packer: set ldflags, install zsh completion

pkgs/development/tools/packer/default.nix

@@ -1,4 +1,4 @@
-{ lib, buildGoPackage, fetchFromGitHub }:
+{ lib, buildGoPackage, fetchFromGitHub, installShellFiles }:
 buildGoPackage rec {
   pname = "packer";
   version = "1.6.6";
@@ -14,6 +14,14 @@ buildGoPackage rec {
     sha256 = "sha256-kFDy8Zlx+D5JDyNlAmB/ICTe4K9s6KDbALP5pom5OQg=";
   };
 
+  buildFlagsArray = [ "-ldflags=-s -w" ];
+
+  nativeBuildInputs = [ installShellFiles ];
+
+  postInstall = ''
+    installShellCompletion --zsh go/src/${goPackagePath}/contrib/zsh-completion/_packer
+  '';
+
   meta = with lib; {
     description = "A tool for creating identical machine images for multiple platforms from a single source configuration";
     homepage    = "https://www.packer.io";