nix: add flake

[gwennlbh]

Description

Add a flake to build a binary using Nix

How I Tested

nix build .?submodules=1

Do not merge before

• Check propagatedBuildInputs with ldd
• Add a apps section to nix run
• Add a way to boot a python shell/interpret a python file with result's site-packages in PYTHONPATH

see also open-dynamic-robot-initiative/master-board#173

I fulfilled the following requirements

• All new code is formatted according to our style guide (for C++ run clang-format, for Python, run flake8 and fix all warnings).
• All new functions/classes are documented and existing documentation is updated according to changes.
• No commented code from testing/debugging is kept (unless there is a good reason to keep it).

[gwennlbh]

i added a workflow file, seems like actions were not turned on for this repo -- is ci useful here?

[nim65s]

because we did not have a package manager for master-board before I guess

[gwennlbh]

I ran the new CI locally with act and it passes

[nim65s]

Hum, github somehow lost part of my review :/

[nim65s]

Suggested change

	shellHook = ''
	controlSitePackages=`echo ${self'.packages.odri_control_interface}/lib/python*/site-packages | head -n 1`
	masterboardSitePackages=`echo ${pkgs.odri_master_board_sdk}/lib/python*/site-packages | head -n 1`
	export PYTHONPATH="$controlSitePackages:$masterboardSitePackages:$PYTHONPATH"
	'';
	PYTHONPATH = lib.concatMapStringsSep ":" (p: "${p}/${pkgs.python3.sitePackages}") [
	self'.packages.odri_control_interface
	pkgs.odri_master_board_sdk
	]

[nim65s]

Or better: pkgs.python3.withPackages (_: [ self'.packages.odri_control_interface pkgs.odri_master_board_sdk ])

[gwennlbh]

Or better: pkgs.python3.withPackages (_: [ self'.packages.odri_control_interface pkgs.odri_master_board_sdk ])

so as buildInputs ? i'm not sure about dropping into a python shell directly, because some python scripts require cli args

[nim65s]

in packages, so yes that is kind of buildInputs

[gwennlbh]

hmmm unfortunately doing that doesnt seem to add the packages to PYTHONPATH. maybe the packages have to be marked as python packages for this to work? i'm leaving it at PYTHONPATH = for now.

[nim65s]

Ok, yes, to tell nix that a derivation has a python module, we need to either define it with pkgs.python3Packages.callPackage instead of pkgs.callPackage (so in nixpkgs use pkgs/top-level/python-packages.nix instead of by-name, or in gepetto/nix put the package in py-pkgs instead of pkgs), or transform it into a module afterwards with pkgs.python3Packages.toPythonModule.

therefore,
here:

pkgs.python3.withPackages (p: [
  (p.toPythonModule pkgs.odri_master_board_sdk)
  (p.toPythonModule self'.packages.odri_control_interface)
])

and/or in gepetto/nix:

git mv {,py-}pkgs/odri-masterboard-sdk.nix
git mv {,py-}pkgs/odri-control-interface.nix

[nim65s]

ref. https://nixos.org/manual/nixpkgs/unstable/#topythonmodule-function

[nim65s]

Oh, yes, it is still here, but as outdated. I'll resolve those.