internal/gocommand/invoke.go - tools - Git at Google

 // Copyright 2020 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 gocommand is a helper for calling the go command.
 package gocommand

 import (
 	"bytes"
 	"context"
 	"errors"
 	"fmt"
 	"io"
 	"log"
 	"os"
 	"reflect"
 	"regexp"
 	"runtime"
 	"strconv"
 	"strings"
 	"sync"
 	"time"

 	exec "golang.org/x/sys/execabs"

 	"golang.org/x/tools/internal/event"
 	"golang.org/x/tools/internal/event/keys"
 	"golang.org/x/tools/internal/event/label"
 	"golang.org/x/tools/internal/event/tag"
 )

 // An Runner will run go command invocations and serialize
 // them if it sees a concurrency error.
 type Runner struct {
 	// once guards the runner initialization.
 	once sync.Once

 	// inFlight tracks available workers.
 	inFlight chan struct{}

 	// serialized guards the ability to run a go command serially,
 	// to avoid deadlocks when claiming workers.
 	serialized chan struct{}
 }

 const maxInFlight = 10

 func (runner *Runner) initialize() {
 	runner.once.Do(func() {
 		runner.inFlight = make(chan struct{}, maxInFlight)
 		runner.serialized = make(chan struct{}, 1)
 	})
 }

 // 1.13: go: updates to go.mod needed, but contents have changed
 // 1.14: go: updating go.mod: existing contents have changed since last read
 var modConcurrencyError = regexp.MustCompile(`go:.*go.mod.*contents have changed`)

 // verb is an event label for the go command verb.
 var verb = keys.NewString("verb", "go command verb")

 func invLabels(inv Invocation) []label.Label {
 	return []label.Label{verb.Of(inv.Verb), tag.Directory.Of(inv.WorkingDir)}
 }

 // Run is a convenience wrapper around RunRaw.
 // It returns only stdout and a "friendly" error.
 func (runner *Runner) Run(ctx context.Context, inv Invocation) (*bytes.Buffer, error) {
 	ctx, done := event.Start(ctx, "gocommand.Runner.Run", invLabels(inv)...)
 	defer done()

 	stdout, _, friendly, _ := runner.RunRaw(ctx, inv)
 	return stdout, friendly
 }

 // RunPiped runs the invocation serially, always waiting for any concurrent
 // invocations to complete first.
 func (runner *Runner) RunPiped(ctx context.Context, inv Invocation, stdout, stderr io.Writer) error {
 	ctx, done := event.Start(ctx, "gocommand.Runner.RunPiped", invLabels(inv)...)
 	defer done()

 	_, err := runner.runPiped(ctx, inv, stdout, stderr)
 	return err
 }

 // RunRaw runs the invocation, serializing requests only if they fight over
 // go.mod changes.
 func (runner *Runner) RunRaw(ctx context.Context, inv Invocation) (*bytes.Buffer, *bytes.Buffer, error, error) {
 	ctx, done := event.Start(ctx, "gocommand.Runner.RunRaw", invLabels(inv)...)
 	defer done()
 	// Make sure the runner is always initialized.
 	runner.initialize()

 	// First, try to run the go command concurrently.
 	stdout, stderr, friendlyErr, err := runner.runConcurrent(ctx, inv)

 	// If we encounter a load concurrency error, we need to retry serially.
 	if friendlyErr == nil || !modConcurrencyError.MatchString(friendlyErr.Error()) {
 		return stdout, stderr, friendlyErr, err
 	}
 	event.Error(ctx, "Load concurrency error, will retry serially", err)

 	// Run serially by calling runPiped.
 	stdout.Reset()
 	stderr.Reset()
 	friendlyErr, err = runner.runPiped(ctx, inv, stdout, stderr)
 	return stdout, stderr, friendlyErr, err
 }

 func (runner *Runner) runConcurrent(ctx context.Context, inv Invocation) (*bytes.Buffer, *bytes.Buffer, error, error) {
 	// Wait for 1 worker to become available.
 	select {
 	case <-ctx.Done():
 		return nil, nil, nil, ctx.Err()
 	case runner.inFlight <- struct{}{}:
 		defer func() { <-runner.inFlight }()
 	}

 	stdout, stderr := &bytes.Buffer{}, &bytes.Buffer{}
 	friendlyErr, err := inv.runWithFriendlyError(ctx, stdout, stderr)
 	return stdout, stderr, friendlyErr, err
 }

 func (runner *Runner) runPiped(ctx context.Context, inv Invocation, stdout, stderr io.Writer) (error, error) {
 	// Make sure the runner is always initialized.
 	runner.initialize()

 	// Acquire the serialization lock. This avoids deadlocks between two
 	// runPiped commands.
 	select {
 	case <-ctx.Done():
 		return nil, ctx.Err()
 	case runner.serialized <- struct{}{}:
 		defer func() { <-runner.serialized }()
 	}

 	// Wait for all in-progress go commands to return before proceeding,
 	// to avoid load concurrency errors.
 	for i := 0; i < maxInFlight; i++ {
 		select {
 		case <-ctx.Done():
 			return nil, ctx.Err()
 		case runner.inFlight <- struct{}{}:
 			// Make sure we always "return" any workers we took.
 			defer func() { <-runner.inFlight }()
 		}
 	}

 	return inv.runWithFriendlyError(ctx, stdout, stderr)
 }

 // An Invocation represents a call to the go command.
 type Invocation struct {
 	Verb       string
 	Args       []string
 	BuildFlags []string

 	// If ModFlag is set, the go command is invoked with -mod=ModFlag.
 	ModFlag string

 	// If ModFile is set, the go command is invoked with -modfile=ModFile.
 	ModFile string

 	// If Overlay is set, the go command is invoked with -overlay=Overlay.
 	Overlay string

 	// If CleanEnv is set, the invocation will run only with the environment
 	// in Env, not starting with os.Environ.
 	CleanEnv   bool
 	Env        []string
 	WorkingDir string
 	Logf       func(format string, args ...interface{})
 }

 func (i *Invocation) runWithFriendlyError(ctx context.Context, stdout, stderr io.Writer) (friendlyError error, rawError error) {
 	rawError = i.run(ctx, stdout, stderr)
 	if rawError != nil {
 		friendlyError = rawError
 		// Check for 'go' executable not being found.
 		if ee, ok := rawError.(*exec.Error); ok && ee.Err == exec.ErrNotFound {
 			friendlyError = fmt.Errorf("go command required, not found: %v", ee)
 		}
 		if ctx.Err() != nil {
 			friendlyError = ctx.Err()
 		}
 		friendlyError = fmt.Errorf("err: %v: stderr: %s", friendlyError, stderr)
 	}
 	return
 }

 func (i *Invocation) run(ctx context.Context, stdout, stderr io.Writer) error {
 	log := i.Logf
 	if log == nil {
 		log = func(string, ...interface{}) {}
 	}

 	goArgs := []string{i.Verb}

 	appendModFile := func() {
 		if i.ModFile != "" {
 			goArgs = append(goArgs, "-modfile="+i.ModFile)
 		}
 	}
 	appendModFlag := func() {
 		if i.ModFlag != "" {
 			goArgs = append(goArgs, "-mod="+i.ModFlag)
 		}
 	}
 	appendOverlayFlag := func() {
 		if i.Overlay != "" {
 			goArgs = append(goArgs, "-overlay="+i.Overlay)
 		}
 	}

 	switch i.Verb {
 	case "env", "version":
 		goArgs = append(goArgs, i.Args...)
 	case "mod":
 		// mod needs the sub-verb before flags.
 		goArgs = append(goArgs, i.Args[0])
 		appendModFile()
 		goArgs = append(goArgs, i.Args[1:]...)
 	case "get":
 		goArgs = append(goArgs, i.BuildFlags...)
 		appendModFile()
 		goArgs = append(goArgs, i.Args...)

 	default: // notably list and build.
 		goArgs = append(goArgs, i.BuildFlags...)
 		appendModFile()
 		appendModFlag()
 		appendOverlayFlag()
 		goArgs = append(goArgs, i.Args...)
 	}
 	cmd := exec.Command("go", goArgs...)
 	cmd.Stdout = stdout
 	cmd.Stderr = stderr

 	// cmd.WaitDelay was added only in go1.20 (see #50436).
 	if waitDelay := reflect.ValueOf(cmd).Elem().FieldByName("WaitDelay"); waitDelay.IsValid() {
 		// https://go.dev/issue/59541: don't wait forever copying stderr
 		// after the command has exited.
 		// After CL 484741 we copy stdout manually, so we we'll stop reading that as
 		// soon as ctx is done. However, we also don't want to wait around forever
 		// for stderr. Give a much-longer-than-reasonable delay and then assume that
 		// something has wedged in the kernel or runtime.
 		waitDelay.Set(reflect.ValueOf(30 * time.Second))
 	}

 	// On darwin the cwd gets resolved to the real path, which breaks anything that
 	// expects the working directory to keep the original path, including the
 	// go command when dealing with modules.
 	// The Go stdlib has a special feature where if the cwd and the PWD are the
 	// same node then it trusts the PWD, so by setting it in the env for the child
 	// process we fix up all the paths returned by the go command.
 	if !i.CleanEnv {
 		cmd.Env = os.Environ()
 	}
 	cmd.Env = append(cmd.Env, i.Env...)
 	if i.WorkingDir != "" {
 		cmd.Env = append(cmd.Env, "PWD="+i.WorkingDir)
 		cmd.Dir = i.WorkingDir
 	}

 	defer func(start time.Time) { log("%s for %v", time.Since(start), cmdDebugStr(cmd)) }(time.Now())

 	return runCmdContext(ctx, cmd)
 }

 // DebugHangingGoCommands may be set by tests to enable additional
 // instrumentation (including panics) for debugging hanging Go commands.
 //
 // See golang/go#54461 for details.
 var DebugHangingGoCommands = false

 // runCmdContext is like exec.CommandContext except it sends os.Interrupt
 // before os.Kill.
 func runCmdContext(ctx context.Context, cmd *exec.Cmd) (err error) {
 	// If cmd.Stdout is not an *os.File, the exec package will create a pipe and
 	// copy it to the Writer in a goroutine until the process has finished and
 	// either the pipe reaches EOF or command's WaitDelay expires.
 	//
 	// However, the output from 'go list' can be quite large, and we don't want to
 	// keep reading (and allocating buffers) if we've already decided we don't
 	// care about the output. We don't want to wait for the process to finish, and
 	// we don't wait to wait for the WaitDelay to expire either.
 	//
 	// Instead, if cmd.Stdout requires a copying goroutine we explicitly replace
 	// it with a pipe (which is an *os.File), which we can close in order to stop
 	// copying output as soon as we realize we don't care about it.
 	var stdoutW *os.File
 	if cmd.Stdout != nil {
 		if _, ok := cmd.Stdout.(*os.File); !ok {
 			var stdoutR *os.File
 			stdoutR, stdoutW, err = os.Pipe()
 			if err != nil {
 				return err
 			}
 			prevStdout := cmd.Stdout
 			cmd.Stdout = stdoutW

 			stdoutErr := make(chan error, 1)
 			go func() {
 				_, err := io.Copy(prevStdout, stdoutR)
 				if err != nil {
 					err = fmt.Errorf("copying stdout: %w", err)
 				}
 				stdoutErr <- err
 			}()
 			defer func() {
 				// We started a goroutine to copy a stdout pipe.
 				// Wait for it to finish, or terminate it if need be.
 				var err2 error
 				select {
 				case err2 = <-stdoutErr:
 					stdoutR.Close()
 				case <-ctx.Done():
 					stdoutR.Close()
 					// Per https://pkg.go.dev/os#File.Close, the call to stdoutR.Close
 					// should cause the Read call in io.Copy to unblock and return
 					// immediately, but we still need to receive from stdoutErr to confirm
 					// that that has happened.
 					<-stdoutErr
 					err2 = ctx.Err()
 				}
 				if err == nil {
 					err = err2
 				}
 			}()

 			// Per https://pkg.go.dev/os/exec#Cmd, “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.”
 			//
 			// Since we're starting a goroutine that writes to cmd.Stdout, we must
 			// also update cmd.Stderr so that that still holds.
 			func() {
 				defer func() { recover() }()
 				if cmd.Stderr == prevStdout {
 					cmd.Stderr = cmd.Stdout
 				}
 			}()
 		}
 	}

 	err = cmd.Start()
 	if stdoutW != nil {
 		// The child process has inherited the pipe file,
 		// so close the copy held in this process.
 		stdoutW.Close()
 		stdoutW = nil
 	}
 	if err != nil {
 		return err
 	}

 	resChan := make(chan error, 1)
 	go func() {
 		resChan <- cmd.Wait()
 	}()

 	// If we're interested in debugging hanging Go commands, stop waiting after a
 	// minute and panic with interesting information.
 	debug := DebugHangingGoCommands
 	if debug {
 		timer := time.NewTimer(1 * time.Minute)
 		defer timer.Stop()
 		select {
 		case err := <-resChan:
 			return err
 		case <-timer.C:
 			HandleHangingGoCommand(cmd.Process)
 		case <-ctx.Done():
 		}
 	} else {
 		select {
 		case err := <-resChan:
 			return err
 		case <-ctx.Done():
 		}
 	}

 	// Cancelled. Interrupt and see if it ends voluntarily.
 	if err := cmd.Process.Signal(os.Interrupt); err == nil {
 		// (We used to wait only 1s but this proved
 		// fragile on loaded builder machines.)
 		timer := time.NewTimer(5 * time.Second)
 		defer timer.Stop()
 		select {
 		case err := <-resChan:
 			return err
 		case <-timer.C:
 		}
 	}

 	// Didn't shut down in response to interrupt. Kill it hard.
 	// TODO(rfindley): per advice from bcmills@, it may be better to send SIGQUIT
 	// on certain platforms, such as unix.
 	if err := cmd.Process.Kill(); err != nil && !errors.Is(err, os.ErrProcessDone) && debug {
 		log.Printf("error killing the Go command: %v", err)
 	}

 	return <-resChan
 }

 func HandleHangingGoCommand(proc *os.Process) {
 	switch runtime.GOOS {
 	case "linux", "darwin", "freebsd", "netbsd":
 		fmt.Fprintln(os.Stderr, `DETECTED A HANGING GO COMMAND

 The gopls test runner has detected a hanging go command. In order to debug
 this, the output of ps and lsof/fstat is printed below.

 See golang/go#54461 for more details.`)

 		fmt.Fprintln(os.Stderr, "\nps axo ppid,pid,command:")
 		fmt.Fprintln(os.Stderr, "-------------------------")
 		psCmd := exec.Command("ps", "axo", "ppid,pid,command")
 		psCmd.Stdout = os.Stderr
 		psCmd.Stderr = os.Stderr
 		if err := psCmd.Run(); err != nil {
 			panic(fmt.Sprintf("running ps: %v", err))
 		}

 		listFiles := "lsof"
 		if runtime.GOOS == "freebsd" || runtime.GOOS == "netbsd" {
 			listFiles = "fstat"
 		}

 		fmt.Fprintln(os.Stderr, "\n"+listFiles+":")
 		fmt.Fprintln(os.Stderr, "-----")
 		listFilesCmd := exec.Command(listFiles)
 		listFilesCmd.Stdout = os.Stderr
 		listFilesCmd.Stderr = os.Stderr
 		if err := listFilesCmd.Run(); err != nil {
 			panic(fmt.Sprintf("running %s: %v", listFiles, err))
 		}
 	}
 	panic(fmt.Sprintf("detected hanging go command (pid %d): see golang/go#54461 for more details", proc.Pid))
 }

 func cmdDebugStr(cmd *exec.Cmd) string {
 	env := make(map[string]string)
 	for _, kv := range cmd.Env {
 		split := strings.SplitN(kv, "=", 2)
 		if len(split) == 2 {
 			k, v := split[0], split[1]
 			env[k] = v
 		}
 	}

 	var args []string
 	for _, arg := range cmd.Args {
 		quoted := strconv.Quote(arg)
 		if quoted[1:len(quoted)-1] != arg || strings.Contains(arg, " ") {
 			args = append(args, quoted)
 		} else {
 			args = append(args, arg)
 		}
 	}
 	return fmt.Sprintf("GOROOT=%v GOPATH=%v GO111MODULE=%v GOPROXY=%v PWD=%v %v", env["GOROOT"], env["GOPATH"], env["GO111MODULE"], env["GOPROXY"], env["PWD"], strings.Join(args, " "))
 }
	// Copyright 2020 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 gocommand is a helper for calling the go command.
	package gocommand

	import (
	"bytes"
	"context"
	"errors"
	"fmt"
	"io"
	"log"
	"os"
	"reflect"
	"regexp"
	"runtime"
	"strconv"
	"strings"
	"sync"
	"time"

	exec "golang.org/x/sys/execabs"

	"golang.org/x/tools/internal/event"
	"golang.org/x/tools/internal/event/keys"
	"golang.org/x/tools/internal/event/label"
	"golang.org/x/tools/internal/event/tag"
	)

	// An Runner will run go command invocations and serialize
	// them if it sees a concurrency error.
	type Runner struct {
	// once guards the runner initialization.
	once sync.Once

	// inFlight tracks available workers.
	inFlight chan struct{}

	// serialized guards the ability to run a go command serially,
	// to avoid deadlocks when claiming workers.
	serialized chan struct{}
	}

	const maxInFlight = 10

	func (runner *Runner) initialize() {
	runner.once.Do(func() {
	runner.inFlight = make(chan struct{}, maxInFlight)
	runner.serialized = make(chan struct{}, 1)
	})
	}

	// 1.13: go: updates to go.mod needed, but contents have changed
	// 1.14: go: updating go.mod: existing contents have changed since last read
	var modConcurrencyError = regexp.MustCompile(`go:.go.mod.contents have changed`)

	// verb is an event label for the go command verb.
	var verb = keys.NewString("verb", "go command verb")

	func invLabels(inv Invocation) []label.Label {
	return []label.Label{verb.Of(inv.Verb), tag.Directory.Of(inv.WorkingDir)}
	}

	// Run is a convenience wrapper around RunRaw.
	// It returns only stdout and a "friendly" error.
	func (runner Runner) Run(ctx context.Context, inv Invocation) (bytes.Buffer, error) {
	ctx, done := event.Start(ctx, "gocommand.Runner.Run", invLabels(inv)...)
	defer done()

	stdout, _, friendly, _ := runner.RunRaw(ctx, inv)
	return stdout, friendly
	}

	// RunPiped runs the invocation serially, always waiting for any concurrent
	// invocations to complete first.
	func (runner *Runner) RunPiped(ctx context.Context, inv Invocation, stdout, stderr io.Writer) error {
	ctx, done := event.Start(ctx, "gocommand.Runner.RunPiped", invLabels(inv)...)
	defer done()

	_, err := runner.runPiped(ctx, inv, stdout, stderr)
	return err
	}

	// RunRaw runs the invocation, serializing requests only if they fight over
	// go.mod changes.
	func (runner Runner) RunRaw(ctx context.Context, inv Invocation) (bytes.Buffer, *bytes.Buffer, error, error) {
	ctx, done := event.Start(ctx, "gocommand.Runner.RunRaw", invLabels(inv)...)
	defer done()
	// Make sure the runner is always initialized.
	runner.initialize()

	// First, try to run the go command concurrently.
	stdout, stderr, friendlyErr, err := runner.runConcurrent(ctx, inv)

	// If we encounter a load concurrency error, we need to retry serially.
	if friendlyErr == nil \|\| !modConcurrencyError.MatchString(friendlyErr.Error()) {
	return stdout, stderr, friendlyErr, err
	}
	event.Error(ctx, "Load concurrency error, will retry serially", err)

	// Run serially by calling runPiped.
	stdout.Reset()
	stderr.Reset()
	friendlyErr, err = runner.runPiped(ctx, inv, stdout, stderr)
	return stdout, stderr, friendlyErr, err
	}

	func (runner Runner) runConcurrent(ctx context.Context, inv Invocation) (bytes.Buffer, *bytes.Buffer, error, error) {
	// Wait for 1 worker to become available.
	select {
	case <-ctx.Done():
	return nil, nil, nil, ctx.Err()
	case runner.inFlight <- struct{}{}:
	defer func() { <-runner.inFlight }()
	}

	stdout, stderr := &bytes.Buffer{}, &bytes.Buffer{}
	friendlyErr, err := inv.runWithFriendlyError(ctx, stdout, stderr)
	return stdout, stderr, friendlyErr, err
	}

	func (runner *Runner) runPiped(ctx context.Context, inv Invocation, stdout, stderr io.Writer) (error, error) {
	// Make sure the runner is always initialized.
	runner.initialize()

	// Acquire the serialization lock. This avoids deadlocks between two
	// runPiped commands.
	select {
	case <-ctx.Done():
	return nil, ctx.Err()
	case runner.serialized <- struct{}{}:
	defer func() { <-runner.serialized }()
	}

	// Wait for all in-progress go commands to return before proceeding,
	// to avoid load concurrency errors.
	for i := 0; i < maxInFlight; i++ {
	select {
	case <-ctx.Done():
	return nil, ctx.Err()
	case runner.inFlight <- struct{}{}:
	// Make sure we always "return" any workers we took.
	defer func() { <-runner.inFlight }()
	}
	}

	return inv.runWithFriendlyError(ctx, stdout, stderr)
	}

	// An Invocation represents a call to the go command.
	type Invocation struct {
	Verb string
	Args []string
	BuildFlags []string

	// If ModFlag is set, the go command is invoked with -mod=ModFlag.
	ModFlag string

	// If ModFile is set, the go command is invoked with -modfile=ModFile.
	ModFile string

	// If Overlay is set, the go command is invoked with -overlay=Overlay.
	Overlay string

	// If CleanEnv is set, the invocation will run only with the environment
	// in Env, not starting with os.Environ.
	CleanEnv bool
	Env []string
	WorkingDir string
	Logf func(format string, args ...interface{})
	}

	func (i *Invocation) runWithFriendlyError(ctx context.Context, stdout, stderr io.Writer) (friendlyError error, rawError error) {
	rawError = i.run(ctx, stdout, stderr)
	if rawError != nil {
	friendlyError = rawError
	// Check for 'go' executable not being found.
	if ee, ok := rawError.(*exec.Error); ok && ee.Err == exec.ErrNotFound {
	friendlyError = fmt.Errorf("go command required, not found: %v", ee)
	}
	if ctx.Err() != nil {
	friendlyError = ctx.Err()
	}
	friendlyError = fmt.Errorf("err: %v: stderr: %s", friendlyError, stderr)
	}
	return
	}

	func (i *Invocation) run(ctx context.Context, stdout, stderr io.Writer) error {
	log := i.Logf
	if log == nil {
	log = func(string, ...interface{}) {}
	}

	goArgs := []string{i.Verb}

	appendModFile := func() {
	if i.ModFile != "" {
	goArgs = append(goArgs, "-modfile="+i.ModFile)
	}
	}
	appendModFlag := func() {
	if i.ModFlag != "" {
	goArgs = append(goArgs, "-mod="+i.ModFlag)
	}
	}
	appendOverlayFlag := func() {
	if i.Overlay != "" {
	goArgs = append(goArgs, "-overlay="+i.Overlay)
	}
	}

	switch i.Verb {
	case "env", "version":
	goArgs = append(goArgs, i.Args...)
	case "mod":
	// mod needs the sub-verb before flags.
	goArgs = append(goArgs, i.Args[0])
	appendModFile()
	goArgs = append(goArgs, i.Args[1:]...)
	case "get":
	goArgs = append(goArgs, i.BuildFlags...)
	appendModFile()
	goArgs = append(goArgs, i.Args...)

	default: // notably list and build.
	goArgs = append(goArgs, i.BuildFlags...)
	appendModFile()
	appendModFlag()
	appendOverlayFlag()
	goArgs = append(goArgs, i.Args...)
	}
	cmd := exec.Command("go", goArgs...)
	cmd.Stdout = stdout
	cmd.Stderr = stderr

	// cmd.WaitDelay was added only in go1.20 (see #50436).
	if waitDelay := reflect.ValueOf(cmd).Elem().FieldByName("WaitDelay"); waitDelay.IsValid() {
	// https://go.dev/issue/59541: don't wait forever copying stderr
	// after the command has exited.
	// After CL 484741 we copy stdout manually, so we we'll stop reading that as
	// soon as ctx is done. However, we also don't want to wait around forever
	// for stderr. Give a much-longer-than-reasonable delay and then assume that
	// something has wedged in the kernel or runtime.
	waitDelay.Set(reflect.ValueOf(30 * time.Second))
	}

	// On darwin the cwd gets resolved to the real path, which breaks anything that
	// expects the working directory to keep the original path, including the
	// go command when dealing with modules.
	// The Go stdlib has a special feature where if the cwd and the PWD are the
	// same node then it trusts the PWD, so by setting it in the env for the child
	// process we fix up all the paths returned by the go command.
	if !i.CleanEnv {
	cmd.Env = os.Environ()
	}
	cmd.Env = append(cmd.Env, i.Env...)
	if i.WorkingDir != "" {
	cmd.Env = append(cmd.Env, "PWD="+i.WorkingDir)
	cmd.Dir = i.WorkingDir
	}

	defer func(start time.Time) { log("%s for %v", time.Since(start), cmdDebugStr(cmd)) }(time.Now())

	return runCmdContext(ctx, cmd)
	}

	// DebugHangingGoCommands may be set by tests to enable additional
	// instrumentation (including panics) for debugging hanging Go commands.
	//
	// See golang/go#54461 for details.
	var DebugHangingGoCommands = false

	// runCmdContext is like exec.CommandContext except it sends os.Interrupt
	// before os.Kill.
	func runCmdContext(ctx context.Context, cmd *exec.Cmd) (err error) {
	// If cmd.Stdout is not an *os.File, the exec package will create a pipe and
	// copy it to the Writer in a goroutine until the process has finished and
	// either the pipe reaches EOF or command's WaitDelay expires.
	//
	// However, the output from 'go list' can be quite large, and we don't want to
	// keep reading (and allocating buffers) if we've already decided we don't
	// care about the output. We don't want to wait for the process to finish, and
	// we don't wait to wait for the WaitDelay to expire either.
	//
	// Instead, if cmd.Stdout requires a copying goroutine we explicitly replace
	// it with a pipe (which is an *os.File), which we can close in order to stop
	// copying output as soon as we realize we don't care about it.
	var stdoutW *os.File
	if cmd.Stdout != nil {
	if _, ok := cmd.Stdout.(*os.File); !ok {
	var stdoutR *os.File
	stdoutR, stdoutW, err = os.Pipe()
	if err != nil {
	return err
	}
	prevStdout := cmd.Stdout
	cmd.Stdout = stdoutW

	stdoutErr := make(chan error, 1)
	go func() {
	_, err := io.Copy(prevStdout, stdoutR)
	if err != nil {
	err = fmt.Errorf("copying stdout: %w", err)
	}
	stdoutErr <- err
	}()
	defer func() {
	// We started a goroutine to copy a stdout pipe.
	// Wait for it to finish, or terminate it if need be.
	var err2 error
	select {
	case err2 = <-stdoutErr:
	stdoutR.Close()
	case <-ctx.Done():
	stdoutR.Close()
	// Per https://pkg.go.dev/os#File.Close, the call to stdoutR.Close
	// should cause the Read call in io.Copy to unblock and return
	// immediately, but we still need to receive from stdoutErr to confirm
	// that that has happened.
	<-stdoutErr
	err2 = ctx.Err()
	}
	if err == nil {
	err = err2
	}
	}()

	// Per https://pkg.go.dev/os/exec#Cmd, “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.”
	//
	// Since we're starting a goroutine that writes to cmd.Stdout, we must
	// also update cmd.Stderr so that that still holds.
	func() {
	defer func() { recover() }()
	if cmd.Stderr == prevStdout {
	cmd.Stderr = cmd.Stdout
	}
	}()
	}
	}

	err = cmd.Start()
	if stdoutW != nil {
	// The child process has inherited the pipe file,
	// so close the copy held in this process.
	stdoutW.Close()
	stdoutW = nil
	}
	if err != nil {
	return err
	}

	resChan := make(chan error, 1)
	go func() {
	resChan <- cmd.Wait()
	}()

	// If we're interested in debugging hanging Go commands, stop waiting after a
	// minute and panic with interesting information.
	debug := DebugHangingGoCommands
	if debug {
	timer := time.NewTimer(1 * time.Minute)
	defer timer.Stop()
	select {
	case err := <-resChan:
	return err
	case <-timer.C:
	HandleHangingGoCommand(cmd.Process)
	case <-ctx.Done():
	}
	} else {
	select {
	case err := <-resChan:
	return err
	case <-ctx.Done():
	}
	}

	// Cancelled. Interrupt and see if it ends voluntarily.
	if err := cmd.Process.Signal(os.Interrupt); err == nil {
	// (We used to wait only 1s but this proved
	// fragile on loaded builder machines.)
	timer := time.NewTimer(5 * time.Second)
	defer timer.Stop()
	select {
	case err := <-resChan:
	return err
	case <-timer.C:
	}
	}

	// Didn't shut down in response to interrupt. Kill it hard.
	// TODO(rfindley): per advice from bcmills@, it may be better to send SIGQUIT
	// on certain platforms, such as unix.
	if err := cmd.Process.Kill(); err != nil && !errors.Is(err, os.ErrProcessDone) && debug {
	log.Printf("error killing the Go command: %v", err)
	}

	return <-resChan
	}

	func HandleHangingGoCommand(proc *os.Process) {
	switch runtime.GOOS {
	case "linux", "darwin", "freebsd", "netbsd":
	fmt.Fprintln(os.Stderr, `DETECTED A HANGING GO COMMAND

	The gopls test runner has detected a hanging go command. In order to debug
	this, the output of ps and lsof/fstat is printed below.

	See golang/go#54461 for more details.`)

	fmt.Fprintln(os.Stderr, "\nps axo ppid,pid,command:")
	fmt.Fprintln(os.Stderr, "-------------------------")
	psCmd := exec.Command("ps", "axo", "ppid,pid,command")
	psCmd.Stdout = os.Stderr
	psCmd.Stderr = os.Stderr
	if err := psCmd.Run(); err != nil {
	panic(fmt.Sprintf("running ps: %v", err))
	}

	listFiles := "lsof"
	if runtime.GOOS == "freebsd" \|\| runtime.GOOS == "netbsd" {
	listFiles = "fstat"
	}

	fmt.Fprintln(os.Stderr, "\n"+listFiles+":")
	fmt.Fprintln(os.Stderr, "-----")
	listFilesCmd := exec.Command(listFiles)
	listFilesCmd.Stdout = os.Stderr
	listFilesCmd.Stderr = os.Stderr
	if err := listFilesCmd.Run(); err != nil {
	panic(fmt.Sprintf("running %s: %v", listFiles, err))
	}
	}
	panic(fmt.Sprintf("detected hanging go command (pid %d): see golang/go#54461 for more details", proc.Pid))
	}

	func cmdDebugStr(cmd *exec.Cmd) string {
	env := make(map[string]string)
	for _, kv := range cmd.Env {
	split := strings.SplitN(kv, "=", 2)
	if len(split) == 2 {
	k, v := split[0], split[1]
	env[k] = v
	}
	}

	var args []string
	for _, arg := range cmd.Args {
	quoted := strconv.Quote(arg)
	if quoted[1:len(quoted)-1] != arg \|\| strings.Contains(arg, " ") {
	args = append(args, quoted)
	} else {
	args = append(args, arg)
	}
	}
	return fmt.Sprintf("GOROOT=%v GOPATH=%v GO111MODULE=%v GOPROXY=%v PWD=%v %v", env["GOROOT"], env["GOPATH"], env["GO111MODULE"], env["GOPROXY"], env["PWD"], strings.Join(args, " "))
	}