[Chore] Flakify xrefcheck

Problem: For historical reasons some Serokell projects use niv to
organize nix-related dependencies. However, the majority of other
projects in our company use nix flakes to organize these dependencies.

Solution: Add flake and provide ci attibutes as flake outputs.

ci.nix

@@ -1,35 +0,0 @@
-# SPDX-FileCopyrightText: 2021 Serokell <https://serokell.io>
-#
-# SPDX-License-Identifier: MPL-2.0
-
-rec {
-  sources = import ./nix/sources.nix;
-  haskell-nix = import sources."haskell.nix" {
-    sourcesOverride = { hackage = sources."hackage.nix"; stackage = sources."stackage.nix"; };
-  };
-  serokell-nix = import sources."serokell.nix";
-  pkgs = import sources.nixpkgs (
-    haskell-nix.nixpkgsArgs // {
-      overlays =
-        haskell-nix.nixpkgsArgs.overlays
-        ++ [ serokell-nix.overlay ]; # contains trailing whitespace check
-    }
-  );
-
-  project-src = pkgs.haskell-nix.haskellLib.cleanGit {
-    name = "xrefcheck";
-    src = pkgs.haskell-nix.haskellLib.cleanSourceWith {
-      filter = path: type: !(pkgs.lib.hasInfix "tests/golden/helpers" path);
-      src = ./.;
-    };
-  };
-
-  # TODO: drop this when `serokell/nixpkgs` acquires stylish-haskell >= 0.13.0.0.
-  pkgs-stylish = import sources.nixpkgs-stylish {};
-
-  xrefcheck-lib-and-tests = (import ./xrefcheck.nix { linux = true; });
-  xrefcheck-static = (import ./xrefcheck.nix { linux-static = true; }).components.exes.xrefcheck;
-  xrefcheck-windows = (import ./xrefcheck.nix { windows = true; }).components.exes.xrefcheck;
-
-  trailing-whitespace-check = pkgs.build.checkTrailingWhitespace project-src;
-}

default.nix

@@ -1,7 +1,14 @@
-# SPDX-FileCopyrightText: 2019 Serokell <https://serokell.io>
-#
+# SPDX-FileCopyrightText: 2023 Serokell <https://serokell.io>
 # SPDX-License-Identifier: MPL-2.0
 
-{ platform ? "linux-static" }:
-
-(import ./xrefcheck.nix { ${platform} = true; }).components.exes.xrefcheck
+let
+  inherit (import
+  (let lock = builtins.fromJSON (builtins.readFile ./flake.lock); in
+    fetchTarball {
+      url = "https://github.com/edolstra/flake-compat/archive/${lock.nodes.flake-compat.locked.rev}.tar.gz";
+      sha256 = lock.nodes.flake-compat.locked.narHash;
+    })
+  { src = ./.; }) defaultNix;
+  system = builtins.currentSystem;
+in defaultNix //
+   (defaultNix.legacyPackages.${system}.lib.attrsets.mapAttrs (_: val: val.${system}) defaultNix)

docker/default.nix

@@ -1,18 +0,0 @@
-# SPDX-FileCopyrightText: 2020 Serokell <https://serokell.io>
-#
-# SPDX-License-Identifier: MPL-2.0
-
-{ pkgs ? import (import ../nix/sources.nix).nixpkgs { } }:
-let
-  executable =
-    (import ../xrefcheck.nix { linux-static = true; }).components.exes.xrefcheck;
-  binOnly = pkgs.runCommand "xrefcheck-bin" { } ''
-    mkdir -p $out/bin
-    cp ${executable}/bin/xrefcheck $out/bin
-    ${pkgs.nukeReferences}/bin/nuke-refs $out/bin/xrefcheck
-  '';
-in pkgs.dockerTools.buildImage {
-  name = "xrefcheck";
-  contents = [ binOnly pkgs.cacert ];
-  config.Entrypoint = "xrefcheck";
-}

flake.lock.license

@@ -0,0 +1,2 @@
+SPDX-FileCopyrightText: 2023 Serokell <https://serokell.io>
+SPDX-License-Identifier: MPL-2.0

flake.nix

@@ -0,0 +1,91 @@
+# SPDX-FileCopyrightText: 2023 Serokell <https://serokell.io>
+# SPDX-License-Identifier: MPL-2.0
+
+{
+  description = "The xrefcheck flake";
+
+  nixConfig.flake-registry = "https://github.com/serokell/flake-registry/raw/master/flake-registry.json";
+
+  outputs = { self, flake-utils, haskell-nix, serokell-nix, ... }:
+    flake-utils.lib.eachSystem [ "x86_64-linux" ] (system:
+    let
+      pkgs = haskell-nix.legacyPackages.${system}.extend serokell-nix.overlay;
+
+      flake = (pkgs.haskell-nix.stackProject {
+        src = ./.;
+        modules = [{
+          packages.xrefcheck = {
+            ghcOptions =
+              [ "-Werror" ];
+
+            components.tests = {
+              ftp-tests = {
+                build-tools = [ pkgs.vsftpd ];
+                preCheck = ''
+                  echo "Starting vsftpd..."
+                  touch /tmp/vsftpd.log
+                  vsftpd \
+                  -orun_as_launching_user=yes \
+                  -olisten_port=2221 \
+                  -olisten=yes \
+                  -oftp_username=$(whoami) \
+                  -oanon_root=${./ftp-tests/ftp_root} \
+                  -opasv_min_port=2222 \
+                  -ohide_file='{.*}' \
+                  -odeny_file='{.*}' \
+                  -oseccomp_sandbox=no \
+                  -olog_ftp_protocol=yes \
+                  -oxferlog_enable=yes \
+                  -ovsftpd_log_file=/tmp/vsftpd.log &
+                  sleep 1
+                  tail -f /tmp/vsftpd.log &
+                '';
+                testFlags = [ "--ftp-host" "ftp://localhost:2221" ];
+              };
+              xrefcheck-tests.build-tools = [ pkgs.git ];
+            };
+          };
+        }];
+      }).flake { crossPlatforms = p: [ p.musl64 p.mingwW64 ]; };
+
+    in
+      pkgs.lib.lists.foldr pkgs.lib.recursiveUpdate {} [
+        { inherit (flake) packages apps; }
+        {
+          legacyPackages = pkgs;
+
+          apps.default = self.apps.${system}."x86_64-unknown-linux-musl:xrefcheck:exe:xrefcheck";
+
+          packages = {
+
+            default = self.packages.${system}.xrefcheck;
+
+            xrefcheck = self.packages.${system}."xrefcheck:exe:xrefcheck";
+
+            xrefcheck-static = self.packages.${system}."x86_64-unknown-linux-musl:xrefcheck:exe:xrefcheck";
+
+            xrefcheck-windows = self.packages.${system}."x86_64-w64-mingw32:xrefcheck:exe:xrefcheck";
+
+            docker-image =
+            let
+              executable = self.packages.${system}.xrefcheck-static;
+              binOnly = pkgs.runCommand "xrefcheck-bin" {} ''
+                mkdir -p $out/bin
+                cp ${executable}/bin/xrefcheck $out/bin
+                ${pkgs.nukeReferences}/bin/nuke-refs $out/bin/xrefcheck
+              '';
+            in pkgs.dockerTools.buildImage {
+              name = "xrefcheck";
+              contents = [ binOnly pkgs.cacert ];
+              config.Entrypoint = "xrefcheck";
+            };
+          };
+
+          checks = {
+            trailing-whitespace = pkgs.build.checkTrailingWhitespace ./.;
+            reuse-lint = pkgs.build.reuseLint ./.;
+          };
+        }
+      ]
+    );
+}

nix/sources.json

@@ -1,74 +0,0 @@
-{
-    "hackage.nix": {
-        "branch": "master",
-        "description": "Automatically generated Nix expressions for Hackage",
-        "homepage": "",
-        "owner": "input-output-hk",
-        "repo": "hackage.nix",
-        "rev": "af1008186119c18e9f4f42e1c463d69d5b5fd288",
-        "sha256": "1569jk15y3xq8wnjnf151xb125r2drr0cpska6mgsbpiddlp0mr6",
-        "type": "tarball",
-        "url": "https://github.com/input-output-hk/hackage.nix/archive/af1008186119c18e9f4f42e1c463d69d5b5fd288.tar.gz",
-        "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
-    },
-    "haskell.nix": {
-        "branch": "master",
-        "description": "Alternative Haskell Infrastructure for Nixpkgs",
-        "homepage": "https://input-output-hk.github.io/haskell.nix",
-        "owner": "input-output-hk",
-        "repo": "haskell.nix",
-        "rev": "b302c7a5b5fe1379f57abb81cbf1c0daabe44616",
-        "sha256": "0cqbm6xxkn5dmm21cxcrv7yvz8lz6kssp5cj4bf837kirbbg037j",
-        "type": "tarball",
-        "url": "https://github.com/input-output-hk/haskell.nix/archive/b302c7a5b5fe1379f57abb81cbf1c0daabe44616.tar.gz",
-        "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
-    },
-    "nixpkgs": {
-        "branch": "master",
-        "description": "Pinned Nixpkgs tree (master follows nixos-unstable-small, only tags have stable history)",
-        "homepage": "",
-        "owner": "serokell",
-        "repo": "nixpkgs",
-        "rev": "7887e272ab2ad8376d54ca5f58df0ed7f67676e6",
-        "sha256": "0sx7ff2ps79izkaqnigyj85vs6jffvx8x9kgl0qf4wv0n3b2wwmj",
-        "type": "tarball",
-        "url": "https://github.com/serokell/nixpkgs/archive/7887e272ab2ad8376d54ca5f58df0ed7f67676e6.tar.gz",
-        "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
-    },
-    "nixpkgs-stylish": {
-        "branch": "master",
-        "description": "Nix Packages collection",
-        "homepage": "",
-        "owner": "NixOS",
-        "repo": "nixpkgs",
-        "rev": "19574af0af3ffaf7c9e359744ed32556f34536bd",
-        "sha256": "0v3c4r8v40jimicdxqvxnzmdypnafm2baam7z131zk6ljhb8jpg9",
-        "type": "tarball",
-        "url": "https://github.com/NixOS/nixpkgs/archive/19574af0af3ffaf7c9e359744ed32556f34536bd.tar.gz",
-        "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
-    },
-    "serokell.nix": {
-        "branch": "master",
-        "description": "Serokell Nix infrastructure library",
-        "homepage": null,
-        "owner": "serokell",
-        "repo": "serokell.nix",
-        "rev": "652105c5fc5564f5d8e682d61bdc0d51bbc1f939",
-        "sha256": "19zkjhyjbksf2fw32h7m3x0v8nvgdy2qkjkxg2qzzb25as245vmj",
-        "type": "tarball",
-        "url": "https://github.com/serokell/serokell.nix/archive/652105c5fc5564f5d8e682d61bdc0d51bbc1f939.tar.gz",
-        "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
-    },
-    "stackage.nix": {
-        "branch": "master",
-        "description": "Automatically generated Nix expressions of Stackage snapshots",
-        "homepage": "",
-        "owner": "input-output-hk",
-        "repo": "stackage.nix",
-        "rev": "9ef56f70c138620b65ea42cade5e493418b0ae50",
-        "sha256": "0jrnv0w2yqkxkfnc64y7qrab7grr84mwp56y6r5x1npw174wpl8v",
-        "type": "tarball",
-        "url": "https://github.com/input-output-hk/stackage.nix/archive/9ef56f70c138620b65ea42cade5e493418b0ae50.tar.gz",
-        "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
-    }
-}

nix/sources.json.license

@@ -1,2 +0,0 @@
-# SPDX-FileCopyrightText: 2019 Serokell <https://serokell.io>
-# SPDX-License-Identifier: MPL-2.0

nix/sources.nix

@@ -1,174 +0,0 @@
-# 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_${saneName}";
-    in
-      if ersatz == "" then drv else
-        # this turns the string into an actual Nix path (for both absolute and
-        # relative paths)
-        if builtins.substring 0 1 ersatz == "/" then /. + ersatz else /. + builtins.getEnv "PWD" + "/${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); }

nix/sources.nix.license

@@ -1,2 +0,0 @@
-# SPDX-FileCopyrightText: 2019 Nicolas Mattia
-# SPDX-License-Identifier: LicenseRef-MIT-Mattia

xrefcheck.nix

@@ -1,47 +0,0 @@
-# SPDX-FileCopyrightText: 2020 Serokell <https://serokell.io>
-#
-# SPDX-License-Identifier: MPL-2.0
-
-{ linux ? false, linux-static ? false, windows ? false }:
-let
-  nixpkgs = (import ./ci.nix).pkgs;
-  src = (import ./ci.nix).project-src;
-  pkgs = if linux-static then nixpkgs.pkgsCross.musl64 else if windows then nixpkgs.pkgsCross.mingwW64 else nixpkgs;
-  project = pkgs.haskell-nix.stackProject {
-    src = pkgs.haskell-nix.haskellLib.cleanGit { src = ./.; keepGitDir = true; };
-    modules = [{
-      packages.xrefcheck = {
-        ghcOptions =
-          [ "-Werror" ];
-
-        components.tests = {
-          ftp-tests = {
-            build-tools = [ pkgs.vsftpd ];
-            preCheck = ''
-              echo "Starting vsftpd..."
-              touch /tmp/vsftpd.log
-              vsftpd \
-              -orun_as_launching_user=yes \
-              -olisten_port=2221 \
-              -olisten=yes \
-              -oftp_username=$(whoami) \
-              -oanon_root=${./ftp-tests/ftp_root} \
-              -opasv_min_port=2222 \
-              -ohide_file='{.*}' \
-              -odeny_file='{.*}' \
-              -oseccomp_sandbox=no \
-              -olog_ftp_protocol=yes \
-              -oxferlog_enable=yes \
-              -ovsftpd_log_file=/tmp/vsftpd.log &
-              sleep 1
-              tail -f /tmp/vsftpd.log &
-            '';
-            testFlags = [ "--ftp-host" "ftp://localhost:2221" ];
-          };
-          xrefcheck-tests.build-tools = [ pkgs.git ];
-        };
-      };
-    }];
-  };
-in
-project.xrefcheck