grafana-alloy: install shell completions

pkgs/by-name/gr/grafana-alloy/package.nix

@@ -9,6 +9,7 @@
 , nodejs
 , grafana-alloy
 , nix-update-script
+, installShellFiles
 , testers
 }:
 
@@ -26,7 +27,7 @@ buildGoModule rec {
   proxyVendor = true;
   vendorHash = "sha256-6Xc2siImM1Dl716uGhtAGcn+PO2OLuYLxanzg8Ho6SA=";
 
-  nativeBuildInputs = [ fixup-yarn-lock yarn nodejs ];
+  nativeBuildInputs = [ fixup-yarn-lock yarn nodejs installShellFiles ];
 
   ldflags =
     let
@@ -93,6 +94,13 @@ buildGoModule rec {
       $out/bin/alloy
   '';
 
+  postInstall = ''
+    installShellCompletion --cmd alloy \
+      --bash <($out/bin/alloy completion bash) \
+      --fish <($out/bin/alloy completion fish) \
+      --zsh <($out/bin/alloy completion zsh)
+  '';
+
   passthru = {
     tests = {
       version = testers.testVersion {