swiftlint: add shell completions support (#506815)

pkgs/by-name/sw/swiftlint/package.nix

@@ -3,6 +3,7 @@
   lib,
   fetchurl,
   unzip,
+  installShellFiles,
   nix-update-script,
   versionCheckHook,
 }:
@@ -19,7 +20,10 @@ stdenvNoCC.mkDerivation rec {
   dontConfigure = true;
   dontBuild = true;
 
-  nativeBuildInputs = [ unzip ];
+  nativeBuildInputs = [
+    unzip
+    installShellFiles
+  ];
 
   sourceRoot = ".";
 
@@ -29,6 +33,13 @@ stdenvNoCC.mkDerivation rec {
     runHook postInstall
   '';
 
+  postInstall = lib.optionalString (stdenvNoCC.buildPlatform.canExecute stdenvNoCC.hostPlatform) ''
+    installShellCompletion --cmd swiftlint \
+      --bash <($out/bin/swiftlint --generate-completion-script bash) \
+      --fish <($out/bin/swiftlint --generate-completion-script fish) \
+      --zsh <($out/bin/swiftlint --generate-completion-script zsh)
+  '';
+
   doInstallCheck = true;
   nativeInstallCheckInputs = [ versionCheckHook ];