case goVersion != "":
			fmt.Fprintf(w, "## go %s\n", goVersion)
		}

		pkgs := modpkgs[m]
		sort.Strings(pkgs)
		for _, pkg := range pkgs {
			fmt.Fprintf(w, "%s\n", pkg)
			vendorPkg(vdir, pkg)
		}
	}

	if includeAllReplacements {
		// Record unused and wildcard replacements at the end of the modules.txt file:
		// without access to the complete build list, the consumer of the vendor

-- modules.txt.required_but_not_explicit --
## workspace
# example.com/p v1.0.0 => ./p
## go 1.21
# example.com/q v1.0.0 => ./q
## explicit; go 1.21
-- required_but_not_explicit_error.txt --
go: inconsistent vendoring in $GOPATH${/}src:
	example.com/p@v1.0.0: is explicitly required in go.mod, but not marked as explicit in vendor/modules.txt

	To ignore the vendor directory, use -mod=readonly or -mod=mod.
	To sync the vendor directory, run:

# A 'go 1.13' vendor/modules.txt file is not usually sufficient
# to pass those checks.
go mod edit -go=1.14

! go list -f {{.Dir}} -tags tools all
stderr '^go: inconsistent vendoring in '$WORK[/\\]auto':$'
stderr '^\texample.com/printversion@v1.0.0: is explicitly required in go.mod, but not marked as explicit in vendor/modules.txt'

type gcimports struct {
	fset     *token.FileSet
	packages map[string]*types.Package
	lookup   Lookup
}

func (m *gcimports) Import(path string) (*types.Package, error) {
	return m.ImportFrom(path, "" /* no vendoring */, 0)
}

func (m *gcimports) ImportFrom(path, srcDir string, mode types.ImportMode) (*types.Package, error) {
	if mode != 0 {
		panic("mode must be 0")
	}

must not already exist.

Init accepts one optional argument, the module path for the new module. If the
module path argument is omitted, init will attempt to infer the module path
using import comments in .go files, vendoring tool configuration files (like
Gopkg.lock), and the current directory (if in GOPATH).

See https://golang.org/ref/mod#go-mod-init for more about 'go mod init'.
`,
	Run: runInit,
}

func init() {

# This test exercises that vendoring works properly using the workspace in the
# the work_prune test case.

go work vendor
cmp vendor/modules.txt modules.txt.want
cmp vendor/example.com/b/b.go b/b.go
cmp vendor/example.com/q/q.go q1_1_0/q.go
go list -m -f '{{.Version}}' example.com/q
stdout '^v1.1.0$'

go list -f '{{.Dir}}' example.com/q
stdout $GOPATH[\\/]src[\\/]vendor[\\/]example.com[\\/]q
go list -f '{{.Dir}}' example.com/b

// The prefixes are component-wise; for example, "golang.org/x"
// matches "golang.org/x/build" but not "golang.org/xyz".
//
// DO NOT ADD TO THIS LIST TO FIX BUILDS.
// Vendoring a new package requires prior discussion.
var allowedPackagePrefixes = []string{
	"golang.org/x",
	"github.com/google/pprof",
	"github.com/ianlancetaylor/demangle",
	"rsc.io/markdown",
}

Vendoring in std and cmd
========================

The Go command maintains copies of external packages needed by the
standard library in the src/vendor and src/cmd/vendor directories.

There are two modules, std and cmd, defined in src/go.mod and
src/cmd/go.mod. When a package outside std or cmd is imported
by a package inside std or cmd, the import path is interpreted
as if it had a "vendor/" prefix. For example, within "crypto/tls",

# This test exercises that vendoring works properly using the workspace in the
# the work_prune test case.

go work vendor
cmp vendor/modules.txt modules.txt.want
go list -f '{{with .Module}}{{.Path}}@{{.Version}}{{end}}' all
cmp stdout want_versions

go list -f '{{.Dir}}' example.com/q
stdout $GOPATH[\\/]src[\\/]vendor[\\/]example.com[\\/]q
go list -f '{{.Dir}}' example.com/b
stdout $GOPATH[\\/]src[\\/]vendor[\\/]example.com[\\/]b

	}

	if vendErrors.Len() > 0 {
		subcmd := "mod"
		if inWorkspaceMode() {
			subcmd = "work"
		}
		base.Fatalf("go: inconsistent vendoring in %s:%s\n\n\tTo ignore the vendor directory, use -mod=readonly or -mod=mod.\n\tTo sync the vendor directory, run:\n\t\tgo %s vendor", filepath.Dir(VendorDir()), vendErrors, subcmd)
	}