Running nixpkgs-update (https://nix-community.org/update-bot/) with UPDATE_INFO: chirpstack-packet-multiplexer 0 -> 1
attrpath: chirpstack-packet-multiplexer
Checking auto update branch...
[version] 
[version] generic version rewriter does not support multiple hashes
[rustCrateVersion] 
[rustCrateVersion] skipping because derivation has updateScript
[golangModuleVersion] 
[golangModuleVersion] Not a buildGoModule package with vendorHash
[npmDepsVersion] 
[npmDepsVersion] No npmDepsHash
[updateScript] 
[updateScript] Success
[updateScript] this derivation will be built:
  /nix/store/ck7kr6kal2852cx02mpcif817kkz6lw1-packages.json.drv
building '/nix/store/ck7kr6kal2852cx02mpcif817kkz6lw1-packages.json.drv'...

Going to be running update for following packages:
 - chirpstack-packet-multiplexer-4.0.0

Press Enter key to continue...
Running update for:
Enqueuing group of 1 packages
 - chirpstack-packet-multiplexer-4.0.0: UPDATING ...
 - chirpstack-packet-multiplexer-4.0.0: DONE.

Packages updated!

Diff after rewrites:
diff --git a/pkgs/by-name/ch/chirpstack-packet-multiplexer/package.nix b/pkgs/by-name/ch/chirpstack-packet-multiplexer/package.nix
index a568e22de12c..a87e8f11759a 100644
--- a/pkgs/by-name/ch/chirpstack-packet-multiplexer/package.nix
+++ b/pkgs/by-name/ch/chirpstack-packet-multiplexer/package.nix
@@ -7,16 +7,16 @@
 }:
 rustPlatform.buildRustPackage rec {
   pname = "chirpstack-packet-multiplexer";
-  version = "4.0.0";
+  version = "4.0.1";
 
   src = fetchFromGitHub {
     owner = "chirpstack";
     repo = "chirpstack-packet-multiplexer";
     tag = "v${version}";
-    hash = "sha256-BMlfYYt3fS3bOZulLqT9QRIZS0T4r/u9Y2VnQdI0oF0=";
+    hash = "sha256-GZygrejsenunkPlvejbi0MEIw226hrcbEYoBCRPQXMM=";
   };
 
-  cargoHash = "sha256-8HyIrViGKVldlA66k1fz+iHJ+ZdsGi1AqGQtxo8WLFQ=";
+  cargoHash = "sha256-DUPhgDfJQ6BhhgiBhYr6qtO8hjB1KcOXlFSbvjo1PHk=";
 
   nativeInstallCheckInputs = [ versionCheckHook ];
 

No auto update branch exists
Old version 4.0.0" not present in master derivation file with contents: {
  lib,
  rustPlatform,
  fetchFromGitHub,
  nix-update-script,
  versionCheckHook,
}:
rustPlatform.buildRustPackage rec {
  pname = "chirpstack-packet-multiplexer";
  version = "4.0.1";

  src = fetchFromGitHub {
    owner = "chirpstack";
    repo = "chirpstack-packet-multiplexer";
    tag = "v${version}";
    hash = "sha256-GZygrejsenunkPlvejbi0MEIw226hrcbEYoBCRPQXMM=";
  };

  cargoHash = "sha256-DUPhgDfJQ6BhhgiBhYr6qtO8hjB1KcOXlFSbvjo1PHk=";

  nativeInstallCheckInputs = [ versionCheckHook ];

  doInstallCheck = true;

  passthru.updateScript = nix-update-script { };

  meta = {
    description = "orward Semtech packet-forwarder data to multiple servers";
    homepage = "https://www.chirpstack.io/";
    license = lib.licenses.mit;
    maintainers = [ lib.maintainers.stv0g ];
    mainProgram = "chirpstack-packet-multiplexer";
  };
}