mlua 0.9.9

High level bindings to Lua 5.4/5.3/5.2/5.1 (including LuaJIT) and Roblox Luau with async/await features and support of writing native Lua modules in Rust.
Documentation 
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use std::io;

use mlua::{Error, ErrorContext, Lua, Result};

#[test]
fn test_error_context() -> Result<()> {
    let lua = Lua::new();

    let func = lua.create_function(|_, ()| {
        Err::<(), _>(Error::runtime("runtime error")).context("some context")
    })?;
    lua.globals().set("func", func)?;

    let msg = lua
        .load("local _, err = pcall(func); return tostring(err)")
        .eval::<String>()?;
    assert!(msg.contains("some context"));
    assert!(msg.contains("runtime error"));

    let func2 = lua.create_function(|lua, ()| {
        lua.globals()
            .get::<_, String>("nonextant")
            .with_context(|_| "failed to find global")
    })?;
    lua.globals().set("func2", func2)?;

    let msg2 = lua
        .load("local _, err = pcall(func2); return tostring(err)")
        .eval::<String>()?;
    assert!(msg2.contains("failed to find global"));
    println!("{msg2}");
    assert!(msg2.contains("error converting Lua nil to String"));

    // Rewrite context message and test `downcast_ref`
    let func3 = lua.create_function(|_, ()| {
        Err::<(), _>(Error::external(io::Error::new(
            io::ErrorKind::Other,
            "other",
        )))
        .context("some context")
        .context("some new context")
    })?;
    let res = func3.call::<_, ()>(()).err().unwrap();
    let Error::CallbackError { cause, .. } = &res else {
        unreachable!()
    };
    assert!(!res.to_string().contains("some context"));
    assert!(res.to_string().contains("some new context"));
    assert!(cause.downcast_ref::<io::Error>().is_some());

    Ok(())
}