Adding upstream version 1.16.10.upstream/1.16.10upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1072 insertions, 0 deletions

diff --git a/src/cmd/go/internal/modload/init.go b/src/cmd/go/internal/modload/init.go
new file mode 100644
index 0000000..8ec1c86
--- /dev/null
+++ b/src/cmd/go/internal/modload/init.go
@@ -0,0 +1,1072 @@
+// Copyright 2018 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 modload
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"go/build"
+	"internal/lazyregexp"
+	"os"
+	"path"
+	"path/filepath"
+	"sort"
+	"strconv"
+	"strings"
+	"sync"
+
+	"cmd/go/internal/base"
+	"cmd/go/internal/cfg"
+	"cmd/go/internal/fsys"
+	"cmd/go/internal/lockedfile"
+	"cmd/go/internal/modconv"
+	"cmd/go/internal/modfetch"
+	"cmd/go/internal/mvs"
+	"cmd/go/internal/search"
+	"cmd/go/internal/str"
+
+	"golang.org/x/mod/modfile"
+	"golang.org/x/mod/module"
+	"golang.org/x/mod/semver"
+)
+
+var (
+	initialized bool
+
+	modRoot string
+	Target  module.Version
+
+	// targetPrefix is the path prefix for packages in Target, without a trailing
+	// slash. For most modules, targetPrefix is just Target.Path, but the
+	// standard-library module "std" has an empty prefix.
+	targetPrefix string
+
+	// targetInGorootSrc caches whether modRoot is within GOROOT/src.
+	// The "std" module is special within GOROOT/src, but not otherwise.
+	targetInGorootSrc bool
+
+	gopath string
+
+	// RootMode determines whether a module root is needed.
+	RootMode Root
+
+	// ForceUseModules may be set to force modules to be enabled when
+	// GO111MODULE=auto or to report an error when GO111MODULE=off.
+	ForceUseModules bool
+
+	allowMissingModuleImports bool
+)
+
+type Root int
+
+const (
+	// AutoRoot is the default for most commands. modload.Init will look for
+	// a go.mod file in the current directory or any parent. If none is found,
+	// modules may be disabled (GO111MODULE=on) or commands may run in a
+	// limited module mode.
+	AutoRoot Root = iota
+
+	// NoRoot is used for commands that run in module mode and ignore any go.mod
+	// file the current directory or in parent directories.
+	NoRoot
+
+	// NeedRoot is used for commands that must run in module mode and don't
+	// make sense without a main module.
+	NeedRoot
+)
+
+// ModFile returns the parsed go.mod file.
+//
+// Note that after calling LoadPackages or LoadAllModules,
+// the require statements in the modfile.File are no longer
+// the source of truth and will be ignored: edits made directly
+// will be lost at the next call to WriteGoMod.
+// To make permanent changes to the require statements
+// in go.mod, edit it before loading.
+func ModFile() *modfile.File {
+	Init()
+	if modFile == nil {
+		die()
+	}
+	return modFile
+}
+
+func BinDir() string {
+	Init()
+	return filepath.Join(gopath, "bin")
+}
+
+// Init determines whether module mode is enabled, locates the root of the
+// current module (if any), sets environment variables for Git subprocesses, and
+// configures the cfg, codehost, load, modfetch, and search packages for use
+// with modules.
+func Init() {
+	if initialized {
+		return
+	}
+	initialized = true
+
+	// Keep in sync with WillBeEnabled. We perform extra validation here, and
+	// there are lots of diagnostics and side effects, so we can't use
+	// WillBeEnabled directly.
+	var mustUseModules bool
+	env := cfg.Getenv("GO111MODULE")
+	switch env {
+	default:
+		base.Fatalf("go: unknown environment setting GO111MODULE=%s", env)
+	case "auto":
+		mustUseModules = ForceUseModules
+	case "on", "":
+		mustUseModules = true
+	case "off":
+		if ForceUseModules {
+			base.Fatalf("go: modules disabled by GO111MODULE=off; see 'go help modules'")
+		}
+		mustUseModules = false
+		return
+	}
+
+	if err := fsys.Init(base.Cwd); err != nil {
+		base.Fatalf("go: %v", err)
+	}
+
+	// Disable any prompting for passwords by Git.
+	// Only has an effect for 2.3.0 or later, but avoiding
+	// the prompt in earlier versions is just too hard.
+	// If user has explicitly set GIT_TERMINAL_PROMPT=1, keep
+	// prompting.
+	// See golang.org/issue/9341 and golang.org/issue/12706.
+	if os.Getenv("GIT_TERMINAL_PROMPT") == "" {
+		os.Setenv("GIT_TERMINAL_PROMPT", "0")
+	}
+
+	// Disable any ssh connection pooling by Git.
+	// If a Git subprocess forks a child into the background to cache a new connection,
+	// that child keeps stdout/stderr open. After the Git subprocess exits,
+	// os /exec expects to be able to read from the stdout/stderr pipe
+	// until EOF to get all the data that the Git subprocess wrote before exiting.
+	// The EOF doesn't come until the child exits too, because the child
+	// is holding the write end of the pipe.
+	// This is unfortunate, but it has come up at least twice
+	// (see golang.org/issue/13453 and golang.org/issue/16104)
+	// and confuses users when it does.
+	// If the user has explicitly set GIT_SSH or GIT_SSH_COMMAND,
+	// assume they know what they are doing and don't step on it.
+	// But default to turning off ControlMaster.
+	if os.Getenv("GIT_SSH") == "" && os.Getenv("GIT_SSH_COMMAND") == "" {
+		os.Setenv("GIT_SSH_COMMAND", "ssh -o ControlMaster=no")
+	}
+
+	if modRoot != "" {
+		// modRoot set before Init was called ("go mod init" does this).
+		// No need to search for go.mod.
+	} else if RootMode == NoRoot {
+		if cfg.ModFile != "" && !base.InGOFLAGS("-modfile") {
+			base.Fatalf("go: -modfile cannot be used with commands that ignore the current module")
+		}
+		modRoot = ""
+	} else {
+		modRoot = findModuleRoot(base.Cwd)
+		if modRoot == "" {
+			if cfg.ModFile != "" {
+				base.Fatalf("go: cannot find main module, but -modfile was set.\n\t-modfile cannot be used to set the module root directory.")
+			}
+			if RootMode == NeedRoot {
+				base.Fatalf("go: %v", ErrNoModRoot)
+			}
+			if !mustUseModules {
+				// GO111MODULE is 'auto', and we can't find a module root.
+				// Stay in GOPATH mode.
+				return
+			}
+		} else if search.InDir(modRoot, os.TempDir()) == "." {
+			// If you create /tmp/go.mod for experimenting,
+			// then any tests that create work directories under /tmp
+			// will find it and get modules when they're not expecting them.
+			// It's a bit of a peculiar thing to disallow but quite mysterious
+			// when it happens. See golang.org/issue/26708.
+			modRoot = ""
+			fmt.Fprintf(os.Stderr, "go: warning: ignoring go.mod in system temp root %v\n", os.TempDir())
+			if !mustUseModules {
+				return
+			}
+		}
+	}
+	if cfg.ModFile != "" && !strings.HasSuffix(cfg.ModFile, ".mod") {
+		base.Fatalf("go: -modfile=%s: file does not have .mod extension", cfg.ModFile)
+	}
+
+	// We're in module mode. Set any global variables that need to be set.
+	cfg.ModulesEnabled = true
+	setDefaultBuildMod()
+	list := filepath.SplitList(cfg.BuildContext.GOPATH)
+	if len(list) == 0 || list[0] == "" {
+		base.Fatalf("missing $GOPATH")
+	}
+	gopath = list[0]
+	if _, err := fsys.Stat(filepath.Join(gopath, "go.mod")); err == nil {
+		base.Fatalf("$GOPATH/go.mod exists but should not")
+	}
+
+	if modRoot == "" {
+		// We're in module mode, but not inside a module.
+		//
+		// Commands like 'go build', 'go run', 'go list' have no go.mod file to
+		// read or write. They would need to find and download the latest versions
+		// of a potentially large number of modules with no way to save version
+		// information. We can succeed slowly (but not reproducibly), but that's
+		// not usually a good experience.
+		//
+		// Instead, we forbid resolving import paths to modules other than std and
+		// cmd. Users may still build packages specified with .go files on the
+		// command line, but they'll see an error if those files import anything
+		// outside std.
+		//
+		// This can be overridden by calling AllowMissingModuleImports.
+		// For example, 'go get' does this, since it is expected to resolve paths.
+		//
+		// See golang.org/issue/32027.
+	} else {
+		modfetch.GoSumFile = strings.TrimSuffix(ModFilePath(), ".mod") + ".sum"
+		search.SetModRoot(modRoot)
+	}
+}
+
+// WillBeEnabled checks whether modules should be enabled but does not
+// initialize modules by installing hooks. If Init has already been called,
+// WillBeEnabled returns the same result as Enabled.
+//
+// This function is needed to break a cycle. The main package needs to know
+// whether modules are enabled in order to install the module or GOPATH version
+// of 'go get', but Init reads the -modfile flag in 'go get', so it shouldn't
+// be called until the command is installed and flags are parsed. Instead of
+// calling Init and Enabled, the main package can call this function.
+func WillBeEnabled() bool {
+	if modRoot != "" || cfg.ModulesEnabled {
+		// Already enabled.
+		return true
+	}
+	if initialized {
+		// Initialized, not enabled.
+		return false
+	}
+
+	// Keep in sync with Init. Init does extra validation and prints warnings or
+	// exits, so it can't call this function directly.
+	env := cfg.Getenv("GO111MODULE")
+	switch env {
+	case "on", "":
+		return true
+	case "auto":
+		break
+	default:
+		return false
+	}
+
+	if modRoot := findModuleRoot(base.Cwd); modRoot == "" {
+		// GO111MODULE is 'auto', and we can't find a module root.
+		// Stay in GOPATH mode.
+		return false
+	} else if search.InDir(modRoot, os.TempDir()) == "." {
+		// If you create /tmp/go.mod for experimenting,
+		// then any tests that create work directories under /tmp
+		// will find it and get modules when they're not expecting them.
+		// It's a bit of a peculiar thing to disallow but quite mysterious
+		// when it happens. See golang.org/issue/26708.
+		return false
+	}
+	return true
+}
+
+// Enabled reports whether modules are (or must be) enabled.
+// If modules are enabled but there is no main module, Enabled returns true
+// and then the first use of module information will call die
+// (usually through MustModRoot).
+func Enabled() bool {
+	Init()
+	return modRoot != "" || cfg.ModulesEnabled
+}
+
+// ModRoot returns the root of the main module.
+// It calls base.Fatalf if there is no main module.
+func ModRoot() string {
+	if !HasModRoot() {
+		die()
+	}
+	return modRoot
+}
+
+// HasModRoot reports whether a main module is present.
+// HasModRoot may return false even if Enabled returns true: for example, 'get'
+// does not require a main module.
+func HasModRoot() bool {
+	Init()
+	return modRoot != ""
+}
+
+// ModFilePath returns the effective path of the go.mod file. Normally, this
+// "go.mod" in the directory returned by ModRoot, but the -modfile flag may
+// change its location. ModFilePath calls base.Fatalf if there is no main
+// module, even if -modfile is set.
+func ModFilePath() string {
+	if !HasModRoot() {
+		die()
+	}
+	if cfg.ModFile != "" {
+		return cfg.ModFile
+	}
+	return filepath.Join(modRoot, "go.mod")
+}
+
+func die() {
+	if cfg.Getenv("GO111MODULE") == "off" {
+		base.Fatalf("go: modules disabled by GO111MODULE=off; see 'go help modules'")
+	}
+	if dir, name := findAltConfig(base.Cwd); dir != "" {
+		rel, err := filepath.Rel(base.Cwd, dir)
+		if err != nil {
+			rel = dir
+		}
+		cdCmd := ""
+		if rel != "." {
+			cdCmd = fmt.Sprintf("cd %s && ", rel)
+		}
+		base.Fatalf("go: cannot find main module, but found %s in %s\n\tto create a module there, run:\n\t%sgo mod init", name, dir, cdCmd)
+	}
+	base.Fatalf("go: %v", ErrNoModRoot)
+}
+
+var ErrNoModRoot = errors.New("go.mod file not found in current directory or any parent directory; see 'go help modules'")
+
+// LoadModFile sets Target and, if there is a main module, parses the initial
+// build list from its go.mod file.
+//
+// LoadModFile may make changes in memory, like adding a go directive and
+// ensuring requirements are consistent. WriteGoMod should be called later to
+// write changes out to disk or report errors in readonly mode.
+//
+// As a side-effect, LoadModFile may change cfg.BuildMod to "vendor" if
+// -mod wasn't set explicitly and automatic vendoring should be enabled.
+func LoadModFile(ctx context.Context) {
+	if len(buildList) > 0 {
+		return
+	}
+
+	Init()
+	if modRoot == "" {
+		Target = module.Version{Path: "command-line-arguments"}
+		targetPrefix = "command-line-arguments"
+		buildList = []module.Version{Target}
+		return
+	}
+
+	gomod := ModFilePath()
+	data, err := lockedfile.Read(gomod)
+	if err != nil {
+		base.Fatalf("go: %v", err)
+	}
+
+	var fixed bool
+	f, err := modfile.Parse(gomod, data, fixVersion(ctx, &fixed))
+	if err != nil {
+		// Errors returned by modfile.Parse begin with file:line.
+		base.Fatalf("go: errors parsing go.mod:\n%s\n", err)
+	}
+	modFile = f
+	index = indexModFile(data, f, fixed)
+
+	if f.Module == nil {
+		// No module declaration. Must add module path.
+		base.Fatalf("go: no module declaration in go.mod. To specify the module path:\n\tgo mod edit -module=example.com/mod")
+	}
+
+	if err := checkModulePathLax(f.Module.Mod.Path); err != nil {
+		base.Fatalf("go: %v", err)
+	}
+
+	setDefaultBuildMod() // possibly enable automatic vendoring
+	modFileToBuildList()
+	if cfg.BuildMod == "vendor" {
+		readVendorList()
+		checkVendorConsistency()
+	}
+}
+
+// CreateModFile initializes a new module by creating a go.mod file.
+//
+// If modPath is empty, CreateModFile will attempt to infer the path from the
+// directory location within GOPATH.
+//
+// If a vendoring configuration file is present, CreateModFile will attempt to
+// translate it to go.mod directives. The resulting build list may not be
+// exactly the same as in the legacy configuration (for example, we can't get
+// packages at multiple versions from the same module).
+func CreateModFile(ctx context.Context, modPath string) {
+	modRoot = base.Cwd
+	Init()
+	modFilePath := ModFilePath()
+	if _, err := fsys.Stat(modFilePath); err == nil {
+		base.Fatalf("go: %s already exists", modFilePath)
+	}
+
+	if modPath == "" {
+		var err error
+		modPath, err = findModulePath(modRoot)
+		if err != nil {
+			base.Fatalf("go: %v", err)
+		}
+	} else if err := checkModulePathLax(modPath); err != nil {
+		base.Fatalf("go: %v", err)
+	}
+
+	fmt.Fprintf(os.Stderr, "go: creating new go.mod: module %s\n", modPath)
+	modFile = new(modfile.File)
+	modFile.AddModuleStmt(modPath)
+	addGoStmt() // Add the go directive before converted module requirements.
+
+	convertedFrom, err := convertLegacyConfig(modPath)
+	if convertedFrom != "" {
+		fmt.Fprintf(os.Stderr, "go: copying requirements from %s\n", base.ShortPath(convertedFrom))
+	}
+	if err != nil {
+		base.Fatalf("go: %v", err)
+	}
+
+	modFileToBuildList()
+	WriteGoMod()
+
+	// Suggest running 'go mod tidy' unless the project is empty. Even if we
+	// imported all the correct requirements above, we're probably missing
+	// some sums, so the next build command in -mod=readonly will likely fail.
+	//
+	// We look for non-hidden .go files or subdirectories to determine whether
+	// this is an existing project. Walking the tree for packages would be more
+	// accurate, but could take much longer.
+	empty := true
+	files, _ := os.ReadDir(modRoot)
+	for _, f := range files {
+		name := f.Name()
+		if strings.HasPrefix(name, ".") || strings.HasPrefix(name, "_") {
+			continue
+		}
+		if strings.HasSuffix(name, ".go") || f.IsDir() {
+			empty = false
+			break
+		}
+	}
+	if !empty {
+		fmt.Fprintf(os.Stderr, "go: to add module requirements and sums:\n\tgo mod tidy\n")
+	}
+}
+
+// checkModulePathLax checks that the path meets some minimum requirements
+// to avoid confusing users or the module cache. The requirements are weaker
+// than those of module.CheckPath to allow room for weakening module path
+// requirements in the future, but strong enough to help users avoid significant
+// problems.
+func checkModulePathLax(p string) error {
+	// TODO(matloob): Replace calls of this function in this CL with calls
+	// to module.CheckImportPath once it's been laxened, if it becomes laxened.
+	// See golang.org/issue/29101 for a discussion about whether to make CheckImportPath
+	// more lax or more strict.
+
+	errorf := func(format string, args ...interface{}) error {
+		return fmt.Errorf("invalid module path %q: %s", p, fmt.Sprintf(format, args...))
+	}
+
+	// Disallow shell characters " ' * < > ? ` | to avoid triggering bugs
+	// with file systems and subcommands. Disallow file path separators : and \
+	// because path separators other than / will confuse the module cache.
+	// See fileNameOK in golang.org/x/mod/module/module.go.
+	shellChars := "`" + `\"'*<>?|`
+	fsChars := `\:`
+	if i := strings.IndexAny(p, shellChars); i >= 0 {
+		return errorf("contains disallowed shell character %q", p[i])
+	}
+	if i := strings.IndexAny(p, fsChars); i >= 0 {
+		return errorf("contains disallowed path separator character %q", p[i])
+	}
+
+	// Ensure path.IsAbs and build.IsLocalImport are false, and that the path is
+	// invariant under path.Clean, also to avoid confusing the module cache.
+	if path.IsAbs(p) {
+		return errorf("is an absolute path")
+	}
+	if build.IsLocalImport(p) {
+		return errorf("is a local import path")
+	}
+	if path.Clean(p) != p {
+		return errorf("is not clean")
+	}
+
+	return nil
+}
+
+// fixVersion returns a modfile.VersionFixer implemented using the Query function.
+//
+// It resolves commit hashes and branch names to versions,
+// canonicalizes versions that appeared in early vgo drafts,
+// and does nothing for versions that already appear to be canonical.
+//
+// The VersionFixer sets 'fixed' if it ever returns a non-canonical version.
+func fixVersion(ctx context.Context, fixed *bool) modfile.VersionFixer {
+	return func(path, vers string) (resolved string, err error) {
+		defer func() {
+			if err == nil && resolved != vers {
+				*fixed = true
+			}
+		}()
+
+		// Special case: remove the old -gopkgin- hack.
+		if strings.HasPrefix(path, "gopkg.in/") && strings.Contains(vers, "-gopkgin-") {
+			vers = vers[strings.Index(vers, "-gopkgin-")+len("-gopkgin-"):]
+		}
+
+		// fixVersion is called speculatively on every
+		// module, version pair from every go.mod file.
+		// Avoid the query if it looks OK.
+		_, pathMajor, ok := module.SplitPathVersion(path)
+		if !ok {
+			return "", &module.ModuleError{
+				Path: path,
+				Err: &module.InvalidVersionError{
+					Version: vers,
+					Err:     fmt.Errorf("malformed module path %q", path),
+				},
+			}
+		}
+		if vers != "" && module.CanonicalVersion(vers) == vers {
+			if err := module.CheckPathMajor(vers, pathMajor); err != nil {
+				return "", module.VersionError(module.Version{Path: path, Version: vers}, err)
+			}
+			return vers, nil
+		}
+
+		info, err := Query(ctx, path, vers, "", nil)
+		if err != nil {
+			return "", err
+		}
+		return info.Version, nil
+	}
+}
+
+// AllowMissingModuleImports allows import paths to be resolved to modules
+// when there is no module root. Normally, this is forbidden because it's slow
+// and there's no way to make the result reproducible, but some commands
+// like 'go get' are expected to do this.
+func AllowMissingModuleImports() {
+	allowMissingModuleImports = true
+}
+
+// modFileToBuildList initializes buildList from the modFile.
+func modFileToBuildList() {
+	Target = modFile.Module.Mod
+	targetPrefix = Target.Path
+	if rel := search.InDir(base.Cwd, cfg.GOROOTsrc); rel != "" {
+		targetInGorootSrc = true
+		if Target.Path == "std" {
+			targetPrefix = ""
+		}
+	}
+
+	list := []module.Version{Target}
+	for _, r := range modFile.Require {
+		if index != nil && index.exclude[r.Mod] {
+			if cfg.BuildMod == "mod" {
+				fmt.Fprintf(os.Stderr, "go: dropping requirement on excluded version %s %s\n", r.Mod.Path, r.Mod.Version)
+			} else {
+				fmt.Fprintf(os.Stderr, "go: ignoring requirement on excluded version %s %s\n", r.Mod.Path, r.Mod.Version)
+			}
+		} else {
+			list = append(list, r.Mod)
+		}
+	}
+	buildList = list
+}
+
+// setDefaultBuildMod sets a default value for cfg.BuildMod if the -mod flag
+// wasn't provided. setDefaultBuildMod may be called multiple times.
+func setDefaultBuildMod() {
+	if cfg.BuildModExplicit {
+		// Don't override an explicit '-mod=' argument.
+		return
+	}
+
+	if cfg.CmdName == "get" || strings.HasPrefix(cfg.CmdName, "mod ") {
+		// 'get' and 'go mod' commands may update go.mod automatically.
+		// TODO(jayconrod): should this narrower? Should 'go mod download' or
+		// 'go mod graph' update go.mod by default?
+		cfg.BuildMod = "mod"
+		return
+	}
+	if modRoot == "" {
+		cfg.BuildMod = "readonly"
+		return
+	}
+
+	if fi, err := fsys.Stat(filepath.Join(modRoot, "vendor")); err == nil && fi.IsDir() {
+		modGo := "unspecified"
+		if index != nil && index.goVersionV != "" {
+			if semver.Compare(index.goVersionV, "v1.14") >= 0 {
+				// The Go version is at least 1.14, and a vendor directory exists.
+				// Set -mod=vendor by default.
+				cfg.BuildMod = "vendor"
+				cfg.BuildModReason = "Go version in go.mod is at least 1.14 and vendor directory exists."
+				return
+			} else {
+				modGo = index.goVersionV[1:]
+			}
+		}
+
+		// Since a vendor directory exists, we should record why we didn't use it.
+		// This message won't normally be shown, but it may appear with import errors.
+		cfg.BuildModReason = fmt.Sprintf("Go version in go.mod is %s, so vendor directory was not used.", modGo)
+	}
+
+	cfg.BuildMod = "readonly"
+}
+
+// convertLegacyConfig imports module requirements from a legacy vendoring
+// configuration file, if one is present.
+func convertLegacyConfig(modPath string) (from string, err error) {
+	for _, name := range altConfigs {
+		cfg := filepath.Join(modRoot, name)
+		data, err := os.ReadFile(cfg)
+		if err == nil {
+			convert := modconv.Converters[name]
+			if convert == nil {
+				return "", nil
+			}
+			cfg = filepath.ToSlash(cfg)
+			err := modconv.ConvertLegacyConfig(modFile, cfg, data)
+			return name, err
+		}
+	}
+	return "", nil
+}
+
+// addGoStmt adds a go directive to the go.mod file if it does not already include one.
+// The 'go' version added, if any, is the latest version supported by this toolchain.
+func addGoStmt() {
+	if modFile.Go != nil && modFile.Go.Version != "" {
+		return
+	}
+	tags := build.Default.ReleaseTags
+	version := tags[len(tags)-1]
+	if !strings.HasPrefix(version, "go") || !modfile.GoVersionRE.MatchString(version[2:]) {
+		base.Fatalf("go: unrecognized default version %q", version)
+	}
+	if err := modFile.AddGoStmt(version[2:]); err != nil {
+		base.Fatalf("go: internal error: %v", err)
+	}
+}
+
+var altConfigs = []string{
+	"Gopkg.lock",
+
+	"GLOCKFILE",
+	"Godeps/Godeps.json",
+	"dependencies.tsv",
+	"glide.lock",
+	"vendor.conf",
+	"vendor.yml",
+	"vendor/manifest",
+	"vendor/vendor.json",
+
+	".git/config",
+}
+
+func findModuleRoot(dir string) (root string) {
+	if dir == "" {
+		panic("dir not set")
+	}
+	dir = filepath.Clean(dir)
+
+	// Look for enclosing go.mod.
+	for {
+		if fi, err := fsys.Stat(filepath.Join(dir, "go.mod")); err == nil && !fi.IsDir() {
+			return dir
+		}
+		d := filepath.Dir(dir)
+		if d == dir {
+			break
+		}
+		dir = d
+	}
+	return ""
+}
+
+func findAltConfig(dir string) (root, name string) {
+	if dir == "" {
+		panic("dir not set")
+	}
+	dir = filepath.Clean(dir)
+	if rel := search.InDir(dir, cfg.BuildContext.GOROOT); rel != "" {
+		// Don't suggest creating a module from $GOROOT/.git/config
+		// or a config file found in any parent of $GOROOT (see #34191).
+		return "", ""
+	}
+	for {
+		for _, name := range altConfigs {
+			if fi, err := fsys.Stat(filepath.Join(dir, name)); err == nil && !fi.IsDir() {
+				return dir, name
+			}
+		}
+		d := filepath.Dir(dir)
+		if d == dir {
+			break
+		}
+		dir = d
+	}
+	return "", ""
+}
+
+func findModulePath(dir string) (string, error) {
+	// TODO(bcmills): once we have located a plausible module path, we should
+	// query version control (if available) to verify that it matches the major
+	// version of the most recent tag.
+	// See https://golang.org/issue/29433, https://golang.org/issue/27009, and
+	// https://golang.org/issue/31549.
+
+	// Cast about for import comments,
+	// first in top-level directory, then in subdirectories.
+	list, _ := os.ReadDir(dir)
+	for _, info := range list {
+		if info.Type().IsRegular() && strings.HasSuffix(info.Name(), ".go") {
+			if com := findImportComment(filepath.Join(dir, info.Name())); com != "" {
+				return com, nil
+			}
+		}
+	}
+	for _, info1 := range list {
+		if info1.IsDir() {
+			files, _ := os.ReadDir(filepath.Join(dir, info1.Name()))
+			for _, info2 := range files {
+				if info2.Type().IsRegular() && strings.HasSuffix(info2.Name(), ".go") {
+					if com := findImportComment(filepath.Join(dir, info1.Name(), info2.Name())); com != "" {
+						return path.Dir(com), nil
+					}
+				}
+			}
+		}
+	}
+
+	// Look for Godeps.json declaring import path.
+	data, _ := os.ReadFile(filepath.Join(dir, "Godeps/Godeps.json"))
+	var cfg1 struct{ ImportPath string }
+	json.Unmarshal(data, &cfg1)
+	if cfg1.ImportPath != "" {
+		return cfg1.ImportPath, nil
+	}
+
+	// Look for vendor.json declaring import path.
+	data, _ = os.ReadFile(filepath.Join(dir, "vendor/vendor.json"))
+	var cfg2 struct{ RootPath string }
+	json.Unmarshal(data, &cfg2)
+	if cfg2.RootPath != "" {
+		return cfg2.RootPath, nil
+	}
+
+	// Look for path in GOPATH.
+	var badPathErr error
+	for _, gpdir := range filepath.SplitList(cfg.BuildContext.GOPATH) {
+		if gpdir == "" {
+			continue
+		}
+		if rel := search.InDir(dir, filepath.Join(gpdir, "src")); rel != "" && rel != "." {
+			path := filepath.ToSlash(rel)
+			// TODO(matloob): replace this with module.CheckImportPath
+			// once it's been laxened.
+			// Only checkModulePathLax here. There are some unpublishable
+			// module names that are compatible with checkModulePathLax
+			// but they already work in GOPATH so don't break users
+			// trying to do a build with modules. gorelease will alert users
+			// publishing their modules to fix their paths.
+			if err := checkModulePathLax(path); err != nil {
+				badPathErr = err
+				break
+			}
+			return path, nil
+		}
+	}
+
+	reason := "outside GOPATH, module path must be specified"
+	if badPathErr != nil {
+		// return a different error message if the module was in GOPATH, but
+		// the module path determined above would be an invalid path.
+		reason = fmt.Sprintf("bad module path inferred from directory in GOPATH: %v", badPathErr)
+	}
+	msg := `cannot determine module path for source directory %s (%s)
+
+Example usage:
+	'go mod init example.com/m' to initialize a v0 or v1 module
+	'go mod init example.com/m/v2' to initialize a v2 module
+
+Run 'go help mod init' for more information.
+`
+	return "", fmt.Errorf(msg, dir, reason)
+}
+
+var (
+	importCommentRE = lazyregexp.New(`(?m)^package[ \t]+[^ \t\r\n/]+[ \t]+//[ \t]+import[ \t]+(\"[^"]+\")[ \t]*\r?\n`)
+)
+
+func findImportComment(file string) string {
+	data, err := os.ReadFile(file)
+	if err != nil {
+		return ""
+	}
+	m := importCommentRE.FindSubmatch(data)
+	if m == nil {
+		return ""
+	}
+	path, err := strconv.Unquote(string(m[1]))
+	if err != nil {
+		return ""
+	}
+	return path
+}
+
+var allowWriteGoMod = true
+
+// DisallowWriteGoMod causes future calls to WriteGoMod to do nothing at all.
+func DisallowWriteGoMod() {
+	allowWriteGoMod = false
+}
+
+// AllowWriteGoMod undoes the effect of DisallowWriteGoMod:
+// future calls to WriteGoMod will update go.mod if needed.
+// Note that any past calls have been discarded, so typically
+// a call to AlowWriteGoMod should be followed by a call to WriteGoMod.
+func AllowWriteGoMod() {
+	allowWriteGoMod = true
+}
+
+// MinReqs returns a Reqs with minimal additional dependencies of Target,
+// as will be written to go.mod.
+func MinReqs() mvs.Reqs {
+	retain := append([]string{}, additionalExplicitRequirements...)
+	for _, m := range buildList[1:] {
+		_, explicit := index.require[m]
+		if explicit || loaded.direct[m.Path] {
+			retain = append(retain, m.Path)
+		}
+	}
+	sort.Strings(retain)
+	str.Uniq(&retain)
+	min, err := mvs.Req(Target, retain, &mvsReqs{buildList: buildList})
+	if err != nil {
+		base.Fatalf("go: %v", err)
+	}
+	return &mvsReqs{buildList: append([]module.Version{Target}, min...)}
+}
+
+// WriteGoMod writes the current build list back to go.mod.
+func WriteGoMod() {
+	// If we're using -mod=vendor we basically ignored
+	// go.mod, so definitely don't try to write back our
+	// incomplete view of the world.
+	if !allowWriteGoMod || cfg.BuildMod == "vendor" {
+		return
+	}
+
+	// If we aren't in a module, we don't have anywhere to write a go.mod file.
+	if modRoot == "" {
+		return
+	}
+
+	if cfg.BuildMod != "readonly" {
+		addGoStmt()
+	}
+
+	if loaded != nil {
+		reqs := MinReqs()
+		min, err := reqs.Required(Target)
+		if err != nil {
+			base.Fatalf("go: %v", err)
+		}
+		var list []*modfile.Require
+		for _, m := range min {
+			list = append(list, &modfile.Require{
+				Mod:      m,
+				Indirect: !loaded.direct[m.Path],
+			})
+		}
+		modFile.SetRequire(list)
+	}
+	modFile.Cleanup()
+
+	dirty := index.modFileIsDirty(modFile)
+	if dirty && cfg.BuildMod == "readonly" {
+		// If we're about to fail due to -mod=readonly,
+		// prefer to report a dirty go.mod over a dirty go.sum
+		if cfg.BuildModExplicit {
+			base.Fatalf("go: updates to go.mod needed, disabled by -mod=readonly")
+		} else if cfg.BuildModReason != "" {
+			base.Fatalf("go: updates to go.mod needed, disabled by -mod=readonly\n\t(%s)", cfg.BuildModReason)
+		} else {
+			base.Fatalf("go: updates to go.mod needed; to update it:\n\tgo mod tidy")
+		}
+	}
+
+	if !dirty && cfg.CmdName != "mod tidy" {
+		// The go.mod file has the same semantic content that it had before
+		// (but not necessarily the same exact bytes).
+		// Don't write go.mod, but write go.sum in case we added or trimmed sums.
+		// 'go mod init' shouldn't write go.sum, since it will be incomplete.
+		if cfg.CmdName != "mod init" {
+			modfetch.WriteGoSum(keepSums(true))
+		}
+		return
+	}
+
+	new, err := modFile.Format()
+	if err != nil {
+		base.Fatalf("go: %v", err)
+	}
+	defer func() {
+		// At this point we have determined to make the go.mod file on disk equal to new.
+		index = indexModFile(new, modFile, false)
+
+		// Update go.sum after releasing the side lock and refreshing the index.
+		// 'go mod init' shouldn't write go.sum, since it will be incomplete.
+		if cfg.CmdName != "mod init" {
+			modfetch.WriteGoSum(keepSums(true))
+		}
+	}()
+
+	// Make a best-effort attempt to acquire the side lock, only to exclude
+	// previous versions of the 'go' command from making simultaneous edits.
+	if unlock, err := modfetch.SideLock(); err == nil {
+		defer unlock()
+	}
+
+	errNoChange := errors.New("no update needed")
+
+	err = lockedfile.Transform(ModFilePath(), func(old []byte) ([]byte, error) {
+		if bytes.Equal(old, new) {
+			// The go.mod file is already equal to new, possibly as the result of some
+			// other process.
+			return nil, errNoChange
+		}
+
+		if index != nil && !bytes.Equal(old, index.data) {
+			// The contents of the go.mod file have changed. In theory we could add all
+			// of the new modules to the build list, recompute, and check whether any
+			// module in *our* build list got bumped to a different version, but that's
+			// a lot of work for marginal benefit. Instead, fail the command: if users
+			// want to run concurrent commands, they need to start with a complete,
+			// consistent module definition.
+			return nil, fmt.Errorf("existing contents have changed since last read")
+		}
+
+		return new, nil
+	})
+
+	if err != nil && err != errNoChange {
+		base.Fatalf("go: updating go.mod: %v", err)
+	}
+}
+
+// keepSums returns a set of module sums to preserve in go.sum. The set
+// includes entries for all modules used to load packages (according to
+// the last load function such as LoadPackages or ImportFromFiles).
+// It also contains entries for go.mod files needed for MVS (the version
+// of these entries ends with "/go.mod").
+//
+// If keepBuildListZips is true, the set also includes sums for zip files for
+// all modules in the build list with replacements applied. 'go get' and
+// 'go mod download' may add sums to this set when adding a requirement on a
+// module without a root package or when downloading a direct or indirect
+// dependency.
+func keepSums(keepBuildListZips bool) map[module.Version]bool {
+	// Re-derive the build list using the current list of direct requirements.
+	// Keep the sum for the go.mod of each visited module version (or its
+	// replacement).
+	modkey := func(m module.Version) module.Version {
+		return module.Version{Path: m.Path, Version: m.Version + "/go.mod"}
+	}
+	keep := make(map[module.Version]bool)
+	var mu sync.Mutex
+	reqs := &keepSumReqs{
+		Reqs: &mvsReqs{buildList: buildList},
+		visit: func(m module.Version) {
+			// If we build using a replacement module, keep the sum for the replacement,
+			// since that's the code we'll actually use during a build.
+			mu.Lock()
+			r := Replacement(m)
+			if r.Path == "" {
+				keep[modkey(m)] = true
+			} else {
+				keep[modkey(r)] = true
+			}
+			mu.Unlock()
+		},
+	}
+	buildList, err := mvs.BuildList(Target, reqs)
+	if err != nil {
+		panic(fmt.Sprintf("unexpected error reloading build list: %v", err))
+	}
+
+	actualMods := make(map[string]module.Version)
+	for _, m := range buildList[1:] {
+		if r := Replacement(m); r.Path != "" {
+			actualMods[m.Path] = r
+		} else {
+			actualMods[m.Path] = m
+		}
+	}
+
+	// Add entries for modules in the build list with paths that are prefixes of
+	// paths of loaded packages. We need to retain sums for modules needed to
+	// report ambiguous import errors. We use our re-derived build list,
+	// since the global build list may have been tidied.
+	if loaded != nil {
+		for _, pkg := range loaded.pkgs {
+			if pkg.testOf != nil || pkg.inStd || module.CheckImportPath(pkg.path) != nil {
+				continue
+			}
+			for prefix := pkg.path; prefix != "."; prefix = path.Dir(prefix) {
+				if m, ok := actualMods[prefix]; ok {
+					keep[m] = true
+				}
+			}
+		}
+	}
+
+	// Add entries for the zip of each module in the build list.
+	// We might not need all of these (tidy does not add them), but they may be
+	// added by a specific 'go get' or 'go mod download' command to resolve
+	// missing import sum errors.
+	if keepBuildListZips {
+		for _, m := range actualMods {
+			keep[m] = true
+		}
+	}
+
+	return keep
+}
+
+// keepSumReqs embeds another Reqs implementation. The Required method
+// calls visit for each version in the module graph.
+type keepSumReqs struct {
+	mvs.Reqs
+	visit func(module.Version)
+}
+
+func (r *keepSumReqs) Required(m module.Version) ([]module.Version, error) {
+	r.visit(m)
+	return r.Reqs.Required(m)
+}
+
+func TrimGoSum() {
+	// Don't retain sums for the zip file of every module in the build list.
+	// We may not need them all to build the main module's packages.
+	keepBuildListZips := false
+	modfetch.TrimGoSum(keepSums(keepBuildListZips))
+}