From 03ed951c167920ab6bcca4b62ab65f483808c680 Mon Sep 17 00:00:00 2001
From: Koichi ITO <koic.ito@gmail.com>
Date: Wed, 1 Sep 2021 14:14:18 +0900
Subject: [PATCH] [Fix #529] Fix a false positive for
 `Rails/LexicallyScopedActionFilter`

Fixes #529.

This PR fixes a false positive for `Rails/LexicallyScopedActionFilter`
when action method is aliased by `alias_method`.
---
 CHANGELOG.md                                  |  1 +
 .../rails/lexically_scoped_action_filter.rb   | 25 +++++++++++--
 .../lexically_scoped_action_filter_spec.rb    | 35 +++++++++++++++++++
 3 files changed, 59 insertions(+), 2 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 5611f5626e..aaf0edfe11 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -11,6 +11,7 @@
 ### Bug fixes
 
 * [#528](https://github.com/rubocop/rubocop-rails/issues/528): Fix a false positive for `Rails/HasManyOrHasOneDependent` when specifying `:dependent` strategy with double splat. ([@koic][])
+* [#529](https://github.com/rubocop/rubocop-rails/issues/529): Fix a false positive for `Rails/LexicallyScopedActionFilter` when action method is aliased by `alias_method`. ([@koic][])
 
 ## Changes
 
diff --git a/lib/rubocop/cop/rails/lexically_scoped_action_filter.rb b/lib/rubocop/cop/rails/lexically_scoped_action_filter.rb
index e27e6905ae..851a4dab6d 100644
--- a/lib/rubocop/cop/rails/lexically_scoped_action_filter.rb
+++ b/lib/rubocop/cop/rails/lexically_scoped_action_filter.rb
@@ -124,9 +124,10 @@ def on_send(node)
           block = parent.each_child_node(:begin).first
           return unless block
 
-          defined_methods = block.each_child_node(:def).map(&:method_name)
+          defined_action_methods = defined_action_methods(block)
+
           methods = array_values(methods_node).reject do |method|
-            defined_methods.include?(method)
+            defined_action_methods.include?(method)
           end
 
           message = message(methods, parent)
@@ -135,6 +136,26 @@ def on_send(node)
 
         private
 
+        def defined_action_methods(block)
+          defined_methods = block.each_child_node(:def).map(&:method_name)
+
+          defined_methods + aliased_action_methods(block, defined_methods)
+        end
+
+        def aliased_action_methods(node, defined_methods)
+          alias_methods = node.each_child_node(:send).select { |send_node| send_node.method?(:alias_method) }
+
+          hash_of_alias_methods = alias_methods.each_with_object({}) do |alias_method, result|
+            result[alias_method.last_argument.value] = alias_method.first_argument.value
+          end
+
+          defined_methods.each_with_object([]) do |defined_method, aliased_method|
+            if (new_method_name = hash_of_alias_methods[defined_method])
+              aliased_method << new_method_name
+            end
+          end
+        end
+
         # @param node [RuboCop::AST::Node]
         # @return [Array<Symbol>]
         def array_values(node) # rubocop:disable Metrics/MethodLength
diff --git a/spec/rubocop/cop/rails/lexically_scoped_action_filter_spec.rb b/spec/rubocop/cop/rails/lexically_scoped_action_filter_spec.rb
index f36e9325ca..491beb156f 100644
--- a/spec/rubocop/cop/rails/lexically_scoped_action_filter_spec.rb
+++ b/spec/rubocop/cop/rails/lexically_scoped_action_filter_spec.rb
@@ -115,6 +115,41 @@ def logout
     RUBY
   end
 
+  it 'does not register an offense when action method is aliased by `alias_method`' do
+    expect_no_offenses(<<~RUBY)
+      class FooController < ApplicationController
+        before_action :authorize!, only: %i[index show]
+
+        def index
+        end
+        alias_method :show, :index
+
+        private
+
+        def authorize!
+        end
+      end
+    RUBY
+  end
+
+  it 'registers an offense when action method is not aliased by `alias_method`' do
+    expect_offense(<<~RUBY)
+      class FooController < ApplicationController
+        before_action :authorize!, only: %i[foo show]
+        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `foo` is not explicitly defined on the class.
+
+        def index
+        end
+        alias_method :show, :index
+
+        private
+
+        def authorize!
+        end
+      end
+    RUBY
+  end
+
   it "doesn't register an offense when using conditional statements" do
     expect_no_offenses <<~RUBY
       class Test < ActionController