github-ci: add fpm support

[zoziha]

• add fpm-deployment ci;
• create a stdlib-fpm branch. (github-ci will do this job, see github-ci: add fpm support #508 (comment))
• add ./ci/fpm.toml and update README.md

Description

We have this urgent need for fortran-stdlib. We hope that stdlib and fpm can interact, and stdlib-fpm will be placed in the fortran-lang/stdlib repository (branch).
The CI scheme here comes from @LKedward (https://github.com/LKedward/stdlib-fpm). I have made some modifications to adapt to specific technical requirements. I am not very familiar with CI. I need to admit that the CI scheme this time has shortcomings, but I believe we can iterate and update it.

User efficiency

In order to improve the efficiency of users of stdlib, we can set the stdlib-fpm branch for stdlib, allowing users to add the following reference in their projects:

[dependencies]
stdlib = { git = "https://github.com/fortran-lang/stdlib", branch = "stdlib-fpm" }

[zoziha]

I checked again, the entire CI process seems to be no problem, except that the fpm test (release) task takes a long time.

If you have any questions, you can give me feedback and I will quickly correct it.

In addition, once we think there is no problem with this CI, that we can pass it. We need to create a branch, stdlib-fpm, to support fpm, see fortran-fans : stdlib-fpm for my stdlib-fpm branch.

[awvwgk]

Depending on the commit action it will create the branch all by itself, the one used for deploying fpm's documentation will create the branch automatically for example (https://github.com/marketplace/actions/deploy-to-github-pages).

[awvwgk]

Also, shouldn't the deployment only happen on push actions for the default branch rather than on PRs as well?

For running the action on a PR we don't have to checkout the stdlib-fpm branch at all but just deploy the converted project to a new directory and test it. The checkout is only required for updating the branch on push and this shouldn't be required when running on PRs.

[zoziha]

Depending on the commit action it will create the branch all by itself, the one used for deploying fpm's documentation will create the branch automatically for example (https://github.com/marketplace/actions/deploy-to-github-pages).

I think stdlib-fpm needs the existence of the fpm.toml file. I think there are two ways that I can think of:

1. Write fpm.toml in stdlib-master. When CI is running, copy the fpm.toml file in stdlib-master to stdlib-fpm. In this case, fpm.toml needs to be maintained in stdlib-master, although I think fpm.toml may not need to be updated frequently.
2. Manually create a stdlib-fpm branch, and manually submit fpm.toml to stdlib-fpm. When CI is running, it is also possible. fpm.toml needs to be maintained in stdlib-fpm in this case.

Thank you for your suggestion @awvwgk , I think both methods are fine.
I prefer the first option. If everyone agrees, I will add a file: fpm.toml to stdlib-master(./ci/fpm.toml).

Also, shouldn't the deployment only happen on push actions for the default branch rather than on PRs as well?

# When a PR occurs, the fpm package of `stdlib` will be generated.
on: [push, pull_request]

Yes, both PR and push will activate fpm-deployment.yml, and I will remove the incorrect comment.

[LKedward]

Great stuff @zoziha - thanks for implementing this!

The CI is failing currently, because it is trying to deploy the stdlib-fpm package but we don't want to deploy for PRs, only on pushes to master - see my suggestion above.

[zoziha]

@awvwgk @LKedward Thank you very much for your answers, now I understand what you mean.
I resubmitted a git push, hope there is no problem.

[LKedward]

Thanks for reviewing and updating Sebastian @awvwgk. It would be good to get another reviewer on this to move it forward.

Changes applied by reviewer

[LKedward]

Latest updates to fpm-deployment.sh look good to me 👍

[jvdp1]

Great and highly needed addition. It will benefit to both stdlib and fpm IMO. Thank you @zoziha .
I approve this PR, pending minor revisions.

[zoziha]

I modified the corresponding content of README.md. @jvdp1 😉

[urbanjost]

Seems like stdlib should go onto the fpm registry but I do not see it there (yet?)

[jvdp1]

With 3 approvals, I will merge this PR. Thank you @zoziha