Move ModuleWithInstanceVariables to Gitlab namespace

And use .rubocop.yml to exclude paths we don't care,
rather than using the cop itself to exclude.

1 files changed, 63 insertions, 0 deletions

diff --git a/rubocop/cop/gitlab/module_with_instance_variables.rb b/rubocop/cop/gitlab/module_with_instance_variables.rb
new file mode 100644
index 00000000000..5c9cde98512
--- /dev/null
+++ b/rubocop/cop/gitlab/module_with_instance_variables.rb
@@ -0,0 +1,63 @@
+module RuboCop
+  module Cop
+    module Gitlab
+      class ModuleWithInstanceVariables < RuboCop::Cop::Cop
+        MSG = <<~EOL.freeze
+          Do not use instance variables in a module. Please read this
+          for the rationale behind it:
+
+          https://docs.gitlab.com/ee/development/module_with_instance_variables.html
+        EOL
+
+        def on_module(node)
+          check_method_definition(node)
+
+          # Not sure why some module would have an extra begin wrapping around
+          node.each_child_node(:begin) do |begin_node|
+            check_method_definition(begin_node)
+          end
+        end
+
+        private
+
+        def check_method_definition(node)
+          node.each_child_node(:def) do |definition|
+            # We allow this pattern:
+            #
+            #     def f
+            #       @f ||= true
+            #     end
+            if only_ivar_or_assignment?(definition)
+              # We don't allow if any other ivar is used
+              definition.each_descendant(:ivar) do |offense|
+                add_offense(offense, :expression)
+              end
+            # We allow initialize method and single ivar
+            elsif !initialize_method?(definition) && !single_ivar?(definition)
+              definition.each_descendant(:ivar, :ivasgn) do |offense|
+                add_offense(offense, :expression)
+              end
+            end
+          end
+        end
+
+        def only_ivar_or_assignment?(definition)
+          node = definition.child_nodes.last
+
+          definition.child_nodes.size == 2 &&
+            node.or_asgn_type? && node.child_nodes.first.ivasgn_type?
+        end
+
+        def single_ivar?(definition)
+          node = definition.child_nodes.last
+
+          definition.child_nodes.size == 2 && node.ivar_type?
+        end
+
+        def initialize_method?(definition)
+          definition.children.first == :initialize
+        end
+      end
+    end
+  end
+end