fetch sources.nix from niv

nix/default.nix

@@ -21,28 +21,49 @@ let
     in
       if localCommonSrc != ""
       then localCommonSrc
-      else
-        let sources = import ./sources.nix; in sources.common;
+      else sources.common;
+
+  sources = import sourcesnix { sourcesFile = ./sources.json; inherit pkgs; };
+
+  sourcesnix = builtins.fetchurl
+    https://raw.githubusercontent.com/nmattia/niv/506b896788d9705899592a303de95d8819504c55/nix/sources.nix;
+
+  pkgs = import commonSrc {
+    inherit system crossSystem config;
+    overlays = [
+      (
+        self: super:
+          let
+            nixFmt = self.lib.nixFmt { root = ../.; };
+          in
+            {
+              sources = super.sources // sources;
+
+              inherit releaseVersion;
+
+              isMaster = super.isMaster or false;
+
+              # The dfinity-sdk.packages.cargo-security-audit job has this RustSec
+              # advisory-db as a dependency so we add it here to the package set so
+              # that job has access to it.
+              # Hydra injects the latest RustSec-advisory-db, otherwise we piggy
+              # back on the one defined in sources.json.
+              RustSec-advisory-db =
+                if ! isNull RustSec-advisory-db
+                then RustSec-advisory-db
+                else self.sources.advisory-db;
+
+              motoko = import self.sources.motoko { system = self.system; };
+              dfinity = (import self.sources.dfinity { inherit (self) system; }).dfinity.rs;
+              napalm = self.callPackage self.sources.napalm {
+                pkgs = self // { nodejs = self.nodejs-12_x; };
+              };
+
+              inherit (nixFmt) nix-fmt;
+              nix-fmt-check = nixFmt.check;
+            } // import ./overlays/dfinity-sdk.nix self super
+      )
+    ] ++ overlays;
+  };
 in
-import commonSrc {
-  inherit system crossSystem config;
-  overlays = import ./overlays ++ [
-    (
-      _self: super:
-        {
-          inherit
-            releaseVersion
-            ;
-          # The dfinity-sdk.packages.cargo-security-audit job has this RustSec
-          # advisory-db as a dependency so we add it here to the package set so
-          # that job has access to it.
-          # Hydra injects the latest RustSec-advisory-db, otherwise we piggy
-          # back on the one defined in sources.json.
-          RustSec-advisory-db =
-            if ! isNull RustSec-advisory-db
-            then RustSec-advisory-db
-            else super.sources.advisory-db;
-        }
-    )
-  ] ++ overlays;
-}
+pkgs