cfgstruct.Bind: support nested config paths (#785)

this will allow some config cleanups in a future pr

Change-Id: Ie873bcee567a72956d9337dfc13ab6ba46c9d1a0

cmd/captplanet/setup.go

@@ -46,8 +46,7 @@ var (
 func init() {
 	rootCmd.AddCommand(setupCmd)
 	cfgstruct.Bind(setupCmd.Flags(), &setupCfg,
-		cfgstruct.ConfDir(defaultConfDir),
-	)
+		cfgstruct.ConfDir(defaultConfDir))
 }
 
 func cmdSetup(cmd *cobra.Command, args []string) (err error) {

pkg/cfgstruct/bind.go

@@ -6,6 +6,7 @@ package cfgstruct
 import (
 	"fmt"
 	"os"
+	"path/filepath"
 	"reflect"
 	"regexp"
 	"strconv"
@@ -14,15 +15,33 @@ import (
 )
 
 // BindOpt is an option for the Bind method
-type BindOpt func(vars map[string]string)
+type BindOpt func(vars map[string]confVar)
 
-// ConfDir sets a variable for default options called $CONFDIR
+// ConfDir sets variables for default options called $CONFDIR and $CONFNAME.
 func ConfDir(confdir string) BindOpt {
-	return BindOpt(func(vars map[string]string) {
-		vars["CONFDIR"] = os.ExpandEnv(confdir)
+	val := filepath.Clean(os.ExpandEnv(confdir))
+	return BindOpt(func(vars map[string]confVar) {
+		vars["CONFDIR"] = confVar{val: val, nested: false}
+		vars["CONFNAME"] = confVar{val: val, nested: false}
 	})
 }
 
+// ConfDirNested sets variables for default options called $CONFDIR and $CONFNAME.
+// ConfDirNested also appends the parent struct field name to the paths before
+// descending into substructs.
+func ConfDirNested(confdir string) BindOpt {
+	val := filepath.Clean(os.ExpandEnv(confdir))
+	return BindOpt(func(vars map[string]confVar) {
+		vars["CONFDIR"] = confVar{val: val, nested: true}
+		vars["CONFNAME"] = confVar{val: val, nested: true}
+	})
+}
+
+type confVar struct {
+	val    string
+	nested bool
+}
+
 // Bind sets flags on a FlagSet that match the configuration struct
 // 'config'. This works by traversing the config struct using the 'reflect'
 // package.
@@ -32,7 +51,7 @@ func Bind(flags FlagSet, config interface{}, opts ...BindOpt) {
 		panic(fmt.Sprintf("invalid config type: %#v. "+
 			"Expecting pointer to struct.", config))
 	}
-	vars := map[string]string{}
+	vars := map[string]confVar{}
 	for _, opt := range opts {
 		opt(vars)
 	}
@@ -44,13 +63,25 @@ var (
 )
 
 func bindConfig(flags FlagSet, prefix string, val reflect.Value,
-	vars map[string]string) {
+	vars map[string]confVar) {
 	if val.Kind() != reflect.Struct {
 		panic(fmt.Sprintf("invalid config type: %#v. Expecting struct.",
 			val.Interface()))
 	}
 	typ := val.Type()
 
+	resolvedVars := make(map[string]string, len(vars))
+	{
+		structpath := strings.Replace(prefix, ".", "/", -1)
+		for k, v := range vars {
+			if !v.nested {
+				resolvedVars[k] = v.val
+				continue
+			}
+			resolvedVars[k] = filepath.Join(v.val, structpath)
+		}
+	}
+
 	for i := 0; i < typ.NumField(); i++ {
 		field := typ.Field(i)
 		fieldval := val.Field(i)
@@ -107,7 +138,8 @@ func bindConfig(flags FlagSet, prefix string, val reflect.Value,
 				check(err)
 				flags.Float64Var(fieldaddr.(*float64), flagname, val, help)
 			case reflect.TypeOf(string("")):
-				flags.StringVar(fieldaddr.(*string), flagname, expand(vars, def), help)
+				flags.StringVar(
+					fieldaddr.(*string), flagname, expand(resolvedVars, def), help)
 			case reflect.TypeOf(bool(false)):
 				val, err := strconv.ParseBool(def)
 				check(err)

pkg/cfgstruct/bind_test.go

@@ -74,3 +74,37 @@ func TestBind(t *testing.T) {
 	assertEqual(c.Fields[0].AnotherInt, int(0))
 	assertEqual(c.Fields[3].AnotherInt, int(1))
 }
+
+func TestConfDir(t *testing.T) {
+	f := flag.NewFlagSet("test", flag.PanicOnError)
+	var c struct {
+		String    string `default:"-$CONFDIR+"`
+		MyStruct1 struct {
+			String    string `default:"1${CONFDIR}2"`
+			MyStruct2 struct {
+				String string `default:"2${CONFDIR}3"`
+			}
+		}
+	}
+	Bind(f, &c, ConfDir("confpath"))
+	assertEqual(f.Lookup("string").DefValue, "-confpath+")
+	assertEqual(f.Lookup("my-struct1.string").DefValue, "1confpath2")
+	assertEqual(f.Lookup("my-struct1.my-struct2.string").DefValue, "2confpath3")
+}
+
+func TestNesting(t *testing.T) {
+	f := flag.NewFlagSet("test", flag.PanicOnError)
+	var c struct {
+		String    string `default:"-$CONFDIR+"`
+		MyStruct1 struct {
+			String    string `default:"1${CONFDIR}2"`
+			MyStruct2 struct {
+				String string `default:"2${CONFDIR}3"`
+			}
+		}
+	}
+	Bind(f, &c, ConfDirNested("confpath"))
+	assertEqual(f.Lookup("string").DefValue, "-confpath+")
+	assertEqual(f.Lookup("my-struct1.string").DefValue, "1confpath/my-struct12")
+	assertEqual(f.Lookup("my-struct1.my-struct2.string").DefValue, "2confpath/my-struct1/my-struct23")
+}