From 839c1a190fb7e7e3b89062c66b885456c1dfb85b Mon Sep 17 00:00:00 2001
From: Earlopain <14981592+Earlopain@users.noreply.github.com>
Date: Mon, 14 Sep 2026 14:16:00 +0200
Subject: [PATCH] [Fix #22254] Put real storage behind `PM_STRING_EMPTY`

Some places memcpy the source, and NULL there is undefined behaviour.

Fixes https://bugs.ruby-lang.org/issues/22254
---
 include/prism/internal/stringy.h | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/include/prism/internal/stringy.h b/include/prism/internal/stringy.h
index 1aaa23ea75..f6716c8790 100644
--- a/include/prism/internal/stringy.h
+++ b/include/prism/internal/stringy.h
@@ -3,11 +3,16 @@
 
 #include "prism/stringy.h"
 
+/*
+ * Backing storage for an empty string.
+ */
+static const uint8_t empty_source[] = "";
+
 /*
  * Defines an empty string. This is useful for initializing a string that will
  * be filled in later.
  */
-#define PM_STRING_EMPTY ((pm_string_t) { .type = PM_STRING_CONSTANT, .source = NULL, .length = 0 })
+#define PM_STRING_EMPTY ((pm_string_t) { .type = PM_STRING_CONSTANT, .source = empty_source, .length = 0 })
 
 /*
  * Initialize a shared string that is based on initial input.