spago: add update script for automatically updating to new versions

pkgs/development/tools/purescript/spago/update.sh

@@ -0,0 +1,30 @@
+#!/usr/bin/env nix-shell
+#!nix-shell -i bash -p cabal2nix curl jq
+#
+# This script will update the spago derivation to the latest version using
+# cabal2nix.
+#
+# Note that you should always try building spago after updating it here, since
+# some of the overrides in pkgs/development/haskell/configuration-nix.nix may
+# need to be updated/changed.
+
+set -eo pipefail
+
+# This is the directory of this update.sh script.
+script_dir="$( cd "$( dirname "${BASH_SOURCE[0]}" )" >/dev/null 2>&1 && pwd )"
+
+# Spago derivation created with cabal2nix.
+spago_derivation_file="${script_dir}/default.nix"
+
+# This is the current revision of spago in Nixpkgs.
+old_version="$(sed -En 's/.*\bversion = "(.*?)".*/\1/p' "$spago_derivation_file")"
+
+# This is the latest release version of spago on GitHub.
+new_version=$(curl --silent "https://api.github.com/repos/spacchetti/spago/releases" | jq '.[0].tag_name' --raw-output)
+
+echo "Updating spago from old version $old_version to new version $new_version."
+echo "Running cabal2nix and outputting to ${spago_derivation_file}..."
+
+cabal2nix --revision "$new_version" "https://github.com/spacchetti/spago.git" > "$spago_derivation_file"
+
+echo "Finished."