Add nix build

.envrc

+use_nix
+eval "$(lorri direnv)"

nix/default.nix

+{ sources ? import ./sources.nix
+}:
+let
+  # default nixpkgs
+  pkgs = import sources.nixpkgs { };
+
+  # gitignore.nix 
+  gitignoreSource = (import sources."gitignore.nix" { inherit (pkgs) lib; }).gitignoreSource;
+
+  # pre-commit-hooks = (import sources."pre-commit-hooks.nix");
+
+  rust = (import ./rust.nix { inherit sources; });
+
+  src = gitignoreSource ./..;
+in
+{
+  inherit pkgs src;
+
+  # provided by shell.nix
+  devTools = with pkgs; [
+    niv wasm-pack wasmtime valgrind protobuf clang llvm rocksdb
+    # inherit (pre-commit-hooks) pre-commit nixpkgs-fmt nix-linter;
+    rust
+  ];
+
+  # to be built by github actions
+  ci = {
+    # pre-commit-check = pre-commit-hooks.run {
+    #   inherit src;
+    #   hooks = {
+    #     shellcheck.enable = true;
+    #     nixpkgs-fmt.enable = true;
+    #     nix-linter.enable = true;
+    #     # cargo-check.enable = true;
+    #     # rustfmt.enable = true;
+    #     # clippy.enable = true;
+    #   };
+    #   # generated files
+    #   excludes = [ "^nix/sources\.nix$" ];
+    # };
+  };
+}

nix/rust.nix

+{ sources ? import ./sources.nix }:
+let
+  pkgs =
+    import sources.nixpkgs { overlays = [ (import sources.nixpkgs-mozilla) ]; };
+  channel = "nightly";
+  date = "2021-03-18";
+  targets = [ "wasm32-unknown-unknown" "wasm32-wasi" ];
+  chan = pkgs.rustChannelOfTargets channel date targets;
+in
+chan

nix/sources.json

+{
+    "niv": {
+        "branch": "master",
+        "description": "Easy dependency management for Nix projects",
+        "homepage": "https://github.com/nmattia/niv",
+        "owner": "nmattia",
+        "repo": "niv",
+        "rev": "af958e8057f345ee1aca714c1247ef3ba1c15f5e",
+        "sha256": "1qjavxabbrsh73yck5dcq8jggvh3r2jkbr6b5nlz5d9yrqm9255n",
+        "type": "tarball",
+        "url": "https://github.com/nmattia/niv/archive/af958e8057f345ee1aca714c1247ef3ba1c15f5e.tar.gz",
+        "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
+    },
+    "nixpkgs": {
+        "branch": "release-20.03",
+        "description": "Nix Packages collection",
+        "homepage": "",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "6d1a044fc9ff3cc96fca5fa3ba9c158522bbf2a5",
+        "sha256": "07a3nyrj3pwl017ig0rbn5rbmbf14gl3vqggvkyrdby01726p5fg",
+        "type": "tarball",
+        "url": "https://github.com/NixOS/nixpkgs/archive/6d1a044fc9ff3cc96fca5fa3ba9c158522bbf2a5.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": "",
+        "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

+# This file has been generated by Niv.
+
+let
+
+  #
+  # The fetchers. fetch_<type> fetches specs of type <type>.
+  #
+
+  fetch_file = pkgs: spec:
+    if spec.builtin or true then
+      builtins_fetchurl { inherit (spec) url sha256; }
+    else
+      pkgs.fetchurl { inherit (spec) url sha256; };
+
+  fetch_tarball = pkgs: name: spec:
+    let
+      ok = str: ! builtins.isNull (builtins.match "[a-zA-Z0-9+-._?=]" str);
+      # sanitize the name, though nix will still fail if name starts with period
+      name' = stringAsChars (x: if ! ok x then "-" else x) "${name}-src";
+    in
+      if spec.builtin or true then
+        builtins_fetchTarball { name = name'; inherit (spec) url sha256; }
+      else
+        pkgs.fetchzip { name = name'; inherit (spec) url sha256; };
+
+  fetch_git = spec:
+    builtins.fetchGit { url = spec.repo; inherit (spec) rev ref; };
+
+  fetch_local = spec: spec.path;
+
+  fetch_builtin-tarball = name: throw
+    ''[${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
+  #
+
+  # The set of packages used when specs are fetched using non-builtins.
+  mkPkgs = sources:
+    let
+      sourcesNixpkgs =
+        import (builtins_fetchTarball { inherit (sources.nixpkgs) url sha256; }) {};
+      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 spec
+    else if spec.type == "tarball" then fetch_tarball pkgs name spec
+    else if spec.type == "git" then fetch_git 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));
+  concatStrings = builtins.concatStringsSep "";
+
+  # fetchTarball version that is compatible between all the versions of Nix
+  builtins_fetchTarball = { url, name, sha256 }@attrs:
+    let
+      inherit (builtins) lessThan nixVersion fetchTarball;
+    in
+      if lessThan nixVersion "1.12" then
+        fetchTarball { inherit name url; }
+      else
+        fetchTarball attrs;
+
+  # fetchurl version that is compatible between all the versions of Nix
+  builtins_fetchurl = { url, sha256 }@attrs:
+    let
+      inherit (builtins) lessThan nixVersion fetchurl;
+    in
+      if lessThan nixVersion "1.12" then
+        fetchurl { inherit url; }
+      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)
+    , pkgs ? mkPkgs sources
+    }: 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); }

shell.nix

+{ project ? import ./nix/default.nix { }
+}:
+
+project.pkgs.mkShell {
+  buildInputs = project.devTools;
+  LIBCLANG_PATH = "${project.pkgs.llvmPackages.libclang}/lib/libclang.so";
+  PROTOC = "${project.pkgs.protobuf}/bin/protoc";
+  ROCKSDB = "${project.pkgs.rocksdb}/lib/librocksdb.so";
+}