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  	"errors"
    17  	"fmt"
    18  	"internal/lazyregexp"
    19  	"io"
    20  	"io/fs"
    21  	"os"
    22  	"os/exec"
    23  	"path/filepath"
    24  	"runtime"
    25  	"strconv"
    26  	"strings"
    27  	"sync"
    28  	"time"
    29  )
    30  
    31  // A Shell runs shell commands and performs shell-like file system operations.
    32  //
    33  // Shell tracks context related to running commands, and form a tree much like
    34  // context.Context.
    35  type Shell struct {
    36  	action       *Action // nil for the root shell
    37  	*shellShared         // per-Builder state shared across Shells
    38  }
    39  
    40  // shellShared is Shell state shared across all Shells derived from a single
    41  // root shell (generally a single Builder).
    42  type shellShared struct {
    43  	workDir string // $WORK, immutable
    44  
    45  	printLock sync.Mutex
    46  	printer   load.Printer
    47  	scriptDir string // current directory in printed script
    48  
    49  	mkdirCache par.Cache[string, error] // a cache of created directories
    50  }
    51  
    52  // NewShell returns a new Shell.
    53  //
    54  // Shell will internally serialize calls to the printer.
    55  // If printer is nil, it uses load.DefaultPrinter.
    56  func NewShell(workDir string, printer load.Printer) *Shell {
    57  	if printer == nil {
    58  		printer = load.DefaultPrinter()
    59  	}
    60  	shared := &shellShared{
    61  		workDir: workDir,
    62  		printer: printer,
    63  	}
    64  	return &Shell{shellShared: shared}
    65  }
    66  
    67  func (sh *Shell) pkg() *load.Package {
    68  	if sh.action == nil {
    69  		return nil
    70  	}
    71  	return sh.action.Package
    72  }
    73  
    74  // Printf emits a to this Shell's output stream, formatting it like fmt.Printf.
    75  // It is safe to call concurrently.
    76  func (sh *Shell) Printf(format string, a ...any) {
    77  	sh.printLock.Lock()
    78  	defer sh.printLock.Unlock()
    79  	sh.printer.Printf(sh.pkg(), format, a...)
    80  }
    81  
    82  func (sh *Shell) printfLocked(format string, a ...any) {
    83  	sh.printer.Printf(sh.pkg(), format, a...)
    84  }
    85  
    86  // Errorf reports an error on sh's package and sets the process exit status to 1.
    87  func (sh *Shell) Errorf(format string, a ...any) {
    88  	sh.printLock.Lock()
    89  	defer sh.printLock.Unlock()
    90  	sh.printer.Errorf(sh.pkg(), format, a...)
    91  }
    92  
    93  // WithAction returns a Shell identical to sh, but bound to Action a.
    94  func (sh *Shell) WithAction(a *Action) *Shell {
    95  	sh2 := *sh
    96  	sh2.action = a
    97  	return &sh2
    98  }
    99  
   100  // Shell returns a shell for running commands on behalf of Action a.
   101  func (b *Builder) Shell(a *Action) *Shell {
   102  	if a == nil {
   103  		// The root shell has a nil Action. The point of this method is to
   104  		// create a Shell bound to an Action, so disallow nil Actions here.
   105  		panic("nil Action")
   106  	}
   107  	if a.sh == nil {
   108  		a.sh = b.backgroundSh.WithAction(a)
   109  	}
   110  	return a.sh
   111  }
   112  
   113  // BackgroundShell returns a Builder-wide Shell that's not bound to any Action.
   114  // Try not to use this unless there's really no sensible Action available.
   115  func (b *Builder) BackgroundShell() *Shell {
   116  	return b.backgroundSh
   117  }
   118  
   119  // moveOrCopyFile is like 'mv src dst' or 'cp src dst'.
   120  func (sh *Shell) moveOrCopyFile(dst, src string, perm fs.FileMode, force bool) error {
   121  	if cfg.BuildN {
   122  		sh.ShowCmd("", "mv %s %s", src, dst)
   123  		return nil
   124  	}
   125  
   126  	// If we can update the mode and rename to the dst, do it.
   127  	// Otherwise fall back to standard copy.
   128  
   129  	// If the source is in the build cache, we need to copy it.
   130  	dir, _ := cache.DefaultDir()
   131  	if strings.HasPrefix(src, dir) {
   132  		return sh.CopyFile(dst, src, perm, force)
   133  	}
   134  
   135  	// On Windows, always copy the file, so that we respect the NTFS
   136  	// permissions of the parent folder. https://golang.org/issue/22343.
   137  	// What matters here is not cfg.Goos (the system we are building
   138  	// for) but runtime.GOOS (the system we are building on).
   139  	if runtime.GOOS == "windows" {
   140  		return sh.CopyFile(dst, src, perm, force)
   141  	}
   142  
   143  	// If the destination directory has the group sticky bit set,
   144  	// we have to copy the file to retain the correct permissions.
   145  	// https://golang.org/issue/18878
   146  	if fi, err := os.Stat(filepath.Dir(dst)); err == nil {
   147  		if fi.IsDir() && (fi.Mode()&fs.ModeSetgid) != 0 {
   148  			return sh.CopyFile(dst, src, perm, force)
   149  		}
   150  	}
   151  
   152  	// The perm argument is meant to be adjusted according to umask,
   153  	// but we don't know what the umask is.
   154  	// Create a dummy file to find out.
   155  	// This avoids build tags and works even on systems like Plan 9
   156  	// where the file mask computation incorporates other information.
   157  	mode := perm
   158  	f, err := os.OpenFile(filepath.Clean(dst)+"-go-tmp-umask", os.O_WRONLY|os.O_CREATE|os.O_EXCL, perm)
   159  	if err == nil {
   160  		fi, err := f.Stat()
   161  		if err == nil {
   162  			mode = fi.Mode() & 0777
   163  		}
   164  		name := f.Name()
   165  		f.Close()
   166  		os.Remove(name)
   167  	}
   168  
   169  	if err := os.Chmod(src, mode); err == nil {
   170  		if err := os.Rename(src, dst); err == nil {
   171  			if cfg.BuildX {
   172  				sh.ShowCmd("", "mv %s %s", src, dst)
   173  			}
   174  			return nil
   175  		}
   176  	}
   177  
   178  	return sh.CopyFile(dst, src, perm, force)
   179  }
   180  
   181  // copyFile is like 'cp src dst'.
   182  func (sh *Shell) CopyFile(dst, src string, perm fs.FileMode, force bool) error {
   183  	if cfg.BuildN || cfg.BuildX {
   184  		sh.ShowCmd("", "cp %s %s", src, dst)
   185  		if cfg.BuildN {
   186  			return nil
   187  		}
   188  	}
   189  
   190  	sf, err := os.Open(src)
   191  	if err != nil {
   192  		return err
   193  	}
   194  	defer sf.Close()
   195  
   196  	// Be careful about removing/overwriting dst.
   197  	// Do not remove/overwrite if dst exists and is a directory
   198  	// or a non-empty non-object file.
   199  	if fi, err := os.Stat(dst); err == nil {
   200  		if fi.IsDir() {
   201  			return fmt.Errorf("build output %q already exists and is a directory", dst)
   202  		}
   203  		if !force && fi.Mode().IsRegular() && fi.Size() != 0 && !isObject(dst) {
   204  			return fmt.Errorf("build output %q already exists and is not an object file", dst)
   205  		}
   206  	}
   207  
   208  	// On Windows, remove lingering ~ file from last attempt.
   209  	if runtime.GOOS == "windows" {
   210  		if _, err := os.Stat(dst + "~"); err == nil {
   211  			os.Remove(dst + "~")
   212  		}
   213  	}
   214  
   215  	mayberemovefile(dst)
   216  	df, err := os.OpenFile(dst, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, perm)
   217  	if err != nil && runtime.GOOS == "windows" {
   218  		// Windows does not allow deletion of a binary file
   219  		// while it is executing. Try to move it out of the way.
   220  		// If the move fails, which is likely, we'll try again the
   221  		// next time we do an install of this binary.
   222  		if err := os.Rename(dst, dst+"~"); err == nil {
   223  			os.Remove(dst + "~")
   224  		}
   225  		df, err = os.OpenFile(dst, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, perm)
   226  	}
   227  	if err != nil {
   228  		return fmt.Errorf("copying %s: %w", src, err) // err should already refer to dst
   229  	}
   230  
   231  	_, err = io.Copy(df, sf)
   232  	df.Close()
   233  	if err != nil {
   234  		mayberemovefile(dst)
   235  		return fmt.Errorf("copying %s to %s: %v", src, dst, err)
   236  	}
   237  	return nil
   238  }
   239  
   240  // mayberemovefile removes a file only if it is a regular file
   241  // When running as a user with sufficient privileges, we may delete
   242  // even device files, for example, which is not intended.
   243  func mayberemovefile(s string) {
   244  	if fi, err := os.Lstat(s); err == nil && !fi.Mode().IsRegular() {
   245  		return
   246  	}
   247  	os.Remove(s)
   248  }
   249  
   250  // writeFile writes the text to file.
   251  func (sh *Shell) writeFile(file string, text []byte) error {
   252  	if cfg.BuildN || cfg.BuildX {
   253  		switch {
   254  		case len(text) == 0:
   255  			sh.ShowCmd("", "echo -n > %s # internal", file)
   256  		case bytes.IndexByte(text, '\n') == len(text)-1:
   257  			// One line. Use a simpler "echo" command.
   258  			sh.ShowCmd("", "echo '%s' > %s # internal", bytes.TrimSuffix(text, []byte("\n")), file)
   259  		default:
   260  			// Use the most general form.
   261  			sh.ShowCmd("", "cat >%s << 'EOF' # internal\n%sEOF", file, text)
   262  		}
   263  	}
   264  	if cfg.BuildN {
   265  		return nil
   266  	}
   267  	return os.WriteFile(file, text, 0666)
   268  }
   269  
   270  // Mkdir makes the named directory.
   271  func (sh *Shell) Mkdir(dir string) error {
   272  	// Make Mkdir(a.Objdir) a no-op instead of an error when a.Objdir == "".
   273  	if dir == "" {
   274  		return nil
   275  	}
   276  
   277  	// We can be a little aggressive about being
   278  	// sure directories exist. Skip repeated calls.
   279  	return sh.mkdirCache.Do(dir, func() error {
   280  		if cfg.BuildN || cfg.BuildX {
   281  			sh.ShowCmd("", "mkdir -p %s", dir)
   282  			if cfg.BuildN {
   283  				return nil
   284  			}
   285  		}
   286  
   287  		return os.MkdirAll(dir, 0777)
   288  	})
   289  }
   290  
   291  // RemoveAll is like 'rm -rf'. It attempts to remove all paths even if there's
   292  // an error, and returns the first error.
   293  func (sh *Shell) RemoveAll(paths ...string) error {
   294  	if cfg.BuildN || cfg.BuildX {
   295  		// Don't say we are removing the directory if we never created it.
   296  		show := func() bool {
   297  			for _, path := range paths {
   298  				if _, ok := sh.mkdirCache.Get(path); ok {
   299  					return true
   300  				}
   301  				if _, err := os.Stat(path); !os.IsNotExist(err) {
   302  					return true
   303  				}
   304  			}
   305  			return false
   306  		}
   307  		if show() {
   308  			sh.ShowCmd("", "rm -rf %s", strings.Join(paths, " "))
   309  		}
   310  	}
   311  	if cfg.BuildN {
   312  		return nil
   313  	}
   314  
   315  	var err error
   316  	for _, path := range paths {
   317  		if err2 := os.RemoveAll(path); err2 != nil && err == nil {
   318  			err = err2
   319  		}
   320  	}
   321  	return err
   322  }
   323  
   324  // Symlink creates a symlink newname -> oldname.
   325  func (sh *Shell) Symlink(oldname, newname string) error {
   326  	// It's not an error to try to recreate an existing symlink.
   327  	if link, err := os.Readlink(newname); err == nil && link == oldname {
   328  		return nil
   329  	}
   330  
   331  	if cfg.BuildN || cfg.BuildX {
   332  		sh.ShowCmd("", "ln -s %s %s", oldname, newname)
   333  		if cfg.BuildN {
   334  			return nil
   335  		}
   336  	}
   337  	return os.Symlink(oldname, newname)
   338  }
   339  
   340  // fmtCmd formats a command in the manner of fmt.Sprintf but also:
   341  //
   342  //	fmtCmd replaces the value of b.WorkDir with $WORK.
   343  func (sh *Shell) fmtCmd(dir string, format string, args ...any) string {
   344  	cmd := fmt.Sprintf(format, args...)
   345  	if sh.workDir != "" && !strings.HasPrefix(cmd, "cat ") {
   346  		cmd = strings.ReplaceAll(cmd, sh.workDir, "$WORK")
   347  		escaped := strconv.Quote(sh.workDir)
   348  		escaped = escaped[1 : len(escaped)-1] // strip quote characters
   349  		if escaped != sh.workDir {
   350  			cmd = strings.ReplaceAll(cmd, escaped, "$WORK")
   351  		}
   352  	}
   353  	return cmd
   354  }
   355  
   356  // ShowCmd prints the given command to standard output
   357  // for the implementation of -n or -x.
   358  //
   359  // ShowCmd also replaces the name of the current script directory with dot (.)
   360  // but only when it is at the beginning of a space-separated token.
   361  //
   362  // If dir is not "" or "/" and not the current script directory, ShowCmd first
   363  // prints a "cd" command to switch to dir and updates the script directory.
   364  func (sh *Shell) ShowCmd(dir string, format string, args ...any) {
   365  	// Use the output lock directly so we can manage scriptDir.
   366  	sh.printLock.Lock()
   367  	defer sh.printLock.Unlock()
   368  
   369  	cmd := sh.fmtCmd(dir, format, args...)
   370  
   371  	if dir != "" && dir != "/" {
   372  		if dir != sh.scriptDir {
   373  			// Show changing to dir and update the current directory.
   374  			sh.printfLocked("%s", sh.fmtCmd("", "cd %s\n", dir))
   375  			sh.scriptDir = dir
   376  		}
   377  		// Replace scriptDir is our working directory. Replace it
   378  		// with "." in the command.
   379  		dot := " ."
   380  		if dir[len(dir)-1] == filepath.Separator {
   381  			dot += string(filepath.Separator)
   382  		}
   383  		cmd = strings.ReplaceAll(" "+cmd, " "+dir, dot)[1:]
   384  	}
   385  
   386  	sh.printfLocked("%s\n", cmd)
   387  }
   388  
   389  // reportCmd reports the output and exit status of a command. The cmdOut and
   390  // cmdErr arguments are the output and exit error of the command, respectively.
   391  //
   392  // The exact reporting behavior is as follows:
   393  //
   394  //	cmdOut  cmdErr  Result
   395  //	""      nil     print nothing, return nil
   396  //	!=""    nil     print output, return nil
   397  //	""      !=nil   print nothing, return cmdErr (later printed)
   398  //	!=""    !=nil   print nothing, ignore err, return output as error (later printed)
   399  //
   400  // reportCmd returns a non-nil error if and only if cmdErr != nil. It assumes
   401  // that the command output, if non-empty, is more detailed than the command
   402  // error (which is usually just an exit status), so prefers using the output as
   403  // the ultimate error. Typically, the caller should return this error from an
   404  // Action, which it will be printed by the Builder.
   405  //
   406  // reportCmd formats the output as "# desc" followed by the given output. The
   407  // output is expected to contain references to 'dir', usually the source
   408  // directory for the package that has failed to build. reportCmd rewrites
   409  // mentions of dir with a relative path to dir when the relative path is
   410  // shorter. This is usually more pleasant. For example, if fmt doesn't compile
   411  // and we are in src/html, the output is
   412  //
   413  //	$ go build
   414  //	# fmt
   415  //	../fmt/print.go:1090: undefined: asdf
   416  //	$
   417  //
   418  // instead of
   419  //
   420  //	$ go build
   421  //	# fmt
   422  //	/usr/gopher/go/src/fmt/print.go:1090: undefined: asdf
   423  //	$
   424  //
   425  // reportCmd also replaces references to the work directory with $WORK, replaces
   426  // cgo file paths with the original file path, and replaces cgo-mangled names
   427  // with "C.name".
   428  //
   429  // desc is optional. If "", a.Package.Desc() is used.
   430  //
   431  // dir is optional. If "", a.Package.Dir is used.
   432  func (sh *Shell) reportCmd(desc, dir string, cmdOut []byte, cmdErr error) error {
   433  	if len(cmdOut) == 0 && cmdErr == nil {
   434  		// Common case
   435  		return nil
   436  	}
   437  	if len(cmdOut) == 0 && cmdErr != nil {
   438  		// Just return the error.
   439  		//
   440  		// TODO: This is what we've done for a long time, but it may be a
   441  		// mistake because it loses all of the extra context and results in
   442  		// ultimately less descriptive output. We should probably just take the
   443  		// text of cmdErr as the output in this case and do everything we
   444  		// otherwise would. We could chain the errors if we feel like it.
   445  		return cmdErr
   446  	}
   447  
   448  	// Fetch defaults from the package.
   449  	var p *load.Package
   450  	a := sh.action
   451  	if a != nil {
   452  		p = a.Package
   453  	}
   454  	var importPath string
   455  	if p != nil {
   456  		importPath = p.ImportPath
   457  		if desc == "" {
   458  			desc = p.Desc()
   459  		}
   460  		if dir == "" {
   461  			dir = p.Dir
   462  		}
   463  	}
   464  
   465  	out := string(cmdOut)
   466  
   467  	if !strings.HasSuffix(out, "\n") {
   468  		out = out + "\n"
   469  	}
   470  
   471  	// Replace workDir with $WORK
   472  	out = replacePrefix(out, sh.workDir, "$WORK")
   473  
   474  	// Rewrite mentions of dir with a relative path to dir
   475  	// when the relative path is shorter.
   476  	for {
   477  		// Note that dir starts out long, something like
   478  		// /foo/bar/baz/root/a
   479  		// The target string to be reduced is something like
   480  		// (blah-blah-blah) /foo/bar/baz/root/sibling/whatever.go:blah:blah
   481  		// /foo/bar/baz/root/a doesn't match /foo/bar/baz/root/sibling, but the prefix
   482  		// /foo/bar/baz/root does.  And there may be other niblings sharing shorter
   483  		// prefixes, the only way to find them is to look.
   484  		// This doesn't always produce a relative path --
   485  		// /foo is shorter than ../../.., for example.
   486  		if reldir := base.ShortPath(dir); reldir != dir {
   487  			out = replacePrefix(out, dir, reldir)
   488  			if filepath.Separator == '\\' {
   489  				// Don't know why, sometimes this comes out with slashes, not backslashes.
   490  				wdir := strings.ReplaceAll(dir, "\\", "/")
   491  				out = replacePrefix(out, wdir, reldir)
   492  			}
   493  		}
   494  		dirP := filepath.Dir(dir)
   495  		if dir == dirP {
   496  			break
   497  		}
   498  		dir = dirP
   499  	}
   500  
   501  	// Fix up output referring to cgo-generated code to be more readable.
   502  	// Replace x.go:19[/tmp/.../x.cgo1.go:18] with x.go:19.
   503  	// Replace *[100]_Ctype_foo with *[100]C.foo.
   504  	// If we're using -x, assume we're debugging and want the full dump, so disable the rewrite.
   505  	if !cfg.BuildX && cgoLine.MatchString(out) {
   506  		out = cgoLine.ReplaceAllString(out, "")
   507  		out = cgoTypeSigRe.ReplaceAllString(out, "C.")
   508  	}
   509  
   510  	// Usually desc is already p.Desc(), but if not, signal cmdError.Error to
   511  	// add a line explicitly mentioning the import path.
   512  	needsPath := importPath != "" && p != nil && desc != p.Desc()
   513  
   514  	err := &cmdError{desc, out, importPath, needsPath}
   515  	if cmdErr != nil {
   516  		// The command failed. Report the output up as an error.
   517  		return err
   518  	}
   519  	// The command didn't fail, so just print the output as appropriate.
   520  	if a != nil && a.output != nil {
   521  		// The Action is capturing output.
   522  		a.output = append(a.output, err.Error()...)
   523  	} else {
   524  		// Write directly to the Builder output.
   525  		sh.Printf("%s", err)
   526  	}
   527  	return nil
   528  }
   529  
   530  // replacePrefix is like strings.ReplaceAll, but only replaces instances of old
   531  // that are preceded by ' ', '\t', or appear at the beginning of a line.
   532  func replacePrefix(s, old, new string) string {
   533  	n := strings.Count(s, old)
   534  	if n == 0 {
   535  		return s
   536  	}
   537  
   538  	s = strings.ReplaceAll(s, " "+old, " "+new)
   539  	s = strings.ReplaceAll(s, "\n"+old, "\n"+new)
   540  	s = strings.ReplaceAll(s, "\n\t"+old, "\n\t"+new)
   541  	if strings.HasPrefix(s, old) {
   542  		s = new + s[len(old):]
   543  	}
   544  	return s
   545  }
   546  
   547  type cmdError struct {
   548  	desc       string
   549  	text       string
   550  	importPath string
   551  	needsPath  bool // Set if desc does not already include the import path
   552  }
   553  
   554  func (e *cmdError) Error() string {
   555  	var msg string
   556  	if e.needsPath {
   557  		// Ensure the import path is part of the message.
   558  		// Clearly distinguish the description from the import path.
   559  		msg = fmt.Sprintf("# %s\n# [%s]\n", e.importPath, e.desc)
   560  	} else {
   561  		msg = "# " + e.desc + "\n"
   562  	}
   563  	return msg + e.text
   564  }
   565  
   566  func (e *cmdError) ImportPath() string {
   567  	return e.importPath
   568  }
   569  
   570  var cgoLine = lazyregexp.New(`\[[^\[\]]+\.(cgo1|cover)\.go:[0-9]+(:[0-9]+)?\]`)
   571  var cgoTypeSigRe = lazyregexp.New(`\b_C2?(type|func|var|macro)_\B`)
   572  
   573  // run runs the command given by cmdline in the directory dir.
   574  // If the command fails, run prints information about the failure
   575  // and returns a non-nil error.
   576  func (sh *Shell) run(dir string, desc string, env []string, cmdargs ...any) error {
   577  	out, err := sh.runOut(dir, env, cmdargs...)
   578  	if desc == "" {
   579  		desc = sh.fmtCmd(dir, "%s", strings.Join(str.StringList(cmdargs...), " "))
   580  	}
   581  	return sh.reportCmd(desc, dir, out, err)
   582  }
   583  
   584  // runOut runs the command given by cmdline in the directory dir.
   585  // It returns the command output and any errors that occurred.
   586  // It accumulates execution time in a.
   587  func (sh *Shell) runOut(dir string, env []string, cmdargs ...any) ([]byte, error) {
   588  	a := sh.action
   589  
   590  	cmdline := str.StringList(cmdargs...)
   591  
   592  	for _, arg := range cmdline {
   593  		// GNU binutils commands, including gcc and gccgo, interpret an argument
   594  		// @foo anywhere in the command line (even following --) as meaning
   595  		// "read and insert arguments from the file named foo."
   596  		// Don't say anything that might be misinterpreted that way.
   597  		if strings.HasPrefix(arg, "@") {
   598  			return nil, fmt.Errorf("invalid command-line argument %s in command: %s", arg, joinUnambiguously(cmdline))
   599  		}
   600  	}
   601  
   602  	if cfg.BuildN || cfg.BuildX {
   603  		var envcmdline string
   604  		for _, e := range env {
   605  			if j := strings.IndexByte(e, '='); j != -1 {
   606  				if strings.ContainsRune(e[j+1:], '\'') {
   607  					envcmdline += fmt.Sprintf("%s=%q", e[:j], e[j+1:])
   608  				} else {
   609  					envcmdline += fmt.Sprintf("%s='%s'", e[:j], e[j+1:])
   610  				}
   611  				envcmdline += " "
   612  			}
   613  		}
   614  		envcmdline += joinUnambiguously(cmdline)
   615  		sh.ShowCmd(dir, "%s", envcmdline)
   616  		if cfg.BuildN {
   617  			return nil, nil
   618  		}
   619  	}
   620  
   621  	var buf bytes.Buffer
   622  	path, err := pathcache.LookPath(cmdline[0])
   623  	if err != nil {
   624  		return nil, err
   625  	}
   626  	cmd := exec.Command(path, cmdline[1:]...)
   627  	if cmd.Path != "" {
   628  		cmd.Args[0] = cmd.Path
   629  	}
   630  	cmd.Stdout = &buf
   631  	cmd.Stderr = &buf
   632  	cleanup := passLongArgsInResponseFiles(cmd)
   633  	defer cleanup()
   634  	if dir != "." {
   635  		cmd.Dir = dir
   636  	}
   637  	cmd.Env = cmd.Environ() // Pre-allocate with correct PWD.
   638  
   639  	// Add the TOOLEXEC_IMPORTPATH environment variable for -toolexec tools.
   640  	// It doesn't really matter if -toolexec isn't being used.
   641  	// Note that a.Package.Desc is not really an import path,
   642  	// but this is consistent with 'go list -f {{.ImportPath}}'.
   643  	// Plus, it is useful to uniquely identify packages in 'go list -json'.
   644  	if a != nil && a.Package != nil {
   645  		cmd.Env = append(cmd.Env, "TOOLEXEC_IMPORTPATH="+a.Package.Desc())
   646  	}
   647  
   648  	cmd.Env = append(cmd.Env, env...)
   649  	start := time.Now()
   650  	err = cmd.Run()
   651  	if a != nil && a.json != nil {
   652  		aj := a.json
   653  		aj.Cmd = append(aj.Cmd, joinUnambiguously(cmdline))
   654  		aj.CmdReal += time.Since(start)
   655  		if ps := cmd.ProcessState; ps != nil {
   656  			aj.CmdUser += ps.UserTime()
   657  			aj.CmdSys += ps.SystemTime()
   658  		}
   659  	}
   660  
   661  	// err can be something like 'exit status 1'.
   662  	// Add information about what program was running.
   663  	// Note that if buf.Bytes() is non-empty, the caller usually
   664  	// shows buf.Bytes() and does not print err at all, so the
   665  	// prefix here does not make most output any more verbose.
   666  	if err != nil {
   667  		err = errors.New(cmdline[0] + ": " + err.Error())
   668  	}
   669  	return buf.Bytes(), err
   670  }
   671  
   672  // joinUnambiguously prints the slice, quoting where necessary to make the
   673  // output unambiguous.
   674  // TODO: See issue 5279. The printing of commands needs a complete redo.
   675  func joinUnambiguously(a []string) string {
   676  	var buf strings.Builder
   677  	for i, s := range a {
   678  		if i > 0 {
   679  			buf.WriteByte(' ')
   680  		}
   681  		q := strconv.Quote(s)
   682  		// A gccgo command line can contain -( and -).
   683  		// Make sure we quote them since they are special to the shell.
   684  		// The trimpath argument can also contain > (part of =>) and ;. Quote those too.
   685  		if s == "" || strings.ContainsAny(s, " ()>;") || len(q) > len(s)+2 {
   686  			buf.WriteString(q)
   687  		} else {
   688  			buf.WriteString(s)
   689  		}
   690  	}
   691  	return buf.String()
   692  }
   693
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