spago: 0.20.1 -> 0.20.2

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

@@ -1,5 +1,5 @@
 #!/usr/bin/env nix-shell
-#!nix-shell -i bash -p cabal2nix curl jq
+#!nix-shell -i bash -p cabal2nix curl jq haskellPackages.cabal2nix-unstable -I nixpkgs=.
 #
 # This script will update the spago derivation to the latest version using
 # cabal2nix.
@@ -25,7 +25,10 @@ new_version=$(curl --silent "https://api.github.com/repos/purescript/spago/relea
 echo "Updating spago from old version $old_version to new version $new_version."
 echo "Running cabal2nix and outputting to ${spago_derivation_file}..."
 
-cabal2nix --revision "$new_version" "https://github.com/purescript/spago.git" > "$spago_derivation_file"
+echo "# This has been automatically generated by the script" > "$spago_derivation_file"
+echo "# ./update.sh.  This should not be changed by hand." >> "$spago_derivation_file"
+
+cabal2nix --revision "$new_version" "https://github.com/purescript/spago.git" >> "$spago_derivation_file"
 
 # TODO: This should ideally also automatically update the docsSearchVersion
 # from pkgs/development/haskell/configuration-nix.nix.