Fix missing newline on dstr footer

Author: prikha

lib/unparser/writer/dynamic_string.rb

@@ -27,7 +27,7 @@ class DynamicString
       # mutant:disable
       def dispatch
         if heredoc?
-          write(HEREDOC_HEADER)
+          write(heredoc_header)
           buffer.push_heredoc(heredoc_body)
         elsif round_tripping_segmented_source
           write(round_tripping_segmented_source)
@@ -106,8 +106,34 @@ def heredoc_body
       end
       memoize :heredoc_body
 
+      def heredoc_header
+        needs_chomp? ? "#{HEREDOC_HEADER}.chomp" : HEREDOC_HEADER
+      end
+      memoize :heredoc_header
+
+      def needs_chomp?
+        # Check if the content naturally ends with a newline
+        # If not, we need .chomp to maintain semantic equivalence
+        !content_ends_with_newline?
+      end
+      memoize :needs_chomp?
+
+      def content_ends_with_newline?
+        # The last child determines if the content ends with a newline
+        return false if children.empty?
+
+        last_child = children.last
+        case last_child.type
+        when :str
+          last_child.children.first.end_with?("\n")
+        else
+          false # Interpolations don't add newlines
+        end
+      end
+      memoize :content_ends_with_newline?
+
       def heredoc_source
-        "#{HEREDOC_HEADER}\n#{heredoc_body}"
+        "#{heredoc_header}\n#{heredoc_body}"
       end
       memoize :heredoc_source
 
@@ -116,6 +142,7 @@ class Heredoc
 
         def emit
           emit_heredoc_body
+          write("\n") unless buffer.content.end_with?("\n")
           write(HEREDOC_FOOTER)
         end
 

spec/unit/unparser/writer/dynamic_string_spec.rb

@@ -0,0 +1,24 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe Unparser::Writer::DynamicString do
+  context 'when dynamic string doesn not end with newline' do
+    let(:original_code) { "\"a\\nb\nc\#{1}d\"" }
+    
+    it 'maintains semantic equivalence when evaluated' do
+      original_ast = Unparser.parse(original_code)
+      generated_code = Unparser.unparse(original_ast)
+
+      # Must be parseable
+      expect { Unparser.parse(generated_code) }.not_to raise_error
+      
+      # Both should evaluate to the same result
+      original_result = eval(original_code)
+      generated_result = eval(generated_code)
+      expect(generated_result).to eq(original_result)
+
+      expect(generated_code).to eq("<<-HEREDOC.chomp\na\nb\nc\#{1}d\nHEREDOC\n")
+    end
+  end
+end