From 171eaf32d7170edd7944705577878d99dfd9a755 Mon Sep 17 00:00:00 2001
From: fatkodima <fatkodima123@gmail.com>
Date: Wed, 14 Oct 2020 17:47:46 +0300
Subject: [PATCH] Fix an error for `Style/StringConcatenation` when correcting
 nested concatenable parts

---
 CHANGELOG.md                                       |  4 ++++
 lib/rubocop/cop/style/string_concatenation.rb      | 14 +++++++++++++-
 .../rubocop/cop/style/string_concatenation_spec.rb | 12 ++++++++++++
 3 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 6b09e1597ec..3551215a559 100644
--- a/CHANGELOG.md
+++ b/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
diff --git a/lib/rubocop/cop/style/string_concatenation.rb b/lib/rubocop/cop/style/string_concatenation.rb
index 8f33df333d9..dae12524997 100644
--- a/lib/rubocop/cop/style/string_concatenation.rb
+++ b/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|
diff --git a/spec/rubocop/cop/style/string_concatenation_spec.rb b/spec/rubocop/cop/style/string_concatenation_spec.rb
index 85207e6dcd2..189348765f0 100644
--- a/spec/rubocop/cop/style/string_concatenation_spec.rb
+++ b/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