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Source file src/cmd/doc/main.go

Documentation: cmd/doc

  // Copyright 2015 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.
  // Doc (usually run as go doc) accepts zero, one or two arguments.
  // Zero arguments:
  //	go doc
  // Show the documentation for the package in the current directory.
  // One argument:
  //	go doc <pkg>
  //	go doc <sym>[.<methodOrField>]
  //	go doc [<pkg>.]<sym>[.<methodOrField>]
  //	go doc [<pkg>.][<sym>.]<methodOrField>
  // The first item in this list that succeeds is the one whose documentation
  // is printed. If there is a symbol but no package, the package in the current
  // directory is chosen. However, if the argument begins with a capital
  // letter it is always assumed to be a symbol in the current directory.
  // Two arguments:
  //	go doc <pkg> <sym>[.<methodOrField>]
  // Show the documentation for the package, symbol, and method or field. The
  // first argument must be a full package path. This is similar to the
  // command-line usage for the godoc command.
  // For commands, unless the -cmd flag is present "go doc command"
  // shows only the package-level docs for the package.
  // For complete documentation, run "go help doc".
  package main
  import (
  var (
  	unexported bool // -u flag
  	matchCase  bool // -c flag
  	showCmd    bool // -cmd flag
  // usage is a replacement usage function for the flags package.
  func usage() {
  	fmt.Fprintf(os.Stderr, "Usage of [go] doc:\n")
  	fmt.Fprintf(os.Stderr, "\tgo doc\n")
  	fmt.Fprintf(os.Stderr, "\tgo doc <pkg>\n")
  	fmt.Fprintf(os.Stderr, "\tgo doc <sym>[.<method>]\n")
  	fmt.Fprintf(os.Stderr, "\tgo doc [<pkg>].<sym>[.<method>]\n")
  	fmt.Fprintf(os.Stderr, "\tgo doc <pkg> <sym>[.<method>]\n")
  	fmt.Fprintf(os.Stderr, "For more information run\n")
  	fmt.Fprintf(os.Stderr, "\tgo help doc\n\n")
  	fmt.Fprintf(os.Stderr, "Flags:\n")
  func main() {
  	log.SetPrefix("doc: ")
  	err := do(os.Stdout, flag.CommandLine, os.Args[1:])
  	if err != nil {
  // do is the workhorse, broken out of main to make testing easier.
  func do(writer io.Writer, flagSet *flag.FlagSet, args []string) (err error) {
  	flagSet.Usage = usage
  	unexported = false
  	matchCase = false
  	flagSet.BoolVar(&unexported, "u", false, "show unexported symbols as well as exported")
  	flagSet.BoolVar(&matchCase, "c", false, "symbol matching honors case (paths not affected)")
  	flagSet.BoolVar(&showCmd, "cmd", false, "show symbols with package docs even if package is a command")
  	var paths []string
  	var symbol, method string
  	// Loop until something is printed.
  	for i := 0; ; i++ {
  		buildPackage, userPath, sym, more := parseArgs(flagSet.Args())
  		if i > 0 && !more { // Ignore the "more" bit on the first iteration.
  			return failMessage(paths, symbol, method)
  		if buildPackage == nil {
  			return fmt.Errorf("no such package: %s", userPath)
  		symbol, method = parseSymbol(sym)
  		pkg := parsePackage(writer, buildPackage, userPath)
  		paths = append(paths, pkg.prettyPath())
  		defer func() {
  			e := recover()
  			if e == nil {
  			pkgError, ok := e.(PackageError)
  			if ok {
  				err = pkgError
  		// The builtin package needs special treatment: its symbols are lower
  		// case but we want to see them, always.
  		if pkg.build.ImportPath == "builtin" {
  			unexported = true
  		switch {
  		case symbol == "":
  			pkg.packageDoc() // The package exists, so we got some output.
  		case method == "":
  			if pkg.symbolDoc(symbol) {
  			if pkg.methodDoc(symbol, method) {
  			if pkg.fieldDoc(symbol, method) {
  // failMessage creates a nicely formatted error message when there is no result to show.
  func failMessage(paths []string, symbol, method string) error {
  	var b bytes.Buffer
  	if len(paths) > 1 {
  	b.WriteString(" ")
  	for i, path := range paths {
  		if i > 0 {
  			b.WriteString(", ")
  	if method == "" {
  		return fmt.Errorf("no symbol %s in package%s", symbol, &b)
  	return fmt.Errorf("no method or field %s.%s in package%s", symbol, method, &b)
  // parseArgs analyzes the arguments (if any) and returns the package
  // it represents, the part of the argument the user used to identify
  // the path (or "" if it's the current package) and the symbol
  // (possibly with a .method) within that package.
  // parseSymbol is used to analyze the symbol itself.
  // The boolean final argument reports whether it is possible that
  // there may be more directories worth looking at. It will only
  // be true if the package path is a partial match for some directory
  // and there may be more matches. For example, if the argument
  // is rand.Float64, we must scan both crypto/rand and math/rand
  // to find the symbol, and the first call will return crypto/rand, true.
  func parseArgs(args []string) (pkg *build.Package, path, symbol string, more bool) {
  	switch len(args) {
  	case 0:
  		// Easy: current directory.
  		return importDir(pwd()), "", "", false
  	case 1:
  		// Done below.
  	case 2:
  		// Package must be findable and importable.
  		packagePath, ok := findPackage(args[0])
  		if !ok {
  			return nil, args[0], args[1], false
  		return importDir(packagePath), args[0], args[1], true
  	// Usual case: one argument.
  	arg := args[0]
  	// If it contains slashes, it begins with a package path.
  	// First, is it a complete package path as it is? If so, we are done.
  	// This avoids confusion over package paths that have other
  	// package paths as their prefix.
  	pkg, err := build.Import(arg, "", build.ImportComment)
  	if err == nil {
  		return pkg, arg, "", false
  	// Another disambiguator: If the symbol starts with an upper
  	// case letter, it can only be a symbol in the current directory.
  	// Kills the problem caused by case-insensitive file systems
  	// matching an upper case name as a package name.
  	if isUpper(arg) {
  		pkg, err := build.ImportDir(".", build.ImportComment)
  		if err == nil {
  			return pkg, "", arg, false
  	// If it has a slash, it must be a package path but there is a symbol.
  	// It's the last package path we care about.
  	slash := strings.LastIndex(arg, "/")
  	// There may be periods in the package path before or after the slash
  	// and between a symbol and method.
  	// Split the string at various periods to see what we find.
  	// In general there may be ambiguities but this should almost always
  	// work.
  	var period int
  	// slash+1: if there's no slash, the value is -1 and start is 0; otherwise
  	// start is the byte after the slash.
  	for start := slash + 1; start < len(arg); start = period + 1 {
  		period = strings.Index(arg[start:], ".")
  		symbol := ""
  		if period < 0 {
  			period = len(arg)
  		} else {
  			period += start
  			symbol = arg[period+1:]
  		// Have we identified a package already?
  		pkg, err := build.Import(arg[0:period], "", build.ImportComment)
  		if err == nil {
  			return pkg, arg[0:period], symbol, false
  		// See if we have the basename or tail of a package, as in json for encoding/json
  		// or ivy/value for robpike.io/ivy/value.
  		path, ok := findPackage(arg[0:period])
  		if ok {
  			return importDir(path), arg[0:period], symbol, true
  		dirs.Reset() // Next iteration of for loop must scan all the directories again.
  	// If it has a slash, we've failed.
  	if slash >= 0 {
  		log.Fatalf("no such package %s", arg[0:period])
  	// Guess it's a symbol in the current directory.
  	return importDir(pwd()), "", arg, false
  // importDir is just an error-catching wrapper for build.ImportDir.
  func importDir(dir string) *build.Package {
  	pkg, err := build.ImportDir(dir, build.ImportComment)
  	if err != nil {
  	return pkg
  // parseSymbol breaks str apart into a symbol and method.
  // Both may be missing or the method may be missing.
  // If present, each must be a valid Go identifier.
  func parseSymbol(str string) (symbol, method string) {
  	if str == "" {
  	elem := strings.Split(str, ".")
  	switch len(elem) {
  	case 1:
  	case 2:
  		method = elem[1]
  		log.Printf("too many periods in symbol specification")
  	symbol = elem[0]
  // isIdentifier checks that the name is valid Go identifier, and
  // logs and exits if it is not.
  func isIdentifier(name string) {
  	if len(name) == 0 {
  		log.Fatal("empty symbol")
  	for i, ch := range name {
  		if unicode.IsLetter(ch) || ch == '_' || i > 0 && unicode.IsDigit(ch) {
  		log.Fatalf("invalid identifier %q", name)
  // isExported reports whether the name is an exported identifier.
  // If the unexported flag (-u) is true, isExported returns true because
  // it means that we treat the name as if it is exported.
  func isExported(name string) bool {
  	return unexported || isUpper(name)
  // isUpper reports whether the name starts with an upper case letter.
  func isUpper(name string) bool {
  	ch, _ := utf8.DecodeRuneInString(name)
  	return unicode.IsUpper(ch)
  // findPackage returns the full file name path that first matches the
  // (perhaps partial) package path pkg. The boolean reports if any match was found.
  func findPackage(pkg string) (string, bool) {
  	if pkg == "" || isUpper(pkg) { // Upper case symbol cannot be a package name.
  		return "", false
  	pkgString := filepath.Clean(string(filepath.Separator) + pkg)
  	for {
  		path, ok := dirs.Next()
  		if !ok {
  			return "", false
  		if strings.HasSuffix(path, pkgString) {
  			return path, true
  // splitGopath splits $GOPATH into a list of roots.
  func splitGopath() []string {
  	return filepath.SplitList(build.Default.GOPATH)
  // pwd returns the current directory.
  func pwd() string {
  	wd, err := os.Getwd()
  	if err != nil {
  	return wd

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