func stdlib()

in go/tools/builders/stdlib.go [28:166]
94 lines of code
19 McCabe index (conditional complexity)

func stdlib(args []string) error {
	// process the args
	flags := flag.NewFlagSet("stdlib", flag.ExitOnError)
	goenv := envFlags(flags)
	out := flags.String("out", "", "Path to output go root")
	race := flags.Bool("race", false, "Build in race mode")
	shared := flags.Bool("shared", false, "Build in shared mode")
	dynlink := flags.Bool("dynlink", false, "Build in dynlink mode")
	if err := flags.Parse(args); err != nil {
		return err
	}
	if err := goenv.checkFlags(); err != nil {
		return err
	}
	goroot := os.Getenv("GOROOT")
	if goroot == "" {
		return fmt.Errorf("GOROOT not set")
	}
	output := abs(*out)

	// Fail fast if cgo is required but a toolchain is not configured.
	if os.Getenv("CGO_ENABLED") == "1" && filepath.Base(os.Getenv("CC")) == "vc_installation_error.bat" {
		return fmt.Errorf(`cgo is required, but a C toolchain has not been configured.
You may need to use the flags --cpu=x64_windows --compiler=mingw-gcc.`)
	}

	// Link in the bare minimum needed to the new GOROOT
	if err := replicate(goroot, output, replicatePaths("src", "pkg/tool", "pkg/include")); err != nil {
		return err
	}

	output, err := processPath(output)
	if err != nil {
		return err
	}

	// Now switch to the newly created GOROOT
	os.Setenv("GOROOT", output)

	// Create a temporary cache directory. "go build" requires this starting
	// in Go 1.12.
	cachePath := filepath.Join(output, ".gocache")
	os.Setenv("GOCACHE", cachePath)
	defer os.RemoveAll(cachePath)

	// Disable modules for the 'go install' command. Depending on the sandboxing
	// mode, there may be a go.mod file in a parent directory which will turn
	// modules on in "auto" mode.
	os.Setenv("GO111MODULE", "off")

	// Make sure we have an absolute path to the C compiler.
	// TODO(#1357): also take absolute paths of includes and other paths in flags.
	os.Setenv("CC", abs(os.Getenv("CC")))

	// Ensure paths are absolute.
	absPaths := []string{}
	for _, path := range filepath.SplitList(os.Getenv("PATH")) {
		absPaths = append(absPaths, abs(path))
	}
	os.Setenv("PATH", strings.Join(absPaths, string(os.PathListSeparator)))

	sandboxPath := abs(".")

	// Strip path prefix from source files in debug information.
	os.Setenv("CGO_CFLAGS", os.Getenv("CGO_CFLAGS")+" "+strings.Join(defaultCFlags(output), " "))
	os.Setenv("CGO_LDFLAGS", os.Getenv("CGO_LDFLAGS")+" "+strings.Join(defaultLdFlags(), " "))

	// Allow flags in CGO_LDFLAGS that wouldn't pass the security check.
	// Workaround for golang.org/issue/42565.
	var b strings.Builder
	sep := ""
	cgoLdflags, _ := splitQuoted(os.Getenv("CGO_LDFLAGS"))
	for _, f := range cgoLdflags {
		b.WriteString(sep)
		sep = "|"
		b.WriteString(regexp.QuoteMeta(f))
		// If the flag if -framework, the flag value needs to be in the same
		// condition.
		if f == "-framework" {
			sep = " "
		}
	}
	os.Setenv("CGO_LDFLAGS_ALLOW", b.String())

	// Build the commands needed to build the std library in the right mode
	// NOTE: the go command stamps compiled .a files with build ids, which are
	// cryptographic sums derived from the inputs. This prevents us from
	// creating reproducible builds because the build ids are hashed from
	// CGO_CFLAGS, which frequently contains absolute paths. As a workaround,
	// we strip the build ids, since they won't be used after this.
	installArgs := goenv.goCmd("install", "-toolexec", abs(os.Args[0])+" filterbuildid")
	if len(build.Default.BuildTags) > 0 {
		installArgs = append(installArgs, "-tags", strings.Join(build.Default.BuildTags, ","))
	}

	gcflags := []string{}
	ldflags := []string{"-trimpath", sandboxPath}
	asmflags := []string{"-trimpath", output}
	if *race {
		installArgs = append(installArgs, "-race")
	}
	if *shared {
		gcflags = append(gcflags, "-shared")
		ldflags = append(ldflags, "-shared")
		asmflags = append(asmflags, "-shared")
	}
	if *dynlink {
		gcflags = append(gcflags, "-dynlink")
		ldflags = append(ldflags, "-dynlink")
		asmflags = append(asmflags, "-dynlink")
	}

	// Since Go 1.10, an all= prefix indicates the flags should apply to the package
	// and its dependencies, rather than just the package itself. This was the
	// default behavior before Go 1.10.
	allSlug := ""
	for _, t := range build.Default.ReleaseTags {
		if t == "go1.10" {
			allSlug = "all="
			break
		}
	}
	installArgs = append(installArgs, "-gcflags="+allSlug+strings.Join(gcflags, " "))
	installArgs = append(installArgs, "-ldflags="+allSlug+strings.Join(ldflags, " "))
	installArgs = append(installArgs, "-asmflags="+allSlug+strings.Join(asmflags, " "))

	// Modifying CGO flags to use only absolute path
	// because go is having its own sandbox, all CGO flags must use absolute path
	if err := absEnv(cgoEnvVars, cgoAbsEnvFlags); err != nil {
		return fmt.Errorf("error modifying cgo environment to absolute path: %v", err)
	}

	// TODO(#1885): don't install runtime/cgo in pure mode.
	installArgs = append(installArgs, "std", "runtime/cgo")
	if err := goenv.runCommand(installArgs); err != nil {
		return err
	}
	return nil
}