[Fix #9945] Fix heredoc indentation in trailing space corrections

changelog/fix_heredoc_trailing_spaces.md

@@ -0,0 +1 @@
+* [#9945](https://github.com/rubocop/rubocop/issues/9945): Fix auto-correction of lines in heredocs with only spaces in `Layout/TrailingWhitespace`. ([@jonas054][])

lib/rubocop/cop/layout/heredoc_indentation.rb

@@ -143,13 +143,6 @@ def base_indent_level(node)
           indent_level(base_line)
         end
 
-        def indent_level(str)
-          indentations = str.lines
-                            .map { |line| line[/^\s*/] }
-                            .reject { |line| line.end_with?("\n") }
-          indentations.empty? ? 0 : indentations.min_by(&:size).size
-        end
-
         # Returns '~', '-' or nil
         def heredoc_indent_type(node)
           node.source[/^<<([~-])/, 1]

lib/rubocop/cop/layout/trailing_whitespace.rb

@@ -41,6 +41,7 @@ module Layout
       #
       class TrailingWhitespace < Base
         include RangeHelp
+        include Heredoc
         extend AutoCorrector
 
         MSG = 'Trailing whitespace detected.'
@@ -54,6 +55,8 @@ def on_new_investigation
           end
         end
 
+        def on_heredoc(_node); end
+
         private
 
         def process_line(line, lineno)
@@ -63,13 +66,33 @@ def process_line(line, lineno)
           range = offense_range(lineno, line)
           add_offense(range) do |corrector|
             if heredoc
-              corrector.wrap(range, "\#{'", "'}") unless static?(heredoc)
+              process_line_in_heredoc(corrector, range, heredoc)
             else
               corrector.remove(range)
             end
           end
         end
 
+        def process_line_in_heredoc(corrector, range, heredoc)
+          indent_level = indent_level(find_heredoc(range.line).loc.heredoc_body.source)
+          whitespace_only = whitespace_only?(range)
+          if whitespace_only && whitespace_is_indentation?(range, indent_level)
+            corrector.remove(range)
+          elsif !static?(heredoc)
+            range = range_between(range.begin_pos + indent_level, range.end_pos) if whitespace_only
+            corrector.wrap(range, "\#{'", "'}")
+          end
+        end
+
+        def whitespace_is_indentation?(range, level)
+          range.source[/ +/].length <= level
+        end
+
+        def whitespace_only?(range)
+          source = range_with_surrounding_space(range: range).source
+          source.start_with?("\n") && source.end_with?("\n")
+        end
+
         def static?(heredoc)
           heredoc.loc.expression.source.end_with? "'"
         end

lib/rubocop/cop/mixin/heredoc.rb

@@ -20,6 +20,13 @@ def on_heredoc(_node)
 
       private
 
+      def indent_level(str)
+        indentations = str.lines
+                          .map { |line| line[/^\s*/] }
+                          .reject { |line| line.end_with?("\n") }
+        indentations.empty? ? 0 : indentations.min_by(&:size).size
+      end
+
       def delimiter_string(node)
         node.source.match(OPENING_DELIMITER).captures[1]
       end

spec/rubocop/cop/layout/trailing_whitespace_spec.rb

@@ -144,6 +144,49 @@
       RUBY
     end
 
+    it 'corrects by removing trailing whitespace used for indentation in a heredoc string' do
+      expect_offense(<<~RUBY)
+        x = <<~EXAMPLE
+          no trailing
+         #{trailing_whitespace}
+        ^^ Trailing whitespace detected.
+          no trailing
+        #{trailing_whitespace}
+        ^ Trailing whitespace detected.
+          no trailing
+        EXAMPLE
+      RUBY
+
+      expect_correction(<<~RUBY)
+        x = <<~EXAMPLE
+          no trailing
+
+          no trailing
+
+          no trailing
+        EXAMPLE
+      RUBY
+    end
+
+    it 'corrects a whitespace line in a heredoc string that is longer than the indentation' do
+      expect_offense(<<~RUBY)
+        x = <<~EXAMPLE
+          no trailing
+          #{trailing_whitespace}
+        ^^^ Trailing whitespace detected.
+          no trailing
+        EXAMPLE
+      RUBY
+
+      expect_correction(<<~RUBY)
+        x = <<~EXAMPLE
+          no trailing
+          \#{' '}
+          no trailing
+        EXAMPLE
+      RUBY
+    end
+
     it 'does not correct trailing whitespace in a static heredoc string' do
       expect_offense(<<~RUBY)
         x = <<~'EXAMPLE'