Provide some guidance on updated scaffold features getting applied to already-created projects

[alexeagle]

A scaffold can gain features over time. Anyone who already stamped out the scaffold essentially got a fork of the commit history to the scaffold template.

Like version control, a user who created their project from the scaffold might want to "merge" some of those improvements to the project they've already created. Or, they might have answered "No" to a prompt the first time, but then when they run again they say "Yes".

Of course the --no-clobber flag isn't sufficient for this: it would create new files but has no way to add contents into existing ones.
And like version control, merge conflicts can happen and would need some affordance for resolving (most tools would do it nicely if we literally wrote merge conflict range markers into their file)

Starting a discussion since I'm not sure if there's already a good way to do this, or it's a feature that needs some design thought.

[hay-kot]

This isn't really something I've considered in the design, I think that it would be possible to add this kind of feature, but based on my research it would be a pretty huge lift and I'm not convinced on the use case - at least for anything I've used scaffold for. So there is no way to do this currently.

As for a general design, I think taking inspiration from copier would probably be a good start. It looks like it does exactly what you're describing, but I haven't dug deep into the depths of how it's being done, or if there are templates that are taking advantage of this.

Do you have a more concrete example I could use to understand this use-case better?

[alexeagle]

As an example, we have a tool that creates a new Bazel workspace, https://github.com/aspect-build/aspect-workflows-template
I'm actively adding features to the template. As an example, aspect-build/aspect-workflows-template@9acae34 adds some new tools like docker-compose.

We have some users like @domenic_donato who have used that to stamp out a new Python project. He has found it necessary to create a new project from the latest scaffold, then do some diffing by hand to figure out what improvements I have made and bring those into his workspace.

[alexeagle]

https://copier.readthedocs.io/en/latest/updating/ seems like a thoughtful design with a constrained public API, maybe a model for what could be done here.

[crenus]

Is this something still being tracked or worked on?

I am currently using copier and debating moving away from mainly because its built in python, so extending it and my use case just requires a bunch of external dependencies making for a rougher experience.

Mainly though, the update feature is something that I really like about it and hoping to keep in moving elsewhere. Being able to update as drift happens or centrally manage files from a template is really powerful. Can even then integrate with CI to auto open PR's with said updates etc., whether that is common CI pipelines, docs, features added, or developer styles.

[hay-kot]

Hey! This isn't really something on my radar for features. I don't really have a need for this kind of thing and don't currently have the free time to implement this big of a feature. Happy to look at PRs and do reviews for anyone interested in contributing and maintaining the feature.