internal/pkgdoc/funcs.go - website - Git at Google

 // 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 pkgdoc

 import (
 	"bufio"
 	"bytes"
 	"fmt"
 	"go/ast"
 	"go/doc"
 	"go/format"
 	"go/printer"
 	"go/token"
 	"html/template"
 	"io"
 	"log"
 	"path"
 	"regexp"
 	"strings"
 	"unicode"
 	"unicode/utf8"

 	"golang.org/x/website/internal/api"
 	"golang.org/x/website/internal/texthtml"
 )

 var slashSlash = []byte("//")

 // Node formats the given AST node as HTML.
 // Identifiers in the rendered node
 // are turned into links to their documentation.
 func (p *Page) Node(node interface{}) template.HTML {
 	var buf1 bytes.Buffer
 	p.docs.writeNode(&buf1, p, p.fset, node)

 	var buf2 bytes.Buffer
 	n, _ := node.(ast.Node)
 	buf2.Write(texthtml.Format(buf1.Bytes(), texthtml.Config{
 		AST:        n,
 		GoComments: true,
 		OldDocs:    p.OldDocs,
 	}))
 	return template.HTML(buf2.String())
 }

 // NodeTOC formats the given AST node as HTML
 // for inclusion in the table of contents.
 func (p *Page) NodeTOC(node interface{}) template.HTML {
 	var buf1 bytes.Buffer
 	p.docs.writeNode(&buf1, p, p.fset, node)

 	var buf2 bytes.Buffer
 	buf2.Write(texthtml.Format(buf1.Bytes(), texthtml.Config{
 		GoComments: true,
 		OldDocs:    p.OldDocs,
 	}))

 	return sanitize(template.HTML(buf2.String()))
 }

 const tabWidth = 4

 // writeNode writes the AST node x to w.
 //
 // The provided fset must be non-nil. The pageInfo is optional. If
 // present, the pageInfo is used to add comments to struct fields to
 // say which version of Go introduced them.
 func (d *docs) writeNode(w io.Writer, pageInfo *Page, fset *token.FileSet, x interface{}) {
 	// convert trailing tabs into spaces using a tconv filter
 	// to ensure a good outcome in most browsers (there may still
 	// be tabs in comments and strings, but converting those into
 	// the right number of spaces is much harder)
 	//
 	// TODO(gri) rethink printer flags - perhaps tconv can be eliminated
 	//           with an another printer mode (which is more efficiently
 	//           implemented in the printer than here with another layer)

 	var pkgName, structName string
 	var apiInfo api.PkgDB
 	if gd, ok := x.(*ast.GenDecl); ok && pageInfo != nil && pageInfo.PDoc != nil &&
 		gd.Tok == token.TYPE && len(gd.Specs) != 0 {
 		pkgName = pageInfo.PDoc.ImportPath
 		if ts, ok := gd.Specs[0].(*ast.TypeSpec); ok {
 			if _, ok := ts.Type.(*ast.StructType); ok {
 				structName = ts.Name.Name
 			}
 		}
 		apiInfo = d.api[pkgName]
 	}

 	var out = w
 	var buf bytes.Buffer
 	if structName != "" {
 		out = &buf
 	}

 	mode := printer.TabIndent | printer.UseSpaces
 	err := (&printer.Config{Mode: mode, Tabwidth: tabWidth}).Fprint(tabSpacer(out, tabWidth), fset, x)
 	if err != nil {
 		log.Print(err)
 	}

 	// Add comments to struct fields saying which Go version introduced them.
 	if structName != "" {
 		fieldSince := apiInfo.Field[structName]
 		typeSince := apiInfo.Type[structName]
 		// Add/rewrite comments on struct fields to note which Go version added them.
 		var buf2 bytes.Buffer
 		buf2.Grow(buf.Len() + len(" // Added in Go 1.n")*10)
 		bs := bufio.NewScanner(&buf)
 		for bs.Scan() {
 			line := bs.Bytes()
 			field := firstIdent(line)
 			var since string
 			if field != "" {
 				since = fieldSince[field]
 				if since != "" && since == typeSince {
 					// Don't highlight field versions if they were the
 					// same as the struct itself.
 					since = ""
 				}
 			}
 			if since == "" {
 				buf2.Write(line)
 			} else {
 				if bytes.Contains(line, slashSlash) {
 					line = bytes.TrimRight(line, " \t.")
 					buf2.Write(line)
 					buf2.WriteString("; added in Go ")
 				} else {
 					buf2.Write(line)
 					buf2.WriteString(" // Go ")
 				}
 				buf2.WriteString(since)
 			}
 			buf2.WriteByte('\n')
 		}
 		w.Write(buf2.Bytes())
 	}
 }

 // firstIdent returns the first identifier in x.
 // This actually parses "identifiers" that begin with numbers too, but we
 // never feed it such input, so it's fine.
 func firstIdent(x []byte) string {
 	x = bytes.TrimSpace(x)
 	i := bytes.IndexFunc(x, func(r rune) bool { return !unicode.IsLetter(r) && !unicode.IsNumber(r) })
 	if i == -1 {
 		return string(x)
 	}
 	return string(x[:i])
 }

 // Comment formats the given documentation comment as HTML.
 func (p *Page) Comment(comment string) template.HTML {
 	// TODO: After Go 1.20 is out, this can be simplified to:
 	//return template.HTML(p.PDoc.HTML(comment))
 	// While deleting the go118.go and go119.go files.
 	return template.HTML(docPackageHTML(p.PDoc, comment))
 }

 // sanitize sanitizes the argument src by replacing newlines with
 // blanks, removing extra blanks, and by removing trailing whitespace
 // and commas before closing parentheses.
 func sanitize(src template.HTML) template.HTML {
 	buf := make([]byte, len(src))
 	j := 0      // buf index
 	comma := -1 // comma index if >= 0
 	for i := 0; i < len(src); i++ {
 		ch := src[i]
 		switch ch {
 		case '\t', '\n', ' ':
 			// ignore whitespace at the beginning, after a blank, or after opening parentheses
 			if j == 0 {
 				continue
 			}
 			if p := buf[j-1]; p == ' ' || p == '(' || p == '{' || p == '[' {
 				continue
 			}
 			// replace all whitespace with blanks
 			ch = ' '
 		case ',':
 			comma = j
 		case ')', '}', ']':
 			// remove any trailing comma
 			if comma >= 0 {
 				j = comma
 			}
 			// remove any trailing whitespace
 			if j > 0 && buf[j-1] == ' ' {
 				j--
 			}
 		default:
 			comma = -1
 		}
 		buf[j] = ch
 		j++
 	}
 	// remove trailing blank, if any
 	if j > 0 && buf[j-1] == ' ' {
 		j--
 	}
 	return template.HTML(buf[:j])
 }

 // Since reports the Go version that introduced the API feature
 // identified by kind, receiver, name.
 func (p *Page) Since(kind, receiver, name string) string {
 	pkg := p.PDoc.ImportPath
 	return p.docs.api.Func(pkg, kind, receiver, name)
 }

 type Example struct {
 	Page   *Page
 	Name   string
 	Doc    string
 	Code   template.HTML
 	Play   string
 	Output string
 }

 // Example renders the examples for the given function name as HTML.
 func (p *Page) FmtExamples(funcName string) []*Example {
 	var list []*Example
 	for _, eg := range p.Examples {
 		name := trimExampleSuffix(eg.Name)

 		if name != funcName {
 			continue
 		}

 		// print code
 		cnode := &printer.CommentedNode{Node: eg.Code, Comments: eg.Comments}
 		code := p.Node(cnode)
 		out := eg.Output
 		wholeFile := true

 		// Additional formatting if this is a function body.
 		if n := len(code); n >= 2 && code[0] == '{' && code[n-1] == '}' {
 			wholeFile = false
 			// remove surrounding braces
 			code = code[1 : n-1]
 			// unindent
 			code = template.HTML(replaceLeadingIndentation(string(code), strings.Repeat(" ", tabWidth), ""))
 			// remove output comment
 			if loc := exampleOutputRx.FindStringIndex(string(code)); loc != nil {
 				code = template.HTML(strings.TrimSpace(string(code)[:loc[0]]))
 			}
 		}

 		// Write out the playground code in standard Go style
 		// (use tabs, no comment highlight, etc).
 		play := ""
 		if eg.Play != nil {
 			var buf bytes.Buffer
 			eg.Play.Comments = filterOutBuildAnnotations(eg.Play.Comments)
 			if err := format.Node(&buf, p.fset, eg.Play); err != nil {
 				log.Print(err)
 			} else {
 				play = buf.String()
 			}
 		}

 		// Drop output, as the output comment will appear in the code.
 		if wholeFile && play == "" {
 			out = ""
 		}

 		list = append(list, &Example{
 			Page:   p,
 			Name:   eg.Name,
 			Doc:    eg.Doc,
 			Code:   code,
 			Play:   play,
 			Output: out,
 		})
 	}
 	return list
 }

 // replaceLeadingIndentation replaces oldIndent at the beginning of each line
 // with newIndent. This is used for formatting examples. Raw strings that
 // span multiple lines are handled specially: oldIndent is not removed (since
 // go/printer will not add any indentation there), but newIndent is added
 // (since we may still want leading indentation).
 func replaceLeadingIndentation(body, oldIndent, newIndent string) string {
 	// Handle indent at the beginning of the first line. After this, we handle
 	// indentation only after a newline.
 	var buf bytes.Buffer
 	if strings.HasPrefix(body, oldIndent) {
 		buf.WriteString(newIndent)
 		body = body[len(oldIndent):]
 	}

 	// Use a state machine to keep track of whether we're in a string or
 	// rune literal while we process the rest of the code.
 	const (
 		codeState = iota
 		runeState
 		interpretedStringState
 		rawStringState
 	)
 	searchChars := []string{
 		"'\"`\n", // codeState
 		`\'`,     // runeState
 		`\"`,     // interpretedStringState
 		"`\n",    // rawStringState
 		// newlineState does not need to search
 	}
 	state := codeState
 	for {
 		i := strings.IndexAny(body, searchChars[state])
 		if i < 0 {
 			buf.WriteString(body)
 			break
 		}
 		c := body[i]
 		buf.WriteString(body[:i+1])
 		body = body[i+1:]
 		switch state {
 		case codeState:
 			switch c {
 			case '\'':
 				state = runeState
 			case '"':
 				state = interpretedStringState
 			case '`':
 				state = rawStringState
 			case '\n':
 				if strings.HasPrefix(body, oldIndent) {
 					buf.WriteString(newIndent)
 					body = body[len(oldIndent):]
 				}
 			}

 		case runeState:
 			switch c {
 			case '\\':
 				r, size := utf8.DecodeRuneInString(body)
 				buf.WriteRune(r)
 				body = body[size:]
 			case '\'':
 				state = codeState
 			}

 		case interpretedStringState:
 			switch c {
 			case '\\':
 				r, size := utf8.DecodeRuneInString(body)
 				buf.WriteRune(r)
 				body = body[size:]
 			case '"':
 				state = codeState
 			}

 		case rawStringState:
 			switch c {
 			case '`':
 				state = codeState
 			case '\n':
 				buf.WriteString(newIndent)
 			}
 		}
 	}
 	return buf.String()
 }

 var exampleOutputRx = regexp.MustCompile(`(?i)//[[:space:]]*(unordered )?output:`)

 func filterOutBuildAnnotations(cg []*ast.CommentGroup) []*ast.CommentGroup {
 	if len(cg) == 0 {
 		return cg
 	}

 	for i := range cg {
 		if !strings.HasPrefix(cg[i].Text(), "+build ") {
 			// Found the first non-build tag, return from here until the end
 			// of the slice.
 			return cg[i:]
 		}
 	}

 	// There weren't any non-build tags, return an empty slice.
 	return []*ast.CommentGroup{}
 }

 // ExampleName takes an example function name and returns its display
 // name. For example, "Foo_Bar_quux" becomes "Foo.Bar (Quux)".
 func (*Page) ExampleName(s string) string {
 	name, suffix := splitExampleName(s)
 	// replace _ with . for method names
 	name = strings.Replace(name, "_", ".", 1)
 	// use "Package" if no name provided
 	if name == "" {
 		name = "Package"
 	}
 	return name + suffix
 }

 // ExampleSuffix takes an example function name and returns its suffix in
 // parenthesized form. For example, "Foo_Bar_quux" becomes " (Quux)".
 func (*Page) ExampleSuffix(name string) string {
 	_, suffix := splitExampleName(name)
 	return suffix
 }

 // SrcPosLink returns a link to the specific source code position containing n,
 // which must be either an ast.Node or a *doc.Note.
 func (p *Page) SrcPosLink(n interface{}) template.HTML {
 	// n must be an ast.Node or a *doc.Note
 	var pos, end token.Pos

 	switch n := n.(type) {
 	case ast.Node:
 		pos = n.Pos()
 		end = n.End()
 	case *doc.Note:
 		pos = n.Pos
 		end = n.End
 	default:
 		panic(fmt.Sprintf("wrong type for SrcPosLink template formatter: %T", n))
 	}

 	var relpath string
 	var line int
 	var low, high int // selection offset range

 	if pos.IsValid() {
 		xp := p.fset.Position(pos)
 		relpath = xp.Filename
 		line = xp.Line
 		low = xp.Offset
 	}
 	if end.IsValid() {
 		high = p.fset.Position(end).Offset
 	}

 	return srcPosLink(relpath, line, low, high)
 }

 func srcPosLink(s string, line, low, high int) template.HTML {
 	s = path.Clean("/" + s)
 	if !strings.HasPrefix(s, "/src/") {
 		s = "/src" + s
 	}
 	var buf bytes.Buffer
 	template.HTMLEscape(&buf, []byte(s))
 	// selection ranges are of form "s=low:high"
 	if low < high {
 		fmt.Fprintf(&buf, "?s=%d:%d", low, high) // no need for URL escaping
 		// if we have a selection, position the page
 		// such that the selection is a bit below the top
 		line -= 10
 		if line < 1 {
 			line = 1
 		}
 	}
 	// line id's in html-printed source are of the
 	// form "L%d" where %d stands for the line number
 	if line > 0 {
 		fmt.Fprintf(&buf, "#L%d", line) // no need for URL escaping
 	}
 	return template.HTML(buf.String())
 }
	// 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 pkgdoc

	import (
	"bufio"
	"bytes"
	"fmt"
	"go/ast"
	"go/doc"
	"go/format"
	"go/printer"
	"go/token"
	"html/template"
	"io"
	"log"
	"path"
	"regexp"
	"strings"
	"unicode"
	"unicode/utf8"

	"golang.org/x/website/internal/api"
	"golang.org/x/website/internal/texthtml"
	)

	var slashSlash = []byte("//")

	// Node formats the given AST node as HTML.
	// Identifiers in the rendered node
	// are turned into links to their documentation.
	func (p *Page) Node(node interface{}) template.HTML {
	var buf1 bytes.Buffer
	p.docs.writeNode(&buf1, p, p.fset, node)

	var buf2 bytes.Buffer
	n, _ := node.(ast.Node)
	buf2.Write(texthtml.Format(buf1.Bytes(), texthtml.Config{
	AST: n,
	GoComments: true,
	OldDocs: p.OldDocs,
	}))
	return template.HTML(buf2.String())
	}

	// NodeTOC formats the given AST node as HTML
	// for inclusion in the table of contents.
	func (p *Page) NodeTOC(node interface{}) template.HTML {
	var buf1 bytes.Buffer
	p.docs.writeNode(&buf1, p, p.fset, node)

	var buf2 bytes.Buffer
	buf2.Write(texthtml.Format(buf1.Bytes(), texthtml.Config{
	GoComments: true,
	OldDocs: p.OldDocs,
	}))

	return sanitize(template.HTML(buf2.String()))
	}

	const tabWidth = 4

	// writeNode writes the AST node x to w.
	//
	// The provided fset must be non-nil. The pageInfo is optional. If
	// present, the pageInfo is used to add comments to struct fields to
	// say which version of Go introduced them.
	func (d docs) writeNode(w io.Writer, pageInfo Page, fset *token.FileSet, x interface{}) {
	// convert trailing tabs into spaces using a tconv filter
	// to ensure a good outcome in most browsers (there may still
	// be tabs in comments and strings, but converting those into
	// the right number of spaces is much harder)
	//
	// TODO(gri) rethink printer flags - perhaps tconv can be eliminated
	// with an another printer mode (which is more efficiently
	// implemented in the printer than here with another layer)

	var pkgName, structName string
	var apiInfo api.PkgDB
	if gd, ok := x.(*ast.GenDecl); ok && pageInfo != nil && pageInfo.PDoc != nil &&
	gd.Tok == token.TYPE && len(gd.Specs) != 0 {
	pkgName = pageInfo.PDoc.ImportPath
	if ts, ok := gd.Specs[0].(*ast.TypeSpec); ok {
	if _, ok := ts.Type.(*ast.StructType); ok {
	structName = ts.Name.Name
	}
	}
	apiInfo = d.api[pkgName]
	}

	var out = w
	var buf bytes.Buffer
	if structName != "" {
	out = &buf
	}

	mode := printer.TabIndent \| printer.UseSpaces
	err := (&printer.Config{Mode: mode, Tabwidth: tabWidth}).Fprint(tabSpacer(out, tabWidth), fset, x)
	if err != nil {
	log.Print(err)
	}

	// Add comments to struct fields saying which Go version introduced them.
	if structName != "" {
	fieldSince := apiInfo.Field[structName]
	typeSince := apiInfo.Type[structName]
	// Add/rewrite comments on struct fields to note which Go version added them.
	var buf2 bytes.Buffer
	buf2.Grow(buf.Len() + len(" // Added in Go 1.n")*10)
	bs := bufio.NewScanner(&buf)
	for bs.Scan() {
	line := bs.Bytes()
	field := firstIdent(line)
	var since string
	if field != "" {
	since = fieldSince[field]
	if since != "" && since == typeSince {
	// Don't highlight field versions if they were the
	// same as the struct itself.
	since = ""
	}
	}
	if since == "" {
	buf2.Write(line)
	} else {
	if bytes.Contains(line, slashSlash) {
	line = bytes.TrimRight(line, " \t.")
	buf2.Write(line)
	buf2.WriteString("; added in Go ")
	} else {
	buf2.Write(line)
	buf2.WriteString(" // Go ")
	}
	buf2.WriteString(since)
	}
	buf2.WriteByte('\n')
	}
	w.Write(buf2.Bytes())
	}
	}

	// firstIdent returns the first identifier in x.
	// This actually parses "identifiers" that begin with numbers too, but we
	// never feed it such input, so it's fine.
	func firstIdent(x []byte) string {
	x = bytes.TrimSpace(x)
	i := bytes.IndexFunc(x, func(r rune) bool { return !unicode.IsLetter(r) && !unicode.IsNumber(r) })
	if i == -1 {
	return string(x)
	}
	return string(x[:i])
	}

	// Comment formats the given documentation comment as HTML.
	func (p *Page) Comment(comment string) template.HTML {
	// TODO: After Go 1.20 is out, this can be simplified to:
	//return template.HTML(p.PDoc.HTML(comment))
	// While deleting the go118.go and go119.go files.
	return template.HTML(docPackageHTML(p.PDoc, comment))
	}

	// sanitize sanitizes the argument src by replacing newlines with
	// blanks, removing extra blanks, and by removing trailing whitespace
	// and commas before closing parentheses.
	func sanitize(src template.HTML) template.HTML {
	buf := make([]byte, len(src))
	j := 0 // buf index
	comma := -1 // comma index if >= 0
	for i := 0; i < len(src); i++ {
	ch := src[i]
	switch ch {
	case '\t', '\n', ' ':
	// ignore whitespace at the beginning, after a blank, or after opening parentheses
	if j == 0 {
	continue
	}
	if p := buf[j-1]; p == ' ' \|\| p == '(' \|\| p == '{' \|\| p == '[' {
	continue
	}
	// replace all whitespace with blanks
	ch = ' '
	case ',':
	comma = j
	case ')', '}', ']':
	// remove any trailing comma
	if comma >= 0 {
	j = comma
	}
	// remove any trailing whitespace
	if j > 0 && buf[j-1] == ' ' {
	j--
	}
	default:
	comma = -1
	}
	buf[j] = ch
	j++
	}
	// remove trailing blank, if any
	if j > 0 && buf[j-1] == ' ' {
	j--
	}
	return template.HTML(buf[:j])
	}

	// Since reports the Go version that introduced the API feature
	// identified by kind, receiver, name.
	func (p *Page) Since(kind, receiver, name string) string {
	pkg := p.PDoc.ImportPath
	return p.docs.api.Func(pkg, kind, receiver, name)
	}

	type Example struct {
	Page *Page
	Name string
	Doc string
	Code template.HTML
	Play string
	Output string
	}

	// Example renders the examples for the given function name as HTML.
	func (p Page) FmtExamples(funcName string) []Example {
	var list []*Example
	for _, eg := range p.Examples {
	name := trimExampleSuffix(eg.Name)

	if name != funcName {
	continue
	}

	// print code
	cnode := &printer.CommentedNode{Node: eg.Code, Comments: eg.Comments}
	code := p.Node(cnode)
	out := eg.Output
	wholeFile := true

	// Additional formatting if this is a function body.
	if n := len(code); n >= 2 && code[0] == '{' && code[n-1] == '}' {
	wholeFile = false
	// remove surrounding braces
	code = code[1 : n-1]
	// unindent
	code = template.HTML(replaceLeadingIndentation(string(code), strings.Repeat(" ", tabWidth), ""))
	// remove output comment
	if loc := exampleOutputRx.FindStringIndex(string(code)); loc != nil {
	code = template.HTML(strings.TrimSpace(string(code)[:loc[0]]))
	}
	}

	// Write out the playground code in standard Go style
	// (use tabs, no comment highlight, etc).
	play := ""
	if eg.Play != nil {
	var buf bytes.Buffer
	eg.Play.Comments = filterOutBuildAnnotations(eg.Play.Comments)
	if err := format.Node(&buf, p.fset, eg.Play); err != nil {
	log.Print(err)
	} else {
	play = buf.String()
	}
	}

	// Drop output, as the output comment will appear in the code.
	if wholeFile && play == "" {
	out = ""
	}

	list = append(list, &Example{
	Page: p,
	Name: eg.Name,
	Doc: eg.Doc,
	Code: code,
	Play: play,
	Output: out,
	})
	}
	return list
	}

	// replaceLeadingIndentation replaces oldIndent at the beginning of each line
	// with newIndent. This is used for formatting examples. Raw strings that
	// span multiple lines are handled specially: oldIndent is not removed (since
	// go/printer will not add any indentation there), but newIndent is added
	// (since we may still want leading indentation).
	func replaceLeadingIndentation(body, oldIndent, newIndent string) string {
	// Handle indent at the beginning of the first line. After this, we handle
	// indentation only after a newline.
	var buf bytes.Buffer
	if strings.HasPrefix(body, oldIndent) {
	buf.WriteString(newIndent)
	body = body[len(oldIndent):]
	}

	// Use a state machine to keep track of whether we're in a string or
	// rune literal while we process the rest of the code.
	const (
	codeState = iota
	runeState
	interpretedStringState
	rawStringState
	)
	searchChars := []string{
	"'\"`\n", // codeState
	`\'`, // runeState
	`\"`, // interpretedStringState
	"`\n", // rawStringState
	// newlineState does not need to search
	}
	state := codeState
	for {
	i := strings.IndexAny(body, searchChars[state])
	if i < 0 {
	buf.WriteString(body)
	break
	}
	c := body[i]
	buf.WriteString(body[:i+1])
	body = body[i+1:]
	switch state {
	case codeState:
	switch c {
	case '\'':
	state = runeState
	case '"':
	state = interpretedStringState
	case '`':
	state = rawStringState
	case '\n':
	if strings.HasPrefix(body, oldIndent) {
	buf.WriteString(newIndent)
	body = body[len(oldIndent):]
	}
	}

	case runeState:
	switch c {
	case '\\':
	r, size := utf8.DecodeRuneInString(body)
	buf.WriteRune(r)
	body = body[size:]
	case '\'':
	state = codeState
	}

	case interpretedStringState:
	switch c {
	case '\\':
	r, size := utf8.DecodeRuneInString(body)
	buf.WriteRune(r)
	body = body[size:]
	case '"':
	state = codeState
	}

	case rawStringState:
	switch c {
	case '`':
	state = codeState
	case '\n':
	buf.WriteString(newIndent)
	}
	}
	}
	return buf.String()
	}

	var exampleOutputRx = regexp.MustCompile(`(?i)//[[:space:]]*(unordered )?output:`)

	func filterOutBuildAnnotations(cg []ast.CommentGroup) []ast.CommentGroup {
	if len(cg) == 0 {
	return cg
	}

	for i := range cg {
	if !strings.HasPrefix(cg[i].Text(), "+build ") {
	// Found the first non-build tag, return from here until the end
	// of the slice.
	return cg[i:]
	}
	}

	// There weren't any non-build tags, return an empty slice.
	return []*ast.CommentGroup{}
	}

	// ExampleName takes an example function name and returns its display
	// name. For example, "Foo_Bar_quux" becomes "Foo.Bar (Quux)".
	func (*Page) ExampleName(s string) string {
	name, suffix := splitExampleName(s)
	// replace _ with . for method names
	name = strings.Replace(name, "_", ".", 1)
	// use "Package" if no name provided
	if name == "" {
	name = "Package"
	}
	return name + suffix
	}

	// ExampleSuffix takes an example function name and returns its suffix in
	// parenthesized form. For example, "Foo_Bar_quux" becomes " (Quux)".
	func (*Page) ExampleSuffix(name string) string {
	_, suffix := splitExampleName(name)
	return suffix
	}

	// SrcPosLink returns a link to the specific source code position containing n,
	// which must be either an ast.Node or a *doc.Note.
	func (p *Page) SrcPosLink(n interface{}) template.HTML {
	// n must be an ast.Node or a *doc.Note
	var pos, end token.Pos

	switch n := n.(type) {
	case ast.Node:
	pos = n.Pos()
	end = n.End()
	case *doc.Note:
	pos = n.Pos
	end = n.End
	default:
	panic(fmt.Sprintf("wrong type for SrcPosLink template formatter: %T", n))
	}

	var relpath string
	var line int
	var low, high int // selection offset range

	if pos.IsValid() {
	xp := p.fset.Position(pos)
	relpath = xp.Filename
	line = xp.Line
	low = xp.Offset
	}
	if end.IsValid() {
	high = p.fset.Position(end).Offset
	}

	return srcPosLink(relpath, line, low, high)
	}

	func srcPosLink(s string, line, low, high int) template.HTML {
	s = path.Clean("/" + s)
	if !strings.HasPrefix(s, "/src/") {
	s = "/src" + s
	}
	var buf bytes.Buffer
	template.HTMLEscape(&buf, []byte(s))
	// selection ranges are of form "s=low:high"
	if low < high {
	fmt.Fprintf(&buf, "?s=%d:%d", low, high) // no need for URL escaping
	// if we have a selection, position the page
	// such that the selection is a bit below the top
	line -= 10
	if line < 1 {
	line = 1
	}
	}
	// line id's in html-printed source are of the
	// form "L%d" where %d stands for the line number
	if line > 0 {
	fmt.Fprintf(&buf, "#L%d", line) // no need for URL escaping
	}
	return template.HTML(buf.String())
	}