Fix Layout/TrailingWhitespace auto-correction in heredoc

CHANGELOG.md

@@ -151,6 +151,7 @@
 * [#8661](https://github.com/rubocop-hq/rubocop/pull/8661): Fix an incorrect auto-correct for `Style/MultilineTernaryOperator` when returning a multiline ternary operator expression. ([@koic][])
 * [#8526](https://github.com/rubocop-hq/rubocop/pull/8526): Fix a false positive for `Style/CaseEquality` cop when the receiver is not a camel cased constant. ([@koic][])
 * [#8673](https://github.com/rubocop-hq/rubocop/issues/8673): Fix the JSON parse error when specifying `--format=json` and `--stdin` options. ([@koic][])
+* [#8692](https://github.com/rubocop-hq/rubocop/pull/8692): Fix `Layout/TrailingWhitespace` auto-correction in heredoc. ([@marcandre][])
 
 ### Changes
 

docs/modules/ROOT/pages/cops_layout.adoc

@@ -6369,6 +6369,17 @@ x = 0
 code = <<~RUBY
   x = 0
 RUBY
+
+# ok
+code = <<~RUBY
+  x = 0 #{}
+RUBY
+
+# good
+trailing_whitespace = ' '
+code = <<~RUBY
+  x = 0#{trailing_whitespace}
+RUBY
 ----
 
 ==== AllowInHeredoc: true (default)

lib/rubocop/cop/layout/trailing_whitespace.rb

@@ -21,6 +21,17 @@ module Layout
       #     x = 0
       #   RUBY
       #
+      #   # ok
+      #   code = <<~RUBY
+      #     x = 0 #{}
+      #   RUBY
+      #
+      #   # good
+      #   trailing_whitespace = ' '
+      #   code = <<~RUBY
+      #     x = 0#{trailing_whitespace}
+      #   RUBY
+      #
       # @example AllowInHeredoc: true (default)
       #   # The line in this example contains spaces after the 0.
       #   # good
@@ -35,28 +46,36 @@ class TrailingWhitespace < Base
         MSG = 'Trailing whitespace detected.'
 
         def on_new_investigation
-          heredoc_ranges = extract_heredoc_ranges(processed_source.ast)
+          @heredoc_ranges = extract_heredoc_ranges(processed_source.ast)
           processed_source.lines.each_with_index do |line, index|
-            lineno = index + 1
-
             next unless line.end_with?(' ', "\t")
-            next if skip_heredoc? && inside_heredoc?(heredoc_ranges, lineno)
 
-            range = offense_range(lineno, line)
-            add_offense(range) do |corrector|
-              corrector.remove(range)
-            end
+            process_line(line, index + 1)
           end
         end
 
         private
 
+        def process_line(line, lineno)
+          in_heredoc = inside_heredoc?(lineno)
+          return if skip_heredoc? && in_heredoc
+
+          range = offense_range(lineno, line)
+          add_offense(range) do |corrector|
+            if in_heredoc
+              corrector.insert_after(range, '#{}') # rubocop:disable Lint/InterpolationCheck
+            else
+              corrector.remove(range)
+            end
+          end
+        end
+
         def skip_heredoc?
           cop_config.fetch('AllowInHeredoc', false)
         end
 
-        def inside_heredoc?(heredoc_ranges, line_number)
-          heredoc_ranges.any? { |r| r.include?(line_number) }
+        def inside_heredoc?(line_number)
+          @heredoc_ranges.any? { |r| r.include?(line_number) }
         end
 
         def extract_heredoc_ranges(ast)

spec/rubocop/cop/layout/trailing_whitespace_spec.rb

@@ -89,4 +89,25 @@
       expect(offenses.size).to eq(1)
     end
   end
+
+  context 'when `AllowInHeredoc` is set to false' do
+    let(:cop_config) { { 'AllowInHeredoc' => false } }
+
+    it 'corrects safely trailing whitespace in a heredoc string' do
+      expect_offense(<<~RUBY)
+        x = <<~EXAMPLE
+          has trailing#{trailing_whitespace}
+                      ^ Trailing whitespace detected.
+          no trailing
+        EXAMPLE
+      RUBY
+
+      expect_correction(<<~RUBY)
+        x = <<~EXAMPLE
+          has trailing \#{}
+          no trailing
+        EXAMPLE
+      RUBY
+    end
+  end
 end