[Fix #11919] Fix an error for Lint/UselessAssignment

Fixes #11919.

This PR fixes an error for `Lint/UselessAssignment`
when a variable is assigned and unreferenced in `for`.

changelog/fix_error_for_lint_useless_assignment.md

@@ -0,0 +1 @@
+* [#11919](https://github.com/rubocop/rubocop/issues/11919): Fix an error for `Lint/UselessAssignment` when a variable is assigned and unreferenced in `for`. ([@koic][])

lib/rubocop/cop/lint/useless_assignment.rb

@@ -136,7 +136,8 @@ def variable_like_method_invocation?(node)
         def autocorrect(corrector, assignment)
           if assignment.exception_assignment?
             remove_exception_assignment_part(corrector, assignment.node)
-          elsif assignment.multiple_assignment? || assignment.rest_assignment?
+          elsif assignment.multiple_assignment? || assignment.rest_assignment? ||
+                assignment.for_assignment?
             rename_variable_with_underscore(corrector, assignment.node)
           elsif assignment.operator_assignment?
             remove_trailing_character_from_operator(corrector, assignment.node)

lib/rubocop/cop/variable_force/assignment.rb

@@ -69,6 +69,12 @@ def rest_assignment?
           meta_assignment_node.type == REST_ASSIGNMENT_TYPE
         end
 
+        def for_assignment?
+          return false unless meta_assignment_node
+
+          meta_assignment_node.for_type?
+        end
+
         def operator
           assignment_node = meta_assignment_node || @node
           assignment_node.loc.operator.source
@@ -78,7 +84,8 @@ def meta_assignment_node
           unless instance_variable_defined?(:@meta_assignment_node)
             @meta_assignment_node = operator_assignment_node ||
                                     multiple_assignment_node ||
-                                    rest_assignment_node
+                                    rest_assignment_node ||
+                                    for_assignment_node
           end
 
           @meta_assignment_node
@@ -109,6 +116,12 @@ def rest_assignment_node
 
           node.parent
         end
+
+        def for_assignment_node
+          return nil unless node.parent&.for_type?
+
+          node.parent
+        end
       end
     end
   end

spec/rubocop/cop/lint/useless_assignment_spec.rb

@@ -255,6 +255,31 @@ module x::Foo
     end
   end
 
+  context 'when a variable is assigned and unreferenced in `for`' do
+    it 'registers an offense' do
+      expect_offense(<<~RUBY)
+        for item in items
+            ^^^^ Useless assignment to variable - `item`. Did you mean `items`?
+        end
+      RUBY
+
+      expect_correction(<<~RUBY)
+        for _ in items
+        end
+      RUBY
+    end
+  end
+
+  context 'when a variable is assigned and referenced in `for`' do
+    it 'does not register an offense' do
+      expect_no_offenses(<<~RUBY)
+        for item in items
+          do_something(item)
+        end
+      RUBY
+    end
+  end
+
   context 'when a variable is assigned and unreferenced in top level' do
     it 'registers an offense' do
       expect_offense(<<~RUBY)

spec/rubocop/cop/variable_force/assignment_spec.rb

@@ -129,6 +129,21 @@ def some_method
         expect(assignment.meta_assignment_node.type).to eq(:splat)
       end
     end
+
+    context 'when it is `for` assignment' do
+      let(:source) do
+        <<~RUBY
+          def some_method
+            for item in items
+            end
+          end
+        RUBY
+      end
+
+      it 'returns splat node' do
+        expect(assignment.meta_assignment_node.type).to eq(:for)
+      end
+    end
   end
 
   describe '#operator' do