Fix a false negative for Layout/IndentationWidth

changelog/fix_false_negative_for_layout_indentation_width.md

@@ -0,0 +1 @@
+* [#9791](https://github.com/rubocop/rubocop/pull/9791): Fix a false negative for `Layout/IndentationWidth` when using `ensure` in `do` ... `end` block. ([@koic][])

lib/rubocop/cop/layout/indentation_width.rb

@@ -313,9 +313,12 @@ def indentation_to_check?(base_loc, body_node)
             check_rescue?(body_node)
           elsif body_node.ensure_type?
             block_body, = *body_node
-            return unless block_body
 
-            check_rescue?(block_body) if block_body.rescue_type?
+            if block_body&.rescue_type?
+              check_rescue?(block_body)
+            else
+              !block_body.nil?
+            end
           else
             true
           end

spec/rubocop/cop/layout/indentation_width_spec.rb

@@ -1437,6 +1437,27 @@ def bar
         RUBY
       end
 
+      it 'does not register an offense for good indentation of `do` ... `ensure` ... `end` block' do
+        expect_no_offenses(<<~RUBY)
+          do_something do
+            foo
+          ensure
+            handle_error
+          end
+        RUBY
+      end
+
+      it 'registers an offense for bad indentation of `do` ... `ensure` ... `end` block' do
+        expect_offense(<<~RUBY)
+          do_something do
+              foo
+          ^^^^ Use 2 (not 4) spaces for indentation.
+          ensure
+            handle_error
+          end
+        RUBY
+      end
+
       context 'when using safe navigation operator' do
         it 'registers an offense for bad indentation of a {} body' do
           expect_offense(<<~RUBY)