[Fix #6673] Fix Style/DocumentationMethod for inline module_function

Cop now recognizes documentation comments for `def`
inline with `module_function`.

CHANGELOG.md

@@ -23,6 +23,7 @@
 * [#6670](https://github.com/rubocop-hq/rubocop/issues/6670): Fix a false positive for `Style/SafeNavigation` when a method call safeguarded with a negative check for the object. ([@koic][])
 * [#6633](https://github.com/rubocop-hq/rubocop/issues/6633): Fix `Lint/SafeNavigation` complaining about use of `to_d`. ([@tejasbubane][])
 * [#6575](https://github.com/rubocop-hq/rubocop/issues/6575): Fix `Naming/PredicateName` suggesting invalid rename. ([@tejasbubane][])
+* [#6673](https://github.com/rubocop-hq/rubocop/issues/6673): Fix `Style/DocumentationMethod` cop to recognize documentation comments for `def` inline with `module_function`. ([@tejasbubane][])
 
 ### Changes
 

lib/rubocop/cop/style/documentation_method.rb

@@ -53,8 +53,13 @@ class DocumentationMethod < Cop
 
         MSG = 'Missing method documentation comment.'.freeze
 
+        def_node_matcher :module_function_node?, <<-PATTERN
+          (send nil? :module_function ...)
+        PATTERN
+
         def on_def(node)
-          check(node)
+          parent = node.parent
+          module_function_node?(parent) ? check(parent) : check(node)
         end
         alias on_defs on_def
 

spec/rubocop/cop/style/documentation_method_spec.rb

@@ -459,7 +459,7 @@ def baz
 
     context 'when declaring methods in a module' do
       context 'without documentation comment' do
-        context 'wheh method is public' do
+        context 'when method is public' do
           it 'registers an offense' do
             expect_offense(<<-CODE.strip_indent)
               module Foo
@@ -570,6 +570,30 @@ module Foo
             end
           end
         end
+
+        context 'when method is module_function' do
+          it 'registers an offense for inline def' do
+            expect_offense(<<-CODE.strip_indent)
+              module Foo
+                module_function def bar
+                ^^^^^^^^^^^^^^^^^^^^^^^ Missing method documentation comment.
+                end
+              end
+            CODE
+          end
+
+          it 'registers an offense for separate def' do
+            expect_offense(<<-CODE.strip_indent)
+              module Foo
+                def bar
+                ^^^^^^^ Missing method documentation comment.
+                end
+
+                module_function :bar
+              end
+            CODE
+          end
+        end
       end
 
       context 'with documentation comment' do
@@ -594,6 +618,28 @@ def bar; end
             CODE
           end
         end
+
+        context 'when method is module_function' do
+          it 'does not register an offense for inline def' do
+            expect_no_offenses(<<-CODE.strip_indent)
+              module Foo
+                # Documentation
+                module_function def bar; end
+              end
+            CODE
+          end
+
+          it 'does not register an offense for separate def' do
+            expect_no_offenses(<<-CODE.strip_indent)
+              module Foo
+                # Documentation
+                def bar; end
+
+                module_function :bar
+              end
+            CODE
+          end
+        end
       end
 
       context 'with both public and private methods' do