Fix crash regression when invsize formspec gets used

The invsize formspec element is outdated. Even though,
it is still supported, only a deprecation warning is shown,
introduced by commit [1]. The lua context passed to the
log_deprecated method added by commit [1] is NULL for the
invsize deprecation warning, as its run on the client and not
the server.

Commit [1] has removed checks for NULL inside the log_deprecated
method, resulting in a crash when a formspec with an invsize
element is parsed. This commit puts the check back.

Fixes #3260.

Referenced commits:

[1]: b5acec0a3c5701c53854ff7afdf4008863e6e8df "Add proper lua api deprecated handling"

[2]: 7b8d372947aae232ddf598155e972bb4dda157a "Use warningstream for deprecated field messages and refactor log_deprecated"

1 files changed, 8 insertions, 4 deletions

diff --git a/src/script/common/c_internal.cpp b/src/script/common/c_internal.cpp
index 073ff1541..b349f9dd1 100644
--- a/src/script/common/c_internal.cpp
+++ b/src/script/common/c_internal.cpp
@@ -179,10 +179,14 @@ void log_deprecated(lua_State *L, const std::string &message)
 
 	if (do_log) {
 		warningstream << message << std::endl;
-		if (do_error)
-			script_error(L, LUA_ERRRUN, NULL, NULL);
-		else
-			infostream << script_get_backtrace(L) << std::endl;
+		// L can be NULL if we get called by log_deprecated(const std::string &msg)
+		// from scripting_game.cpp.
+		if (L) {
+			if (do_error)
+				script_error(L, LUA_ERRRUN, NULL, NULL);
+			else
+				infostream << script_get_backtrace(L) << std::endl;
+		}
 	}
 }