Implement proper Nix verioning

bin/package.nix

@@ -2,7 +2,10 @@ let
   pkgs = import ../nix {};
   specJson = pkgs.writeTextFile
     { name = "spec-json";
-      text = builtins.readFile ../nix/nixpkgs/nixpkgs-src.json;
+      text =
+        let
+          versions = builtins.fromJSON (builtins.readFile ../nix/versions.json);
+        in builtins.toJSON versions.nixpkgs;
       destination = "/spec.json";
     };
   lib64 = pkgs.runCommand "lib64" {}

nix/default.nix

@@ -1,4 +1,5 @@
-{ nixpkgs ? import ./nixpkgs }:
+with { fetch = import ./fetch.nix; };
+{ nixpkgs ? fetch.nixpkgs }:
 import nixpkgs {
   config = { };
   overlays = [

nix/fetch.nix

@@ -0,0 +1,26 @@
+# A record, from name to path, of the third-party packages
+let
+  versions = builtins.fromJSON (builtins.readFile ./versions.json);
+  fetchTarball =
+    # fetchTarball version that is compatible between all the versions of
+    # Nix
+    { url, sha256 }@attrs:
+    let
+      inherit (builtins) lessThan nixVersion fetchTarball;
+    in
+      if lessThan nixVersion "1.12" then
+        fetchTarball { inherit url; }
+      else
+        fetchTarball attrs;
+  mapAttrs = builtins.mapAttrs or
+    (f: set: with builtins;
+      listToAttrs (map (attr: { name = attr; value = f attr set.${attr}; }) (attrNames set)));
+in
+  mapAttrs (_: spec:
+      fetchTarball {
+        url =
+          with spec;
+          "https://github.com/${owner}/${repo}/archive/${rev}.tar.gz";
+        sha256 = spec.sha256;
+      }
+    ) versions

nix/nixpkgs/default.nix

@@ -1,6 +0,0 @@
-let
-  spec = builtins.fromJSON (builtins.readFile ./nixpkgs-src.json);
-  rev = spec.rev;
-  url = "https://github.com/${spec.owner}/${spec.repo}/archive/${spec.rev}.tar.gz";
-in
-  builtins.fetchTarball url

nix/nixpkgs/nixpkgs-src.json

@@ -1,6 +0,0 @@
-{
-  "owner": "NixOS",
-  "repo": "nixpkgs",
-  "rev": "584270e39743020d8aa056b40eea00fcaa2b595f",
-  "sha256": "1p8hrz7xz73gzcqw62f3zfkmf3pkwwn1b41xzs7ayxafkmzsh0hw"
-}

nix/update

@@ -1,24 +0,0 @@
-#!/usr/bin/env nix-shell
-#!nix-shell -i bash -p bash nix curl jq
-# vim: filetype=sh
-# Updates the nixpkgs.json to the latest release
-# See https://gist.github.com/zimbatm/de5350245874361762b6a4dfe5366530
-set -euo pipefail
-
-branch=master
-
-owner=NixOS
-repo=nixpkgs
-rev=$(curl -sfL https://api.github.com/repos/$owner/$repo/git/refs/heads/$branch | jq -r .object.sha)
-url=https://github.com/$owner/$repo/archive/$rev.tar.gz
-
-release_sha256=$(nix-prefetch-url --unpack "$url")
-
-cat <<NIXPKGS | tee nix/nixpkgs/nixpkgs-src.json
-{
-  "owner": "$owner",
-  "repo": "$repo",
-  "rev": "$rev",
-  "sha256": "$release_sha256"
-}
-NIXPKGS

nix/versions.json

@@ -0,0 +1,9 @@
+{
+  "nixpkgs": {
+    "owner": "NixOS",
+    "repo": "nixpkgs",
+    "branch": "master",
+    "rev": "584270e39743020d8aa056b40eea00fcaa2b595f",
+    "sha256": "1p8hrz7xz73gzcqw62f3zfkmf3pkwwn1b41xzs7ayxafkmzsh0hw"
+  }
+}

script/update

@@ -0,0 +1,102 @@
+#!/usr/bin/env nix-shell
+#!nix-shell -i bash -p bash nix curl jq --pure
+# vim: filetype=sh
+set -euo pipefail
+
+banner() {
+    echo
+    echo "--- $*"
+    echo
+}
+
+
+update() {
+    local versions="$1"
+    local package="$2"
+    echo "Versions file: $versions"
+    echo "Package to update: $package"
+    local owner=$(cat $versions | jq -r ".[\"$package\"].owner")
+    local repo=$(cat $versions | jq -r ".[\"$package\"].repo")
+    local branch=$(cat $versions | jq -r ".[\"$package\"].branch")
+    local rev=$(cat $versions | jq -r ".[\"$package\"].rev")
+    local sha256=$(cat $versions | jq -r ".[\"$package\"].sha256")
+
+    echo "Owner: $owner"
+    echo "Repository: $repo"
+    echo "Branch: $branch"
+
+
+    case "$PREFETCH_ONLY" in
+        TRUE)
+        local new_rev=$rev
+        echo "Using existing revision"
+        ;;
+        FALSE)
+        local new_rev=$(curl -sfL \
+            https://api.github.com/repos/$owner/$repo/git/refs/heads/$branch \
+            | jq -r .object.sha)
+        echo "Fetching latest revision on branch $branch"
+        ;;
+    esac
+    echo "The following revision will be used:"
+    echo "  $new_rev"
+
+    local url=https://github.com/$owner/$repo/archive/$new_rev.tar.gz
+    local new_sha256=$(nix-prefetch-url --unpack "$url")
+
+    echo "The following url will be used:"
+    echo "  $url"
+
+    echo "The following sha256 will be used:"
+    echo "  $new_sha256"
+
+    res=$(cat $versions \
+        | jq -rM ".[\"$package\"].rev = \"$new_rev\"" \
+        | jq -rM ".[\"$package\"].sha256 = \"$new_sha256\""
+        )
+
+    echo "New versions file:"
+    echo "$res"
+
+    echo "$res" > $versions
+}
+
+ROOT="$( cd "$( dirname "${BASH_SOURCE[0]}" )"/.. >/dev/null && pwd )"
+VERSIONS_DEF="$ROOT/nix/versions.json"
+PACKAGES_DEF="$(cat $VERSIONS_DEF | jq -r 'keys | .[]')"
+
+VERSIONS="$VERSIONS_DEF"
+echo "Using versions file ${VERSIONS}"
+
+PREFETCH_ONLY="FALSE"
+PACKAGES=""
+
+
+while [[ $# -gt 0 ]]
+do
+key="$1"
+
+case $key in
+    --prefetch)
+    PREFETCH_ONLY="TRUE"
+    shift
+    ;;
+    *)
+    PACKAGES="$key $PACKAGES"
+    shift # past value
+    ;;
+esac
+done
+
+if [ -z "$PACKAGES" ];
+then
+    PACKAGES="$PACKAGES_DEF"
+fi
+
+echo "Using packages:"
+for p in $PACKAGES; do echo " - $p"; done
+
+for p in $PACKAGES; do
+    banner "$p"
+    update "$VERSIONS" "$p"
+done

tests/extended-config/nix/default.nix

@@ -1,5 +1,7 @@
 let
-  spec = builtins.fromJSON (builtins.readFile ../../../nix/nixpkgs/nixpkgs-src.json);
+  spec =
+    let versions = builtins.fromJSON (builtins.readFile ../../../nix/versions.json);
+    in versions.nixpkgs;
   nixpkgs =
         (builtins.fetchTarball
             { url = "https://github.com/${spec.owner}/${spec.repo}/archive/${spec.rev}.tar.gz";