[Fix #11018] Add AllowedMethods and AllowedPatterns for `Lint/Nes…

…tedMethodDefinition`

Fixes #11018 and #8860.

This PR adds `AllowedMethods` and `AllowedPatterns` for `Lint/NestedMethodDefinition`.
For example, `has_many`, `extending`, and other Rails APIs can be specified in RuboCop Rails config.

`class_eval`, `instance_eval`, `module_eval`, `class_exec`, `instance_exec`, and
`module_exec` leave hard-coded for core methods.

changelog/new_add_allowed_methods_and_patterns_to_lint_nested_method_definition.md

@@ -0,0 +1 @@
+* [#11018](https://github.com/rubocop/rubocop/issues/11018): Add `AllowedMethods` and `AllowedPatterns` for `Lint/NestedMethodDefinition`. ([@koic][])

config/default.yml

@@ -1957,6 +1957,8 @@ Lint/NestedMethodDefinition:
   Description: 'Do not use nested method definitions.'
   StyleGuide: '#no-nested-methods'
   Enabled: true
+  AllowedMethods: []
+  AllowedPatterns: []
   VersionAdded: '0.32'
 
 Lint/NestedPercentLiteral:

lib/rubocop/cop/lint/nested_method_definition.rb

@@ -30,6 +30,9 @@ module Lint
       #
       #   # good
       #
+      #   # `class_eval`, `instance_eval`, `module_eval`, `class_exec`, `instance_exec`, and
+      #   # `module_exec` blocks are allowed by default.
+      #
       #   def foo
       #     self.class.class_eval do
       #       def bar
@@ -54,7 +57,47 @@ module Lint
       #       end
       #     end
       #   end
+      #
+      # @example AllowedMethods: [] (default)
+      #   # bad
+      #   def do_something
+      #     has_many :articles do
+      #       def find_or_create_by_name(name)
+      #       end
+      #     end
+      #   end
+      #
+      # @example AllowedMethods: ['has_many']
+      #   # bad
+      #   def do_something
+      #     has_many :articles do
+      #       def find_or_create_by_name(name)
+      #       end
+      #     end
+      #   end
+      #
+      # @example AllowedPatterns: [] (default)
+      #   # bad
+      #   def foo(obj)
+      #     obj.do_baz do
+      #       def bar
+      #       end
+      #     end
+      #   end
+      #
+      # @example AllowedPatterns: ['baz']
+      #   # good
+      #   def foo(obj)
+      #     obj.do_baz do
+      #       def bar
+      #       end
+      #     end
+      #   end
+      #
       class NestedMethodDefinition < Base
+        include AllowedMethods
+        include AllowedPattern
+
         MSG = 'Method definitions must not be nested. Use `lambda` instead.'
 
         def on_def(node)
@@ -77,7 +120,13 @@ def on_def(node)
 
         def scoping_method_call?(child)
           child.sclass_type? || eval_call?(child) || exec_call?(child) ||
-            class_or_module_or_struct_new_call?(child)
+            class_or_module_or_struct_new_call?(child) || allowed_method_name?(child)
+        end
+
+        def allowed_method_name?(node)
+          name = node.method_name
+
+          allowed_method?(name) || matches_allowed_pattern?(name)
         end
 
         # @!method eval_call?(node)

spec/rubocop/cop/lint/nested_method_definition_spec.rb

@@ -266,4 +266,62 @@ def y
       end
     RUBY
   end
+
+  context 'when `AllowedMethods: [has_many]`' do
+    let(:cop_config) do
+      { 'AllowedMethods' => ['has_many'] }
+    end
+
+    it 'does not register offense for nested definition inside `has_many`' do
+      expect_no_offenses(<<~RUBY)
+        def do_something
+          has_many :articles do
+            def find_or_create_by_name(name)
+            end
+          end
+        end
+      RUBY
+    end
+
+    it 'registers offense for nested definition inside `denied_method`' do
+      expect_offense(<<~RUBY)
+        def do_something
+          denied_method :articles do
+            def find_or_create_by_name(name)
+            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Method definitions must not be nested. Use `lambda` instead.
+            end
+          end
+        end
+      RUBY
+    end
+  end
+
+  context 'when `AllowedPatterns: [baz]`' do
+    let(:cop_config) do
+      { 'AllowedPatterns' => ['baz'] }
+    end
+
+    it 'does not register offense for nested definition inside `do_baz`' do
+      expect_no_offenses(<<~RUBY)
+        def foo(obj)
+          obj.do_baz do
+            def bar
+            end
+          end
+        end
+      RUBY
+    end
+
+    it 'registers offense for nested definition inside `do_qux`' do
+      expect_offense(<<~RUBY)
+        def foo(obj)
+          obj.do_qux do
+            def bar
+            ^^^^^^^ Method definitions must not be nested. Use `lambda` instead.
+            end
+          end
+        end
+      RUBY
+    end
+  end
 end