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diff --git a/src/os/exec/exec.go b/src/os/exec/exec.go
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+// Copyright 2009 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 exec runs external commands. It wraps os.StartProcess to make it
+// easier to remap stdin and stdout, connect I/O with pipes, and do other
+// adjustments.
+//
+// Unlike the "system" library call from C and other languages, the
+// os/exec package intentionally does not invoke the system shell and
+// does not expand any glob patterns or handle other expansions,
+// pipelines, or redirections typically done by shells. The package
+// behaves more like C's "exec" family of functions. To expand glob
+// patterns, either call the shell directly, taking care to escape any
+// dangerous input, or use the path/filepath package's Glob function.
+// To expand environment variables, use package os's ExpandEnv.
+//
+// Note that the examples in this package assume a Unix system.
+// They may not run on Windows, and they do not run in the Go Playground
+// used by golang.org and godoc.org.
+package exec
+
+import (
+ "bytes"
+ "context"
+ "errors"
+ "internal/syscall/execenv"
+ "io"
+ "os"
+ "path/filepath"
+ "runtime"
+ "strconv"
+ "strings"
+ "sync"
+ "syscall"
+)
+
+// Error is returned by LookPath when it fails to classify a file as an
+// executable.
+type Error struct {
+ // Name is the file name for which the error occurred.
+ Name string
+ // Err is the underlying error.
+ Err error
+}
+
+func (e *Error) Error() string {
+ return "exec: " + strconv.Quote(e.Name) + ": " + e.Err.Error()
+}
+
+func (e *Error) Unwrap() error { return e.Err }
+
+// Cmd represents an external command being prepared or run.
+//
+// A Cmd cannot be reused after calling its Run, Output or CombinedOutput
+// methods.
+type Cmd struct {
+ // Path is the path of the command to run.
+ //
+ // This is the only field that must be set to a non-zero
+ // value. If Path is relative, it is evaluated relative
+ // to Dir.
+ Path string
+
+ // Args holds command line arguments, including the command as Args[0].
+ // If the Args field is empty or nil, Run uses {Path}.
+ //
+ // In typical use, both Path and Args are set by calling Command.
+ Args []string
+
+ // Env specifies the environment of the process.
+ // Each entry is of the form "key=value".
+ // If Env is nil, the new process uses the current process's
+ // environment.
+ // If Env contains duplicate environment keys, only the last
+ // value in the slice for each duplicate key is used.
+ // As a special case on Windows, SYSTEMROOT is always added if
+ // missing and not explicitly set to the empty string.
+ Env []string
+
+ // Dir specifies the working directory of the command.
+ // If Dir is the empty string, Run runs the command in the
+ // calling process's current directory.
+ Dir string
+
+ // Stdin specifies the process's standard input.
+ //
+ // If Stdin is nil, the process reads from the null device (os.DevNull).
+ //
+ // If Stdin is an *os.File, the process's standard input is connected
+ // directly to that file.
+ //
+ // Otherwise, during the execution of the command a separate
+ // goroutine reads from Stdin and delivers that data to the command
+ // over a pipe. In this case, Wait does not complete until the goroutine
+ // stops copying, either because it has reached the end of Stdin
+ // (EOF or a read error) or because writing to the pipe returned an error.
+ Stdin io.Reader
+
+ // Stdout and Stderr specify the process's standard output and error.
+ //
+ // If either is nil, Run connects the corresponding file descriptor
+ // to the null device (os.DevNull).
+ //
+ // If either is an *os.File, the corresponding output from the process
+ // is connected directly to that file.
+ //
+ // Otherwise, during the execution of the command a separate goroutine
+ // reads from the process over a pipe and delivers that data to the
+ // corresponding Writer. In this case, Wait does not complete until the
+ // goroutine reaches EOF or encounters an error.
+ //
+ // If Stdout and Stderr are the same writer, and have a type that can
+ // be compared with ==, at most one goroutine at a time will call Write.
+ Stdout io.Writer
+ Stderr io.Writer
+
+ // ExtraFiles specifies additional open files to be inherited by the
+ // new process. It does not include standard input, standard output, or
+ // standard error. If non-nil, entry i becomes file descriptor 3+i.
+ //
+ // ExtraFiles is not supported on Windows.
+ ExtraFiles []*os.File
+
+ // SysProcAttr holds optional, operating system-specific attributes.
+ // Run passes it to os.StartProcess as the os.ProcAttr's Sys field.
+ SysProcAttr *syscall.SysProcAttr
+
+ // Process is the underlying process, once started.
+ Process *os.Process
+
+ // ProcessState contains information about an exited process,
+ // available after a call to Wait or Run.
+ ProcessState *os.ProcessState
+
+ ctx context.Context // nil means none
+ lookPathErr error // LookPath error, if any.
+ finished bool // when Wait was called
+ childFiles []*os.File
+ closeAfterStart []io.Closer
+ closeAfterWait []io.Closer
+ goroutine []func() error
+ errch chan error // one send per goroutine
+ waitDone chan struct{}
+}
+
+// Command returns the Cmd struct to execute the named program with
+// the given arguments.
+//
+// It sets only the Path and Args in the returned structure.
+//
+// If name contains no path separators, Command uses LookPath to
+// resolve name to a complete path if possible. Otherwise it uses name
+// directly as Path.
+//
+// The returned Cmd's Args field is constructed from the command name
+// followed by the elements of arg, so arg should not include the
+// command name itself. For example, Command("echo", "hello").
+// Args[0] is always name, not the possibly resolved Path.
+//
+// On Windows, processes receive the whole command line as a single string
+// and do their own parsing. Command combines and quotes Args into a command
+// line string with an algorithm compatible with applications using
+// CommandLineToArgvW (which is the most common way). Notable exceptions are
+// msiexec.exe and cmd.exe (and thus, all batch files), which have a different
+// unquoting algorithm. In these or other similar cases, you can do the
+// quoting yourself and provide the full command line in SysProcAttr.CmdLine,
+// leaving Args empty.
+func Command(name string, arg ...string) *Cmd {
+ cmd := &Cmd{
+ Path: name,
+ Args: append([]string{name}, arg...),
+ }
+ if filepath.Base(name) == name {
+ if lp, err := LookPath(name); err != nil {
+ cmd.lookPathErr = err
+ } else {
+ cmd.Path = lp
+ }
+ }
+ return cmd
+}
+
+// CommandContext is like Command but includes a context.
+//
+// The provided context is used to kill the process (by calling
+// os.Process.Kill) if the context becomes done before the command
+// completes on its own.
+func CommandContext(ctx context.Context, name string, arg ...string) *Cmd {
+ if ctx == nil {
+ panic("nil Context")
+ }
+ cmd := Command(name, arg...)
+ cmd.ctx = ctx
+ return cmd
+}
+
+// String returns a human-readable description of c.
+// It is intended only for debugging.
+// In particular, it is not suitable for use as input to a shell.
+// The output of String may vary across Go releases.
+func (c *Cmd) String() string {
+ if c.lookPathErr != nil {
+ // failed to resolve path; report the original requested path (plus args)
+ return strings.Join(c.Args, " ")
+ }
+ // report the exact executable path (plus args)
+ b := new(strings.Builder)
+ b.WriteString(c.Path)
+ for _, a := range c.Args[1:] {
+ b.WriteByte(' ')
+ b.WriteString(a)
+ }
+ return b.String()
+}
+
+// interfaceEqual protects against panics from doing equality tests on
+// two interfaces with non-comparable underlying types.
+func interfaceEqual(a, b interface{}) bool {
+ defer func() {
+ recover()
+ }()
+ return a == b
+}
+
+func (c *Cmd) envv() ([]string, error) {
+ if c.Env != nil {
+ return c.Env, nil
+ }
+ return execenv.Default(c.SysProcAttr)
+}
+
+func (c *Cmd) argv() []string {
+ if len(c.Args) > 0 {
+ return c.Args
+ }
+ return []string{c.Path}
+}
+
+// skipStdinCopyError optionally specifies a function which reports
+// whether the provided stdin copy error should be ignored.
+var skipStdinCopyError func(error) bool
+
+func (c *Cmd) stdin() (f *os.File, err error) {
+ if c.Stdin == nil {
+ f, err = os.Open(os.DevNull)
+ if err != nil {
+ return
+ }
+ c.closeAfterStart = append(c.closeAfterStart, f)
+ return
+ }
+
+ if f, ok := c.Stdin.(*os.File); ok {
+ return f, nil
+ }
+
+ pr, pw, err := os.Pipe()
+ if err != nil {
+ return
+ }
+
+ c.closeAfterStart = append(c.closeAfterStart, pr)
+ c.closeAfterWait = append(c.closeAfterWait, pw)
+ c.goroutine = append(c.goroutine, func() error {
+ _, err := io.Copy(pw, c.Stdin)
+ if skip := skipStdinCopyError; skip != nil && skip(err) {
+ err = nil
+ }
+ if err1 := pw.Close(); err == nil {
+ err = err1
+ }
+ return err
+ })
+ return pr, nil
+}
+
+func (c *Cmd) stdout() (f *os.File, err error) {
+ return c.writerDescriptor(c.Stdout)
+}
+
+func (c *Cmd) stderr() (f *os.File, err error) {
+ if c.Stderr != nil && interfaceEqual(c.Stderr, c.Stdout) {
+ return c.childFiles[1], nil
+ }
+ return c.writerDescriptor(c.Stderr)
+}
+
+func (c *Cmd) writerDescriptor(w io.Writer) (f *os.File, err error) {
+ if w == nil {
+ f, err = os.OpenFile(os.DevNull, os.O_WRONLY, 0)
+ if err != nil {
+ return
+ }
+ c.closeAfterStart = append(c.closeAfterStart, f)
+ return
+ }
+
+ if f, ok := w.(*os.File); ok {
+ return f, nil
+ }
+
+ pr, pw, err := os.Pipe()
+ if err != nil {
+ return
+ }
+
+ c.closeAfterStart = append(c.closeAfterStart, pw)
+ c.closeAfterWait = append(c.closeAfterWait, pr)
+ c.goroutine = append(c.goroutine, func() error {
+ _, err := io.Copy(w, pr)
+ pr.Close() // in case io.Copy stopped due to write error
+ return err
+ })
+ return pw, nil
+}
+
+func (c *Cmd) closeDescriptors(closers []io.Closer) {
+ for _, fd := range closers {
+ fd.Close()
+ }
+}
+
+// Run starts the specified command and waits for it to complete.
+//
+// The returned error is nil if the command runs, has no problems
+// copying stdin, stdout, and stderr, and exits with a zero exit
+// status.
+//
+// If the command starts but does not complete successfully, the error is of
+// type *ExitError. Other error types may be returned for other situations.
+//
+// If the calling goroutine has locked the operating system thread
+// with runtime.LockOSThread and modified any inheritable OS-level
+// thread state (for example, Linux or Plan 9 name spaces), the new
+// process will inherit the caller's thread state.
+func (c *Cmd) Run() error {
+ if err := c.Start(); err != nil {
+ return err
+ }
+ return c.Wait()
+}
+
+// lookExtensions finds windows executable by its dir and path.
+// It uses LookPath to try appropriate extensions.
+// lookExtensions does not search PATH, instead it converts `prog` into `.\prog`.
+func lookExtensions(path, dir string) (string, error) {
+ if filepath.Base(path) == path {
+ path = filepath.Join(".", path)
+ }
+ if dir == "" {
+ return LookPath(path)
+ }
+ if filepath.VolumeName(path) != "" {
+ return LookPath(path)
+ }
+ if len(path) > 1 && os.IsPathSeparator(path[0]) {
+ return LookPath(path)
+ }
+ dirandpath := filepath.Join(dir, path)
+ // We assume that LookPath will only add file extension.
+ lp, err := LookPath(dirandpath)
+ if err != nil {
+ return "", err
+ }
+ ext := strings.TrimPrefix(lp, dirandpath)
+ return path + ext, nil
+}
+
+// Start starts the specified command but does not wait for it to complete.
+//
+// If Start returns successfully, the c.Process field will be set.
+//
+// The Wait method will return the exit code and release associated resources
+// once the command exits.
+func (c *Cmd) Start() error {
+ if c.lookPathErr != nil {
+ c.closeDescriptors(c.closeAfterStart)
+ c.closeDescriptors(c.closeAfterWait)
+ return c.lookPathErr
+ }
+ if runtime.GOOS == "windows" {
+ lp, err := lookExtensions(c.Path, c.Dir)
+ if err != nil {
+ c.closeDescriptors(c.closeAfterStart)
+ c.closeDescriptors(c.closeAfterWait)
+ return err
+ }
+ c.Path = lp
+ }
+ if c.Process != nil {
+ return errors.New("exec: already started")
+ }
+ if c.ctx != nil {
+ select {
+ case <-c.ctx.Done():
+ c.closeDescriptors(c.closeAfterStart)
+ c.closeDescriptors(c.closeAfterWait)
+ return c.ctx.Err()
+ default:
+ }
+ }
+
+ c.childFiles = make([]*os.File, 0, 3+len(c.ExtraFiles))
+ type F func(*Cmd) (*os.File, error)
+ for _, setupFd := range []F{(*Cmd).stdin, (*Cmd).stdout, (*Cmd).stderr} {
+ fd, err := setupFd(c)
+ if err != nil {
+ c.closeDescriptors(c.closeAfterStart)
+ c.closeDescriptors(c.closeAfterWait)
+ return err
+ }
+ c.childFiles = append(c.childFiles, fd)
+ }
+ c.childFiles = append(c.childFiles, c.ExtraFiles...)
+
+ envv, err := c.envv()
+ if err != nil {
+ return err
+ }
+
+ c.Process, err = os.StartProcess(c.Path, c.argv(), &os.ProcAttr{
+ Dir: c.Dir,
+ Files: c.childFiles,
+ Env: addCriticalEnv(dedupEnv(envv)),
+ Sys: c.SysProcAttr,
+ })
+ if err != nil {
+ c.closeDescriptors(c.closeAfterStart)
+ c.closeDescriptors(c.closeAfterWait)
+ return err
+ }
+
+ c.closeDescriptors(c.closeAfterStart)
+
+ // Don't allocate the channel unless there are goroutines to fire.
+ if len(c.goroutine) > 0 {
+ c.errch = make(chan error, len(c.goroutine))
+ for _, fn := range c.goroutine {
+ go func(fn func() error) {
+ c.errch <- fn()
+ }(fn)
+ }
+ }
+
+ if c.ctx != nil {
+ c.waitDone = make(chan struct{})
+ go func() {
+ select {
+ case <-c.ctx.Done():
+ c.Process.Kill()
+ case <-c.waitDone:
+ }
+ }()
+ }
+
+ return nil
+}
+
+// An ExitError reports an unsuccessful exit by a command.
+type ExitError struct {
+ *os.ProcessState
+
+ // Stderr holds a subset of the standard error output from the
+ // Cmd.Output method if standard error was not otherwise being
+ // collected.
+ //
+ // If the error output is long, Stderr may contain only a prefix
+ // and suffix of the output, with the middle replaced with
+ // text about the number of omitted bytes.
+ //
+ // Stderr is provided for debugging, for inclusion in error messages.
+ // Users with other needs should redirect Cmd.Stderr as needed.
+ Stderr []byte
+}
+
+func (e *ExitError) Error() string {
+ return e.ProcessState.String()
+}
+
+// Wait waits for the command to exit and waits for any copying to
+// stdin or copying from stdout or stderr to complete.
+//
+// The command must have been started by Start.
+//
+// The returned error is nil if the command runs, has no problems
+// copying stdin, stdout, and stderr, and exits with a zero exit
+// status.
+//
+// If the command fails to run or doesn't complete successfully, the
+// error is of type *ExitError. Other error types may be
+// returned for I/O problems.
+//
+// If any of c.Stdin, c.Stdout or c.Stderr are not an *os.File, Wait also waits
+// for the respective I/O loop copying to or from the process to complete.
+//
+// Wait releases any resources associated with the Cmd.
+func (c *Cmd) Wait() error {
+ if c.Process == nil {
+ return errors.New("exec: not started")
+ }
+ if c.finished {
+ return errors.New("exec: Wait was already called")
+ }
+ c.finished = true
+
+ state, err := c.Process.Wait()
+ if c.waitDone != nil {
+ close(c.waitDone)
+ }
+ c.ProcessState = state
+
+ var copyError error
+ for range c.goroutine {
+ if err := <-c.errch; err != nil && copyError == nil {
+ copyError = err
+ }
+ }
+
+ c.closeDescriptors(c.closeAfterWait)
+
+ if err != nil {
+ return err
+ } else if !state.Success() {
+ return &ExitError{ProcessState: state}
+ }
+
+ return copyError
+}
+
+// Output runs the command and returns its standard output.
+// Any returned error will usually be of type *ExitError.
+// If c.Stderr was nil, Output populates ExitError.Stderr.
+func (c *Cmd) Output() ([]byte, error) {
+ if c.Stdout != nil {
+ return nil, errors.New("exec: Stdout already set")
+ }
+ var stdout bytes.Buffer
+ c.Stdout = &stdout
+
+ captureErr := c.Stderr == nil
+ if captureErr {
+ c.Stderr = &prefixSuffixSaver{N: 32 << 10}
+ }
+
+ err := c.Run()
+ if err != nil && captureErr {
+ if ee, ok := err.(*ExitError); ok {
+ ee.Stderr = c.Stderr.(*prefixSuffixSaver).Bytes()
+ }
+ }
+ return stdout.Bytes(), err
+}
+
+// CombinedOutput runs the command and returns its combined standard
+// output and standard error.
+func (c *Cmd) CombinedOutput() ([]byte, error) {
+ if c.Stdout != nil {
+ return nil, errors.New("exec: Stdout already set")
+ }
+ if c.Stderr != nil {
+ return nil, errors.New("exec: Stderr already set")
+ }
+ var b bytes.Buffer
+ c.Stdout = &b
+ c.Stderr = &b
+ err := c.Run()
+ return b.Bytes(), err
+}
+
+// StdinPipe returns a pipe that will be connected to the command's
+// standard input when the command starts.
+// The pipe will be closed automatically after Wait sees the command exit.
+// A caller need only call Close to force the pipe to close sooner.
+// For example, if the command being run will not exit until standard input
+// is closed, the caller must close the pipe.
+func (c *Cmd) StdinPipe() (io.WriteCloser, error) {
+ if c.Stdin != nil {
+ return nil, errors.New("exec: Stdin already set")
+ }
+ if c.Process != nil {
+ return nil, errors.New("exec: StdinPipe after process started")
+ }
+ pr, pw, err := os.Pipe()
+ if err != nil {
+ return nil, err
+ }
+ c.Stdin = pr
+ c.closeAfterStart = append(c.closeAfterStart, pr)
+ wc := &closeOnce{File: pw}
+ c.closeAfterWait = append(c.closeAfterWait, wc)
+ return wc, nil
+}
+
+type closeOnce struct {
+ *os.File
+
+ once sync.Once
+ err error
+}
+
+func (c *closeOnce) Close() error {
+ c.once.Do(c.close)
+ return c.err
+}
+
+func (c *closeOnce) close() {
+ c.err = c.File.Close()
+}
+
+// StdoutPipe returns a pipe that will be connected to the command's
+// standard output when the command starts.
+//
+// Wait will close the pipe after seeing the command exit, so most callers
+// need not close the pipe themselves. It is thus incorrect to call Wait
+// before all reads from the pipe have completed.
+// For the same reason, it is incorrect to call Run when using StdoutPipe.
+// See the example for idiomatic usage.
+func (c *Cmd) StdoutPipe() (io.ReadCloser, error) {
+ if c.Stdout != nil {
+ return nil, errors.New("exec: Stdout already set")
+ }
+ if c.Process != nil {
+ return nil, errors.New("exec: StdoutPipe after process started")
+ }
+ pr, pw, err := os.Pipe()
+ if err != nil {
+ return nil, err
+ }
+ c.Stdout = pw
+ c.closeAfterStart = append(c.closeAfterStart, pw)
+ c.closeAfterWait = append(c.closeAfterWait, pr)
+ return pr, nil
+}
+
+// StderrPipe returns a pipe that will be connected to the command's
+// standard error when the command starts.
+//
+// Wait will close the pipe after seeing the command exit, so most callers
+// need not close the pipe themselves. It is thus incorrect to call Wait
+// before all reads from the pipe have completed.
+// For the same reason, it is incorrect to use Run when using StderrPipe.
+// See the StdoutPipe example for idiomatic usage.
+func (c *Cmd) StderrPipe() (io.ReadCloser, error) {
+ if c.Stderr != nil {
+ return nil, errors.New("exec: Stderr already set")
+ }
+ if c.Process != nil {
+ return nil, errors.New("exec: StderrPipe after process started")
+ }
+ pr, pw, err := os.Pipe()
+ if err != nil {
+ return nil, err
+ }
+ c.Stderr = pw
+ c.closeAfterStart = append(c.closeAfterStart, pw)
+ c.closeAfterWait = append(c.closeAfterWait, pr)
+ return pr, nil
+}
+
+// prefixSuffixSaver is an io.Writer which retains the first N bytes
+// and the last N bytes written to it. The Bytes() methods reconstructs
+// it with a pretty error message.
+type prefixSuffixSaver struct {
+ N int // max size of prefix or suffix
+ prefix []byte
+ suffix []byte // ring buffer once len(suffix) == N
+ suffixOff int // offset to write into suffix
+ skipped int64
+
+ // TODO(bradfitz): we could keep one large []byte and use part of it for
+ // the prefix, reserve space for the '... Omitting N bytes ...' message,
+ // then the ring buffer suffix, and just rearrange the ring buffer
+ // suffix when Bytes() is called, but it doesn't seem worth it for
+ // now just for error messages. It's only ~64KB anyway.
+}
+
+func (w *prefixSuffixSaver) Write(p []byte) (n int, err error) {
+ lenp := len(p)
+ p = w.fill(&w.prefix, p)
+
+ // Only keep the last w.N bytes of suffix data.
+ if overage := len(p) - w.N; overage > 0 {
+ p = p[overage:]
+ w.skipped += int64(overage)
+ }
+ p = w.fill(&w.suffix, p)
+
+ // w.suffix is full now if p is non-empty. Overwrite it in a circle.
+ for len(p) > 0 { // 0, 1, or 2 iterations.
+ n := copy(w.suffix[w.suffixOff:], p)
+ p = p[n:]
+ w.skipped += int64(n)
+ w.suffixOff += n
+ if w.suffixOff == w.N {
+ w.suffixOff = 0
+ }
+ }
+ return lenp, nil
+}
+
+// fill appends up to len(p) bytes of p to *dst, such that *dst does not
+// grow larger than w.N. It returns the un-appended suffix of p.
+func (w *prefixSuffixSaver) fill(dst *[]byte, p []byte) (pRemain []byte) {
+ if remain := w.N - len(*dst); remain > 0 {
+ add := minInt(len(p), remain)
+ *dst = append(*dst, p[:add]...)
+ p = p[add:]
+ }
+ return p
+}
+
+func (w *prefixSuffixSaver) Bytes() []byte {
+ if w.suffix == nil {
+ return w.prefix
+ }
+ if w.skipped == 0 {
+ return append(w.prefix, w.suffix...)
+ }
+ var buf bytes.Buffer
+ buf.Grow(len(w.prefix) + len(w.suffix) + 50)
+ buf.Write(w.prefix)
+ buf.WriteString("\n... omitting ")
+ buf.WriteString(strconv.FormatInt(w.skipped, 10))
+ buf.WriteString(" bytes ...\n")
+ buf.Write(w.suffix[w.suffixOff:])
+ buf.Write(w.suffix[:w.suffixOff])
+ return buf.Bytes()
+}
+
+func minInt(a, b int) int {
+ if a < b {
+ return a
+ }
+ return b
+}
+
+// dedupEnv returns a copy of env with any duplicates removed, in favor of
+// later values.
+// Items not of the normal environment "key=value" form are preserved unchanged.
+func dedupEnv(env []string) []string {
+ return dedupEnvCase(runtime.GOOS == "windows", env)
+}
+
+// dedupEnvCase is dedupEnv with a case option for testing.
+// If caseInsensitive is true, the case of keys is ignored.
+func dedupEnvCase(caseInsensitive bool, env []string) []string {
+ out := make([]string, 0, len(env))
+ saw := make(map[string]int, len(env)) // key => index into out
+ for _, kv := range env {
+ eq := strings.Index(kv, "=")
+ if eq < 0 {
+ out = append(out, kv)
+ continue
+ }
+ k := kv[:eq]
+ if caseInsensitive {
+ k = strings.ToLower(k)
+ }
+ if dupIdx, isDup := saw[k]; isDup {
+ out[dupIdx] = kv
+ continue
+ }
+ saw[k] = len(out)
+ out = append(out, kv)
+ }
+ return out
+}
+
+// addCriticalEnv adds any critical environment variables that are required
+// (or at least almost always required) on the operating system.
+// Currently this is only used for Windows.
+func addCriticalEnv(env []string) []string {
+ if runtime.GOOS != "windows" {
+ return env
+ }
+ for _, kv := range env {
+ eq := strings.Index(kv, "=")
+ if eq < 0 {
+ continue
+ }
+ k := kv[:eq]
+ if strings.EqualFold(k, "SYSTEMROOT") {
+ // We already have it.
+ return env
+ }
+ }
+ return append(env, "SYSTEMROOT="+os.Getenv("SYSTEMROOT"))
+}