Fix repeated Rakefile merges

gems/prism-merge/lib/prism/merge.rb

@@ -742,7 +742,12 @@ def ruby_dsl_signature_for(node, require_aliases: nil)
       when :git_source, :gem, :eval_gemfile, :platform, :group, :task
         [:ruby_dsl_call, call.name, ruby_dsl_first_argument(call)]
       when :desc
-        [:ruby_dsl_desc, call.slice]
+        argument = call.arguments&.arguments
+        if call.receiver.nil? && call.block.nil? && argument&.one? && argument.first.is_a?(::Prism::StringNode)
+          [:ruby_dsl_desc, argument.first.unescaped]
+        else
+          [:ruby_dsl_desc, call.slice]
+        end
       end
     end
 

gems/prism-merge/lib/prism/merge/node_emission_support.rb

@@ -400,6 +400,8 @@ def emit_node(result:, node:, analysis:, source:, matched_template_node: nil)
         last_filtered_leading_line = nil
 
         if source == :destination
+          emitted_dest_lines = result.line_metadata.filter_map { |metadata| metadata[:dest_line] }.to_set
+          leading_comments = leading_comments.reject { |comment| emitted_dest_lines.include?(comment.location.start_line) }
           leading_comments, = collapse_matched_template_leading_prefix(
             leading_comments,
             matched_template_node

gems/prism-merge/spec/fixtures_integration_spec.rb

@@ -69,6 +69,40 @@ def json_ready(value)
     expect(result[:output]).to include('gem "rake"')
   end
 
+  it 'keeps Rake descriptions stable across formatting differences and repeated merges' do
+    template = <<~RUBY
+      desc "Default tasks aggregator"
+      task :default do
+        puts :template
+      end
+
+      desc "Generate YARD documentation"
+      task :yard do
+        puts :yard
+      end
+    RUBY
+    destination = <<~RUBY
+      desc("Default tasks aggregator")
+      task :default do
+        puts :destination
+      end
+
+      # Alef-generated content
+      task :alef do
+        puts :alef
+      end
+    RUBY
+    options = { preference: :destination, add_template_only_nodes: true,
+                signature_generator: PRISM_MERGE.ruby_dsl_signature_generator }
+    once = PRISM_MERGE.merge_ruby(template, destination, 'ruby', **options).fetch(:output)
+    twice = PRISM_MERGE.merge_ruby(template, once, 'ruby', **options).fetch(:output)
+
+    expect(twice).to eq(once)
+    expect(once.scan('Default tasks aggregator').size).to eq(1)
+    expect(once.scan('Generate YARD documentation').size).to eq(1)
+    expect(once).to include('puts :destination', '# Alef-generated content', 'puts :alef', 'task :yard')
+  end
+
   it 'adds template-only top-level nodes at their template anchor' do
     result = PRISM_MERGE.merge_ruby(
       <<~RUBY,

gems/prism-merge/spec/reproducible_merge_spec.rb

@@ -106,6 +106,31 @@
     end
   end
 
+  it 'emits destination comments attached to adjacent nodes only once on repeated merges' do
+    template = <<~RUBY
+      begin
+        require "stone_checksums"
+      rescue LoadError
+        puts :missing
+      end
+    RUBY
+    destination = template + <<~RUBY
+      # This file is auto-generated by alef — DO NOT EDIT.
+      # alef:hash:123
+      # To regenerate: alef generate
+      # To verify freshness: alef verify
+
+      require "bundler"
+    RUBY
+    options = { preference: :destination, add_template_only_nodes: true,
+                signature_generator: Prism::Merge.ruby_dsl_signature_generator }
+    once = Prism::Merge.merge_ruby(template, destination, 'ruby', **options).fetch(:output)
+    twice = Prism::Merge.merge_ruby(template, once, 'ruby', **options).fetch(:output)
+
+    expect(once).to eq(destination)
+    expect(twice).to eq(once)
+  end
+
   describe 'Ruby merge with comment-only destination (regression)' do
     # A scaffold reduced to just its magic comment merges into a full template.
     # The destination pragma arrives as an unmatched statement node because the