chore(ffi): allow async fns in ffi_fn macro

This wraps the inner asynchronous function with a
`::futures::executor::block_on`, allowing for asynchronous function to
be more easily called by the FFI.

Signed-off-by: JP-Ellis <josh@jpellis.me>

Author: JP-Ellis

rust/pact_ffi/src/util/ffi.rs

@@ -31,4 +31,31 @@ macro_rules! ffi_fn {
     ($(#[$doc:meta])* fn $name:ident($($arg:ident: $arg_ty:ty),*) $body:block ) => {
         $crate::ffi_fn!($(#[$doc])* fn $name($($arg: $arg_ty),*) -> () $body {});
     };
+
+    // Support async functions as well, by wrapping them in a block_on call
+    ($(#[$doc:meta])* async fn $name:ident($($arg:ident: $arg_ty:ty),*) -> $ret:ty $body:block $fail:block ) => {
+        $(#[$doc])*
+        #[no_mangle]
+        #[allow(clippy::or_fun_call)]
+        #[allow(clippy::not_unsafe_ptr_arg_deref)]
+        pub extern fn $name($($arg: $arg_ty),*) -> $ret {
+            use $crate::error::catch_panic;
+
+            ::tracing::debug!("{}::{} FFI function invoked", module_path!(), stringify!($name));
+
+            $(
+                ::tracing::trace!("@param {} = {:?}", stringify!($arg), $arg);
+            )*
+
+            let output = catch_panic(|| ::futures::executor::block_on(async { Ok($body) })).unwrap_or($fail);
+
+            ::tracing::trace!(output = ?output, "{} FFI function completed", stringify!($name));
+
+            output
+        }
+    };
+
+    ($(#[$doc:meta])* async fn $name:ident($($arg:ident: $arg_ty:ty),*) $body:block ) => {
+        $crate::ffi_fn!($(#[$doc])* async fn $name($($arg: $arg_ty),*) -> () $body {});
+    };
 }