rework features, add abi support, add fd args

nix/package.nix

@@ -0,0 +1,45 @@
+{
+  lib,
+  rustPlatform,
+  features ? [ ],
+  abi ? 6,
+  ...
+}:
+let
+  details = (builtins.fromTOML (builtins.readFile ../Cargo.toml)).package;
+in
+rustPlatform.buildRustPackage (finalAttrs: {
+  pname = details.name;
+  inherit (details) version;
+  src = lib.cleanSourceWith {
+    src = lib.cleanSource ../.;
+    filter =
+      path_t: type:
+      let
+        path = toString path_t;
+        baseName = baseNameOf path;
+        parentDir = baseNameOf (dirOf path);
+        matchesSuffix = lib.any (suffix: lib.hasSuffix suffix baseName) [
+          ".rs"
+          ".toml"
+        ];
+        isCargoFile = baseName == "Cargo.lock";
+        isCargoConf = parentDir == ".cargo" && baseName == "config";
+      in
+      type == "directory" || matchesSuffix || isCargoFile || isCargoConf;
+  };
+  cargoLock.lockFile = ../Cargo.lock;
+  buildNoDefaultFeatures = true;
+  buildFeatures = features ++ [
+    "nix"
+    "abi-${toString abi}"
+  ];
+
+  meta = {
+    description = details.description;
+    homepage = details.repository;
+    license = lib.licenses.gpl3Plus;
+    maintainers = [ lib.maintainers.atagen ];
+    mainProgram = details.name;
+  };
+})