[Rails5] Set request.format in commits_controller

Since Rails 5.0 `request.format` is being set depending on the route extension.

In commits pages we pass a ref as a URL parameter.
If the ref is an extension-like, Rails converts it and sets to
`request.format`.

E.g. if the ref is `some_branch.atom`, Rails starts responding with
`atom` format, but it should response with `html` because `.atom` is the
part of ref name, not the format.

This commit explicitly sets `request.format` to `:html` when needed.

app/controllers/projects/commits_controller.rb

@@ -9,6 +9,7 @@ class Projects::CommitsController < Projects::ApplicationController
   before_action :assign_ref_vars
   before_action :authorize_download_code!
   before_action :set_commits
+  before_action :set_request_format, only: :show
 
   def show
     @merge_request = MergeRequestsFinder.new(current_user, project_id: @project.id).execute.opened
@@ -61,6 +62,19 @@ class Projects::CommitsController < Projects::ApplicationController
     @commits = prepare_commits_for_rendering(@commits)
   end
 
+  # Rails 5 sets request.format from the extension.
+  # Explicitly set to :html.
+  def set_request_format
+    request.format = :html if set_request_format?
+  end
+
+  # Rails 5 sets request.format from extension.
+  # In this case if the ref ends with `.atom`, it's expected to be the html response,
+  # not the atom one. So explicitly set request.format as :html to act like rails4.
+  def set_request_format?
+    request.format.to_s == "text/html" || @commits.ref.ends_with?("atom")
+  end
+
   def whitelist_query_limiting
     Gitlab::QueryLimiting.whitelist('https://gitlab.com/gitlab-org/gitlab-ce/issues/42330')
   end

changelogs/unreleased/blackst0ne-rails5-set-request-format-in--commits-controller.yml

+---
+title: "[Rails5] Set request.format in commits_controller"
+merge_request: 20023
+author: "@blackst0ne"
+type: fixed