update.nix: Run update scripts in parallel

To make updating large attribute sets faster, the update scripts
are now run in parallel.

Please note the following changes in semantics:

- The string passed to updateScript needs to be a path to an executable file.
- The updateScript can also be a list: the tail elements will then be passed
  to the head as command line arguments.

maintainers/scripts/update.nix

@@ -1,6 +1,8 @@
 { package ? null
 , maintainer ? null
 , path ? null
+, max-workers ? null
+, keep-going ? null
 }:
 
 # TODO: add assert statements
@@ -105,26 +107,23 @@ let
         % nix-shell maintainers/scripts/update.nix --argstr path gnome3
 
     to run update script for all package under an attribute path.
+
+    You can also add
+
+        --argstr max-workers 8
+
+    to increase the number of jobs in parallel, or
+
+        --argstr keep-going true
+
+    to continue running when a single update fails.
   '';
 
-  runUpdateScript = package: ''
-    echo -ne " - ${package.name}: UPDATING ..."\\r
-    ${package.updateScript} &> ${(builtins.parseDrvName package.name).name}.log
-    CODE=$?
-    if [ "$CODE" != "0" ]; then
-      echo " - ${package.name}: ERROR       "
-      echo ""
-      echo "--- SHOWING ERROR LOG FOR ${package.name} ----------------------"
-      echo ""
-      cat ${(builtins.parseDrvName package.name).name}.log
-      echo ""
-      echo "--- SHOWING ERROR LOG FOR ${package.name} ----------------------"
-      exit $CODE
-    else
-      rm ${(builtins.parseDrvName package.name).name}.log
-    fi
-    echo " - ${package.name}: DONE.       "
-  '';
+  packageData = package: {
+    name = package.name;
+    pname = (builtins.parseDrvName package.name).name;
+    updateScript = pkgs.lib.toList package.updateScript;
+  };
 
 in pkgs.stdenv.mkDerivation {
   name = "nixpkgs-update-script";
@@ -139,21 +138,7 @@ in pkgs.stdenv.mkDerivation {
     exit 1
   '';
   shellHook = ''
-    echo ""
-    echo "Going to be running update for following packages:"
-    echo "${builtins.concatStringsSep "\n" (map (x: " - ${x.name}") packages)}"
-    echo ""
-    read -n1 -r -p "Press space to continue..." confirm
-    if [ "$confirm" = "" ]; then
-      echo ""
-      echo "Running update for:"
-      ${builtins.concatStringsSep "\n" (map runUpdateScript packages)}
-      echo ""
-      echo "Packages updated!"
-      exit 0
-    else
-      echo "Aborting!"
-      exit 1
-    fi
+    unset shellHook # do not contaminate nested shells
+    exec ${pkgs.python3.interpreter} ${./update.py} ${pkgs.writeText "packages.json" (builtins.toJSON (map packageData packages))}${pkgs.lib.optionalString (max-workers != null) " --max-workers=${max-workers}"}${pkgs.lib.optionalString (keep-going == "true") " --keep-going"}
   '';
 }