add npm fetcher

src/fetchers/npm/default.nix

@@ -0,0 +1,41 @@
+{
+  fetchurl,
+  lib,
+  python3,
+
+  utils,
+  ...
+}:
+{
+
+  inputs = [
+    "pname"
+    "version"
+  ];
+
+  versionField = "version";
+
+  # defaultUpdater = "";
+
+  outputs = { pname, version, ... }@inp:
+    let
+      b = builtins;
+
+      submodule = lib.last (lib.splitString "/" pname);
+      url = "https://registry.npmjs.org/${pname}/-/${submodule}-${version}.tgz";
+    in
+    {
+
+      calcHash = algo: utils.hashPath algo (
+        b.fetchurl { inherit url; }
+      );
+
+      fetched = hash:
+        (fetchurl {
+          inherit url;
+          sha256 = hash;
+        }).overrideAttrs (old: {
+          outputHashMode = "recursive";
+        });
+    };
+}

src/fetchers/pypi-sdist/default.nix

@@ -1,5 +1,5 @@
 {
-  http,
+  fetchurl,
   python3,
 
   utils,
@@ -19,34 +19,24 @@
   outputs = { pname, version, extension ? "tar.gz", ... }@inp:
     let
       b = builtins;
+
+      firstChar = builtins.substring 0 1 pname;
+      url =
+        "https://files.pythonhosted.org/packages/source/"
+        + "${firstChar}/${pname}/${pname}-${version}.${extension}";
     in
     {
 
       calcHash = algo: utils.hashPath algo (
-        let
-          firstChar = builtins.substring 0 1 pname;
-          result = b.http {
-            url =
-              "https://files.pythonhosted.org/packages/source/"
-              + "${firstChar}/${pname}/${pname}-${version}.${extension}";
-          };
-        in
-          result
-      
+        b.fetchurl { inherit url; }
       );
 
       fetched = hash:
-        let
-          firstChar = builtins.substring 0 1 pname;
-          result = (http {
-            url =
-              "https://files.pythonhosted.org/packages/source/"
-              + "${firstChar}/${pname}/${pname}-${version}.${extension}";
-            sha256 = hash;
-          }).overrideAttrs (old: {
-            outputHashMode = "recursive";
-          });
-        in
-          result;
+        (fetchurl {
+          inherit url;
+          sha256 = hash;
+        }).overrideAttrs (old: {
+          outputHashMode = "recursive";
+        });
     };
 }