[FPM] add fpm support

[zoziha]

Initial support fpm:
I don't know if this is feasible, but I want stdlib to support fpm as soon as possible so that the two can feed back to each other.
My method:

1. Use make dev -f Makefile.manual to generate f90 files from the src folder to the src/fpm folder;
2. Use fpm.toml to build the fpm version of stdlib.

I added a src/fpm folder and subordinate files, and added stdlib's initial support for fpm. I don't know if this is very feasible, but it has passed the fpm build.

[zoziha]

attention: src/fpm

[jvdp1]

Thank you @zoziha. Nice and highly needed proposition. After a quick look, I wonder if src/fpm should already contain the files (since they will be generated by the Makefile).
Question: why not generating files inside src, instead of src/fpm?

Note that @LKedward proposed another (but similar) solution for fpm supporting stdlib. However, from a high level, I would prefer yours (i.e. everything is contained in one single place).

[zoziha]

Thank you @zoziha. Nice and highly needed proposition. After a quick look, I wonder if src/fpm should already contain the files (since they will be generated by the Makefile).

Yes, src/fpm already contains the generated files, so that other people can directly compile these files through fpm.toml without the need for make dev -f Makefile.manual.

Question: why not generating files inside src, instead of src/fpm?

Because I don’t really know whether it’s wise to modify the files directly under src. After all, the src folder files are the source code files of meta-programming, so I chose to generate a separate space just to facilitate fpm compilation. Of course, we can discuss how to do more reasonable.

Note that @LKedward proposed another (but similar) solution for fpm supporting stdlib. However, from a high level, I would prefer yours (i.e. everything is contained in one single place).

I’m sorry I don’t know that solution also has an implementation of stdlib-fpm, maybe this is why I want to add fpm support directly in the stdlib library website, because in general, users prefer to get the stdlib-fpm package through the official stdlib library link.

[LKedward]

Thanks @zoziha - yes as Jeremie pointed out, my solution is to generate the source files automatically in the CI. This is generally more robust than checking the preprocessed files into git. To have everything in one place, I'd like to implement the same workflow here to deploy the generated files to a separate branch. For the time being, you can use my stdlib fpm package linked above for testing the two together - I'm using it myself more and more as stdlib grows and it's a really quick way to spin up an stdlib project and test its functionality.

[zoziha]

To have everything in one place, I'd like to implement the same workflow here to deploy the generated files to a separate branch.

Thanks @LKedward , I agree with you. I think stdlib can set up a stdlib-fpm branch, automatically generate source code files through github-ci, and declare the reference of this master branch in README.md, like:

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

#279 (comment)
Maybe in the future fpm can support fypp by itself, but at least now we can make stdlib a fpm package, and then iteratively update.
I hope everyone can use stdlib as soon as possible through fpm to make stdlib full of vitality.

[jvdp1]

Thanks @LKedward , I agree with you. I think stdlib can set up a stdlib-fpm branch, automatically generate source code files through github-ci, and declare the reference of this master branch in README.md, like:

I likes this plan!
Supporting stdlib through fpm is quite a recurrent topic, and IMO, highly important for the development and popularity of both stdlib and fpm.
@LKedward could fpm already support such an approach (e.g., with the branch option)? What would be needed to be done? Maybe @zoziha could help you in this?

[LKedward]

Yes, fpm already allows you to specify a branch for git dependencies. I believe I can just copy the CI workflow from my stdlib-fpm repo with a few small changes - hopefully I can find some time soon to get it working for a PR.

[ivan-pi]

I imagine in many cases, users will only need one or two modules from stdlib and not the entire library. Some users are facing problems with the compilation time (#438) in connection with the large number generic routines in stdlib_stats. Having fpm clone and build the entire stdlib is sub-optimal if the module is not used at all.

I am not sure what would be the best way to address this long term. Maybe add more control over stdlib directly to fpm?

[zoziha]

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" }

Developer efficiency

However, the efficiency of developers has not been improved. stdlib now uses make and cmake tools to build code, which means that when we add functions to stdlib, we not only need to take care of the function implementation, but also need to maintain more make and cmake configurations files (In the development process, it is easy to cause git conflicts with other developers, and it is easy to forget or write the configuration files incorrectly, which increases the development cost.) can we consider using fpm to empower developers?
Although the solution of the src/fpm folder is a clumsy way, it allows developers to use the easiest fpm to develop stdlib (In the future, stdlib will also need to support fpm). Developers only need to consider function implementation, function testing, fpm.toml and use a simple makefile to convert fypp code to f90 code.
I don’t know if there will be any technical difficulties.

Possible solution

For developers:

Like zoziha/forlab, mete-programming source codes in meta-src folder, generation source codes in src folder to support fpm.

make         # use makefile convert fypp to f90
fpm test <test_name>         # easy-to-test

Gradually use fpm instead of make/cmake, allow developers to use makefile in stdlib to convert *.fypp to *.f90, allow developers to use fpm.toml in stdlib to develop and test code, and developers only submit meta-programming source codes to stdlib-master.
Set the stdlib-fpm branch in stdlib for users, and convert *.fypp in stdlib-master into *.f90 files through github-ci.

For users:

Users can use the following reference to use stdlib,

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

If fpm supports fypp in the future, the stdlib-fpm branch can be retired.

[zoziha]

Hello, I am very happy to announce that I have implemented stdlib-fpm using the @LKedward 's solution(github-ci) under my branch:

1. fortrans-fans/add_master_fpm_ci + fortran-fans/stdlib-fpm
2. fortran-fans/add_fpm_ci2(PR github-ci: add fpm support #508 ) + fortran-lang/stdlib-fpm(needed, todo.)

That we can use stdlib as follows:

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

Before that, I need an administrator with permission for fortran-lang to set up an empty stdlib-fpm branch in fortran-lang/stdlib repo, so that I can submit a PR.