Allow to generate a standalone tarball with all dependencies

[certik]

fpm should have a feature like fpm tarball --include-deps that will create a tarball of the current fpm package together with all dependencies and a build system such as CMake (#69), so that one can unpack this tarball at a machine without internet connection, and build everything from scratch (all the dependencies and the main application).

There are many usages of this feature:

• an application that must run on an HPC machine without internet connection, and I want to distribute it as a tarball that is built using cmake (a common expectation)
• fpm itself --- we can distribute fpm source code like this, and anybody with cmake can then build it from source (no other dependencies needed)

[awvwgk]

I was trying to figure out what it takes to implement a command like this, but there are a some things that are unclear. First, I would propose to name the command fpm dist rather than fpm tarball.

The second thing that comes to mind is, in case we use fpm dist --cmake and generate a CMake based build system, how do we make CMake fetch the dependencies? FetchContent works fine, but only if the upstream project supports CMake as well.
On solution would be to rely on a release artefact created by fpm and uploaded somewhere instead of the default git-archive.

Finally, how do we handle the case of fpm dist --cmake --include-deps? Of course we can recursively generate the CMake files for all the projects and include them in a tarball, but some dependencies come with their own CMake files, would we overwrite (maybe with a fpm dist --cmake --include-deps --overwrite)?

As a note, in case anyone wants to give this a real try. Implementing a fpm dist --meson will probably be way less painful than implementing robust CMake.

[band-a-prend]

Is there a way to build fpm fully offline? If I do git clone and do bootstrap procedure as described and then run

./build/bootstrap/fpm build

the build is OK.

If I tried to build in isolated environment against system installed /usr/include/toml-f and /usr/include/m_cli2 modules with following fpm.toml instead of base:

name = "fpm"
version = "0.7.0"
license = "MIT"
author = "fpm maintainers"
maintainer = ""
copyright = "2020 fpm contributors"

[build]
external-modules = ["tomlf", "m_cli2"]

and command, e.g.

./build/bootstrap/fpm build --flag "-I/usr/include/toml-f -I/usr/include/m_cli2"

(where tomlf*.mod and m_cli2.mod are respected to the same git commit_sha tarballs as within initial fpm.toml) then on linking phase I got multiple errors like undefined reference to __m_cli2_MOD_... and undefined reference to __tomlf_....

P.S.
After built bootstrap version under build/booststrap directory the tomlf*.mod and m_cli2.mod files are presented too.

[band-a-prend]

Well it's seems the problem is with m_cli2 as exteranl demo1.f90 of m_cli2 doesn't compile for me (I don't see library built only .mod file).

The problem with toml-f was due to I forgot to link toml-f library and it was fixed by addition link = "toml-f to [build] section

name = "fpm"
version = "0.7.0"
license = "MIT"
author = "fpm maintainers"
maintainer = ""
copyright = "2020 fpm contributors"

[build]
external-modules = ["tomlf", "m_cli2"]
link = "toml-f"

[band-a-prend]

I solve the problem:
M_CLI2 Makefile doesn't build shared library that is required for other external projects.
I have to build object file M_CLI2.o with additional flag -fPIC and then to build shared library with command:

gfortran -Wl,-soname,libm_cli2.so.1 -shared -o libm_cli2.so.1 M_CLI2.o

with creating symlink libm_cli2.so for libm_cli2.so.1.

[build]
external-modules = ["tomlf", "m_cli2"]
link = ["toml-f", "m_cli2"]