如何只为更改的模板运行go generate？

Question

We use some code templates in our repo, and we rely on go:generate to generate all the needed codes from these templates.
Because there are several templates and from each template we generate several actual codes, consistency of generated codes has become an issue: we needed a command to run and be sure that all generated codes are up to date with their corresponding templates. To do this, we have a simple bash command that find all files that have go:generate in them, and runs go generate in their directory.
The problem is that this approach is really slow: most of the templates have not changed, so there is no need to generate their codes again.
Is there any way to tell go generate to only run if the template is newer than the file? Or, is there any better approach other than this?
Thank you very much.

Answer 1

First, you don't need that bash script that looks for go:generate in files, the go tool itself can do that for you. Just use

go generate ./...

to recurse in subfolders.

Next, when a code generation runs, I would store the template file's last modification timestamp in the generated code, either in a comment or in a const / var. The app that is run by go generate could first check if the template's last mod time is newer that the stored one in the code, and only proceed if so.

This file last mod time should be enough. But if for some reason you can't rely on it, the template could have a "version", which should be incremented when the template is changed. And have the generator "transfer" this version into the final code, which can be used to check if the template is newer than the code generated from it.