Visualize trailing whitespace

Author: jamescook

lib/rubocop_interactive/actions.rb

@@ -129,8 +129,10 @@ def disable_line(offense)
         { status: :disabled }
       elsif current_line.include?('rubocop:disable')
         # Already has a disable directive - append this cop to it
+        # Match existing "# rubocop:disable ..." comment and append cop name
+        disable_pattern = /(# rubocop:disable [^\n]+)/
         lines[line_index] = current_line.sub(
-          /(# rubocop:disable [^\n]+)/,
+          disable_pattern,
           "\\1, #{offense.cop_name}"
         )
         File.write(offense.file_path, lines.join)

lib/rubocop_interactive/patch_generator.rb

@@ -177,14 +177,14 @@ def extract_window(original_lines, corrected_lines, target_line)
       (start_idx..end_idx).each do |i|
         change = diffs[i]
         if change.unchanged?
-          result << " #{change.old_element}"
+          result << visualize_trailing_whitespace(" #{change.old_element}")
         elsif change.changed?
-          result << "-#{change.old_element}"
-          result << "+#{change.new_element}"
+          result << visualize_trailing_whitespace("-#{change.old_element}")
+          result << visualize_trailing_whitespace("+#{change.new_element}")
         elsif change.deleting?
-          result << "-#{change.old_element}"
+          result << visualize_trailing_whitespace("-#{change.old_element}")
         elsif change.adding?
-          result << "+#{change.new_element}"
+          result << visualize_trailing_whitespace("+#{change.new_element}")
         end
       end
 
@@ -233,18 +233,39 @@ def generate_diff(original_lines, corrected_lines)
       result = []
       diffs.each do |change|
         if change.unchanged?
-          result << " #{change.old_element}"
+          result << visualize_trailing_whitespace(" #{change.old_element}")
         elsif change.changed?
-          result << "-#{change.old_element}"
-          result << "+#{change.new_element}"
+          result << visualize_trailing_whitespace("-#{change.old_element}")
+          result << visualize_trailing_whitespace("+#{change.new_element}")
         elsif change.deleting?
-          result << "-#{change.old_element}"
+          result << visualize_trailing_whitespace("-#{change.old_element}")
         elsif change.adding?
-          result << "+#{change.new_element}"
+          result << visualize_trailing_whitespace("+#{change.new_element}")
         end
       end
 
       result
     end
+
+    def visualize_trailing_whitespace(line)
+      # Check if line (without newline) has trailing whitespace
+      # Match: <diff prefix><content><trailing whitespace>
+      pattern = /
+        ^([-+\ ])      # Diff prefix: -, +, or space
+        (.*?)          # Content (non-greedy)
+        ([ \t]+)       # Trailing whitespace (spaces or tabs)
+        $              # End of line
+      /x
+
+      if line.chomp =~ pattern
+        prefix = $1
+        content = $2
+        trailing = $3
+        markers = trailing.gsub(' ', '·').gsub("\t", '→')
+        "#{prefix}#{content}#{markers}\n"
+      else
+        line
+      end
+    end
   end
 end

test/patch_generator_cops_test.rb

@@ -205,7 +205,7 @@ def test_layout_trailing_whitespace
       result = RubocopInteractive::PatchGenerator.generate(offense)
 
       assert result, "Should generate patch for Layout/TrailingWhitespace"
-      assert_match(/-def example\s+\n/, result[:lines], "Should show line with trailing spaces")
+      assert_match(/-def example···\n/, result[:lines], "Should show line with trailing space markers")
       assert_match(/\+def example\n/, result[:lines], "Should show line without trailing spaces")
     end
   end