[release-18.0] viper: register dynamic config with both disk and live (…

…#14453) (#14455)

Signed-off-by: deepthi <deepthi@planetscale.com>
Co-authored-by: vitess-bot[bot] <108069721+vitess-bot[bot]@users.noreply.github.com>

go/viperutil/internal/sync/sync.go

@@ -289,10 +289,29 @@ func (v *Viper) loadFromDisk() {
 
 // begin implementation of registry.Bindable for sync.Viper
 
-func (v *Viper) BindEnv(vars ...string) error                 { return v.disk.BindEnv(vars...) }
-func (v *Viper) BindPFlag(key string, flag *pflag.Flag) error { return v.disk.BindPFlag(key, flag) }
-func (v *Viper) RegisterAlias(alias string, key string)       { v.disk.RegisterAlias(alias, key) }
-func (v *Viper) SetDefault(key string, value any)             { v.disk.SetDefault(key, value) }
+func (v *Viper) BindEnv(vars ...string) error {
+	if err := v.disk.BindEnv(vars...); err != nil {
+		return err
+	}
+	return v.live.BindEnv(vars...)
+}
+
+func (v *Viper) BindPFlag(key string, flag *pflag.Flag) error {
+	if err := v.disk.BindPFlag(key, flag); err != nil {
+		return err
+	}
+	return v.live.BindPFlag(key, flag)
+}
+
+func (v *Viper) RegisterAlias(alias string, key string) {
+	v.disk.RegisterAlias(alias, key)
+	v.live.RegisterAlias(alias, key)
+}
+
+func (v *Viper) SetDefault(key string, value any) {
+	v.disk.SetDefault(key, value)
+	v.live.SetDefault(key, value)
+}
 
 // end implementation of registry.Bindable for sync.Viper
 

go/viperutil/internal/sync/sync_test.go

@@ -93,7 +93,10 @@ func TestWatchConfig(t *testing.T) {
 
 	sv := vipersync.New()
 	A := viperutil.Configure("a", viperutil.Options[int]{Dynamic: true})
-	B := viperutil.Configure("b", viperutil.Options[int]{Dynamic: true})
+	B := viperutil.Configure("b", viperutil.Options[int]{FlagName: "b", Dynamic: true, Default: 5})
+
+	// Check that default values are actually used
+	require.Equal(t, B.Get(), B.Default())
 
 	A.(*value.Dynamic[int]).Base.BoundGetFunc = vipersync.AdaptGetter("a", func(v *viper.Viper) func(key string) int {
 		return v.GetInt