index: deprecate legacy index format

internal/feature/registry.go

@@ -5,11 +5,13 @@ var Flag = New()
 
 // flag names are written in kebab-case
 const (
-	ExampleFeature FlagName = "example-feature"
+	ExampleFeature       FlagName = "example-feature"
+	DeprecateLegacyIndex FlagName = "deprecate-legacy-index"
 )
 
 func init() {
 	Flag.SetFlags(map[FlagName]FlagDesc{
-		ExampleFeature: {Type: Alpha, Description: "just for testing"},
+		ExampleFeature:       {Type: Alpha, Description: "just for testing"},
+		DeprecateLegacyIndex: {Type: Beta, Description: "disable support for index format used by restic 0.1.0. Use `restic repair index` to update the index if necessary."},
 	})
 }