Add `Function::wrap`/`Function::wrap_mut`/`Function::wrap_async` to wrap functions into a type that implements `IntoLua` trait.

This is useful to avoid calling `lua.create_function*` every time when `Function` handle is needed.

src/conversion.rs

@@ -19,7 +19,14 @@ use crate::userdata::{AnyUserData, UserData};
 use crate::value::{FromLua, IntoLua, Nil, Value};
 
 #[cfg(feature = "unstable")]
-use crate::{function::OwnedFunction, table::OwnedTable, userdata::OwnedAnyUserData};
+use crate::{
+    function::{OwnedFunction, WrappedFunction},
+    table::OwnedTable,
+    userdata::OwnedAnyUserData,
+};
+
+#[cfg(all(feature = "async", feature = "unstable"))]
+use crate::function::WrappedAsyncFunction;
 
 impl<'lua> IntoLua<'lua> for Value<'lua> {
     #[inline]
@@ -129,6 +136,22 @@ impl<'lua> FromLua<'lua> for OwnedFunction {
     }
 }
 
+#[cfg(feature = "unstable")]
+impl<'lua> IntoLua<'lua> for WrappedFunction<'lua> {
+    #[inline]
+    fn into_lua(self, lua: &'lua Lua) -> Result<Value<'lua>> {
+        lua.create_callback(self.0).map(Value::Function)
+    }
+}
+
+#[cfg(all(feature = "async", feature = "unstable"))]
+impl<'lua> IntoLua<'lua> for WrappedAsyncFunction<'lua> {
+    #[inline]
+    fn into_lua(self, lua: &'lua Lua) -> Result<Value<'lua>> {
+        lua.create_async_callback(self.0).map(Value::Function)
+    }
+}
+
 impl<'lua> IntoLua<'lua> for Thread<'lua> {
     #[inline]
     fn into_lua(self, _: &'lua Lua) -> Result<Value<'lua>> {

src/function.rs

@@ -11,9 +11,20 @@ use crate::util::{
 };
 use crate::value::{FromLuaMulti, IntoLuaMulti};
 
+#[cfg(feature = "unstable")]
+use {
+    crate::lua::Lua,
+    crate::types::{Callback, MaybeSend},
+    crate::value::IntoLua,
+    std::cell::RefCell,
+};
+
 #[cfg(feature = "async")]
 use {futures_core::future::LocalBoxFuture, futures_util::future};
 
+#[cfg(all(feature = "async", feature = "unstable"))]
+use {crate::types::AsyncCallback, futures_core::Future, futures_util::TryFutureExt};
+
 /// Handle to an internal Lua function.
 #[derive(Clone, Debug)]
 pub struct Function<'lua>(pub(crate) LuaRef<'lua>);
@@ -408,6 +419,64 @@ impl<'lua> PartialEq for Function<'lua> {
     }
 }
 
+#[cfg(feature = "unstable")]
+pub(crate) struct WrappedFunction<'lua>(pub(crate) Callback<'lua, 'static>);
+
+#[cfg(all(feature = "async", feature = "unstable"))]
+pub(crate) struct WrappedAsyncFunction<'lua>(pub(crate) AsyncCallback<'lua, 'static>);
+
+#[cfg(feature = "unstable")]
+#[cfg_attr(docsrs, doc(cfg(feature = "unstable")))]
+impl<'lua> Function<'lua> {
+    /// Wraps a Rust function or closure, returning an opaque type that implements [`IntoLua`] trait.
+    #[inline]
+    pub fn wrap<F, A, R>(func: F) -> impl IntoLua<'lua>
+    where
+        F: Fn(&'lua Lua, A) -> Result<R> + MaybeSend + 'static,
+        A: FromLuaMulti<'lua>,
+        R: IntoLuaMulti<'lua>,
+    {
+        WrappedFunction(Box::new(move |lua, args| {
+            func(lua, A::from_lua_multi(args, lua)?)?.into_lua_multi(lua)
+        }))
+    }
+
+    /// Wraps a Rust mutable closure, returning an opaque type that implements [`IntoLua`] trait.
+    #[inline]
+    pub fn wrap_mut<F, A, R>(func: F) -> impl IntoLua<'lua>
+    where
+        F: FnMut(&'lua Lua, A) -> Result<R> + MaybeSend + 'static,
+        A: FromLuaMulti<'lua>,
+        R: IntoLuaMulti<'lua>,
+    {
+        let func = RefCell::new(func);
+        WrappedFunction(Box::new(move |lua, args| {
+            let mut func = func
+                .try_borrow_mut()
+                .map_err(|_| Error::RecursiveMutCallback)?;
+            func(lua, A::from_lua_multi(args, lua)?)?.into_lua_multi(lua)
+        }))
+    }
+
+    #[cfg(feature = "async")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "async")))]
+    pub fn wrap_async<F, A, FR, R>(func: F) -> impl IntoLua<'lua>
+    where
+        F: Fn(&'lua Lua, A) -> FR + MaybeSend + 'static,
+        A: FromLuaMulti<'lua>,
+        FR: Future<Output = Result<R>> + 'lua,
+        R: IntoLuaMulti<'lua>,
+    {
+        WrappedAsyncFunction(Box::new(move |lua, args| {
+            let args = match A::from_lua_multi(args, lua) {
+                Ok(args) => args,
+                Err(e) => return Box::pin(future::err(e)),
+            };
+            Box::pin(func(lua, args).and_then(move |ret| future::ready(ret.into_lua_multi(lua))))
+        }))
+    }
+}
+
 #[cfg(test)]
 mod assertions {
     use super::*;

tests/async.rs

@@ -30,6 +30,20 @@ async fn test_async_function() -> Result<()> {
     Ok(())
 }
 
+#[cfg(feature = "unstable")]
+#[tokio::test]
+async fn test_async_function_wrap() -> Result<()> {
+    let lua = Lua::new();
+
+    let f = Function::wrap_async(|_, s: String| async move { Ok(s) });
+    lua.globals().set("f", f)?;
+
+    let res: String = lua.load(r#"f("hello")"#).eval_async().await?;
+    assert_eq!(res, "hello");
+
+    Ok(())
+}
+
 #[tokio::test]
 async fn test_async_sleep() -> Result<()> {
     let lua = Lua::new();

tests/function.rs

@@ -167,3 +167,36 @@ fn test_function_info() -> Result<()> {
 
     Ok(())
 }
+
+#[cfg(feature = "unstable")]
+#[test]
+fn test_function_wrap() -> Result<()> {
+    use mlua::Error;
+
+    let lua = Lua::new();
+
+    lua.globals()
+        .set("f", Function::wrap(|_, s: String| Ok(s)))?;
+    lua.load(r#"assert(f("hello") == "hello")"#).exec().unwrap();
+
+    let mut _i = false;
+    lua.globals().set(
+        "f",
+        Function::wrap_mut(move |lua, ()| {
+            _i = true;
+            lua.globals().get::<_, Function>("f")?.call::<_, ()>(())
+        }),
+    )?;
+    match lua.globals().get::<_, Function>("f")?.call::<_, ()>(()) {
+        Err(Error::CallbackError { ref cause, .. }) => match *cause.as_ref() {
+            Error::CallbackError { ref cause, .. } => match *cause.as_ref() {
+                Error::RecursiveMutCallback { .. } => {}
+                ref other => panic!("incorrect result: {other:?}"),
+            },
+            ref other => panic!("incorrect result: {other:?}"),
+        },
+        other => panic!("incorrect result: {other:?}"),
+    };
+
+    Ok(())
+}