Support Thread::resume_error call (Luau)

This method uses Luau-specific C API extension `lua_resumerror`
that allow to throw an error immediately when resuming a thead.
Closes #500 #513

Author: khvzak

mlua-sys/src/luau/compat.rs

@@ -10,6 +10,8 @@ use super::lauxlib::*;
 use super::lua::*;
 use super::luacode::*;
 
+pub const LUA_RESUMEERROR: c_int = -1;
+
 unsafe fn compat53_reverse(L: *mut lua_State, mut a: c_int, mut b: c_int) {
     while a < b {
         lua_pushvalue(L, a);
@@ -284,6 +286,19 @@ pub unsafe fn lua_resume(L: *mut lua_State, from: *mut lua_State, narg: c_int, n
     ret
 }
 
+#[inline(always)]
+pub unsafe fn lua_resumex(L: *mut lua_State, from: *mut lua_State, narg: c_int, nres: *mut c_int) -> c_int {
+    let ret = if narg == LUA_RESUMEERROR {
+        lua_resumeerror(L, from)
+    } else {
+        lua_resume_(L, from, narg)
+    };
+    if (ret == LUA_OK || ret == LUA_YIELD) && !(nres.is_null()) {
+        *nres = lua_gettop(L);
+    }
+    ret
+}
+
 //
 // lauxlib ported functions
 //

src/thread.rs

@@ -173,14 +173,50 @@ impl Thread {
         }
     }
 
+    /// Resumes execution of this thread, immediately raising an error.
+    ///
+    /// This is a Luau specific extension.
+    #[cfg(feature = "luau")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "luau")))]
+    pub fn resume_error<R>(&self, error: impl crate::IntoLua) -> Result<R>
+    where
+        R: FromLuaMulti,
+    {
+        let lua = self.0.lua.lock();
+        match self.status_inner(&lua) {
+            ThreadStatusInner::New(_) | ThreadStatusInner::Yielded(_) => {}
+            _ => return Err(Error::CoroutineUnresumable),
+        };
+
+        let state = lua.state();
+        let thread_state = self.state();
+        unsafe {
+            let _sg = StackGuard::new(state);
+            let _thread_sg = StackGuard::with_top(thread_state, 0);
+
+            check_stack(state, 1)?;
+            error.push_into_stack(&lua)?;
+            ffi::lua_xmove(state, thread_state, 1);
+
+            let (_, nresults) = self.resume_inner(&lua, ffi::LUA_RESUMEERROR)?;
+            check_stack(state, nresults + 1)?;
+            ffi::lua_xmove(thread_state, state, nresults);
+
+            R::from_stack_multi(nresults, &lua)
+        }
+    }
+
     /// Resumes execution of this thread.
     ///
     /// It's similar to `resume()` but leaves `nresults` values on the thread stack.
     unsafe fn resume_inner(&self, lua: &RawLua, nargs: c_int) -> Result<(ThreadStatusInner, c_int)> {
         let state = lua.state();
         let thread_state = self.state();
         let mut nresults = 0;
+        #[cfg(not(feature = "luau"))]
         let ret = ffi::lua_resume(thread_state, state, nargs, &mut nresults as *mut c_int);
+        #[cfg(feature = "luau")]
+        let ret = ffi::lua_resumex(thread_state, state, nargs, &mut nresults as *mut c_int);
         match ret {
             ffi::LUA_OK => Ok((ThreadStatusInner::Finished, nresults)),
             ffi::LUA_YIELD => Ok((ThreadStatusInner::Yielded(0), nresults)),

tests/thread.rs

@@ -227,3 +227,28 @@ fn test_thread_pointer() -> Result<()> {
 
     Ok(())
 }
+
+#[test]
+#[cfg(feature = "luau")]
+fn test_thread_resume_error() -> Result<()> {
+    let lua = Lua::new();
+
+    let thread = lua
+        .load(
+            r#"
+        coroutine.create(function()
+            local ok, err = pcall(coroutine.yield, 123)
+            assert(not ok, "yield should fail")
+            assert(err == "myerror", "unexpected error: " .. tostring(err))
+            return "success"
+        end)
+    "#,
+        )
+        .eval::<Thread>()?;
+
+    assert_eq!(thread.resume::<i64>(())?, 123);
+    let status = thread.resume_error::<String>("myerror").unwrap();
+    assert_eq!(status, "success");
+
+    Ok(())
+}