[Rails5] Fix snippets_finder arel queries

There is a bug https://github.com/rails/arel/issues/531 in Rails 5.0 and
5.1 in Arel/ActiveRecord.

This commit converts arel based queries to their raw counterparts to
make the finder work in Rails 5.0.

These changes should be reverted when on Rails 5.2 as since that version
such queries work well again. See the bug link.

app/finders/snippets_finder.rb

@@ -54,7 +54,10 @@ class SnippetsFinder < UnionFinder
   end
 
   def authorized_snippets
-    Snippet.where(feature_available_projects.or(not_project_related))
+    # This query was intentionally converted to a raw one to get it work in Rails 5.0.
+    # In Rails 5.0 and 5.1 there's a bug: https://github.com/rails/arel/issues/531
+    # Please convert it back when on rails 5.2 as it works again as expected since 5.2.
+    Snippet.where("#{feature_available_projects} OR #{not_project_related}")
       .public_or_visible_to_user(current_user)
   end
 
@@ -86,18 +89,20 @@ class SnippetsFinder < UnionFinder
 
   def feature_available_projects
     # Don't return any project related snippets if the user cannot read cross project
-    return table[:id].eq(nil) unless Ability.allowed?(current_user, :read_cross_project)
+    return table[:id].eq(nil).to_sql unless Ability.allowed?(current_user, :read_cross_project)
 
     projects = projects_for_user do |part|
       part.with_feature_available_for_user(:snippets, current_user)
     end.select(:id)
 
-    arel_query = Arel::Nodes::SqlLiteral.new(projects.to_sql)
+    # This query was intentionally converted to a raw one to get it work in Rails 5.0.
-    table[:project_id].in(arel_query)
+    # In Rails 5.0 and 5.1 there's a bug: https://github.com/rails/arel/issues/531
+    # Please convert it back when on rails 5.2 as it works again as expected since 5.2.
+    "snippets.project_id IN (#{projects.to_sql})"
   end
 
   def not_project_related
-    table[:project_id].eq(nil)
+    table[:project_id].eq(nil).to_sql
   end
 
   def table

changelogs/unreleased/blackst0ne-rails5-fix-snippets-finder.yml

@@ -0,0 +1,5 @@
+---
+title: "[Rails5] Fix snippets_finder arel queries"
+merge_request: 19796
+author: "@blackst0ne"
+type: fixed