Merge pull request #488 from dtolnay/async

Improve async fn error message with link to workaround

Author: dtolnay

syntax/parse.rs

@@ -373,6 +373,12 @@ fn parse_extern_fn(
             "variadic function is not supported yet",
         ));
     }
+    if foreign_fn.sig.asyncness.is_some() {
+        return Err(Error::new_spanned(
+            foreign_fn,
+            "async function is not directly supported yet, but see https://cxx.rs/async.html for a working approach",
+        ));
+    }
 
     let mut doc = Doc::new();
     let mut cxx_name = None;

tests/ui/async_fn.rs

@@ -0,0 +1,10 @@
+#[cxx::bridge]
+mod ffi {
+    extern "Rust" {
+        async fn f();
+    }
+}
+
+async fn f() {}
+
+fn main() {}

tests/ui/async_fn.stderr

@@ -0,0 +1,5 @@
+error: async function is not directly supported yet, but see https://cxx.rs/async.html for a working approach
+ --> $DIR/async_fn.rs:4:9
+  |
+4 |         async fn f();
+  |         ^^^^^^^^^^^^^