WIP: add cop to namespace methods

config/default.yml

@@ -70,3 +70,6 @@ Discourse/Plugins/CallRequiresPlugin:
 
 Discourse/Plugins/DiscourseEvent:
   Enabled: true
+
+Discourse/Plugins/NamespaceMethods:
+  Enabled: true

lib/rubocop/cop/discourse/plugins/namespace_methods.rb

@@ -0,0 +1,24 @@
+# frozen_string_literal: true
+
+module RuboCop
+  module Cop
+    module Discourse
+      module Plugins
+        class NamespaceMethods < Base
+          MSG = "Don’t define methods outside a class or a module."
+
+          def on_def(node)
+            return if inside_namespace?(node)
+            add_offense(node, message: MSG)
+          end
+
+          private
+
+          def inside_namespace?(node)
+            node.each_ancestor.detect { _1.class_type? || _1.module_type? }
+          end
+        end
+      end
+    end
+  end
+end

spec/lib/rubocop/cop/plugins/namespace_methods_spec.rb

@@ -0,0 +1,86 @@
+# frozen_string_literal: true
+
+require "spec_helper"
+
+RSpec.describe RuboCop::Cop::Discourse::Plugins::NamespaceMethods, :config do
+  subject(:cop) { described_class.new(config) }
+
+  let(:config) { RuboCop::Config.new }
+
+  context "when defining a method outside any namespace" do
+    it "registers an offense" do
+      expect_offense(<<~RUBY)
+        def my_method
+        ^^^^^^^^^^^^^ Discourse/Plugins/NamespaceMethods: Don’t define methods outside a class or a module.
+          "my_value"
+        end
+
+        class MyClass
+          def my_method
+            "my_method"
+          end
+        end
+      RUBY
+    end
+  end
+
+  context "when defining a method inside a class" do
+    context "when defining an instance method" do
+      it "does not register an offense" do
+        expect_no_offenses(<<~RUBY)
+          class MyClass
+            def my_method
+              "my_value"
+            end
+          end
+        RUBY
+      end
+    end
+
+    context "when defining a class method" do
+      it "does not register an offense" do
+        expect_no_offenses(<<~RUBY)
+          class MyClass
+            class << self
+              def my_method
+                "my_value"
+              end
+
+              def another_method
+                "plop"
+              end
+            end
+          end
+        RUBY
+      end
+    end
+  end
+
+  context "when defining a method inside a module" do
+    context "when defining an instance method" do
+      it "does not register an offense" do
+        expect_no_offenses(<<~RUBY)
+          module MyModule
+            def my_method
+              "my_value"
+            end
+          end
+        RUBY
+      end
+    end
+
+    context "when defining a class method" do
+      it "does not register an offense" do
+        expect_no_offenses(<<~RUBY)
+          module MyModule
+            class << self
+              def my_method
+                "my_value"
+              end
+            end
+          end
+        RUBY
+      end
+    end
+  end
+end