From 05029d96a475c5d2b2e28431cbe8c55c02093118 Mon Sep 17 00:00:00 2001
From: ydah <13041216+ydah@users.noreply.github.com>
Date: Tue, 1 Nov 2022 18:38:46 +0900
Subject: [PATCH] Fix a false positive for `Style/Alias`cop when alias in a
 method def

The following cases will result in a NoMethodError
if replaced with alias_method.
Therefore, it is correct to regard it
as a violation and not to replace it.

```ruby
def foo
  alias :ala :bala
end
```
---
 ...ix_fix_a_false_positive_for_style_alias.md |  1 +
 lib/rubocop/cop/style/alias.rb                | 10 ++++-
 spec/rubocop/cop/style/alias_spec.rb          | 42 ++++++++++++++++---
 3 files changed, 46 insertions(+), 7 deletions(-)
 create mode 100644 changelog/fix_fix_a_false_positive_for_style_alias.md

diff --git a/changelog/fix_fix_a_false_positive_for_style_alias.md b/changelog/fix_fix_a_false_positive_for_style_alias.md
new file mode 100644
index 00000000000..ed29efa0aba
--- /dev/null
+++ b/changelog/fix_fix_a_false_positive_for_style_alias.md
@@ -0,0 +1 @@
+* [#11014](https://github.com/rubocop/rubocop/pull/11014): Fix a false positive for `Style/Alias`cop when alias in a method def. ([@ydah][])
diff --git a/lib/rubocop/cop/style/alias.rb b/lib/rubocop/cop/style/alias.rb
index 7a25c626369..fe70ff01dd2 100644
--- a/lib/rubocop/cop/style/alias.rb
+++ b/lib/rubocop/cop/style/alias.rb
@@ -7,6 +7,11 @@ module Style
       # depending on configuration.
       # It also flags uses of `alias :symbol` rather than `alias bareword`.
       #
+      # However, it will always enforce `method_alias` when used `alias`
+      # in an instance method definition and in a singleton method definition.
+      # If used in a block, always enforce `alias_method`
+      # unless it is an `instance_eval` block.
+      #
       # @example EnforcedStyle: prefer_alias (default)
       #   # bad
       #   alias_method :bar, :foo
@@ -22,6 +27,7 @@ module Style
       #
       #   # good
       #   alias_method :bar, :foo
+      #
       class Alias < Base
         include ConfigurableEnforcedStyle
         extend AutoCorrector
@@ -71,7 +77,9 @@ def alias_keyword_possible?(node)
         end
 
         def alias_method_possible?(node)
-          scope_type(node) != :instance_eval && node.children.none?(&:gvar_type?)
+          scope_type(node) != :instance_eval &&
+            node.children.none?(&:gvar_type?) &&
+            node&.parent&.type != :def
         end
 
         def add_offense_for_args(node, &block)
diff --git a/spec/rubocop/cop/style/alias_spec.rb b/spec/rubocop/cop/style/alias_spec.rb
index fdcb1b3cfd7..e7e527604df 100644
--- a/spec/rubocop/cop/style/alias_spec.rb
+++ b/spec/rubocop/cop/style/alias_spec.rb
@@ -106,22 +106,52 @@ module M
       RUBY
     end
 
-    it 'does not register an offense for alias_method with explicit receiver' do
+    it 'does not register registers an offense for alias in a def' do
       expect_no_offenses(<<~RUBY)
-        class C
-          receiver.alias_method :ala, :bala
+        def foo
+          alias :ala :bala
         end
       RUBY
     end
 
-    it 'does not register an offense for alias_method in a method def' do
-      expect_no_offenses(<<~RUBY)
-        def method
+    it 'registers an offense for alias in a defs' do
+      expect_offense(<<~RUBY)
+        def some_obj.foo
+          alias :ala :bala
+          ^^^^^ Use `alias_method` instead of `alias`.
+        end
+      RUBY
+
+      expect_correction(<<~RUBY)
+        def some_obj.foo
           alias_method :ala, :bala
         end
       RUBY
     end
 
+    it 'registers an offense for alias in a block' do
+      expect_offense(<<~RUBY)
+        included do
+          alias :ala :bala
+          ^^^^^ Use `alias_method` instead of `alias`.
+        end
+      RUBY
+
+      expect_correction(<<~RUBY)
+        included do
+          alias_method :ala, :bala
+        end
+      RUBY
+    end
+
+    it 'does not register an offense for alias_method with explicit receiver' do
+      expect_no_offenses(<<~RUBY)
+        class C
+          receiver.alias_method :ala, :bala
+        end
+      RUBY
+    end
+
     it 'does not register an offense for alias_method in self.method def' do
       expect_no_offenses(<<~RUBY)
         def self.method