ci(build): Get libtexpdf into build using flake inputs

[doronbehar]

After experimenting with building projects that depend on git submodules, I reached the conclusion that this is the most comfortable way of handling such dependencies. You may like this approach since updating libtexpdf for the flakes will only require:

nix flake update

and the above will also update libtexpdf to it's latest version. Using a specific version of libtexpdf is possible using:

nix build --override-input libtexpdf-src "github:sile-typesetter/libtexpdf/my_feature_branch"

You can also do the above while disabling changing the flake.lock file:

nix build --override-input libtexpdf-src "github:sile-typesetter/libtexpdf/my_feature_branch" --no-write-lock-file

[alerque]

Thanks! This makes perfect sense and if Nix was the only thing in play here I'd be all for it. As it is I'm a bit unsure since this workflow now splits the workflows that update the upstream source build vs. the Nix flake. I am not sure I want it to be a separate action that could be out of sync. I'll probably fiddle with a way to get them both updated at the same time or otherwise kept in sync. Just triggering nix flake update at the same time seems a bit aggressive since it updates a whole bunch of other pinned things.

[doronbehar]

There's also the option:

nix flake lock --commit-lock-file --override-input libtexpdf-src github:sile-typesetter/libtexpdf/$(git submodule status -- libtexpdf | awk '{print $1}')

[doronbehar]

I hope you tested that nix command. I slightly afraid it is missing a `--write-lock-file` flag but I'm not sure.

[alerque]

Yes I put it through a few paces by downgrading libtexpdf and updating it again, it seemed to work as expected. The lock file definitely gets updated with the expected submodule update. I had to remove the --commit-lock-file because it didn't play nice with our commit message requirements, but also it is nice to have it be part of the same commit as the submodule anyway. Thanks for the help with this!