Fix loader for kwargs mutation ruby4

.github/workflows/ci.yml

@@ -10,7 +10,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        ruby: [2.7, 3.0, 3.1, 3.2, 3.3]
+        ruby: [2.7, 3.0, 3.1, 3.2, 3.3, 3.4, 4.0]
         graphql_version: ['~> 1.13', '~> 2.0']
     steps:
     - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2

lib/graphql/batch/loader.rb

@@ -1,10 +1,11 @@
 module GraphQL::Batch
   class Loader
-    # Use new argument forwarding syntax if available as an optimization
     if RUBY_ENGINE && Gem::Version.new(RUBY_VERSION) >= Gem::Version.new("2.7")
       class_eval(<<~RUBY, __FILE__, __LINE__ + 1)
-        def self.for(...)
-          current_executor.loader(loader_key_for(...)) { new(...) }
+        def self.for(*group_args, **group_kwargs, &block)
+          current_executor.loader(loader_key_for(*group_args, **group_kwargs)) do
+            new(*group_args, **group_kwargs, &block)
+          end
         end
       RUBY
     else

test/loader_test.rb

@@ -63,6 +63,21 @@ def perform(_keys)
     end
   end
 
+  class KwargsGroupCountLoader < GraphQL::Batch::Loader
+    def initialize(group, key: :id, preload: true, not_found_value: nil, **conditions)
+    end
+
+    def perform(keys)
+      keys.each { |key| fulfill(key, keys.size) }
+    end
+
+    # Mimics RecordLoader.load: destructures kwargs with defaults and **rest,
+    # then re-passes them to .for()
+    def self.load_via_intermediary(group, load_key, key: :id, preload: true, not_found_value: nil, **conditions)
+      self.for(group, key: key, preload: preload, not_found_value: not_found_value, **conditions).load(load_key)
+    end
+  end
+
   def setup
     GraphQL::Batch::Executor.current = GraphQL::Batch::Executor.new
   end
@@ -92,6 +107,27 @@ def test_query_group
     assert_equal [2, 1, 2], group.sync
   end
 
+  # Reproduces a Ruby 4.0 bug where kwargs forwarded through ... get mutated
+  # when they were destructured and re-assembled by an intermediary method.
+  # Direct .for() calls don't trigger this; the kwargs must pass through a
+  # method that destructures them into named parameters (with defaults and
+  # **rest) then re-passes them to .for().
+  def test_query_group_with_kwargs_via_intermediary
+    group = Promise.all([
+      KwargsGroupCountLoader.load_via_intermediary('two', :a),
+      KwargsGroupCountLoader.load_via_intermediary('one', :a),
+      KwargsGroupCountLoader.load_via_intermediary('two', :b),
+    ])
+    assert_equal [2, 1, 2], group.sync
+  end
+
+  def test_loader_key_not_mutated_by_for_via_intermediary
+    KwargsGroupCountLoader.load_via_intermediary('test', :a).sync
+    loader = GraphQL::Batch::Executor.current.instance_variable_get(:@loaders).values.first
+    expected_kwargs = { key: :id, preload: true, not_found_value: nil }
+    assert_equal expected_kwargs, loader.loader_key[1]
+  end
+
   def test_query_many
     assert_equal [:a, :b, :c], EchoLoader.load_many([:a, :b, :c]).sync
   end