Merge pull request #14607 from dvandersluis/redundant-format-control-chars

Fix `Style/RedundantFormat` handling control characters like `\n`

Author: koic

changelog/fix_fix_style_redundant_format_handling_control_20251016160803.md

@@ -0,0 +1 @@
+* [#14607](https://github.com/rubocop/rubocop/pull/14607): Fix `Style/RedundantFormat` handling control characters like `\n`. ([@dvandersluis][])

lib/rubocop/cop/style/redundant_format.rb

@@ -89,7 +89,7 @@ class RedundantFormat < Base
 
         def on_send(node)
           format_without_additional_args?(node) do |value|
-            replacement = value.source
+            replacement = escape_control_chars(value.source)
 
             add_offense(node, message: message(node, replacement)) do |corrector|
               corrector.replace(node, replacement)
@@ -229,7 +229,12 @@ def quote(string, node)
             end
           end
 
-          "#{start_delimiter}#{string}#{end_delimiter}"
+          "#{start_delimiter}#{escape_control_chars(string)}#{end_delimiter}"
+        end
+
+        # Escape any control characters in the string (eg. `\t` or `\n` become `\\t` or `\\n`)
+        def escape_control_chars(string)
+          string.gsub(/\p{Cc}/) { |s| s.dump[1..-2] }
         end
 
         def argument_values(arguments)

spec/rubocop/cop/style/redundant_format_spec.rb

@@ -84,6 +84,17 @@
             'foo'
           RUBY
         end
+
+        it 'registers an offense when the argument is a control character' do
+          expect_offense(<<~'RUBY', method: method)
+            %{method}("\n")
+            ^{method}^^^^^^ Use `"\n"` directly instead of `%{method}`.
+          RUBY
+
+          expect_correction(<<~'RUBY')
+            "\n"
+          RUBY
+        end
       end
 
       context 'with literal arguments' do
@@ -453,6 +464,19 @@
           RUBY
         end
       end
+
+      context 'when the string contains control characters' do
+        it 'registers an offense with the correct message' do
+          expect_offense(<<~'RUBY', method: method)
+            %{method}("%s\a\b\t\n\v\f\r\e", 'foo')
+            ^{method}^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Use `"foo\a\b\t\n\v\f\r\e"` directly instead of `%{method}`.
+          RUBY
+
+          expect_correction(<<~'RUBY')
+            "foo\a\b\t\n\v\f\r\e"
+          RUBY
+        end
+      end
     end
   end
 end