Don't generate a Go file, if that would be empty

Signed-off-by: Kazuyoshi Kato <[email protected]>

cmd/protoc-gen-go-fieldpath/generator.go

@@ -159,13 +159,6 @@ func collectChildlen(parent *protogen.Message) ([]*protogen.Message, error) {
 }
 
 func generate(plugin *protogen.Plugin, input *protogen.File) error {
-	file := plugin.NewGeneratedFile(input.GeneratedFilenamePrefix+"_fieldpath.pb.go", input.GoImportPath)
-	file.P("// Code generated by protoc-gen-go-fieldpath. DO NOT EDIT.")
-	file.P("// source: ", input.Desc.Path())
-	file.P("package ", input.GoPackageName)
-
-	gen := newGenerator(file)
-
 	var messages []*protogen.Message
 	for _, m := range input.Messages {
 		messages = append(messages, m)
@@ -176,6 +169,18 @@ func generate(plugin *protogen.Plugin, input *protogen.File) error {
 		messages = append(messages, children...)
 	}
 
+	if len(messages) == 0 {
+		// Don't generate a Go file, if that would be empty.
+		return nil
+	}
+
+	file := plugin.NewGeneratedFile(input.GeneratedFilenamePrefix+"_fieldpath.pb.go", input.GoImportPath)
+	file.P("// Code generated by protoc-gen-go-fieldpath. DO NOT EDIT.")
+	file.P("// source: ", input.Desc.Path())
+	file.P("package ", input.GoPackageName)
+
+	gen := newGenerator(file)
+
 	for _, m := range messages {
 		gen.genFieldMethod(m)
 	}