}
	switch {
	case os.IsNotExist(err) && gosumIdx >= 0:
		// go.sum was deleted.
		rewrite = true
		archive.Files = append(archive.Files[:gosumIdx], archive.Files[gosumIdx+1:]...)
	case err == nil && gosumIdx < 0:
		// go.sum was created.
		rewrite = true
		gosumIdx = gomodIdx + 1
		archive.Files = append(archive.Files, txtar.File{})
		copy(archive.Files[gosumIdx+1:], archive.Files[gosumIdx:])

stdout go1.999testmod

# GOTOOLCHAIN with GOSUMDB enabled but at a bad URL should operate in cache and not try badurl
env oldsumdb=$GOSUMDB
env GOSUMDB=$oldsumdb' http://badurl'
go version
! stderr downloading
stdout go1.999testmod

# GOTOOLCHAIN with GOSUMB=off should fail, because it cannot access even the cached sumdb info
# without the sumdb name.
env GOSUMDB=off
! go version

# Test default GOPROXY and GOSUMDB
[go-builder] env GOPROXY=
[go-builder] env GOSUMDB=
[go-builder] go env GOPROXY
[go-builder] stdout '^https://proxy.golang.org,direct$'
[go-builder] go env GOSUMDB
[go-builder] stdout '^sum.golang.org$'
[go-builder] env GOPROXY=https://proxy.golang.org
[go-builder] go env GOSUMDB
[go-builder] stdout '^sum.golang.org$'

# Download direct from github.

[!net:proxy.golang.org] skip
[!net:sum.golang.org] skip

# Test query for non-defaults in the env

env GOROOT=./a
env GOTOOLCHAIN=local
env GOSUMDB=nodefault
env GOPROXY=nodefault
env GO111MODULE=auto
env CGO_CFLAGS=nodefault
env CGO_CPPFLAGS=nodefault

go env -changed
# linux output like GOTOOLCHAIN='local'
# windows output like GOTOOLCHAIN=local
stdout 'GOTOOLCHAIN=''?local''?'
stdout 'GOSUMDB=''?nodefault''?'
stdout 'GOPROXY=''?nodefault''?'
stdout 'GO111MODULE=''?auto''?'

[!net:proxy.golang.org] skip
[!net:sum.golang.org] skip

env GO111MODULE=on
[go-builder] env GOSUMDB=
[!go-builder] env GOSUMDB=sum.golang.org  # Set explicitly in case GOROOT/go.env is modified.
env GOPATH=$WORK/gopath1

# With a file-based proxy with an empty checksum directory,
# downloading a new module should fail, even if a subsequent
# proxy contains a more complete mirror of the sum database.
#

	GOFLAGS
	GOGCCFLAGS
	GOHOSTARCH
	GOHOSTOS
	GOINSECURE
	GOMIPS
	GOMIPS64
	GOMODCACHE
	GONOPROXY
	GONOSUMDB
	GOOS
	GOPATH
	GOPPC64
	GOPRIVATE
	GOPROXY
	GORISCV64
	GOROOT
	GOSUMDB
	GOTMPDIR
	GOTOOLCHAIN
	GOTOOLDIR
	GOVCS
	GOWASM
	GOWORK
	GO_EXTLINK_ENABLED
	PKG_CONFIG

        GONOPROXY=""
        GONOSUMDB=""
        GOOS="darwin"
        GOPATH="/Users/gopher/go"
        GOPRIVATE=""
        GOPROXY="https://proxy.golang.org,direct"
        GOROOT="/usr/local/go"
        GOSUMDB="sum.golang.org"
        GOTMPDIR=""
        GOTOOLDIR="/usr/local/go/pkg/tool/darwin_arm64"
        GOVCS=""
        GOVERSION="go1.20.7"
        GCCGO="gccgo"
        AR="ar"
        CC="clang"

# @latest, @upgrade, and @patch should prefer compatible versions over
# +incompatible ones, even if offered by a proxy.

[!net:github.com] skip
[!net:proxy.golang.org] skip

env GO111MODULE=on
env GOPROXY=
env GOSUMDB=

# github.com/russross/blackfriday v2.0.0+incompatible exists,
# and should be resolved if we ask for it explicitly.

go list -m github.com/russross/blackfriday@v2.0.0+incompatible

	GOWASM, goWASMChanged       = EnvOrAndChanged("GOWASM", fmt.Sprint(buildcfg.GOWASM))

	GOPROXY, GOPROXYChanged     = EnvOrAndChanged("GOPROXY", "")
	GOSUMDB, GOSUMDBChanged     = EnvOrAndChanged("GOSUMDB", "")
	GOPRIVATE                   = Getenv("GOPRIVATE")
	GONOPROXY, GONOPROXYChanged = EnvOrAndChanged("GONOPROXY", GOPRIVATE)
	GONOSUMDB, GONOSUMDBChanged = EnvOrAndChanged("GONOSUMDB", GOPRIVATE)

		{Name: "GOPRIVATE", Value: cfg.GOPRIVATE},
		{Name: "GOPROXY", Value: cfg.GOPROXY, Changed: cfg.GOPROXYChanged},
		{Name: "GOROOT", Value: cfg.GOROOT},
		{Name: "GOSUMDB", Value: cfg.GOSUMDB, Changed: cfg.GOSUMDBChanged},
		{Name: "GOTMPDIR", Value: cfg.Getenv("GOTMPDIR")},
		{Name: "GOTOOLCHAIN"},
		{Name: "GOTOOLDIR", Value: build.ToolDir},
		{Name: "GOVCS", Value: cfg.GOVCS},