rqbit: Install shell completions

pkgs/by-name/rq/rqbit/package.nix

@@ -3,6 +3,7 @@
   stdenv,
   rustPlatform,
   fetchFromGitHub,
+  installShellFiles,
   pkg-config,
   openssl,
   buildNpmPackage,
@@ -47,7 +48,10 @@ rustPlatform.buildRustPackage {
 
   cargoHash = "sha256-gYasOjrG0oeT/6Ben57MKAvBtgpoSmZ93RZQqSXAxIc=";
 
-  nativeBuildInputs = lib.optionals stdenv.hostPlatform.isLinux [ pkg-config ];
+  nativeBuildInputs = [
+    installShellFiles
+  ]
+  ++ lib.optionals stdenv.hostPlatform.isLinux [ pkg-config ];
 
   buildInputs = lib.optionals stdenv.hostPlatform.isLinux [ openssl ];
 
@@ -62,6 +66,12 @@ rustPlatform.buildRustPackage {
     rm crates/librqbit/build.rs
   '';
 
+  postInstall = lib.optionalString (stdenv.buildPlatform.canExecute stdenv.hostPlatform) ''
+    for shell in bash fish zsh; do
+      installShellCompletion --cmd rqbit --$shell <($out/bin/rqbit completions $shell)
+    done
+  '';
+
   nativeInstallCheckInputs = [
     versionCheckHook
   ];