sift: add bash completion

pkgs/tools/text/sift/default.nix

@@ -1,4 +1,4 @@
-{ lib, buildGoPackage, fetchFromGitHub }:
+{ lib, buildGoPackage, fetchFromGitHub, installShellFiles }:
 
 buildGoPackage rec {
   pname = "sift";
@@ -7,6 +7,8 @@ buildGoPackage rec {
 
   goPackagePath = "github.com/svent/sift";
 
+  nativeBuildInputs = [ installShellFiles ];
+
   src = fetchFromGitHub {
     inherit rev;
     owner = "svent";
@@ -14,6 +16,10 @@ buildGoPackage rec {
     sha256 = "0bgy0jf84z1c3msvb60ffj4axayfchdkf0xjnsbx9kad1v10g7i1";
   };
 
+  postInstall = ''
+    installShellCompletion --cmd sift --bash go/src/github.com/svent/sift/sift-completion.bash
+  '';
+
   goDeps = ./deps.nix;
 
   meta = with lib; {