Allow NewHook() to return an error (for future changes).

gengokit/generator/gen.go

@@ -71,7 +71,11 @@ func generateResponseFile(templFP string, data *gengokit.Data, prevFile io.Reade
 		}
 
 	case handlers.HookPath:
-		hook := handlers.NewHook(prevFile)
+		hook, err := handlers.NewHook(prevFile)
+		if err != nil {
+			return nil, errors.Wrapf(err, "cannot parse previous hooks: %s", templFP)
+		}
+
 		genCode, err = hook.Render(templFP, data)
 		if err != nil {
 			return nil, errors.Wrapf(err, "cannot render template: %s", templFP)

gengokit/handlers/hooks.go

@@ -11,10 +11,10 @@ import (
 const HookPath = "handlers/hooks.gotemplate"
 
 // NewHook returns a new HookRender
-func NewHook(prev io.Reader) gengokit.Renderable {
+func NewHook(prev io.Reader) (gengokit.Renderable, error) {
 	return &HookRender{
 		prev: prev,
-	}
+	}, nil
 }
 
 type HookRender struct {