pkgs: add flake-warn to print out when flakes are out of date

flake.nix

@@ -227,6 +227,7 @@
             isUnstable = true;
           };
           femtolisp = pkgs.callPackage ./pkgs/femtolisp.nix { };
+          flake-warn = pkgs.callPackage ./pkgs/flake-warn.nix { inherit pkgs; };
           kurinto = pkgs.callPackage ./pkgs/kurinto.nix { };
           mcchunkie = pkgs.callPackage ./pkgs/mcchunkie.nix { inherit pkgs; };
           yaegi = pkgs.callPackage ./pkgs/yaegi.nix { inherit pkgs; };

pkgs/flake-warn.nix

@@ -0,0 +1,25 @@
+{ stdenv, lib, substituteAll, jq, nix, coreutils, ... }:
+
+stdenv.mkDerivation rec {
+  pname = "flake-warn";
+  version = "1.0.0";
+
+  buildCommand = ''
+    install -Dm755 $script $out/bin/${pname}
+  '';
+
+  script = substituteAll {
+    src = ./flake-warn.sh;
+    isExecutable = true;
+    inherit jq nix coreutils;
+    inherit (stdenv) shell;
+  };
+
+  meta = {
+    description = "script to warn when flake inputs are out of date";
+    homepage = "https://github.com/qbit/xin";
+    license = lib.licenses.isc;
+    maintainer = with lib.maintainers; [ qbit ];
+    mainProgram = "flake-warn";
+  };
+}

pkgs/flake-warn.sh

@@ -0,0 +1,14 @@
+#!@shell@ -e
+
+BOLD=$(tput bold)  
+NORMAL=$(tput sgr0)  
+
+FLAKE_EPOCH=$(@nix@/bin/nix flake metadata --json | @jq@/bin/jq .lastModified)  
+NOW_EPOCH=$(@coreutils@/bin/date +"%s")  
+
+EPOCH_DIFF=$(($NOW_EPOCH - $FLAKE_EPOCH))  
+
+if [ $EPOCH_DIFF -gt 60480 ]; then  
+	echo "${BOLD}WARNING: inputs haven't been updated in $(($EPOCH_DIFF / 86400)) days!${NORMAL}"  
+fi  
+