Description:
The lastest gitlab (8.17.2) lacks webpack (it has something to do with NodeJS, see my fix below).

This is the entry in the log file :

---------------------------------------------------------------
ActionView::Template::Error (Could not load compiled manifest from /usr/share/webapps/gitlab/public/assets/webpack/manifest.json - have you run `rake webpack:compile`? (original error No such file or directory @ rb_sysopen - /usr/share/webapps/gitlab/public/assets/webpack/manifest.json)):
28: = stylesheet_link_tag "application", media: "all"
29: = stylesheet_link_tag "print", media: "print"
30:
31: = javascript_include_tag(*webpack_asset_paths("application"))
32:
33: - if content_for?(:page_specific_javascripts)
34: = yield :page_specific_javascripts
app/views/layouts/_head.html.haml:31:in `_app_views_layouts__head_html_haml___4496552953264907693_55123640'
app/views/layouts/application.html.haml:3:in `_app_views_layouts_application_html_haml___2149553463195357828_55885660'
app/views/layouts/project.html.haml:25:in `_app_views_layouts_project_html_haml___19517622230222845_36756840'
app/controllers/projects/tree_controller.rb:27:in `show'
lib/gitlab/middleware/multipart.rb:93:in `call'
lib/gitlab/request_profiler/middleware.rb:14:in `call'
lib/gitlab/middleware/go.rb:16:in `call'
---------------------------------------------------------------


Steps to reproduce:

To obtain this, I upgraded gitlab from 8.16.6-1 to 8.17.2-1, then ran the usual

sudo su - gitlab -s /bin/sh -c "cd '/usr/share/webapps/gitlab'; bundle-2.3 exec rake db:migrate RAILS_ENV=production"

and

sudo systemctl daemon-reload
sudo systemctl restart gitlab-sidekiq gitlab-unicorn gitlab-workhorse

Steps to fix (on an already installed system):

cd /usr/share/webapps/gitlab
sudo npm install --production
chown -R gitlab *
sudo su - gitlab -s /bin/sh -c "cd '/usr/share/webapps/gitlab'; bundle-2.3 exec rake gitlab:assets:clean gitlab:assets:compile cache:clear RAILS_ENV=production"
sudo chown -R root *
sudo chown gitlab ./db/schema.rb

These steps are based on this issue : https://gitlab.com/gitlab-org/gitlab-ce/issues/28586