src/cmd/doc/main.go - go - Git at Google

 // 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.
 //
 // The -src flag causes doc to print the full source code for the symbol, such
 // as the body of a struct, function or method.
 //
 // The -all flag causes doc to print all documentation for the package and
 // all its visible symbols. The argument must identify a package.
 //
 // For complete documentation, run "go help doc".
 package main

 import (
 	"bytes"
 	"flag"
 	"fmt"
 	"go/build"
 	"go/token"
 	"io"
 	"log"
 	"os"
 	"path"
 	"path/filepath"
 	"strings"
 )

 var (
 	unexported bool // -u flag
 	matchCase  bool // -c flag
 	showAll    bool // -all flag
 	showCmd    bool // -cmd flag
 	showSrc    bool // -src flag
 	short      bool // -short 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>[.<methodOrField>]\n")
 	fmt.Fprintf(os.Stderr, "\tgo doc [<pkg>.]<sym>[.<methodOrField>]\n")
 	fmt.Fprintf(os.Stderr, "\tgo doc [<pkg>.][<sym>.]<methodOrField>\n")
 	fmt.Fprintf(os.Stderr, "\tgo doc <pkg> <sym>[.<methodOrField>]\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")
 	flag.PrintDefaults()
 	os.Exit(2)
 }

 func main() {
 	log.SetFlags(0)
 	log.SetPrefix("doc: ")
 	dirsInit()
 	err := do(os.Stdout, flag.CommandLine, os.Args[1:])
 	if err != nil {
 		log.Fatal(err)
 	}
 }

 // 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(&showAll, "all", false, "show all documentation for package")
 	flagSet.BoolVar(&showCmd, "cmd", false, "show symbols with package docs even if package is a command")
 	flagSet.BoolVar(&showSrc, "src", false, "show source code for symbol")
 	flagSet.BoolVar(&short, "short", false, "one-line representation for each symbol")
 	flagSet.Parse(args)
 	var paths []string
 	var symbol, method string
 	// Loop until something is printed.
 	dirs.Reset()
 	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)
 		}

 		// The builtin package needs special treatment: its symbols are lower
 		// case but we want to see them, always.
 		if buildPackage.ImportPath == "builtin" {
 			unexported = true
 		}

 		symbol, method = parseSymbol(sym)
 		pkg := parsePackage(writer, buildPackage, userPath)
 		paths = append(paths, pkg.prettyPath())

 		defer func() {
 			pkg.flush()
 			e := recover()
 			if e == nil {
 				return
 			}
 			pkgError, ok := e.(PackageError)
 			if ok {
 				err = pkgError
 				return
 			}
 			panic(e)
 		}()

 		// We have a package.
 		if showAll && symbol == "" {
 			pkg.allDoc()
 			return
 		}

 		switch {
 		case symbol == "":
 			pkg.packageDoc() // The package exists, so we got some output.
 			return
 		case method == "":
 			if pkg.symbolDoc(symbol) {
 				return
 			}
 		default:
 			if pkg.methodDoc(symbol, method) {
 				return
 			}
 			if pkg.fieldDoc(symbol, method) {
 				return
 			}
 		}
 	}
 }

 // 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("s")
 	}
 	b.WriteString(" ")
 	for i, path := range paths {
 		if i > 0 {
 			b.WriteString(", ")
 		}
 		b.WriteString(path)
 	}
 	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) {
 	wd, err := os.Getwd()
 	if err != nil {
 		log.Fatal(err)
 	}
 	if len(args) == 0 {
 		// Easy: current directory.
 		return importDir(wd), "", "", false
 	}
 	arg := args[0]
 	// We have an argument. If it is a directory name beginning with . or ..,
 	// use the absolute path name. This discriminates "./errors" from "errors"
 	// if the current directory contains a non-standard errors package.
 	if isDotSlash(arg) {
 		arg = filepath.Join(wd, arg)
 	}
 	switch len(args) {
 	default:
 		usage()
 	case 1:
 		// Done below.
 	case 2:
 		// Package must be findable and importable.
 		pkg, err := build.Import(args[0], wd, build.ImportComment)
 		if err == nil {
 			return pkg, args[0], args[1], false
 		}
 		for {
 			packagePath, ok := findNextPackage(arg)
 			if !ok {
 				break
 			}
 			if pkg, err := build.ImportDir(packagePath, build.ImportComment); err == nil {
 				return pkg, arg, args[1], true
 			}
 		}
 		return nil, args[0], args[1], false
 	}
 	// Usual case: one argument.
 	// If it contains slashes, it begins with either a package path
 	// or an absolute directory.
 	// 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.
 	var importErr error
 	if filepath.IsAbs(arg) {
 		pkg, importErr = build.ImportDir(arg, build.ImportComment)
 		if importErr == nil {
 			return pkg, arg, "", false
 		}
 	} else {
 		pkg, importErr = build.Import(arg, wd, build.ImportComment)
 		if importErr == nil {
 			return pkg, arg, "", false
 		}
 	}
 	// Another disambiguator: If the argument 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 !strings.ContainsAny(arg, `/\`) && token.IsExported(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], wd, 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.
 		pkgName := arg[:period]
 		for {
 			path, ok := findNextPackage(pkgName)
 			if !ok {
 				break
 			}
 			if pkg, err = build.ImportDir(path, build.ImportComment); err == nil {
 				return pkg, 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 {
 		// build.Import should always include the path in its error message,
 		// and we should avoid repeating it. Unfortunately, build.Import doesn't
 		// return a structured error. That can't easily be fixed, since it
 		// invokes 'go list' and returns the error text from the loaded package.
 		// TODO(golang.org/issue/34750): load using golang.org/x/tools/go/packages
 		// instead of go/build.
 		importErrStr := importErr.Error()
 		if strings.Contains(importErrStr, arg[:period]) {
 			log.Fatal(importErrStr)
 		} else {
 			log.Fatalf("no such package %s: %s", arg[:period], importErrStr)
 		}
 	}
 	// Guess it's a symbol in the current directory.
 	return importDir(wd), "", arg, false
 }

 // dotPaths lists all the dotted paths legal on Unix-like and
 // Windows-like file systems. We check them all, as the chance
 // of error is minute and even on Windows people will use ./
 // sometimes.
 var dotPaths = []string{
 	`./`,
 	`../`,
 	`.\`,
 	`..\`,
 }

 // isDotSlash reports whether the path begins with a reference
 // to the local . or .. directory.
 func isDotSlash(arg string) bool {
 	if arg == "." || arg == ".." {
 		return true
 	}
 	for _, dotPath := range dotPaths {
 		if strings.HasPrefix(arg, dotPath) {
 			return true
 		}
 	}
 	return 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 {
 		log.Fatal(err)
 	}
 	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 == "" {
 		return
 	}
 	elem := strings.Split(str, ".")
 	switch len(elem) {
 	case 1:
 	case 2:
 		method = elem[1]
 	default:
 		log.Printf("too many periods in symbol specification")
 		usage()
 	}
 	symbol = elem[0]
 	return
 }

 // 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 || token.IsExported(name)
 }

 // findNextPackage returns the next full file name path that matches the
 // (perhaps partial) package path pkg. The boolean reports if any match was found.
 func findNextPackage(pkg string) (string, bool) {
 	if filepath.IsAbs(pkg) {
 		if dirs.offset == 0 {
 			dirs.offset = -1
 			return pkg, true
 		}
 		return "", false
 	}
 	if pkg == "" || token.IsExported(pkg) { // Upper case symbol cannot be a package name.
 		return "", false
 	}
 	pkg = path.Clean(pkg)
 	pkgSuffix := "/" + pkg
 	for {
 		d, ok := dirs.Next()
 		if !ok {
 			return "", false
 		}
 		if d.importPath == pkg || strings.HasSuffix(d.importPath, pkgSuffix) {
 			return d.dir, true
 		}
 	}
 }

 var buildCtx = build.Default

 // splitGopath splits $GOPATH into a list of roots.
 func splitGopath() []string {
 	return filepath.SplitList(buildCtx.GOPATH)
 }
	// 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.
	//
	// The -src flag causes doc to print the full source code for the symbol, such
	// as the body of a struct, function or method.
	//
	// The -all flag causes doc to print all documentation for the package and
	// all its visible symbols. The argument must identify a package.
	//
	// For complete documentation, run "go help doc".
	package main

	import (
	"bytes"
	"flag"
	"fmt"
	"go/build"
	"go/token"
	"io"
	"log"
	"os"
	"path"
	"path/filepath"
	"strings"
	)

	var (
	unexported bool // -u flag
	matchCase bool // -c flag
	showAll bool // -all flag
	showCmd bool // -cmd flag
	showSrc bool // -src flag
	short bool // -short 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>[.<methodOrField>]\n")
	fmt.Fprintf(os.Stderr, "\tgo doc [<pkg>.]<sym>[.<methodOrField>]\n")
	fmt.Fprintf(os.Stderr, "\tgo doc [<pkg>.][<sym>.]<methodOrField>\n")
	fmt.Fprintf(os.Stderr, "\tgo doc <pkg> <sym>[.<methodOrField>]\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")
	flag.PrintDefaults()
	os.Exit(2)
	}

	func main() {
	log.SetFlags(0)
	log.SetPrefix("doc: ")
	dirsInit()
	err := do(os.Stdout, flag.CommandLine, os.Args[1:])
	if err != nil {
	log.Fatal(err)
	}
	}

	// 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(&showAll, "all", false, "show all documentation for package")
	flagSet.BoolVar(&showCmd, "cmd", false, "show symbols with package docs even if package is a command")
	flagSet.BoolVar(&showSrc, "src", false, "show source code for symbol")
	flagSet.BoolVar(&short, "short", false, "one-line representation for each symbol")
	flagSet.Parse(args)
	var paths []string
	var symbol, method string
	// Loop until something is printed.
	dirs.Reset()
	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)
	}

	// The builtin package needs special treatment: its symbols are lower
	// case but we want to see them, always.
	if buildPackage.ImportPath == "builtin" {
	unexported = true
	}

	symbol, method = parseSymbol(sym)
	pkg := parsePackage(writer, buildPackage, userPath)
	paths = append(paths, pkg.prettyPath())

	defer func() {
	pkg.flush()
	e := recover()
	if e == nil {
	return
	}
	pkgError, ok := e.(PackageError)
	if ok {
	err = pkgError
	return
	}
	panic(e)
	}()

	// We have a package.
	if showAll && symbol == "" {
	pkg.allDoc()
	return
	}

	switch {
	case symbol == "":
	pkg.packageDoc() // The package exists, so we got some output.
	return
	case method == "":
	if pkg.symbolDoc(symbol) {
	return
	}
	default:
	if pkg.methodDoc(symbol, method) {
	return
	}
	if pkg.fieldDoc(symbol, method) {
	return
	}
	}
	}
	}

	// 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("s")
	}
	b.WriteString(" ")
	for i, path := range paths {
	if i > 0 {
	b.WriteString(", ")
	}
	b.WriteString(path)
	}
	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) {
	wd, err := os.Getwd()
	if err != nil {
	log.Fatal(err)
	}
	if len(args) == 0 {
	// Easy: current directory.
	return importDir(wd), "", "", false
	}
	arg := args[0]
	// We have an argument. If it is a directory name beginning with . or ..,
	// use the absolute path name. This discriminates "./errors" from "errors"
	// if the current directory contains a non-standard errors package.
	if isDotSlash(arg) {
	arg = filepath.Join(wd, arg)
	}
	switch len(args) {
	default:
	usage()
	case 1:
	// Done below.
	case 2:
	// Package must be findable and importable.
	pkg, err := build.Import(args[0], wd, build.ImportComment)
	if err == nil {
	return pkg, args[0], args[1], false
	}
	for {
	packagePath, ok := findNextPackage(arg)
	if !ok {
	break
	}
	if pkg, err := build.ImportDir(packagePath, build.ImportComment); err == nil {
	return pkg, arg, args[1], true
	}
	}
	return nil, args[0], args[1], false
	}
	// Usual case: one argument.
	// If it contains slashes, it begins with either a package path
	// or an absolute directory.
	// 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.
	var importErr error
	if filepath.IsAbs(arg) {
	pkg, importErr = build.ImportDir(arg, build.ImportComment)
	if importErr == nil {
	return pkg, arg, "", false
	}
	} else {
	pkg, importErr = build.Import(arg, wd, build.ImportComment)
	if importErr == nil {
	return pkg, arg, "", false
	}
	}
	// Another disambiguator: If the argument 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 !strings.ContainsAny(arg, `/\`) && token.IsExported(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], wd, 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.
	pkgName := arg[:period]
	for {
	path, ok := findNextPackage(pkgName)
	if !ok {
	break
	}
	if pkg, err = build.ImportDir(path, build.ImportComment); err == nil {
	return pkg, 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 {
	// build.Import should always include the path in its error message,
	// and we should avoid repeating it. Unfortunately, build.Import doesn't
	// return a structured error. That can't easily be fixed, since it
	// invokes 'go list' and returns the error text from the loaded package.
	// TODO(golang.org/issue/34750): load using golang.org/x/tools/go/packages
	// instead of go/build.
	importErrStr := importErr.Error()
	if strings.Contains(importErrStr, arg[:period]) {
	log.Fatal(importErrStr)
	} else {
	log.Fatalf("no such package %s: %s", arg[:period], importErrStr)
	}
	}
	// Guess it's a symbol in the current directory.
	return importDir(wd), "", arg, false
	}

	// dotPaths lists all the dotted paths legal on Unix-like and
	// Windows-like file systems. We check them all, as the chance
	// of error is minute and even on Windows people will use ./
	// sometimes.
	var dotPaths = []string{
	`./`,
	`../`,
	`.\`,
	`..\`,
	}

	// isDotSlash reports whether the path begins with a reference
	// to the local . or .. directory.
	func isDotSlash(arg string) bool {
	if arg == "." \|\| arg == ".." {
	return true
	}
	for _, dotPath := range dotPaths {
	if strings.HasPrefix(arg, dotPath) {
	return true
	}
	}
	return 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 {
	log.Fatal(err)
	}
	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 == "" {
	return
	}
	elem := strings.Split(str, ".")
	switch len(elem) {
	case 1:
	case 2:
	method = elem[1]
	default:
	log.Printf("too many periods in symbol specification")
	usage()
	}
	symbol = elem[0]
	return
	}

	// 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 \|\| token.IsExported(name)
	}

	// findNextPackage returns the next full file name path that matches the
	// (perhaps partial) package path pkg. The boolean reports if any match was found.
	func findNextPackage(pkg string) (string, bool) {
	if filepath.IsAbs(pkg) {
	if dirs.offset == 0 {
	dirs.offset = -1
	return pkg, true
	}
	return "", false
	}
	if pkg == "" \|\| token.IsExported(pkg) { // Upper case symbol cannot be a package name.
	return "", false
	}
	pkg = path.Clean(pkg)
	pkgSuffix := "/" + pkg
	for {
	d, ok := dirs.Next()
	if !ok {
	return "", false
	}
	if d.importPath == pkg \|\| strings.HasSuffix(d.importPath, pkgSuffix) {
	return d.dir, true
	}
	}
	}

	var buildCtx = build.Default

	// splitGopath splits $GOPATH into a list of roots.
	func splitGopath() []string {
	return filepath.SplitList(buildCtx.GOPATH)
	}