godoc/vfs/namespace.go - tools - Git at Google

 // 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.

 package vfs

 import (
 	"fmt"
 	"io"
 	"os"
 	pathpkg "path"
 	"sort"
 	"strings"
 	"time"
 )

 // Setting debugNS = true will enable debugging prints about
 // name space translations.
 const debugNS = false

 // A NameSpace is a file system made up of other file systems
 // mounted at specific locations in the name space.
 //
 // The representation is a map from mount point locations
 // to the list of file systems mounted at that location.  A traditional
 // Unix mount table would use a single file system per mount point,
 // but we want to be able to mount multiple file systems on a single
 // mount point and have the system behave as if the union of those
 // file systems were present at the mount point.
 // For example, if the OS file system has a Go installation in
 // c:\Go and additional Go path trees in  d:\Work1 and d:\Work2, then
 // this name space creates the view we want for the godoc server:
 //
 //	NameSpace{
 //		"/": {
 //			{old: "/", fs: OS(`c:\Go`), new: "/"},
 //		},
 //		"/src/pkg": {
 //			{old: "/src/pkg", fs: OS(`c:\Go`), new: "/src/pkg"},
 //			{old: "/src/pkg", fs: OS(`d:\Work1`), new: "/src"},
 //			{old: "/src/pkg", fs: OS(`d:\Work2`), new: "/src"},
 //		},
 //	}
 //
 // This is created by executing:
 //
 //	ns := NameSpace{}
 //	ns.Bind("/", OS(`c:\Go`), "/", BindReplace)
 //	ns.Bind("/src/pkg", OS(`d:\Work1`), "/src", BindAfter)
 //	ns.Bind("/src/pkg", OS(`d:\Work2`), "/src", BindAfter)
 //
 // A particular mount point entry is a triple (old, fs, new), meaning that to
 // operate on a path beginning with old, replace that prefix (old) with new
 // and then pass that path to the FileSystem implementation fs.
 //
 // If you do not explicitly mount a FileSystem at the root mountpoint "/" of the
 // NameSpace like above, Stat("/") will return a "not found" error which could
 // break typical directory traversal routines. In such cases, use NewNameSpace()
 // to get a NameSpace pre-initialized with an emulated empty directory at root.
 //
 // Given this name space, a ReadDir of /src/pkg/code will check each prefix
 // of the path for a mount point (first /src/pkg/code, then /src/pkg, then /src,
 // then /), stopping when it finds one.  For the above example, /src/pkg/code
 // will find the mount point at /src/pkg:
 //
 //	{old: "/src/pkg", fs: OS(`c:\Go`), new: "/src/pkg"},
 //	{old: "/src/pkg", fs: OS(`d:\Work1`), new: "/src"},
 //	{old: "/src/pkg", fs: OS(`d:\Work2`), new: "/src"},
 //
 // ReadDir will when execute these three calls and merge the results:
 //
 //	OS(`c:\Go`).ReadDir("/src/pkg/code")
 //	OS(`d:\Work1').ReadDir("/src/code")
 //	OS(`d:\Work2').ReadDir("/src/code")
 //
 // Note that the "/src/pkg" in "/src/pkg/code" has been replaced by
 // just "/src" in the final two calls.
 //
 // OS is itself an implementation of a file system: it implements
 // OS(`c:\Go`).ReadDir("/src/pkg/code") as ioutil.ReadDir(`c:\Go\src\pkg\code`).
 //
 // Because the new path is evaluated by fs (here OS(root)), another way
 // to read the mount table is to mentally combine fs+new, so that this table:
 //
 //	{old: "/src/pkg", fs: OS(`c:\Go`), new: "/src/pkg"},
 //	{old: "/src/pkg", fs: OS(`d:\Work1`), new: "/src"},
 //	{old: "/src/pkg", fs: OS(`d:\Work2`), new: "/src"},
 //
 // reads as:
 //
 //	"/src/pkg" -> c:\Go\src\pkg
 //	"/src/pkg" -> d:\Work1\src
 //	"/src/pkg" -> d:\Work2\src
 //
 // An invariant (a redundancy) of the name space representation is that
 // ns[mtpt][i].old is always equal to mtpt (in the example, ns["/src/pkg"]'s
 // mount table entries always have old == "/src/pkg").  The 'old' field is
 // useful to callers, because they receive just a []mountedFS and not any
 // other indication of which mount point was found.
 //
 type NameSpace map[string][]mountedFS

 // A mountedFS handles requests for path by replacing
 // a prefix 'old' with 'new' and then calling the fs methods.
 type mountedFS struct {
 	old string
 	fs  FileSystem
 	new string
 }

 // hasPathPrefix reports whether x == y or x == y + "/" + more.
 func hasPathPrefix(x, y string) bool {
 	return x == y || strings.HasPrefix(x, y) && (strings.HasSuffix(y, "/") || strings.HasPrefix(x[len(y):], "/"))
 }

 // translate translates path for use in m, replacing old with new.
 //
 // mountedFS{"/src/pkg", fs, "/src"}.translate("/src/pkg/code") == "/src/code".
 func (m mountedFS) translate(path string) string {
 	path = pathpkg.Clean("/" + path)
 	if !hasPathPrefix(path, m.old) {
 		panic("translate " + path + " but old=" + m.old)
 	}
 	return pathpkg.Join(m.new, path[len(m.old):])
 }

 func (NameSpace) String() string {
 	return "ns"
 }

 // Fprint writes a text representation of the name space to w.
 func (ns NameSpace) Fprint(w io.Writer) {
 	fmt.Fprint(w, "name space {\n")
 	var all []string
 	for mtpt := range ns {
 		all = append(all, mtpt)
 	}
 	sort.Strings(all)
 	for _, mtpt := range all {
 		fmt.Fprintf(w, "\t%s:\n", mtpt)
 		for _, m := range ns[mtpt] {
 			fmt.Fprintf(w, "\t\t%s %s\n", m.fs, m.new)
 		}
 	}
 	fmt.Fprint(w, "}\n")
 }

 // clean returns a cleaned, rooted path for evaluation.
 // It canonicalizes the path so that we can use string operations
 // to analyze it.
 func (NameSpace) clean(path string) string {
 	return pathpkg.Clean("/" + path)
 }

 type BindMode int

 const (
 	BindReplace BindMode = iota
 	BindBefore
 	BindAfter
 )

 // Bind causes references to old to redirect to the path new in newfs.
 // If mode is BindReplace, old redirections are discarded.
 // If mode is BindBefore, this redirection takes priority over existing ones,
 // but earlier ones are still consulted for paths that do not exist in newfs.
 // If mode is BindAfter, this redirection happens only after existing ones
 // have been tried and failed.
 func (ns NameSpace) Bind(old string, newfs FileSystem, new string, mode BindMode) {
 	old = ns.clean(old)
 	new = ns.clean(new)
 	m := mountedFS{old, newfs, new}
 	var mtpt []mountedFS
 	switch mode {
 	case BindReplace:
 		mtpt = append(mtpt, m)
 	case BindAfter:
 		mtpt = append(mtpt, ns.resolve(old)...)
 		mtpt = append(mtpt, m)
 	case BindBefore:
 		mtpt = append(mtpt, m)
 		mtpt = append(mtpt, ns.resolve(old)...)
 	}

 	// Extend m.old, m.new in inherited mount point entries.
 	for i := range mtpt {
 		m := &mtpt[i]
 		if m.old != old {
 			if !hasPathPrefix(old, m.old) {
 				// This should not happen.  If it does, panic so
 				// that we can see the call trace that led to it.
 				panic(fmt.Sprintf("invalid Bind: old=%q m={%q, %s, %q}", old, m.old, m.fs.String(), m.new))
 			}
 			suffix := old[len(m.old):]
 			m.old = pathpkg.Join(m.old, suffix)
 			m.new = pathpkg.Join(m.new, suffix)
 		}
 	}

 	ns[old] = mtpt
 }

 // resolve resolves a path to the list of mountedFS to use for path.
 func (ns NameSpace) resolve(path string) []mountedFS {
 	path = ns.clean(path)
 	for {
 		if m := ns[path]; m != nil {
 			if debugNS {
 				fmt.Printf("resolve %s: %v\n", path, m)
 			}
 			return m
 		}
 		if path == "/" {
 			break
 		}
 		path = pathpkg.Dir(path)
 	}
 	return nil
 }

 // Open implements the FileSystem Open method.
 func (ns NameSpace) Open(path string) (ReadSeekCloser, error) {
 	var err error
 	for _, m := range ns.resolve(path) {
 		if debugNS {
 			fmt.Printf("tx %s: %v\n", path, m.translate(path))
 		}
 		tp := m.translate(path)
 		r, err1 := m.fs.Open(tp)
 		if err1 == nil {
 			return r, nil
 		}
 		// IsNotExist errors in overlay FSes can mask real errors in
 		// the underlying FS, so ignore them if there is another error.
 		if err == nil || os.IsNotExist(err) {
 			err = err1
 		}
 	}
 	if err == nil {
 		err = &os.PathError{Op: "open", Path: path, Err: os.ErrNotExist}
 	}
 	return nil, err
 }

 // stat implements the FileSystem Stat and Lstat methods.
 func (ns NameSpace) stat(path string, f func(FileSystem, string) (os.FileInfo, error)) (os.FileInfo, error) {
 	var err error
 	for _, m := range ns.resolve(path) {
 		fi, err1 := f(m.fs, m.translate(path))
 		if err1 == nil {
 			return fi, nil
 		}
 		if err == nil {
 			err = err1
 		}
 	}
 	if err == nil {
 		err = &os.PathError{Op: "stat", Path: path, Err: os.ErrNotExist}
 	}
 	return nil, err
 }

 func (ns NameSpace) Stat(path string) (os.FileInfo, error) {
 	return ns.stat(path, FileSystem.Stat)
 }

 func (ns NameSpace) Lstat(path string) (os.FileInfo, error) {
 	return ns.stat(path, FileSystem.Lstat)
 }

 // dirInfo is a trivial implementation of os.FileInfo for a directory.
 type dirInfo string

 func (d dirInfo) Name() string       { return string(d) }
 func (d dirInfo) Size() int64        { return 0 }
 func (d dirInfo) Mode() os.FileMode  { return os.ModeDir | 0555 }
 func (d dirInfo) ModTime() time.Time { return startTime }
 func (d dirInfo) IsDir() bool        { return true }
 func (d dirInfo) Sys() interface{}   { return nil }

 var startTime = time.Now()

 // ReadDir implements the FileSystem ReadDir method.  It's where most of the magic is.
 // (The rest is in resolve.)
 //
 // Logically, ReadDir must return the union of all the directories that are named
 // by path.  In order to avoid misinterpreting Go packages, of all the directories
 // that contain Go source code, we only include the files from the first,
 // but we include subdirectories from all.
 //
 // ReadDir must also return directory entries needed to reach mount points.
 // If the name space looks like the example in the type NameSpace comment,
 // but c:\Go does not have a src/pkg subdirectory, we still want to be able
 // to find that subdirectory, because we've mounted d:\Work1 and d:\Work2
 // there.  So if we don't see "src" in the directory listing for c:\Go, we add an
 // entry for it before returning.
 //
 func (ns NameSpace) ReadDir(path string) ([]os.FileInfo, error) {
 	path = ns.clean(path)

 	// List matching directories and determine whether any of them contain
 	// Go files.
 	var (
 		dirs       [][]os.FileInfo
 		goDirIndex = -1
 		readDirErr error
 	)

 	for _, m := range ns.resolve(path) {
 		dir, err := m.fs.ReadDir(m.translate(path))
 		if err != nil {
 			if readDirErr == nil {
 				readDirErr = err
 			}
 			continue
 		}

 		dirs = append(dirs, dir)

 		if goDirIndex < 0 {
 			for _, f := range dir {
 				if !f.IsDir() && strings.HasSuffix(f.Name(), ".go") {
 					goDirIndex = len(dirs) - 1
 					break
 				}
 			}
 		}
 	}

 	// Build a list of files and subdirectories. If a directory contains Go files,
 	// only include files from that directory. Otherwise, include files from
 	// all directories. Include subdirectories from all directories regardless
 	// of whether Go files are present.
 	haveName := make(map[string]bool)
 	var all []os.FileInfo
 	for i, dir := range dirs {
 		for _, f := range dir {
 			name := f.Name()
 			if !haveName[name] && (f.IsDir() || goDirIndex < 0 || goDirIndex == i) {
 				all = append(all, f)
 				haveName[name] = true
 			}
 		}
 	}

 	// Add any missing directories needed to reach mount points.
 	for old := range ns {
 		if hasPathPrefix(old, path) && old != path {
 			// Find next element after path in old.
 			elem := old[len(path):]
 			elem = strings.TrimPrefix(elem, "/")
 			if i := strings.Index(elem, "/"); i >= 0 {
 				elem = elem[:i]
 			}
 			if !haveName[elem] {
 				haveName[elem] = true
 				all = append(all, dirInfo(elem))
 			}
 		}
 	}

 	if len(all) == 0 {
 		return nil, readDirErr
 	}

 	sort.Sort(byName(all))
 	return all, nil
 }

 // RootType returns the RootType for the given path in the namespace.
 func (ns NameSpace) RootType(path string) RootType {
 	// We resolve the given path to a list of mountedFS and then return
 	// the root type for the filesystem which contains the path.
 	for _, m := range ns.resolve(path) {
 		_, err := m.fs.ReadDir(m.translate(path))
 		// Found a match, return the filesystem's root type
 		if err == nil {
 			return m.fs.RootType(path)
 		}
 	}
 	return ""
 }

 // byName implements sort.Interface.
 type byName []os.FileInfo

 func (f byName) Len() int           { return len(f) }
 func (f byName) Less(i, j int) bool { return f[i].Name() < f[j].Name() }
 func (f byName) Swap(i, j int)      { f[i], f[j] = f[j], f[i] }
	// 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.

	package vfs

	import (
	"fmt"
	"io"
	"os"
	pathpkg "path"
	"sort"
	"strings"
	"time"
	)

	// Setting debugNS = true will enable debugging prints about
	// name space translations.
	const debugNS = false

	// A NameSpace is a file system made up of other file systems
	// mounted at specific locations in the name space.
	//
	// The representation is a map from mount point locations
	// to the list of file systems mounted at that location. A traditional
	// Unix mount table would use a single file system per mount point,
	// but we want to be able to mount multiple file systems on a single
	// mount point and have the system behave as if the union of those
	// file systems were present at the mount point.
	// For example, if the OS file system has a Go installation in
	// c:\Go and additional Go path trees in d:\Work1 and d:\Work2, then
	// this name space creates the view we want for the godoc server:
	//
	// NameSpace{
	// "/": {
	// {old: "/", fs: OS(`c:\Go`), new: "/"},
	// },
	// "/src/pkg": {
	// {old: "/src/pkg", fs: OS(`c:\Go`), new: "/src/pkg"},
	// {old: "/src/pkg", fs: OS(`d:\Work1`), new: "/src"},
	// {old: "/src/pkg", fs: OS(`d:\Work2`), new: "/src"},
	// },
	// }
	//
	// This is created by executing:
	//
	// ns := NameSpace{}
	// ns.Bind("/", OS(`c:\Go`), "/", BindReplace)
	// ns.Bind("/src/pkg", OS(`d:\Work1`), "/src", BindAfter)
	// ns.Bind("/src/pkg", OS(`d:\Work2`), "/src", BindAfter)
	//
	// A particular mount point entry is a triple (old, fs, new), meaning that to
	// operate on a path beginning with old, replace that prefix (old) with new
	// and then pass that path to the FileSystem implementation fs.
	//
	// If you do not explicitly mount a FileSystem at the root mountpoint "/" of the
	// NameSpace like above, Stat("/") will return a "not found" error which could
	// break typical directory traversal routines. In such cases, use NewNameSpace()
	// to get a NameSpace pre-initialized with an emulated empty directory at root.
	//
	// Given this name space, a ReadDir of /src/pkg/code will check each prefix
	// of the path for a mount point (first /src/pkg/code, then /src/pkg, then /src,
	// then /), stopping when it finds one. For the above example, /src/pkg/code
	// will find the mount point at /src/pkg:
	//
	// {old: "/src/pkg", fs: OS(`c:\Go`), new: "/src/pkg"},
	// {old: "/src/pkg", fs: OS(`d:\Work1`), new: "/src"},
	// {old: "/src/pkg", fs: OS(`d:\Work2`), new: "/src"},
	//
	// ReadDir will when execute these three calls and merge the results:
	//
	// OS(`c:\Go`).ReadDir("/src/pkg/code")
	// OS(`d:\Work1').ReadDir("/src/code")
	// OS(`d:\Work2').ReadDir("/src/code")
	//
	// Note that the "/src/pkg" in "/src/pkg/code" has been replaced by
	// just "/src" in the final two calls.
	//
	// OS is itself an implementation of a file system: it implements
	// OS(`c:\Go`).ReadDir("/src/pkg/code") as ioutil.ReadDir(`c:\Go\src\pkg\code`).
	//
	// Because the new path is evaluated by fs (here OS(root)), another way
	// to read the mount table is to mentally combine fs+new, so that this table:
	//
	// {old: "/src/pkg", fs: OS(`c:\Go`), new: "/src/pkg"},
	// {old: "/src/pkg", fs: OS(`d:\Work1`), new: "/src"},
	// {old: "/src/pkg", fs: OS(`d:\Work2`), new: "/src"},
	//
	// reads as:
	//
	// "/src/pkg" -> c:\Go\src\pkg
	// "/src/pkg" -> d:\Work1\src
	// "/src/pkg" -> d:\Work2\src
	//
	// An invariant (a redundancy) of the name space representation is that
	// ns[mtpt][i].old is always equal to mtpt (in the example, ns["/src/pkg"]'s
	// mount table entries always have old == "/src/pkg"). The 'old' field is
	// useful to callers, because they receive just a []mountedFS and not any
	// other indication of which mount point was found.
	//
	type NameSpace map[string][]mountedFS

	// A mountedFS handles requests for path by replacing
	// a prefix 'old' with 'new' and then calling the fs methods.
	type mountedFS struct {
	old string
	fs FileSystem
	new string
	}

	// hasPathPrefix reports whether x == y or x == y + "/" + more.
	func hasPathPrefix(x, y string) bool {
	return x == y \|\| strings.HasPrefix(x, y) && (strings.HasSuffix(y, "/") \|\| strings.HasPrefix(x[len(y):], "/"))
	}

	// translate translates path for use in m, replacing old with new.
	//
	// mountedFS{"/src/pkg", fs, "/src"}.translate("/src/pkg/code") == "/src/code".
	func (m mountedFS) translate(path string) string {
	path = pathpkg.Clean("/" + path)
	if !hasPathPrefix(path, m.old) {
	panic("translate " + path + " but old=" + m.old)
	}
	return pathpkg.Join(m.new, path[len(m.old):])
	}

	func (NameSpace) String() string {
	return "ns"
	}

	// Fprint writes a text representation of the name space to w.
	func (ns NameSpace) Fprint(w io.Writer) {
	fmt.Fprint(w, "name space {\n")
	var all []string
	for mtpt := range ns {
	all = append(all, mtpt)
	}
	sort.Strings(all)
	for _, mtpt := range all {
	fmt.Fprintf(w, "\t%s:\n", mtpt)
	for _, m := range ns[mtpt] {
	fmt.Fprintf(w, "\t\t%s %s\n", m.fs, m.new)
	}
	}
	fmt.Fprint(w, "}\n")
	}

	// clean returns a cleaned, rooted path for evaluation.
	// It canonicalizes the path so that we can use string operations
	// to analyze it.
	func (NameSpace) clean(path string) string {
	return pathpkg.Clean("/" + path)
	}

	type BindMode int

	const (
	BindReplace BindMode = iota
	BindBefore
	BindAfter
	)

	// Bind causes references to old to redirect to the path new in newfs.
	// If mode is BindReplace, old redirections are discarded.
	// If mode is BindBefore, this redirection takes priority over existing ones,
	// but earlier ones are still consulted for paths that do not exist in newfs.
	// If mode is BindAfter, this redirection happens only after existing ones
	// have been tried and failed.
	func (ns NameSpace) Bind(old string, newfs FileSystem, new string, mode BindMode) {
	old = ns.clean(old)
	new = ns.clean(new)
	m := mountedFS{old, newfs, new}
	var mtpt []mountedFS
	switch mode {
	case BindReplace:
	mtpt = append(mtpt, m)
	case BindAfter:
	mtpt = append(mtpt, ns.resolve(old)...)
	mtpt = append(mtpt, m)
	case BindBefore:
	mtpt = append(mtpt, m)
	mtpt = append(mtpt, ns.resolve(old)...)
	}

	// Extend m.old, m.new in inherited mount point entries.
	for i := range mtpt {
	m := &mtpt[i]
	if m.old != old {
	if !hasPathPrefix(old, m.old) {
	// This should not happen. If it does, panic so
	// that we can see the call trace that led to it.
	panic(fmt.Sprintf("invalid Bind: old=%q m={%q, %s, %q}", old, m.old, m.fs.String(), m.new))
	}
	suffix := old[len(m.old):]
	m.old = pathpkg.Join(m.old, suffix)
	m.new = pathpkg.Join(m.new, suffix)
	}
	}

	ns[old] = mtpt
	}

	// resolve resolves a path to the list of mountedFS to use for path.
	func (ns NameSpace) resolve(path string) []mountedFS {
	path = ns.clean(path)
	for {
	if m := ns[path]; m != nil {
	if debugNS {
	fmt.Printf("resolve %s: %v\n", path, m)
	}
	return m
	}
	if path == "/" {
	break
	}
	path = pathpkg.Dir(path)
	}
	return nil
	}

	// Open implements the FileSystem Open method.
	func (ns NameSpace) Open(path string) (ReadSeekCloser, error) {
	var err error
	for _, m := range ns.resolve(path) {
	if debugNS {
	fmt.Printf("tx %s: %v\n", path, m.translate(path))
	}
	tp := m.translate(path)
	r, err1 := m.fs.Open(tp)
	if err1 == nil {
	return r, nil
	}
	// IsNotExist errors in overlay FSes can mask real errors in
	// the underlying FS, so ignore them if there is another error.
	if err == nil \|\| os.IsNotExist(err) {
	err = err1
	}
	}
	if err == nil {
	err = &os.PathError{Op: "open", Path: path, Err: os.ErrNotExist}
	}
	return nil, err
	}

	// stat implements the FileSystem Stat and Lstat methods.
	func (ns NameSpace) stat(path string, f func(FileSystem, string) (os.FileInfo, error)) (os.FileInfo, error) {
	var err error
	for _, m := range ns.resolve(path) {
	fi, err1 := f(m.fs, m.translate(path))
	if err1 == nil {
	return fi, nil
	}
	if err == nil {
	err = err1
	}
	}
	if err == nil {
	err = &os.PathError{Op: "stat", Path: path, Err: os.ErrNotExist}
	}
	return nil, err
	}

	func (ns NameSpace) Stat(path string) (os.FileInfo, error) {
	return ns.stat(path, FileSystem.Stat)
	}

	func (ns NameSpace) Lstat(path string) (os.FileInfo, error) {
	return ns.stat(path, FileSystem.Lstat)
	}

	// dirInfo is a trivial implementation of os.FileInfo for a directory.
	type dirInfo string

	func (d dirInfo) Name() string { return string(d) }
	func (d dirInfo) Size() int64 { return 0 }
	func (d dirInfo) Mode() os.FileMode { return os.ModeDir \| 0555 }
	func (d dirInfo) ModTime() time.Time { return startTime }
	func (d dirInfo) IsDir() bool { return true }
	func (d dirInfo) Sys() interface{} { return nil }

	var startTime = time.Now()

	// ReadDir implements the FileSystem ReadDir method. It's where most of the magic is.
	// (The rest is in resolve.)
	//
	// Logically, ReadDir must return the union of all the directories that are named
	// by path. In order to avoid misinterpreting Go packages, of all the directories
	// that contain Go source code, we only include the files from the first,
	// but we include subdirectories from all.
	//
	// ReadDir must also return directory entries needed to reach mount points.
	// If the name space looks like the example in the type NameSpace comment,
	// but c:\Go does not have a src/pkg subdirectory, we still want to be able
	// to find that subdirectory, because we've mounted d:\Work1 and d:\Work2
	// there. So if we don't see "src" in the directory listing for c:\Go, we add an
	// entry for it before returning.
	//
	func (ns NameSpace) ReadDir(path string) ([]os.FileInfo, error) {
	path = ns.clean(path)

	// List matching directories and determine whether any of them contain
	// Go files.
	var (
	dirs [][]os.FileInfo
	goDirIndex = -1
	readDirErr error
	)

	for _, m := range ns.resolve(path) {
	dir, err := m.fs.ReadDir(m.translate(path))
	if err != nil {
	if readDirErr == nil {
	readDirErr = err
	}
	continue
	}

	dirs = append(dirs, dir)

	if goDirIndex < 0 {
	for _, f := range dir {
	if !f.IsDir() && strings.HasSuffix(f.Name(), ".go") {
	goDirIndex = len(dirs) - 1
	break
	}
	}
	}
	}

	// Build a list of files and subdirectories. If a directory contains Go files,
	// only include files from that directory. Otherwise, include files from
	// all directories. Include subdirectories from all directories regardless
	// of whether Go files are present.
	haveName := make(map[string]bool)
	var all []os.FileInfo
	for i, dir := range dirs {
	for _, f := range dir {
	name := f.Name()
	if !haveName[name] && (f.IsDir() \|\| goDirIndex < 0 \|\| goDirIndex == i) {
	all = append(all, f)
	haveName[name] = true
	}
	}
	}

	// Add any missing directories needed to reach mount points.
	for old := range ns {
	if hasPathPrefix(old, path) && old != path {
	// Find next element after path in old.
	elem := old[len(path):]
	elem = strings.TrimPrefix(elem, "/")
	if i := strings.Index(elem, "/"); i >= 0 {
	elem = elem[:i]
	}
	if !haveName[elem] {
	haveName[elem] = true
	all = append(all, dirInfo(elem))
	}
	}
	}

	if len(all) == 0 {
	return nil, readDirErr
	}

	sort.Sort(byName(all))
	return all, nil
	}

	// RootType returns the RootType for the given path in the namespace.
	func (ns NameSpace) RootType(path string) RootType {
	// We resolve the given path to a list of mountedFS and then return
	// the root type for the filesystem which contains the path.
	for _, m := range ns.resolve(path) {
	_, err := m.fs.ReadDir(m.translate(path))
	// Found a match, return the filesystem's root type
	if err == nil {
	return m.fs.RootType(path)
	}
	}
	return ""
	}

	// byName implements sort.Interface.
	type byName []os.FileInfo

	func (f byName) Len() int { return len(f) }
	func (f byName) Less(i, j int) bool { return f[i].Name() < f[j].Name() }
	func (f byName) Swap(i, j int) { f[i], f[j] = f[j], f[i] }