Fix required positional repeated _ parameters

Co-Authored-By: Matt Valentine-House <matt@eightbitraptor.com>

prism_compile.c

@@ -6431,7 +6431,11 @@ pm_compile_node(rb_iseq_t *iseq, const pm_node_t *node, LINK_ANCHOR *const ret,
                   case PM_REQUIRED_PARAMETER_NODE: {
                     pm_required_parameter_node_t * param = (pm_required_parameter_node_t *)required;
 
-                    if (!PM_NODE_FLAG_P(required, PM_PARAMETER_FLAGS_REPEATED_PARAMETER)) {
+                    if (PM_NODE_FLAG_P(required, PM_PARAMETER_FLAGS_REPEATED_PARAMETER)) {
+                        ID local = pm_constant_id_lookup(scope_node, param->name);
+                        local_table_for_iseq->ids[local_index] = local;
+                    }
+                    else {
                         pm_insert_local_index(param->name, local_index, index_lookup_table, local_table_for_iseq, scope_node);
                     }
                     break;

test/ruby/test_compile_prism.rb

@@ -1545,6 +1545,10 @@ a
       CODE
     end
 
+    def test_repeated_required_underscore
+      assert_prism_eval("def self.m(a, _, _, b); end; method(:m).parameters")
+    end
+
     def test_locals_in_parameters
       assert_prism_eval("def self.m(a = b = c = 1); [a, b, c]; end; self.m")
     end