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// 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.
// This file exercises the import parser but also checks that
// some low-level packages do not have new dependencies added.
package build
import (
// pkgDeps defines the expected dependencies between packages in
// the Go source tree. It is a statement of policy.
// Changes should not be made to this map without prior discussion.
// The map contains two kinds of entries:
// 1) Lower-case keys are standard import paths and list the
// allowed imports in that package.
// 2) Upper-case keys define aliases for package sets, which can then
// be used as dependencies by other rules.
var pkgDeps = map[string][]string{
// L0 is the lowest level, core, nearly unavoidable packages.
"errors": {"runtime", "internal/reflectlite"},
"io": {"errors", "sync", "sync/atomic"},
"runtime": {"unsafe", "runtime/internal/atomic", "runtime/internal/sys", "runtime/internal/math", "internal/cpu", "internal/bytealg"},
"runtime/internal/sys": {},
"runtime/internal/atomic": {"unsafe", "internal/cpu"},
"runtime/internal/math": {"runtime/internal/sys"},
"internal/race": {"runtime", "unsafe"},
"sync": {"internal/race", "runtime", "sync/atomic", "unsafe"},
"sync/atomic": {"unsafe"},
"unsafe": {},
"internal/cpu": {},
"internal/bytealg": {"unsafe", "internal/cpu"},
"internal/reflectlite": {"runtime", "unsafe"},
"L0": {
// L1 adds simple functions and strings processing,
// but not Unicode tables.
"math": {"internal/cpu", "unsafe", "math/bits"},
"math/bits": {"unsafe"},
"math/cmplx": {"math"},
"math/rand": {"L0", "math"},
"strconv": {"L0", "unicode/utf8", "math", "math/bits"},
"unicode/utf16": {},
"unicode/utf8": {},
"L1": {
// L2 adds Unicode and strings processing.
"bufio": {"L0", "unicode/utf8", "bytes"},
"bytes": {"L0", "unicode", "unicode/utf8"},
"path": {"L0", "unicode/utf8", "strings"},
"strings": {"L0", "unicode", "unicode/utf8"},
"unicode": {},
"L2": {
// L3 adds reflection and some basic utility packages
// and interface definitions, but nothing that makes
// system calls.
"crypto": {"L2", "hash"}, // interfaces
"crypto/cipher": {"L2", "crypto/subtle", "crypto/internal/subtle", "encoding/binary"},
"crypto/internal/subtle": {"unsafe", "reflect"}, // reflect behind a appengine tag
"crypto/subtle": {},
"encoding/base32": {"L2"},
"encoding/base64": {"L2", "encoding/binary"},
"encoding/binary": {"L2", "reflect"},
"hash": {"L2"}, // interfaces
"hash/adler32": {"L2", "hash"},
"hash/crc32": {"L2", "hash"},
"hash/crc64": {"L2", "hash"},
"hash/fnv": {"L2", "hash"},
"image": {"L2", "image/color"}, // interfaces
"image/color": {"L2"}, // interfaces
"image/color/palette": {"L2", "image/color"},
"internal/fmtsort": {"reflect", "sort"},
"reflect": {"L2"},
"sort": {"internal/reflectlite"},
"L3": {
// End of linear dependency definitions.
// Operating system access.
"syscall": {"L0", "internal/oserror", "internal/race", "internal/syscall/windows/sysdll", "syscall/js", "unicode/utf16"},
"syscall/js": {"L0"},
"internal/oserror": {"L0"},
"internal/syscall/unix": {"L0", "syscall"},
"internal/syscall/windows": {"L0", "syscall", "internal/syscall/windows/sysdll"},
"internal/syscall/windows/registry": {"L0", "syscall", "internal/syscall/windows/sysdll", "unicode/utf16"},
"time": {
// "L0" without the "io" package:
// Other time dependencies:
"internal/poll": {"L0", "internal/oserror", "internal/race", "syscall", "time", "unicode/utf16", "unicode/utf8", "internal/syscall/windows"},
"internal/testlog": {"L0"},
"os": {"L1", "os", "syscall", "time", "internal/oserror", "internal/poll", "internal/syscall/windows", "internal/syscall/unix", "internal/testlog"},
"path/filepath": {"L2", "os", "syscall", "internal/syscall/windows"},
"io/ioutil": {"L2", "os", "path/filepath", "time"},
"os/exec": {"L2", "os", "context", "path/filepath", "syscall"},
"os/signal": {"L2", "os", "syscall"},
// OS enables basic operating system functionality,
// but not direct use of package syscall, nor os/signal.
"OS": {
// Formatted I/O: few dependencies (L1) but we must add reflect and internal/fmtsort.
"fmt": {"L1", "os", "reflect", "internal/fmtsort"},
"log": {"L1", "os", "fmt", "time"},
// Packages used by testing must be low-level (L2+fmt).
"regexp": {"L2", "regexp/syntax"},
"regexp/syntax": {"L2"},
"runtime/debug": {"L2", "fmt", "io/ioutil", "os", "time"},
"runtime/pprof": {"L2", "compress/gzip", "context", "encoding/binary", "fmt", "io/ioutil", "os", "text/tabwriter", "time"},
"runtime/trace": {"L0", "context", "fmt"},
"text/tabwriter": {"L2"},
"testing": {"L2", "flag", "fmt", "internal/race", "os", "runtime/debug", "runtime/pprof", "runtime/trace", "time"},
"testing/iotest": {"L2", "log"},
"testing/quick": {"L2", "flag", "fmt", "reflect", "time"},
"internal/testenv": {"L2", "OS", "flag", "testing", "syscall"},
"internal/lazyregexp": {"L2", "OS", "regexp"},
"internal/lazytemplate": {"L2", "OS", "text/template"},
// L4 is defined as L3+fmt+log+time, because in general once
// you're using L3 packages, use of fmt, log, or time is not a big deal.
"L4": {
// Go parser.
"go/ast": {"L4", "OS", "go/scanner", "go/token"},
"go/doc": {"L4", "OS", "go/ast", "go/token", "regexp", "internal/lazyregexp", "text/template"},
"go/parser": {"L4", "OS", "go/ast", "go/scanner", "go/token"},
"go/printer": {"L4", "OS", "go/ast", "go/scanner", "go/token", "text/tabwriter"},
"go/scanner": {"L4", "OS", "go/token"},
"go/token": {"L4"},
"go/format": {"L4", "GOPARSER", "internal/format"},
"internal/format": {"L4", "GOPARSER"},
// Go type checking.
"go/constant": {"L4", "go/token", "math/big"},
"go/importer": {"L4", "go/build", "go/internal/gccgoimporter", "go/internal/gcimporter", "go/internal/srcimporter", "go/token", "go/types"},
"go/internal/gcimporter": {"L4", "OS", "go/build", "go/constant", "go/token", "go/types", "text/scanner"},
"go/internal/gccgoimporter": {"L4", "OS", "debug/elf", "go/constant", "go/token", "go/types", "internal/xcoff", "text/scanner"},
"go/internal/srcimporter": {"L4", "OS", "fmt", "go/ast", "go/build", "go/parser", "go/token", "go/types", "path/filepath"},
"go/types": {"L4", "GOPARSER", "container/heap", "go/constant"},
// One of a kind.
"archive/tar": {"L4", "OS", "syscall", "os/user"},
"archive/zip": {"L4", "OS", "compress/flate"},
"container/heap": {"sort"},
"compress/bzip2": {"L4"},
"compress/flate": {"L4"},
"compress/gzip": {"L4", "compress/flate"},
"compress/lzw": {"L4"},
"compress/zlib": {"L4", "compress/flate"},
"context": {"errors", "internal/oserror", "internal/reflectlite", "sync", "time"},
"database/sql": {"L4", "container/list", "context", "database/sql/driver", "database/sql/internal"},
"database/sql/driver": {"L4", "context", "time", "database/sql/internal"},
"debug/dwarf": {"L4"},
"debug/elf": {"L4", "OS", "debug/dwarf", "compress/zlib"},
"debug/gosym": {"L4"},
"debug/macho": {"L4", "OS", "debug/dwarf", "compress/zlib"},
"debug/pe": {"L4", "OS", "debug/dwarf", "compress/zlib"},
"debug/plan9obj": {"L4", "OS"},
"encoding": {"L4"},
"encoding/ascii85": {"L4"},
"encoding/asn1": {"L4", "math/big"},
"encoding/csv": {"L4"},
"encoding/gob": {"L4", "OS", "encoding"},
"encoding/hex": {"L4"},
"encoding/json": {"L4", "encoding"},
"encoding/pem": {"L4"},
"encoding/xml": {"L4", "encoding"},
"flag": {"L4", "OS"},
"go/build": {"L4", "OS", "GOPARSER", "internal/goroot", "internal/goversion"},
"html": {"L4"},
"image/draw": {"L4", "image/internal/imageutil"},
"image/gif": {"L4", "compress/lzw", "image/color/palette", "image/draw"},
"image/internal/imageutil": {"L4"},
"image/jpeg": {"L4", "image/internal/imageutil"},
"image/png": {"L4", "compress/zlib"},
"index/suffixarray": {"L4", "regexp"},
"internal/goroot": {"L4", "OS"},
"internal/singleflight": {"sync"},
"internal/trace": {"L4", "OS", "container/heap"},
"internal/xcoff": {"L4", "OS", "debug/dwarf"},
"math/big": {"L4"},
"mime": {"L4", "OS", "syscall", "internal/syscall/windows/registry"},
"mime/quotedprintable": {"L4"},
"net/internal/socktest": {"L4", "OS", "syscall", "internal/syscall/windows"},
"net/url": {"L4"},
"plugin": {"L0", "OS", "CGO"},
"runtime/pprof/internal/profile": {"L4", "OS", "compress/gzip", "regexp"},
"testing/internal/testdeps": {"L4", "internal/testlog", "runtime/pprof", "regexp"},
"text/scanner": {"L4", "OS"},
"text/template/parse": {"L4"},
"html/template": {
"L4", "OS", "encoding/json", "html", "text/template",
"text/template": {
"L4", "OS", "net/url", "text/template/parse",
// Cgo.
// If you add a dependency on CGO, you must add the package to
// cgoPackages in cmd/dist/test.go.
"runtime/cgo": {"L0", "C"},
"CGO": {"C", "runtime/cgo"},
// Fake entry to satisfy the pseudo-import "C"
// that shows up in programs that use cgo.
"C": {},
// Race detector/MSan uses cgo.
"runtime/race": {"C"},
"runtime/msan": {"C"},
// Plan 9 alone needs io/ioutil and os.
"os/user": {"L4", "CGO", "io/ioutil", "os", "syscall", "internal/syscall/windows", "internal/syscall/windows/registry"},
// Internal package used only for testing.
"os/signal/internal/pty": {"CGO", "fmt", "os", "syscall"},
// Basic networking.
// Because net must be used by any package that wants to
// do networking portably, it must have a small dependency set: just L0+basic os.
"net": {
"L0", "CGO",
"context", "math/rand", "os", "sort", "syscall", "time",
"internal/nettrace", "internal/poll", "internal/syscall/unix",
"internal/syscall/windows", "internal/singleflight", "internal/race",
"", "", "",
// NET enables use of basic network-related packages.
"NET": {
// Uses of networking.
"log/syslog": {"L4", "OS", "net"},
"net/mail": {"L4", "NET", "OS", "mime"},
"net/textproto": {"L4", "OS", "net"},
// Core crypto.
"crypto/aes": {"L3"},
"crypto/des": {"L3"},
"crypto/hmac": {"L3"},
"crypto/internal/randutil": {"io", "sync"},
"crypto/md5": {"L3"},
"crypto/rc4": {"L3"},
"crypto/sha1": {"L3"},
"crypto/sha256": {"L3"},
"crypto/sha512": {"L3"},
// Random byte, number generation.
// This would be part of core crypto except that it imports
// math/big, which imports fmt.
"crypto/rand": {"L4", "CRYPTO", "OS", "math/big", "syscall", "syscall/js", "internal/syscall/unix"},
// Not part of CRYPTO because it imports crypto/rand and crypto/sha512.
"crypto/ed25519": {"L3", "CRYPTO", "crypto/rand", "crypto/ed25519/internal/edwards25519"},
"crypto/ed25519/internal/edwards25519": {"encoding/binary"},
// Mathematical crypto: dependencies on fmt (L4) and math/big.
// We could avoid some of the fmt, but math/big imports fmt anyway.
"crypto/dsa": {"L4", "CRYPTO", "math/big"},
"crypto/ecdsa": {"L4", "CRYPTO", "crypto/elliptic", "math/big", "encoding/asn1"},
"crypto/elliptic": {"L4", "CRYPTO", "math/big"},
"crypto/rsa": {"L4", "CRYPTO", "crypto/rand", "math/big"},
"crypto/tls": {
"L4", "CRYPTO-MATH", "OS", "", "",
"container/list", "crypto/x509", "encoding/pem", "net", "syscall", "crypto/ed25519",
"crypto/x509": {
"L4", "CRYPTO-MATH", "OS", "CGO", "crypto/ed25519",
"crypto/x509/pkix", "encoding/pem", "encoding/hex", "net", "os/user", "syscall", "net/url",
"", "",
"crypto/x509/pkix": {"L4", "CRYPTO-MATH", "encoding/hex"},
// Simple net+crypto-aware packages.
"mime/multipart": {"L4", "OS", "mime", "crypto/rand", "net/textproto", "mime/quotedprintable"},
"net/smtp": {"L4", "CRYPTO", "NET", "crypto/tls"},
// HTTP, kingpin of dependencies.
"net/http": {
"L4", "NET", "OS",
"net/http/internal": {"L4"},
"net/http/httptrace": {"context", "crypto/tls", "internal/nettrace", "net", "net/textproto", "reflect", "time"},
// HTTP-using packages.
"expvar": {"L4", "OS", "encoding/json", "net/http"},
"net/http/cgi": {"L4", "NET", "OS", "crypto/tls", "net/http", "regexp"},
"net/http/cookiejar": {"L4", "NET", "net/http"},
"net/http/fcgi": {"L4", "NET", "OS", "context", "net/http", "net/http/cgi"},
"net/http/httptest": {
"L4", "NET", "OS", "crypto/tls", "flag", "net/http", "net/http/internal", "crypto/x509",
"net/http/httputil": {"L4", "NET", "OS", "context", "net/http", "net/http/internal", ""},
"net/http/pprof": {"L4", "OS", "html/template", "net/http", "runtime/pprof", "runtime/trace"},
"net/rpc": {"L4", "NET", "encoding/gob", "html/template", "net/http", "go/token"},
"net/rpc/jsonrpc": {"L4", "NET", "encoding/json", "net/rpc"},
// isMacro reports whether p is a package dependency macro
// (uppercase name).
func isMacro(p string) bool {
return 'A' <= p[0] && p[0] <= 'Z'
func allowed(pkg string) map[string]bool {
m := map[string]bool{}
var allow func(string)
allow = func(p string) {
if m[p] {
m[p] = true // set even for macros, to avoid loop on cycle
// Upper-case names are macro-expanded.
if isMacro(p) {
for _, pp := range pkgDeps[p] {
for _, pp := range pkgDeps[pkg] {
return m
// listStdPkgs returns the same list of packages as "go list std".
func listStdPkgs(goroot string) ([]string, error) {
// Based on cmd/go's matchPackages function.
var pkgs []string
src := filepath.Join(goroot, "src") + string(filepath.Separator)
walkFn := func(path string, fi os.FileInfo, err error) error {
if err != nil || !fi.IsDir() || path == src {
return nil
base := filepath.Base(path)
if strings.HasPrefix(base, ".") || strings.HasPrefix(base, "_") || base == "testdata" {
return filepath.SkipDir
name := filepath.ToSlash(path[len(src):])
if name == "builtin" || name == "cmd" || strings.Contains(name, "") {
return filepath.SkipDir
pkgs = append(pkgs, name)
return nil
if err := filepath.Walk(src, walkFn); err != nil {
return nil, err
return pkgs, nil
func TestDependencies(t *testing.T) {
iOS := runtime.GOOS == "darwin" && (runtime.GOARCH == "arm" || runtime.GOARCH == "arm64")
if runtime.GOOS == "nacl" || iOS {
// Tests run in a limited file system and we do not
// provide access to every source file.
t.Skipf("skipping on %s/%s, missing full GOROOT", runtime.GOOS, runtime.GOARCH)
ctxt := Default
all, err := listStdPkgs(ctxt.GOROOT)
if err != nil {
sawImport := map[string]map[string]bool{} // from package => to package => true
for _, pkg := range all {
imports, err := findImports(pkg)
if err != nil {
if sawImport[pkg] == nil {
sawImport[pkg] = map[string]bool{}
ok := allowed(pkg)
var bad []string
for _, imp := range imports {
sawImport[pkg][imp] = true
if !ok[imp] {
bad = append(bad, imp)
if bad != nil {
t.Errorf("unexpected dependency: %s imports %v", pkg, bad)
// depPath returns the path between the given from and to packages.
// It returns the empty string if there's no dependency path.
var depPath func(string, string) string
depPath = func(from, to string) string {
if sawImport[from][to] {
return from + " => " + to
for pkg := range sawImport[from] {
if p := depPath(pkg, to); p != "" {
return from + " => " + p
return ""
// Also test some high-level policy goals are being met by not finding
// these dependency paths:
badPaths := []struct{ from, to string }{
{"net", "unicode"},
{"os", "unicode"},
for _, path := range badPaths {
if how := depPath(path.from,; how != "" {
t.Errorf("policy violation: %s", how)
var buildIgnore = []byte("\n// +build ignore")
func findImports(pkg string) ([]string, error) {
dir := filepath.Join(Default.GOROOT, "src", pkg)
files, err := ioutil.ReadDir(dir)
if err != nil {
return nil, err
var imports []string
var haveImport = map[string]bool{}
for _, file := range files {
name := file.Name()
if name == "slice_go14.go" || name == "slice_go18.go" {
// These files are for compiler bootstrap with older versions of Go and not built in the standard build.
if !strings.HasSuffix(name, ".go") || strings.HasSuffix(name, "_test.go") {
f, err := os.Open(filepath.Join(dir, name))
if err != nil {
return nil, err
var imp []string
data, err := readImports(f, false, &imp)
if err != nil {
return nil, fmt.Errorf("reading %v: %v", name, err)
if bytes.Contains(data, buildIgnore) {
for _, quoted := range imp {
path, err := strconv.Unquote(quoted)
if err != nil {
if !haveImport[path] {
haveImport[path] = true
imports = append(imports, path)
return imports, nil