Add error-send feature

2 files changed, 13 insertions, 5 deletions

diff --git a/Cargo.toml b/Cargo.toml
index 92ff33f..867df06 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -37,7 +37,8 @@ luau-vector4 = ["luau", "ffi/luau-vector4"]
 vendored = ["ffi/vendored"]
 module = ["mlua_derive", "ffi/module"]
 async = ["futures-util"]
-send = []
+send = ["error-send"]
+error-send = []
 serialize = ["serde", "erased-serde", "serde-value"]
 macros = ["mlua_derive/macros"]
 unstable = []
@@ -85,7 +86,7 @@ required-features = ["async", "serialize", "macros"]
 
 [[example]]
 name = "async_http_server"
-required-features = ["async", "macros"]
+required-features = ["async", "macros", "error-send"]
 
 [[example]]
 name = "async_tcp_server"
diff --git a/src/error.rs b/src/error.rs
index f04a440..dc44686 100644
--- a/src/error.rs
+++ b/src/error.rs
@@ -9,6 +9,11 @@ use std::sync::Arc;
 
 use crate::private::Sealed;
 
+#[cfg(feature = "error-send")]
+type StdErrorObj = dyn StdError + Send + Sync;
+#[cfg(not(feature = "error-send"))]
+type StdErrorObj = dyn StdError;
+
 /// Error type returned by `mlua` methods.
 #[derive(Debug, Clone)]
 #[non_exhaustive]
@@ -189,7 +194,7 @@ pub enum Error {
     /// Returning `Err(ExternalError(...))` from a Rust callback will raise the error as a Lua
     /// error. The Rust code that originally invoked the Lua code then receives a `CallbackError`,
     /// from which the original error (and a stack traceback) can be recovered.
-    ExternalError(Arc<dyn StdError + Send + Sync>),
+    ExternalError(Arc<StdErrorObj>),
     /// An error with additional context.
     WithContext {
         /// A string containing additional context.
@@ -345,7 +350,7 @@ impl Error {
 
     /// Wraps an external error object.
     #[inline]
-    pub fn external<T: Into<Box<dyn StdError + Send + Sync>>>(err: T) -> Self {
+    pub fn external<T: Into<Box<StdErrorObj>>>(err: T) -> Self {
         Error::ExternalError(err.into().into())
     }
 
@@ -386,16 +391,18 @@ impl Error {
     }
 }
 
+/// Trait for converting [`std::error::Error`] into Lua [`Error`].
 pub trait ExternalError {
     fn into_lua_err(self) -> Error;
 }
 
-impl<E: Into<Box<dyn StdError + Send + Sync>>> ExternalError for E {
+impl<E: Into<Box<StdErrorObj>>> ExternalError for E {
     fn into_lua_err(self) -> Error {
         Error::external(self)
     }
 }
 
+/// Trait for converting [`std::result::Result`] into Lua [`Result`].
 pub trait ExternalResult<T> {
     fn into_lua_err(self) -> Result<T>;
 }