src

module.go (27529B)

---

 // 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 module defines the module.Version type along with support code.
 //
 // The [module.Version] type is a simple Path, Version pair:
 //
 //	type Version struct {
 //		Path string
 //		Version string
 //	}
 //
 // There are no restrictions imposed directly by use of this structure,
 // but additional checking functions, most notably [Check], verify that
 // a particular path, version pair is valid.
 //
 // # Escaped Paths
 //
 // Module paths appear as substrings of file system paths
 // (in the download cache) and of web server URLs in the proxy protocol.
 // In general we cannot rely on file systems to be case-sensitive,
 // nor can we rely on web servers, since they read from file systems.
 // That is, we cannot rely on the file system to keep rsc.io/QUOTE
 // and rsc.io/quote separate. Windows and macOS don't.
 // Instead, we must never require two different casings of a file path.
 // Because we want the download cache to match the proxy protocol,
 // and because we want the proxy protocol to be possible to serve
 // from a tree of static files (which might be stored on a case-insensitive
 // file system), the proxy protocol must never require two different casings
 // of a URL path either.
 //
 // One possibility would be to make the escaped form be the lowercase
 // hexadecimal encoding of the actual path bytes. This would avoid ever
 // needing different casings of a file path, but it would be fairly illegible
 // to most programmers when those paths appeared in the file system
 // (including in file paths in compiler errors and stack traces)
 // in web server logs, and so on. Instead, we want a safe escaped form that
 // leaves most paths unaltered.
 //
 // The safe escaped form is to replace every uppercase letter
 // with an exclamation mark followed by the letter's lowercase equivalent.
 //
 // For example,
 //
 //	github.com/Azure/azure-sdk-for-go ->  github.com/!azure/azure-sdk-for-go.
 //	github.com/GoogleCloudPlatform/cloudsql-proxy -> github.com/!google!cloud!platform/cloudsql-proxy
 //	github.com/Sirupsen/logrus -> github.com/!sirupsen/logrus.
 //
 // Import paths that avoid upper-case letters are left unchanged.
 // Note that because import paths are ASCII-only and avoid various
 // problematic punctuation (like : < and >), the escaped form is also ASCII-only
 // and avoids the same problematic punctuation.
 //
 // Import paths have never allowed exclamation marks, so there is no
 // need to define how to escape a literal !.
 //
 // # Unicode Restrictions
 //
 // Today, paths are disallowed from using Unicode.
 //
 // Although paths are currently disallowed from using Unicode,
 // we would like at some point to allow Unicode letters as well, to assume that
 // file systems and URLs are Unicode-safe (storing UTF-8), and apply
 // the !-for-uppercase convention for escaping them in the file system.
 // But there are at least two subtle considerations.
 //
 // First, note that not all case-fold equivalent distinct runes
 // form an upper/lower pair.
 // For example, U+004B ('K'), U+006B ('k'), and U+212A ('K' for Kelvin)
 // are three distinct runes that case-fold to each other.
 // When we do add Unicode letters, we must not assume that upper/lower
 // are the only case-equivalent pairs.
 // Perhaps the Kelvin symbol would be disallowed entirely, for example.
 // Or perhaps it would escape as "!!k", or perhaps as "(212A)".
 //
 // Second, it would be nice to allow Unicode marks as well as letters,
 // but marks include combining marks, and then we must deal not
 // only with case folding but also normalization: both U+00E9 ('é')
 // and U+0065 U+0301 ('e' followed by combining acute accent)
 // look the same on the page and are treated by some file systems
 // as the same path. If we do allow Unicode marks in paths, there
 // must be some kind of normalization to allow only one canonical
 // encoding of any character used in an import path.
 package module
 
 // IMPORTANT NOTE
 //
 // This file essentially defines the set of valid import paths for the go command.
 // There are many subtle considerations, including Unicode ambiguity,
 // security, network, and file system representations.
 //
 // This file also defines the set of valid module path and version combinations,
 // another topic with many subtle considerations.
 //
 // Changes to the semantics in this file require approval from rsc.
 
 import (
 	"cmp"
 	"errors"
 	"fmt"
 	"path"
 	"slices"
 	"strings"
 	"unicode"
 	"unicode/utf8"
 
 	"golang.org/x/mod/semver"
 )
 
 // A Version (for clients, a module.Version) is defined by a module path and version pair.
 // These are stored in their plain (unescaped) form.
 type Version struct {
 	// Path is a module path, like "golang.org/x/text" or "rsc.io/quote/v2".
 	Path string
 
 	// Version is usually a semantic version in canonical form.
 	// There are three exceptions to this general rule.
 	// First, the top-level target of a build has no specific version
 	// and uses Version = "".
 	// Second, during MVS calculations the version "none" is used
 	// to represent the decision to take no version of a given module.
 	// Third, filesystem paths found in "replace" directives are
 	// represented by a path with an empty version.
 	Version string `json:",omitempty"`
 }
 
 // String returns a representation of the Version suitable for logging
 // (Path@Version, or just Path if Version is empty).
 func (m Version) String() string {
 	if m.Version == "" {
 		return m.Path
 	}
 	return m.Path + "@" + m.Version
 }
 
 // A ModuleError indicates an error specific to a module.
 type ModuleError struct {
 	Path    string
 	Version string
 	Err     error
 }
 
 // VersionError returns a [ModuleError] derived from a [Version] and error,
 // or err itself if it is already such an error.
 func VersionError(v Version, err error) error {
 	var mErr *ModuleError
 	if errors.As(err, &mErr) && mErr.Path == v.Path && mErr.Version == v.Version {
 		return err
 	}
 	return &ModuleError{
 		Path:    v.Path,
 		Version: v.Version,
 		Err:     err,
 	}
 }
 
 func (e *ModuleError) Error() string {
 	if v, ok := e.Err.(*InvalidVersionError); ok {
 		return fmt.Sprintf("%s@%s: invalid %s: %v", e.Path, v.Version, v.noun(), v.Err)
 	}
 	if e.Version != "" {
 		return fmt.Sprintf("%s@%s: %v", e.Path, e.Version, e.Err)
 	}
 	return fmt.Sprintf("module %s: %v", e.Path, e.Err)
 }
 
 func (e *ModuleError) Unwrap() error { return e.Err }
 
 // An InvalidVersionError indicates an error specific to a version, with the
 // module path unknown or specified externally.
 //
 // A [ModuleError] may wrap an InvalidVersionError, but an InvalidVersionError
 // must not wrap a ModuleError.
 type InvalidVersionError struct {
 	Version string
 	Pseudo  bool
 	Err     error
 }
 
 // noun returns either "version" or "pseudo-version", depending on whether
 // e.Version is a pseudo-version.
 func (e *InvalidVersionError) noun() string {
 	if e.Pseudo {
 		return "pseudo-version"
 	}
 	return "version"
 }
 
 func (e *InvalidVersionError) Error() string {
 	return fmt.Sprintf("%s %q invalid: %s", e.noun(), e.Version, e.Err)
 }
 
 func (e *InvalidVersionError) Unwrap() error { return e.Err }
 
 // An InvalidPathError indicates a module, import, or file path doesn't
 // satisfy all naming constraints. See [CheckPath], [CheckImportPath],
 // and [CheckFilePath] for specific restrictions.
 type InvalidPathError struct {
 	Kind string // "module", "import", or "file"
 	Path string
 	Err  error
 }
 
 func (e *InvalidPathError) Error() string {
 	return fmt.Sprintf("malformed %s path %q: %v", e.Kind, e.Path, e.Err)
 }
 
 func (e *InvalidPathError) Unwrap() error { return e.Err }
 
 // Check checks that a given module path, version pair is valid.
 // In addition to the path being a valid module path
 // and the version being a valid semantic version,
 // the two must correspond.
 // For example, the path "yaml/v2" only corresponds to
 // semantic versions beginning with "v2.".
 func Check(path, version string) error {
 	if err := CheckPath(path); err != nil {
 		return err
 	}
 	if !semver.IsValid(version) {
 		return &ModuleError{
 			Path: path,
 			Err:  &InvalidVersionError{Version: version, Err: errors.New("not a semantic version")},
 		}
 	}
 	_, pathMajor, _ := SplitPathVersion(path)
 	if err := CheckPathMajor(version, pathMajor); err != nil {
 		return &ModuleError{Path: path, Err: err}
 	}
 	return nil
 }
 
 // firstPathOK reports whether r can appear in the first element of a module path.
 // The first element of the path must be an LDH domain name, at least for now.
 // To avoid case ambiguity, the domain name must be entirely lower case.
 func firstPathOK(r rune) bool {
 	return r == '-' || r == '.' ||
 		'0' <= r && r <= '9' ||
 		'a' <= r && r <= 'z'
 }
 
 // modPathOK reports whether r can appear in a module path element.
 // Paths can be ASCII letters, ASCII digits, and limited ASCII punctuation: - . _ and ~.
 //
 // This matches what "go get" has historically recognized in import paths,
 // and avoids confusing sequences like '%20' or '+' that would change meaning
 // if used in a URL.
 //
 // TODO(rsc): We would like to allow Unicode letters, but that requires additional
 // care in the safe encoding (see "escaped paths" above).
 func modPathOK(r rune) bool {
 	if r < utf8.RuneSelf {
 		return r == '-' || r == '.' || r == '_' || r == '~' ||
 			'0' <= r && r <= '9' ||
 			'A' <= r && r <= 'Z' ||
 			'a' <= r && r <= 'z'
 	}
 	return false
 }
 
 // importPathOK reports whether r can appear in a package import path element.
 //
 // Import paths are intermediate between module paths and file paths: we
 // disallow characters that would be confusing or ambiguous as arguments to
 // 'go get' (such as '@' and ' ' ), but allow certain characters that are
 // otherwise-unambiguous on the command line and historically used for some
 // binary names (such as '++' as a suffix for compiler binaries and wrappers).
 func importPathOK(r rune) bool {
 	return modPathOK(r) || r == '+'
 }
 
 // fileNameOK reports whether r can appear in a file name.
 // For now we allow all Unicode letters but otherwise limit to pathOK plus a few more punctuation characters.
 // If we expand the set of allowed characters here, we have to
 // work harder at detecting potential case-folding and normalization collisions.
 // See note about "escaped paths" above.
 func fileNameOK(r rune) bool {
 	if r < utf8.RuneSelf {
 		// Entire set of ASCII punctuation, from which we remove characters:
 		//     ! " # $ % & ' ( ) * + , - . / : ; < = > ? @ [ \ ] ^ _ ` { | } ~
 		// We disallow some shell special characters: " ' * < > ? ` |
 		// (Note that some of those are disallowed by the Windows file system as well.)
 		// We also disallow path separators / : and \ (fileNameOK is only called on path element characters).
 		// We allow spaces (U+0020) in file names.
 		const allowed = "!#$%&()+,-.=@[]^_{}~ "
 		if '0' <= r && r <= '9' || 'A' <= r && r <= 'Z' || 'a' <= r && r <= 'z' {
 			return true
 		}
 		return strings.ContainsRune(allowed, r)
 	}
 	// It may be OK to add more ASCII punctuation here, but only carefully.
 	// For example Windows disallows < > \, and macOS disallows :, so we must not allow those.
 	return unicode.IsLetter(r)
 }
 
 // CheckPath checks that a module path is valid.
 // A valid module path is a valid import path, as checked by [CheckImportPath],
 // with three additional constraints.
 // First, the leading path element (up to the first slash, if any),
 // by convention a domain name, must contain only lower-case ASCII letters,
 // ASCII digits, dots (U+002E), and dashes (U+002D);
 // it must contain at least one dot and cannot start with a dash.
 // Second, for a final path element of the form /vN, where N looks numeric
 // (ASCII digits and dots) must not begin with a leading zero, must not be /v1,
 // and must not contain any dots. For paths beginning with "gopkg.in/",
 // this second requirement is replaced by a requirement that the path
 // follow the gopkg.in server's conventions.
 // Third, no path element may begin with a dot.
 func CheckPath(path string) (err error) {
 	defer func() {
 		if err != nil {
 			err = &InvalidPathError{Kind: "module", Path: path, Err: err}
 		}
 	}()
 
 	if err := checkPath(path, modulePath); err != nil {
 		return err
 	}
 	i := strings.Index(path, "/")
 	if i < 0 {
 		i = len(path)
 	}
 	if i == 0 {
 		return fmt.Errorf("leading slash")
 	}
 	if !strings.Contains(path[:i], ".") {
 		return fmt.Errorf("missing dot in first path element")
 	}
 	if path[0] == '-' {
 		return fmt.Errorf("leading dash in first path element")
 	}
 	for _, r := range path[:i] {
 		if !firstPathOK(r) {
 			return fmt.Errorf("invalid char %q in first path element", r)
 		}
 	}
 	if _, _, ok := SplitPathVersion(path); !ok {
 		return fmt.Errorf("invalid version")
 	}
 	return nil
 }
 
 // CheckImportPath checks that an import path is valid.
 //
 // A valid import path consists of one or more valid path elements
 // separated by slashes (U+002F). (It must not begin with nor end in a slash.)
 //
 // A valid path element is a non-empty string made up of
 // ASCII letters, ASCII digits, and limited ASCII punctuation: - . _ and ~.
 // It must not end with a dot (U+002E), nor contain two dots in a row.
 //
 // The element prefix up to the first dot must not be a reserved file name
 // on Windows, regardless of case (CON, com1, NuL, and so on). The element
 // must not have a suffix of a tilde followed by one or more ASCII digits
 // (to exclude paths elements that look like Windows short-names).
 //
 // CheckImportPath may be less restrictive in the future, but see the
 // top-level package documentation for additional information about
 // subtleties of Unicode.
 func CheckImportPath(path string) error {
 	if err := checkPath(path, importPath); err != nil {
 		return &InvalidPathError{Kind: "import", Path: path, Err: err}
 	}
 	return nil
 }
 
 // pathKind indicates what kind of path we're checking. Module paths,
 // import paths, and file paths have different restrictions.
 type pathKind int
 
 const (
 	modulePath pathKind = iota
 	importPath
 	filePath
 )
 
 // checkPath checks that a general path is valid. kind indicates what
 // specific constraints should be applied.
 //
 // checkPath returns an error describing why the path is not valid.
 // Because these checks apply to module, import, and file paths,
 // and because other checks may be applied, the caller is expected to wrap
 // this error with [InvalidPathError].
 func checkPath(path string, kind pathKind) error {
 	if !utf8.ValidString(path) {
 		return fmt.Errorf("invalid UTF-8")
 	}
 	if path == "" {
 		return fmt.Errorf("empty string")
 	}
 	if path[0] == '-' && kind != filePath {
 		return fmt.Errorf("leading dash")
 	}
 	if strings.Contains(path, "//") {
 		return fmt.Errorf("double slash")
 	}
 	if path[len(path)-1] == '/' {
 		return fmt.Errorf("trailing slash")
 	}
 	elemStart := 0
 	for i, r := range path {
 		if r == '/' {
 			if err := checkElem(path[elemStart:i], kind); err != nil {
 				return err
 			}
 			elemStart = i + 1
 		}
 	}
 	if err := checkElem(path[elemStart:], kind); err != nil {
 		return err
 	}
 	return nil
 }
 
 // checkElem checks whether an individual path element is valid.
 func checkElem(elem string, kind pathKind) error {
 	if elem == "" {
 		return fmt.Errorf("empty path element")
 	}
 	if strings.Count(elem, ".") == len(elem) {
 		return fmt.Errorf("invalid path element %q", elem)
 	}
 	if elem[0] == '.' && kind == modulePath {
 		return fmt.Errorf("leading dot in path element")
 	}
 	if elem[len(elem)-1] == '.' {
 		return fmt.Errorf("trailing dot in path element")
 	}
 	for _, r := range elem {
 		ok := false
 		switch kind {
 		case modulePath:
 			ok = modPathOK(r)
 		case importPath:
 			ok = importPathOK(r)
 		case filePath:
 			ok = fileNameOK(r)
 		default:
 			panic(fmt.Sprintf("internal error: invalid kind %v", kind))
 		}
 		if !ok {
 			return fmt.Errorf("invalid char %q", r)
 		}
 	}
 
 	// Windows disallows a bunch of path elements, sadly.
 	// See https://docs.microsoft.com/en-us/windows/desktop/fileio/naming-a-file
 	short := elem
 	if i := strings.Index(short, "."); i >= 0 {
 		short = short[:i]
 	}
 	for _, bad := range badWindowsNames {
 		if strings.EqualFold(bad, short) {
 			return fmt.Errorf("%q disallowed as path element component on Windows", short)
 		}
 	}
 
 	if kind == filePath {
 		// don't check for Windows short-names in file names. They're
 		// only an issue for import paths.
 		return nil
 	}
 
 	// Reject path components that look like Windows short-names.
 	// Those usually end in a tilde followed by one or more ASCII digits.
 	if tilde := strings.LastIndexByte(short, '~'); tilde >= 0 && tilde < len(short)-1 {
 		suffix := short[tilde+1:]
 		suffixIsDigits := true
 		for _, r := range suffix {
 			if r < '0' || r > '9' {
 				suffixIsDigits = false
 				break
 			}
 		}
 		if suffixIsDigits {
 			return fmt.Errorf("trailing tilde and digits in path element")
 		}
 	}
 
 	return nil
 }
 
 // CheckFilePath checks that a slash-separated file path is valid.
 // The definition of a valid file path is the same as the definition
 // of a valid import path except that the set of allowed characters is larger:
 // all Unicode letters, ASCII digits, the ASCII space character (U+0020),
 // and the ASCII punctuation characters
 // “!#$%&()+,-.=@[]^_{}~”.
 // (The excluded punctuation characters, " * < > ? ` ' | / \ and :,
 // have special meanings in certain shells or operating systems.)
 //
 // CheckFilePath may be less restrictive in the future, but see the
 // top-level package documentation for additional information about
 // subtleties of Unicode.
 func CheckFilePath(path string) error {
 	if err := checkPath(path, filePath); err != nil {
 		return &InvalidPathError{Kind: "file", Path: path, Err: err}
 	}
 	return nil
 }
 
 // badWindowsNames are the reserved file path elements on Windows.
 // See https://docs.microsoft.com/en-us/windows/desktop/fileio/naming-a-file
 var badWindowsNames = []string{
 	"CON",
 	"PRN",
 	"AUX",
 	"NUL",
 	"COM1",
 	"COM2",
 	"COM3",
 	"COM4",
 	"COM5",
 	"COM6",
 	"COM7",
 	"COM8",
 	"COM9",
 	"LPT1",
 	"LPT2",
 	"LPT3",
 	"LPT4",
 	"LPT5",
 	"LPT6",
 	"LPT7",
 	"LPT8",
 	"LPT9",
 }
 
 // SplitPathVersion returns prefix and major version such that prefix+pathMajor == path
 // and version is either empty or "/vN" for N >= 2.
 // As a special case, gopkg.in paths are recognized directly;
 // they require ".vN" instead of "/vN", and for all N, not just N >= 2.
 // SplitPathVersion returns with ok = false when presented with
 // a path whose last path element does not satisfy the constraints
 // applied by [CheckPath], such as "example.com/pkg/v1" or "example.com/pkg/v1.2".
 func SplitPathVersion(path string) (prefix, pathMajor string, ok bool) {
 	if strings.HasPrefix(path, "gopkg.in/") {
 		return splitGopkgIn(path)
 	}
 
 	i := len(path)
 	dot := false
 	for i > 0 && ('0' <= path[i-1] && path[i-1] <= '9' || path[i-1] == '.') {
 		if path[i-1] == '.' {
 			dot = true
 		}
 		i--
 	}
 	if i <= 1 || i == len(path) || path[i-1] != 'v' || path[i-2] != '/' {
 		return path, "", true
 	}
 	prefix, pathMajor = path[:i-2], path[i-2:]
 	if dot || len(pathMajor) <= 2 || pathMajor[2] == '0' || pathMajor == "/v1" {
 		return path, "", false
 	}
 	return prefix, pathMajor, true
 }
 
 // splitGopkgIn is like SplitPathVersion but only for gopkg.in paths.
 func splitGopkgIn(path string) (prefix, pathMajor string, ok bool) {
 	if !strings.HasPrefix(path, "gopkg.in/") {
 		return path, "", false
 	}
 	i := len(path)
 	if strings.HasSuffix(path, "-unstable") {
 		i -= len("-unstable")
 	}
 	for i > 0 && ('0' <= path[i-1] && path[i-1] <= '9') {
 		i--
 	}
 	if i <= 1 || path[i-1] != 'v' || path[i-2] != '.' {
 		// All gopkg.in paths must end in vN for some N.
 		return path, "", false
 	}
 	prefix, pathMajor = path[:i-2], path[i-2:]
 	if len(pathMajor) <= 2 || pathMajor[2] == '0' && pathMajor != ".v0" {
 		return path, "", false
 	}
 	return prefix, pathMajor, true
 }
 
 // MatchPathMajor reports whether the semantic version v
 // matches the path major version pathMajor.
 //
 // MatchPathMajor returns true if and only if [CheckPathMajor] returns nil.
 func MatchPathMajor(v, pathMajor string) bool {
 	return CheckPathMajor(v, pathMajor) == nil
 }
 
 // CheckPathMajor returns a non-nil error if the semantic version v
 // does not match the path major version pathMajor.
 func CheckPathMajor(v, pathMajor string) error {
 	// TODO(jayconrod): return errors or panic for invalid inputs. This function
 	// (and others) was covered by integration tests for cmd/go, and surrounding
 	// code protected against invalid inputs like non-canonical versions.
 	if strings.HasPrefix(pathMajor, ".v") && strings.HasSuffix(pathMajor, "-unstable") {
 		pathMajor = strings.TrimSuffix(pathMajor, "-unstable")
 	}
 	if strings.HasPrefix(v, "v0.0.0-") && pathMajor == ".v1" {
 		// Allow old bug in pseudo-versions that generated v0.0.0- pseudoversion for gopkg .v1.
 		// For example, gopkg.in/yaml.v2@v2.2.1's go.mod requires gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405.
 		return nil
 	}
 	m := semver.Major(v)
 	if pathMajor == "" {
 		if m == "v0" || m == "v1" || semver.Build(v) == "+incompatible" {
 			return nil
 		}
 		pathMajor = "v0 or v1"
 	} else if pathMajor[0] == '/' || pathMajor[0] == '.' {
 		if m == pathMajor[1:] {
 			return nil
 		}
 		pathMajor = pathMajor[1:]
 	}
 	return &InvalidVersionError{
 		Version: v,
 		Err:     fmt.Errorf("should be %s, not %s", pathMajor, semver.Major(v)),
 	}
 }
 
 // PathMajorPrefix returns the major-version tag prefix implied by pathMajor.
 // An empty PathMajorPrefix allows either v0 or v1.
 //
 // Note that [MatchPathMajor] may accept some versions that do not actually begin
 // with this prefix: namely, it accepts a 'v0.0.0-' prefix for a '.v1'
 // pathMajor, even though that pathMajor implies 'v1' tagging.
 func PathMajorPrefix(pathMajor string) string {
 	if pathMajor == "" {
 		return ""
 	}
 	if pathMajor[0] != '/' && pathMajor[0] != '.' {
 		panic("pathMajor suffix " + pathMajor + " passed to PathMajorPrefix lacks separator")
 	}
 	if strings.HasPrefix(pathMajor, ".v") && strings.HasSuffix(pathMajor, "-unstable") {
 		pathMajor = strings.TrimSuffix(pathMajor, "-unstable")
 	}
 	m := pathMajor[1:]
 	if m != semver.Major(m) {
 		panic("pathMajor suffix " + pathMajor + "passed to PathMajorPrefix is not a valid major version")
 	}
 	return m
 }
 
 // CanonicalVersion returns the canonical form of the version string v.
 // It is the same as [semver.Canonical] except that it preserves the special build suffix "+incompatible".
 func CanonicalVersion(v string) string {
 	cv := semver.Canonical(v)
 	if semver.Build(v) == "+incompatible" {
 		cv += "+incompatible"
 	}
 	return cv
 }
 
 // Sort sorts the list by Path, breaking ties by comparing [Version] fields.
 // The Version fields are interpreted as semantic versions (using [semver.Compare])
 // optionally followed by a tie-breaking suffix introduced by a slash character,
 // like in "v0.0.1/go.mod".
 func Sort(list []Version) {
 	slices.SortFunc(list, func(i, j Version) int {
 		if i.Path != j.Path {
 			return strings.Compare(i.Path, j.Path)
 		}
 		// To help go.sum formatting, allow version/file.
 		// Compare semver prefix by semver rules,
 		// file by string order.
 		vi := i.Version
 		vj := j.Version
 		var fi, fj string
 		if k := strings.Index(vi, "/"); k >= 0 {
 			vi, fi = vi[:k], vi[k:]
 		}
 		if k := strings.Index(vj, "/"); k >= 0 {
 			vj, fj = vj[:k], vj[k:]
 		}
 		if vi != vj {
 			return semver.Compare(vi, vj)
 		}
 		return cmp.Compare(fi, fj)
 	})
 }
 
 // EscapePath returns the escaped form of the given module path.
 // It fails if the module path is invalid.
 func EscapePath(path string) (escaped string, err error) {
 	if err := CheckPath(path); err != nil {
 		return "", err
 	}
 
 	return escapeString(path)
 }
 
 // EscapeVersion returns the escaped form of the given module version.
 // Versions are allowed to be in non-semver form but must be valid file names
 // and not contain exclamation marks.
 func EscapeVersion(v string) (escaped string, err error) {
 	if err := checkElem(v, filePath); err != nil || strings.Contains(v, "!") {
 		return "", &InvalidVersionError{
 			Version: v,
 			Err:     fmt.Errorf("disallowed version string"),
 		}
 	}
 	return escapeString(v)
 }
 
 func escapeString(s string) (escaped string, err error) {
 	haveUpper := false
 	for _, r := range s {
 		if r == '!' || r >= utf8.RuneSelf {
 			// This should be disallowed by CheckPath, but diagnose anyway.
 			// The correctness of the escaping loop below depends on it.
 			return "", fmt.Errorf("internal error: inconsistency in EscapePath")
 		}
 		if 'A' <= r && r <= 'Z' {
 			haveUpper = true
 		}
 	}
 
 	if !haveUpper {
 		return s, nil
 	}
 
 	var buf []byte
 	for _, r := range s {
 		if 'A' <= r && r <= 'Z' {
 			buf = append(buf, '!', byte(r+'a'-'A'))
 		} else {
 			buf = append(buf, byte(r))
 		}
 	}
 	return string(buf), nil
 }
 
 // UnescapePath returns the module path for the given escaped path.
 // It fails if the escaped path is invalid or describes an invalid path.
 func UnescapePath(escaped string) (path string, err error) {
 	path, ok := unescapeString(escaped)
 	if !ok {
 		return "", fmt.Errorf("invalid escaped module path %q", escaped)
 	}
 	if err := CheckPath(path); err != nil {
 		return "", fmt.Errorf("invalid escaped module path %q: %v", escaped, err)
 	}
 	return path, nil
 }
 
 // UnescapeVersion returns the version string for the given escaped version.
 // It fails if the escaped form is invalid or describes an invalid version.
 // Versions are allowed to be in non-semver form but must be valid file names
 // and not contain exclamation marks.
 func UnescapeVersion(escaped string) (v string, err error) {
 	v, ok := unescapeString(escaped)
 	if !ok {
 		return "", fmt.Errorf("invalid escaped version %q", escaped)
 	}
 	if err := checkElem(v, filePath); err != nil {
 		return "", fmt.Errorf("invalid escaped version %q: %v", v, err)
 	}
 	return v, nil
 }
 
 func unescapeString(escaped string) (string, bool) {
 	var buf []byte
 
 	bang := false
 	for _, r := range escaped {
 		if r >= utf8.RuneSelf {
 			return "", false
 		}
 		if bang {
 			bang = false
 			if r < 'a' || 'z' < r {
 				return "", false
 			}
 			buf = append(buf, byte(r+'A'-'a'))
 			continue
 		}
 		if r == '!' {
 			bang = true
 			continue
 		}
 		if 'A' <= r && r <= 'Z' {
 			return "", false
 		}
 		buf = append(buf, byte(r))
 	}
 	if bang {
 		return "", false
 	}
 	return string(buf), true
 }
 
 // MatchPrefixPatterns reports whether any path prefix of target matches one of
 // the glob patterns (as defined by [path.Match]) in the comma-separated globs
 // list. This implements the algorithm used when matching a module path to the
 // GOPRIVATE environment variable, as described by 'go help module-private'.
 //
 // It ignores any empty or malformed patterns in the list.
 // Trailing slashes on patterns are ignored.
 func MatchPrefixPatterns(globs, target string) bool {
 	for globs != "" {
 		// Extract next non-empty glob in comma-separated list.
 		var glob string
 		if before, after, ok := strings.Cut(globs, ","); ok {
 			glob, globs = before, after
 		} else {
 			glob, globs = globs, ""
 		}
 		glob = strings.TrimSuffix(glob, "/")
 		if glob == "" {
 			continue
 		}
 
 		// A glob with N+1 path elements (N slashes) needs to be matched
 		// against the first N+1 path elements of target,
 		// which end just before the N+1'th slash.
 		n := strings.Count(glob, "/")
 		prefix := target
 		// Walk target, counting slashes, truncating at the N+1'th slash.
 		for i := 0; i < len(target); i++ {
 			if target[i] == '/' {
 				if n == 0 {
 					prefix = target[:i]
 					break
 				}
 				n--
 			}
 		}
 		if n > 0 {
 			// Not enough prefix elements.
 			continue
 		}
 		matched, _ := path.Match(glob, prefix)
 		if matched {
 			return true
 		}
 	}
 	return false
 }