feat: Copier Scaffolder Action

[mspiegel31]

Hey, I just made a Pull Request!

This is a scaffolder action to allow the creation of templates using the copier template engine. Copier is somewhat unique in the templating space, as it is version-aware. This means that templates generated from a project are able to stay up-to-date with the template as they are modified over time. Their update algorithm can be found here

Screenshots

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• Tests for new functionality and regression tests for bug fixes
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[awanlin]

Hi @mspiegel31, just wanted to share this - #20266 - as it would be good to know the path forward before reviewing.

@freben can you provide some feedback, please?

[mspiegel31]

@awanlin thanks for the heads-up! I think this would be great to have in backstage core, and this PR does add some extensions to @backstage/backend-common, so hopefully it's something that is worth looking at while #20266 is being worked through.

[awanlin]

Also there already seems to be a module: https://github.com/telia-oss/scaffolder-backend-module-copier

[awanlin]

@awanlin thanks for the heads-up! I think this would be great to have in backstage core, and this PR does add some extensions to @backstage/backend-common, so hopefully it's something that is worth looking at while #20266 is being worked through.

Let's wait to hear what @freben thinks 🤔

[mspiegel31]

Also there already seems to be a module: https://github.com/telia-oss/scaffolder-backend-module-copier

that's true! However, that module leverages the fetchContents function from @backstage/plugin-scaffolder-backend, which means that projects generated from templates won't have any version control information. Since that's the "killer feature" of copier, it doesn't make much sense to use that particular action.

additionally, it does look there are just some copy-pasted pieces from the cookiecutter action in that codebase. There is no such thing as a copier.json file, for example; copier uses yaml for its configuration.

tl;dr I think this PR gives a more feature-complete solution, and does provide a way to get the functionality asked for in #14416

[backstage-goalie]

Changed Packages

Package Name	Package Path	Changeset Bump	Current Version
@backstage/backend-common	packages/backend-common	minor	v0.19.7-next.1
example-backend	packages/backend	none	v0.2.88-next.1
@backstage/plugin-scaffolder-backend-module-copier	plugins/scaffolder-backend-module-copier	major	v0.0.0

[github-actions]

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[freben]

In the spirit of open source, it'd be really nice to contribute the improvements to the existing open source plugin, I feel. Maybe reach out to them?

[mspiegel31]

@freben I'll see what I can do. This PR does contain some enhancements to backend-common; are contributions to that module also affected by #20266 or is it just net-new plugins?

[tudi2d]

Tja @tobias-estefors (main contributor of Telia's scaffolder-backend-module-copier)! Would you be open for contribution on your scaffolder module? Would you be open to collaborate & review the changes? :)