdentList(list []*ast.Ident) (hasExported bool) {
+	for i, x := range list {
+		if token.IsExported(x.Name) {
+			hasExported = true
+		} else {
+			list[i] = underscore
+		}
+	}
+	return hasExported
+}
+
+// hasExportedName reports whether list contains any exported names.
+func hasExportedName(list []*ast.Ident) bool {
+	for _, x := range list {
+		if x.IsExported() {
+			return true
+		}
+	}
+	return false
+}
+
+// removeAnonymousField removes anonymous fields named name from an interface.
+func removeAnonymousField(name string, ityp *ast.InterfaceType) {
+	list := ityp.Methods.List // we know that ityp.Methods != nil
+	j := 0
+	for _, field := range list {
+		keepField := true
+		if n := len(field.Names); n == 0 {
+			// anonymous field
+			if fname, _ := baseTypeName(field.Type); fname == name {
+				keepField = false
+			}
+		}
+		if keepField {
+			list[j] = field
+			j++
+		}
+	}
+	if j < len(list) {
+		ityp.Incomplete = true
+	}
+	ityp.Methods.List = list[0:j]
+}
+
+// filterFieldList removes unexported fields (field names) from the field list
+// in place and reports whether fields were removed. Anonymous fields are
+// recorded with the parent type. filterType is called with the types of
+// all remaining fields.
+func (r *reader) filterFieldList(parent *namedType, fields *ast.FieldList, ityp *ast.InterfaceType) (removedFields bool) {
+	if fields == nil {
+		return
+	}
+	list := fields.List
+	j := 0
+	for _, field := range list {
+		keepField := false
+		if n := len(field.Names); n == 0 {
+			// anonymous field or embedded type or union element
+			fname := r.recordAnonymousField(parent, field.Type)
+			if fname != "" {
+				if token.IsExported(fname) {
+					keepField = true
+				} else if ityp != nil && predeclaredTypes[fname] {
+					// possibly an embedded predeclared type; keep it for now but
+					// remember this interface so that it can be fixed if name is also
+					// defined locally
+					keepField = true
+					r.remember(fname, ityp)
+				}
+			} else {
+				// If we're operating on an interface, assume that this is an embedded
+				// type or union element.
+				//
+				// TODO(rfindley): consider traversing into approximation/unions
+				// elements to see if they are entirely unexported.
+				keepField = ityp != nil
+			}
+		} else {
+			field.Names = filterIdentList(field.Names)
+			if len(field.Names) < n {
+				removedFields = true
+			}
+			if len(field.Names) > 0 {
+				keepField = true
+			}
+		}
+		if keepField {
+			r.filterType(nil, field.Type)
+			list[j] = field
+			j++
+		}
+	}
+	if j < len(list) {
+		removedFields = true
+	}
+	fields.List = list[0:j]
+	return
+}
+
+// filterParamList applies filterType to each parameter type in fields.
+func (r *reader) filterParamList(fields *ast.FieldList) {
+	if fields != nil {
+		for _, f := range fields.List {
+			r.filterType(nil, f.Type)
+		}
+	}
+}
+
+// filterType strips any unexported struct fields or method types from typ
+// in place. If fields (or methods) have been removed, the corresponding
+// struct or interface type has the Incomplete field set to true.
+func (r *reader) filterType(parent *namedType, typ ast.Expr) {
+	switch t := typ.(type) {
+	case *ast.Ident:
+		// nothing to do
+	case *ast.ParenExpr:
+		r.filterType(nil, t.X)
+	case *ast.StarExpr: // possibly an embedded type literal
+		r.filterType(nil, t.X)
+	case *ast.UnaryExpr:
+		if t.Op == token.TILDE { // approximation element
+			r.filterType(nil, t.X)
+		}
+	case *ast.BinaryExpr:
+		if t.Op == token.OR { // union
+			r.filterType(nil, t.X)
+			r.filterType(nil, t.Y)
+		}
+	case *ast.ArrayType:
+		r.filterType(nil, t.Elt)
+	case *ast.StructType:
+		if r.filterFieldList(parent, t.Fields, nil) {
+			t.Incomplete = true
+		}
+	case *ast.FuncType:
+		r.filterParamList(t.TypeParams)
+		r.filterParamList(t.Params)
+		r.filterParamList(t.Results)
+	case *ast.InterfaceType:
+		if r.filterFieldList(parent, t.Methods, t) {
+			t.Incomplete = true
+		}
+	case *ast.MapType:
+		r.filterType(nil, t.Key)
+		r.filterType(nil, t.Value)
+	case *ast.ChanType:
+		r.filterType(nil, t.Value)
+	}
+}
+
+func (r *reader) filterSpec(spec ast.Spec) bool {
+	switch s := spec.(type) {
+	case *ast.ImportSpec:
+		// always keep imports so we can collect them
+		return true
+	case *ast.ValueSpec:
+		s.Values = filterExprList(s.Values, token.IsExported, true)
+		if len(s.Values) > 0 || s.Type == nil && len(s.Values) == 0 {
+			// If there are values declared on RHS, just replace the unexported
+			// identifiers on the LHS with underscore, so that it matches
+			// the sequence of expression on the RHS.
+			//
+			// Similarly, if there are no type and values, then this expression
+			// must be following an iota expression, where order matters.
+			if updateIdentList(s.Names) {
+				r.filterType(nil, s.Type)
+				return true
+			}
+		} else {
+			s.Names = filterIdentList(s.Names)
+			if len(s.Names) > 0 {
+				r.filterType(nil, s.Type)
+				return true
+			}
+		}
+	case *ast.TypeSpec:
+		// Don't filter type parameters here, by analogy with function parameters
+		// which are not filtered for top-level function declarations.
+		if name := s.Name.Name; token.IsExported(name) {
+			r.filterType(r.lookupType(s.Name.Name), s.Type)
+			return true
+		} else if IsPredeclared(name) {
+			if r.shadowedPredecl == nil {
+				r.shadowedPredecl = make(map[string]bool)
+			}
+			r.shadowedPredecl[name] = true
+		}
+	}
+	return false
+}
+
+// copyConstType returns a copy of typ with position pos.
+// typ must be a valid constant type.
+// In practice, only (possibly qualified) identifiers are possible.
+func copyConstType(typ ast.Expr, pos token.Pos) ast.Expr {
+	switch typ := typ.(type) {
+	case *ast.Ident:
+		return &ast.Ident{Name: typ.Name, NamePos: pos}
+	case *ast.SelectorExpr:
+		if id, ok := typ.X.(*ast.Ident); ok {
+			// presumably a qualified identifier
+			return &ast.SelectorExpr{
+				Sel: ast.NewIdent(typ.Sel.Name),
+				X:   &ast.Ident{Name: id.Name, NamePos: pos},
+			}
+		}
+	}
+	return nil // shouldn't happen, but be conservative and don't panic
+}
+
+func (r *reader) filterSpecList(list []ast.Spec, tok token.Token) []ast.Spec {
+	if tok == token.CONST {
+		// Propagate any type information that would get lost otherwise
+		// when unexported constants are filtered.
+		var prevType ast.Expr
+		for _, spec := range list {
+			spec := spec.(*ast.ValueSpec)
+			if spec.Type == nil && len(spec.Values) == 0 && prevType != nil {
+				// provide current spec with an explicit type
+				spec.Type = copyConstType(prevType, spec.Pos())
+			}
+			if hasExportedName(spec.Names) {
+				// exported names are preserved so there's no need to propagate the type
+				prevType = nil
+			} else {
+				prevType = spec.Type
+			}
+		}
+	}
+
+	j := 0
+	for _, s := range list {
+		if r.filterSpec(s) {
+			list[j] = s
+			j++
+		}
+	}
+	return list[0:j]
+}
+
+func (r *reader) filterDecl(decl ast.Decl) bool {
+	switch d := decl.(type) {
+	case *ast.GenDecl:
+		d.Specs = r.filterSpecList(d.Specs, d.Tok)
+		return len(d.Specs) > 0
+	case *ast.FuncDecl:
+		// ok to filter these methods early because any
+		// conflicting method will be filtered here, too -
+		// thus, removing these methods early will not lead
+		// to the false removal of possible conflicts
+		return token.IsExported(d.Name.Name)
+	}
+	return false
+}
+
+// fileExports removes unexported declarations from src in place.
+func (r *reader) fileExports(src *ast.File) {
+	j := 0
+	for _, d := range src.Decls {
+		if r.filterDecl(d) {
+			src.Decls[j] = d
+			j++
+		}
+	}
+	src.Decls = src.Decls[0:j]
+}
diff --git a/src/go/doc/filter.go b/src/go/doc/filter.go
new file mode 100644
index 0000000..f8d3e1f
--- /dev/null
+++ b/src/go/doc/filter.go
@@ -0,0 +1,106 @@
+// 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.
+
+package doc
+
+import "go/ast"
+
+type Filter func(string) bool
+
+func matchFields(fields *ast.FieldList, f Filter) bool {
+	if fields != nil {
+		for _, field := range fields.List {
+			for _, name := range field.Names {
+				if f(name.Name) {
+					return true
+				}
+			}
+		}
+	}
+	return false
+}
+
+func matchDecl(d *ast.GenDecl, f Filter) bool {
+	for _, d := range d.Specs {
+		switch v := d.(type) {
+		case *ast.ValueSpec:
+			for _, name := range v.Names {
+				if f(name.Name) {
+					return true
+				}
+			}
+		case *ast.TypeSpec:
+			if f(v.Name.Name) {
+				return true
+			}
+			// We don't match ordinary parameters in filterFuncs, so by analogy don't
+			// match type parameters here.
+			switch t := v.Type.(type) {
+			case *ast.StructType:
+				if matchFields(t.Fields, f) {
+					return true
+				}
+			case *ast.InterfaceType:
+				if matchFields(t.Methods, f) {
+					return true
+				}
+			}
+		}
+	}
+	return false
+}
+
+func filterValues(a []*Value, f Filter) []*Value {
+	w := 0
+	for _, vd := range a {
+		if matchDecl(vd.Decl, f) {
+			a[w] = vd
+			w++
+		}
+	}
+	return a[0:w]
+}
+
+func filterFuncs(a []*Func, f Filter) []*Func {
+	w := 0
+	for _, fd := range a {
+		if f(fd.Name) {
+			a[w] = fd
+			w++
+		}
+	}
+	return a[0:w]
+}
+
+func filterTypes(a []*Type, f Filter) []*Type {
+	w := 0
+	for _, td := range a {
+		n := 0 // number of matches
+		if matchDecl(td.Decl, f) {
+			n = 1
+		} else {
+			// type name doesn't match, but we may have matching consts, vars, factories or methods
+			td.Consts = filterValues(td.Consts, f)
+			td.Vars = filterValues(td.Vars, f)
+			td.Funcs = filterFuncs(td.Funcs, f)
+			td.Methods = filterFuncs(td.Methods, f)
+			n += len(td.Consts) + len(td.Vars) + len(td.Funcs) + len(td.Methods)
+		}
+		if n > 0 {
+			a[w] = td
+			w++
+		}
+	}
+	return a[0:w]
+}
+
+// Filter eliminates documentation for names that don't pass through the filter f.
+// TODO(gri): Recognize "Type.Method" as a name.
+func (p *Package) Filter(f Filter) {
+	p.Consts = filterValues(p.Consts, f)
+	p.Vars = filterValues(p.Vars, f)
+	p.Types = filterTypes(p.Types, f)
+	p.Funcs = filterFuncs(p.Funcs, f)
+	p.Doc = "" // don't show top-level package doc
+}
diff --git a/src/go/doc/headscan.go b/src/go/doc/headscan.go
new file mode 100644
index 0000000..82f5fed
--- /dev/null
+++ b/src/go/doc/headscan.go
@@ -0,0 +1,109 @@
+// Copyright 2011 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.
+
+//go:build ignore
+
+/*
+The headscan command extracts comment headings from package files;
+it is used to detect false positives which may require an adjustment
+to the comment formatting heuristics in comment.go.
+
+Usage: headscan [-root root_directory]
+
+By default, the $GOROOT/src directory is scanned.
+*/
+package main
+
+import (
+	"flag"
+	"fmt"
+	"go/doc"
+	"go/parser"
+	"go/token"
+	"io/fs"
+	"os"
+	"path/filepath"
+	"regexp"
+	"runtime"
+	"strings"
+)
+
+var (
+	root    = flag.String("root", filepath.Join(runtime.GOROOT(), "src"), "root of filesystem tree to scan")
+	verbose = flag.Bool("v", false, "verbose mode")
+)
+
+// ToHTML in comment.go assigns a (possibly blank) ID to each heading
+var html_h = regexp.MustCompile(`<h3 id="[^"]*">`)
+
+const html_endh = "</h3>\n"
+
+func isGoFile(fi fs.FileInfo) bool {
+	return strings.HasSuffix(fi.Name(), ".go") &&
+		!strings.HasSuffix(fi.Name(), "_test.go")
+}
+
+func appendHeadings(list []string, comment string) []string {
+	var buf strings.Builder
+	doc.ToHTML(&buf, comment, nil)
+	for s := buf.String(); s != ""; {
+		loc := html_h.FindStringIndex(s)
+		if len(loc) == 0 {
+			break
+		}
+		var inner string
+		inner, s, _ = strings.Cut(s[loc[1]:], html_endh)
+		list = append(list, inner)
+	}
+	return list
+}
+
+func main() {
+	flag.Parse()
+	fset := token.NewFileSet()
+	nheadings := 0
+	err := filepath.WalkDir(*root, func(path string, info fs.DirEntry, err error) error {
+		if !info.IsDir() {
+			return nil
+		}
+		pkgs, err := parser.ParseDir(fset, path, isGoFile, parser.ParseComments)
+		if err != nil {
+			if *verbose {
+				fmt.Fprintln(os.Stderr, err)
+			}
+			return nil
+		}
+		for _, pkg := range pkgs {
+			d := doc.New(pkg, path, doc.Mode(0))
+			list := appendHeadings(nil, d.Doc)
+			for _, d := range d.Consts {
+				list = appendHeadings(list, d.Doc)
+			}
+			for _, d := range d.Types {
+				list = appendHeadings(list, d.Doc)
+			}
+			for _, d := range d.Vars {
+				list = appendHeadings(list, d.Doc)
+			}
+			for _, d := range d.Funcs {
+				list = appendHeadings(list, d.Doc)
+			}
+			if len(list) > 0 {
+				// directories may contain multiple packages;
+				// print path and package name
+				fmt.Printf("%s (package %s)\n", path, pkg.Name)
+				for _, h := range list {
+					fmt.Printf("\t%s\n", h)
+				}
+				nheadings += len(list)
+			}
+		}
+		return nil
+	})
+	if err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(1)
+	}
+	fmt.Println(nheadings, "headings found")
+}
diff --git a/src/go/doc/reader.go b/src/go/doc/reader.go
new file mode 100644
index 0000000..8f9fda4
--- /dev/null
+++ b/src/go/doc/reader.go
@@ -0,0 +1,1029 @@
+// 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.
+
+package doc
+
+import (
+	"fmt"
+	"go/ast"
+	"go/token"
+	"internal/lazyregexp"
+	"path"
+	"sort"
+	"strconv"
+	"strings"
+	"unicode"
+	"unicode/utf8"
+)
+
+// ----------------------------------------------------------------------------
+// function/method sets
+//
+// Internally, we treat functions like methods and collect them in method sets.
+
+// A methodSet describes a set of methods. Entries where Decl == nil are conflict
+// entries (more than one method with the same name at the same embedding level).
+type methodSet map[string]*Func
+
+// recvString returns a string representation of recv of the form "T", "*T",
+// "T[A, ...]", "*T[A, ...]" or "BADRECV" (if not a proper receiver type).
+func recvString(recv ast.Expr) string {
+	switch t := recv.(type) {
+	case *ast.Ident:
+		return t.Name
+	case *ast.StarExpr:
+		return "*" + recvString(t.X)
+	case *ast.IndexExpr:
+		// Generic type with one parameter.
+		return fmt.Sprintf("%s[%s]", recvString(t.X), recvParam(t.Index))
+	case *ast.IndexListExpr:
+		// Generic type with multiple parameters.
+		if len(t.Indices) > 0 {
+			var b strings.Builder
+			b.WriteString(recvString(t.X))
+			b.WriteByte('[')
+			b.WriteString(recvParam(t.Indices[0]))
+			for _, e := range t.Indices[1:] {
+				b.WriteString(", ")
+				b.WriteString(recvParam(e))
+			}
+			b.WriteByte(']')
+			return b.String()
+		}
+	}
+	return "BADRECV"
+}
+
+func recvParam(p ast.Expr) string {
+	if id, ok := p.(*ast.Ident); ok {
+		return id.Name
+	}
+	return "BADPARAM"
+}
+
+// set creates the corresponding Func for f and adds it to mset.
+// If there are multiple f's with the same name, set keeps the first
+// one with documentation; conflicts are ignored. The boolean
+// specifies whether to leave the AST untouched.
+func (mset methodSet) set(f *ast.FuncDecl, preserveAST bool) {
+	name := f.Name.Name
+	if g := mset[name]; g != nil && g.Doc != "" {
+		// A function with the same name has already been registered;
+		// since it has documentation, assume f is simply another
+		// implementation and ignore it. This does not happen if the
+		// caller is using go/build.ScanDir to determine the list of
+		// files implementing a package.
+		return
+	}
+	// function doesn't exist or has no documentation; use f
+	recv := ""
+	if f.Recv != nil {
+		var typ ast.Expr
+		// be careful in case of incorrect ASTs
+		if list := f.Recv.List; len(list) == 1 {
+			typ = list[0].Type
+		}
+		recv = recvString(typ)
+	}
+	mset[name] = &Func{
+		Doc:  f.Doc.Text(),
+		Name: name,
+		Decl: f,
+		Recv: recv,
+		Orig: recv,
+	}
+	if !preserveAST {
+		f.Doc = nil // doc consumed - remove from AST
+	}
+}
+
+// add adds method m to the method set; m is ignored if the method set
+// already contains a method with the same name at the same or a higher
+// level than m.
+func (mset methodSet) add(m *Func) {
+	old := mset[m.Name]
+	if old == nil || m.Level < old.Level {
+		mset[m.Name] = m
+		return
+	}
+	if m.Level == old.Level {
+		// conflict - mark it using a method with nil Decl
+		mset[m.Name] = &Func{
+			Name:  m.Name,
+			Level: m.Level,
+		}
+	}
+}
+
+// ----------------------------------------------------------------------------
+// Named types
+
+// baseTypeName returns the name of the base type of x (or "")
+// and whether the type is imported or not.
+func baseTypeName(x ast.Expr) (name string, imported bool) {
+	switch t := x.(type) {
+	case *ast.Ident:
+		return t.Name, false
+	case *ast.IndexExpr:
+		return baseTypeName(t.X)
+	case *ast.IndexListExpr:
+		return baseTypeName(t.X)
+	case *ast.SelectorExpr:
+		if _, ok := t.X.(*ast.Ident); ok {
+			// only possible for qualified type names;
+			// assume type is imported
+			return t.Sel.Name, true
+		}
+	case *ast.ParenExpr:
+		return baseTypeName(t.X)
+	case *ast.StarExpr:
+		return baseTypeName(t.X)
+	}
+	return "", false
+}
+
+// An embeddedSet describes a set of embedded types.
+type embeddedSet map[*namedType]bool
+
+// A namedType represents a named unqualified (package local, or possibly
+// predeclared) type. The namedType for a type name is always found via
+// reader.lookupType.
+type namedType struct {
+	doc  string       // doc comment for type
+	name string       // type name
+	decl *ast.GenDecl // nil if declaration hasn't been seen yet
+
+	isEmbedded bool        // true if this type is embedded
+	isStruct   bool        // true if this type is a struct
+	embedded   embeddedSet // true if the embedded type is a pointer
+
+	// associated declarations
+	values  []*Value // consts and vars
+	funcs   methodSet
+	methods methodSet
+}
+
+// ----------------------------------------------------------------------------
+// AST reader
+
+// reader accumulates documentation for a single package.
+// It modifies the AST: Comments (declaration documentation)
+// that have been collected by the reader are set to nil
+// in the respective AST nodes so that they are not printed
+// twice (once when printing the documentation and once when
+// printing the corresponding AST node).
+type reader struct {
+	mode Mode
+
+	// package properties
+	doc       string // package documentation, if any
+	filenames []string
+	notes     map[string][]*Note
+
+	// imports
+	imports      map[string]int
+	hasDotImp    bool // if set, package contains a dot import
+	importByName map[string]string
+
+	// declarations
+	values []*Value // consts and vars
+	order  int      // sort order of const and var declarations (when we can't use a name)
+	types  map[string]*namedType
+	funcs  methodSet
+
+	// support for package-local shadowing of predeclared types
+	shadowedPredecl map[string]bool
+	fixmap          map[string][]*ast.InterfaceType
+}
+
+func (r *reader) isVisible(name string) bool {
+	return r.mode&AllDecls != 0 || token.IsExported(name)
+}
+
+// lookupType returns the base type with the given name.
+// If the base type has not been encountered yet, a new
+// type with the given name but no associated declaration
+// is added to the type map.
+func (r *reader) lookupType(name string) *namedType {
+	if name == "" || name == "_" {
+		return nil // no type docs for anonymous types
+	}
+	if typ, found := r.types[name]; found {
+		return typ
+	}
+	// type not found - add one without declaration
+	typ := &namedType{
+		name:     name,
+		embedded: make(embeddedSet),
+		funcs:    make(methodSet),
+		methods:  make(methodSet),
+	}
+	r.types[name] = typ
+	return typ
+}
+
+// recordAnonymousField registers fieldType as the type of an
+// anonymous field in the parent type. If the field is imported
+// (qualified name) or the parent is nil, the field is ignored.
+// The function returns the field name.
+func (r *reader) recordAnonymousField(parent *namedType, fieldType ast.Expr) (fname string) {
+	fname, imp := baseTypeName(fieldType)
+	if parent == nil || imp {
+		return
+	}
+	if ftype := r.lookupType(fname); ftype != nil {
+		ftype.isEmbedded = true
+		_, ptr := fieldType.(*ast.StarExpr)
+		parent.embedded[ftype] = ptr
+	}
+	return
+}
+
+func (r *reader) readDoc(comment *ast.CommentGroup) {
+	// By convention there should be only one package comment
+	// but collect all of them if there are more than one.
+	text := comment.Text()
+	if r.doc == "" {
+		r.doc = text
+		return
+	}
+	r.doc += "\n" + text
+}
+
+func (r *reader) remember(predecl string, typ *ast.InterfaceType) {
+	if r.fixmap == nil {
+		r.fixmap = make(map[string][]*ast.InterfaceType)
+	}
+	r.fixmap[predecl] = append(r.fixmap[predecl], typ)
+}
+
+func specNames(specs []ast.Spec) []string {
+	names := make([]string, 0, len(specs)) // reasonable estimate
+	for _, s := range specs {
+		// s guaranteed to be an *ast.ValueSpec by readValue
+		for _, ident := range s.(*ast.ValueSpec).Names {
+			names = append(names, ident.Name)
+		}
+	}
+	return names
+}
+
+// readValue processes a const or var declaration.
+func (r *reader) readValue(decl *ast.GenDecl) {
+	// determine if decl should be associated with a type
+	// Heuristic: For each typed entry, determine the type name, if any.
+	//            If there is exactly one type name that is sufficiently
+	//            frequent, associate the decl with the respective type.
+	domName := ""
+	domFreq := 0
+	prev := ""
+	n := 0
+	for _, spec := range decl.Specs {
+		s, ok := spec.(*ast.ValueSpec)
+		if !ok {
+			continue // should not happen, but be conservative
+		}
+		name := ""
+		switch {
+		case s.Type != nil:
+			// a type is present; determine its name
+			if n, imp := baseTypeName(s.Type); !imp {
+				name = n
+			}
+		case decl.Tok == token.CONST && len(s.Values) == 0:
+			// no type or value is present but we have a constant declaration;
+			// use the previous type name (possibly the empty string)
+			name = prev
+		}
+		if name != "" {
+			// entry has a named type
+			if domName != "" && domName != name {
+				// more than one type name - do not associate
+				// with any type
+				domName = ""
+				break
+			}
+			domName = name
+			domFreq++
+		}
+		prev = name
+		n++
+	}
+
+	// nothing to do w/o a legal declaration
+	if n == 0 {
+		return
+	}
+
+	// determine values list with which to associate the Value for this decl
+	values := &r.values
+	const threshold = 0.75
+	if domName != "" && r.isVisible(domName) && domFreq >= int(float64(len(decl.Specs))*threshold) {
+		// typed entries are sufficiently frequent
+		if typ := r.lookupType(domName); typ != nil {
+			values = &typ.values // associate with that type
+		}
+	}
+
+	*values = append(*values, &Value{
+		Doc:   decl.Doc.Text(),
+		Names: specNames(decl.Specs),
+		Decl:  decl,
+		order: r.order,
+	})
+	if r.mode&PreserveAST == 0 {
+		decl.Doc = nil // doc consumed - remove from AST
+	}
+	// Note: It's important that the order used here is global because the cleanupTypes
+	// methods may move values associated with types back into the global list. If the
+	// order is list-specific, sorting is not deterministic because the same order value
+	// may appear multiple times (was bug, found when fixing #16153).
+	r.order++
+}
+
+// fields returns a struct's fields or an interface's methods.
+func fields(typ ast.Expr) (list []*ast.Field, isStruct bool) {
+	var fields *ast.FieldList
+	switch t := typ.(type) {
+	case *ast.StructType:
+		fields = t.Fields
+		isStruct = true
+	case *ast.InterfaceType:
+		fields = t.Methods
+	}
+	if fields != nil {
+		list = fields.List
+	}
+	return
+}
+
+// readType processes a type declaration.
+func (r *reader) readType(decl *ast.GenDecl, spec *ast.TypeSpec) {
+	typ := r.lookupType(spec.Name.Name)
+	if typ == nil {
+		return // no name or blank name - ignore the type
+	}
+
+	// A type should be added at most once, so typ.decl
+	// should be nil - if it is not, simply overwrite it.
+	typ.decl = decl
+
+	// compute documentation
+	doc := spec.Doc
+	if doc == nil {
+		// no doc associated with the spec, use the declaration doc, if any
+		doc = decl.Doc
+	}
+	if r.mode&PreserveAST == 0 {
+		spec.Doc = nil // doc consumed - remove from AST
+		decl.Doc = nil // doc consumed - remove from AST
+	}
+	typ.doc = doc.Text()
+
+	// record anonymous fields (they may contribute methods)
+	// (some fields may have been recorded already when filtering
+	// exports, but that's ok)
+	var list []*ast.Field
+	list, typ.isStruct = fields(spec.Type)
+	for _, field := range list {
+		if len(field.Names) == 0 {
+			r.recordAnonymousField(typ, field.Type)
+		}
+	}
+}
+
+// isPredeclared reports whether n denotes a predeclared type.
+func (r *reader) isPredeclared(n string) bool {
+	return predeclaredTypes[n] && r.types[n] == nil
+}
+
+// readFunc processes a func or method declaration.
+func (r *reader) readFunc(fun *ast.FuncDecl) {
+	// strip function body if requested.
+	if r.mode&PreserveAST == 0 {
+		fun.Body = nil
+	}
+
+	// associate methods with the receiver type, if any
+	if fun.Recv != nil {
+		// method
+		if len(fun.Recv.List) == 0 {
+			// should not happen (incorrect AST); (See issue 17788)
+			// don't show this method
+			return
+		}
+		recvTypeName, imp := baseTypeName(fun.Recv.List[0].Type)
+		if imp {
+			// should not happen (incorrect AST);
+			// don't show this method
+			return
+		}
+		if typ := r.lookupType(recvTypeName); typ != nil {
+			typ.methods.set(fun, r.mode&PreserveAST != 0)
+		}
+		// otherwise ignore the method
+		// TODO(gri): There may be exported methods of non-exported types
+		// that can be called because of exported values (consts, vars, or
+		// function results) of that type. Could determine if that is the
+		// case and then show those methods in an appropriate section.
+		return
+	}
+
+	// Associate factory functions with the first visible result type, as long as
+	// others are predeclared types.
+	if fun.Type.Results.NumFields() >= 1 {
+		var typ *namedType // type to associate the function with
+		numResultTypes := 0
+		for _, res := range fun.Type.Results.List {
+			factoryType := res.Type
+			if t, ok := factoryType.(*ast.ArrayType); ok {
+				// We consider functions that return slices or arrays of type
+				// T (or pointers to T) as factory functions of T.
+				factoryType = t.Elt
+			}
+			if n, imp := baseTypeName(factoryType); !imp && r.isVisible(n) && !r.isPredeclared(n) {
+				if lookupTypeParam(n, fun.Type.TypeParams) != nil {
+					// Issue #49477: don't associate fun with its type parameter result.
+					// A type parameter is not a defined type.
+					continue
+				}
+				if t := r.lookupType(n); t != nil {
+					typ = t
+					numResultTypes++
+					if numResultTypes > 1 {
+						break
+					}
+				}
+			}
+		}
+		// If there is exactly one result type,
+		// associate the function with that type.
+		if numResultTypes == 1 {
+			typ.funcs.set(fun, r.mode&PreserveAST != 0)
+			return
+		}
+	}
+
+	// just an ordinary function
+	r.funcs.set(fun, r.mode&PreserveAST != 0)
+}
+
+// lookupTypeParam searches for type parameters named name within the tparams
+// field list, returning the relevant identifier if found, or nil if not.
+func lookupTypeParam(name string, tparams *ast.FieldList) *ast.Ident {
+	if tparams == nil {
+		return nil
+	}
+	for _, field := range tparams.List {
+		for _, id := range field.Names {
+			if id.Name == name {
+				return id
+			}
+		}
+	}
+	return nil
+}
+
+var (
+	noteMarker    = `([A-Z][A-Z]+)\(([^)]+)\):?`                // MARKER(uid), MARKER at least 2 chars, uid at least 1 char
+	noteMarkerRx  = lazyregexp.New(`^[ \t]*` + noteMarker)      // MARKER(uid) at text start
+	noteCommentRx = lazyregexp.New(`^/[/*][ \t]*` + noteMarker) // MARKER(uid) at comment start
+)
+
+// clean replaces each sequence of space, \r, or \t characters
+// with a single space and removes any trailing and leading spaces.
+func clean(s string) string {
+	var b []byte
+	p := byte(' ')
+	for i := 0; i < len(s); i++ {
+		q := s[i]
+		if q == '\r' || q == '\t' {
+			q = ' '
+		}
+		if q != ' ' || p != ' ' {
+			b = append(b, q)
+			p = q
+		}
+	}
+	// remove trailing blank, if any
+	if n := len(b); n > 0 && p == ' ' {
+		b = b[0 : n-1]
+	}
+	return string(b)
+}
+
+// readNote collects a single note from a sequence of comments.
+func (r *reader) readNote(list []*ast.Comment) {
+	text := (&ast.CommentGroup{List: list}).Text()
+	if m := noteMarkerRx.FindStringSubmatchIndex(text); m != nil {
+		// The note body starts after the marker.
+		// We remove any formatting so that we don't
+		// get spurious line breaks/indentation when
+		// showing the TODO body.
+		body := clean(text[m[1]:])
+		if body != "" {
+			marker := text[m[2]:m[3]]
+			r.notes[marker] = append(r.notes[marker], &Note{
+				Pos:  list[0].Pos(),
+				End:  list[len(list)-1].End(),
+				UID:  text[m[4]:m[5]],
+				Body: body,
+			})
+		}
+	}
+}
+
+// readNotes extracts notes from comments.
+// A note must start at the beginning of a comment with "MARKER(uid):"
+// and is followed by the note body (e.g., "// BUG(gri): fix this").
+// The note ends at the end of the comment group or at the start of
+// another note in the same comment group, whichever comes first.
+func (r *reader) readNotes(comments []*ast.CommentGroup) {
+	for _, group := range comments {
+		i := -1 // comment index of most recent note start, valid if >= 0
+		list := group.List
+		for j, c := range list {
+			if noteCommentRx.MatchString(c.Text) {
+				if i >= 0 {
+					r.readNote(list[i:j])
+				}
+				i = j
+			}
+		}
+		if i >= 0 {
+			r.readNote(list[i:])
+		}
+	}
+}
+
+// readFile adds the AST for a source file to the reader.
+func (r *reader) readFile(src *ast.File) {
+	// add package documentation
+	if src.Doc != nil {
+		r.readDoc(src.Doc)
+		if r.mode&PreserveAST == 0 {
+			src.Doc = nil // doc consumed - remove from AST
+		}
+	}
+
+	// add all declarations but for functions which are processed in a separate pass
+	for _, decl := range src.Decls {
+		switch d := decl.(type) {
+		case *ast.GenDecl:
+			switch d.Tok {
+			case token.IMPORT:
+				// imports are handled individually
+				for _, spec := range d.Specs {
+					if s, ok := spec.(*ast.ImportSpec); ok {
+						if import_, err := strconv.Unquote(s.Path.Value); err == nil {
+							r.imports[import_] = 1
+							var name string
+							if s.Name != nil {
+								name = s.Name.Name
+								if name == "." {
+									r.hasDotImp = true
+								}
+							}
+							if name != "." {
+								if name == "" {
+									name = assumedPackageName(import_)
+								}
+								old, ok := r.importByName[name]
+								if !ok {
+									r.importByName[name] = import_
+								} else if old != import_ && old != "" {
+									r.importByName[name] = "" // ambiguous
+								}
+							}
+						}
+					}
+				}
+			case token.CONST, token.VAR:
+				// constants and variables are always handled as a group
+				r.readValue(d)
+			case token.TYPE:
+				// types are handled individually
+				if len(d.Specs) == 1 && !d.Lparen.IsValid() {
+					// common case: single declaration w/o parentheses
+					// (if a single declaration is parenthesized,
+					// create a new fake declaration below, so that
+					// go/doc type declarations always appear w/o
+					// parentheses)
+					if s, ok := d.Specs[0].(*ast.TypeSpec); ok {
+						r.readType(d, s)
+					}
+					break
+				}
+				for _, spec := range d.Specs {
+					if s, ok := spec.(*ast.TypeSpec); ok {
+						// use an individual (possibly fake) declaration
+						// for each type; this also ensures that each type
+						// gets to (re-)use the declaration documentation
+						// if there's none associated with the spec itself
+						fake := &ast.GenDecl{
+							Doc: d.Doc,
+							// don't use the existing TokPos because it
+							// will lead to the wrong selection range for
+							// the fake declaration if there are more
+							// than one type in the group (this affects
+							// src/cmd/godoc/godoc.go's posLink_urlFunc)
+							TokPos: s.Pos(),
+							Tok:    token.TYPE,
+							Specs:  []ast.Spec{s},
+						}
+						r.readType(fake, s)
+					}
+				}
+			}
+		}
+	}
+
+	// collect MARKER(...): annotations
+	r.readNotes(src.Comments)
+	if r.mode&PreserveAST == 0 {
+		src.Comments = nil // consumed unassociated comments - remove from AST
+	}
+}
+
+func (r *reader) readPackage(pkg *ast.Package, mode Mode) {
+	// initialize reader
+	r.filenames = make([]string, len(pkg.Files))
+	r.imports = make(map[string]int)
+	r.mode = mode
+	r.types = make(map[string]*namedType)
+	r.funcs = make(methodSet)
+	r.notes = make(map[string][]*Note)
+	r.importByName = make(map[string]string)
+
+	// sort package files before reading them so that the
+	// result does not depend on map iteration order
+	i := 0
+	for filename := range pkg.Files {
+		r.filenames[i] = filename
+		i++
+	}
+	sort.Strings(r.filenames)
+
+	// process files in sorted order
+	for _, filename := range r.filenames {
+		f := pkg.Files[filename]
+		if mode&AllDecls == 0 {
+			r.fileExports(f)
+		}
+		r.readFile(f)
+	}
+
+	for name, path := range r.importByName {
+		if path == "" {
+			delete(r.importByName, name)
+		}
+	}
+
+	// process functions now that we have better type information
+	for _, f := range pkg.Files {
+		for _, decl := range f.Decls {
+			if d, ok := decl.(*ast.FuncDecl); ok {
+				r.readFunc(d)
+			}
+		}
+	}
+}
+
+// ----------------------------------------------------------------------------
+// Types
+
+func customizeRecv(f *Func, recvTypeName string, embeddedIsPtr bool, level int) *Func {
+	if f == nil || f.Decl == nil || f.Decl.Recv == nil || len(f.Decl.Recv.List) != 1 {
+		return f // shouldn't happen, but be safe
+	}
+
+	// copy existing receiver field and set new type
+	newField := *f.Decl.Recv.List[0]
+	origPos := newField.Type.Pos()
+	_, origRecvIsPtr := newField.Type.(*ast.StarExpr)
+	newIdent := &ast.Ident{NamePos: origPos, Name: recvTypeName}
+	var typ ast.Expr = newIdent
+	if !embeddedIsPtr && origRecvIsPtr {
+		newIdent.NamePos++ // '*' is one character
+		typ = &ast.StarExpr{Star: origPos, X: newIdent}
+	}
+	newField.Type = typ
+
+	// copy existing receiver field list and set new receiver field
+	newFieldList := *f.Decl.Recv
+	newFieldList.List = []*ast.Field{&newField}
+
+	// copy existing function declaration and set new receiver field list
+	newFuncDecl := *f.Decl
+	newFuncDecl.Recv = &newFieldList
+
+	// copy existing function documentation and set new declaration
+	newF := *f
+	newF.Decl = &newFuncDecl
+	newF.Recv = recvString(typ)
+	// the Orig field never changes
+	newF.Level = level
+
+	return &newF
+}
+
+// collectEmbeddedMethods collects the embedded methods of typ in mset.
+func (r *reader) collectEmbeddedMethods(mset methodSet, typ *namedType, recvTypeName string, embeddedIsPtr bool, level int, visited embeddedSet) {
+	visited[typ] = true
+	for embedded, isPtr := range typ.embedded {
+		// Once an embedded type is embedded as a pointer type
+		// all embedded types in those types are treated like
+		// pointer types for the purpose of the receiver type
+		// computation; i.e., embeddedIsPtr is sticky for this
+		// embedding hierarchy.
+		thisEmbeddedIsPtr := embeddedIsPtr || isPtr
+		for _, m := range embedded.methods {
+			// only top-level methods are embedded
+			if m.Level == 0 {
+				mset.add(customizeRecv(m, recvTypeName, thisEmbeddedIsPtr, level))
+			}
+		}
+		if !visited[embedded] {
+			r.collectEmbeddedMethods(mset, embedded, recvTypeName, thisEmbeddedIsPtr, level+1, visited)
+		}
+	}
+	delete(visited, typ)
+}
+
+// computeMethodSets determines the actual method sets for each type encountered.
+func (r *reader) computeMethodSets() {
+	for _, t := range r.types {
+		// collect embedded methods for t
+		if t.isStruct {
+			// struct
+			r.collectEmbeddedMethods(t.methods, t, t.name, false, 1, make(embeddedSet))
+		} else {
+			// interface
+			// TODO(gri) fix this
+		}
+	}
+
+	// For any predeclared names that are declared locally, don't treat them as
+	// exported fields anymore.
+	for predecl := range r.shadowedPredecl {
+		for _, ityp := range r.fixmap[predecl] {
+			removeAnonymousField(predecl, ityp)
+		}
+	}
+}
+
+// cleanupTypes removes the association of functions and methods with
+// types that have no declaration. Instead, these functions and methods
+// are shown at the package level. It also removes types with missing
+// declarations or which are not visible.
+func (r *reader) cleanupTypes() {
+	for _, t := range r.types {
+		visible := r.isVisible(t.name)
+		predeclared := predeclaredTypes[t.name]
+
+		if t.decl == nil && (predeclared || visible && (t.isEmbedded || r.hasDotImp)) {
+			// t.name is a predeclared type (and was not redeclared in this package),
+			// or it was embedded somewhere but its declaration is missing (because
+			// the AST is incomplete), or we have a dot-import (and all bets are off):
+			// move any associated values, funcs, and methods back to the top-level so
+			// that they are not lost.
+			// 1) move values
+			r.values = append(r.values, t.values...)
+			// 2) move factory functions
+			for name, f := range t.funcs {
+				// in a correct AST, package-level function names
+				// are all different - no need to check for conflicts
+				r.funcs[name] = f
+			}
+			// 3) move methods
+			if !predeclared {
+				for name, m := range t.methods {
+					// don't overwrite functions with the same name - drop them
+					if _, found := r.funcs[name]; !found {
+						r.funcs[name] = m
+					}
+				}
+			}
+		}
+		// remove types w/o declaration or which are not visible
+		if t.decl == nil || !visible {
+			delete(r.types, t.name)
+		}
+	}
+}
+
+// ----------------------------------------------------------------------------
+// Sorting
+
+type data struct {
+	n    int
+	swap func(i, j int)
+	less func(i, j int) bool
+}
+
+func (d *data) Len() int           { return d.n }
+func (d *data) Swap(i, j int)      { d.swap(i, j) }
+func (d *data) Less(i, j int) bool { return d.less(i, j) }
+
+// sortBy is a helper function for sorting.
+func sortBy(less func(i, j int) bool, swap func(i, j int), n int) {
+	sort.Sort(&data{n, swap, less})
+}
+
+func sortedKeys(m map[string]int) []string {
+	list := make([]string, len(m))
+	i := 0
+	for key := range m {
+		list[i] = key
+		i++
+	}
+	sort.Strings(list)
+	return list
+}
+
+// sortingName returns the name to use when sorting d into place.
+func sortingName(d *ast.GenDecl) string {
+	if len(d.Specs) == 1 {
+		if s, ok := d.Specs[0].(*ast.ValueSpec); ok {
+			return s.Names[0].Name
+		}
+	}
+	return ""
+}
+
+func sortedValues(m []*Value, tok token.Token) []*Value {
+	list := make([]*Value, len(m)) // big enough in any case
+	i := 0
+	for _, val := range m {
+		if val.Decl.Tok == tok {
+			list[i] = val
+			i++
+		}
+	}
+	list = list[0:i]
+
+	sortBy(
+		func(i, j int) bool {
+			if ni, nj := sortingName(list[i].Decl), sortingName(list[j].Decl); ni != nj {
+				return ni < nj
+			}
+			return list[i].order < list[j].order
+		},
+		func(i, j int) { list[i], list[j] = list[j], list[i] },
+		len(list),
+	)
+
+	return list
+}
+
+func sortedTypes(m map[string]*namedType, allMethods bool) []*Type {
+	list := make([]*Type, len(m))
+	i := 0
+	for _, t := range m {
+		list[i] = &Type{
+			Doc:     t.doc,
+			Name:    t.name,
+			Decl:    t.decl,
+			Consts:  sortedValues(t.values, token.CONST),
+			Vars:    sortedValues(t.values, token.VAR),
+			Funcs:   sortedFuncs(t.funcs, true),
+			Methods: sortedFuncs(t.methods, allMethods),
+		}
+		i++
+	}
+
+	sortBy(
+		func(i, j int) bool { return list[i].Name < list[j].Name },
+		func(i, j int) { list[i], list[j] = list[j], list[i] },
+		len(list),
+	)
+
+	return list
+}
+
+func removeStar(s string) string {
+	if len(s) > 0 && s[0] == '*' {
+		return s[1:]
+	}
+	return s
+}
+
+func sortedFuncs(m methodSet, allMethods bool) []*Func {
+	list := make([]*Func, len(m))
+	i := 0
+	for _, m := range m {
+		// determine which methods to include
+		switch {
+		case m.Decl == nil:
+			// exclude conflict entry
+		case allMethods, m.Level == 0, !token.IsExported(removeStar(m.Orig)):
+			// forced inclusion, method not embedded, or method
+			// embedded but original receiver type not exported
+			list[i] = m
+			i++
+		}
+	}
+	list = list[0:i]
+	sortBy(
+		func(i, j int) bool { return list[i].Name < list[j].Name },
+		func(i, j int) { list[i], list[j] = list[j], list[i] },
+		len(list),
+	)
+	return list
+}
+
+// noteBodies returns a list of note body strings given a list of notes.
+// This is only used to populate the deprecated Package.Bugs field.
+func noteBodies(notes []*Note) []string {
+	var list []string
+	for _, n := range notes {
+		list = append(list, n.Body)
+	}
+	return list
+}
+
+// ----------------------------------------------------------------------------
+// Predeclared identifiers
+
+// IsPredeclared reports whether s is a predeclared identifier.
+func IsPredeclared(s string) bool {
+	return predeclaredTypes[s] || predeclaredFuncs[s] || predeclaredConstants[s]
+}
+
+var predeclaredTypes = map[string]bool{
+	"any":        true,
+	"bool":       true,
+	"byte":       true,
+	"comparable": true,
+	"complex64":  true,
+	"complex128": true,
+	"error":      true,
+	"float32":    true,
+	"float64":    true,
+	"int":        true,
+	"int8":       true,
+	"int16":      true,
+	"int32":      true,
+	"int64":      true,
+	"rune":       true,
+	"string":     true,
+	"uint":       true,
+	"uint8":      true,
+	"uint16":     true,
+	"uint32":     true,
+	"uint64":     true,
+	"uintptr":    true,
+}
+
+var predeclaredFuncs = map[string]bool{
+	"append":  true,
+	"cap":     true,
+	"close":   true,
+	"complex": true,
+	"copy":    true,
+	"delete":  true,
+	"imag":    true,
+	"len":     true,
+	"make":    true,
+	"new":     true,
+	"panic":   true,
+	"print":   true,
+	"println": true,
+	"real":    true,
+	"recover": true,
+}
+
+var predeclaredConstants = map[string]bool{
+	"false": true,
+	"iota":  true,
+	"nil":   true,
+	"true":  true,
+}
+
+// assumedPackageName returns the assumed package name
+// for a given import path. This is a copy of
+// golang.org/x/tools/internal/imports.ImportPathToAssumedName.
+func assumedPackageName(importPath string) string {
+	notIdentifier := func(ch rune) bool {
+		return !('a' <= ch && ch <= 'z' || 'A' <= ch && ch <= 'Z' ||
+			'0' <= ch && ch <= '9' ||
+			ch == '_' ||
+			ch >= utf8.RuneSelf && (unicode.IsLetter(ch) || unicode.IsDigit(ch)))
+	}
+
+	base := path.Base(importPath)
+	if strings.HasPrefix(base, "v") {
+		if _, err := strconv.Atoi(base[1:]); err == nil {
+			dir := path.Dir(importPath)
+			if dir != "." {
+				base = path.Base(dir)
+			}
+		}
+	}
+	base = strings.TrimPrefix(base, "go-")
+	if i := strings.IndexFunc(base, notIdentifier); i >= 0 {
+		base = base[:i]
+	}
+	return base
+}
diff --git a/src/go/doc/synopsis.go b/src/go/doc/synopsis.go
new file mode 100644
index 0000000..3c9e7e9
--- /dev/null
+++ b/src/go/doc/synopsis.go
@@ -0,0 +1,78 @@
+// Copyright 2012 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 doc
+
+import (
+	"go/doc/comment"
+	"strings"
+	"unicode"
+)
+
+// firstSentence returns the first sentence in s.
+// The sentence ends after the first period followed by space and
+// not preceded by exactly one uppercase letter.
+func firstSentence(s string) string {
+	var ppp, pp, p rune
+	for i, q := range s {
+		if q == '\n' || q == '\r' || q == '\t' {
+			q = ' '
+		}
+		if q == ' ' && p == '.' && (!unicode.IsUpper(pp) || unicode.IsUpper(ppp)) {
+			return s[:i]
+		}
+		if p == '。' || p == '．' {
+			return s[:i]
+		}
+		ppp, pp, p = pp, p, q
+	}
+	return s
+}
+
+// Synopsis returns a cleaned version of the first sentence in text.
+//
+// Deprecated: New programs should use [Package.Synopsis] instead,
+// which handles links in text properly.
+func Synopsis(text string) string {
+	var p Package
+	return p.Synopsis(text)
+}
+
+// IllegalPrefixes is a list of lower-case prefixes that identify
+// a comment as not being a doc comment.
+// This helps to avoid misinterpreting the common mistake
+// of a copyright notice immediately before a package statement
+// as being a doc comment.
+var IllegalPrefixes = []string{
+	"copyright",
+	"all rights",
+	"author",
+}
+
+// Synopsis returns a cleaned version of the first sentence in text.
+// That sentence ends after the first period followed by space and not
+// preceded by exactly one uppercase letter, or at the first paragraph break.
+// The result string has no \n, \r, or \t characters and uses only single
+// spaces between words. If text starts with any of the IllegalPrefixes,
+// the result is the empty string.
+func (p *Package) Synopsis(text string) string {
+	text = firstSentence(text)
+	lower := strings.ToLower(text)
+	for _, prefix := range IllegalPrefixes {
+		if strings.HasPrefix(lower, prefix) {
+			return ""
+		}
+	}
+	pr := p.Printer()
+	pr.TextWidth = -1
+	d := p.Parser().Parse(text)
+	if len(d.Content) == 0 {
+		return ""
+	}
+	if _, ok := d.Content[0].(*comment.Paragraph); !ok {
+		return ""
+	}
+	d.Content = d.Content[:1] // might be blank lines, code blocks, etc in “first sentence”
+	return strings.TrimSpace(string(pr.Text(d)))
+}
diff --git a/src/go/doc/synopsis_test.go b/src/go/doc/synopsis_test.go
new file mode 100644
index 0000000..158c734
--- /dev/null
+++ b/src/go/doc/synopsis_test.go
@@ -0,0 +1,52 @@
+// Copyright 2012 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 doc
+
+import "testing"
+
+var tests = []struct {
+	txt string
+	fsl int
+	syn string
+}{
+	{"", 0, ""},
+	{"foo", 3, "foo"},
+	{"foo.", 4, "foo."},
+	{"foo.bar", 7, "foo.bar"},
+	{"  foo.  ", 6, "foo."},
+	{"  foo\t  bar.\n", 12, "foo bar."},
+	{"  foo\t  bar.\n", 12, "foo bar."},
+	{"a  b\n\nc\r\rd\t\t", 12, "a b"},
+	{"a  b\n\nc\r\rd\t\t  . BLA", 15, "a b"},
+	{"Package poems by T.S.Eliot. To rhyme...", 27, "Package poems by T.S.Eliot."},
+	{"Package poems by T. S. Eliot. To rhyme...", 29, "Package poems by T. S. Eliot."},
+	{"foo implements the foo ABI. The foo ABI is...", 27, "foo implements the foo ABI."},
+	{"Package\nfoo. ..", 12, "Package foo."},
+	{"P . Q.", 3, "P ."},
+	{"P. Q.   ", 8, "P. Q."},
+	{"Package Καλημέρα κόσμε.", 36, "Package Καλημέρα κόσμε."},
+	{"Package こんにちは 世界\n", 31, "Package こんにちは 世界"},
+	{"Package こんにちは。世界", 26, "Package こんにちは。"},
+	{"Package 안녕．世界", 17, "Package 안녕．"},
+	{"Package foo does bar.", 21, "Package foo does bar."},
+	{"Copyright 2012 Google, Inc. Package foo does bar.", 27, ""},
+	{"All Rights reserved. Package foo does bar.", 20, ""},
+	{"All rights reserved. Package foo does bar.", 20, ""},
+	{"Authors: foo@bar.com. Package foo does bar.", 21, ""},
+	{"typically invoked as ``go tool asm'',", 37, "typically invoked as “go tool asm”,"},
+}
+
+func TestSynopsis(t *testing.T) {
+	for _, e := range tests {
+		fs := firstSentence(e.txt)
+		if fs != e.txt[:e.fsl] {
+			t.Errorf("firstSentence(%q) = %q, want %q", e.txt, fs, e.txt[:e.fsl])
+		}
+		syn := Synopsis(e.txt)
+		if syn != e.syn {
+			t.Errorf("Synopsis(%q) = %q, want %q", e.txt, syn, e.syn)
+		}
+	}
+}
diff --git a/src/go/doc/testdata/a.0.golden b/src/go/doc/testdata/a.0.golden
new file mode 100644
index 0000000..7e680b8
--- /dev/null
+++ b/src/go/doc/testdata/a.0.golden
@@ -0,0 +1,52 @@
+// comment 0  comment 1 
+PACKAGE a
+
+IMPORTPATH
+	testdata/a
+
+FILENAMES
+	testdata/a0.go
+	testdata/a1.go
+
+BUGS .Bugs is now deprecated, please use .Notes instead
+	bug0
+
+	bug1
+
+
+BUGS
+BUG(uid)	bug0
+
+BUG(uid)	bug1
+
+
+NOTES
+NOTE(uid)	
+
+NOTE(foo)	1 of 4 - this is the first line of note 1
+	- note 1 continues on this 2nd line
+	- note 1 continues on this 3rd line
+
+NOTE(foo)	2 of 4
+
+NOTE(bar)	3 of 4
+
+NOTE(bar)	4 of 4
+	- this is the last line of note 4
+
+NOTE(bam)	This note which contains a (parenthesized) subphrase
+	 must appear in its entirety.
+
+NOTE(xxx)	The ':' after the marker and uid is optional.
+
+
+SECBUGS
+SECBUG(uid)	sec hole 0
+	need to fix asap
+
+
+TODOS
+TODO(uid)	todo0
+
+TODO(uid)	todo1
+
diff --git a/src/go/doc/testdata/a.1.golden b/src/go/doc/testdata/a.1.golden
new file mode 100644
index 0000000..7e680b8
--- /dev/null
+++ b/src/go/doc/testdata/a.1.golden
@@ -0,0 +1,52 @@
+// comment 0  comment 1 
+PACKAGE a
+
+IMPORTPATH
+	testdata/a
+
+FILENAMES
+	testdata/a0.go
+	testdata/a1.go
+
+BUGS .Bugs is now deprecated, please use .Notes instead
+	bug0
+
+	bug1
+
+
+BUGS
+BUG(uid)	bug0
+
+BUG(uid)	bug1
+
+
+NOTES
+NOTE(uid)	
+
+NOTE(foo)	1 of 4 - this is the first line of note 1
+	- note 1 continues on this 2nd line
+	- note 1 continues on this 3rd line
+
+NOTE(foo)	2 of 4
+
+NOTE(bar)	3 of 4
+
+NOTE(bar)	4 of 4
+	- this is the last line of note 4
+
+NOTE(bam)	This note which contains a (parenthesized) subphrase
+	 must appear in its entirety.
+
+NOTE(xxx)	The ':' after the marker and uid is optional.
+
+
+SECBUGS
+SECBUG(uid)	sec hole 0
+	need to fix asap
+
+
+TODOS
+TODO(uid)	todo0
+
+TODO(uid)	todo1
+
diff --git a/src/go/doc/testdata/a.2.golden b/src/go/doc/testdata/a.2.golden
new file mode 100644
index 0000000..7e680b8
--- /dev/null
+++ b/src/go/doc/testdata/a.2.golden
@@ -0,0 +1,52 @@
+// comment 0  comment 1 
+PACKAGE a
+
+IMPORTPATH
+	testdata/a
+
+FILENAMES
+	testdata/a0.go
+	testdata/a1.go
+
+BUGS .Bugs is now deprecated, please use .Notes instead
+	bug0
+
+	bug1
+
+
+BUGS
+BUG(uid)	bug0
+
+BUG(uid)	bug1
+
+
+NOTES
+NOTE(uid)	
+
+NOTE(foo)	1 of 4 - this is the first line of note 1
+	- note 1 continues on this 2nd line
+	- note 1 continues on this 3rd line
+
+NOTE(foo)	2 of 4
+
+NOTE(bar)	3 of 4
+
+NOTE(bar)	4 of 4
+	- this is the last line of note 4
+
+NOTE(bam)	This note which contains a (parenthesized) subphrase
+	 must appear in its entirety.
+
+NOTE(xxx)	The ':' after the marker and uid is optional.
+
+
+SECBUGS
+SECBUG(uid)	sec hole 0
+	need to fix asap
+
+
+TODOS
+TODO(uid)	todo0
+
+TODO(uid)	todo1
+
diff --git a/src/go/doc/testdata/a0.go b/src/go/doc/testdata/a0.go
new file mode 100644
index 0000000..2420c8a
--- /dev/null
+++ b/src/go/doc/testdata/a0.go
@@ -0,0 +1,40 @@
+// Copyright 2012 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.
+
+// comment 0
+package a
+
+//BUG(uid): bug0
+
+//TODO(uid): todo0
+
+// A note with some spaces after it, should be ignored (watch out for
+// emacs modes that remove trailing whitespace).
+//NOTE(uid):
+
+// SECBUG(uid): sec hole 0
+// need to fix asap
+
+// Multiple notes may be in the same comment group and should be
+// recognized individually. Notes may start in the middle of a
+// comment group as long as they start at the beginning of an
+// individual comment.
+//
+// NOTE(foo): 1 of 4 - this is the first line of note 1
+// - note 1 continues on this 2nd line
+// - note 1 continues on this 3rd line
+// NOTE(foo): 2 of 4
+// NOTE(bar): 3 of 4
+/* NOTE(bar): 4 of 4 */
+// - this is the last line of note 4
+//
+//
+
+// NOTE(bam): This note which contains a (parenthesized) subphrase
+//            must appear in its entirety.
+
+// NOTE(xxx) The ':' after the marker and uid is optional.
+
+// NOTE(): NO uid - should not show up.
+// NOTE()  NO uid - should not show up.
diff --git a/src/go/doc/testdata/a1.go b/src/go/doc/testdata/a1.go
new file mode 100644
index 0000000..9fad1e0
--- /dev/null
+++ b/src/go/doc/testdata/a1.go
@@ -0,0 +1,12 @@
+// Copyright 2012 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.
+
+// comment 1
+package a
+
+//BUG(uid): bug1
+
+//TODO(uid): todo1
+
+//TODO(): ignored
diff --git a/src/go/doc/testdata/b.0.golden b/src/go/doc/testdata/b.0.golden
new file mode 100644
index 0000000..c06246a
--- /dev/null
+++ b/src/go/doc/testdata/b.0.golden
@@ -0,0 +1,74 @@
+// 
+PACKAGE b
+
+IMPORTPATH
+	testdata/b
+
+IMPORTS
+	a
+
+FILENAMES
+	testdata/b.go
+
+CONSTANTS
+	// 
+	const (
+		C1	notExported	= iota
+		C2
+	
+		C4
+		C5
+	)
+
+	// 
+	const C notExported = 0
+
+	// 
+	const Pi = 3.14	// Pi
+
+
+VARIABLES
+	// 
+	var (
+		U1, U2, U4, U5	notExported
+	
+		U7	notExported	= 7
+	)
+
+	// 
+	var MaxInt int	// MaxInt
+
+	// 
+	var V notExported
+
+	// 
+	var V1, V2, V4, V5 notExported
+
+
+FUNCTIONS
+	// Associated with comparable type if AllDecls is set. 
+	func ComparableFactory() comparable
+
+	// 
+	func F(x int) int
+
+	// 
+	func F1() notExported
+
+	// Always under the package functions list. 
+	func NotAFactory() int
+
+	// Associated with uint type if AllDecls is set. 
+	func UintFactory() uint
+
+
+TYPES
+	// 
+	type T struct{}	// T
+
+	// 
+	var V T	// v
+
+	// 
+	func (x *T) M()
+
diff --git a/src/go/doc/testdata/b.1.golden b/src/go/doc/testdata/b.1.golden
new file mode 100644
index 0000000..2b62c34
--- /dev/null
+++ b/src/go/doc/testdata/b.1.golden
@@ -0,0 +1,89 @@
+// 
+PACKAGE b
+
+IMPORTPATH
+	testdata/b
+
+IMPORTS
+	a
+
+FILENAMES
+	testdata/b.go
+
+CONSTANTS
+	// 
+	const Pi = 3.14	// Pi
+
+
+VARIABLES
+	// 
+	var MaxInt int	// MaxInt
+
+
+FUNCTIONS
+	// 
+	func F(x int) int
+
+	// Always under the package functions list. 
+	func NotAFactory() int
+
+
+TYPES
+	// 
+	type T struct{}	// T
+
+	// 
+	var V T	// v
+
+	// 
+	func (x *T) M()
+
+	// Should only appear if AllDecls is set. 
+	type comparable struct{}	// overrides a predeclared type comparable
+
+	// Associated with comparable type if AllDecls is set. 
+	func ComparableFactory() comparable
+
+	// 
+	type notExported int
+
+	// 
+	const (
+		C1	notExported	= iota
+		C2
+		c3
+		C4
+		C5
+	)
+
+	// 
+	const C notExported = 0
+
+	// 
+	var (
+		U1, U2, u3, U4, U5	notExported
+		u6			notExported
+		U7			notExported	= 7
+	)
+
+	// 
+	var V notExported
+
+	// 
+	var V1, V2, v3, V4, V5 notExported
+
+	// 
+	func F1() notExported
+
+	// 
+	func f2() notExported
+
+	// Should only appear if AllDecls is set. 
+	type uint struct{}	// overrides a predeclared type uint
+
+	// Associated with uint type if AllDecls is set. 
+	func UintFactory() uint
+
+	// Associated with uint type if AllDecls is set. 
+	func uintFactory() uint
+
diff --git a/src/go/doc/testdata/b.2.golden b/src/go/doc/testdata/b.2.golden
new file mode 100644
index 0000000..c06246a
--- /dev/null
+++ b/src/go/doc/testdata/b.2.golden
@@ -0,0 +1,74 @@
+// 
+PACKAGE b
+
+IMPORTPATH
+	testdata/b
+
+IMPORTS
+	a
+
+FILENAMES
+	testdata/b.go
+
+CONSTANTS
+	// 
+	const (
+		C1	notExported	= iota
+		C2
+	
+		C4
+		C5
+	)
+
+	// 
+	const C notExported = 0
+
+	// 
+	const Pi = 3.14	// Pi
+
+
+VARIABLES
+	// 
+	var (
+		U1, U2, U4, U5	notExported
+	
+		U7	notExported	= 7
+	)
+
+	// 
+	var MaxInt int	// MaxInt
+
+	// 
+	var V notExported
+
+	// 
+	var V1, V2, V4, V5 notExported
+
+
+FUNCTIONS
+	// Associated with comparable type if AllDecls is set. 
+	func ComparableFactory() comparable
+
+	// 
+	func F(x int) int
+
+	// 
+	func F1() notExported
+
+	// Always under the package functions list. 
+	func NotAFactory() int
+
+	// Associated with uint type if AllDecls is set. 
+	func UintFactory() uint
+
+
+TYPES
+	// 
+	type T struct{}	// T
+
+	// 
+	var V T	// v
+
+	// 
+	func (x *T) M()
+
diff --git a/src/go/doc/testdata/b.go b/src/go/doc/testdata/b.go
new file mode 100644
index 0000000..61b512b
--- /dev/null
+++ b/src/go/doc/testdata/b.go
@@ -0,0 +1,64 @@
+// Copyright 2012 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 b
+
+import "a"
+
+// ----------------------------------------------------------------------------
+// Basic declarations
+
+const Pi = 3.14   // Pi
+var MaxInt int    // MaxInt
+type T struct{}   // T
+var V T           // v
+func F(x int) int {} // F
+func (x *T) M()   {} // M
+
+// Corner cases: association with (presumed) predeclared types
+
+// Always under the package functions list.
+func NotAFactory() int {}
+
+// Associated with uint type if AllDecls is set.
+func UintFactory() uint {}
+
+// Associated with uint type if AllDecls is set.
+func uintFactory() uint {}
+
+// Associated with comparable type if AllDecls is set.
+func ComparableFactory() comparable {}
+
+// Should only appear if AllDecls is set.
+type uint struct{} // overrides a predeclared type uint
+
+// Should only appear if AllDecls is set.
+type comparable struct{} // overrides a predeclared type comparable
+
+// ----------------------------------------------------------------------------
+// Exported declarations associated with non-exported types must always be shown.
+
+type notExported int
+
+const C notExported = 0
+
+const (
+	C1 notExported = iota
+	C2
+	c3
+	C4
+	C5
+)
+
+var V notExported
+var V1, V2, v3, V4, V5 notExported
+
+var (
+	U1, U2, u3, U4, U5 notExported
+	u6                 notExported
+	U7                 notExported = 7
+)
+
+func F1() notExported {}
+func f2() notExported {}
diff --git a/src/go/doc/testdata/benchmark.go b/src/go/doc/testdata/benchmark.go
new file mode 100644
index 0000000..dbf6b4f
--- /dev/null
+++ b/src/go/doc/testdata/benchmark.go
@@ -0,0 +1,293 @@
+// 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.
+
+package testing
+
+import (
+	"flag"
+	"fmt"
+	"os"
+	"runtime"
+	"time"
+)
+
+var matchBenchmarks = flag.String("test.bench", "", "regular expression to select benchmarks to run")
+var benchTime = flag.Duration("test.benchtime", 1*time.Second, "approximate run time for each benchmark")
+
+// An internal type but exported because it is cross-package; part of the implementation
+// of go test.
+type InternalBenchmark struct {
+	Name string
+	F    func(b *B)
+}
+
+// B is a type passed to Benchmark functions to manage benchmark
+// timing and to specify the number of iterations to run.
+type B struct {
+	common
+	N         int
+	benchmark InternalBenchmark
+	bytes     int64
+	timerOn   bool
+	result    BenchmarkResult
+}
+
+// StartTimer starts timing a test. This function is called automatically
+// before a benchmark starts, but it can also used to resume timing after
+// a call to StopTimer.
+func (b *B) StartTimer() {
+	if !b.timerOn {
+		b.start = time.Now()
+		b.timerOn = true
+	}
+}
+
+// StopTimer stops timing a test. This can be used to pause the timer
+// while performing complex initialization that you don't
+// want to measure.
+func (b *B) StopTimer() {
+	if b.timerOn {
+		b.duration += time.Since(b.start)
+		b.timerOn = false
+	}
+}
+
+// ResetTimer sets the elapsed benchmark time to zero.
+// It does not affect whether the timer is running.
+func (b *B) ResetTimer() {
+	if b.timerOn {
+		b.start = time.Now()
+	}
+	b.duration = 0
+}
+
+// SetBytes records the number of bytes processed in a single operation.
+// If this is called, the benchmark will report ns/op and MB/s.
+func (b *B) SetBytes(n int64) { b.bytes = n }
+
+func (b *B) nsPerOp() int64 {
+	if b.N <= 0 {
+		return 0
+	}
+	return b.duration.Nanoseconds() / int64(b.N)
+}
+
+// runN runs a single benchmark for the specified number of iterations.
+func (b *B) runN(n int) {
+	// Try to get a comparable environment for each run
+	// by clearing garbage from previous runs.
+	runtime.GC()
+	b.N = n
+	b.ResetTimer()
+	b.StartTimer()
+	b.benchmark.F(b)
+	b.StopTimer()
+}
+
+func min(x, y int) int {
+	if x > y {
+		return y
+	}
+	return x
+}
+
+func max(x, y int) int {
+	if x < y {
+		return y
+	}
+	return x
+}
+
+// roundDown10 rounds a number down to the nearest power of 10.
+func roundDown10(n int) int {
+	var tens = 0
+	// tens = floor(log_10(n))
+	for n > 10 {
+		n = n / 10
+		tens++
+	}
+	// result = 10^tens
+	result := 1
+	for i := 0; i < tens; i++ {
+		result *= 10
+	}
+	return result
+}
+
+// roundUp rounds x up to a number of the form [1eX, 2eX, 5eX].
+func roundUp(n int) int {
+	base := roundDown10(n)
+	if n < (2 * base) {
+		return 2 * base
+	}
+	if n < (5 * base) {
+		return 5 * base
+	}
+	return 10 * base
+}
+
+// run times the benchmark function in a separate goroutine.
+func (b *B) run() BenchmarkResult {
+	go b.launch()
+	<-b.signal
+	return b.result
+}
+
+// launch launches the benchmark function. It gradually increases the number
+// of benchmark iterations until the benchmark runs for a second in order
+// to get a reasonable measurement. It prints timing information in this form
+//		testing.BenchmarkHello	100000		19 ns/op
+// launch is run by the fun function as a separate goroutine.
+func (b *B) launch() {
+	// Run the benchmark for a single iteration in case it's expensive.
+	n := 1
+
+	// Signal that we're done whether we return normally
+	// or by FailNow's runtime.Goexit.
+	defer func() {
+		b.signal <- b
+	}()
+
+	b.runN(n)
+	// Run the benchmark for at least the specified amount of time.
+	d := *benchTime
+	for !b.failed && b.duration < d && n < 1e9 {
+		last := n
+		// Predict iterations/sec.
+		if b.nsPerOp() == 0 {
+			n = 1e9
+		} else {
+			n = int(d.Nanoseconds() / b.nsPerOp())
+		}
+		// Run more iterations than we think we'll need for a second (1.5x).
+		// Don't grow too fast in case we had timing errors previously.
+		// Be sure to run at least one more than last time.
+		n = max(min(n+n/2, 100*last), last+1)
+		// Round up to something easy to read.
+		n = roundUp(n)
+		b.runN(n)
+	}
+	b.result = BenchmarkResult{b.N, b.duration, b.bytes}
+}
+
+// The results of a benchmark run.
+type BenchmarkResult struct {
+	N     int           // The number of iterations.
+	T     time.Duration // The total time taken.
+	Bytes int64         // Bytes processed in one iteration.
+}
+
+func (r BenchmarkResult) NsPerOp() int64 {
+	if r.N <= 0 {
+		return 0
+	}
+	return r.T.Nanoseconds() / int64(r.N)
+}
+
+func (r BenchmarkResult) mbPerSec() float64 {
+	if r.Bytes <= 0 || r.T <= 0 || r.N <= 0 {
+		return 0
+	}
+	return (float64(r.Bytes) * float64(r.N) / 1e6) / r.T.Seconds()
+}
+
+func (r BenchmarkResult) String() string {
+	mbs := r.mbPerSec()
+	mb := ""
+	if mbs != 0 {
+		mb = fmt.Sprintf("\t%7.2f MB/s", mbs)
+	}
+	nsop := r.NsPerOp()
+	ns := fmt.Sprintf("%10d ns/op", nsop)
+	if r.N > 0 && nsop < 100 {
+		// The format specifiers here make sure that
+		// the ones digits line up for all three possible formats.
+		if nsop < 10 {
+			ns = fmt.Sprintf("%13.2f ns/op", float64(r.T.Nanoseconds())/float64(r.N))
+		} else {
+			ns = fmt.Sprintf("%12.1f ns/op", float64(r.T.Nanoseconds())/float64(r.N))
+		}
+	}
+	return fmt.Sprintf("%8d\t%s%s", r.N, ns, mb)
+}
+
+// An internal function but exported because it is cross-package; part of the implementation
+// of go test.
+func RunBenchmarks(matchString func(pat, str string) (bool, error), benchmarks []InternalBenchmark) {
+	// If no flag was specified, don't run benchmarks.
+	if len(*matchBenchmarks) == 0 {
+		return
+	}
+	for _, Benchmark := range benchmarks {
+		matched, err := matchString(*matchBenchmarks, Benchmark.Name)
+		if err != nil {
+			fmt.Fprintf(os.Stderr, "testing: invalid regexp for -test.bench: %s\n", err)
+			os.Exit(1)
+		}
+		if !matched {
+			continue
+		}
+		for _, procs := range cpuList {
+			runtime.GOMAXPROCS(procs)
+			b := &B{
+				common: common{
+					signal: make(chan any),
+				},
+				benchmark: Benchmark,
+			}
+			benchName := Benchmark.Name
+			if procs != 1 {
+				benchName = fmt.Sprintf("%s-%d", Benchmark.Name, procs)
+			}
+			fmt.Printf("%s\t", benchName)
+			r := b.run()
+			if b.failed {
+				// The output could be very long here, but probably isn't.
+				// We print it all, regardless, because we don't want to trim the reason
+				// the benchmark failed.
+				fmt.Printf("--- FAIL: %s\n%s", benchName, b.output)
+				continue
+			}
+			fmt.Printf("%v\n", r)
+			// Unlike with tests, we ignore the -chatty flag and always print output for
+			// benchmarks since the output generation time will skew the results.
+			if len(b.output) > 0 {
+				b.trimOutput()
+				fmt.Printf("--- BENCH: %s\n%s", benchName, b.output)
+			}
+			if p := runtime.GOMAXPROCS(-1); p != procs {
+				fmt.Fprintf(os.Stderr, "testing: %s left GOMAXPROCS set to %d\n", benchName, p)
+			}
+		}
+	}
+}
+
+// trimOutput shortens the output from a benchmark, which can be very long.
+func (b *B) trimOutput() {
+	// The output is likely to appear multiple times because the benchmark
+	// is run multiple times, but at least it will be seen. This is not a big deal
+	// because benchmarks rarely print, but just in case, we trim it if it's too long.
+	const maxNewlines = 10
+	for nlCount, j := 0, 0; j < len(b.output); j++ {
+		if b.output[j] == '\n' {
+			nlCount++
+			if nlCount >= maxNewlines {
+				b.output = append(b.output[:j], "\n\t... [output truncated]\n"...)
+				break
+			}
+		}
+	}
+}
+
+// Benchmark benchmarks a single function. Useful for creating
+// custom benchmarks that do not use go test.
+func Benchmark(f func(b *B)) BenchmarkResult {
+	b := &B{
+		common: common{
+			signal: make(chan any),
+		},
+		benchmark: InternalBenchmark{"", f},
+	}
+	return b.run()
+}
diff --git a/src/go/doc/testdata/blank.0.golden b/src/go/doc/testdata/blank.0.golden
new file mode 100644
index 0000000..70f2929
--- /dev/null
+++ b/src/go/doc/testdata/blank.0.golden
@@ -0,0 +1,62 @@
+// Package blank is a go/doc test for the handling of _. See issue ...
+PACKAGE blank
+
+IMPORTPATH
+	testdata/blank
+
+IMPORTS
+	os
+
+FILENAMES
+	testdata/blank.go
+
+CONSTANTS
+	// T constants counting from unexported constants. 
+	const (
+		C1	T
+		C2
+	
+		C3
+	
+		C4	int
+	)
+
+	// Constants with a single type that is not propagated. 
+	const (
+		Default		= 0644
+		Useless		= 0312
+		WideOpen	= 0777
+	)
+
+	// Constants with an imported type that is propagated. 
+	const (
+		M1	os.FileMode
+		M2
+		M3
+	)
+
+	// Package constants. 
+	const (
+		I1	int
+		I2
+	)
+
+
+TYPES
+	// S has a padding field. 
+	type S struct {
+		H	uint32
+	
+		A	uint8
+		// contains filtered or unexported fields
+	}
+
+	// 
+	type T int
+
+	// T constants counting from a blank constant. 
+	const (
+		T1	T
+		T2
+	)
+
diff --git a/src/go/doc/testdata/blank.1.golden b/src/go/doc/testdata/blank.1.golden
new file mode 100644
index 0000000..8098cb6
--- /dev/null
+++ b/src/go/doc/testdata/blank.1.golden
@@ -0,0 +1,83 @@
+// Package blank is a go/doc test for the handling of _. See issue ...
+PACKAGE blank
+
+IMPORTPATH
+	testdata/blank
+
+IMPORTS
+	os
+
+FILENAMES
+	testdata/blank.go
+
+CONSTANTS
+	// T constants counting from unexported constants. 
+	const (
+		tweedledee	T	= iota
+		tweedledum
+		C1
+		C2
+		alice
+		C3
+		redQueen	int	= iota
+		C4
+	)
+
+	// Constants with a single type that is not propagated. 
+	const (
+		zero		os.FileMode	= 0
+		Default				= 0644
+		Useless				= 0312
+		WideOpen			= 0777
+	)
+
+	// Constants with an imported type that is propagated. 
+	const (
+		zero	os.FileMode	= 0
+		M1
+		M2
+		M3
+	)
+
+	// Package constants. 
+	const (
+		_	int	= iota
+		I1
+		I2
+	)
+
+	// Unexported constants counting from blank iota. See issue 9615. 
+	const (
+		_	= iota
+		one	= iota + 1
+	)
+
+
+VARIABLES
+	// 
+	var _ = T(55)
+
+
+FUNCTIONS
+	// 
+	func _()
+
+
+TYPES
+	// S has a padding field. 
+	type S struct {
+		H	uint32
+		_	uint8
+		A	uint8
+	}
+
+	// 
+	type T int
+
+	// T constants counting from a blank constant. 
+	const (
+		_	T	= iota
+		T1
+		T2
+	)
+
diff --git a/src/go/doc/testdata/blank.2.golden b/src/go/doc/testdata/blank.2.golden
new file mode 100644
index 0000000..70f2929
--- /dev/null
+++ b/src/go/doc/testdata/blank.2.golden
@@ -0,0 +1,62 @@
+// Package blank is a go/doc test for the handling of _. See issue ...
+PACKAGE blank
+
+IMPORTPATH
+	testdata/blank
+
+IMPORTS
+	os
+
+FILENAMES
+	testdata/blank.go
+
+CONSTANTS
+	// T constants counting from unexported constants. 
+	const (
+		C1	T
+		C2
+	
+		C3
+	
+		C4	int
+	)
+
+	// Constants with a single type that is not propagated. 
+	const (
+		Default		= 0644
+		Useless		= 0312
+		WideOpen	= 0777
+	)
+
+	// Constants with an imported type that is propagated. 
+	const (
+		M1	os.FileMode
+		M2
+		M3
+	)
+
+	// Package constants. 
+	const (
+		I1	int
+		I2
+	)
+
+
+TYPES
+	// S has a padding field. 
+	type S struct {
+		H	uint32
+	
+		A	uint8
+		// contains filtered or unexported fields
+	}
+
+	// 
+	type T int
+
+	// T constants counting from a blank constant. 
+	const (
+		T1	T
+		T2
+	)
+
diff --git a/src/go/doc/testdata/blank.go b/src/go/doc/testdata/blank.go
new file mode 100644
index 0000000..5ea6186
--- /dev/null
+++ b/src/go/doc/testdata/blank.go
@@ -0,0 +1,75 @@
+// Copyright 2014 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 blank is a go/doc test for the handling of _.
+// See issue 5397.
+package blank
+
+import "os"
+
+type T int
+
+// T constants counting from a blank constant.
+const (
+	_ T = iota
+	T1
+	T2
+)
+
+// T constants counting from unexported constants.
+const (
+	tweedledee T = iota
+	tweedledum
+	C1
+	C2
+	alice
+	C3
+	redQueen int = iota
+	C4
+)
+
+// Constants with a single type that is not propagated.
+const (
+	zero     os.FileMode = 0
+	Default              = 0644
+	Useless              = 0312
+	WideOpen             = 0777
+)
+
+// Constants with an imported type that is propagated.
+const (
+	zero os.FileMode = 0
+	M1
+	M2
+	M3
+)
+
+// Package constants.
+const (
+	_ int = iota
+	I1
+	I2
+)
+
+// Unexported constants counting from blank iota.
+// See issue 9615.
+const (
+	_   = iota
+	one = iota + 1
+)
+
+// Blanks not in doc output:
+
+// S has a padding field.
+type S struct {
+	H uint32
+	_ uint8
+	A uint8
+}
+
+func _() {}
+
+type _ T
+
+var _ = T(55)
diff --git a/src/go/doc/testdata/bugpara.0.golden b/src/go/doc/testdata/bugpara.0.golden
new file mode 100644
index 0000000..5804859
--- /dev/null
+++ b/src/go/doc/testdata/bugpara.0.golden
@@ -0,0 +1,20 @@
+// 
+PACKAGE bugpara
+
+IMPORTPATH
+	testdata/bugpara
+
+FILENAMES
+	testdata/bugpara.go
+
+BUGS .Bugs is now deprecated, please use .Notes instead
+	Sometimes bugs have multiple paragraphs.
+	
+	Like this one.
+
+
+BUGS
+BUG(rsc)	Sometimes bugs have multiple paragraphs.
+	
+	Like this one.
+
diff --git a/src/go/doc/testdata/bugpara.1.golden b/src/go/doc/testdata/bugpara.1.golden
new file mode 100644
index 0000000..5804859
--- /dev/null
+++ b/src/go/doc/testdata/bugpara.1.golden
@@ -0,0 +1,20 @@
+// 
+PACKAGE bugpara
+
+IMPORTPATH
+	testdata/bugpara
+
+FILENAMES
+	testdata/bugpara.go
+
+BUGS .Bugs is now deprecated, please use .Notes instead
+	Sometimes bugs have multiple paragraphs.
+	
+	Like this one.
+
+
+BUGS
+BUG(rsc)	Sometimes bugs have multiple paragraphs.
+	
+	Like this one.
+
diff --git a/src/go/doc/testdata/bugpara.2.golden b/src/go/doc/testdata/bugpara.2.golden
new file mode 100644
index 0000000..5804859
--- /dev/null
+++ b/src/go/doc/testdata/bugpara.2.golden
@@ -0,0 +1,20 @@
+// 
+PACKAGE bugpara
+
+IMPORTPATH
+	testdata/bugpara
+
+FILENAMES
+	testdata/bugpara.go
+
+BUGS .Bugs is now deprecated, please use .Notes instead
+	Sometimes bugs have multiple paragraphs.
+	
+	Like this one.
+
+
+BUGS
+BUG(rsc)	Sometimes bugs have multiple paragraphs.
+	
+	Like this one.
+
diff --git a/src/go/doc/testdata/bugpara.go b/src/go/doc/testdata/bugpara.go
new file mode 100644
index 0000000..0360a6f
--- /dev/null
+++ b/src/go/doc/testdata/bugpara.go
@@ -0,0 +1,9 @@
+// Copyright 2013 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 bugpara
+
+// BUG(rsc): Sometimes bugs have multiple paragraphs.
+//
+// Like this one.
diff --git a/src/go/doc/testdata/c.0.golden b/src/go/doc/testdata/c.0.golden
new file mode 100644
index 0000000..e21959b
--- /dev/null
+++ b/src/go/doc/testdata/c.0.golden
@@ -0,0 +1,48 @@
+// 
+PACKAGE c
+
+IMPORTPATH
+	testdata/c
+
+IMPORTS
+	a
+
+FILENAMES
+	testdata/c.go
+
+TYPES
+	// A (should see this) 
+	type A struct{}
+
+	// B (should see this) 
+	type B struct{}
+
+	// C (should see this) 
+	type C struct{}
+
+	// D (should see this) 
+	type D struct{}
+
+	// E1 (should see this) 
+	type E1 struct{}
+
+	// E (should see this for E2 and E3) 
+	type E2 struct{}
+
+	// E (should see this for E2 and E3) 
+	type E3 struct{}
+
+	// E4 (should see this) 
+	type E4 struct{}
+
+	// 
+	type T1 struct{}
+
+	// 
+	func (t1 *T1) M()
+
+	// T2 must not show methods of local T1 
+	type T2 struct {
+		a.T1	// not the same as locally declared T1
+	}
+
diff --git a/src/go/doc/testdata/c.1.golden b/src/go/doc/testdata/c.1.golden
new file mode 100644
index 0000000..e21959b
--- /dev/null
+++ b/src/go/doc/testdata/c.1.golden
@@ -0,0 +1,48 @@
+// 
+PACKAGE c
+
+IMPORTPATH
+	testdata/c
+
+IMPORTS
+	a
+
+FILENAMES
+	testdata/c.go
+
+TYPES
+	// A (should see this) 
+	type A struct{}
+
+	// B (should see this) 
+	type B struct{}
+
+	// C (should see this) 
+	type C struct{}
+
+	// D (should see this) 
+	type D struct{}
+
+	// E1 (should see this) 
+	type E1 struct{}
+
+	// E (should see this for E2 and E3) 
+	type E2 struct{}
+
+	// E (should see this for E2 and E3) 
+	type E3 struct{}
+
+	// E4 (should see this) 
+	type E4 struct{}
+
+	// 
+	type T1 struct{}
+
+	// 
+	func (t1 *T1) M()
+
+	// T2 must not show methods of local T1 
+	type T2 struct {
+		a.T1	// not the same as locally declared T1
+	}
+
diff --git a/src/go/doc/testdata/c.2.golden b/src/go/doc/testdata/c.2.golden
new file mode 100644
index 0000000..e21959b
--- /dev/null
+++ b/src/go/doc/testdata/c.2.golden
@@ -0,0 +1,48 @@
+// 
+PACKAGE c
+
+IMPORTPATH
+	testdata/c
+
+IMPORTS
+	a
+
+FILENAMES
+	testdata/c.go
+
+TYPES
+	// A (should see this) 
+	type A struct{}
+
+	// B (should see this) 
+	type B struct{}
+
+	// C (should see this) 
+	type C struct{}
+
+	// D (should see this) 
+	type D struct{}
+
+	// E1 (should see this) 
+	type E1 struct{}
+
+	// E (should see this for E2 and E3) 
+	type E2 struct{}
+
+	// E (should see this for E2 and E3) 
+	type E3 struct{}
+
+	// E4 (should see this) 
+	type E4 struct{}
+
+	// 
+	type T1 struct{}
+
+	// 
+	func (t1 *T1) M()
+
+	// T2 must not show methods of local T1 
+	type T2 struct {
+		a.T1	// not the same as locally declared T1
+	}
+
diff --git a/src/go/doc/testdata/c.go b/src/go/doc/testdata/c.go
new file mode 100644
index 0000000..e0f3919
--- /dev/null
+++ b/src/go/doc/testdata/c.go
@@ -0,0 +1,62 @@
+// Copyright 2012 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 c
+
+import "a"
+
+// ----------------------------------------------------------------------------
+// Test that empty declarations don't cause problems
+
+const ()
+
+type ()
+
+var ()
+
+// ----------------------------------------------------------------------------
+// Test that types with documentation on both, the Decl and the Spec node
+// are handled correctly.
+
+// A (should see this)
+type A struct{}
+
+// B (should see this)
+type (
+	B struct{}
+)
+
+type (
+	// C (should see this)
+	C struct{}
+)
+
+// D (should not see this)
+type (
+	// D (should see this)
+	D struct{}
+)
+
+// E (should see this for E2 and E3)
+type (
+	// E1 (should see this)
+	E1 struct{}
+	E2 struct{}
+	E3 struct{}
+	// E4 (should see this)
+	E4 struct{}
+)
+
+// ----------------------------------------------------------------------------
+// Test that local and imported types are different when
+// handling anonymous fields.
+
+type T1 struct{}
+
+func (t1 *T1) M() {}
+
+// T2 must not show methods of local T1
+type T2 struct {
+	a.T1 // not the same as locally declared T1
+}
diff --git a/src/go/doc/testdata/d.0.golden b/src/go/doc/testdata/d.0.golden
new file mode 100644
index 0000000..c005199
--- /dev/null
+++ b/src/go/doc/testdata/d.0.golden
@@ -0,0 +1,104 @@
+// 
+PACKAGE d
+
+IMPORTPATH
+	testdata/d
+
+FILENAMES
+	testdata/d1.go
+	testdata/d2.go
+
+CONSTANTS
+	// CBx constants should appear before CAx constants. 
+	const (
+		CB2	= iota	// before CB1
+		CB1		// before CB0
+		CB0		// at end
+	)
+
+	// CAx constants should appear after CBx constants. 
+	const (
+		CA2	= iota	// before CA1
+		CA1		// before CA0
+		CA0		// at end
+	)
+
+	// C0 should be first. 
+	const C0 = 0
+
+	// C1 should be second. 
+	const C1 = 1
+
+	// C2 should be third. 
+	const C2 = 2
+
+	// 
+	const (
+		// Single const declarations inside ()'s are considered ungrouped
+		// and show up in sorted order.
+		Cungrouped = 0
+	)
+
+
+VARIABLES
+	// VBx variables should appear before VAx variables. 
+	var (
+		VB2	int	// before VB1
+		VB1	int	// before VB0
+		VB0	int	// at end
+	)
+
+	// VAx variables should appear after VBx variables. 
+	var (
+		VA2	int	// before VA1
+		VA1	int	// before VA0
+		VA0	int	// at end
+	)
+
+	// V0 should be first. 
+	var V0 uintptr
+
+	// V1 should be second. 
+	var V1 uint
+
+	// V2 should be third. 
+	var V2 int
+
+	// 
+	var (
+		// Single var declarations inside ()'s are considered ungrouped
+		// and show up in sorted order.
+		Vungrouped = 0
+	)
+
+
+FUNCTIONS
+	// F0 should be first. 
+	func F0()
+
+	// F1 should be second. 
+	func F1()
+
+	// F2 should be third. 
+	func F2()
+
+
+TYPES
+	// T0 should be first. 
+	type T0 struct{}
+
+	// T1 should be second. 
+	type T1 struct{}
+
+	// T2 should be third. 
+	type T2 struct{}
+
+	// TG0 should be first. 
+	type TG0 struct{}
+
+	// TG1 should be second. 
+	type TG1 struct{}
+
+	// TG2 should be third. 
+	type TG2 struct{}
+
diff --git a/src/go/doc/testdata/d.1.golden b/src/go/doc/testdata/d.1.golden
new file mode 100644
index 0000000..c005199
--- /dev/null
+++ b/src/go/doc/testdata/d.1.golden
@@ -0,0 +1,104 @@
+// 
+PACKAGE d
+
+IMPORTPATH
+	testdata/d
+
+FILENAMES
+	testdata/d1.go
+	testdata/d2.go
+
+CONSTANTS
+	// CBx constants should appear before CAx constants. 
+	const (
+		CB2	= iota	// before CB1
+		CB1		// before CB0
+		CB0		// at end
+	)
+
+	// CAx constants should appear after CBx constants. 
+	const (
+		CA2	= iota	// before CA1
+		CA1		// before CA0
+		CA0		// at end
+	)
+
+	// C0 should be first. 
+	const C0 = 0
+
+	// C1 should be second. 
+	const C1 = 1
+
+	// C2 should be third. 
+	const C2 = 2
+
+	// 
+	const (
+		// Single const declarations inside ()'s are considered ungrouped
+		// and show up in sorted order.
+		Cungrouped = 0
+	)
+
+
+VARIABLES
+	// VBx variables should appear before VAx variables. 
+	var (
+		VB2	int	// before VB1
+		VB1	int	// before VB0
+		VB0	int	// at end
+	)
+
+	// VAx variables should appear after VBx variables. 
+	var (
+		VA2	int	// before VA1
+		VA1	int	// before VA0
+		VA0	int	// at end
+	)
+
+	// V0 should be first. 
+	var V0 uintptr
+
+	// V1 should be second. 
+	var V1 uint
+
+	// V2 should be third. 
+	var V2 int
+
+	// 
+	var (
+		// Single var declarations inside ()'s are considered ungrouped
+		// and show up in sorted order.
+		Vungrouped = 0
+	)
+
+
+FUNCTIONS
+	// F0 should be first. 
+	func F0()
+
+	// F1 should be second. 
+	func F1()
+
+	// F2 should be third. 
+	func F2()
+
+
+TYPES
+	// T0 should be first. 
+	type T0 struct{}
+
+	// T1 should be second. 
+	type T1 struct{}
+
+	// T2 should be third. 
+	type T2 struct{}
+
+	// TG0 should be first. 
+	type TG0 struct{}
+
+	// TG1 should be second. 
+	type TG1 struct{}
+
+	// TG2 should be third. 
+	type TG2 struct{}
+
diff --git a/src/go/doc/testdata/d.2.golden b/src/go/doc/testdata/d.2.golden
new file mode 100644
index 0000000..c005199
--- /dev/null
+++ b/src/go/doc/testdata/d.2.golden
@@ -0,0 +1,104 @@
+// 
+PACKAGE d
+
+IMPORTPATH
+	testdata/d
+
+FILENAMES
+	testdata/d1.go
+	testdata/d2.go
+
+CONSTANTS
+	// CBx constants should appear before CAx constants. 
+	const (
+		CB2	= iota	// before CB1
+		CB1		// before CB0
+		CB0		// at end
+	)
+
+	// CAx constants should appear after CBx constants. 
+	const (
+		CA2	= iota	// before CA1
+		CA1		// before CA0
+		CA0		// at end
+	)
+
+	// C0 should be first. 
+	const C0 = 0
+
+	// C1 should be second. 
+	const C1 = 1
+
+	// C2 should be third. 
+	const C2 = 2
+
+	// 
+	const (
+		// Single const declarations inside ()'s are considered ungrouped
+		// and show up in sorted order.
+		Cungrouped = 0
+	)
+
+
+VARIABLES
+	// VBx variables should appear before VAx variables. 
+	var (
+		VB2	int	// before VB1
+		VB1	int	// before VB0
+		VB0	int	// at end
+	)
+
+	// VAx variables should appear after VBx variables. 
+	var (
+		VA2	int	// before VA1
+		VA1	int	// before VA0
+		VA0	int	// at end
+	)
+
+	// V0 should be first. 
+	var V0 uintptr
+
+	// V1 should be second. 
+	var V1 uint
+
+	// V2 should be third. 
+	var V2 int
+
+	// 
+	var (
+		// Single var declarations inside ()'s are considered ungrouped
+		// and show up in sorted order.
+		Vungrouped = 0
+	)
+
+
+FUNCTIONS
+	// F0 should be first. 
+	func F0()
+
+	// F1 should be second. 
+	func F1()
+
+	// F2 should be third. 
+	func F2()
+
+
+TYPES
+	// T0 should be first. 
+	type T0 struct{}
+
+	// T1 should be second. 
+	type T1 struct{}
+
+	// T2 should be third. 
+	type T2 struct{}
+
+	// TG0 should be first. 
+	type TG0 struct{}
+
+	// TG1 should be second. 
+	type TG1 struct{}
+
+	// TG2 should be third. 
+	type TG2 struct{}
+
diff --git a/src/go/doc/testdata/d1.go b/src/go/doc/testdata/d1.go
new file mode 100644
index 0000000..ebd6941
--- /dev/null
+++ b/src/go/doc/testdata/d1.go
@@ -0,0 +1,57 @@
+// Copyright 2012 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.
+
+// Test cases for sort order of declarations.
+
+package d
+
+// C2 should be third.
+const C2 = 2
+
+// V2 should be third.
+var V2 int
+
+// CBx constants should appear before CAx constants.
+const (
+	CB2 = iota // before CB1
+	CB1        // before CB0
+	CB0        // at end
+)
+
+// VBx variables should appear before VAx variables.
+var (
+	VB2 int // before VB1
+	VB1 int // before VB0
+	VB0 int // at end
+)
+
+const (
+	// Single const declarations inside ()'s are considered ungrouped
+	// and show up in sorted order.
+	Cungrouped = 0
+)
+
+var (
+	// Single var declarations inside ()'s are considered ungrouped
+	// and show up in sorted order.
+	Vungrouped = 0
+)
+
+// T2 should be third.
+type T2 struct{}
+
+// Grouped types are sorted nevertheless.
+type (
+	// TG2 should be third.
+	TG2 struct{}
+
+	// TG1 should be second.
+	TG1 struct{}
+
+	// TG0 should be first.
+	TG0 struct{}
+)
+
+// F2 should be third.
+func F2() {}
diff --git a/src/go/doc/testdata/d2.go b/src/go/doc/testdata/d2.go
new file mode 100644
index 0000000..2f56f4f
--- /dev/null
+++ b/src/go/doc/testdata/d2.go
@@ -0,0 +1,45 @@
+// Copyright 2012 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.
+
+// Test cases for sort order of declarations.
+
+package d
+
+// C1 should be second.
+const C1 = 1
+
+// C0 should be first.
+const C0 = 0
+
+// V1 should be second.
+var V1 uint
+
+// V0 should be first.
+var V0 uintptr
+
+// CAx constants should appear after CBx constants.
+const (
+	CA2 = iota // before CA1
+	CA1        // before CA0
+	CA0        // at end
+)
+
+// VAx variables should appear after VBx variables.
+var (
+	VA2 int // before VA1
+	VA1 int // before VA0
+	VA0 int // at end
+)
+
+// T1 should be second.
+type T1 struct{}
+
+// T0 should be first.
+type T0 struct{}
+
+// F1 should be second.
+func F1() {}
+
+// F0 should be first.
+func F0() {}
diff --git a/src/go/doc/testdata/e.0.golden b/src/go/doc/testdata/e.0.golden
new file mode 100644
index 0000000..6987e58
--- /dev/null
+++ b/src/go/doc/testdata/e.0.golden
@@ -0,0 +1,109 @@
+// The package e is a go/doc test for embedded methods. 
+PACKAGE e
+
+IMPORTPATH
+	testdata/e
+
+FILENAMES
+	testdata/e.go
+
+TYPES
+	// T1 has no embedded (level 1) M method due to conflict. 
+	type T1 struct {
+		// contains filtered or unexported fields
+	}
+
+	// T2 has only M as top-level method. 
+	type T2 struct {
+		// contains filtered or unexported fields
+	}
+
+	// T2.M should appear as method of T2. 
+	func (T2) M()
+
+	// T3 has only M as top-level method. 
+	type T3 struct {
+		// contains filtered or unexported fields
+	}
+
+	// T3.M should appear as method of T3. 
+	func (T3) M()
+
+	// 
+	type T4 struct{}
+
+	// T4.M should appear as method of T5 only if AllMethods is set. 
+	func (*T4) M()
+
+	// 
+	type T5 struct {
+		T4
+	}
+
+	// 
+	type U1 struct {
+		*U1
+	}
+
+	// U1.M should appear as method of U1. 
+	func (*U1) M()
+
+	// 
+	type U2 struct {
+		*U3
+	}
+
+	// U2.M should appear as method of U2 and as method of U3 only if ...
+	func (*U2) M()
+
+	// 
+	type U3 struct {
+		*U2
+	}
+
+	// U3.N should appear as method of U3 and as method of U2 only if ...
+	func (*U3) N()
+
+	// 
+	type U4 struct {
+		// contains filtered or unexported fields
+	}
+
+	// U4.M should appear as method of U4. 
+	func (*U4) M()
+
+	// 
+	type V1 struct {
+		*V2
+		*V5
+	}
+
+	// 
+	type V2 struct {
+		*V3
+	}
+
+	// 
+	type V3 struct {
+		*V4
+	}
+
+	// 
+	type V4 struct {
+		*V5
+	}
+
+	// V4.M should appear as method of V2 and V3 if AllMethods is set. 
+	func (*V4) M()
+
+	// 
+	type V5 struct {
+		*V6
+	}
+
+	// 
+	type V6 struct{}
+
+	// V6.M should appear as method of V1 and V5 if AllMethods is set. 
+	func (*V6) M()
+
diff --git a/src/go/doc/testdata/e.1.golden b/src/go/doc/testdata/e.1.golden
new file mode 100644
index 0000000..cbe22e0
--- /dev/null
+++ b/src/go/doc/testdata/e.1.golden
@@ -0,0 +1,144 @@
+// The package e is a go/doc test for embedded methods. 
+PACKAGE e
+
+IMPORTPATH
+	testdata/e
+
+FILENAMES
+	testdata/e.go
+
+TYPES
+	// T1 has no embedded (level 1) M method due to conflict. 
+	type T1 struct {
+		t1
+		t2
+	}
+
+	// T2 has only M as top-level method. 
+	type T2 struct {
+		t1
+	}
+
+	// T2.M should appear as method of T2. 
+	func (T2) M()
+
+	// T3 has only M as top-level method. 
+	type T3 struct {
+		t1e
+		t2e
+	}
+
+	// T3.M should appear as method of T3. 
+	func (T3) M()
+
+	// 
+	type T4 struct{}
+
+	// T4.M should appear as method of T5 only if AllMethods is set. 
+	func (*T4) M()
+
+	// 
+	type T5 struct {
+		T4
+	}
+
+	// 
+	type U1 struct {
+		*U1
+	}
+
+	// U1.M should appear as method of U1. 
+	func (*U1) M()
+
+	// 
+	type U2 struct {
+		*U3
+	}
+
+	// U2.M should appear as method of U2 and as method of U3 only if ...
+	func (*U2) M()
+
+	// 
+	type U3 struct {
+		*U2
+	}
+
+	// U3.N should appear as method of U3 and as method of U2 only if ...
+	func (*U3) N()
+
+	// 
+	type U4 struct {
+		*u5
+	}
+
+	// U4.M should appear as method of U4. 
+	func (*U4) M()
+
+	// 
+	type V1 struct {
+		*V2
+		*V5
+	}
+
+	// 
+	type V2 struct {
+		*V3
+	}
+
+	// 
+	type V3 struct {
+		*V4
+	}
+
+	// 
+	type V4 struct {
+		*V5
+	}
+
+	// V4.M should appear as method of V2 and V3 if AllMethods is set. 
+	func (*V4) M()
+
+	// 
+	type V5 struct {
+		*V6
+	}
+
+	// 
+	type V6 struct{}
+
+	// V6.M should appear as method of V1 and V5 if AllMethods is set. 
+	func (*V6) M()
+
+	// 
+	type t1 struct{}
+
+	// t1.M should not appear as method in a Tx type. 
+	func (t1) M()
+
+	// 
+	type t1e struct {
+		t1
+	}
+
+	// t1.M should not appear as method in a Tx type. 
+	func (t1e) M()
+
+	// 
+	type t2 struct{}
+
+	// t2.M should not appear as method in a Tx type. 
+	func (t2) M()
+
+	// 
+	type t2e struct {
+		t2
+	}
+
+	// t2.M should not appear as method in a Tx type. 
+	func (t2e) M()
+
+	// 
+	type u5 struct {
+		*U4
+	}
+
diff --git a/src/go/doc/testdata/e.2.golden b/src/go/doc/testdata/e.2.golden
new file mode 100644
index 0000000..e7b05e8
--- /dev/null
+++ b/src/go/doc/testdata/e.2.golden
@@ -0,0 +1,130 @@
+// The package e is a go/doc test for embedded methods. 
+PACKAGE e
+
+IMPORTPATH
+	testdata/e
+
+FILENAMES
+	testdata/e.go
+
+TYPES
+	// T1 has no embedded (level 1) M method due to conflict. 
+	type T1 struct {
+		// contains filtered or unexported fields
+	}
+
+	// T2 has only M as top-level method. 
+	type T2 struct {
+		// contains filtered or unexported fields
+	}
+
+	// T2.M should appear as method of T2. 
+	func (T2) M()
+
+	// T3 has only M as top-level method. 
+	type T3 struct {
+		// contains filtered or unexported fields
+	}
+
+	// T3.M should appear as method of T3. 
+	func (T3) M()
+
+	// 
+	type T4 struct{}
+
+	// T4.M should appear as method of T5 only if AllMethods is set. 
+	func (*T4) M()
+
+	// 
+	type T5 struct {
+		T4
+	}
+
+	// T4.M should appear as method of T5 only if AllMethods is set. 
+	func (*T5) M()
+
+	// 
+	type U1 struct {
+		*U1
+	}
+
+	// U1.M should appear as method of U1. 
+	func (*U1) M()
+
+	// 
+	type U2 struct {
+		*U3
+	}
+
+	// U2.M should appear as method of U2 and as method of U3 only if ...
+	func (*U2) M()
+
+	// U3.N should appear as method of U3 and as method of U2 only if ...
+	func (U2) N()
+
+	// 
+	type U3 struct {
+		*U2
+	}
+
+	// U2.M should appear as method of U2 and as method of U3 only if ...
+	func (U3) M()
+
+	// U3.N should appear as method of U3 and as method of U2 only if ...
+	func (*U3) N()
+
+	// 
+	type U4 struct {
+		// contains filtered or unexported fields
+	}
+
+	// U4.M should appear as method of U4. 
+	func (*U4) M()
+
+	// 
+	type V1 struct {
+		*V2
+		*V5
+	}
+
+	// V6.M should appear as method of V1 and V5 if AllMethods is set. 
+	func (V1) M()
+
+	// 
+	type V2 struct {
+		*V3
+	}
+
+	// V4.M should appear as method of V2 and V3 if AllMethods is set. 
+	func (V2) M()
+
+	// 
+	type V3 struct {
+		*V4
+	}
+
+	// V4.M should appear as method of V2 and V3 if AllMethods is set. 
+	func (V3) M()
+
+	// 
+	type V4 struct {
+		*V5
+	}
+
+	// V4.M should appear as method of V2 and V3 if AllMethods is set. 
+	func (*V4) M()
+
+	// 
+	type V5 struct {
+		*V6
+	}
+
+	// V6.M should appear as method of V1 and V5 if AllMethods is set. 
+	func (V5) M()
+
+	// 
+	type V6 struct{}
+
+	// V6.M should appear as method of V1 and V5 if AllMethods is set. 
+	func (*V6) M()
+
diff --git a/src/go/doc/testdata/e.go b/src/go/doc/testdata/e.go
new file mode 100644
index 0000000..ec432e3
--- /dev/null
+++ b/src/go/doc/testdata/e.go
@@ -0,0 +1,147 @@
+// Copyright 2012 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.
+
+// The package e is a go/doc test for embedded methods.
+package e
+
+// ----------------------------------------------------------------------------
+// Conflicting methods M must not show up.
+
+type t1 struct{}
+
+// t1.M should not appear as method in a Tx type.
+func (t1) M() {}
+
+type t2 struct{}
+
+// t2.M should not appear as method in a Tx type.
+func (t2) M() {}
+
+// T1 has no embedded (level 1) M method due to conflict.
+type T1 struct {
+	t1
+	t2
+}
+
+// ----------------------------------------------------------------------------
+// Higher-level method M wins over lower-level method M.
+
+// T2 has only M as top-level method.
+type T2 struct {
+	t1
+}
+
+// T2.M should appear as method of T2.
+func (T2) M() {}
+
+// ----------------------------------------------------------------------------
+// Higher-level method M wins over lower-level conflicting methods M.
+
+type t1e struct {
+	t1
+}
+
+type t2e struct {
+	t2
+}
+
+// T3 has only M as top-level method.
+type T3 struct {
+	t1e
+	t2e
+}
+
+// T3.M should appear as method of T3.
+func (T3) M() {}
+
+// ----------------------------------------------------------------------------
+// Don't show conflicting methods M embedded via an exported and non-exported
+// type.
+
+// T1 has no embedded (level 1) M method due to conflict.
+type T4 struct {
+	t2
+	T2
+}
+
+// ----------------------------------------------------------------------------
+// Don't show embedded methods of exported anonymous fields unless AllMethods
+// is set.
+
+type T4 struct{}
+
+// T4.M should appear as method of T5 only if AllMethods is set.
+func (*T4) M() {}
+
+type T5 struct {
+	T4
+}
+
+// ----------------------------------------------------------------------------
+// Recursive type declarations must not lead to endless recursion.
+
+type U1 struct {
+	*U1
+}
+
+// U1.M should appear as method of U1.
+func (*U1) M() {}
+
+type U2 struct {
+	*U3
+}
+
+// U2.M should appear as method of U2 and as method of U3 only if AllMethods is set.
+func (*U2) M() {}
+
+type U3 struct {
+	*U2
+}
+
+// U3.N should appear as method of U3 and as method of U2 only if AllMethods is set.
+func (*U3) N() {}
+
+type U4 struct {
+	*u5
+}
+
+// U4.M should appear as method of U4.
+func (*U4) M() {}
+
+type u5 struct {
+	*U4
+}
+
+// ----------------------------------------------------------------------------
+// A higher-level embedded type (and its methods) wins over the same type (and
+// its methods) embedded at a lower level.
+
+type V1 struct {
+	*V2
+	*V5
+}
+
+type V2 struct {
+	*V3
+}
+
+type V3 struct {
+	*V4
+}
+
+type V4 struct {
+	*V5
+}
+
+type V5 struct {
+	*V6
+}
+
+type V6 struct{}
+
+// V4.M should appear as method of V2 and V3 if AllMethods is set.
+func (*V4) M() {}
+
+// V6.M should appear as method of V1 and V5 if AllMethods is set.
+func (*V6) M() {}
diff --git a/src/go/doc/testdata/error1.0.golden b/src/go/doc/testdata/error1.0.golden
new file mode 100644
index 0000000..6c6fe5d
--- /dev/null
+++ b/src/go/doc/testdata/error1.0.golden
@@ -0,0 +1,30 @@
+// 
+PACKAGE error1
+
+IMPORTPATH
+	testdata/error1
+
+FILENAMES
+	testdata/error1.go
+
+TYPES
+	// 
+	type I0 interface {
+		// When embedded, the predeclared error interface
+		// must remain visible in interface types.
+		error
+	}
+
+	// 
+	type S0 struct {
+		// contains filtered or unexported fields
+	}
+
+	// 
+	type T0 struct {
+		ExportedField interface {
+			// error should be visible
+			error
+		}
+	}
+
diff --git a/src/go/doc/testdata/error1.1.golden b/src/go/doc/testdata/error1.1.golden
new file mode 100644
index 0000000..a8dc2e7
--- /dev/null
+++ b/src/go/doc/testdata/error1.1.golden
@@ -0,0 +1,32 @@
+// 
+PACKAGE error1
+
+IMPORTPATH
+	testdata/error1
+
+FILENAMES
+	testdata/error1.go
+
+TYPES
+	// 
+	type I0 interface {
+		// When embedded, the predeclared error interface
+		// must remain visible in interface types.
+		error
+	}
+
+	// 
+	type S0 struct {
+		// In struct types, an embedded error must only be visible
+		// if AllDecls is set.
+		error
+	}
+
+	// 
+	type T0 struct {
+		ExportedField interface {
+			// error should be visible
+			error
+		}
+	}
+
diff --git a/src/go/doc/testdata/error1.2.golden b/src/go/doc/testdata/error1.2.golden
new file mode 100644
index 0000000..6c6fe5d
--- /dev/null
+++ b/src/go/doc/testdata/error1.2.golden
@@ -0,0 +1,30 @@
+// 
+PACKAGE error1
+
+IMPORTPATH
+	testdata/error1
+
+FILENAMES
+	testdata/error1.go
+
+TYPES
+	// 
+	type I0 interface {
+		// When embedded, the predeclared error interface
+		// must remain visible in interface types.
+		error
+	}
+
+	// 
+	type S0 struct {
+		// contains filtered or unexported fields
+	}
+
+	// 
+	type T0 struct {
+		ExportedField interface {
+			// error should be visible
+			error
+		}
+	}
+
diff --git a/src/go/doc/testdata/error1.go b/src/go/doc/testdata/error1.go
new file mode 100644
index 0000000..3c777a7
--- /dev/null
+++ b/src/go/doc/testdata/error1.go
@@ -0,0 +1,24 @@
+// Copyright 2012 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 error1
+
+type I0 interface {
+	// When embedded, the predeclared error interface
+	// must remain visible in interface types.
+	error
+}
+
+type T0 struct {
+	ExportedField interface {
+		// error should be visible
+		error
+	}
+}
+
+type S0 struct {
+	// In struct types, an embedded error must only be visible
+	// if AllDecls is set.
+	error
+}
diff --git a/src/go/doc/testdata/error2.0.golden b/src/go/doc/testdata/error2.0.golden
new file mode 100644
index 0000000..dedfe41
--- /dev/null
+++ b/src/go/doc/testdata/error2.0.golden
@@ -0,0 +1,27 @@
+// 
+PACKAGE error2
+
+IMPORTPATH
+	testdata/error2
+
+FILENAMES
+	testdata/error2.go
+
+TYPES
+	// 
+	type I0 interface {
+		// contains filtered or unexported methods
+	}
+
+	// 
+	type S0 struct {
+		// contains filtered or unexported fields
+	}
+
+	// 
+	type T0 struct {
+		ExportedField interface {
+			// contains filtered or unexported methods
+		}
+	}
+
diff --git a/src/go/doc/testdata/error2.1.golden b/src/go/doc/testdata/error2.1.golden
new file mode 100644
index 0000000..dbcc1b0
--- /dev/null
+++ b/src/go/doc/testdata/error2.1.golden
@@ -0,0 +1,37 @@
+// 
+PACKAGE error2
+
+IMPORTPATH
+	testdata/error2
+
+FILENAMES
+	testdata/error2.go
+
+TYPES
+	// 
+	type I0 interface {
+		// When embedded, the locally-declared error interface
+		// is only visible if all declarations are shown.
+		error
+	}
+
+	// 
+	type S0 struct {
+		// In struct types, an embedded error must only be visible
+		// if AllDecls is set.
+		error
+	}
+
+	// 
+	type T0 struct {
+		ExportedField interface {
+			// error should not be visible
+			error
+		}
+	}
+
+	// This error declaration shadows the predeclared error type. 
+	type error interface {
+		Error() string
+	}
+
diff --git a/src/go/doc/testdata/error2.2.golden b/src/go/doc/testdata/error2.2.golden
new file mode 100644
index 0000000..dedfe41
--- /dev/null
+++ b/src/go/doc/testdata/error2.2.golden
@@ -0,0 +1,27 @@
+// 
+PACKAGE error2
+
+IMPORTPATH
+	testdata/error2
+
+FILENAMES
+	testdata/error2.go
+
+TYPES
+	// 
+	type I0 interface {
+		// contains filtered or unexported methods
+	}
+
+	// 
+	type S0 struct {
+		// contains filtered or unexported fields
+	}
+
+	// 
+	type T0 struct {
+		ExportedField interface {
+			// contains filtered or unexported methods
+		}
+	}
+
diff --git a/src/go/doc/testdata/error2.go b/src/go/doc/testdata/error2.go
new file mode 100644
index 0000000..6ee96c2
--- /dev/null
+++ b/src/go/doc/testdata/error2.go
@@ -0,0 +1,29 @@
+// Copyright 2012 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 error2
+
+type I0 interface {
+	// When embedded, the locally-declared error interface
+	// is only visible if all declarations are shown.
+	error
+}
+
+type T0 struct {
+	ExportedField interface {
+		// error should not be visible
+		error
+	}
+}
+
+type S0 struct {
+	// In struct types, an embedded error must only be visible
+	// if AllDecls is set.
+	error
+}
+
+// This error declaration shadows the predeclared error type.
+type error interface {
+	Error() string
+}
diff --git a/src/go/doc/testdata/example.go b/src/go/doc/testdata/example.go
new file mode 100644
index 0000000..0b70339
--- /dev/null
+++ b/src/go/doc/testdata/example.go
@@ -0,0 +1,81 @@
+// 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.
+
+package testing
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+	"os"
+	"strings"
+	"time"
+)
+
+type InternalExample struct {
+	Name   string
+	F      func()
+	Output string
+}
+
+func RunExamples(examples []InternalExample) (ok bool) {
+	ok = true
+
+	var eg InternalExample
+
+	stdout, stderr := os.Stdout, os.Stderr
+	defer func() {
+		os.Stdout, os.Stderr = stdout, stderr
+		if e := recover(); e != nil {
+			fmt.Printf("--- FAIL: %s\npanic: %v\n", eg.Name, e)
+			os.Exit(1)
+		}
+	}()
+
+	for _, eg = range examples {
+		if *chatty {
+			fmt.Printf("=== RUN: %s\n", eg.Name)
+		}
+
+		// capture stdout and stderr
+		r, w, err := os.Pipe()
+		if err != nil {
+			fmt.Fprintln(os.Stderr, err)
+			os.Exit(1)
+		}
+		os.Stdout, os.Stderr = w, w
+		outC := make(chan string)
+		go func() {
+			buf := new(bytes.Buffer)
+			_, err := io.Copy(buf, r)
+			if err != nil {
+				fmt.Fprintf(stderr, "testing: copying pipe: %v\n", err)
+				os.Exit(1)
+			}
+			outC <- buf.String()
+		}()
+
+		// run example
+		t0 := time.Now()
+		eg.F()
+		dt := time.Since(t0)
+
+		// close pipe, restore stdout/stderr, get output
+		w.Close()
+		os.Stdout, os.Stderr = stdout, stderr
+		out := <-outC
+
+		// report any errors
+		tstr := fmt.Sprintf("(%.2f seconds)", dt.Seconds())
+		if g, e := strings.TrimSpace(out), strings.TrimSpace(eg.Output); g != e {
+			fmt.Printf("--- FAIL: %s %s\ngot:\n%s\nwant:\n%s\n",
+				eg.Name, tstr, g, e)
+			ok = false
+		} else if *chatty {
+			fmt.Printf("--- PASS: %s %s\n", eg.Name, tstr)
+		}
+	}
+
+	return
+}
diff --git a/src/go/doc/testdata/examples/README.md b/src/go/doc/testdata/examples/README.md
new file mode 100644
index 0000000..a1c18e8
--- /dev/null
+++ b/src/go/doc/testdata/examples/README.md
@@ -0,0 +1,12 @@
+These files are processed by example_test.go:TestExamples.
+
+A .golden file is a txtar file with two sections for each example that should be
+created by doc.Examples from the corresponding .go file.
+
+One section, named EXAMPLE_NAME.Output, contains the example's output,
+the value of the field Example.Output.
+
+The other, named EXAMPLE_NAME.Play, contains the formatted code for a playable
+version of the example, the value of the field Example.Play.
+
+If a section is missing, it is treated as being empty.
diff --git a/src/go/doc/testdata/examples/empty.go b/src/go/doc/testdata/examples/empty.go
new file mode 100644
index 0000000..0b10420
--- /dev/null
+++ b/src/go/doc/testdata/examples/empty.go
@@ -0,0 +1,8 @@
+// Copyright 2021 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 p
+
+func Example() {}
+func Example_a()
diff --git a/src/go/doc/testdata/examples/empty.golden b/src/go/doc/testdata/examples/empty.golden
new file mode 100644
index 0000000..2aafd20
--- /dev/null
+++ b/src/go/doc/testdata/examples/empty.golden
@@ -0,0 +1,6 @@
+-- .Play --
+package main
+
+func main() {}
+func main()
+
diff --git a/src/go/doc/testdata/examples/generic_constraints.go b/src/go/doc/testdata/examples/generic_constraints.go
new file mode 100644
index 0000000..ea5d2b3
--- /dev/null
+++ b/src/go/doc/testdata/examples/generic_constraints.go
@@ -0,0 +1,38 @@
+// Copyright 2021 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 p_test
+
+import (
+	"fmt"
+	"time"
+)
+
+type C1 interface {
+	string | int
+}
+
+type C2 interface {
+	M(time.Time)
+}
+
+type G[T C1] int
+
+func g[T C2](x T) {}
+
+type Tm int
+
+func (Tm) M(time.Time) {}
+
+type Foo int
+
+func Example() {
+	fmt.Println("hello")
+}
+
+func ExampleGeneric() {
+	var x G[string]
+	g(Tm(3))
+	fmt.Println(x)
+}
diff --git a/src/go/doc/testdata/examples/generic_constraints.golden b/src/go/doc/testdata/examples/generic_constraints.golden
new file mode 100644
index 0000000..6c7b0ed
--- /dev/null
+++ b/src/go/doc/testdata/examples/generic_constraints.golden
@@ -0,0 +1,39 @@
+-- .Play --
+package main
+
+import (
+	"fmt"
+)
+
+func main() {
+	fmt.Println("hello")
+}
+-- Generic.Play --
+package main
+
+import (
+	"fmt"
+	"time"
+)
+
+type C1 interface {
+	string | int
+}
+
+type C2 interface {
+	M(time.Time)
+}
+
+type G[T C1] int
+
+func g[T C2](x T) {}
+
+type Tm int
+
+func (Tm) M(time.Time) {}
+
+func main() {
+	var x G[string]
+	g(Tm(3))
+	fmt.Println(x)
+}
diff --git a/src/go/doc/testdata/examples/import_groups.go b/src/go/doc/testdata/examples/import_groups.go
new file mode 100644
index 0000000..05f21ca
--- /dev/null
+++ b/src/go/doc/testdata/examples/import_groups.go
@@ -0,0 +1,23 @@
+// 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 foo_test
+
+import (
+	"fmt"
+	"time"
+
+	"golang.org/x/time/rate"
+)
+
+func Example() {
+	fmt.Println("Hello, world!")
+	// Output: Hello, world!
+}
+
+func ExampleLimiter() {
+	// Uses fmt, time and rate.
+	l := rate.NewLimiter(rate.Every(time.Second), 1)
+	fmt.Println(l)
+}
diff --git a/src/go/doc/testdata/examples/import_groups.golden b/src/go/doc/testdata/examples/import_groups.golden
new file mode 100644
index 0000000..efe2cc1
--- /dev/null
+++ b/src/go/doc/testdata/examples/import_groups.golden
@@ -0,0 +1,27 @@
+-- .Play --
+package main
+
+import (
+	"fmt"
+)
+
+func main() {
+	fmt.Println("Hello, world!")
+}
+-- .Output --
+Hello, world!
+-- Limiter.Play --
+package main
+
+import (
+	"fmt"
+	"time"
+
+	"golang.org/x/time/rate"
+)
+
+func main() {
+	// Uses fmt, time and rate.
+	l := rate.NewLimiter(rate.Every(time.Second), 1)
+	fmt.Println(l)
+}
diff --git a/src/go/doc/testdata/examples/import_groups_named.go b/src/go/doc/testdata/examples/import_groups_named.go
new file mode 100644
index 0000000..377022b
--- /dev/null
+++ b/src/go/doc/testdata/examples/import_groups_named.go
@@ -0,0 +1,23 @@
+// 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 foo_test
+
+import (
+	"fmt"
+	tm "time"
+
+	r "golang.org/x/time/rate"
+)
+
+func Example() {
+	fmt.Println("Hello, world!")
+	// Output: Hello, world!
+}
+
+func ExampleLimiter() {
+	// Uses fmt, time and rate.
+	l := r.NewLimiter(r.Every(tm.Second), 1)
+	fmt.Println(l)
+}
diff --git a/src/go/doc/testdata/examples/import_groups_named.golden b/src/go/doc/testdata/examples/import_groups_named.golden
new file mode 100644
index 0000000..9baf373
--- /dev/null
+++ b/src/go/doc/testdata/examples/import_groups_named.golden
@@ -0,0 +1,27 @@
+-- .Play --
+package main
+
+import (
+	"fmt"
+)
+
+func main() {
+	fmt.Println("Hello, world!")
+}
+-- .Output --
+Hello, world!
+-- Limiter.Play --
+package main
+
+import (
+	"fmt"
+	tm "time"
+
+	r "golang.org/x/time/rate"
+)
+
+func main() {
+	// Uses fmt, time and rate.
+	l := r.NewLimiter(r.Every(tm.Second), 1)
+	fmt.Println(l)
+}
diff --git a/src/go/doc/testdata/examples/inspect_signature.go b/src/go/doc/testdata/examples/inspect_signature.go
new file mode 100644
index 0000000..c4a36e7
--- /dev/null
+++ b/src/go/doc/testdata/examples/inspect_signature.go
@@ -0,0 +1,23 @@
+// Copyright 2021 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 foo_test
+
+import (
+	"bytes"
+	"io"
+)
+
+func getReader() io.Reader { return nil }
+
+func do(b bytes.Reader) {}
+
+func Example() {
+	getReader()
+	do()
+	// Output:
+}
+
+func ExampleIgnored() {
+}
diff --git a/src/go/doc/testdata/examples/inspect_signature.golden b/src/go/doc/testdata/examples/inspect_signature.golden
new file mode 100644
index 0000000..c0d9b2e
--- /dev/null
+++ b/src/go/doc/testdata/examples/inspect_signature.golden
@@ -0,0 +1,24 @@
+-- .Play --
+package main
+
+import (
+	"bytes"
+	"io"
+)
+
+func getReader() io.Reader { return nil }
+
+func do(b bytes.Reader) {}
+
+func main() {
+	getReader()
+	do()
+}
+-- Ignored.Play --
+package main
+
+import ()
+
+func main() {
+}
+
diff --git a/src/go/doc/testdata/examples/iota.go b/src/go/doc/testdata/examples/iota.go
new file mode 100644
index 0000000..c878b77
--- /dev/null
+++ b/src/go/doc/testdata/examples/iota.go
@@ -0,0 +1,34 @@
+// Copyright 2021 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 foo_test
+
+const (
+	a = iota
+	b
+)
+
+const (
+	c = 3
+	d = 4
+)
+
+const (
+	e = iota
+	f
+)
+
+// The example refers to only one of the constants in the iota group, but we
+// must keep all of them because of the iota. The second group of constants can
+// be trimmed. The third has an iota, but is unused, so it can be eliminated.
+
+func Example() {
+	_ = b
+	_ = d
+}
+
+// Need two examples to hit the playExample function.
+
+func Example2() {
+}
diff --git a/src/go/doc/testdata/examples/iota.golden b/src/go/doc/testdata/examples/iota.golden
new file mode 100644
index 0000000..7487702
--- /dev/null
+++ b/src/go/doc/testdata/examples/iota.golden
@@ -0,0 +1,23 @@
+-- .Play --
+package main
+
+import ()
+
+const (
+	a = iota
+	b
+)
+
+const d = 4
+
+func main() {
+	_ = b
+	_ = d
+}
+-- 2.Play --
+package main
+
+import ()
+
+func main() {
+}
diff --git a/src/go/doc/testdata/examples/issue43658.go b/src/go/doc/testdata/examples/issue43658.go
new file mode 100644
index 0000000..385223a
--- /dev/null
+++ b/src/go/doc/testdata/examples/issue43658.go
@@ -0,0 +1,223 @@
+// Copyright ©2016 The Gonum Authors. All rights reserved.
+// Copyright 2021 The Go Authors. All rights reserved.
+// (above line required for our license-header checker)
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package community_test
+
+import (
+	"fmt"
+	"log"
+	"sort"
+
+	"golang.org/x/exp/rand"
+
+	"gonum.org/v1/gonum/graph/community"
+	"gonum.org/v1/gonum/graph/internal/ordered"
+	"gonum.org/v1/gonum/graph/simple"
+)
+
+func ExampleProfile_simple() {
+	// Profile calls Modularize which implements the Louvain modularization algorithm.
+	// Since this is a randomized algorithm we use a defined random source to ensure
+	// consistency between test runs. In practice, results will not differ greatly
+	// between runs with different PRNG seeds.
+	src := rand.NewSource(1)
+
+	// Create dumbell graph:
+	//
+	//  0       4
+	//  |\     /|
+	//  | 2 - 3 |
+	//  |/     \|
+	//  1       5
+	//
+	g := simple.NewUndirectedGraph()
+	for u, e := range smallDumbell {
+		for v := range e {
+			g.SetEdge(simple.Edge{F: simple.Node(u), T: simple.Node(v)})
+		}
+	}
+
+	// Get the profile of internal node weight for resolutions
+	// between 0.1 and 10 using logarithmic bisection.
+	p, err := community.Profile(
+		community.ModularScore(g, community.Weight, 10, src),
+		true, 1e-3, 0.1, 10,
+	)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	// Print out each step with communities ordered.
+	for _, d := range p {
+		comm := d.Communities()
+		for _, c := range comm {
+			sort.Sort(ordered.ByID(c))
+		}
+		sort.Sort(ordered.BySliceIDs(comm))
+		fmt.Printf("Low:%.2v High:%.2v Score:%v Communities:%v Q=%.3v\n",
+			d.Low, d.High, d.Score, comm, community.Q(g, comm, d.Low))
+	}
+
+	// Output:
+	// Low:0.1 High:0.29 Score:14 Communities:[[0 1 2 3 4 5]] Q=0.9
+	// Low:0.29 High:2.3 Score:12 Communities:[[0 1 2] [3 4 5]] Q=0.714
+	// Low:2.3 High:3.5 Score:4 Communities:[[0 1] [2] [3] [4 5]] Q=-0.31
+	// Low:3.5 High:10 Score:0 Communities:[[0] [1] [2] [3] [4] [5]] Q=-0.607
+}
+
+// intset is an integer set.
+type intset map[int]struct{}
+
+func linksTo(i ...int) intset {
+	if len(i) == 0 {
+		return nil
+	}
+	s := make(intset)
+	for _, v := range i {
+		s[v] = struct{}{}
+	}
+	return s
+}
+
+var (
+	smallDumbell = []intset{
+		0: linksTo(1, 2),
+		1: linksTo(2),
+		2: linksTo(3),
+		3: linksTo(4, 5),
+		4: linksTo(5),
+		5: nil,
+	}
+
+	// http://www.slate.com/blogs/the_world_/2014/07/17/the_middle_east_friendship_chart.html
+	middleEast = struct{ friends, complicated, enemies []intset }{
+		// green cells
+		friends: []intset{
+			0:  nil,
+			1:  linksTo(5, 7, 9, 12),
+			2:  linksTo(11),
+			3:  linksTo(4, 5, 10),
+			4:  linksTo(3, 5, 10),
+			5:  linksTo(1, 3, 4, 8, 10, 12),
+			6:  nil,
+			7:  linksTo(1, 12),
+			8:  linksTo(5, 9, 11),
+			9:  linksTo(1, 8, 12),
+			10: linksTo(3, 4, 5),
+			11: linksTo(2, 8),
+			12: linksTo(1, 5, 7, 9),
+		},
+
+		// yellow cells
+		complicated: []intset{
+			0:  linksTo(2, 4),
+			1:  linksTo(4, 8),
+			2:  linksTo(0, 3, 4, 5, 8, 9),
+			3:  linksTo(2, 8, 11),
+			4:  linksTo(0, 1, 2, 8),
+			5:  linksTo(2),
+			6:  nil,
+			7:  linksTo(9, 11),
+			8:  linksTo(1, 2, 3, 4, 10, 12),
+			9:  linksTo(2, 7, 11),
+			10: linksTo(8),
+			11: linksTo(3, 7, 9, 12),
+			12: linksTo(8, 11),
+		},
+
+		// red cells
+		enemies: []intset{
+			0:  linksTo(1, 3, 5, 6, 7, 8, 9, 10, 11, 12),
+			1:  linksTo(0, 2, 3, 6, 10, 11),
+			2:  linksTo(1, 6, 7, 10, 12),
+			3:  linksTo(0, 1, 6, 7, 9, 12),
+			4:  linksTo(6, 7, 9, 11, 12),
+			5:  linksTo(0, 6, 7, 9, 11),
+			6:  linksTo(0, 1, 2, 3, 4, 5, 7, 8, 9, 10, 11, 12),
+			7:  linksTo(0, 2, 3, 4, 5, 6, 8, 10),
+			8:  linksTo(0, 6, 7),
+			9:  linksTo(0, 3, 4, 5, 6, 10),
+			10: linksTo(0, 1, 2, 6, 7, 9, 11, 12),
+			11: linksTo(0, 1, 4, 5, 6, 10),
+			12: linksTo(0, 2, 3, 4, 6, 10),
+		},
+	}
+)
+
+var friends, enemies *simple.WeightedUndirectedGraph
+
+func init() {
+	friends = simple.NewWeightedUndirectedGraph(0, 0)
+	for u, e := range middleEast.friends {
+		// Ensure unconnected nodes are included.
+		if friends.Node(int64(u)) == nil {
+			friends.AddNode(simple.Node(u))
+		}
+		for v := range e {
+			friends.SetWeightedEdge(simple.WeightedEdge{F: simple.Node(u), T: simple.Node(v), W: 1})
+		}
+	}
+	enemies = simple.NewWeightedUndirectedGraph(0, 0)
+	for u, e := range middleEast.enemies {
+		// Ensure unconnected nodes are included.
+		if enemies.Node(int64(u)) == nil {
+			enemies.AddNode(simple.Node(u))
+		}
+		for v := range e {
+			enemies.SetWeightedEdge(simple.WeightedEdge{F: simple.Node(u), T: simple.Node(v), W: -1})
+		}
+	}
+}
+
+func ExampleProfile_multiplex() {
+	// Profile calls ModularizeMultiplex which implements the Louvain modularization
+	// algorithm. Since this is a randomized algorithm we use a defined random source
+	// to ensure consistency between test runs. In practice, results will not differ
+	// greatly between runs with different PRNG seeds.
+	src := rand.NewSource(1)
+
+	// The undirected graphs, friends and enemies, are the political relationships
+	// in the Middle East as described in the Slate article:
+	// http://www.slate.com/blogs/the_world_/2014/07/17/the_middle_east_friendship_chart.html
+	g, err := community.NewUndirectedLayers(friends, enemies)
+	if err != nil {
+		log.Fatal(err)
+	}
+	weights := []float64{1, -1}
+
+	// Get the profile of internal node weight for resolutions
+	// between 0.1 and 10 using logarithmic bisection.
+	p, err := community.Profile(
+		community.ModularMultiplexScore(g, weights, true, community.WeightMultiplex, 10, src),
+		true, 1e-3, 0.1, 10,
+	)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	// Print out each step with communities ordered.
+	for _, d := range p {
+		comm := d.Communities()
+		for _, c := range comm {
+			sort.Sort(ordered.ByID(c))
+		}
+		sort.Sort(ordered.BySliceIDs(comm))
+		fmt.Printf("Low:%.2v High:%.2v Score:%v Communities:%v Q=%.3v\n",
+			d.Low, d.High, d.Score, comm, community.QMultiplex(g, comm, weights, []float64{d.Low}))
+	}
+
+	// Output:
+	// Low:0.1 High:0.72 Score:26 Communities:[[0] [1 7 9 12] [2 8 11] [3 4 5 10] [6]] Q=[24.7 1.97]
+	// Low:0.72 High:1.1 Score:24 Communities:[[0 6] [1 7 9 12] [2 8 11] [3 4 5 10]] Q=[16.9 14.1]
+	// Low:1.1 High:1.2 Score:18 Communities:[[0 2 6 11] [1 7 9 12] [3 4 5 8 10]] Q=[9.16 25.1]
+	// Low:1.2 High:1.6 Score:10 Communities:[[0 3 4 5 6 10] [1 7 9 12] [2 8 11]] Q=[10.5 26.7]
+	// Low:1.6 High:1.6 Score:8 Communities:[[0 1 6 7 9 12] [2 8 11] [3 4 5 10]] Q=[5.56 39.8]
+	// Low:1.6 High:1.8 Score:2 Communities:[[0 2 3 4 5 6 10] [1 7 8 9 11 12]] Q=[-1.82 48.6]
+	// Low:1.8 High:2.3 Score:-6 Communities:[[0 2 3 4 5 6 8 10 11] [1 7 9 12]] Q=[-5 57.5]
+	// Low:2.3 High:2.4 Score:-10 Communities:[[0 1 2 6 7 8 9 11 12] [3 4 5 10]] Q=[-11.2 79]
+	// Low:2.4 High:4.3 Score:-52 Communities:[[0 1 2 3 4 5 6 7 8 9 10 11 12]] Q=[-46.1 117]
+	// Low:4.3 High:10 Score:-54 Communities:[[0 1 2 3 4 6 7 8 9 10 11 12] [5]] Q=[-82 254]
+}
diff --git a/src/go/doc/testdata/examples/issue43658.golden b/src/go/doc/testdata/examples/issue43658.golden
new file mode 100644
index 0000000..5200d14
--- /dev/null
+++ b/src/go/doc/testdata/examples/issue43658.golden
@@ -0,0 +1,156 @@
+-- Profile_simple.Play --
+package main
+
+import (
+	"fmt"
+	"log"
+	"sort"
+
+	"golang.org/x/exp/rand"
+
+	"gonum.org/v1/gonum/graph/community"
+	"gonum.org/v1/gonum/graph/internal/ordered"
+	"gonum.org/v1/gonum/graph/simple"
+)
+
+func main() {
+	// Profile calls Modularize which implements the Louvain modularization algorithm.
+	// Since this is a randomized algorithm we use a defined random source to ensure
+	// consistency between test runs. In practice, results will not differ greatly
+	// between runs with different PRNG seeds.
+	src := rand.NewSource(1)
+
+	// Create dumbell graph:
+	//
+	//  0       4
+	//  |\     /|
+	//  | 2 - 3 |
+	//  |/     \|
+	//  1       5
+	//
+	g := simple.NewUndirectedGraph()
+	for u, e := range smallDumbell {
+		for v := range e {
+			g.SetEdge(simple.Edge{F: simple.Node(u), T: simple.Node(v)})
+		}
+	}
+
+	// Get the profile of internal node weight for resolutions
+	// between 0.1 and 10 using logarithmic bisection.
+	p, err := community.Profile(
+		community.ModularScore(g, community.Weight, 10, src),
+		true, 1e-3, 0.1, 10,
+	)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	// Print out each step with communities ordered.
+	for _, d := range p {
+		comm := d.Communities()
+		for _, c := range comm {
+			sort.Sort(ordered.ByID(c))
+		}
+		sort.Sort(ordered.BySliceIDs(comm))
+		fmt.Printf("Low:%.2v High:%.2v Score:%v Communities:%v Q=%.3v\n",
+			d.Low, d.High, d.Score, comm, community.Q(g, comm, d.Low))
+	}
+
+}
+
+// intset is an integer set.
+type intset map[int]struct{}
+
+func linksTo(i ...int) intset {
+	if len(i) == 0 {
+		return nil
+	}
+	s := make(intset)
+	for _, v := range i {
+		s[v] = struct{}{}
+	}
+	return s
+}
+
+var smallDumbell = []intset{
+	0: linksTo(1, 2),
+	1: linksTo(2),
+	2: linksTo(3),
+	3: linksTo(4, 5),
+	4: linksTo(5),
+	5: nil,
+}
+
+-- Profile_simple.Output --
+Low:0.1 High:0.29 Score:14 Communities:[[0 1 2 3 4 5]] Q=0.9
+Low:0.29 High:2.3 Score:12 Communities:[[0 1 2] [3 4 5]] Q=0.714
+Low:2.3 High:3.5 Score:4 Communities:[[0 1] [2] [3] [4 5]] Q=-0.31
+Low:3.5 High:10 Score:0 Communities:[[0] [1] [2] [3] [4] [5]] Q=-0.607
+
+-- Profile_multiplex.Play --
+
+package main
+
+import (
+	"fmt"
+	"log"
+	"sort"
+
+	"golang.org/x/exp/rand"
+
+	"gonum.org/v1/gonum/graph/community"
+	"gonum.org/v1/gonum/graph/internal/ordered"
+	"gonum.org/v1/gonum/graph/simple"
+)
+
+var friends, enemies *simple.WeightedUndirectedGraph
+
+func main() {
+	// Profile calls ModularizeMultiplex which implements the Louvain modularization
+	// algorithm. Since this is a randomized algorithm we use a defined random source
+	// to ensure consistency between test runs. In practice, results will not differ
+	// greatly between runs with different PRNG seeds.
+	src := rand.NewSource(1)
+
+	// The undirected graphs, friends and enemies, are the political relationships
+	// in the Middle East as described in the Slate article:
+	// http://www.slate.com/blogs/the_world_/2014/07/17/the_middle_east_friendship_chart.html
+	g, err := community.NewUndirectedLayers(friends, enemies)
+	if err != nil {
+		log.Fatal(err)
+	}
+	weights := []float64{1, -1}
+
+	// Get the profile of internal node weight for resolutions
+	// between 0.1 and 10 using logarithmic bisection.
+	p, err := community.Profile(
+		community.ModularMultiplexScore(g, weights, true, community.WeightMultiplex, 10, src),
+		true, 1e-3, 0.1, 10,
+	)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	// Print out each step with communities ordered.
+	for _, d := range p {
+		comm := d.Communities()
+		for _, c := range comm {
+			sort.Sort(ordered.ByID(c))
+		}
+		sort.Sort(ordered.BySliceIDs(comm))
+		fmt.Printf("Low:%.2v High:%.2v Score:%v Communities:%v Q=%.3v\n",
+			d.Low, d.High, d.Score, comm, community.QMultiplex(g, comm, weights, []float64{d.Low}))
+	}
+
+}
+-- Profile_multiplex.Output --
+Low:0.1 High:0.72 Score:26 Communities:[[0] [1 7 9 12] [2 8 11] [3 4 5 10] [6]] Q=[24.7 1.97]
+Low:0.72 High:1.1 Score:24 Communities:[[0 6] [1 7 9 12] [2 8 11] [3 4 5 10]] Q=[16.9 14.1]
+Low:1.1 High:1.2 Score:18 Communities:[[0 2 6 11] [1 7 9 12] [3 4 5 8 10]] Q=[9.16 25.1]
+Low:1.2 High:1.6 Score:10 Communities:[[0 3 4 5 6 10] [1 7 9 12] [2 8 11]] Q=[10.5 26.7]
+Low:1.6 High:1.6 Score:8 Communities:[[0 1 6 7 9 12] [2 8 11] [3 4 5 10]] Q=[5.56 39.8]
+Low:1.6 High:1.8 Score:2 Communities:[[0 2 3 4 5 6 10] [1 7 8 9 11 12]] Q=[-1.82 48.6]
+Low:1.8 High:2.3 Score:-6 Communities:[[0 2 3 4 5 6 8 10 11] [1 7 9 12]] Q=[-5 57.5]
+Low:2.3 High:2.4 Score:-10 Communities:[[0 1 2 6 7 8 9 11 12] [3 4 5 10]] Q=[-11.2 79]
+Low:2.4 High:4.3 Score:-52 Communities:[[0 1 2 3 4 5 6 7 8 9 10 11 12]] Q=[-46.1 117]
+Low:4.3 High:10 Score:-54 Communities:[[0 1 2 3 4 6 7 8 9 10 11 12] [5]] Q=[-82 254]
diff --git a/src/go/doc/testdata/examples/multiple.go b/src/go/doc/testdata/examples/multiple.go
new file mode 100644
index 0000000..2728264
--- /dev/null
+++ b/src/go/doc/testdata/examples/multiple.go
@@ -0,0 +1,98 @@
+// Copyright 2021 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 foo_test
+
+import (
+	"flag"
+	"fmt"
+	"log"
+	"os/exec"
+	"sort"
+)
+
+func ExampleHello() {
+	fmt.Println("Hello, world!")
+	// Output: Hello, world!
+}
+
+func ExampleImport() {
+	out, err := exec.Command("date").Output()
+	if err != nil {
+		log.Fatal(err)
+	}
+	fmt.Printf("The date is %s\n", out)
+}
+
+func ExampleKeyValue() {
+	v := struct {
+		a string
+		b int
+	}{
+		a: "A",
+		b: 1,
+	}
+	fmt.Print(v)
+	// Output: a: "A", b: 1
+}
+
+func ExampleKeyValueImport() {
+	f := flag.Flag{
+		Name: "play",
+	}
+	fmt.Print(f)
+	// Output: Name: "play"
+}
+
+var keyValueTopDecl = struct {
+	a string
+	b int
+}{
+	a: "B",
+	b: 2,
+}
+
+func ExampleKeyValueTopDecl() {
+	fmt.Print(keyValueTopDecl)
+	// Output: a: "B", b: 2
+}
+
+// Person represents a person by name and age.
+type Person struct {
+	Name string
+	Age  int
+}
+
+// String returns a string representation of the Person.
+func (p Person) String() string {
+	return fmt.Sprintf("%s: %d", p.Name, p.Age)
+}
+
+// ByAge implements sort.Interface for []Person based on
+// the Age field.
+type ByAge []Person
+
+// Len returns the number of elements in ByAge.
+func (a ByAge) Len() int { return len(a) }
+
+// Swap swaps the elements in ByAge.
+func (a ByAge) Swap(i, j int)      { a[i], a[j] = a[j], a[i] }
+func (a ByAge) Less(i, j int) bool { return a[i].Age < a[j].Age }
+
+// people is the array of Person
+var people = []Person{
+	{"Bob", 31},
+	{"John", 42},
+	{"Michael", 17},
+	{"Jenny", 26},
+}
+
+func ExampleSort() {
+	fmt.Println(people)
+	sort.Sort(ByAge(people))
+	fmt.Println(people)
+	// Output:
+	// [Bob: 31 John: 42 Michael: 17 Jenny: 26]
+	// [Michael: 17 Jenny: 26 Bob: 31 John: 42]
+}
diff --git a/src/go/doc/testdata/examples/multiple.golden b/src/go/doc/testdata/examples/multiple.golden
new file mode 100644
index 0000000..d2d791e
--- /dev/null
+++ b/src/go/doc/testdata/examples/multiple.golden
@@ -0,0 +1,129 @@
+-- Hello.Play --
+package main
+
+import (
+	"fmt"
+)
+
+func main() {
+	fmt.Println("Hello, world!")
+}
+-- Hello.Output --
+Hello, world!
+-- Import.Play --
+package main
+
+import (
+	"fmt"
+	"log"
+	"os/exec"
+)
+
+func main() {
+	out, err := exec.Command("date").Output()
+	if err != nil {
+		log.Fatal(err)
+	}
+	fmt.Printf("The date is %s\n", out)
+}
+-- KeyValue.Play --
+package main
+
+import (
+	"fmt"
+)
+
+func main() {
+	v := struct {
+		a string
+		b int
+	}{
+		a: "A",
+		b: 1,
+	}
+	fmt.Print(v)
+}
+-- KeyValue.Output --
+a: "A", b: 1
+-- KeyValueImport.Play --
+package main
+
+import (
+	"flag"
+	"fmt"
+)
+
+func main() {
+	f := flag.Flag{
+		Name: "play",
+	}
+	fmt.Print(f)
+}
+-- KeyValueImport.Output --
+Name: "play"
+-- KeyValueTopDecl.Play --
+package main
+
+import (
+	"fmt"
+)
+
+var keyValueTopDecl = struct {
+	a string
+	b int
+}{
+	a: "B",
+	b: 2,
+}
+
+func main() {
+	fmt.Print(keyValueTopDecl)
+}
+-- KeyValueTopDecl.Output --
+a: "B", b: 2
+-- Sort.Play --
+package main
+
+import (
+	"fmt"
+	"sort"
+)
+
+// Person represents a person by name and age.
+type Person struct {
+	Name string
+	Age  int
+}
+
+// String returns a string representation of the Person.
+func (p Person) String() string {
+	return fmt.Sprintf("%s: %d", p.Name, p.Age)
+}
+
+// ByAge implements sort.Interface for []Person based on
+// the Age field.
+type ByAge []Person
+
+// Len returns the number of elements in ByAge.
+func (a ByAge) Len() int { return len(a) }
+
+// Swap swaps the elements in ByAge.
+func (a ByAge) Swap(i, j int)      { a[i], a[j] = a[j], a[i] }
+func (a ByAge) Less(i, j int) bool { return a[i].Age < a[j].Age }
+
+// people is the array of Person
+var people = []Person{
+	{"Bob", 31},
+	{"John", 42},
+	{"Michael", 17},
+	{"Jenny", 26},
+}
+
+func main() {
+	fmt.Println(people)
+	sort.Sort(ByAge(people))
+	fmt.Println(people)
+}
+-- Sort.Output --
+[Bob: 31 John: 42 Michael: 17 Jenny: 26]
+[Michael: 17 Jenny: 26 Bob: 31 John: 42]
diff --git a/src/go/doc/testdata/examples/values.go b/src/go/doc/testdata/examples/values.go
new file mode 100644
index 0000000..64b0de4
--- /dev/null
+++ b/src/go/doc/testdata/examples/values.go
@@ -0,0 +1,22 @@
+// Copyright 2021 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 foo_test
+
+// Variable declaration with fewer values than names.
+
+func f() (int, int) {
+	return 1, 2
+}
+
+var a, b = f()
+
+// Need two examples to hit playExample.
+
+func ExampleA() {
+	_ = a
+}
+
+func ExampleB() {
+}
diff --git a/src/go/doc/testdata/examples/values.golden b/src/go/doc/testdata/examples/values.golden
new file mode 100644
index 0000000..00c1991
--- /dev/null
+++ b/src/go/doc/testdata/examples/values.golden
@@ -0,0 +1,21 @@
+-- A.Play --
+package main
+
+import ()
+
+func f() (int, int) {
+	return 1, 2
+}
+
+var a, b = f()
+
+func main() {
+	_ = a
+}
+-- B.Play --
+package main
+
+import ()
+
+func main() {
+}
diff --git a/src/go/doc/testdata/examples/whole_file.go b/src/go/doc/testdata/examples/whole_file.go
new file mode 100644
index 0000000..61954ce
--- /dev/null
+++ b/src/go/doc/testdata/examples/whole_file.go
@@ -0,0 +1,23 @@
+// Copyright 2021 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 foo_test
+
+import "fmt"
+
+type X int
+
+func (X) Foo() {
+}
+
+func (X) TestBlah() {
+}
+
+func (X) BenchmarkFoo() {
+}
+
+func Example() {
+	fmt.Println("Hello, world!")
+	// Output: Hello, world!
+}
diff --git a/src/go/doc/testdata/examples/whole_file.golden b/src/go/doc/testdata/examples/whole_file.golden
new file mode 100644
index 0000000..74a2291
--- /dev/null
+++ b/src/go/doc/testdata/examples/whole_file.golden
@@ -0,0 +1,21 @@
+-- .Play --
+package main
+
+import "fmt"
+
+type X int
+
+func (X) Foo() {
+}
+
+func (X) TestBlah() {
+}
+
+func (X) BenchmarkFoo() {
+}
+
+func main() {
+	fmt.Println("Hello, world!")
+}
+-- .Output --
+Hello, world!
diff --git a/src/go/doc/testdata/examples/whole_function.go b/src/go/doc/testdata/examples/whole_function.go
new file mode 100644
index 0000000..1754ee3
--- /dev/null
+++ b/src/go/doc/testdata/examples/whole_function.go
@@ -0,0 +1,13 @@
+// Copyright 2021 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 foo_test
+
+func Foo(x int) {
+}
+
+func Example() {
+	fmt.Println("Hello, world!")
+	// Output: Hello, world!
+}
diff --git a/src/go/doc/testdata/examples/whole_function.golden b/src/go/doc/testdata/examples/whole_function.golden
new file mode 100644
index 0000000..7d5b5cb
--- /dev/null
+++ b/src/go/doc/testdata/examples/whole_function.golden
@@ -0,0 +1,11 @@
+-- .Play --
+package main
+
+func Foo(x int) {
+}
+
+func main() {
+	fmt.Println("Hello, world!")
+}
+-- .Output --
+Hello, world!
diff --git a/src/go/doc/testdata/examples/whole_function_external.go b/src/go/doc/testdata/examples/whole_function_external.go
new file mode 100644
index 0000000..0e0e2f5
--- /dev/null
+++ b/src/go/doc/testdata/examples/whole_function_external.go
@@ -0,0 +1,12 @@
+// Copyright 2021 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 foo_test
+
+func foo(int)
+
+func Example() {
+	foo(42)
+	// Output:
+}
diff --git a/src/go/doc/testdata/examples/whole_function_external.golden b/src/go/doc/testdata/examples/whole_function_external.golden
new file mode 100644
index 0000000..ec8f114
--- /dev/null
+++ b/src/go/doc/testdata/examples/whole_function_external.golden
@@ -0,0 +1,8 @@
+-- .Play --
+package main
+
+func foo(int)
+
+func main() {
+	foo(42)
+}
diff --git a/src/go/doc/testdata/f.0.golden b/src/go/doc/testdata/f.0.golden
new file mode 100644
index 0000000..8175901
--- /dev/null
+++ b/src/go/doc/testdata/f.0.golden
@@ -0,0 +1,13 @@
+// The package f is a go/doc test for functions and factory ...
+PACKAGE f
+
+IMPORTPATH
+	testdata/f
+
+FILENAMES
+	testdata/f.go
+
+FUNCTIONS
+	// Exported must always be visible. Was issue 2824. 
+	func Exported() private
+
diff --git a/src/go/doc/testdata/f.1.golden b/src/go/doc/testdata/f.1.golden
new file mode 100644
index 0000000..ba68e88
--- /dev/null
+++ b/src/go/doc/testdata/f.1.golden
@@ -0,0 +1,16 @@
+// The package f is a go/doc test for functions and factory ...
+PACKAGE f
+
+IMPORTPATH
+	testdata/f
+
+FILENAMES
+	testdata/f.go
+
+TYPES
+	// 
+	type private struct{}
+
+	// Exported must always be visible. Was issue 2824. 
+	func Exported() private
+
diff --git a/src/go/doc/testdata/f.2.golden b/src/go/doc/testdata/f.2.golden
new file mode 100644
index 0000000..8175901
--- /dev/null
+++ b/src/go/doc/testdata/f.2.golden
@@ -0,0 +1,13 @@
+// The package f is a go/doc test for functions and factory ...
+PACKAGE f
+
+IMPORTPATH
+	testdata/f
+
+FILENAMES
+	testdata/f.go
+
+FUNCTIONS
+	// Exported must always be visible. Was issue 2824. 
+	func Exported() private
+
diff --git a/src/go/doc/testdata/f.go b/src/go/doc/testdata/f.go
new file mode 100644
index 0000000..7e9add9
--- /dev/null
+++ b/src/go/doc/testdata/f.go
@@ -0,0 +1,14 @@
+// Copyright 2012 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.
+
+// The package f is a go/doc test for functions and factory methods.
+package f
+
+// ----------------------------------------------------------------------------
+// Factory functions for non-exported types must not get lost.
+
+type private struct{}
+
+// Exported must always be visible. Was issue 2824.
+func Exported() private {}
diff --git a/src/go/doc/testdata/g.0.golden b/src/go/doc/testdata/g.0.golden
new file mode 100644
index 0000000..487cf06
--- /dev/null
+++ b/src/go/doc/testdata/g.0.golden
@@ -0,0 +1,32 @@
+// The package g is a go/doc test for mixed exported/unexported ...
+PACKAGE g
+
+IMPORTPATH
+	testdata/g
+
+FILENAMES
+	testdata/g.go
+
+CONSTANTS
+	// 
+	const (
+		A, _	= iota, iota
+		_, D
+		E, _
+		G, H
+	)
+
+
+VARIABLES
+	// 
+	var (
+		_, C2, _	= 1, 2, 3
+		C4, _, C6	= 4, 5, 6
+		_, C8, _	= 7, 8, 9
+	)
+
+	// 
+	var (
+		_, X = f()
+	)
+
diff --git a/src/go/doc/testdata/g.1.golden b/src/go/doc/testdata/g.1.golden
new file mode 100644
index 0000000..438441a
--- /dev/null
+++ b/src/go/doc/testdata/g.1.golden
@@ -0,0 +1,34 @@
+// The package g is a go/doc test for mixed exported/unexported ...
+PACKAGE g
+
+IMPORTPATH
+	testdata/g
+
+FILENAMES
+	testdata/g.go
+
+CONSTANTS
+	// 
+	const (
+		A, b	= iota, iota
+		c, D
+		E, f
+		G, H
+	)
+
+
+VARIABLES
+	// 
+	var (
+		c1, C2, c3	= 1, 2, 3
+		C4, c5, C6	= 4, 5, 6
+		c7, C8, c9	= 7, 8, 9
+		xx, yy, zz	= 0, 0, 0	// all unexported and hidden
+	)
+
+	// 
+	var (
+		x, X	= f()
+		y, z	= f()
+	)
+
diff --git a/src/go/doc/testdata/g.2.golden b/src/go/doc/testdata/g.2.golden
new file mode 100644
index 0000000..487cf06
--- /dev/null
+++ b/src/go/doc/testdata/g.2.golden
@@ -0,0 +1,32 @@
+// The package g is a go/doc test for mixed exported/unexported ...
+PACKAGE g
+
+IMPORTPATH
+	testdata/g
+
+FILENAMES
+	testdata/g.go
+
+CONSTANTS
+	// 
+	const (
+		A, _	= iota, iota
+		_, D
+		E, _
+		G, H
+	)
+
+
+VARIABLES
+	// 
+	var (
+		_, C2, _	= 1, 2, 3
+		C4, _, C6	= 4, 5, 6
+		_, C8, _	= 7, 8, 9
+	)
+
+	// 
+	var (
+		_, X = f()
+	)
+
diff --git a/src/go/doc/testdata/g.go b/src/go/doc/testdata/g.go
new file mode 100644
index 0000000..ceeb417
--- /dev/null
+++ b/src/go/doc/testdata/g.go
@@ -0,0 +1,25 @@
+// Copyright 2018 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.
+
+// The package g is a go/doc test for mixed exported/unexported values.
+package g
+
+const (
+	A, b = iota, iota
+	c, D
+	E, f
+	G, H
+)
+
+var (
+	c1, C2, c3 = 1, 2, 3
+	C4, c5, C6 = 4, 5, 6
+	c7, C8, c9 = 7, 8, 9
+	xx, yy, zz = 0, 0, 0 // all unexported and hidden
+)
+
+var (
+	x, X = f()
+	y, z = f()
+)
diff --git a/src/go/doc/testdata/generics.0.golden b/src/go/doc/testdata/generics.0.golden
new file mode 100644
index 0000000..91c874c
--- /dev/null
+++ b/src/go/doc/testdata/generics.0.golden
@@ -0,0 +1,76 @@
+// Package generics contains the new syntax supporting generic ...
+PACKAGE generics
+
+IMPORTPATH
+	testdata/generics
+
+FILENAMES
+	testdata/generics.go
+
+FUNCTIONS
+	// AnotherFunc has an implicit constraint interface.  Neither type ...
+	func AnotherFunc[T ~struct{ f int }](_ struct{ f int })
+
+	// Func has an instantiated constraint. 
+	func Func[T Constraint[string, Type[int]]]()
+
+	// Single is not a factory function. 
+	func Single[T any]() *T
+
+	// Slice is not a factory function. 
+	func Slice[T any]() []T
+
+
+TYPES
+	// AFuncType demonstrates filtering of parameters and type ...
+	type AFuncType[T ~struct{ f int }] func(_ struct {
+		// contains filtered or unexported fields
+	})
+
+	// Constraint is a constraint interface with two type parameters. 
+	type Constraint[P, Q interface{ string | ~int | Type[int] }] interface {
+		~int | ~byte | Type[string]
+		M() P
+	}
+
+	// NewEmbeddings demonstrates how we filter the new embedded ...
+	type NewEmbeddings interface {
+		string	// should not be filtered
+	
+		struct {
+			// contains filtered or unexported fields
+		}
+		~struct {
+			// contains filtered or unexported fields
+		}
+		*struct {
+			// contains filtered or unexported fields
+		}
+		struct {
+			// contains filtered or unexported fields
+		} | ~struct {
+			// contains filtered or unexported fields
+		}
+		// contains filtered or unexported methods
+	}
+
+	// Parameterized types should be shown. 
+	type Type[P any] struct {
+		Field P
+	}
+
+	// Variables with an instantiated type should be shown. 
+	var X Type[int]
+
+	// Constructors for parameterized types should be shown. 
+	func Constructor[lowerCase any]() Type[lowerCase]
+
+	// MethodA uses a different name for its receiver type parameter. 
+	func (t Type[A]) MethodA(p A)
+
+	// MethodB has a blank receiver type parameter. 
+	func (t Type[_]) MethodB()
+
+	// MethodC has a lower-case receiver type parameter. 
+	func (t Type[c]) MethodC()
+
diff --git a/src/go/doc/testdata/generics.1.golden b/src/go/doc/testdata/generics.1.golden
new file mode 100644
index 0000000..923a4ce
--- /dev/null
+++ b/src/go/doc/testdata/generics.1.golden
@@ -0,0 +1,66 @@
+// Package generics contains the new syntax supporting generic ...
+PACKAGE generics
+
+IMPORTPATH
+	testdata/generics
+
+FILENAMES
+	testdata/generics.go
+
+FUNCTIONS
+	// AnotherFunc has an implicit constraint interface.  Neither type ...
+	func AnotherFunc[T ~struct{ f int }](_ struct{ f int })
+
+	// Func has an instantiated constraint. 
+	func Func[T Constraint[string, Type[int]]]()
+
+	// Single is not a factory function. 
+	func Single[T any]() *T
+
+	// Slice is not a factory function. 
+	func Slice[T any]() []T
+
+
+TYPES
+	// AFuncType demonstrates filtering of parameters and type ...
+	type AFuncType[T ~struct{ f int }] func(_ struct{ f int })
+
+	// Constraint is a constraint interface with two type parameters. 
+	type Constraint[P, Q interface{ string | ~int | Type[int] }] interface {
+		~int | ~byte | Type[string]
+		M() P
+	}
+
+	// NewEmbeddings demonstrates how we filter the new embedded ...
+	type NewEmbeddings interface {
+		string	// should not be filtered
+		int16
+		struct{ f int }
+		~struct{ f int }
+		*struct{ f int }
+		struct{ f int } | ~struct{ f int }
+	}
+
+	// Parameterized types should be shown. 
+	type Type[P any] struct {
+		Field P
+	}
+
+	// Variables with an instantiated type should be shown. 
+	var X Type[int]
+
+	// Constructors for parameterized types should be shown. 
+	func Constructor[lowerCase any]() Type[lowerCase]
+
+	// MethodA uses a different name for its receiver type parameter. 
+	func (t Type[A]) MethodA(p A)
+
+	// MethodB has a blank receiver type parameter. 
+	func (t Type[_]) MethodB()
+
+	// MethodC has a lower-case receiver type parameter. 
+	func (t Type[c]) MethodC()
+
+	// int16 shadows the predeclared type int16. 
+	type int16 int
+
diff --git a/src/go/doc/testdata/generics.2.golden b/src/go/doc/testdata/generics.2.golden
new file mode 100644
index 0000000..91c874c
--- /dev/null
+++ b/src/go/doc/testdata/generics.2.golden
@@ -0,0 +1,76 @@
+// Package generics contains the new syntax supporting generic ...
+PACKAGE generics
+
+IMPORTPATH
+	testdata/generics
+
+FILENAMES
+	testdata/generics.go
+
+FUNCTIONS
+	// AnotherFunc has an implicit constraint interface.  Neither type ...
+	func AnotherFunc[T ~struct{ f int }](_ struct{ f int })
+
+	// Func has an instantiated constraint. 
+	func Func[T Constraint[string, Type[int]]]()
+
+	// Single is not a factory function. 
+	func Single[T any]() *T
+
+	// Slice is not a factory function. 
+	func Slice[T any]() []T
+
+
+TYPES
+	// AFuncType demonstrates filtering of parameters and type ...
+	type AFuncType[T ~struct{ f int }] func(_ struct {
+		// contains filtered or unexported fields
+	})
+
+	// Constraint is a constraint interface with two type parameters. 
+	type Constraint[P, Q interface{ string | ~int | Type[int] }] interface {
+		~int | ~byte | Type[string]
+		M() P
+	}
+
+	// NewEmbeddings demonstrates how we filter the new embedded ...
+	type NewEmbeddings interface {
+		string	// should not be filtered
+	
+		struct {
+			// contains filtered or unexported fields
+		}
+		~struct {
+			// contains filtered or unexported fields
+		}
+		*struct {
+			// contains filtered or unexported fields
+		}
+		struct {
+			// contains filtered or unexported fields
+		} | ~struct {
+			// contains filtered or unexported fields
+		}
+		// contains filtered or unexported methods
+	}
+
+	// Parameterized types should be shown. 
+	type Type[P any] struct {
+		Field P
+	}
+
+	// Variables with an instantiated type should be shown. 
+	var X Type[int]
+
+	// Constructors for parameterized types should be shown. 
+	func Constructor[lowerCase any]() Type[lowerCase]
+
+	// MethodA uses a different name for its receiver type parameter. 
+	func (t Type[A]) MethodA(p A)
+
+	// MethodB has a blank receiver type parameter. 
+	func (t Type[_]) MethodB()
+
+	// MethodC has a lower-case receiver type parameter. 
+	func (t Type[c]) MethodC()
+
diff --git a/src/go/doc/testdata/generics.go b/src/go/doc/testdata/generics.go
new file mode 100644
index 0000000..ba7187e
--- /dev/null
+++ b/src/go/doc/testdata/generics.go
@@ -0,0 +1,74 @@
+// Copyright 2021 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 generics contains the new syntax supporting generic programming in
+// Go.
+package generics
+
+// Variables with an instantiated type should be shown.
+var X Type[int]
+
+// Parameterized types should be shown.
+type Type[P any] struct {
+	Field P
+}
+
+// Constructors for parameterized types should be shown.
+func Constructor[lowerCase any]() Type[lowerCase] {
+	return Type[lowerCase]{}
+}
+
+// MethodA uses a different name for its receiver type parameter.
+func (t Type[A]) MethodA(p A) {}
+
+// MethodB has a blank receiver type parameter.
+func (t Type[_]) MethodB() {}
+
+// MethodC has a lower-case receiver type parameter.
+func (t Type[c]) MethodC() {}
+
+// Constraint is a constraint interface with two type parameters.
+type Constraint[P, Q interface{ string | ~int | Type[int] }] interface {
+	~int | ~byte | Type[string]
+	M() P
+}
+
+// int16 shadows the predeclared type int16.
+type int16 int
+
+// NewEmbeddings demonstrates how we filter the new embedded elements.
+type NewEmbeddings interface {
+	string // should not be filtered
+	int16
+	struct{ f int }
+	~struct{ f int }
+	*struct{ f int }
+	struct{ f int } | ~struct{ f int }
+}
+
+// Func has an instantiated constraint.
+func Func[T Constraint[string, Type[int]]]() {}
+
+// AnotherFunc has an implicit constraint interface.
+//
+// Neither type parameters nor regular parameters should be filtered.
+func AnotherFunc[T ~struct{ f int }](_ struct{ f int }) {}
+
+// AFuncType demonstrates filtering of parameters and type parameters. Here we
+// don't filter type parameters (to be consistent with function declarations),
+// but DO filter the RHS.
+type AFuncType[T ~struct{ f int }] func(_ struct{ f int })
+
+// See issue #49477: type parameters should not be interpreted as named types
+// for the purpose of determining whether a function is a factory function.
+
+// Slice is not a factory function.
+func Slice[T any]() []T {
+	return nil
+}
+
+// Single is not a factory function.
+func Single[T any]() *T {
+	return nil
+}
diff --git a/src/go/doc/testdata/issue12839.0.golden b/src/go/doc/testdata/issue12839.0.golden
new file mode 100644
index 0000000..6b59774
--- /dev/null
+++ b/src/go/doc/testdata/issue12839.0.golden
@@ -0,0 +1,51 @@
+// Package issue12839 is a go/doc test to test association of a ...
+PACKAGE issue12839
+
+IMPORTPATH
+	testdata/issue12839
+
+IMPORTS
+	p
+
+FILENAMES
+	testdata/issue12839.go
+
+FUNCTIONS
+	// F1 should not be associated with T1 
+	func F1() (*T1, *T2)
+
+	// F10 should not be associated with T1. 
+	func F10() (T1, T2, error)
+
+	// F4 should not be associated with a type (same as F1) 
+	func F4() (a T1, b T2)
+
+	// F9 should not be associated with T1. 
+	func F9() (int, T1, T2)
+
+
+TYPES
+	// 
+	type T1 struct{}
+
+	// F2 should be associated with T1 
+	func F2() (a, b, c T1)
+
+	// F3 should be associated with T1 because b.T3 is from a ...
+	func F3() (a T1, b p.T3)
+
+	// F5 should be associated with T1. 
+	func F5() (T1, error)
+
+	// F6 should be associated with T1. 
+	func F6() (*T1, error)
+
+	// F7 should be associated with T1. 
+	func F7() (T1, string)
+
+	// F8 should be associated with T1. 
+	func F8() (int, T1, string)
+
+	// 
+	type T2 struct{}
+
diff --git a/src/go/doc/testdata/issue12839.1.golden b/src/go/doc/testdata/issue12839.1.golden
new file mode 100644
index 0000000..4b9b9f6
--- /dev/null
+++ b/src/go/doc/testdata/issue12839.1.golden
@@ -0,0 +1,54 @@
+// Package issue12839 is a go/doc test to test association of a ...
+PACKAGE issue12839
+
+IMPORTPATH
+	testdata/issue12839
+
+IMPORTS
+	p
+
+FILENAMES
+	testdata/issue12839.go
+
+FUNCTIONS
+	// F1 should not be associated with T1 
+	func F1() (*T1, *T2)
+
+	// F10 should not be associated with T1. 
+	func F10() (T1, T2, error)
+
+	// F4 should not be associated with a type (same as F1) 
+	func F4() (a T1, b T2)
+
+	// F9 should not be associated with T1. 
+	func F9() (int, T1, T2)
+
+
+TYPES
+	// 
+	type T1 struct{}
+
+	// F2 should be associated with T1 
+	func F2() (a, b, c T1)
+
+	// F3 should be associated with T1 because b.T3 is from a ...
+	func F3() (a T1, b p.T3)
+
+	// F5 should be associated with T1. 
+	func F5() (T1, error)
+
+	// F6 should be associated with T1. 
+	func F6() (*T1, error)
+
+	// F7 should be associated with T1. 
+	func F7() (T1, string)
+
+	// F8 should be associated with T1. 
+	func F8() (int, T1, string)
+
+	// 
+	func (t T1) hello() string
+
+	// 
+	type T2 struct{}
+
diff --git a/src/go/doc/testdata/issue12839.2.golden b/src/go/doc/testdata/issue12839.2.golden
new file mode 100644
index 0000000..6b59774
--- /dev/null
+++ b/src/go/doc/testdata/issue12839.2.golden
@@ -0,0 +1,51 @@
+// Package issue12839 is a go/doc test to test association of a ...
+PACKAGE issue12839
+
+IMPORTPATH
+	testdata/issue12839
+
+IMPORTS
+	p
+
+FILENAMES
+	testdata/issue12839.go
+
+FUNCTIONS
+	// F1 should not be associated with T1 
+	func F1() (*T1, *T2)
+
+	// F10 should not be associated with T1. 
+	func F10() (T1, T2, error)
+
+	// F4 should not be associated with a type (same as F1) 
+	func F4() (a T1, b T2)
+
+	// F9 should not be associated with T1. 
+	func F9() (int, T1, T2)
+
+
+TYPES
+	// 
+	type T1 struct{}
+
+	// F2 should be associated with T1 
+	func F2() (a, b, c T1)
+
+	// F3 should be associated with T1 because b.T3 is from a ...
+	func F3() (a T1, b p.T3)
+
+	// F5 should be associated with T1. 
+	func F5() (T1, error)
+
+	// F6 should be associated with T1. 
+	func F6() (*T1, error)
+
+	// F7 should be associated with T1. 
+	func F7() (T1, string)
+
+	// F8 should be associated with T1. 
+	func F8() (int, T1, string)
+
+	// 
+	type T2 struct{}
+
diff --git a/src/go/doc/testdata/issue12839.go b/src/go/doc/testdata/issue12839.go
new file mode 100644
index 0000000..51c7ac1
--- /dev/null
+++ b/src/go/doc/testdata/issue12839.go
@@ -0,0 +1,69 @@
+// Copyright 2018 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 issue12839 is a go/doc test to test association of a function
+// that returns multiple types.
+// See golang.org/issue/12839.
+// (See also golang.org/issue/27928.)
+package issue12839
+
+import "p"
+
+type T1 struct{}
+
+type T2 struct{}
+
+func (t T1) hello() string {
+	return "hello"
+}
+
+// F1 should not be associated with T1
+func F1() (*T1, *T2) {
+	return &T1{}, &T2{}
+}
+
+// F2 should be associated with T1
+func F2() (a, b, c T1) {
+	return T1{}, T1{}, T1{}
+}
+
+// F3 should be associated with T1 because b.T3 is from a different package
+func F3() (a T1, b p.T3) {
+	return T1{}, p.T3{}
+}
+
+// F4 should not be associated with a type (same as F1)
+func F4() (a T1, b T2) {
+	return T1{}, T2{}
+}
+
+// F5 should be associated with T1.
+func F5() (T1, error) {
+	return T1{}, nil
+}
+
+// F6 should be associated with T1.
+func F6() (*T1, error) {
+	return &T1{}, nil
+}
+
+// F7 should be associated with T1.
+func F7() (T1, string) {
+	return T1{}, nil
+}
+
+// F8 should be associated with T1.
+func F8() (int, T1, string) {
+	return 0, T1{}, nil
+}
+
+// F9 should not be associated with T1.
+func F9() (int, T1, T2) {
+	return 0, T1{}, T2{}
+}
+
+// F10 should not be associated with T1.
+func F10() (T1, T2, error) {
+	return T1{}, T2{}, nil
+}
diff --git a/src/go/doc/testdata/issue13742.0.golden b/src/go/doc/testdata/issue13742.0.golden
new file mode 100644
index 0000000..8dee9aa
--- /dev/null
+++ b/src/go/doc/testdata/issue13742.0.golden
@@ -0,0 +1,25 @@
+// 
+PACKAGE issue13742
+
+IMPORTPATH
+	testdata/issue13742
+
+IMPORTS
+	go/ast
+
+FILENAMES
+	testdata/issue13742.go
+
+FUNCTIONS
+	// Both F0 and G0 should appear as functions. 
+	func F0(Node)
+
+	// Both F1 and G1 should appear as functions. 
+	func F1(ast.Node)
+
+	// 
+	func G0() Node
+
+	// 
+	func G1() ast.Node
+
diff --git a/src/go/doc/testdata/issue13742.1.golden b/src/go/doc/testdata/issue13742.1.golden
new file mode 100644
index 0000000..8dee9aa
--- /dev/null
+++ b/src/go/doc/testdata/issue13742.1.golden
@@ -0,0 +1,25 @@
+// 
+PACKAGE issue13742
+
+IMPORTPATH
+	testdata/issue13742
+
+IMPORTS
+	go/ast
+
+FILENAMES
+	testdata/issue13742.go
+
+FUNCTIONS
+	// Both F0 and G0 should appear as functions. 
+	func F0(Node)
+
+	// Both F1 and G1 should appear as functions. 
+	func F1(ast.Node)
+
+	// 
+	func G0() Node
+
+	// 
+	func G1() ast.Node
+
diff --git a/src/go/doc/testdata/issue13742.2.golden b/src/go/doc/testdata/issue13742.2.golden
new file mode 100644
index 0000000..8dee9aa
--- /dev/null
+++ b/src/go/doc/testdata/issue13742.2.golden
@@ -0,0 +1,25 @@
+// 
+PACKAGE issue13742
+
+IMPORTPATH
+	testdata/issue13742
+
+IMPORTS
+	go/ast
+
+FILENAMES
+	testdata/issue13742.go
+
+FUNCTIONS
+	// Both F0 and G0 should appear as functions. 
+	func F0(Node)
+
+	// Both F1 and G1 should appear as functions. 
+	func F1(ast.Node)
+
+	// 
+	func G0() Node
+
+	// 
+	func G1() ast.Node
+
diff --git a/src/go/doc/testdata/issue13742.go b/src/go/doc/testdata/issue13742.go
new file mode 100644
index 0000000..dbc1941
--- /dev/null
+++ b/src/go/doc/testdata/issue13742.go
@@ -0,0 +1,18 @@
+// Copyright 2016 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 issue13742
+
+import (
+	"go/ast"
+	. "go/ast"
+)
+
+// Both F0 and G0 should appear as functions.
+func F0(Node)  {}
+func G0() Node { return nil }
+
+// Both F1 and G1 should appear as functions.
+func F1(ast.Node)  {}
+func G1() ast.Node { return nil }
diff --git a/src/go/doc/testdata/issue16153.0.golden b/src/go/doc/testdata/issue16153.0.golden
new file mode 100644
index 0000000..189260b
--- /dev/null
+++ b/src/go/doc/testdata/issue16153.0.golden
@@ -0,0 +1,32 @@
+// 
+PACKAGE issue16153
+
+IMPORTPATH
+	testdata/issue16153
+
+FILENAMES
+	testdata/issue16153.go
+
+CONSTANTS
+	// 
+	const (
+		X3	int64	= iota
+		Y3		= 1
+	)
+
+	// 
+	const (
+		X4	int64	= iota
+		Y4
+	)
+
+	// original test case 
+	const (
+		Y1 = 256
+	)
+
+	// variations 
+	const (
+		Y2 uint8
+	)
+
diff --git a/src/go/doc/testdata/issue16153.1.golden b/src/go/doc/testdata/issue16153.1.golden
new file mode 100644
index 0000000..803df3e
--- /dev/null
+++ b/src/go/doc/testdata/issue16153.1.golden
@@ -0,0 +1,34 @@
+// 
+PACKAGE issue16153
+
+IMPORTPATH
+	testdata/issue16153
+
+FILENAMES
+	testdata/issue16153.go
+
+CONSTANTS
+	// original test case 
+	const (
+		x1	uint8	= 255
+		Y1		= 256
+	)
+
+	// variations 
+	const (
+		x2	uint8	= 255
+		Y2
+	)
+
+	// 
+	const (
+		X3	int64	= iota
+		Y3		= 1
+	)
+
+	// 
+	const (
+		X4	int64	= iota
+		Y4
+	)
+
diff --git a/src/go/doc/testdata/issue16153.2.golden b/src/go/doc/testdata/issue16153.2.golden
new file mode 100644
index 0000000..189260b
--- /dev/null
+++ b/src/go/doc/testdata/issue16153.2.golden
@@ -0,0 +1,32 @@
+// 
+PACKAGE issue16153
+
+IMPORTPATH
+	testdata/issue16153
+
+FILENAMES
+	testdata/issue16153.go
+
+CONSTANTS
+	// 
+	const (
+		X3	int64	= iota
+		Y3		= 1
+	)
+
+	// 
+	const (
+		X4	int64	= iota
+		Y4
+	)
+
+	// original test case 
+	const (
+		Y1 = 256
+	)
+
+	// variations 
+	const (
+		Y2 uint8
+	)
+
diff --git a/src/go/doc/testdata/issue16153.go b/src/go/doc/testdata/issue16153.go
new file mode 100644
index 0000000..528be42
--- /dev/null
+++ b/src/go/doc/testdata/issue16153.go
@@ -0,0 +1,27 @@
+// Copyright 2017 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 issue16153
+
+// original test case
+const (
+	x1 uint8 = 255
+	Y1       = 256
+)
+
+// variations
+const (
+	x2 uint8 = 255
+	Y2
+)
+
+const (
+	X3 int64 = iota
+	Y3       = 1
+)
+
+const (
+	X4 int64 = iota
+	Y4
+)
diff --git a/src/go/doc/testdata/issue17788.0.golden b/src/go/doc/testdata/issue17788.0.golden
new file mode 100644
index 0000000..42c00da
--- /dev/null
+++ b/src/go/doc/testdata/issue17788.0.golden
@@ -0,0 +1,8 @@
+// 
+PACKAGE issue17788
+
+IMPORTPATH
+	testdata/issue17788
+
+FILENAMES
+	testdata/issue17788.go
diff --git a/src/go/doc/testdata/issue17788.1.golden b/src/go/doc/testdata/issue17788.1.golden
new file mode 100644
index 0000000..42c00da
--- /dev/null
+++ b/src/go/doc/testdata/issue17788.1.golden
@@ -0,0 +1,8 @@
+// 
+PACKAGE issue17788
+
+IMPORTPATH
+	testdata/issue17788
+
+FILENAMES
+	testdata/issue17788.go
diff --git a/src/go/doc/testdata/issue17788.2.golden b/src/go/doc/testdata/issue17788.2.golden
new file mode 100644
index 0000000..42c00da
--- /dev/null
+++ b/src/go/doc/testdata/issue17788.2.golden
@@ -0,0 +1,8 @@
+// 
+PACKAGE issue17788
+
+IMPORTPATH
+	testdata/issue17788
+
+FILENAMES
+	testdata/issue17788.go
diff --git a/src/go/doc/testdata/issue17788.go b/src/go/doc/testdata/issue17788.go
new file mode 100644
index 0000000..883ad5f
--- /dev/null
+++ b/src/go/doc/testdata/issue17788.go
@@ -0,0 +1,8 @@
+// Copyright 2016 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 issue17788
+
+func ( /* receiver type */ ) f0() {
+}
diff --git a/src/go/doc/testdata/issue22856.0.golden b/src/go/doc/testdata/issue22856.0.golden
new file mode 100644
index 0000000..a88f43f
--- /dev/null
+++ b/src/go/doc/testdata/issue22856.0.golden
@@ -0,0 +1,45 @@
+// 
+PACKAGE issue22856
+
+IMPORTPATH
+	testdata/issue22856
+
+FILENAMES
+	testdata/issue22856.go
+
+FUNCTIONS
+	// NewPointerSliceOfSlice is not a factory function because slices ...
+	func NewPointerSliceOfSlice() [][]*T
+
+	// NewSlice3 is not a factory function because 3 nested slices of ...
+	func NewSlice3() [][][]T
+
+	// NewSliceOfSlice is not a factory function because slices of a ...
+	func NewSliceOfSlice() [][]T
+
+
+TYPES
+	// 
+	type T struct{}
+
+	// 
+	func New() T
+
+	// 
+	func NewArray() [1]T
+
+	// 
+	func NewPointer() *T
+
+	// 
+	func NewPointerArray() [1]*T
+
+	// 
+	func NewPointerOfPointer() **T
+
+	// 
+	func NewPointerSlice() []*T
+
+	// 
+	func NewSlice() []T
+
diff --git a/src/go/doc/testdata/issue22856.1.golden b/src/go/doc/testdata/issue22856.1.golden
new file mode 100644
index 0000000..a88f43f
--- /dev/null
+++ b/src/go/doc/testdata/issue22856.1.golden
@@ -0,0 +1,45 @@
+// 
+PACKAGE issue22856
+
+IMPORTPATH
+	testdata/issue22856
+
+FILENAMES
+	testdata/issue22856.go
+
+FUNCTIONS
+	// NewPointerSliceOfSlice is not a factory function because slices ...
+	func NewPointerSliceOfSlice() [][]*T
+
+	// NewSlice3 is not a factory function because 3 nested slices of ...
+	func NewSlice3() [][][]T
+
+	// NewSliceOfSlice is not a factory function because slices of a ...
+	func NewSliceOfSlice() [][]T
+
+
+TYPES
+	// 
+	type T struct{}
+
+	// 
+	func New() T
+
+	// 
+	func NewArray() [1]T
+
+	// 
+	func NewPointer() *T
+
+	// 
+	func NewPointerArray() [1]*T
+
+	// 
+	func NewPointerOfPointer() **T
+
+	// 
+	func NewPointerSlice() []*T
+
+	// 
+	func NewSlice() []T
+
diff --git a/src/go/doc/testdata/issue22856.2.golden b/src/go/doc/testdata/issue22856.2.golden
new file mode 100644
index 0000000..a88f43f
--- /dev/null
+++ b/src/go/doc/testdata/issue22856.2.golden
@@ -0,0 +1,45 @@
+// 
+PACKAGE issue22856
+
+IMPORTPATH
+	testdata/issue22856
+
+FILENAMES
+	testdata/issue22856.go
+
+FUNCTIONS
+	// NewPointerSliceOfSlice is not a factory function because slices ...
+	func NewPointerSliceOfSlice() [][]*T
+
+	// NewSlice3 is not a factory function because 3 nested slices of ...
+	func NewSlice3() [][][]T
+
+	// NewSliceOfSlice is not a factory function because slices of a ...
+	func NewSliceOfSlice() [][]T
+
+
+TYPES
+	// 
+	type T struct{}
+
+	// 
+	func New() T
+
+	// 
+	func NewArray() [1]T
+
+	// 
+	func NewPointer() *T
+
+	// 
+	func NewPointerArray() [1]*T
+
+	// 
+	func NewPointerOfPointer() **T
+
+	// 
+	func NewPointerSlice() []*T
+
+	// 
+	func NewSlice() []T
+
diff --git a/src/go/doc/testdata/issue22856.go b/src/go/doc/testdata/issue22856.go
new file mode 100644
index 0000000..f456998
--- /dev/null
+++ b/src/go/doc/testdata/issue22856.go
@@ -0,0 +1,27 @@
+// Copyright 2017 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 issue22856
+
+type T struct{}
+
+func New() T                   { return T{} }
+func NewPointer() *T           { return &T{} }
+func NewPointerSlice() []*T    { return []*T{&T{}} }
+func NewSlice() []T            { return []T{T{}} }
+func NewPointerOfPointer() **T { x := &T{}; return &x }
+func NewArray() [1]T           { return [1]T{T{}} }
+func NewPointerArray() [1]*T   { return [1]*T{&T{}} }
+
+// NewSliceOfSlice is not a factory function because slices of a slice of
+// type *T are not factory functions of type T.
+func NewSliceOfSlice() [][]T { return []T{[]T{}} }
+
+// NewPointerSliceOfSlice is not a factory function because slices of a
+// slice of type *T are not factory functions of type T.
+func NewPointerSliceOfSlice() [][]*T { return []*T{[]*T{}} }
+
+// NewSlice3 is not a factory function because 3 nested slices of type T
+// are not factory functions of type T.
+func NewSlice3() [][][]T { return []T{[]T{[]T{}}} }
diff --git a/src/go/doc/testdata/pkgdoc/doc.go b/src/go/doc/testdata/pkgdoc/doc.go
new file mode 100644
index 0000000..3f822c7
--- /dev/null
+++ b/src/go/doc/testdata/pkgdoc/doc.go
@@ -0,0 +1,24 @@
+// 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 pkgdoc
+
+import (
+	crand "crypto/rand"
+	"math/rand"
+)
+
+type T int
+
+type U int
+
+func (T) M() {}
+
+var _ = rand.Int
+var _ = crand.Reader
+
+type G[T any] struct{ x T }
+
+func (g G[T]) M1() {}
+func (g *G[T]) M2() {}
diff --git a/src/go/doc/testdata/predeclared.0.golden b/src/go/doc/testdata/predeclared.0.golden
new file mode 100644
index 0000000..9f37b06
--- /dev/null
+++ b/src/go/doc/testdata/predeclared.0.golden
@@ -0,0 +1,8 @@
+// Package predeclared is a go/doc test for handling of exported ...
+PACKAGE predeclared
+
+IMPORTPATH
+	testdata/predeclared
+
+FILENAMES
+	testdata/predeclared.go
diff --git a/src/go/doc/testdata/predeclared.1.golden b/src/go/doc/testdata/predeclared.1.golden
new file mode 100644
index 0000000..2ff8ee6
--- /dev/null
+++ b/src/go/doc/testdata/predeclared.1.golden
@@ -0,0 +1,22 @@
+// Package predeclared is a go/doc test for handling of exported ...
+PACKAGE predeclared
+
+IMPORTPATH
+	testdata/predeclared
+
+FILENAMES
+	testdata/predeclared.go
+
+TYPES
+	// 
+	type bool int
+
+	// Must not be visible. 
+	func (b bool) String() string
+
+	// 
+	type error struct{}
+
+	// Must not be visible. 
+	func (e error) Error() string
+
diff --git a/src/go/doc/testdata/predeclared.2.golden b/src/go/doc/testdata/predeclared.2.golden
new file mode 100644
index 0000000..9f37b06
--- /dev/null
+++ b/src/go/doc/testdata/predeclared.2.golden
@@ -0,0 +1,8 @@
+// Package predeclared is a go/doc test for handling of exported ...
+PACKAGE predeclared
+
+IMPORTPATH
+	testdata/predeclared
+
+FILENAMES
+	testdata/predeclared.go
diff --git a/src/go/doc/testdata/predeclared.go b/src/go/doc/testdata/predeclared.go
new file mode 100644
index 0000000..c6dd806
--- /dev/null
+++ b/src/go/doc/testdata/predeclared.go
@@ -0,0 +1,22 @@
+// Copyright 2016 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 predeclared is a go/doc test for handling of
+// exported methods on locally-defined predeclared types.
+// See issue 9860.
+package predeclared
+
+type error struct{}
+
+// Must not be visible.
+func (e error) Error() string {
+	return ""
+}
+
+type bool int
+
+// Must not be visible.
+func (b bool) String() string {
+	return ""
+}
diff --git a/src/go/doc/testdata/template.txt b/src/go/doc/testdata/template.txt
new file mode 100644
index 0000000..1b07382
--- /dev/null
+++ b/src/go/doc/testdata/template.txt
@@ -0,0 +1,68 @@
+{{synopsis .Doc}}
+PACKAGE {{.Name}}
+
+IMPORTPATH
+	{{.ImportPath}}
+
+{{with .Imports}}IMPORTS
+{{range .}}	{{.}}
+{{end}}
+{{end}}{{/*
+
+*/}}FILENAMES
+{{range .Filenames}}	{{.}}
+{{end}}{{/*
+
+*/}}{{with .Consts}}
+CONSTANTS
+{{range .}}	{{synopsis .Doc}}
+	{{node .Decl $.FSet}}
+
+{{end}}{{end}}{{/*
+
+*/}}{{with .Vars}}
+VARIABLES
+{{range .}}	{{synopsis .Doc}}
+	{{node .Decl $.FSet}}
+
+{{end}}{{end}}{{/*
+
+*/}}{{with .Funcs}}
+FUNCTIONS
+{{range .}}	{{synopsis .Doc}}
+	{{node .Decl $.FSet}}
+
+{{end}}{{end}}{{/*
+
+*/}}{{with .Types}}
+TYPES
+{{range .}}	{{synopsis .Doc}}
+	{{node .Decl $.FSet}}
+
+{{range .Consts}}	{{synopsis .Doc}}
+	{{node .Decl $.FSet}}
+
+{{end}}{{/*
+
+*/}}{{range .Vars}}	{{synopsis .Doc}}
+	{{node .Decl $.FSet}}
+
+{{end}}{{/*
+
+*/}}{{range .Funcs}}	{{synopsis .Doc}}
+	{{node .Decl $.FSet}}
+
+{{end}}{{/*
+
+*/}}{{range .Methods}}	{{synopsis .Doc}}
+	{{node .Decl $.FSet}}
+
+{{end}}{{end}}{{end}}{{/*
+
+*/}}{{with .Bugs}}
+BUGS .Bugs is now deprecated, please use .Notes instead
+{{range .}}{{indent "\t" .}}
+{{end}}{{end}}{{with .Notes}}{{range $marker, $content := .}}
+{{$marker}}S
+{{range $content}}{{$marker}}({{.UID}}){{indent "\t" .Body}}
+{{end}}{{end}}{{end}}
\ No newline at end of file
diff --git a/src/go/doc/testdata/testing.0.golden b/src/go/doc/testdata/testing.0.golden
new file mode 100644
index 0000000..61dac8b
--- /dev/null
+++ b/src/go/doc/testdata/testing.0.golden
@@ -0,0 +1,156 @@
+// Package testing provides support for automated testing of Go ...
+PACKAGE testing
+
+IMPORTPATH
+	testdata/testing
+
+IMPORTS
+	bytes
+	flag
+	fmt
+	io
+	os
+	runtime
+	runtime/pprof
+	strconv
+	strings
+	time
+
+FILENAMES
+	testdata/benchmark.go
+	testdata/example.go
+	testdata/testing.go
+
+FUNCTIONS
+	// An internal function but exported because it is cross-package; ...
+	func Main(matchString func(pat, str string) (bool, error), tests []InternalTest, benchmarks []InternalBenchmark, examples []InternalExample)
+
+	// An internal function but exported because it is cross-package; ...
+	func RunBenchmarks(matchString func(pat, str string) (bool, error), benchmarks []InternalBenchmark)
+
+	// 
+	func RunExamples(examples []InternalExample) (ok bool)
+
+	// 
+	func RunTests(matchString func(pat, str string) (bool, error), tests []InternalTest) (ok bool)
+
+	// Short reports whether the -test.short flag is set. 
+	func Short() bool
+
+
+TYPES
+	// B is a type passed to Benchmark functions to manage benchmark ...
+	type B struct {
+		N int
+		// contains filtered or unexported fields
+	}
+
+	// Error is equivalent to Log() followed by Fail(). 
+	func (c *B) Error(args ...any)
+
+	// Errorf is equivalent to Logf() followed by Fail(). 
+	func (c *B) Errorf(format string, args ...any)
+
+	// Fail marks the function as having failed but continues ...
+	func (c *B) Fail()
+
+	// FailNow marks the function as having failed and stops its ...
+	func (c *B) FailNow()
+
+	// Failed reports whether the function has failed. 
+	func (c *B) Failed() bool
+
+	// Fatal is equivalent to Log() followed by FailNow(). 
+	func (c *B) Fatal(args ...any)
+
+	// Fatalf is equivalent to Logf() followed by FailNow(). 
+	func (c *B) Fatalf(format string, args ...any)
+
+	// Log formats its arguments using default formatting, analogous ...
+	func (c *B) Log(args ...any)
+
+	// Logf formats its arguments according to the format, analogous ...
+	func (c *B) Logf(format string, args ...any)
+
+	// ResetTimer sets the elapsed benchmark time to zero. It does not ...
+	func (b *B) ResetTimer()
+
+	// SetBytes records the number of bytes processed in a single ...
+	func (b *B) SetBytes(n int64)
+
+	// StartTimer starts timing a test. This function is called ...
+	func (b *B) StartTimer()
+
+	// StopTimer stops timing a test. This can be used to pause the ...
+	func (b *B) StopTimer()
+
+	// The results of a benchmark run. 
+	type BenchmarkResult struct {
+		N	int		// The number of iterations.
+		T	time.Duration	// The total time taken.
+		Bytes	int64		// Bytes processed in one iteration.
+	}
+
+	// Benchmark benchmarks a single function. Useful for creating ...
+	func Benchmark(f func(b *B)) BenchmarkResult
+
+	// 
+	func (r BenchmarkResult) NsPerOp() int64
+
+	// 
+	func (r BenchmarkResult) String() string
+
+	// An internal type but exported because it is cross-package; part ...
+	type InternalBenchmark struct {
+		Name	string
+		F	func(b *B)
+	}
+
+	// 
+	type InternalExample struct {
+		Name	string
+		F	func()
+		Output	string
+	}
+
+	// An internal type but exported because it is cross-package; part ...
+	type InternalTest struct {
+		Name	string
+		F	func(*T)
+	}
+
+	// T is a type passed to Test functions to manage test state and ...
+	type T struct {
+		// contains filtered or unexported fields
+	}
+
+	// Error is equivalent to Log() followed by Fail(). 
+	func (c *T) Error(args ...any)
+
+	// Errorf is equivalent to Logf() followed by Fail(). 
+	func (c *T) Errorf(format string, args ...any)
+
+	// Fail marks the function as having failed but continues ...
+	func (c *T) Fail()
+
+	// FailNow marks the function as having failed and stops its ...
+	func (c *T) FailNow()
+
+	// Failed reports whether the function has failed. 
+	func (c *T) Failed() bool
+
+	// Fatal is equivalent to Log() followed by FailNow(). 
+	func (c *T) Fatal(args ...any)
+
+	// Fatalf is equivalent to Logf() followed by FailNow(). 
+	func (c *T) Fatalf(format string, args ...any)
+
+	// Log formats its arguments using default formatting, analogous ...
+	func (c *T) Log(args ...any)
+
+	// Logf formats its arguments according to the format, analogous ...
+	func (c *T) Logf(format string, args ...any)
+
+	// Parallel signals that this test is to be run in parallel with ...
+	func (t *T) Parallel()
+
diff --git a/src/go/doc/testdata/testing.1.golden b/src/go/doc/testdata/testing.1.golden
new file mode 100644
index 0000000..1655af1
--- /dev/null
+++ b/src/go/doc/testdata/testing.1.golden
@@ -0,0 +1,298 @@
+// Package testing provides support for automated testing of Go ...
+PACKAGE testing
+
+IMPORTPATH
+	testdata/testing
+
+IMPORTS
+	bytes
+	flag
+	fmt
+	io
+	os
+	runtime
+	runtime/pprof
+	strconv
+	strings
+	time
+
+FILENAMES
+	testdata/benchmark.go
+	testdata/example.go
+	testdata/testing.go
+
+VARIABLES
+	// 
+	var (
+		// The short flag requests that tests run more quickly, but its functionality
+		// is provided by test writers themselves. The testing package is just its
+		// home. The all.bash installation script sets it to make installation more
+		// efficient, but by default the flag is off so a plain "go test" will do a
+		// full test of the package.
+		short	= flag.Bool("test.short", false, "run smaller test suite to save time")
+	
+		// Report as tests are run; default is silent for success.
+		chatty		= flag.Bool("test.v", false, "verbose: print additional output")
+		match		= flag.String("test.run", "", "regular expression to select tests to run")
+		memProfile	= flag.String("test.memprofile", "", "write a memory profile to the named file after execution")
+		memProfileRate	= flag.Int("test.memprofilerate", 0, "if >=0, sets runtime.MemProfileRate")
+		cpuProfile	= flag.String("test.cpuprofile", "", "write a cpu profile to the named file during execution")
+		timeout		= flag.Duration("test.timeout", 0, "if positive, sets an aggregate time limit for all tests")
+		cpuListStr	= flag.String("test.cpu", "", "comma-separated list of number of CPUs to use for each test")
+		parallel	= flag.Int("test.parallel", runtime.GOMAXPROCS(0), "maximum test parallelism")
+	
+		cpuList	[]int
+	)
+
+	// 
+	var benchTime = flag.Duration("test.benchtime", 1*time.Second, "approximate run time for each benchmark")
+
+	// 
+	var matchBenchmarks = flag.String("test.bench", "", "regular expression to select benchmarks to run")
+
+	// 
+	var timer *time.Timer
+
+
+FUNCTIONS
+	// An internal function but exported because it is cross-package; ...
+	func Main(matchString func(pat, str string) (bool, error), tests []InternalTest, benchmarks []InternalBenchmark, examples []InternalExample)
+
+	// An internal function but exported because it is cross-package; ...
+	func RunBenchmarks(matchString func(pat, str string) (bool, error), benchmarks []InternalBenchmark)
+
+	// 
+	func RunExamples(examples []InternalExample) (ok bool)
+
+	// 
+	func RunTests(matchString func(pat, str string) (bool, error), tests []InternalTest) (ok bool)
+
+	// Short reports whether the -test.short flag is set. 
+	func Short() bool
+
+	// after runs after all testing. 
+	func after()
+
+	// alarm is called if the timeout expires. 
+	func alarm()
+
+	// before runs before all testing. 
+	func before()
+
+	// decorate inserts the final newline if needed and indentation ...
+	func decorate(s string, addFileLine bool) string
+
+	// 
+	func max(x, y int) int
+
+	// 
+	func min(x, y int) int
+
+	// 
+	func parseCpuList()
+
+	// roundDown10 rounds a number down to the nearest power of 10. 
+	func roundDown10(n int) int
+
+	// roundUp rounds x up to a number of the form [1eX, 2eX, 5eX]. 
+	func roundUp(n int) int
+
+	// startAlarm starts an alarm if requested. 
+	func startAlarm()
+
+	// stopAlarm turns off the alarm. 
+	func stopAlarm()
+
+	// 
+	func tRunner(t *T, test *InternalTest)
+
+
+TYPES
+	// B is a type passed to Benchmark functions to manage benchmark ...
+	type B struct {
+		common
+		N		int
+		benchmark	InternalBenchmark
+		bytes		int64
+		timerOn		bool
+		result		BenchmarkResult
+	}
+
+	// Error is equivalent to Log() followed by Fail(). 
+	func (c *B) Error(args ...any)
+
+	// Errorf is equivalent to Logf() followed by Fail(). 
+	func (c *B) Errorf(format string, args ...any)
+
+	// Fail marks the function as having failed but continues ...
+	func (c *B) Fail()
+
+	// FailNow marks the function as having failed and stops its ...
+	func (c *B) FailNow()
+
+	// Failed reports whether the function has failed. 
+	func (c *B) Failed() bool
+
+	// Fatal is equivalent to Log() followed by FailNow(). 
+	func (c *B) Fatal(args ...any)
+
+	// Fatalf is equivalent to Logf() followed by FailNow(). 
+	func (c *B) Fatalf(format string, args ...any)
+
+	// Log formats its arguments using default formatting, analogous ...
+	func (c *B) Log(args ...any)
+
+	// Logf formats its arguments according to the format, analogous ...
+	func (c *B) Logf(format string, args ...any)
+
+	// ResetTimer sets the elapsed benchmark time to zero. It does not ...
+	func (b *B) ResetTimer()
+
+	// SetBytes records the number of bytes processed in a single ...
+	func (b *B) SetBytes(n int64)
+
+	// StartTimer starts timing a test. This function is called ...
+	func (b *B) StartTimer()
+
+	// StopTimer stops timing a test. This can be used to pause the ...
+	func (b *B) StopTimer()
+
+	// launch launches the benchmark function. It gradually increases ...
+	func (b *B) launch()
+
+	// log generates the output. It's always at the same stack depth. 
+	func (c *B) log(s string)
+
+	// 
+	func (b *B) nsPerOp() int64
+
+	// run times the benchmark function in a separate goroutine. 
+	func (b *B) run() BenchmarkResult
+
+	// runN runs a single benchmark for the specified number of ...
+	func (b *B) runN(n int)
+
+	// trimOutput shortens the output from a benchmark, which can be ...
+	func (b *B) trimOutput()
+
+	// The results of a benchmark run. 
+	type BenchmarkResult struct {
+		N	int		// The number of iterations.
+		T	time.Duration	// The total time taken.
+		Bytes	int64		// Bytes processed in one iteration.
+	}
+
+	// Benchmark benchmarks a single function. Useful for creating ...
+	func Benchmark(f func(b *B)) BenchmarkResult
+
+	// 
+	func (r BenchmarkResult) NsPerOp() int64
+
+	// 
+	func (r BenchmarkResult) String() string
+
+	// 
+	func (r BenchmarkResult) mbPerSec() float64
+
+	// An internal type but exported because it is cross-package; part ...
+	type InternalBenchmark struct {
+		Name	string
+		F	func(b *B)
+	}
+
+	// 
+	type InternalExample struct {
+		Name	string
+		F	func()
+		Output	string
+	}
+
+	// An internal type but exported because it is cross-package; part ...
+	type InternalTest struct {
+		Name	string
+		F	func(*T)
+	}
+
+	// T is a type passed to Test functions to manage test state and ...
+	type T struct {
+		common
+		name		string		// Name of test.
+		startParallel	chan bool	// Parallel tests will wait on this.
+	}
+
+	// Error is equivalent to Log() followed by Fail(). 
+	func (c *T) Error(args ...any)
+
+	// Errorf is equivalent to Logf() followed by Fail(). 
+	func (c *T) Errorf(format string, args ...any)
+
+	// Fail marks the function as having failed but continues ...
+	func (c *T) Fail()
+
+	// FailNow marks the function as having failed and stops its ...
+	func (c *T) FailNow()
+
+	// Failed reports whether the function has failed. 
+	func (c *T) Failed() bool
+
+	// Fatal is equivalent to Log() followed by FailNow(). 
+	func (c *T) Fatal(args ...any)
+
+	// Fatalf is equivalent to Logf() followed by FailNow(). 
+	func (c *T) Fatalf(format string, args ...any)
+
+	// Log formats its arguments using default formatting, analogous ...
+	func (c *T) Log(args ...any)
+
+	// Logf formats its arguments according to the format, analogous ...
+	func (c *T) Logf(format string, args ...any)
+
+	// Parallel signals that this test is to be run in parallel with ...
+	func (t *T) Parallel()
+
+	// log generates the output. It's always at the same stack depth. 
+	func (c *T) log(s string)
+
+	// 
+	func (t *T) report()
+
+	// common holds the elements common between T and B and captures ...
+	type common struct {
+		output		[]byte		// Output generated by test or benchmark.
+		failed		bool		// Test or benchmark has failed.
+		start		time.Time	// Time test or benchmark started
+		duration	time.Duration
+		self		any		// To be sent on signal channel when done.
+		signal		chan any	// Output for serial tests.
+	}
+
+	// Error is equivalent to Log() followed by Fail(). 
+	func (c *common) Error(args ...any)
+
+	// Errorf is equivalent to Logf() followed by Fail(). 
+	func (c *common) Errorf(format string, args ...any)
+
+	// Fail marks the function as having failed but continues ...
+	func (c *common) Fail()
+
+	// FailNow marks the function as having failed and stops its ...
+	func (c *common) FailNow()
+
+	// Failed reports whether the function has failed. 
+	func (c *common) Failed() bool
+
+	// Fatal is equivalent to Log() followed by FailNow(). 
+	func (c *common) Fatal(args ...any)
+
+	// Fatalf is equivalent to Logf() followed by FailNow(). 
+	func (c *common) Fatalf(format string, args ...any)
+
+	// Log formats its arguments using default formatting, analogous ...
+	func (c *common) Log(args ...any)
+
+	// Logf formats its arguments according to the format, analogous ...
+	func (c *common) Logf(format string, args ...any)
+
+	// log generates the output. It's always at the same stack depth. 
+	func (c *common) log(s string)
+
diff --git a/src/go/doc/testdata/testing.2.golden b/src/go/doc/testdata/testing.2.golden
new file mode 100644
index 0000000..61dac8b
--- /dev/null
+++ b/src/go/doc/testdata/testing.2.golden
@@ -0,0 +1,156 @@
+// Package testing provides support for automated testing of Go ...
+PACKAGE testing
+
+IMPORTPATH
+	testdata/testing
+
+IMPORTS
+	bytes
+	flag
+	fmt
+	io
+	os
+	runtime
+	runtime/pprof
+	strconv
+	strings
+	time
+
+FILENAMES
+	testdata/benchmark.go
+	testdata/example.go
+	testdata/testing.go
+
+FUNCTIONS
+	// An internal function but exported because it is cross-package; ...
+	func Main(matchString func(pat, str string) (bool, error), tests []InternalTest, benchmarks []InternalBenchmark, examples []InternalExample)
+
+	// An internal function but exported because it is cross-package; ...
+	func RunBenchmarks(matchString func(pat, str string) (bool, error), benchmarks []InternalBenchmark)
+
+	// 
+	func RunExamples(examples []InternalExample) (ok bool)
+
+	// 
+	func RunTests(matchString func(pat, str string) (bool, error), tests []InternalTest) (ok bool)
+
+	// Short reports whether the -test.short flag is set. 
+	func Short() bool
+
+
+TYPES
+	// B is a type passed to Benchmark functions to manage benchmark ...
+	type B struct {
+		N int
+		// contains filtered or unexported fields
+	}
+
+	// Error is equivalent to Log() followed by Fail(). 
+	func (c *B) Error(args ...any)
+
+	// Errorf is equivalent to Logf() followed by Fail(). 
+	func (c *B) Errorf(format string, args ...any)
+
+	// Fail marks the function as having failed but continues ...
+	func (c *B) Fail()
+
+	// FailNow marks the function as having failed and stops its ...
+	func (c *B) FailNow()
+
+	// Failed reports whether the function has failed. 
+	func (c *B) Failed() bool
+
+	// Fatal is equivalent to Log() followed by FailNow(). 
+	func (c *B) Fatal(args ...any)
+
+	// Fatalf is equivalent to Logf() followed by FailNow(). 
+	func (c *B) Fatalf(format string, args ...any)
+
+	// Log formats its arguments using default formatting, analogous ...
+	func (c *B) Log(args ...any)
+
+	// Logf formats its arguments according to the format, analogous ...
+	func (c *B) Logf(format string, args ...any)
+
+	// ResetTimer sets the elapsed benchmark time to zero. It does not ...
+	func (b *B) ResetTimer()
+
+	// SetBytes records the number of bytes processed in a single ...
+	func (b *B) SetBytes(n int64)
+
+	// StartTimer starts timing a test. This function is called ...
+	func (b *B) StartTimer()
+
+	// StopTimer stops timing a test. This can be used to pause the ...
+	func (b *B) StopTimer()
+
+	// The results of a benchmark run. 
+	type BenchmarkResult struct {
+		N	int		// The number of iterations.
+		T	time.Duration	// The total time taken.
+		Bytes	int64		// Bytes processed in one iteration.
+	}
+
+	// Benchmark benchmarks a single function. Useful for creating ...
+	func Benchmark(f func(b *B)) BenchmarkResult
+
+	// 
+	func (r BenchmarkResult) NsPerOp() int64
+
+	// 
+	func (r BenchmarkResult) String() string
+
+	// An internal type but exported because it is cross-package; part ...
+	type InternalBenchmark struct {
+		Name	string
+		F	func(b *B)
+	}
+
+	// 
+	type InternalExample struct {
+		Name	string
+		F	func()
+		Output	string
+	}
+
+	// An internal type but exported because it is cross-package; part ...
+	type InternalTest struct {
+		Name	string
+		F	func(*T)
+	}
+
+	// T is a type passed to Test functions to manage test state and ...
+	type T struct {
+		// contains filtered or unexported fields
+	}
+
+	// Error is equivalent to Log() followed by Fail(). 
+	func (c *T) Error(args ...any)
+
+	// Errorf is equivalent to Logf() followed by Fail(). 
+	func (c *T) Errorf(format string, args ...any)
+
+	// Fail marks the function as having failed but continues ...
+	func (c *T) Fail()
+
+	// FailNow marks the function as having failed and stops its ...
+	func (c *T) FailNow()
+
+	// Failed reports whether the function has failed. 
+	func (c *T) Failed() bool
+
+	// Fatal is equivalent to Log() followed by FailNow(). 
+	func (c *T) Fatal(args ...any)
+
+	// Fatalf is equivalent to Logf() followed by FailNow(). 
+	func (c *T) Fatalf(format string, args ...any)
+
+	// Log formats its arguments using default formatting, analogous ...
+	func (c *T) Log(args ...any)
+
+	// Logf formats its arguments according to the format, analogous ...
+	func (c *T) Logf(format string, args ...any)
+
+	// Parallel signals that this test is to be run in parallel with ...
+	func (t *T) Parallel()
+
diff --git a/src/go/doc/testdata/testing.go b/src/go/doc/testdata/testing.go
new file mode 100644
index 0000000..d3076c9
--- /dev/null
+++ b/src/go/doc/testdata/testing.go
@@ -0,0 +1,404 @@
+// 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.
+
+// Package testing provides support for automated testing of Go packages.
+// It is intended to be used in concert with the “go test” utility, which automates
+// execution of any function of the form
+//     func TestXxx(*testing.T)
+// where Xxx can be any alphanumeric string (but the first letter must not be in
+// [a-z]) and serves to identify the test routine.
+// These TestXxx routines should be declared within the package they are testing.
+//
+// Functions of the form
+//     func BenchmarkXxx(*testing.B)
+// are considered benchmarks, and are executed by go test when the -test.bench
+// flag is provided.
+//
+// A sample benchmark function looks like this:
+//     func BenchmarkHello(b *testing.B) {
+//         for i := 0; i < b.N; i++ {
+//             fmt.Sprintf("hello")
+//         }
+//     }
+// The benchmark package will vary b.N until the benchmark function lasts
+// long enough to be timed reliably. The output
+//     testing.BenchmarkHello    10000000    282 ns/op
+// means that the loop ran 10000000 times at a speed of 282 ns per loop.
+//
+// If a benchmark needs some expensive setup before running, the timer
+// may be stopped:
+//     func BenchmarkBigLen(b *testing.B) {
+//         b.StopTimer()
+//         big := NewBig()
+//         b.StartTimer()
+//         for i := 0; i < b.N; i++ {
+//             big.Len()
+//         }
+//     }
+package testing
+
+import (
+	"flag"
+	"fmt"
+	"os"
+	"runtime"
+	"runtime/pprof"
+	"strconv"
+	"strings"
+	"time"
+)
+
+var (
+	// The short flag requests that tests run more quickly, but its functionality
+	// is provided by test writers themselves. The testing package is just its
+	// home. The all.bash installation script sets it to make installation more
+	// efficient, but by default the flag is off so a plain "go test" will do a
+	// full test of the package.
+	short = flag.Bool("test.short", false, "run smaller test suite to save time")
+
+	// Report as tests are run; default is silent for success.
+	chatty         = flag.Bool("test.v", false, "verbose: print additional output")
+	match          = flag.String("test.run", "", "regular expression to select tests to run")
+	memProfile     = flag.String("test.memprofile", "", "write a memory profile to the named file after execution")
+	memProfileRate = flag.Int("test.memprofilerate", 0, "if >=0, sets runtime.MemProfileRate")
+	cpuProfile     = flag.String("test.cpuprofile", "", "write a cpu profile to the named file during execution")
+	timeout        = flag.Duration("test.timeout", 0, "if positive, sets an aggregate time limit for all tests")
+	cpuListStr     = flag.String("test.cpu", "", "comma-separated list of number of CPUs to use for each test")
+	parallel       = flag.Int("test.parallel", runtime.GOMAXPROCS(0), "maximum test parallelism")
+
+	cpuList []int
+)
+
+// common holds the elements common between T and B and
+// captures common methods such as Errorf.
+type common struct {
+	output   []byte    // Output generated by test or benchmark.
+	failed   bool      // Test or benchmark has failed.
+	start    time.Time // Time test or benchmark started
+	duration time.Duration
+	self     any      // To be sent on signal channel when done.
+	signal   chan any // Output for serial tests.
+}
+
+// Short reports whether the -test.short flag is set.
+func Short() bool {
+	return *short
+}
+
+// decorate inserts the final newline if needed and indentation tabs for formatting.
+// If addFileLine is true, it also prefixes the string with the file and line of the call site.
+func decorate(s string, addFileLine bool) string {
+	if addFileLine {
+		_, file, line, ok := runtime.Caller(3) // decorate + log + public function.
+		if ok {
+			// Truncate file name at last file name separator.
+			if index := strings.LastIndex(file, "/"); index >= 0 {
+				file = file[index+1:]
+			} else if index = strings.LastIndex(file, "\\"); index >= 0 {
+				file = file[index+1:]
+			}
+		} else {
+			file = "???"
+			line = 1
+		}
+		s = fmt.Sprintf("%s:%d: %s", file, line, s)
+	}
+	s = "\t" + s // Every line is indented at least one tab.
+	n := len(s)
+	if n > 0 && s[n-1] != '\n' {
+		s += "\n"
+		n++
+	}
+	for i := 0; i < n-1; i++ { // -1 to avoid final newline
+		if s[i] == '\n' {
+			// Second and subsequent lines are indented an extra tab.
+			return s[0:i+1] + "\t" + decorate(s[i+1:n], false)
+		}
+	}
+	return s
+}
+
+// T is a type passed to Test functions to manage test state and support formatted test logs.
+// Logs are accumulated during execution and dumped to standard error when done.
+type T struct {
+	common
+	name          string    // Name of test.
+	startParallel chan bool // Parallel tests will wait on this.
+}
+
+// Fail marks the function as having failed but continues execution.
+func (c *common) Fail() { c.failed = true }
+
+// Failed reports whether the function has failed.
+func (c *common) Failed() bool { return c.failed }
+
+// FailNow marks the function as having failed and stops its execution.
+// Execution will continue at the next Test.
+func (c *common) FailNow() {
+	c.Fail()
+
+	// Calling runtime.Goexit will exit the goroutine, which
+	// will run the deferred functions in this goroutine,
+	// which will eventually run the deferred lines in tRunner,
+	// which will signal to the test loop that this test is done.
+	//
+	// A previous version of this code said:
+	//
+	//	c.duration = ...
+	//	c.signal <- c.self
+	//	runtime.Goexit()
+	//
+	// This previous version duplicated code (those lines are in
+	// tRunner no matter what), but worse the goroutine teardown
+	// implicit in runtime.Goexit was not guaranteed to complete
+	// before the test exited. If a test deferred an important cleanup
+	// function (like removing temporary files), there was no guarantee
+	// it would run on a test failure. Because we send on c.signal during
+	// a top-of-stack deferred function now, we know that the send
+	// only happens after any other stacked defers have completed.
+	runtime.Goexit()
+}
+
+// log generates the output. It's always at the same stack depth.
+func (c *common) log(s string) {
+	c.output = append(c.output, decorate(s, true)...)
+}
+
+// Log formats its arguments using default formatting, analogous to Println(),
+// and records the text in the error log.
+func (c *common) Log(args ...any) { c.log(fmt.Sprintln(args...)) }
+
+// Logf formats its arguments according to the format, analogous to Printf(),
+// and records the text in the error log.
+func (c *common) Logf(format string, args ...any) { c.log(fmt.Sprintf(format, args...)) }
+
+// Error is equivalent to Log() followed by Fail().
+func (c *common) Error(args ...any) {
+	c.log(fmt.Sprintln(args...))
+	c.Fail()
+}
+
+// Errorf is equivalent to Logf() followed by Fail().
+func (c *common) Errorf(format string, args ...any) {
+	c.log(fmt.Sprintf(format, args...))
+	c.Fail()
+}
+
+// Fatal is equivalent to Log() followed by FailNow().
+func (c *common) Fatal(args ...any) {
+	c.log(fmt.Sprintln(args...))
+	c.FailNow()
+}
+
+// Fatalf is equivalent to Logf() followed by FailNow().
+func (c *common) Fatalf(format string, args ...any) {
+	c.log(fmt.Sprintf(format, args...))
+	c.FailNow()
+}
+
+// Parallel signals that this test is to be run in parallel with (and only with)
+// other parallel tests in this CPU group.
+func (t *T) Parallel() {
+	t.signal <- (*T)(nil) // Release main testing loop
+	<-t.startParallel     // Wait for serial tests to finish
+}
+
+// An internal type but exported because it is cross-package; part of the implementation
+// of go test.
+type InternalTest struct {
+	Name string
+	F    func(*T)
+}
+
+func tRunner(t *T, test *InternalTest) {
+	t.start = time.Now()
+
+	// When this goroutine is done, either because test.F(t)
+	// returned normally or because a test failure triggered
+	// a call to runtime.Goexit, record the duration and send
+	// a signal saying that the test is done.
+	defer func() {
+		t.duration = time.Since(t.start)
+		t.signal <- t
+	}()
+
+	test.F(t)
+}
+
+// An internal function but exported because it is cross-package; part of the implementation
+// of go test.
+func Main(matchString func(pat, str string) (bool, error), tests []InternalTest, benchmarks []InternalBenchmark, examples []InternalExample) {
+	flag.Parse()
+	parseCpuList()
+
+	before()
+	startAlarm()
+	testOk := RunTests(matchString, tests)
+	exampleOk := RunExamples(examples)
+	if !testOk || !exampleOk {
+		fmt.Println("FAIL")
+		os.Exit(1)
+	}
+	fmt.Println("PASS")
+	stopAlarm()
+	RunBenchmarks(matchString, benchmarks)
+	after()
+}
+
+func (t *T) report() {
+	tstr := fmt.Sprintf("(%.2f seconds)", t.duration.Seconds())
+	format := "--- %s: %s %s\n%s"
+	if t.failed {
+		fmt.Printf(format, "FAIL", t.name, tstr, t.output)
+	} else if *chatty {
+		fmt.Printf(format, "PASS", t.name, tstr, t.output)
+	}
+}
+
+func RunTests(matchString func(pat, str string) (bool, error), tests []InternalTest) (ok bool) {
+	ok = true
+	if len(tests) == 0 {
+		fmt.Fprintln(os.Stderr, "testing: warning: no tests to run")
+		return
+	}
+	for _, procs := range cpuList {
+		runtime.GOMAXPROCS(procs)
+		// We build a new channel tree for each run of the loop.
+		// collector merges in one channel all the upstream signals from parallel tests.
+		// If all tests pump to the same channel, a bug can occur where a test
+		// kicks off a goroutine that Fails, yet the test still delivers a completion signal,
+		// which skews the counting.
+		var collector = make(chan any)
+
+		numParallel := 0
+		startParallel := make(chan bool)
+
+		for i := 0; i < len(tests); i++ {
+			matched, err := matchString(*match, tests[i].Name)
+			if err != nil {
+				fmt.Fprintf(os.Stderr, "testing: invalid regexp for -test.run: %s\n", err)
+				os.Exit(1)
+			}
+			if !matched {
+				continue
+			}
+			testName := tests[i].Name
+			if procs != 1 {
+				testName = fmt.Sprintf("%s-%d", tests[i].Name, procs)
+			}
+			t := &T{
+				common: common{
+					signal: make(chan any),
+				},
+				name:          testName,
+				startParallel: startParallel,
+			}
+			t.self = t
+			if *chatty {
+				fmt.Printf("=== RUN %s\n", t.name)
+			}
+			go tRunner(t, &tests[i])
+			out := (<-t.signal).(*T)
+			if out == nil { // Parallel run.
+				go func() {
+					collector <- <-t.signal
+				}()
+				numParallel++
+				continue
+			}
+			t.report()
+			ok = ok && !out.failed
+		}
+
+		running := 0
+		for numParallel+running > 0 {
+			if running < *parallel && numParallel > 0 {
+				startParallel <- true
+				running++
+				numParallel--
+				continue
+			}
+			t := (<-collector).(*T)
+			t.report()
+			ok = ok && !t.failed
+			running--
+		}
+	}
+	return
+}
+
+// before runs before all testing.
+func before() {
+	if *memProfileRate > 0 {
+		runtime.MemProfileRate = *memProfileRate
+	}
+	if *cpuProfile != "" {
+		f, err := os.Create(*cpuProfile)
+		if err != nil {
+			fmt.Fprintf(os.Stderr, "testing: %s", err)
+			return
+		}
+		if err := pprof.StartCPUProfile(f); err != nil {
+			fmt.Fprintf(os.Stderr, "testing: can't start cpu profile: %s", err)
+			f.Close()
+			return
+		}
+		// Could save f so after can call f.Close; not worth the effort.
+	}
+
+}
+
+// after runs after all testing.
+func after() {
+	if *cpuProfile != "" {
+		pprof.StopCPUProfile() // flushes profile to disk
+	}
+	if *memProfile != "" {
+		f, err := os.Create(*memProfile)
+		if err != nil {
+			fmt.Fprintf(os.Stderr, "testing: %s", err)
+			return
+		}
+		if err = pprof.WriteHeapProfile(f); err != nil {
+			fmt.Fprintf(os.Stderr, "testing: can't write %s: %s", *memProfile, err)
+		}
+		f.Close()
+	}
+}
+
+var timer *time.Timer
+
+// startAlarm starts an alarm if requested.
+func startAlarm() {
+	if *timeout > 0 {
+		timer = time.AfterFunc(*timeout, alarm)
+	}
+}
+
+// stopAlarm turns off the alarm.
+func stopAlarm() {
+	if *timeout > 0 {
+		timer.Stop()
+	}
+}
+
+// alarm is called if the timeout expires.
+func alarm() {
+	panic("test timed out")
+}
+
+func parseCpuList() {
+	if len(*cpuListStr) == 0 {
+		cpuList = append(cpuList, runtime.GOMAXPROCS(-1))
+	} else {
+		for _, val := range strings.Split(*cpuListStr, ",") {
+			cpu, err := strconv.Atoi(val)
+			if err != nil || cpu <= 0 {
+				fmt.Fprintf(os.Stderr, "testing: invalid value %q for -test.cpu", val)
+				os.Exit(1)
+			}
+			cpuList = append(cpuList, cpu)
+		}
+	}
+}