From 3c90340fe64fb18e66f02a648ebce8ad629482a5 Mon Sep 17 00:00:00 2001
From: Yingchi Long <i@lyc.dev>
Date: Mon, 3 Jul 2023 16:02:54 +0800
Subject: [PATCH] libexpr: use `thread_local` to make the parser thread-safe

If we call `adjustLoc`, the global variable `prev_yylloc` is shared
between threads and racy.

Currently, nix itself does not concurrently parsing files, but this is
helpful for libexpr users. (The parser is thread-safe except this.)
---
 src/libexpr/lexer.l | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/libexpr/lexer.l b/src/libexpr/lexer.l
index 462b3b602..a3a8608d9 100644
--- a/src/libexpr/lexer.l
+++ b/src/libexpr/lexer.l
@@ -36,7 +36,7 @@ static inline PosIdx makeCurPos(const YYLTYPE & loc, ParseData * data)
 #define CUR_POS makeCurPos(*yylloc, data)
 
 // backup to recover from yyless(0)
-YYLTYPE prev_yylloc;
+thread_local YYLTYPE prev_yylloc;
 
 static void initLoc(YYLTYPE * loc)
 {