if err != nil {
		return "", err
	}
	return filepath.Join(cfg.GOMODCACHE, "cache/download", enc, "/@v"), nil
}

func CachePath(ctx context.Context, m module.Version, suffix string) (string, error) {
	if gover.IsToolchain(m.Path) {
		return "", ErrToolchain
	}
	dir, err := cacheDir(ctx, m.Path)
	if err != nil {
		return "", err
	}
	if !gover.ModIsValid(m.Path, m.Version) {

		}

		// Module path or pattern.
		var match func(string) bool
		if arg == "all" {
			match = func(p string) bool { return !gover.IsToolchain(p) }
		} else if strings.Contains(arg, "...") {
			mp := pkgpattern.MatchPattern(arg)
			match = func(p string) bool { return mp(p) && !gover.IsToolchain(p) }
		} else {
			var v string
			if mg == nil {
				var ok bool
				v, ok = rs.rootSelected(arg)
				if !ok {

			base.Errorf("%s", err)
			ok = false
		}
	}
	if ok {
		fmt.Printf("all modules verified\n")
	}
}

func verifyMod(ctx context.Context, mod module.Version) []error {
	if gover.IsToolchain(mod.Path) {
		// "go" and "toolchain" have no disk footprint; nothing to verify.
		return nil
	}
	if modload.MainModules.Contains(mod.Path) {
		return nil
	}
	var errs []error

func (q *query) matchesPath(path string) bool {
	if q.matchWildcard != nil && !gover.IsToolchain(path) {
		return q.matchWildcard(path)
	}
	return path == q.pattern
}

// canMatchInModule reports whether the given module path can potentially
// contain q.pattern.
func (q *query) canMatchInModule(mPath string) bool {
	if gover.IsToolchain(mPath) {
		return false
	}
	if q.canMatchWildcardInModule != nil {

			}
		}
		if HasModRoot() {
			walkPkgs(VendorDir(), "", pruneVendor)
		}
		return
	}

	for _, mod := range modules {
		if gover.IsToolchain(mod.Path) || !treeCanMatch(mod.Path) {
			continue
		}

		var (
			root, modPrefix string
			isLocal         bool
		)
		if MainModules.Contains(mod.Path) {
			if MainModules.ModRoot(mod) == "" {

func goModSummary(m module.Version) (*modFileSummary, error) {
	if m.Version == "" && !inWorkspaceMode() && MainModules.Contains(m.Path) {
		panic("internal error: goModSummary called on a main module")
	}
	if gover.IsToolchain(m.Path) {
		return rawGoModSummary(m)
	}

	if cfg.BuildMod == "vendor" {
		summary := &modFileSummary{
			module: module.Version{Path: m.Path},
		}

		readVendorList(VendorDir())

		info.GoVersion = v.(string)
	}

	// completeFromModCache fills in the extra fields in m using the module cache.
	completeFromModCache := func(m *modinfo.ModulePublic) {
		if gover.IsToolchain(m.Path) {
			return
		}

		checksumOk := func(suffix string) bool {
			return rs == nil || m.Version == "" || !mustHaveSums() ||
				modfetch.HaveSum(module.Version{Path: m.Path, Version: m.Version + suffix})

// AllowedFunc of qm.
func (qm *queryMatcher) allowsVersion(ctx context.Context, v string) bool {
	if qm.prefix != "" && !strings.HasPrefix(v, qm.prefix) {
		if gover.IsToolchain(qm.path) && strings.TrimSuffix(qm.prefix, ".") == v {
			// Allow 1.21 to match "1.21." prefix.
		} else {
			return false
		}
	}
	if qm.filter != nil && !qm.filter(v) {
		return false
	}

		if gover.IsToolchain(path) {
			continue
		}
		old := r.initialVersion[path]
		new := reason.version
		if old != new && (old != "" || new != "none") {
			changes[path] = change{path, old, new}
		}
	}

	// Collect changes to explicit requirements in go.mod.
	for _, req := range oldReqs {
		if gover.IsToolchain(req.Path) {
			continue
		}

		}
	}

	if !strings.Contains(pkgArg, "@") || build.IsLocalImport(pkgArg) || filepath.IsAbs(pkgArg) {
		return false
	}
	path, version, _ := strings.Cut(pkgArg, "@")
	if path == "" || version == "" || gover.IsToolchain(path) {
		return false
	}

	if !modcacherwSeen && base.InGOFLAGS("-modcacherw") {
		fs := flag.NewFlagSet("goInstallVersion", flag.ExitOnError)
		fs.Var(modcacherwVal, "modcacherw", modcacherwFlag.Usage)