Support custom comment prefixes on schema artifacts

elasticgraph-schema_definition/lib/elastic_graph/schema_definition/schema_artifact_manager.rb

@@ -183,17 +183,19 @@ def new_yaml_artifact(file_name, desired_contents, extra_comment_lines: [])
           desired_contents,
           ->(hash) { ::YAML.dump(hash) },
           ->(string) { ::YAML.safe_load(string) },
-          extra_comment_lines
+          extra_comment_lines,
+          "#"
         )
       end
 
-      def new_raw_artifact(file_name, desired_contents)
+      def new_raw_artifact(file_name, desired_contents, comment_prefix: "#")
         SchemaArtifact.new(
           ::File.join(@schema_artifacts_directory, file_name),
           desired_contents,
           _ = :itself.to_proc,
           _ = :itself.to_proc,
-          []
+          [],
+          comment_prefix
         )
       end
 
@@ -215,7 +217,7 @@ def pruned_runtime_metadata(graphql_schema_string)
     end
 
     # @private
-    class SchemaArtifact < Support::MemoizableData.define(:file_name, :desired_contents, :dumper, :loader, :extra_comment_lines)
+    class SchemaArtifact < Support::MemoizableData.define(:file_name, :desired_contents, :dumper, :loader, :extra_comment_lines, :comment_prefix)
       def dump(output)
         if out_of_date?
           dirname = File.dirname(file_name)
@@ -271,7 +273,7 @@ def comment_preamble
         ]
 
         lines = extra_comment_lines + [""] + lines unless extra_comment_lines.empty?
-        lines.map { |line| "# #{line}".strip }.join("\n")
+        lines.map { |line| "#{comment_prefix} #{line}".rstrip }.join("\n")
       end
     end
   end

elasticgraph-schema_definition/sig/elastic_graph/schema_definition/schema_artifact_manager.rbs

@@ -34,7 +34,11 @@ module ElasticGraph
         ?extra_comment_lines: ::Array[::String]
       ) -> SchemaArtifact[::Hash[::String, untyped]]
 
-      def new_raw_artifact: (::String, ::String) -> SchemaArtifact[::String]
+      def new_raw_artifact: (
+        ::String,
+        ::String,
+        ?comment_prefix: ::String
+      ) -> SchemaArtifact[::String]
       def pruned_runtime_metadata: (::String) -> SchemaArtifacts::RuntimeMetadata::Schema
     end
 
@@ -44,13 +48,15 @@ module ElasticGraph
       attr_reader dumper: ^(T) -> ::String
       attr_reader loader: ^(::String) -> T
       attr_reader extra_comment_lines: ::Array[::String]
+      attr_reader comment_prefix: ::String
 
       def initialize: (
         ::String,
         T,
         ^(T) -> ::String,
         ^(::String) -> T,
-        ::Array[::String]) -> void
+        ::Array[::String],
+        ::String) -> void
     end
 
     class SchemaArtifact[T] < SchemaArtifactSupertype[T]

elasticgraph-schema_definition/spec/unit/elastic_graph/schema_definition/schema_artifact_spec.rb

@@ -0,0 +1,35 @@
+# Copyright 2024 - 2026 Block, Inc.
+#
+# Use of this source code is governed by an MIT-style
+# license that can be found in the LICENSE file or at
+# https://opensource.org/licenses/MIT.
+#
+# frozen_string_literal: true
+
+require "elastic_graph/schema_definition/schema_artifact_manager"
+require "stringio"
+
+module ElasticGraph
+  module SchemaDefinition
+    RSpec.describe SchemaArtifact, :in_temp_dir do
+      it "renders the comment preamble using the configured comment prefix so artifacts can use their format's comment syntax" do
+        artifact = SchemaArtifact.new(
+          "widgets.proto",
+          "message Widget {}",
+          :itself.to_proc,
+          :itself.to_proc,
+          [],
+          "//"
+        )
+
+        artifact.dump(::StringIO.new)
+
+        expect(::File.read("widgets.proto")).to eq(<<~EOS.strip)
+          // Generated by `bundle exec rake schema_artifacts:dump`.
+          // DO NOT EDIT BY HAND. Any edits will be lost the next time the rake task is run.
+          message Widget {}
+        EOS
+      end
+    end
+  end
+end