alistral: Add shell completions (#474218)

pkgs/by-name/al/alistral/package.nix

@@ -6,6 +6,8 @@
   nix-update-script,
   pkg-config,
   openssl,
+  installShellFiles,
+  writableTmpDirAsHomeHook,
 }:
 
 rustPlatform.buildRustPackage (finalAttrs: {
@@ -27,6 +29,12 @@ rustPlatform.buildRustPackage (finalAttrs: {
 
   nativeBuildInputs = [
     pkg-config
+  ]
+  ++ lib.optionals (stdenv.buildPlatform.canExecute stdenv.hostPlatform) [
+    installShellFiles
+    # When invoked in postInstall, alistral tries to write logfiles to its config dir on invocation, and fails if it can't find a writable one.
+    # The config dir falls back to a directory relative to $HOME on both Darwin and Linux, so setting a writable $HOME is enough.
+    writableTmpDirAsHomeHook
   ];
 
   buildInputs = [
@@ -38,6 +46,13 @@ rustPlatform.buildRustPackage (finalAttrs: {
 
   passthru.updateScript = nix-update-script { };
 
+  postInstall = lib.optionalString (stdenv.buildPlatform.canExecute stdenv.hostPlatform) ''
+    installShellCompletion --cmd alistral \
+      --bash <($out/bin/alistral --generate bash) \
+      --fish <($out/bin/alistral --generate fish) \
+      --zsh <($out/bin/alistral --generate zsh)
+  '';
+
   meta = {
     homepage = "https://rustynova016.github.io/Alistral/";
     changelog = "https://github.com/RustyNova016/Alistral/blob/${finalAttrs.src.tag}/CHANGELOG.md";