Index forwarded parameters

Co-authored-by: Andy Waite <[email protected]>

lib/ruby_indexer/lib/ruby_indexer/declaration_listener.rb

@@ -685,9 +685,12 @@ def list_params(parameters_node)
 
       keyword_rest = parameters_node.keyword_rest
 
-      if keyword_rest.is_a?(Prism::KeywordRestParameterNode)
+      case keyword_rest
+      when Prism::KeywordRestParameterNode
         keyword_rest_name = parameter_name(keyword_rest) || Entry::KeywordRestParameter::DEFAULT_NAME
         parameters << Entry::KeywordRestParameter.new(name: keyword_rest_name)
+      when Prism::ForwardingParameterNode
+        parameters << Entry::ForwardingParameter.new
       end
 
       parameters_node.posts.each do |post|

lib/ruby_indexer/lib/ruby_indexer/entry.rb

@@ -302,6 +302,17 @@ def decorated_name
       end
     end
 
+    # A forwarding method parameter, e.g. `def foo(...)`
+    class ForwardingParameter < Parameter
+      extend T::Sig
+
+      sig { void }
+      def initialize
+        # You can't name a forwarding parameter, it's always called `...`
+        super(name: :"...")
+      end
+    end
+
     class Member < Entry
       extend T::Sig
       extend T::Helpers

lib/ruby_indexer/test/method_test.rb

@@ -330,6 +330,33 @@ def bar(**nil)
       assert_empty(parameters)
     end
 
+    def test_methods_with_argument_forwarding
+      index(<<~RUBY)
+        class Foo
+          def bar(...)
+          end
+
+          def baz(a, ...)
+          end
+        end
+      RUBY
+
+      entry = T.must(@index["bar"].first)
+      assert_instance_of(Entry::Method, entry, "Expected `bar` to be indexed")
+
+      parameters = entry.signatures.first.parameters
+      assert_equal(1, parameters.length)
+      assert_instance_of(Entry::ForwardingParameter, parameters.first)
+
+      entry = T.must(@index["baz"].first)
+      assert_instance_of(Entry::Method, entry, "Expected `baz` to be indexed")
+
+      parameters = entry.signatures.first.parameters
+      assert_equal(2, parameters.length)
+      assert_instance_of(Entry::RequiredParameter, parameters[0])
+      assert_instance_of(Entry::ForwardingParameter, parameters[1])
+    end
+
     def test_keeps_track_of_method_owner
       index(<<~RUBY)
         class Foo