gitlab: Get rid of most 'already initialized constant'-warnings

On start, unicorn, sidekiq and other parts running ruby code emits
quite a few warnings similar to

/var/gitlab/state/config/application.rb:202: warning: already initialized constant Gitlab::Application::LOOSE_EE_APP_ASSETS
/nix/store/ysb0lgbzxp7a9y4yl8d4f9wrrzy9kafc-gitlab-ee-12.3.5/share/gitlab/config/application.rb:202: warning: previous definition of LOOSE_EE_APP_ASSETS was here
/var/gitlab/state/lib/gitlab.rb:38: warning: already initialized constant Gitlab::COM_URL
/nix/store/ysb0lgbzxp7a9y4yl8d4f9wrrzy9kafc-gitlab-ee-12.3.5/share/gitlab/lib/gitlab.rb:38: warning: previous definition of COM_URL was here

This seems to be caused by the same ruby files being evaluated
multiple times due to the paths being different - sometimes they're
loaded using the direct path and sometimes through a symlink, due to
our split between config and package data. To fix this, we make sure
that the offending files in the state directory always reference the
store path, regardless of that being the real file or a symlink.

nixos/modules/services/misc/gitlab.nix

@@ -666,7 +666,6 @@ in {
       "d ${gitlabConfig.production.shared.path}/artifacts 0750 ${cfg.user} ${cfg.group} -"
       "d ${gitlabConfig.production.shared.path}/lfs-objects 0750 ${cfg.user} ${cfg.group} -"
       "d ${gitlabConfig.production.shared.path}/pages 0750 ${cfg.user} ${cfg.group} -"
-      "L+ ${cfg.statePath}/lib - - - - ${cfg.packages.gitlab}/share/gitlab/lib"
       "L+ /run/gitlab/config - - - - ${cfg.statePath}/config"
       "L+ /run/gitlab/log - - - - ${cfg.statePath}/log"
       "L+ /run/gitlab/tmp - - - - ${cfg.statePath}/tmp"

pkgs/applications/version-management/gitlab/default.nix

@@ -1,7 +1,7 @@
 { stdenv, lib, fetchurl, fetchFromGitLab, bundlerEnv
 , ruby, tzdata, git, nettools, nixosTests, nodejs
 , gitlabEnterprise ? false, callPackage, yarn
-, yarn2nix-moretea
+, yarn2nix-moretea, replace
 }:
 
 let
@@ -118,6 +118,13 @@ stdenv.mkDerivation {
 
     sed -i '/ask_to_continue/d' lib/tasks/gitlab/two_factor.rake
     sed -ri -e '/log_level/a config.logger = Logger.new(STDERR)' config/environments/production.rb
+
+    # Always require lib-files and application.rb through their store
+    # path, not their relative state directory path. This gets rid of
+    # warnings and means we don't have to link back to lib from the
+    # state directory.
+    ${replace}/bin/replace-literal -f -r -e '../lib' "$out/share/gitlab/lib" config
+    ${replace}/bin/replace-literal -f -r -e "require_relative 'application'" "require_relative '$out/share/gitlab/config/application'" config
   '';
 
   buildPhase = ''