Assertion failed: (((!(((((((to))->tt_)) & 0x0F)) == (0)) || to != &(L->l_G)->nilvalue)) && "invalid index"), function lua_copy, file lapi.c, line 260.

[HactarCE]

Steps to reproduce

use mlua::prelude::*;

fn main() {
    mlua_issue_491().unwrap();
}

fn mlua_issue_491() -> LuaResult<()> {
    let lua = Lua::new();

    let pair_of_tables = (lua.create_table()?, lua.create_table()?);
    lua.create_function(move |_lua, ()| {
        _ = &pair_of_tables;
        Ok(())
    })?;

    for i in 0..10000 {
        println!("{i}");
        lua.create_table()?;
    }

    Ok(())
}

• mlua 0.10.1 with features lua54 and vendored
• rustc 1.82.0 (f6e511eec 2024-10-15)
• Apple M2 Max running macOS Sequoia 15.1.1

On my machine, this produces the following output deterministically when run in debug mode:

...
323
324
Assertion failed: (((!(((((((to))->tt_)) & 0x0F)) == (0)) || to != &(L->l_G)->nilvalue)) && "invalid index"), function lua_copy, file lapi.c, line 260.
fish: Job 1, 'cargo run' terminated by signal SIGABRT (Abort)

This bug also occurs with lua53, lua52, and lua51, although the last number printed varies (still well below 1000).

I'm unable to reproduce this in release mode.

I found this because it happens around 5% of the time that I launch Hyperspeedcube 2. In that case, the closure is capturing a (Lua, LuaTable) instead of (LuaTable, LuaTable).

[khvzak]

thank you for the report and example how to reproduce!

[HactarCE]

Thank you so much for the prompt fix! It makes me unreasonably happy to see the cursed reproduction as a regression test.