clightning: add option useBcliPlugin

This decouples modules `clightning` and `trustedcoin`.
`clightning` no longer depends on `trustedcoin`, which restores
the acyclic dependency graph described in `modules.nix`

modules/clightning-plugins/trustedcoin.nix

@@ -14,10 +14,12 @@ let cfg = config.services.clightning.plugins.trustedcoin; in
   };
 
   config = mkIf cfg.enable {
-    services.clightning.extraConfig = ''
-      plugin=${cfg.package}/bin/trustedcoin
-      disable-plugin=bcli
-    '';
+    services.clightning = {
+      useBcliPlugin = false;
+      extraConfig = ''
+        plugin=${cfg.package}/bin/trustedcoin
+      '';
+    };
 
     # Trustedcoin does not honor the clightning's proxy configuration.
     # Ref.: https://github.com/nbd-wtf/trustedcoin/pull/19

modules/clightning.nix

@@ -49,6 +49,15 @@ let
         parameters, as fully qualified data source name.
       '';
     };
+    useBcliPlugin = mkOption {
+      type = types.bool;
+      default = true;
+      description = ''
+        Use bitcoind (via plugin `bcli`) for getting block data.
+        This option is disabled by plugins that use other sources for
+        fetching block data, like `trustedcoin`.
+      '';
+    };
     extraConfig = mkOption {
       type = types.lines;
       default = "";
@@ -107,7 +116,13 @@ let
   network = bitcoind.makeNetworkName "bitcoin" "regtest";
   configFile = pkgs.writeText "config" ''
     network=${network}
-    ${optionalString (!cfg.plugins.trustedcoin.enable) "bitcoin-datadir=${bitcoind.dataDir}"}
+    ${
+      if cfg.useBcliPlugin then ''
+        bitcoin-datadir=${config.services.bitcoind.dataDir}
+      '' else ''
+        disable-plugin=bcli
+      ''
+    }
     ${optionalString (cfg.proxy != null) "proxy=${cfg.proxy}"}
     always-use-proxy=${boolToString cfg.always-use-proxy}
     bind-addr=${cfg.address}:${toString cfg.port}