GOARCH
	GOARM
	GOARM64
	GOBIN
	GOCACHE
	GOCACHEPROG
	GOENV
	GOEXE
	GOEXPERIMENT
	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

        GOEXE=""
        GOEXPERIMENT=""
        GOFLAGS=""
        GOHOSTARCH="arm64"
        GOHOSTOS="darwin"
        GOINSECURE=""
        GOMODCACHE="/Users/gopher/go/pkg/mod"
        GONOPROXY=""
        GONOSUMDB=""
        GOOS="darwin"
        GOPATH="/Users/gopher/go"
        GOPRIVATE=""
        GOPROXY="https://proxy.golang.org,direct"
        GOROOT="/usr/local/go"
        GOSUMDB="sum.golang.org"

	// equivalent to os.ErrNotFound, which is true for 404 and 410 responses.
	fallBackOnError bool
}

func proxyList() ([]proxySpec, error) {
	proxyOnce.Do(func() {
		if cfg.GONOPROXY != "" && cfg.GOPROXY != "direct" {
			proxyOnce.list = append(proxyOnce.list, proxySpec{url: "noproxy"})
		}

		goproxy := cfg.GOPROXY
		for goproxy != "" {
			var url string
			fallBackOnError := false

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

		{Name: "GOHOSTOS", Value: runtime.GOOS},
		{Name: "GOINSECURE", Value: cfg.GOINSECURE},
		{Name: "GOMODCACHE", Value: cfg.GOMODCACHE, Changed: cfg.GOMODCACHEChanged},
		{Name: "GONOPROXY", Value: cfg.GONOPROXY, Changed: cfg.GONOPROXYChanged},
		{Name: "GONOSUMDB", Value: cfg.GONOSUMDB, Changed: cfg.GONOSUMDBChanged},
		{Name: "GOOS", Value: cfg.Goos, Changed: cfg.Goos != runtime.GOOS},

		"TESTGO_VCSTEST_TLS_HOST=" + httpsURL.Host,
		"TESTGO_VCSTEST_CERT=" + srvCertFile,
		"TESTGONETWORK=panic", // cleared by the [net] condition
		"GOSUMDB=" + testSumDBVerifierKey,
		"GONOPROXY=",
		"GONOSUMDB=",
		"GOVCS=*:all",
		"devnull=" + os.DevNull,
		"goversion=" + gover.Local(),
		"CMDGO_TEST_RUN_MAIN=true",
		"HGRCPATH=",
		"GOTOOLCHAIN=auto",
		"newline=\n",
	}

matching either pattern, including git.corp.example.com/xyzzy, rsc.io/private,
and rsc.io/private/quux.

For fine-grained control over module download and validation, the GONOPROXY
and GONOSUMDB environment variables accept the same kind of glob list
and override GOPRIVATE for the specific decision of whether to use the proxy
and checksum database, respectively.

		Controls where various files are stored. See: 'go help gopath'.
	GOPROXY
		URL of Go module proxy. See https://golang.org/ref/mod#environment-variables
		and https://golang.org/ref/mod#module-proxy for details.
	GOPRIVATE, GONOPROXY, GONOSUMDB
		Comma-separated list of glob patterns (in the syntax of Go's path.Match)
		of module path prefixes that should always be fetched directly
		or that should not be compared against the checksum database.

//	GOPROXY
//		URL of Go module proxy. See https://golang.org/ref/mod#environment-variables
//		and https://golang.org/ref/mod#module-proxy for details.
//	GOPRIVATE, GONOPROXY, GONOSUMDB
//		Comma-separated list of glob patterns (in the syntax of Go's path.Match)
//		of module path prefixes that should always be fetched directly
//		or that should not be compared against the checksum database.