mode = "auto"
	} else if gotoolchain == "path" {
		mode = "path"
	} else {
		min, suffix, plus := strings.Cut(gotoolchain, "+") // go1.2.3+auto
		if min != "local" {
			v := gover.FromToolchain(min)
			if v == "" {
				if plus {
					base.Fatalf("invalid GOTOOLCHAIN %q: invalid minimum toolchain %q", gotoolchain, min)
				}
				base.Fatalf("invalid GOTOOLCHAIN %q", gotoolchain)
			}