[Fix #8897] Change Style/StringConcatenation to accept line-end concatenation between two strings so that Style/LineEndConcatenation can handle it instead.

Author: dvandersluis

changelog/change_change_stylestringconcatenation_to.md

@@ -0,0 +1 @@
+* [#8897](https://github.com/rubocop-hq/rubocop/issues/8897): Change `Style/StringConcatenation` to accept line-end concatenation between two strings so that `Style/LineEndConcatenation` can handle it instead. ([@dvandersluis][])

config/default.yml

@@ -4347,6 +4347,7 @@ Style/StringConcatenation:
   Enabled: true
   Safe: false
   VersionAdded: '0.89'
+  VersionChanged: <<next>>
 
 Style/StringHashKeys:
   Description: 'Prefer symbols instead of strings as hash keys.'

lib/rubocop/cop/style/string_concatenation.rb

@@ -11,6 +11,10 @@ module Style
       # In those cases, it might be useful to extract statements to local
       # variables or methods which you can then interpolate in a string.
       #
+      # NOTE: When concatenation between two strings is broken over multiple
+      # lines, this cop does not register an offense; instead,
+      # `Style/LineEndConcatenation` will pick up the offense if enabled.
+      #
       # @example
       #   # bad
       #   email_with_name = user.name + ' <' + user.email + '>'
@@ -19,6 +23,10 @@ module Style
       #   email_with_name = "#{user.name} <#{user.email}>"
       #   email_with_name = format('%s <%s>', user.name, user.email)
       #
+      #   # accepted, line-end concatenation
+      #   name = 'First' +
+      #     'Last'
+      #
       class StringConcatenation < Base
         include Util
         extend AutoCorrector
@@ -39,6 +47,7 @@ def on_new_investigation
 
         def on_send(node)
           return unless string_concatenation?(node)
+          return if line_end_concatenation?(node)
 
           topmost_plus_node = find_topmost_plus_node(node)
 
@@ -58,6 +67,16 @@ def on_send(node)
 
         private
 
+        def line_end_concatenation?(node)
+          # If the concatenation happens at the end of the line,
+          # and both the receiver and argument are strings, allow
+          # `Style/LineEndConcatenation` to handle it instead.
+          node.receiver.str_type? &&
+            node.first_argument.str_type? &&
+            node.multiline? &&
+            node.source =~ /\+\s*\n/
+        end
+
         def find_topmost_plus_node(node)
           current = node
           while (parent = current.parent) && plus_node?(parent)

spec/rubocop/cop/style/string_concatenation_spec.rb

@@ -55,6 +55,16 @@
   end
 
   context 'multiline' do
+    context 'string continuation' do
+      it 'does not register an offense' do
+        # handled by `Style/LineEndConcatenation` instead.
+        expect_no_offenses(<<~RUBY)
+          "this is a long string " +
+            "this is a continuation"
+        RUBY
+      end
+    end
+
     context 'simple expressions' do
       it 'registers an offense and corrects' do
         expect_offense(<<-RUBY)