Account for untyped functions in RBS indexing

lib/ruby_indexer/lib/ruby_indexer/rbs_indexer.rb

@@ -139,13 +139,23 @@ def signatures(member)
 
     sig { params(overload: RBS::AST::Members::MethodDefinition::Overload).returns(T::Array[Entry::Parameter]) }
     def process_overload(overload)
-      function = T.cast(overload.method_type.type, RBS::Types::Function)
-      parameters = parse_arguments(function)
+      function = overload.method_type.type
 
-      block = overload.method_type.block
-      parameters << Entry::BlockParameter.anonymous if block&.required
+      if function.is_a?(RBS::Types::Function)
+        parameters = parse_arguments(function)
 
-      parameters
+        block = overload.method_type.block
+        parameters << Entry::BlockParameter.anonymous if block&.required
+        return parameters
+      end
+
+      # Untyped functions are a new RBS feature to declare methods that accept any parameters. For our purposes,
+      # accepting any argument is equivalent to `...`
+      if defined?(RBS::Types::UntypedFunction) && function.is_a?(RBS::Types::UntypedFunction)
+        [Entry::ForwardingParameter.new]
+      else
+        []
+      end
     end
 
     sig { params(function: RBS::Types::Function).returns(T::Array[Entry::Parameter]) }

lib/ruby_indexer/test/rbs_indexer_test.rb

@@ -348,6 +348,14 @@ def test_signature_alias
       assert_includes(entry.comments, "Returns `true` if any element of `self` meets a given criterion.")
     end
 
+    def test_indexing_untyped_functions
+      entries = @index.resolve_method("call", "Method")
+
+      parameters = entries.first.signatures.first.parameters
+      assert_equal(1, parameters.length)
+      assert_instance_of(Entry::ForwardingParameter, parameters.first)
+    end
+
     private
 
     def parse_rbs_methods(rbs, method_name)