electrum: add support for LedgerHQ hardware wallet

[k0001]

Motivation for this change

Adding support for LedgerHQ hardware wallet in electrum by adding a dependency on btchip.

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option build-use-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 nox --run "nox-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Fits CONTRIBUTING.md.

---

[k0001]

Could this be backported to 17.09 as well? Thanks.

[joachifm]

Use licenses.asl20. You can test meta eval by nix-instantiate --eval --strict -A foo.meta.

[oxzi]

Is it necessary to add this plugin for each electrum-instance even if the majority won't use it? I feel quite uncomfortable to add unnecessary plugins in a Bitcoin-client.
Perhaps you can disable it by default and let the user enable it by overriding a list of additional plugins?

[k0001]

@joachifm fixed.

@geistesk I don't know. An argument can be made in favor of having a fully functional Electrum out of the box. btchip doesn't have that many dependencies anyway, so the number of dependencies is presumably not a problem. Without btchip, the current situation is that if you try to link a hardware wallet from Electrum it just fails without any useful error message.

[k0001]

@geistesk also, the Electrum we ship in nixpkgs already supports the Trezor hardware wallet.

[FRidh]

these are not needed during runtime?

[k0001]

@FRidh there are definitely references to these three libraries in the btchip code.

[FRidh]

in order for Python modules to find each other, they need to be added as propagatedBuildInputs.

[joachifm]

I'd be fine with making plugins a parameter to the package expression but we can do that in a separate feature.

[oxzi]

@k0001 I fully understand the benefits of a "batteries-included" client. However, on the other side there will be a lot of additional code with possible security-flows in a Bitcoin-client (or any software at all). That's why I'd love to see an overrideable list of possible plugins.

@joachifm If we are going to introduce this feature later, we will probably end up with some "legacy"-dependencies. But I'd like to look into this subject and eventually create a PR.

[nyanloutre]

Is this still on hold ? What work needs to be done for this to get merged ?

[joachifm]

Seems to me that @FRidh's feedback has not been adressed