env.go

     1  // Copyright 2012 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  // Package envcmd implements the “go env” command.
     6  package envcmd
     7  
     8  import (
     9  	"bytes"
    10  	"context"
    11  	"encoding/json"
    12  	"fmt"
    13  	"go/build"
    14  	"internal/buildcfg"
    15  	"io"
    16  	"os"
    17  	"path/filepath"
    18  	"runtime"
    19  	"slices"
    20  	"sort"
    21  	"strings"
    22  	"unicode"
    23  	"unicode/utf8"
    24  
    25  	"cmd/go/internal/base"
    26  	"cmd/go/internal/cache"
    27  	"cmd/go/internal/cfg"
    28  	"cmd/go/internal/fsys"
    29  	"cmd/go/internal/load"
    30  	"cmd/go/internal/modload"
    31  	"cmd/go/internal/work"
    32  	"cmd/internal/quoted"
    33  	"cmd/internal/telemetry"
    34  )
    35  
    36  var CmdEnv = &base.Command{
    37  	UsageLine: "go env [-json] [-changed] [-u] [-w] [var ...]",
    38  	Short:     "print Go environment information",
    39  	Long: `
    40  Env prints Go environment information.
    41  
    42  By default env prints information as a shell script
    43  (on Windows, a batch file). If one or more variable
    44  names is given as arguments, env prints the value of
    45  each named variable on its own line.
    46  
    47  The -json flag prints the environment in JSON format
    48  instead of as a shell script.
    49  
    50  The -u flag requires one or more arguments and unsets
    51  the default setting for the named environment variables,
    52  if one has been set with 'go env -w'.
    53  
    54  The -w flag requires one or more arguments of the
    55  form NAME=VALUE and changes the default settings
    56  of the named environment variables to the given values.
    57  
    58  The -changed flag prints only those settings whose effective
    59  value differs from the default value that would be obtained in
    60  an empty environment with no prior uses of the -w flag.
    61  
    62  For more about environment variables, see 'go help environment'.
    63  	`,
    64  }
    65  
    66  func init() {
    67  	CmdEnv.Run = runEnv // break init cycle
    68  	base.AddChdirFlag(&CmdEnv.Flag)
    69  	base.AddBuildFlagsNX(&CmdEnv.Flag)
    70  }
    71  
    72  var (
    73  	envJson    = CmdEnv.Flag.Bool("json", false, "")
    74  	envU       = CmdEnv.Flag.Bool("u", false, "")
    75  	envW       = CmdEnv.Flag.Bool("w", false, "")
    76  	envChanged = CmdEnv.Flag.Bool("changed", false, "")
    77  )
    78  
    79  func MkEnv() []cfg.EnvVar {
    80  	envFile, envFileChanged, _ := cfg.EnvFile()
    81  	env := []cfg.EnvVar{
    82  		// NOTE: Keep this list (and in general, all lists in source code) sorted by name.
    83  		{Name: "GO111MODULE", Value: cfg.Getenv("GO111MODULE")},
    84  		{Name: "GOARCH", Value: cfg.Goarch, Changed: cfg.Goarch != runtime.GOARCH},
    85  		{Name: "GOAUTH", Value: cfg.GOAUTH, Changed: cfg.GOAUTHChanged},
    86  		{Name: "GOBIN", Value: cfg.GOBIN},
    87  		{Name: "GOCACHE"},
    88  		{Name: "GOCACHEPROG", Value: cfg.GOCACHEPROG, Changed: cfg.GOCACHEPROGChanged},
    89  		{Name: "GODEBUG", Value: os.Getenv("GODEBUG")},
    90  		{Name: "GOENV", Value: envFile, Changed: envFileChanged},
    91  		{Name: "GOEXE", Value: cfg.ExeSuffix},
    92  
    93  		// List the raw value of GOEXPERIMENT, not the cleaned one.
    94  		// The set of default experiments may change from one release
    95  		// to the next, so a GOEXPERIMENT setting that is redundant
    96  		// with the current toolchain might actually be relevant with
    97  		// a different version (for example, when bisecting a regression).
    98  		{Name: "GOEXPERIMENT", Value: cfg.RawGOEXPERIMENT},
    99  
   100  		{Name: "GOFIPS140", Value: cfg.GOFIPS140, Changed: cfg.GOFIPS140Changed},
   101  		{Name: "GOFLAGS", Value: cfg.Getenv("GOFLAGS")},
   102  		{Name: "GOHOSTARCH", Value: runtime.GOARCH},
   103  		{Name: "GOHOSTOS", Value: runtime.GOOS},
   104  		{Name: "GOINSECURE", Value: cfg.GOINSECURE},
   105  		{Name: "GOMODCACHE", Value: cfg.GOMODCACHE, Changed: cfg.GOMODCACHEChanged},
   106  		{Name: "GONOPROXY", Value: cfg.GONOPROXY, Changed: cfg.GONOPROXYChanged},
   107  		{Name: "GONOSUMDB", Value: cfg.GONOSUMDB, Changed: cfg.GONOSUMDBChanged},
   108  		{Name: "GOOS", Value: cfg.Goos, Changed: cfg.Goos != runtime.GOOS},
   109  		{Name: "GOPATH", Value: cfg.BuildContext.GOPATH, Changed: cfg.GOPATHChanged},
   110  		{Name: "GOPRIVATE", Value: cfg.GOPRIVATE},
   111  		{Name: "GOPROXY", Value: cfg.GOPROXY, Changed: cfg.GOPROXYChanged},
   112  		{Name: "GOROOT", Value: cfg.GOROOT},
   113  		{Name: "GOSUMDB", Value: cfg.GOSUMDB, Changed: cfg.GOSUMDBChanged},
   114  		{Name: "GOTELEMETRY", Value: telemetry.Mode()},
   115  		{Name: "GOTELEMETRYDIR", Value: telemetry.Dir()},
   116  		{Name: "GOTMPDIR", Value: cfg.Getenv("GOTMPDIR")},
   117  		{Name: "GOTOOLCHAIN"},
   118  		{Name: "GOTOOLDIR", Value: build.ToolDir},
   119  		{Name: "GOVCS", Value: cfg.GOVCS},
   120  		{Name: "GOVERSION", Value: runtime.Version()},
   121  	}
   122  
   123  	for i := range env {
   124  		switch env[i].Name {
   125  		case "GO111MODULE":
   126  			if env[i].Value != "on" && env[i].Value != "" {
   127  				env[i].Changed = true
   128  			}
   129  		case "GOBIN", "GOEXPERIMENT", "GOFLAGS", "GOINSECURE", "GOPRIVATE", "GOTMPDIR", "GOVCS":
   130  			if env[i].Value != "" {
   131  				env[i].Changed = true
   132  			}
   133  		case "GOCACHE":
   134  			env[i].Value, env[i].Changed, _ = cache.DefaultDir()
   135  		case "GOTOOLCHAIN":
   136  			env[i].Value, env[i].Changed = cfg.EnvOrAndChanged("GOTOOLCHAIN", "")
   137  		case "GODEBUG":
   138  			env[i].Changed = env[i].Value != ""
   139  		}
   140  	}
   141  
   142  	if work.GccgoBin != "" {
   143  		env = append(env, cfg.EnvVar{Name: "GCCGO", Value: work.GccgoBin, Changed: true})
   144  	} else {
   145  		env = append(env, cfg.EnvVar{Name: "GCCGO", Value: work.GccgoName})
   146  	}
   147  
   148  	goarch, val, changed := cfg.GetArchEnv()
   149  	if goarch != "" {
   150  		env = append(env, cfg.EnvVar{Name: goarch, Value: val, Changed: changed})
   151  	}
   152  
   153  	cc := cfg.Getenv("CC")
   154  	ccChanged := true
   155  	if cc == "" {
   156  		ccChanged = false
   157  		cc = cfg.DefaultCC(cfg.Goos, cfg.Goarch)
   158  	}
   159  	cxx := cfg.Getenv("CXX")
   160  	cxxChanged := true
   161  	if cxx == "" {
   162  		cxxChanged = false
   163  		cxx = cfg.DefaultCXX(cfg.Goos, cfg.Goarch)
   164  	}
   165  	ar, arChanged := cfg.EnvOrAndChanged("AR", "ar")
   166  	env = append(env, cfg.EnvVar{Name: "AR", Value: ar, Changed: arChanged})
   167  	env = append(env, cfg.EnvVar{Name: "CC", Value: cc, Changed: ccChanged})
   168  	env = append(env, cfg.EnvVar{Name: "CXX", Value: cxx, Changed: cxxChanged})
   169  
   170  	if cfg.BuildContext.CgoEnabled {
   171  		env = append(env, cfg.EnvVar{Name: "CGO_ENABLED", Value: "1", Changed: cfg.CGOChanged})
   172  	} else {
   173  		env = append(env, cfg.EnvVar{Name: "CGO_ENABLED", Value: "0", Changed: cfg.CGOChanged})
   174  	}
   175  
   176  	return env
   177  }
   178  
   179  func findEnv(env []cfg.EnvVar, name string) string {
   180  	for _, e := range env {
   181  		if e.Name == name {
   182  			return e.Value
   183  		}
   184  	}
   185  	if cfg.CanGetenv(name) {
   186  		return cfg.Getenv(name)
   187  	}
   188  	return ""
   189  }
   190  
   191  // ExtraEnvVars returns environment variables that should not leak into child processes.
   192  func ExtraEnvVars() []cfg.EnvVar {
   193  	gomod := ""
   194  	modload.Init()
   195  	if modload.HasModRoot() {
   196  		gomod = modload.ModFilePath()
   197  	} else if modload.Enabled() {
   198  		gomod = os.DevNull
   199  	}
   200  	modload.InitWorkfile()
   201  	gowork := modload.WorkFilePath()
   202  	// As a special case, if a user set off explicitly, report that in GOWORK.
   203  	if cfg.Getenv("GOWORK") == "off" {
   204  		gowork = "off"
   205  	}
   206  	return []cfg.EnvVar{
   207  		{Name: "GOMOD", Value: gomod},
   208  		{Name: "GOWORK", Value: gowork},
   209  	}
   210  }
   211  
   212  // ExtraEnvVarsCostly returns environment variables that should not leak into child processes
   213  // but are costly to evaluate.
   214  func ExtraEnvVarsCostly() []cfg.EnvVar {
   215  	b := work.NewBuilder("")
   216  	defer func() {
   217  		if err := b.Close(); err != nil {
   218  			base.Fatal(err)
   219  		}
   220  	}()
   221  
   222  	cppflags, cflags, cxxflags, fflags, ldflags, err := b.CFlags(&load.Package{})
   223  	if err != nil {
   224  		// Should not happen - b.CFlags was given an empty package.
   225  		fmt.Fprintf(os.Stderr, "go: invalid cflags: %v\n", err)
   226  		return nil
   227  	}
   228  	cmd := b.GccCmd(".", "")
   229  
   230  	join := func(s []string) string {
   231  		q, err := quoted.Join(s)
   232  		if err != nil {
   233  			return strings.Join(s, " ")
   234  		}
   235  		return q
   236  	}
   237  
   238  	ret := []cfg.EnvVar{
   239  		// Note: Update the switch in runEnv below when adding to this list.
   240  		{Name: "CGO_CFLAGS", Value: join(cflags)},
   241  		{Name: "CGO_CPPFLAGS", Value: join(cppflags)},
   242  		{Name: "CGO_CXXFLAGS", Value: join(cxxflags)},
   243  		{Name: "CGO_FFLAGS", Value: join(fflags)},
   244  		{Name: "CGO_LDFLAGS", Value: join(ldflags)},
   245  		{Name: "PKG_CONFIG", Value: b.PkgconfigCmd()},
   246  		{Name: "GOGCCFLAGS", Value: join(cmd[3:])},
   247  	}
   248  
   249  	for i := range ret {
   250  		ev := &ret[i]
   251  		switch ev.Name {
   252  		case "GOGCCFLAGS": // GOGCCFLAGS cannot be modified
   253  		case "CGO_CPPFLAGS":
   254  			ev.Changed = ev.Value != ""
   255  		case "PKG_CONFIG":
   256  			ev.Changed = ev.Value != cfg.DefaultPkgConfig
   257  		case "CGO_CXXFLAGS", "CGO_CFLAGS", "CGO_FFLAGS", "CGO_LDFLAGS":
   258  			ev.Changed = ev.Value != work.DefaultCFlags
   259  		}
   260  	}
   261  
   262  	return ret
   263  }
   264  
   265  // argKey returns the KEY part of the arg KEY=VAL, or else arg itself.
   266  func argKey(arg string) string {
   267  	i := strings.Index(arg, "=")
   268  	if i < 0 {
   269  		return arg
   270  	}
   271  	return arg[:i]
   272  }
   273  
   274  func runEnv(ctx context.Context, cmd *base.Command, args []string) {
   275  	if *envJson && *envU {
   276  		base.Fatalf("go: cannot use -json with -u")
   277  	}
   278  	if *envJson && *envW {
   279  		base.Fatalf("go: cannot use -json with -w")
   280  	}
   281  	if *envU && *envW {
   282  		base.Fatalf("go: cannot use -u with -w")
   283  	}
   284  
   285  	// Handle 'go env -w' and 'go env -u' before calling buildcfg.Check,
   286  	// so they can be used to recover from an invalid configuration.
   287  	if *envW {
   288  		runEnvW(args)
   289  		return
   290  	}
   291  
   292  	if *envU {
   293  		runEnvU(args)
   294  		return
   295  	}
   296  
   297  	buildcfg.Check()
   298  	if cfg.ExperimentErr != nil {
   299  		base.Fatal(cfg.ExperimentErr)
   300  	}
   301  
   302  	for _, arg := range args {
   303  		if strings.Contains(arg, "=") {
   304  			base.Fatalf("go: invalid variable name %q (use -w to set variable)", arg)
   305  		}
   306  	}
   307  
   308  	env := cfg.CmdEnv
   309  	env = append(env, ExtraEnvVars()...)
   310  
   311  	if err := fsys.Init(); err != nil {
   312  		base.Fatal(err)
   313  	}
   314  
   315  	// Do we need to call ExtraEnvVarsCostly, which is a bit expensive?
   316  	needCostly := false
   317  	if len(args) == 0 {
   318  		// We're listing all environment variables ("go env"),
   319  		// including the expensive ones.
   320  		needCostly = true
   321  	} else {
   322  		needCostly = false
   323  	checkCostly:
   324  		for _, arg := range args {
   325  			switch argKey(arg) {
   326  			case "CGO_CFLAGS",
   327  				"CGO_CPPFLAGS",
   328  				"CGO_CXXFLAGS",
   329  				"CGO_FFLAGS",
   330  				"CGO_LDFLAGS",
   331  				"PKG_CONFIG",
   332  				"GOGCCFLAGS":
   333  				needCostly = true
   334  				break checkCostly
   335  			}
   336  		}
   337  	}
   338  	if needCostly {
   339  		work.BuildInit()
   340  		env = append(env, ExtraEnvVarsCostly()...)
   341  	}
   342  
   343  	if len(args) > 0 {
   344  		// Show only the named vars.
   345  		if !*envChanged {
   346  			if *envJson {
   347  				es := make([]cfg.EnvVar, 0, len(args))
   348  				for _, name := range args {
   349  					e := cfg.EnvVar{Name: name, Value: findEnv(env, name)}
   350  					es = append(es, e)
   351  				}
   352  				env = es
   353  			} else {
   354  				// Print just the values, without names.
   355  				for _, name := range args {
   356  					fmt.Printf("%s\n", findEnv(env, name))
   357  				}
   358  				return
   359  			}
   360  		} else {
   361  			// Show only the changed, named vars.
   362  			var es []cfg.EnvVar
   363  			for _, name := range args {
   364  				for _, e := range env {
   365  					if e.Name == name {
   366  						es = append(es, e)
   367  						break
   368  					}
   369  				}
   370  			}
   371  			env = es
   372  		}
   373  	}
   374  
   375  	// print
   376  	if *envJson {
   377  		printEnvAsJSON(env, *envChanged)
   378  	} else {
   379  		PrintEnv(os.Stdout, env, *envChanged)
   380  	}
   381  }
   382  
   383  func runEnvW(args []string) {
   384  	// Process and sanity-check command line.
   385  	if len(args) == 0 {
   386  		base.Fatalf("go: no KEY=VALUE arguments given")
   387  	}
   388  	osEnv := make(map[string]string)
   389  	for _, e := range cfg.OrigEnv {
   390  		if i := strings.Index(e, "="); i >= 0 {
   391  			osEnv[e[:i]] = e[i+1:]
   392  		}
   393  	}
   394  	add := make(map[string]string)
   395  	for _, arg := range args {
   396  		key, val, found := strings.Cut(arg, "=")
   397  		if !found {
   398  			base.Fatalf("go: arguments must be KEY=VALUE: invalid argument: %s", arg)
   399  		}
   400  		if err := checkEnvWrite(key, val); err != nil {
   401  			base.Fatal(err)
   402  		}
   403  		if _, ok := add[key]; ok {
   404  			base.Fatalf("go: multiple values for key: %s", key)
   405  		}
   406  		add[key] = val
   407  		if osVal := osEnv[key]; osVal != "" && osVal != val {
   408  			fmt.Fprintf(os.Stderr, "warning: go env -w %s=... does not override conflicting OS environment variable\n", key)
   409  		}
   410  	}
   411  
   412  	if err := checkBuildConfig(add, nil); err != nil {
   413  		base.Fatal(err)
   414  	}
   415  
   416  	gotmp, okGOTMP := add["GOTMPDIR"]
   417  	if okGOTMP {
   418  		if !filepath.IsAbs(gotmp) && gotmp != "" {
   419  			base.Fatalf("go: GOTMPDIR must be an absolute path")
   420  		}
   421  	}
   422  
   423  	updateEnvFile(add, nil)
   424  }
   425  
   426  func runEnvU(args []string) {
   427  	// Process and sanity-check command line.
   428  	if len(args) == 0 {
   429  		base.Fatalf("go: 'go env -u' requires an argument")
   430  	}
   431  	del := make(map[string]bool)
   432  	for _, arg := range args {
   433  		if err := checkEnvWrite(arg, ""); err != nil {
   434  			base.Fatal(err)
   435  		}
   436  		del[arg] = true
   437  	}
   438  
   439  	if err := checkBuildConfig(nil, del); err != nil {
   440  		base.Fatal(err)
   441  	}
   442  
   443  	updateEnvFile(nil, del)
   444  }
   445  
   446  // checkBuildConfig checks whether the build configuration is valid
   447  // after the specified configuration environment changes are applied.
   448  func checkBuildConfig(add map[string]string, del map[string]bool) error {
   449  	// get returns the value for key after applying add and del and
   450  	// reports whether it changed. cur should be the current value
   451  	// (i.e., before applying changes) and def should be the default
   452  	// value (i.e., when no environment variables are provided at all).
   453  	get := func(key, cur, def string) (string, bool) {
   454  		if val, ok := add[key]; ok {
   455  			return val, true
   456  		}
   457  		if del[key] {
   458  			val := getOrigEnv(key)
   459  			if val == "" {
   460  				val = def
   461  			}
   462  			return val, true
   463  		}
   464  		return cur, false
   465  	}
   466  
   467  	goos, okGOOS := get("GOOS", cfg.Goos, build.Default.GOOS)
   468  	goarch, okGOARCH := get("GOARCH", cfg.Goarch, build.Default.GOARCH)
   469  	if okGOOS || okGOARCH {
   470  		if err := work.CheckGOOSARCHPair(goos, goarch); err != nil {
   471  			return err
   472  		}
   473  	}
   474  
   475  	goexperiment, okGOEXPERIMENT := get("GOEXPERIMENT", cfg.RawGOEXPERIMENT, buildcfg.DefaultGOEXPERIMENT)
   476  	if okGOEXPERIMENT {
   477  		if _, err := buildcfg.ParseGOEXPERIMENT(goos, goarch, goexperiment); err != nil {
   478  			return err
   479  		}
   480  	}
   481  
   482  	return nil
   483  }
   484  
   485  // PrintEnv prints the environment variables to w.
   486  func PrintEnv(w io.Writer, env []cfg.EnvVar, onlyChanged bool) {
   487  	env = slices.Clone(env)
   488  	slices.SortFunc(env, func(x, y cfg.EnvVar) int { return strings.Compare(x.Name, y.Name) })
   489  
   490  	for _, e := range env {
   491  		if e.Name != "TERM" {
   492  			if runtime.GOOS != "plan9" && bytes.Contains([]byte(e.Value), []byte{0}) {
   493  				base.Fatalf("go: internal error: encountered null byte in environment variable %s on non-plan9 platform", e.Name)
   494  			}
   495  			if onlyChanged && !e.Changed {
   496  				continue
   497  			}
   498  			switch runtime.GOOS {
   499  			default:
   500  				fmt.Fprintf(w, "%s=%s\n", e.Name, shellQuote(e.Value))
   501  			case "plan9":
   502  				if strings.IndexByte(e.Value, '\x00') < 0 {
   503  					fmt.Fprintf(w, "%s='%s'\n", e.Name, strings.ReplaceAll(e.Value, "'", "''"))
   504  				} else {
   505  					v := strings.Split(e.Value, "\x00")
   506  					fmt.Fprintf(w, "%s=(", e.Name)
   507  					for x, s := range v {
   508  						if x > 0 {
   509  							fmt.Fprintf(w, " ")
   510  						}
   511  						fmt.Fprintf(w, "'%s'", strings.ReplaceAll(s, "'", "''"))
   512  					}
   513  					fmt.Fprintf(w, ")\n")
   514  				}
   515  			case "windows":
   516  				if hasNonGraphic(e.Value) {
   517  					base.Errorf("go: stripping unprintable or unescapable characters from %%%q%%", e.Name)
   518  				}
   519  				fmt.Fprintf(w, "set %s=%s\n", e.Name, batchEscape(e.Value))
   520  			}
   521  		}
   522  	}
   523  }
   524  
   525  // isWindowsUnquotableRune reports whether r can't be quoted in a
   526  // Windows "set" command.
   527  // These runes will be replaced by the Unicode replacement character.
   528  func isWindowsUnquotableRune(r rune) bool {
   529  	if r == '\r' || r == '\n' {
   530  		return true
   531  	}
   532  	return !unicode.IsGraphic(r) && !unicode.IsSpace(r)
   533  }
   534  
   535  func hasNonGraphic(s string) bool {
   536  	return strings.ContainsFunc(s, isWindowsUnquotableRune)
   537  }
   538  
   539  func shellQuote(s string) string {
   540  	var sb strings.Builder
   541  	sb.WriteByte('\'')
   542  	for _, r := range s {
   543  		if r == '\'' {
   544  			// Close the single quoted string, add an escaped single quote,
   545  			// and start another single quoted string.
   546  			sb.WriteString(`'\''`)
   547  		} else {
   548  			sb.WriteRune(r)
   549  		}
   550  	}
   551  	sb.WriteByte('\'')
   552  	return sb.String()
   553  }
   554  
   555  func batchEscape(s string) string {
   556  	var sb strings.Builder
   557  	for _, r := range s {
   558  		if isWindowsUnquotableRune(r) {
   559  			sb.WriteRune(unicode.ReplacementChar)
   560  			continue
   561  		}
   562  		switch r {
   563  		case '%':
   564  			sb.WriteString("%%")
   565  		case '<', '>', '|', '&', '^':
   566  			// These are special characters that need to be escaped with ^. See
   567  			// https://learn.microsoft.com/en-us/windows-server/administration/windows-commands/set_1.
   568  			sb.WriteByte('^')
   569  			sb.WriteRune(r)
   570  		default:
   571  			sb.WriteRune(r)
   572  		}
   573  	}
   574  	return sb.String()
   575  }
   576  
   577  func printEnvAsJSON(env []cfg.EnvVar, onlyChanged bool) {
   578  	m := make(map[string]string)
   579  	for _, e := range env {
   580  		if e.Name == "TERM" {
   581  			continue
   582  		}
   583  		if onlyChanged && !e.Changed {
   584  			continue
   585  		}
   586  		m[e.Name] = e.Value
   587  	}
   588  	enc := json.NewEncoder(os.Stdout)
   589  	enc.SetIndent("", "\t")
   590  	if err := enc.Encode(m); err != nil {
   591  		base.Fatalf("go: %s", err)
   592  	}
   593  }
   594  
   595  func getOrigEnv(key string) string {
   596  	for _, v := range cfg.OrigEnv {
   597  		if v, found := strings.CutPrefix(v, key+"="); found {
   598  			return v
   599  		}
   600  	}
   601  	return ""
   602  }
   603  
   604  func checkEnvWrite(key, val string) error {
   605  	switch key {
   606  	case "GOEXE", "GOGCCFLAGS", "GOHOSTARCH", "GOHOSTOS", "GOMOD", "GOWORK", "GOTOOLDIR", "GOVERSION", "GOTELEMETRY", "GOTELEMETRYDIR":
   607  		return fmt.Errorf("%s cannot be modified", key)
   608  	case "GOENV", "GODEBUG":
   609  		return fmt.Errorf("%s can only be set using the OS environment", key)
   610  	}
   611  
   612  	// To catch typos and the like, check that we know the variable.
   613  	// If it's already in the env file, we assume it's known.
   614  	if !cfg.CanGetenv(key) {
   615  		return fmt.Errorf("unknown go command variable %s", key)
   616  	}
   617  
   618  	// Some variables can only have one of a few valid values. If set to an
   619  	// invalid value, the next cmd/go invocation might fail immediately,
   620  	// even 'go env -w' itself.
   621  	switch key {
   622  	case "GO111MODULE":
   623  		switch val {
   624  		case "", "auto", "on", "off":
   625  		default:
   626  			return fmt.Errorf("invalid %s value %q", key, val)
   627  		}
   628  	case "GOPATH":
   629  		if strings.HasPrefix(val, "~") {
   630  			return fmt.Errorf("GOPATH entry cannot start with shell metacharacter '~': %q", val)
   631  		}
   632  		if !filepath.IsAbs(val) && val != "" {
   633  			return fmt.Errorf("GOPATH entry is relative; must be absolute path: %q", val)
   634  		}
   635  	case "GOMODCACHE":
   636  		if !filepath.IsAbs(val) && val != "" {
   637  			return fmt.Errorf("GOMODCACHE entry is relative; must be absolute path: %q", val)
   638  		}
   639  	case "CC", "CXX":
   640  		if val == "" {
   641  			break
   642  		}
   643  		args, err := quoted.Split(val)
   644  		if err != nil {
   645  			return fmt.Errorf("invalid %s: %v", key, err)
   646  		}
   647  		if len(args) == 0 {
   648  			return fmt.Errorf("%s entry cannot contain only space", key)
   649  		}
   650  		if !filepath.IsAbs(args[0]) && args[0] != filepath.Base(args[0]) {
   651  			return fmt.Errorf("%s entry is relative; must be absolute path: %q", key, args[0])
   652  		}
   653  	}
   654  
   655  	if !utf8.ValidString(val) {
   656  		return fmt.Errorf("invalid UTF-8 in %s=... value", key)
   657  	}
   658  	if strings.Contains(val, "\x00") {
   659  		return fmt.Errorf("invalid NUL in %s=... value", key)
   660  	}
   661  	if strings.ContainsAny(val, "\v\r\n") {
   662  		return fmt.Errorf("invalid newline in %s=... value", key)
   663  	}
   664  	return nil
   665  }
   666  
   667  func readEnvFileLines(mustExist bool) []string {
   668  	file, _, err := cfg.EnvFile()
   669  	if file == "" {
   670  		if mustExist {
   671  			base.Fatalf("go: cannot find go env config: %v", err)
   672  		}
   673  		return nil
   674  	}
   675  	data, err := os.ReadFile(file)
   676  	if err != nil && (!os.IsNotExist(err) || mustExist) {
   677  		base.Fatalf("go: reading go env config: %v", err)
   678  	}
   679  	lines := strings.SplitAfter(string(data), "\n")
   680  	if lines[len(lines)-1] == "" {
   681  		lines = lines[:len(lines)-1]
   682  	} else {
   683  		lines[len(lines)-1] += "\n"
   684  	}
   685  	return lines
   686  }
   687  
   688  func updateEnvFile(add map[string]string, del map[string]bool) {
   689  	lines := readEnvFileLines(len(add) == 0)
   690  
   691  	// Delete all but last copy of any duplicated variables,
   692  	// since the last copy is the one that takes effect.
   693  	prev := make(map[string]int)
   694  	for l, line := range lines {
   695  		if key := lineToKey(line); key != "" {
   696  			if p, ok := prev[key]; ok {
   697  				lines[p] = ""
   698  			}
   699  			prev[key] = l
   700  		}
   701  	}
   702  
   703  	// Add variables (go env -w). Update existing lines in file if present, add to end otherwise.
   704  	for key, val := range add {
   705  		if p, ok := prev[key]; ok {
   706  			lines[p] = key + "=" + val + "\n"
   707  			delete(add, key)
   708  		}
   709  	}
   710  	for key, val := range add {
   711  		lines = append(lines, key+"="+val+"\n")
   712  	}
   713  
   714  	// Delete requested variables (go env -u).
   715  	for key := range del {
   716  		if p, ok := prev[key]; ok {
   717  			lines[p] = ""
   718  		}
   719  	}
   720  
   721  	// Sort runs of KEY=VALUE lines
   722  	// (that is, blocks of lines where blocks are separated
   723  	// by comments, blank lines, or invalid lines).
   724  	start := 0
   725  	for i := 0; i <= len(lines); i++ {
   726  		if i == len(lines) || lineToKey(lines[i]) == "" {
   727  			sortKeyValues(lines[start:i])
   728  			start = i + 1
   729  		}
   730  	}
   731  
   732  	file, _, err := cfg.EnvFile()
   733  	if file == "" {
   734  		base.Fatalf("go: cannot find go env config: %v", err)
   735  	}
   736  	data := []byte(strings.Join(lines, ""))
   737  	err = os.WriteFile(file, data, 0666)
   738  	if err != nil {
   739  		// Try creating directory.
   740  		os.MkdirAll(filepath.Dir(file), 0777)
   741  		err = os.WriteFile(file, data, 0666)
   742  		if err != nil {
   743  			base.Fatalf("go: writing go env config: %v", err)
   744  		}
   745  	}
   746  }
   747  
   748  // lineToKey returns the KEY part of the line KEY=VALUE or else an empty string.
   749  func lineToKey(line string) string {
   750  	i := strings.Index(line, "=")
   751  	if i < 0 || strings.Contains(line[:i], "#") {
   752  		return ""
   753  	}
   754  	return line[:i]
   755  }
   756  
   757  // sortKeyValues sorts a sequence of lines by key.
   758  // It differs from sort.Strings in that GO386= sorts after GO=.
   759  func sortKeyValues(lines []string) {
   760  	sort.Slice(lines, func(i, j int) bool {
   761  		return lineToKey(lines[i]) < lineToKey(lines[j])
   762  	})
   763  }
   764
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