From b979f0414c019a9e6f215bb9e99a5dd7ffc3ee67 Mon Sep 17 00:00:00 2001
From: Peter Nelson <peter1138@openttd.org>
Date: Tue, 4 Mar 2025 18:18:28 +0000
Subject: [PATCH] Codechange: Prevent nested encoded strings.

---
 src/strings.cpp | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/src/strings.cpp b/src/strings.cpp
index cba5a84288..5264910d1a 100644
--- a/src/strings.cpp
+++ b/src/strings.cpp
@@ -119,6 +119,16 @@ EncodedString GetEncodedStringWithArgs(StringID str, std::span<const StringParam
 
 		void operator()(const std::string &value)
 		{
+#ifdef WITH_ASSERT
+			/* Don't allow an encoded string to contain another encoded string. */
+			if (!value.empty()) {
+				char32_t c;
+				const char *p = value.data();
+				if (Utf8Decode(&c, p)) {
+					assert(c != SCC_ENCODED && c != SCC_ENCODED_INTERNAL);
+				}
+			}
+#endif /* WITH_ASSERT */
 			Utf8Encode(output, SCC_ENCODED_STRING);
 			fmt::format_to(this->output, "{}", value);
 		}