Add a rubocop for Rails.logger

Suggests to use a JSON structured log instead

Related to https://gitlab.com/gitlab-org/gitlab-ce/issues/54102

2 files changed, 52 insertions, 0 deletions

diff --git a/rubocop/cop/gitlab/rails_logger.rb b/rubocop/cop/gitlab/rails_logger.rb
new file mode 100644
index 00000000000..d1a06a9a100
--- /dev/null
+++ b/rubocop/cop/gitlab/rails_logger.rb
@@ -0,0 +1,51 @@
+# frozen_string_literal: true
+
+require_relative '../../code_reuse_helpers'
+
+module RuboCop
+  module Cop
+    module Gitlab
+      class RailsLogger < ::RuboCop::Cop::Cop
+        include CodeReuseHelpers
+
+        # This cop checks for the Rails.logger in the codebase
+        #
+        # @example
+        #
+        #   # bad
+        #   Rails.logger.error("Project #{project.full_path} could not be saved")
+        #
+        #   # good
+        #   Gitlab::AppLogger.error("Project %{project_path} could not be saved" % { project_path: project.full_path })
+        MSG = 'Use a structured JSON logger instead of `Rails.logger`. ' \
+          'https://docs.gitlab.com/ee/development/logging.html'.freeze
+
+        def_node_matcher :rails_logger?, <<~PATTERN
+          (send (const nil? :Rails) :logger ... )
+        PATTERN
+
+        WHITELISTED_DIRECTORIES = %w[
+          spec
+        ].freeze
+
+        def on_send(node)
+          return if in_whitelisted_directory?(node)
+          return unless rails_logger?(node)
+
+          add_offense(node, location: :expression)
+        end
+
+        def in_whitelisted_directory?(node)
+          path = file_path_for_node(node)
+
+          WHITELISTED_DIRECTORIES.any? do |directory|
+            path.start_with?(
+              File.join(rails_root, directory),
+              File.join(rails_root, 'ee', directory)
+            )
+          end
+        end
+      end
+    end
+  end
+end
diff --git a/rubocop/rubocop.rb b/rubocop/rubocop.rb
index 27c63d92ae5..ba61a634d97 100644
--- a/rubocop/rubocop.rb
+++ b/rubocop/rubocop.rb
@@ -3,6 +3,7 @@ require_relative 'cop/gitlab/predicate_memoization'
 require_relative 'cop/gitlab/httparty'
 require_relative 'cop/gitlab/finder_with_find_by'
 require_relative 'cop/gitlab/union'
+require_relative 'cop/gitlab/rails_logger'
 require_relative 'cop/include_action_view_context'
 require_relative 'cop/include_sidekiq_worker'
 require_relative 'cop/safe_params'