From 24d9877e822c400240a7e86cf8835971ed969ac7 Mon Sep 17 00:00:00 2001
From: Ryo Nihei <nihei.dev@gmail.com>
Date: Fri, 2 Jul 2021 00:04:56 +0900
Subject: Prohibit defining identifiers beginning with an underscore

Identifiers beginning with an underscore are used as auto-generated identifiers.
---
 spec/lexer.go | 3 +++
 1 file changed, 3 insertions(+)

(limited to 'spec/lexer.go')

diff --git a/spec/lexer.go b/spec/lexer.go
index 2be3918..a1bd6fc 100644
--- a/spec/lexer.go
+++ b/spec/lexer.go
@@ -160,6 +160,9 @@ func (l *lexer) lexAndSkipWSs() (*token, error) {
 	case "kw_fragment":
 		return newSymbolToken(tokenKindKWFragment), nil
 	case "identifier":
+		if strings.HasPrefix(tok.Text(), "_") {
+			return nil, synErrAutoGenID
+		}
 		return newIDToken(tok.Text()), nil
 	case "terminal_open":
 		var b strings.Builder
-- 
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