Capture to reserved name variables if already defined [Bug #17533]

parse.y

@@ -12811,12 +12811,13 @@ reg_named_capture_assign_iter(const OnigUChar *name, const OnigUChar *name_end,
     NODE *node, *succ;
 
     if (!len) return ST_CONTINUE;
-    if (len < MAX_WORD_LENGTH && rb_reserved_word(s, (int)len))
-        return ST_CONTINUE;
     if (rb_enc_symname_type(s, len, enc, (1U<<ID_LOCAL)) != ID_LOCAL)
         return ST_CONTINUE;
 
     var = intern_cstr(s, len, enc);
+    if (len < MAX_WORD_LENGTH && rb_reserved_word(s, (int)len)) {
+	if (!lvar_defined(p, var)) return ST_CONTINUE;
+    }
     node = node_assign(p, assignable(p, var, 0, arg->loc), NEW_LIT(ID2SYM(var), arg->loc), NO_LEX_CTXT, arg->loc);
     succ = arg->succ_block;
     if (!succ) succ = NEW_BEGIN(0, arg->loc);

test/ruby/test_regexp.rb

@@ -229,6 +229,17 @@ class TestRegexp < Test::Unit::TestCase
   def test_assign_named_capture_to_reserved_word
     /(?<nil>.)/ =~ "a"
     assert_not_include(local_variables, :nil, "[ruby-dev:32675]")
+
+    def (obj = Object.new).test(s, nil: :ng)
+      /(?<nil>.)/ =~ s
+      binding.local_variable_get(:nil)
+    end
+    assert_equal("b", obj.test("b"))
+
+    tap do |nil: :ng|
+      /(?<nil>.)/ =~ "c"
+      assert_equal("c", binding.local_variable_get(:nil))
+    end
   end
 
   def test_assign_named_capture_to_const