Also add Nix environment

default.nix

@@ -0,0 +1,5 @@
+{
+  pkgs ? import ./pkgs.nix,
+}: let
+  cargo = pkgs.callPackage ./Cargo.nix {};
+in cargo.rootCrate.build

nix/sources.json

@@ -0,0 +1,50 @@
+{
+    "crate2nix": {
+        "branch": "master",
+        "description": "nix build file generator for rust crates",
+        "homepage": "",
+        "owner": "kolloch",
+        "repo": "crate2nix",
+        "rev": "0c81027889259c6a45221a157f9c4a56e7235c85",
+        "sha256": "0wp1i83ralnz0v6a95122d0hfzwlg1281lvv3mzrxcxl8mka8z3n",
+        "type": "tarball",
+        "url": "https://github.com/kolloch/crate2nix/archive/0c81027889259c6a45221a157f9c4a56e7235c85.tar.gz",
+        "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
+    },
+    "niv": {
+        "branch": "master",
+        "description": "Easy dependency management for Nix projects",
+        "homepage": "https://github.com/nmattia/niv",
+        "owner": "nmattia",
+        "repo": "niv",
+        "rev": "ba57d5a29b4e0f2085917010380ef3ddc3cf380f",
+        "sha256": "1kpsvc53x821cmjg1khvp1nz7906gczq8mp83664cr15h94sh8i4",
+        "type": "tarball",
+        "url": "https://github.com/nmattia/niv/archive/ba57d5a29b4e0f2085917010380ef3ddc3cf380f.tar.gz",
+        "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
+    },
+    "nixpkgs": {
+        "branch": "nixos-20.09",
+        "description": "Nix Packages collection",
+        "homepage": "",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "b94726217f7cdc02ddf277b65553762d520da196",
+        "sha256": "1v3v7f2apmsdwv1w6hvsxr8whggjbiaxy00k47pxdzyigxv3s400",
+        "type": "tarball",
+        "url": "https://github.com/NixOS/nixpkgs/archive/b94726217f7cdc02ddf277b65553762d520da196.tar.gz",
+        "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
+    },
+    "nixpkgs-mozilla": {
+        "branch": "master",
+        "description": "mozilla related nixpkgs (extends nixos/nixpkgs repo)",
+        "homepage": null,
+        "owner": "mozilla",
+        "repo": "nixpkgs-mozilla",
+        "rev": "8c007b60731c07dd7a052cce508de3bb1ae849b4",
+        "sha256": "1zybp62zz0h077zm2zmqs2wcg3whg6jqaah9hcl1gv4x8af4zhs6",
+        "type": "tarball",
+        "url": "https://github.com/mozilla/nixpkgs-mozilla/archive/8c007b60731c07dd7a052cce508de3bb1ae849b4.tar.gz",
+        "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
+    }
+}

nix/sources.nix

@@ -0,0 +1,171 @@
+# This file has been generated by Niv.
+
+let
+
+  #
+  # The fetchers. fetch_<type> fetches specs of type <type>.
+  #
+
+  fetch_file = pkgs: name: spec:
+    let
+      name' = sanitizeName name + "-src";
+    in
+      if spec.builtin or true then
+        builtins_fetchurl { inherit (spec) url sha256; name = name'; }
+      else
+        pkgs.fetchurl { inherit (spec) url sha256; name = name'; };
+
+  fetch_tarball = pkgs: name: spec:
+    let
+      name' = sanitizeName name + "-src";
+    in
+      if spec.builtin or true then
+        builtins_fetchTarball { name = name'; inherit (spec) url sha256; }
+      else
+        pkgs.fetchzip { name = name'; inherit (spec) url sha256; };
+
+  fetch_git = name: spec:
+    let
+      ref =
+        if spec ? ref then spec.ref else
+          if spec ? branch then "refs/heads/${spec.branch}" else
+            if spec ? tag then "refs/tags/${spec.tag}" else
+              abort "In git source '${name}': Please specify `ref`, `tag` or `branch`!";
+    in
+      builtins.fetchGit { url = spec.repo; inherit (spec) rev; inherit ref; };
+
+  fetch_local = spec: spec.path;
+
+  fetch_builtin-tarball = name: throw
+    ''[${name}] The niv type "builtin-tarball" is deprecated. You should instead use `builtin = true`.
+        $ niv modify ${name} -a type=tarball -a builtin=true'';
+
+  fetch_builtin-url = name: throw
+    ''[${name}] The niv type "builtin-url" will soon be deprecated. You should instead use `builtin = true`.
+        $ niv modify ${name} -a type=file -a builtin=true'';
+
+  #
+  # Various helpers
+  #
+
+  # https://github.com/NixOS/nixpkgs/pull/83241/files#diff-c6f540a4f3bfa4b0e8b6bafd4cd54e8bR695
+  sanitizeName = name:
+    (
+      concatMapStrings (s: if builtins.isList s then "-" else s)
+        (
+          builtins.split "[^[:alnum:]+._?=-]+"
+            ((x: builtins.elemAt (builtins.match "\\.*(.*)" x) 0) name)
+        )
+    );
+
+  # The set of packages used when specs are fetched using non-builtins.
+  mkPkgs = sources: system:
+    let
+      sourcesNixpkgs =
+        import (builtins_fetchTarball { inherit (sources.nixpkgs) url sha256; }) { inherit system; };
+      hasNixpkgsPath = builtins.any (x: x.prefix == "nixpkgs") builtins.nixPath;
+      hasThisAsNixpkgsPath = <nixpkgs> == ./.;
+    in
+      if builtins.hasAttr "nixpkgs" sources
+      then sourcesNixpkgs
+      else if hasNixpkgsPath && ! hasThisAsNixpkgsPath then
+        import <nixpkgs> {}
+      else
+        abort
+          ''
+            Please specify either <nixpkgs> (through -I or NIX_PATH=nixpkgs=...) or
+            add a package called "nixpkgs" to your sources.json.
+          '';
+
+  # The actual fetching function.
+  fetch = pkgs: name: spec:
+
+    if ! builtins.hasAttr "type" spec then
+      abort "ERROR: niv spec ${name} does not have a 'type' attribute"
+    else if spec.type == "file" then fetch_file pkgs name spec
+    else if spec.type == "tarball" then fetch_tarball pkgs name spec
+    else if spec.type == "git" then fetch_git name spec
+    else if spec.type == "local" then fetch_local spec
+    else if spec.type == "builtin-tarball" then fetch_builtin-tarball name
+    else if spec.type == "builtin-url" then fetch_builtin-url name
+    else
+      abort "ERROR: niv spec ${name} has unknown type ${builtins.toJSON spec.type}";
+
+  # If the environment variable NIV_OVERRIDE_${name} is set, then use
+  # the path directly as opposed to the fetched source.
+  replace = name: drv:
+    let
+      saneName = stringAsChars (c: if isNull (builtins.match "[a-zA-Z0-9]" c) then "_" else c) name;
+      ersatz = builtins.getEnv "NIV_OVERRIDE_${saneName}";
+    in
+      if ersatz == "" then drv else ersatz;
+
+  # Ports of functions for older nix versions
+
+  # a Nix version of mapAttrs if the built-in doesn't exist
+  mapAttrs = builtins.mapAttrs or (
+    f: set: with builtins;
+    listToAttrs (map (attr: { name = attr; value = f attr set.${attr}; }) (attrNames set))
+  );
+
+  # https://github.com/NixOS/nixpkgs/blob/0258808f5744ca980b9a1f24fe0b1e6f0fecee9c/lib/lists.nix#L295
+  range = first: last: if first > last then [] else builtins.genList (n: first + n) (last - first + 1);
+
+  # https://github.com/NixOS/nixpkgs/blob/0258808f5744ca980b9a1f24fe0b1e6f0fecee9c/lib/strings.nix#L257
+  stringToCharacters = s: map (p: builtins.substring p 1 s) (range 0 (builtins.stringLength s - 1));
+
+  # https://github.com/NixOS/nixpkgs/blob/0258808f5744ca980b9a1f24fe0b1e6f0fecee9c/lib/strings.nix#L269
+  stringAsChars = f: s: concatStrings (map f (stringToCharacters s));
+  concatMapStrings = f: list: concatStrings (map f list);
+  concatStrings = builtins.concatStringsSep "";
+
+  # https://github.com/NixOS/nixpkgs/blob/8a9f58a375c401b96da862d969f66429def1d118/lib/attrsets.nix#L331
+  optionalAttrs = cond: as: if cond then as else {};
+
+  # fetchTarball version that is compatible between all the versions of Nix
+  builtins_fetchTarball = { url, name ? null, sha256 }@attrs:
+    let
+      inherit (builtins) lessThan nixVersion fetchTarball;
+    in
+      if lessThan nixVersion "1.12" then
+        fetchTarball ({ inherit url; } // (optionalAttrs (!isNull name) { inherit name; }))
+      else
+        fetchTarball attrs;
+
+  # fetchurl version that is compatible between all the versions of Nix
+  builtins_fetchurl = { url, name ? null, sha256 }@attrs:
+    let
+      inherit (builtins) lessThan nixVersion fetchurl;
+    in
+      if lessThan nixVersion "1.12" then
+        fetchurl ({ inherit url; } // (optionalAttrs (!isNull name) { inherit name; }))
+      else
+        fetchurl attrs;
+
+  # Create the final "sources" from the config
+  mkSources = config:
+    mapAttrs (
+      name: spec:
+        if builtins.hasAttr "outPath" spec
+        then abort
+          "The values in sources.json should not have an 'outPath' attribute"
+        else
+          spec // { outPath = replace name (fetch config.pkgs name spec); }
+    ) config.sources;
+
+  # The "config" used by the fetchers
+  mkConfig =
+    { sourcesFile ? if builtins.pathExists ./sources.json then ./sources.json else null
+    , sources ? if isNull sourcesFile then {} else builtins.fromJSON (builtins.readFile sourcesFile)
+    , system ? builtins.currentSystem
+    , pkgs ? mkPkgs sources system
+    }: rec {
+      # The sources, i.e. the attribute set of spec name to spec
+      inherit sources;
+
+      # The "pkgs" (evaluated nixpkgs) to use for e.g. non-builtin fetchers
+      inherit pkgs;
+    };
+
+in
+mkSources (mkConfig {}) // { __functor = _: settings: mkSources (mkConfig settings); }

pkgs.nix

@@ -0,0 +1,22 @@
+{
+  sources ? import ./nix/sources.nix,
+  rustNightly ? "2020-11-10",
+}: let
+  pkgs = import sources.nixpkgs {
+    overlays = [
+      (import sources.nixpkgs-mozilla)
+      (self: super: let
+        rustChannel = super.rustChannelOf {
+          channel = "nightly";
+          date = rustNightly;
+        };
+      in rec {
+        rustc = rustChannel.rust.override {
+          extensions = [ "rust-src" ];
+        };
+        inherit (rustChannel) cargo rust-fmt rust-std clippy;
+        crate2nix = super.callPackage sources.crate2nix {};
+      })
+    ];
+  };
+in pkgs

shell.nix

@@ -0,0 +1,8 @@
+let
+  pkgs = import ./pkgs.nix {};
+in pkgs.mkShell {
+  buildInputs = with pkgs; [
+    #rust
+    crate2nix
+  ];
+}

test-shell.nix

@@ -0,0 +1,7 @@
+let
+  pkgs = import ./pkgs.nix {};
+in pkgs.mkShell {
+  buildInputs = with pkgs; [
+    (import ./Cargo.nix {}).rootCrate.build
+  ];
+}