nix: initial tooling

nix/package.nix

@@ -0,0 +1,31 @@
+{
+  lib,
+  rustPlatform,
+}:
+rustPlatform.buildRustPackage (finalAttrs: {
+  pname = "eh";
+  version = (builtins.fromTOML (builtins.readFile ../Cargo.toml)).workspace.package.version;
+
+  src = let
+    fs = lib.fileset;
+    s = ../.;
+  in
+    fs.toSource {
+      root = s;
+      fileset = fs.unions (map (dir: (s + /${dir})) [
+        ".cargo"
+        "eh"
+        "xtask"
+        "Cargo.toml"
+        "Cargo.lock"
+      ]);
+    };
+
+  cargoLock.lockFile = "${finalAttrs.src}/Cargo.lock";
+  enableParallelBuilding = true;
+
+  meta = {
+    description = "Ergonomic Nix CLI helper";
+    maintainers = with lib.licenses; [NotAShelf];
+  };
+})

nix/shell.nix

@@ -0,0 +1,19 @@
+{
+  mkShell,
+  rust-analyzer,
+  rustfmt,
+  clippy,
+  cargo,
+  rustPlatform,
+}:
+mkShell {
+  name = "rust";
+  packages = [
+    rust-analyzer
+    rustfmt
+    clippy
+    cargo
+  ];
+
+  RUST_SRC_PATH = "${rustPlatform.rustLibSrc}";
+}