meson.build:54:8: ERROR: Automatic wrap-based subproject downloading is disabled

[jcurtis-cc]

Hi there,

Nix flake working "out of the box" sounds wonderful. After spending a few hours trying to use it on MacOS and Ubuntu and Alpine containers I'm still not getting past:

meson.build:54:8: ERROR: Automatic wrap-based subproject downloading is disabled

Any tips?

[jcurtis-cc]

After installing nix in the container this is the command I'm running:

nix shell github:hdoc/hdoc --extra-experimental-features flakes --extra-experimental-features nix-command --no-write-lock-file

[hdoc]

If you're in a Nix shell then you can build hdoc using the normal commands like in the readme:

meson build             # Configure the build directory
ninja -C build          # Compile hdoc binaries and tests
./build/hdoc --verbose  # Run hdoc over itself, saving the HTML documentation to ./hdoc-output/

Alternatively, it's possible to build hdoc with the Nix build system but Nix enforces purity requirements which makes downloading project source from the internet impossible. It's possible to define all the project sources as part of the Nix flake but I would encourage you to try building in the interactive shell first.

[eli-schwartz]

Relevant: #25 (comment)

Maybe time to switch from subproject(), and over to the combination of dependency() + --wrap-mode=forcefallback?

[hdoc]

The issue here is that Nix expects a hermetic build environment with no network access. Meson, when it notices that the wraps are not present locally, will try to access the network to download the wraps. This causes the Nix build to fail. The solution is to specify the exact hashes of all the wrap sources as well as the Meson patches (where applicable) so that Nix knows about them. Then, Nix will go and download them and place them in the correct location during the build so that Meson has the wraps locally and doesn't need to download them.

We have this implemented internally and will be releasing a new Nix Flake with this functionality as part of our next release. I will make a comment on this PR when that happens.