Do not allow recursive warnings (Lua 5.4)

src/state.rs

@@ -703,18 +703,19 @@ impl Lua {
         unsafe extern "C-unwind" fn warn_proc(ud: *mut c_void, msg: *const c_char, tocont: c_int) {
             let extra = ud as *mut ExtraData;
             callback_error_ext((*extra).raw_lua().state(), extra, |extra, _| {
-                let cb = mlua_expect!(
-                    (*extra).warn_callback.as_ref(),
-                    "no warning callback set in warn_proc"
-                );
+                let warn_callback = (*extra).warn_callback.clone();
+                let warn_callback = mlua_expect!(warn_callback, "no warning callback set in warn_proc");
+                if XRc::strong_count(&warn_callback) > 2 {
+                    return Ok(());
+                }
                 let msg = StdString::from_utf8_lossy(CStr::from_ptr(msg).to_bytes());
-                cb((*extra).lua(), &msg, tocont != 0)
+                warn_callback((*extra).lua(), &msg, tocont != 0)
             });
         }
 
         let lua = self.lock();
         unsafe {
-            (*lua.extra.get()).warn_callback = Some(Box::new(callback));
+            (*lua.extra.get()).warn_callback = Some(XRc::new(callback));
             ffi::lua_setwarnf(lua.state(), Some(warn_proc), lua.extra.get() as *mut c_void);
         }
     }

src/types.rs

@@ -91,10 +91,10 @@ pub(crate) type InterruptCallback = XRc<dyn Fn(&Lua) -> Result<VmState> + Send>;
 pub(crate) type InterruptCallback = XRc<dyn Fn(&Lua) -> Result<VmState>>;
 
 #[cfg(all(feature = "send", feature = "lua54"))]
-pub(crate) type WarnCallback = Box<dyn Fn(&Lua, &str, bool) -> Result<()> + Send>;
+pub(crate) type WarnCallback = XRc<dyn Fn(&Lua, &str, bool) -> Result<()> + Send>;
 
 #[cfg(all(not(feature = "send"), feature = "lua54"))]
-pub(crate) type WarnCallback = Box<dyn Fn(&Lua, &str, bool) -> Result<()>>;
+pub(crate) type WarnCallback = XRc<dyn Fn(&Lua, &str, bool) -> Result<()>>;
 
 /// A trait that adds `Send` requirement if `send` feature is enabled.
 #[cfg(feature = "send")]

tests/tests.rs

@@ -1289,6 +1289,13 @@ fn test_warnings() -> Result<()> {
             if matches!(*cause, Error::RuntimeError(ref err) if err == "warning error")
     ));
 
+    // Recursive warning
+    lua.set_warning_function(|lua, _, _| {
+        lua.warning("inner", false);
+        Ok(())
+    });
+    lua.warning("hello", false);
+
     Ok(())
 }