shell.go

     1  // Copyright 2023 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 work
     6  
     7  import (
     8  	"bytes"
     9  	"cmd/go/internal/base"
    10  	"cmd/go/internal/cache"
    11  	"cmd/go/internal/cfg"
    12  	"cmd/go/internal/load"
    13  	"cmd/go/internal/str"
    14  	"cmd/internal/par"
    15  	"cmd/internal/pathcache"
    16  	"fmt"
    17  	"io"
    18  	"io/fs"
    19  	"os"
    20  	"os/exec"
    21  	"path/filepath"
    22  	"runtime"
    23  	"strconv"
    24  	"strings"
    25  	"sync"
    26  	"time"
    27  )
    28  
    29  // A Shell runs shell commands and performs shell-like file system operations.
    30  //
    31  // Shell tracks context related to running commands, and form a tree much like
    32  // context.Context.
    33  type Shell struct {
    34  	action       *Action // nil for the root shell
    35  	*shellShared         // per-Builder state shared across Shells
    36  }
    37  
    38  // shellShared is Shell state shared across all Shells derived from a single
    39  // root shell (generally a single Builder).
    40  type shellShared struct {
    41  	workDir string // $WORK, immutable
    42  
    43  	printLock sync.Mutex
    44  	printer   load.Printer
    45  	scriptDir string // current directory in printed script
    46  
    47  	mkdirCache par.Cache[string, error] // a cache of created directories
    48  }
    49  
    50  // NewShell returns a new Shell.
    51  //
    52  // Shell will internally serialize calls to the printer.
    53  // If printer is nil, it uses load.DefaultPrinter.
    54  func NewShell(workDir string, printer load.Printer) *Shell {
    55  	if printer == nil {
    56  		printer = load.DefaultPrinter()
    57  	}
    58  	shared := &shellShared{
    59  		workDir: workDir,
    60  		printer: printer,
    61  	}
    62  	return &Shell{shellShared: shared}
    63  }
    64  
    65  func (sh *Shell) pkg() *load.Package {
    66  	if sh.action == nil {
    67  		return nil
    68  	}
    69  	return sh.action.Package
    70  }
    71  
    72  // Printf emits a to this Shell's output stream, formatting it like fmt.Printf.
    73  // It is safe to call concurrently.
    74  func (sh *Shell) Printf(format string, a ...any) {
    75  	sh.printLock.Lock()
    76  	defer sh.printLock.Unlock()
    77  	sh.printer.Printf(sh.pkg(), format, a...)
    78  }
    79  
    80  func (sh *Shell) printfLocked(format string, a ...any) {
    81  	sh.printer.Printf(sh.pkg(), format, a...)
    82  }
    83  
    84  // Errorf reports an error on sh's package and sets the process exit status to 1.
    85  func (sh *Shell) Errorf(format string, a ...any) {
    86  	sh.printLock.Lock()
    87  	defer sh.printLock.Unlock()
    88  	sh.printer.Errorf(sh.pkg(), format, a...)
    89  }
    90  
    91  // WithAction returns a Shell identical to sh, but bound to Action a.
    92  func (sh *Shell) WithAction(a *Action) *Shell {
    93  	sh2 := *sh
    94  	sh2.action = a
    95  	return &sh2
    96  }
    97  
    98  // Shell returns a shell for running commands on behalf of Action a.
    99  func (b *Builder) Shell(a *Action) *Shell {
   100  	if a == nil {
   101  		// The root shell has a nil Action. The point of this method is to
   102  		// create a Shell bound to an Action, so disallow nil Actions here.
   103  		panic("nil Action")
   104  	}
   105  	if a.sh == nil {
   106  		a.sh = b.backgroundSh.WithAction(a)
   107  	}
   108  	return a.sh
   109  }
   110  
   111  // BackgroundShell returns a Builder-wide Shell that's not bound to any Action.
   112  // Try not to use this unless there's really no sensible Action available.
   113  func (b *Builder) BackgroundShell() *Shell {
   114  	return b.backgroundSh
   115  }
   116  
   117  // moveOrCopyFile is like 'mv src dst' or 'cp src dst'.
   118  func (sh *Shell) moveOrCopyFile(dst, src string, perm fs.FileMode, force bool) error {
   119  	if cfg.BuildN {
   120  		sh.ShowCmd("", "mv %s %s", src, dst)
   121  		return nil
   122  	}
   123  
   124  	err := checkDstOverwrite(dst, force)
   125  	if err != nil {
   126  		return err
   127  	}
   128  
   129  	// If we can update the mode and rename to the dst, do it.
   130  	// Otherwise fall back to standard copy.
   131  
   132  	// If the source is in the build cache, we need to copy it.
   133  	dir, _, _ := cache.DefaultDir()
   134  	if strings.HasPrefix(src, dir) {
   135  		return sh.CopyFile(dst, src, perm, force)
   136  	}
   137  
   138  	// On Windows, always copy the file, so that we respect the NTFS
   139  	// permissions of the parent folder. https://golang.org/issue/22343.
   140  	// What matters here is not cfg.Goos (the system we are building
   141  	// for) but runtime.GOOS (the system we are building on).
   142  	if runtime.GOOS == "windows" {
   143  		return sh.CopyFile(dst, src, perm, force)
   144  	}
   145  
   146  	// If the destination directory has the group sticky bit set,
   147  	// we have to copy the file to retain the correct permissions.
   148  	// https://golang.org/issue/18878
   149  	if fi, err := os.Stat(filepath.Dir(dst)); err == nil {
   150  		if fi.IsDir() && (fi.Mode()&fs.ModeSetgid) != 0 {
   151  			return sh.CopyFile(dst, src, perm, force)
   152  		}
   153  	}
   154  
   155  	// The perm argument is meant to be adjusted according to umask,
   156  	// but we don't know what the umask is.
   157  	// Create a dummy file to find out.
   158  	// This avoids build tags and works even on systems like Plan 9
   159  	// where the file mask computation incorporates other information.
   160  	mode := perm
   161  	f, err := os.OpenFile(filepath.Clean(dst)+"-go-tmp-umask", os.O_WRONLY|os.O_CREATE|os.O_EXCL, perm)
   162  	if err == nil {
   163  		fi, err := f.Stat()
   164  		if err == nil {
   165  			mode = fi.Mode() & 0777
   166  		}
   167  		name := f.Name()
   168  		f.Close()
   169  		os.Remove(name)
   170  	}
   171  
   172  	if err := os.Chmod(src, mode); err == nil {
   173  		if err := os.Rename(src, dst); err == nil {
   174  			if cfg.BuildX {
   175  				sh.ShowCmd("", "mv %s %s", src, dst)
   176  			}
   177  			return nil
   178  		}
   179  	}
   180  
   181  	return sh.CopyFile(dst, src, perm, force)
   182  }
   183  
   184  // CopyFile is like 'cp src dst'.
   185  func (sh *Shell) CopyFile(dst, src string, perm fs.FileMode, force bool) error {
   186  	if cfg.BuildN || cfg.BuildX {
   187  		sh.ShowCmd("", "cp %s %s", src, dst)
   188  		if cfg.BuildN {
   189  			return nil
   190  		}
   191  	}
   192  
   193  	sf, err := os.Open(src)
   194  	if err != nil {
   195  		return err
   196  	}
   197  	defer sf.Close()
   198  
   199  	err = checkDstOverwrite(dst, force)
   200  	if err != nil {
   201  		return err
   202  	}
   203  
   204  	// On Windows, remove lingering ~ file from last attempt.
   205  	if runtime.GOOS == "windows" {
   206  		if _, err := os.Stat(dst + "~"); err == nil {
   207  			os.Remove(dst + "~")
   208  		}
   209  	}
   210  
   211  	mayberemovefile(dst)
   212  	df, err := os.OpenFile(dst, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, perm)
   213  	if err != nil && runtime.GOOS == "windows" {
   214  		// Windows does not allow deletion of a binary file
   215  		// while it is executing. Try to move it out of the way.
   216  		// If the move fails, which is likely, we'll try again the
   217  		// next time we do an install of this binary.
   218  		if err := os.Rename(dst, dst+"~"); err == nil {
   219  			os.Remove(dst + "~")
   220  		}
   221  		df, err = os.OpenFile(dst, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, perm)
   222  	}
   223  	if err != nil {
   224  		return fmt.Errorf("copying %s: %w", src, err) // err should already refer to dst
   225  	}
   226  
   227  	_, err = io.Copy(df, sf)
   228  	df.Close()
   229  	if err != nil {
   230  		mayberemovefile(dst)
   231  		return fmt.Errorf("copying %s to %s: %v", src, dst, err)
   232  	}
   233  	return nil
   234  }
   235  
   236  // mayberemovefile removes a file only if it is a regular file
   237  // When running as a user with sufficient privileges, we may delete
   238  // even device files, for example, which is not intended.
   239  func mayberemovefile(s string) {
   240  	if fi, err := os.Lstat(s); err == nil && !fi.Mode().IsRegular() {
   241  		return
   242  	}
   243  	os.Remove(s)
   244  }
   245  
   246  // Be careful about removing/overwriting dst.
   247  // Do not remove/overwrite if dst exists and is a directory
   248  // or a non-empty non-object file.
   249  func checkDstOverwrite(dst string, force bool) error {
   250  	if fi, err := os.Stat(dst); err == nil {
   251  		if fi.IsDir() {
   252  			return fmt.Errorf("build output %q already exists and is a directory", dst)
   253  		}
   254  		if !force && fi.Mode().IsRegular() && fi.Size() != 0 && !isObject(dst) {
   255  			return fmt.Errorf("build output %q already exists and is not an object file", dst)
   256  		}
   257  	}
   258  	return nil
   259  }
   260  
   261  // writeFile writes the text to file.
   262  func (sh *Shell) writeFile(file string, text []byte) error {
   263  	if cfg.BuildN || cfg.BuildX {
   264  		switch {
   265  		case len(text) == 0:
   266  			sh.ShowCmd("", "echo -n > %s # internal", file)
   267  		case bytes.IndexByte(text, '\n') == len(text)-1:
   268  			// One line. Use a simpler "echo" command.
   269  			sh.ShowCmd("", "echo '%s' > %s # internal", bytes.TrimSuffix(text, []byte("\n")), file)
   270  		default:
   271  			// Use the most general form.
   272  			sh.ShowCmd("", "cat >%s << 'EOF' # internal\n%sEOF", file, text)
   273  		}
   274  	}
   275  	if cfg.BuildN {
   276  		return nil
   277  	}
   278  	return os.WriteFile(file, text, 0666)
   279  }
   280  
   281  // Mkdir makes the named directory.
   282  func (sh *Shell) Mkdir(dir string) error {
   283  	// Make Mkdir(a.Objdir) a no-op instead of an error when a.Objdir == "".
   284  	if dir == "" {
   285  		return nil
   286  	}
   287  
   288  	// We can be a little aggressive about being
   289  	// sure directories exist. Skip repeated calls.
   290  	return sh.mkdirCache.Do(dir, func() error {
   291  		if cfg.BuildN || cfg.BuildX {
   292  			sh.ShowCmd("", "mkdir -p %s", dir)
   293  			if cfg.BuildN {
   294  				return nil
   295  			}
   296  		}
   297  
   298  		return os.MkdirAll(dir, 0777)
   299  	})
   300  }
   301  
   302  // RemoveAll is like 'rm -rf'. It attempts to remove all paths even if there's
   303  // an error, and returns the first error.
   304  func (sh *Shell) RemoveAll(paths ...string) error {
   305  	if cfg.BuildN || cfg.BuildX {
   306  		// Don't say we are removing the directory if we never created it.
   307  		show := func() bool {
   308  			for _, path := range paths {
   309  				if _, ok := sh.mkdirCache.Get(path); ok {
   310  					return true
   311  				}
   312  				if _, err := os.Stat(path); !os.IsNotExist(err) {
   313  					return true
   314  				}
   315  			}
   316  			return false
   317  		}
   318  		if show() {
   319  			sh.ShowCmd("", "rm -rf %s", strings.Join(paths, " "))
   320  		}
   321  	}
   322  	if cfg.BuildN {
   323  		return nil
   324  	}
   325  
   326  	var err error
   327  	for _, path := range paths {
   328  		if err2 := os.RemoveAll(path); err2 != nil && err == nil {
   329  			err = err2
   330  		}
   331  	}
   332  	return err
   333  }
   334  
   335  // Symlink creates a symlink newname -> oldname.
   336  func (sh *Shell) Symlink(oldname, newname string) error {
   337  	// It's not an error to try to recreate an existing symlink.
   338  	if link, err := os.Readlink(newname); err == nil && link == oldname {
   339  		return nil
   340  	}
   341  
   342  	if cfg.BuildN || cfg.BuildX {
   343  		sh.ShowCmd("", "ln -s %s %s", oldname, newname)
   344  		if cfg.BuildN {
   345  			return nil
   346  		}
   347  	}
   348  	return os.Symlink(oldname, newname)
   349  }
   350  
   351  // fmtCmd formats a command in the manner of fmt.Sprintf but also:
   352  //
   353  //	fmtCmd replaces the value of b.WorkDir with $WORK.
   354  func (sh *Shell) fmtCmd(dir string, format string, args ...any) string {
   355  	cmd := fmt.Sprintf(format, args...)
   356  	if sh.workDir != "" && !strings.HasPrefix(cmd, "cat ") {
   357  		cmd = strings.ReplaceAll(cmd, sh.workDir, "$WORK")
   358  		escaped := strconv.Quote(sh.workDir)
   359  		escaped = escaped[1 : len(escaped)-1] // strip quote characters
   360  		if escaped != sh.workDir {
   361  			cmd = strings.ReplaceAll(cmd, escaped, "$WORK")
   362  		}
   363  	}
   364  	return cmd
   365  }
   366  
   367  // ShowCmd prints the given command to standard output
   368  // for the implementation of -n or -x.
   369  //
   370  // ShowCmd also replaces the name of the current script directory with dot (.)
   371  // but only when it is at the beginning of a space-separated token.
   372  //
   373  // If dir is not "" or "/" and not the current script directory, ShowCmd first
   374  // prints a "cd" command to switch to dir and updates the script directory.
   375  func (sh *Shell) ShowCmd(dir string, format string, args ...any) {
   376  	// Use the output lock directly so we can manage scriptDir.
   377  	sh.printLock.Lock()
   378  	defer sh.printLock.Unlock()
   379  
   380  	cmd := sh.fmtCmd(dir, format, args...)
   381  
   382  	if dir != "" && dir != "/" {
   383  		if dir != sh.scriptDir {
   384  			// Show changing to dir and update the current directory.
   385  			sh.printfLocked("%s", sh.fmtCmd("", "cd %s\n", dir))
   386  			sh.scriptDir = dir
   387  		}
   388  		// Replace scriptDir is our working directory. Replace it
   389  		// with "." in the command.
   390  		dot := " ."
   391  		if dir[len(dir)-1] == filepath.Separator {
   392  			dot += string(filepath.Separator)
   393  		}
   394  		cmd = strings.ReplaceAll(" "+cmd, " "+dir, dot)[1:]
   395  	}
   396  
   397  	sh.printfLocked("%s\n", cmd)
   398  }
   399  
   400  // reportCmd reports the output and exit status of a command. The cmdOut and
   401  // cmdErr arguments are the output and exit error of the command, respectively.
   402  //
   403  // The exact reporting behavior is as follows:
   404  //
   405  //	cmdOut  cmdErr  Result
   406  //	""      nil     print nothing, return nil
   407  //	!=""    nil     print output, return nil
   408  //	""      !=nil   print nothing, return cmdErr (later printed)
   409  //	!=""    !=nil   print nothing, ignore err, return output as error (later printed)
   410  //
   411  // reportCmd returns a non-nil error if and only if cmdErr != nil. It assumes
   412  // that the command output, if non-empty, is more detailed than the command
   413  // error (which is usually just an exit status), so prefers using the output as
   414  // the ultimate error. Typically, the caller should return this error from an
   415  // Action, which it will be printed by the Builder.
   416  //
   417  // reportCmd formats the output as "# desc" followed by the given output. The
   418  // output is expected to contain references to 'dir', usually the source
   419  // directory for the package that has failed to build. reportCmd rewrites
   420  // mentions of dir with a relative path to dir when the relative path is
   421  // shorter. This is usually more pleasant. For example, if fmt doesn't compile
   422  // and we are in src/html, the output is
   423  //
   424  //	$ go build
   425  //	# fmt
   426  //	../fmt/print.go:1090: undefined: asdf
   427  //	$
   428  //
   429  // instead of
   430  //
   431  //	$ go build
   432  //	# fmt
   433  //	/usr/gopher/go/src/fmt/print.go:1090: undefined: asdf
   434  //	$
   435  //
   436  // reportCmd also replaces references to the work directory with $WORK, replaces
   437  // cgo file paths with the original file path, and replaces cgo-mangled names
   438  // with "C.name".
   439  //
   440  // desc is optional. If "", a.Package.Desc() is used.
   441  //
   442  // dir is optional. If "", a.Package.Dir is used.
   443  func (sh *Shell) reportCmd(desc, dir string, cmdOut []byte, cmdErr error) error {
   444  	if len(cmdOut) == 0 && cmdErr == nil {
   445  		// Common case
   446  		return nil
   447  	}
   448  	if len(cmdOut) == 0 && cmdErr != nil {
   449  		// Just return the error.
   450  		//
   451  		// TODO: This is what we've done for a long time, but it may be a
   452  		// mistake because it loses all of the extra context and results in
   453  		// ultimately less descriptive output. We should probably just take the
   454  		// text of cmdErr as the output in this case and do everything we
   455  		// otherwise would. We could chain the errors if we feel like it.
   456  		return cmdErr
   457  	}
   458  
   459  	// Fetch defaults from the package.
   460  	var p *load.Package
   461  	a := sh.action
   462  	if a != nil {
   463  		p = a.Package
   464  	}
   465  	var importPath string
   466  	if p != nil {
   467  		importPath = p.ImportPath
   468  		if desc == "" {
   469  			desc = p.Desc()
   470  		}
   471  		if dir == "" {
   472  			dir = p.Dir
   473  		}
   474  	}
   475  
   476  	out := string(cmdOut)
   477  
   478  	if !strings.HasSuffix(out, "\n") {
   479  		out = out + "\n"
   480  	}
   481  
   482  	// Replace workDir with $WORK
   483  	out = replacePrefix(out, sh.workDir, "$WORK")
   484  
   485  	// Rewrite mentions of dir with a relative path to dir
   486  	// when the relative path is shorter.
   487  	for {
   488  		// Note that dir starts out long, something like
   489  		// /foo/bar/baz/root/a
   490  		// The target string to be reduced is something like
   491  		// (blah-blah-blah) /foo/bar/baz/root/sibling/whatever.go:blah:blah
   492  		// /foo/bar/baz/root/a doesn't match /foo/bar/baz/root/sibling, but the prefix
   493  		// /foo/bar/baz/root does.  And there may be other niblings sharing shorter
   494  		// prefixes, the only way to find them is to look.
   495  		// This doesn't always produce a relative path --
   496  		// /foo is shorter than ../../.., for example.
   497  		if reldir := base.ShortPath(dir); reldir != dir {
   498  			out = replacePrefix(out, dir, reldir)
   499  			if filepath.Separator == '\\' {
   500  				// Don't know why, sometimes this comes out with slashes, not backslashes.
   501  				wdir := strings.ReplaceAll(dir, "\\", "/")
   502  				out = replacePrefix(out, wdir, reldir)
   503  			}
   504  		}
   505  		dirP := filepath.Dir(dir)
   506  		if dir == dirP {
   507  			break
   508  		}
   509  		dir = dirP
   510  	}
   511  
   512  	// Usually desc is already p.Desc(), but if not, signal cmdError.Error to
   513  	// add a line explicitly mentioning the import path.
   514  	needsPath := importPath != "" && p != nil && desc != p.Desc()
   515  
   516  	err := &cmdError{desc, out, importPath, needsPath}
   517  	if cmdErr != nil {
   518  		// The command failed. Report the output up as an error.
   519  		return err
   520  	}
   521  	// The command didn't fail, so just print the output as appropriate.
   522  	if a != nil && a.output != nil {
   523  		// The Action is capturing output.
   524  		a.output = append(a.output, err.Error()...)
   525  	} else {
   526  		// Write directly to the Builder output.
   527  		sh.Printf("%s", err)
   528  	}
   529  	return nil
   530  }
   531  
   532  // replacePrefix is like strings.ReplaceAll, but only replaces instances of old
   533  // that are preceded by ' ', '\t', or appear at the beginning of a line.
   534  func replacePrefix(s, old, new string) string {
   535  	n := strings.Count(s, old)
   536  	if n == 0 {
   537  		return s
   538  	}
   539  
   540  	s = strings.ReplaceAll(s, " "+old, " "+new)
   541  	s = strings.ReplaceAll(s, "\n"+old, "\n"+new)
   542  	s = strings.ReplaceAll(s, "\n\t"+old, "\n\t"+new)
   543  	if strings.HasPrefix(s, old) {
   544  		s = new + s[len(old):]
   545  	}
   546  	return s
   547  }
   548  
   549  type cmdError struct {
   550  	desc       string
   551  	text       string
   552  	importPath string
   553  	needsPath  bool // Set if desc does not already include the import path
   554  }
   555  
   556  func (e *cmdError) Error() string {
   557  	var msg string
   558  	if e.needsPath {
   559  		// Ensure the import path is part of the message.
   560  		// Clearly distinguish the description from the import path.
   561  		msg = fmt.Sprintf("# %s\n# [%s]\n", e.importPath, e.desc)
   562  	} else {
   563  		msg = "# " + e.desc + "\n"
   564  	}
   565  	return msg + e.text
   566  }
   567  
   568  func (e *cmdError) ImportPath() string {
   569  	return e.importPath
   570  }
   571  
   572  // run runs the command given by cmdline in the directory dir.
   573  // If the command fails, run prints information about the failure
   574  // and returns a non-nil error.
   575  func (sh *Shell) run(dir string, desc string, env []string, cmdargs ...any) error {
   576  	out, err := sh.runOut(dir, env, cmdargs...)
   577  	if desc == "" {
   578  		desc = sh.fmtCmd(dir, "%s", strings.Join(str.StringList(cmdargs...), " "))
   579  	}
   580  	return sh.reportCmd(desc, dir, out, err)
   581  }
   582  
   583  // runOut runs the command given by cmdline in the directory dir.
   584  // It returns the command output and any errors that occurred.
   585  // It accumulates execution time in a.
   586  func (sh *Shell) runOut(dir string, env []string, cmdargs ...any) ([]byte, error) {
   587  	sc, err := sh.startOut(dir, env, nil, nil, cmdargs...)
   588  	if err != nil || sc == nil {
   589  		return nil, err
   590  	}
   591  	return sc.wait()
   592  }
   593  
   594  func (sh *Shell) startOut(dir string, env []string, extraFiles []*os.File, done func(), cmdargs ...any) (*shellCmd, error) {
   595  	for _, f := range extraFiles {
   596  		defer f.Close()
   597  	}
   598  	a := sh.action
   599  
   600  	cmdline := str.StringList(cmdargs...)
   601  
   602  	for _, arg := range cmdline {
   603  		// GNU binutils commands, including gcc and gccgo, interpret an argument
   604  		// @foo anywhere in the command line (even following --) as meaning
   605  		// "read and insert arguments from the file named foo."
   606  		// Don't say anything that might be misinterpreted that way.
   607  		if strings.HasPrefix(arg, "@") {
   608  			return nil, fmt.Errorf("invalid command-line argument %s in command: %s", arg, joinUnambiguously(cmdline))
   609  		}
   610  	}
   611  
   612  	if cfg.BuildN || cfg.BuildX {
   613  		var envcmdline string
   614  		for _, e := range env {
   615  			if j := strings.IndexByte(e, '='); j != -1 {
   616  				if strings.ContainsRune(e[j+1:], '\'') {
   617  					envcmdline += fmt.Sprintf("%s=%q", e[:j], e[j+1:])
   618  				} else {
   619  					envcmdline += fmt.Sprintf("%s='%s'", e[:j], e[j+1:])
   620  				}
   621  				envcmdline += " "
   622  			}
   623  		}
   624  		envcmdline += joinUnambiguously(cmdline)
   625  		sh.ShowCmd(dir, "%s", envcmdline)
   626  		if cfg.BuildN {
   627  			return nil, nil
   628  		}
   629  	}
   630  
   631  	path, err := pathcache.LookPath(cmdline[0])
   632  	if err != nil {
   633  		return nil, err
   634  	}
   635  	cmd := exec.Command(path, cmdline[1:]...)
   636  	if cmd.Path != "" {
   637  		cmd.Args[0] = cmd.Path
   638  	}
   639  	sc := &shellCmd{sh: sh, cmd: cmd, cmdline: cmdline, done: done}
   640  	cmd.Stdout = &sc.buf
   641  	cmd.Stderr = &sc.buf
   642  	cmd.ExtraFiles = extraFiles
   643  	sc.cleanup = passLongArgsInResponseFiles(cmd)
   644  	if dir != "." {
   645  		cmd.Dir = dir
   646  	}
   647  	cmd.Env = cmd.Environ() // Pre-allocate with correct PWD.
   648  
   649  	// Add the TOOLEXEC_IMPORTPATH environment variable for -toolexec tools.
   650  	// It doesn't really matter if -toolexec isn't being used.
   651  	// Note that a.Package.Desc is not really an import path,
   652  	// but this is consistent with 'go list -f {{.ImportPath}}'.
   653  	// Plus, it is useful to uniquely identify packages in 'go list -json'.
   654  	if a != nil && a.Package != nil {
   655  		cmd.Env = append(cmd.Env, "TOOLEXEC_IMPORTPATH="+a.Package.Desc())
   656  	}
   657  
   658  	cmd.Env = append(cmd.Env, env...)
   659  	sc.start = time.Now()
   660  	if err := cmd.Start(); err != nil {
   661  		sc.cleanup()
   662  		return nil, fmt.Errorf("%s: %w", cmdline[0], err)
   663  	}
   664  	return sc, nil
   665  }
   666  
   667  type shellCmd struct {
   668  	sh      *Shell
   669  	cmd     *exec.Cmd
   670  	cmdline []string
   671  	buf     bytes.Buffer
   672  	start   time.Time
   673  	cleanup func()
   674  	done    func()
   675  }
   676  
   677  func (sc *shellCmd) wait() ([]byte, error) {
   678  	err := sc.cmd.Wait()
   679  	sc.cleanup()
   680  	if sc.done != nil {
   681  		sc.done()
   682  	}
   683  	if a := sc.sh.action; a != nil && a.json != nil {
   684  		aj := a.json
   685  		aj.Cmd = append(aj.Cmd, joinUnambiguously(sc.cmdline))
   686  		aj.CmdReal += time.Since(sc.start)
   687  		if ps := sc.cmd.ProcessState; ps != nil {
   688  			aj.CmdUser += ps.UserTime()
   689  			aj.CmdSys += ps.SystemTime()
   690  		}
   691  	}
   692  
   693  	// err can be something like 'exit status 1'.
   694  	// Add information about what program was running.
   695  	// Note that if buf.Bytes() is non-empty, the caller usually
   696  	// shows buf.Bytes() and does not print err at all, so the
   697  	// prefix here does not make most output any more verbose.
   698  	if err != nil {
   699  		err = fmt.Errorf("%s: %w", sc.cmdline[0], err)
   700  	}
   701  	return sc.buf.Bytes(), err
   702  }
   703  
   704  // joinUnambiguously prints the slice, quoting where necessary to make the
   705  // output unambiguous.
   706  // TODO: See issue 5279. The printing of commands needs a complete redo.
   707  func joinUnambiguously(a []string) string {
   708  	var buf strings.Builder
   709  	for i, s := range a {
   710  		if i > 0 {
   711  			buf.WriteByte(' ')
   712  		}
   713  		q := strconv.Quote(s)
   714  		// A gccgo command line can contain -( and -).
   715  		// Make sure we quote them since they are special to the shell.
   716  		// The trimpath argument can also contain > (part of =>) and ;. Quote those too.
   717  		if s == "" || strings.ContainsAny(s, " ()>;") || len(q) > len(s)+2 {
   718  			buf.WriteString(q)
   719  		} else {
   720  			buf.WriteString(s)
   721  		}
   722  	}
   723  	return buf.String()
   724  }
   725
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