Motivation for this change

Many of the dependencies in webtoolkit are actually optional (c.f. https://github.com/emweb/wt#dependencies). This change allows the user to opt-out of these optional dependencies by overriding the package with null.

Reason: firebird (one of the optional dependencies) does not build on armv7l. I did not investigate why, because I had no use for it.

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nix-review --run "nix-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Ensured that relevant documentation is up to date
• Fits CONTRIBUTING.md.

Notify maintainers

cc @