nix: add development environment configuration

.envrc

@@ -0,0 +1 @@
+use nix

rustfmt.toml

@@ -0,0 +1,4 @@
+unstable_features = true
+imports_layout = "mixed"
+merge_imports = true
+reorder_imports = true

shell.nix

@@ -0,0 +1,36 @@
+with import <nixpkgs> {};
+
+let
+  inherit (nur.repos.mozilla) rustChannelOf;
+
+  rustStable = rustChannelOf {
+    channel = "stable";
+    date = "2020-10-08";
+  };
+
+  rustNightly = rustChannelOf {
+    channel = "nightly";
+    date = "2020-10-08";
+  };
+
+  rust = rustStable.rust.override {
+    extensions = [ "rust-src" "llvm-tools-preview" ];
+  };
+
+  llvmPackages = llvmPackages_latest;
+in (mkShell.override { inherit (llvmPackages) stdenv; }) {
+  RUSTFLAGS = "-C link-arg=-fuse-ld=lld";
+  QUICKCHECK_TESTS = 1;
+
+  nativeBuildInputs = [
+    rustNightly.rustfmt-preview
+    rust
+
+    cargo-outdated
+
+    pkgconfig
+  ] ++ (with llvmPackages; [
+    libcxxClang
+    lldClang
+  ]);
+}