Added niv

nix/sources.json

@@ -0,0 +1,26 @@
+{
+    "niv": {
+        "branch": "master",
+        "description": "Easy dependency management for Nix projects",
+        "homepage": "https://github.com/nmattia/niv",
+        "owner": "nmattia",
+        "repo": "niv",
+        "rev": "c25268460b72cea5b7294354ab019997530a6f3d",
+        "sha256": "1fgq1nkycm54f431h6wflh6rr7xsq3q2fq9drbgra2fnrsyn65ll",
+        "type": "tarball",
+        "url": "https://github.com/nmattia/niv/archive/c25268460b72cea5b7294354ab019997530a6f3d.tar.gz",
+        "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
+    },
+    "nixpkgs": {
+        "branch": "nixos-19.09",
+        "description": "A read-only mirror of NixOS/nixpkgs tracking the released channels. Send issues and PRs to",
+        "homepage": "https://github.com/NixOS/nixpkgs",
+        "owner": "NixOS",
+        "repo": "nixpkgs-channels",
+        "rev": "e1843646b04fb564abf6330a9432a76df3269d2f",
+        "sha256": "1h1nv7bb6j0ccx8v0sz3gcwl1jqz3v2bb13ham0ky0rg9cvdv91h",
+        "type": "tarball",
+        "url": "https://github.com/NixOS/nixpkgs-channels/archive/e1843646b04fb564abf6330a9432a76df3269d2f.tar.gz",
+        "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
+    }
+}

nix/sources.nix

@@ -0,0 +1,130 @@
+# This file has been generated by Niv.
+
+# A record, from name to path, of the third-party packages
+with rec
+{
+  pkgs =
+    if hasNixpkgsPath
+    then
+        if hasThisAsNixpkgsPath
+        then import (builtins_fetchTarball { inherit (sources_nixpkgs) url sha256; }) {}
+        else import <nixpkgs> {}
+    else
+        import (builtins_fetchTarball { inherit (sources_nixpkgs) url sha256; }) {};
+
+  sources_nixpkgs =
+    if builtins.hasAttr "nixpkgs" sources
+    then sources.nixpkgs
+    else abort
+    ''
+        Please specify either <nixpkgs> (through -I or NIX_PATH=nixpkgs=...) or
+        add a package called "nixpkgs" to your sources.json.
+    '';
+
+  sources_gitignore =
+    if builtins.hasAttr "gitignore" sources
+    then sources.gitignore
+    else abort
+    ''
+        Please add "gitignore" to your sources.json:
+        niv add hercules-ci/gitignore
+    '';
+
+  inherit (import (builtins_fetchTarball { inherit (sources_gitignore) url sha256; }) {
+    inherit (pkgs) lib;
+  }) gitignoreSource;
+
+  # fetchTarball version that is compatible between all the versions of Nix
+  builtins_fetchTarball =
+      { url, sha256 ? null }@attrs:
+      let
+        inherit (builtins) lessThan nixVersion fetchTarball;
+      in
+        if sha256 == null || lessThan nixVersion "1.12" then
+          fetchTarball { inherit url; }
+        else
+          fetchTarball attrs;
+
+  # fetchurl version that is compatible between all the versions of Nix
+  builtins_fetchurl =
+      { url, sha256 ? null }@attrs:
+      let
+        inherit (builtins) lessThan nixVersion fetchurl;
+      in
+        if sha256 == null || lessThan nixVersion "1.12" then
+          fetchurl { inherit url; }
+        else
+          fetchurl attrs;
+
+  # A wrapper around pkgs.fetchzip that has inspectable arguments,
+  # annoyingly this means we have to specify them
+  fetchzip = { url, sha256  ? null }@attrs: if sha256 == null
+    then builtins.fetchTarball { inherit url; }
+    else pkgs.fetchzip attrs;
+
+  # A wrapper around pkgs.fetchurl that has inspectable arguments,
+  # annoyingly this means we have to specify them
+  fetchurl = { url, sha256 }@attrs: pkgs.fetchurl attrs;
+
+  hasNixpkgsPath = (builtins.tryEval <nixpkgs>).success;
+  hasThisAsNixpkgsPath =
+    (builtins.tryEval <nixpkgs>).success && <nixpkgs> == ./.;
+
+  sources = builtins.fromJSON (builtins.readFile ./sources.json);
+
+  mapAttrs = builtins.mapAttrs or
+    (f: set: with builtins;
+      listToAttrs (map (attr: { name = attr; value = f attr set.${attr}; }) (attrNames set)));
+
+  # borrowed from nixpkgs
+  functionArgs = f: f.__functionArgs or (builtins.functionArgs f);
+  callFunctionWith = autoArgs: f: args:
+    let auto = builtins.intersectAttrs (functionArgs f) autoArgs;
+    in f (auto // args);
+
+  getFetcher = spec:
+    let fetcherName =
+      if builtins.hasAttr "type" spec
+      then builtins.getAttr "type" spec
+      else "builtin-tarball";
+    in builtins.getAttr fetcherName {
+      "tarball" = fetchzip;
+      "builtin-tarball" = builtins_fetchTarball;
+      "file" = fetchurl;
+      "builtin-url" = builtins_fetchurl;
+    };
+};
+# NOTE: spec must _not_ have an "outPath" attribute
+mapAttrs (name: spec:
+  if builtins.hasAttr "outPath" spec
+  then abort
+    "The values in sources.json should not have an 'outPath' attribute"
+  else
+    let
+      host = if (name == "nixpkgs") then "custom_nixpkgs" else name;
+      tryFromPath = builtins.tryEval (builtins.findFile builtins.nixPath host);
+      defaultSpec = (if builtins.hasAttr "url" spec && builtins.hasAttr "sha256" spec
+        then spec //
+            { outPath = callFunctionWith spec (getFetcher spec) { }; }
+        else spec) // (if tryFromPath.success
+          then let path = tryFromPath.value;
+          in {
+            outPath = builtins.trace "using search host <${host}>" (
+              if pkgs.lib.hasPrefix "/nix/store" (builtins.toString path)
+              then path else gitignoreSource path);
+          }
+          else {});
+    in if builtins.hasAttr "rev" spec && builtins.hasAttr "url" spec then
+      defaultSpec //
+        { revOverride = rev: if (rev == null) then defaultSpec else
+              let
+                spec' = removeAttrs (spec // {
+                  rev = rev;
+                  url = builtins.replaceStrings [defaultSpec.rev] [rev] defaultSpec.url;
+                }) [ "sha256" ];
+              in
+                spec' //
+                { outPath = callFunctionWith spec' (getFetcher spec') { };  };
+        }
+      else defaultSpec
+  ) sources

overlays/default.nix

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+sourcePaths: map import (import ./overlay-list.nix) ++
+  [(self: super: { inherit sourcePaths; })]

overlays/niv.nix

@@ -0,0 +1,3 @@
+self: super: {
+  inherit (import self.sourcePaths.niv {}) niv;
+}

overlays/overlay-list.nix

@@ -0,0 +1,3 @@
+[
+  ./niv.nix
+]