Reduce size of pgmconfig package

pkg/plugins/config.go

@@ -5,18 +5,27 @@ package plugins
 
 import (
 	"fmt"
-	"github.com/spf13/pflag"
+	"os"
 	"path/filepath"
+	"runtime"
+
+	"github.com/spf13/pflag"
 	"sigs.k8s.io/kustomize/v3/pkg/pgmconfig"
 	"sigs.k8s.io/kustomize/v3/pkg/types"
 )
 
 const (
-	PluginSymbol            = "KustomizePlugin"
-	BuiltinPluginPackage    = "builtin"
+	// Used with Go plugins.
+	PluginSymbol = "KustomizePlugin"
+
+	// Location of builtins.
+	BuiltinPluginPackage = "builtin"
+
+	// ApiVersion of builtins.
 	BuiltinPluginApiVersion = BuiltinPluginPackage
-	flagEnablePluginsName   = "enable_alpha_plugins"
-	flagEnablePluginsHelp   = `enable plugins, an alpha feature.
+
+	flagEnablePluginsName = "enable_alpha_plugins"
+	flagEnablePluginsHelp = `enable plugins, an alpha feature.
 See https://github.com/kubernetes-sigs/kustomize/blob/master/docs/plugins/README.md
 `
 	flagErrorFmt = `
@@ -36,11 +45,11 @@ func DefaultPluginConfig() *types.PluginConfig {
 	return &types.PluginConfig{
 		Enabled: false,
 		DirectoryPath: filepath.Join(
-			pgmconfig.ConfigRoot(), pgmconfig.PluginRoot),
+			configRoot(), pgmconfig.PluginRoot),
 	}
 }
 
-func NotEnabledErr(name string) error {
+func notEnabledErr(name string) error {
 	return fmt.Errorf(
 		flagErrorFmt,
 		name,
@@ -53,3 +62,28 @@ func AddFlagEnablePlugins(set *pflag.FlagSet, v *bool) {
 		v, flagEnablePluginsName,
 		false, flagEnablePluginsHelp)
 }
+
+// Use https://github.com/kirsle/configdir instead?
+func configRoot() string {
+	dir := os.Getenv(pgmconfig.XdgConfigHome)
+	if len(dir) == 0 {
+		dir = filepath.Join(
+			homeDir(), pgmconfig.DefaultConfigSubdir)
+	}
+	return filepath.Join(dir, pgmconfig.ProgramName)
+}
+
+func homeDir() string {
+	home := os.Getenv(homeEnv())
+	if len(home) > 0 {
+		return home
+	}
+	return "~"
+}
+
+func homeEnv() string {
+	if runtime.GOOS == "windows" {
+		return "USERPROFILE"
+	}
+	return "HOME"
+}