Fix an error for Style/StringConcatenation when correcting nested concatenable parts

CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## master (unreleased)
 
+### Bug fixes
+
+* [#8892](https://github.com/rubocop-hq/rubocop/issues/8892): Fix an error for `Style/StringConcatenation` when correcting nested concatenable parts. ([@fatkodima][])
+
 ## 0.93.1 (2020-10-12)
 
 ### Bug fixes

lib/rubocop/cop/style/string_concatenation.rb

@@ -33,6 +33,10 @@ class StringConcatenation < Base
           }
         PATTERN
 
+        def on_new_investigation
+          @corrected_nodes = nil
+        end
+
         def on_send(node)
           return unless string_concatenation?(node)
 
@@ -42,8 +46,12 @@ def on_send(node)
           collect_parts(topmost_plus_node, parts)
 
           add_offense(topmost_plus_node) do |corrector|
-            if parts.none? { |part| uncorrectable?(part) }
+            correctable_parts = parts.none? { |part| uncorrectable?(part) }
+            if correctable_parts && !corrected_ancestor?(topmost_plus_node)
               corrector.replace(topmost_plus_node, replacement(parts))
+
+              @corrected_nodes ||= Set.new.compare_by_identity
+              @corrected_nodes.add(topmost_plus_node)
             end
           end
         end
@@ -80,6 +88,10 @@ def uncorrectable?(part)
             part.each_descendant(:block).any?
         end
 
+        def corrected_ancestor?(node)
+          node.each_ancestor(:send).any? { |ancestor| @corrected_nodes&.include?(ancestor) }
+        end
+
         def replacement(parts)
           interpolated_parts =
             parts.map do |part|

spec/rubocop/cop/style/string_concatenation_spec.rb

@@ -36,6 +36,18 @@
     RUBY
   end
 
+  it 'correctly handles nested concatenable parts' do
+    expect_offense(<<~RUBY)
+      (user.vip? ? greeting + ', ' : '') + user.name + ' <' + user.email + '>'
+      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Prefer string interpolation to string concatenation.
+                   ^^^^^^^^^^^^^^^ Prefer string interpolation to string concatenation.
+    RUBY
+
+    expect_correction(<<~RUBY)
+      "\#{(user.vip? ? "\#{greeting}, " : '')}\#{user.name} <\#{user.email}>"
+    RUBY
+  end
+
   it 'does not register an offense when using `+` with all non string arguments' do
     expect_no_offenses(<<~RUBY)
       user.name + user.email