1 files changed, 36 insertions, 0 deletions
diff --git a/third_party/rust/async-trait/src/args.rs b/third_party/rust/async-trait/src/args.rs
new file mode 100644
index 0000000000..72d97e9525
--- /dev/null
+++ b/third_party/rust/async-trait/src/args.rs
@@ -0,0 +1,36 @@
+use proc_macro2::Span;
+use syn::parse::{Error, Parse, ParseStream, Result};
+use syn::Token;
+
+#[derive(Copy, Clone)]
+pub struct Args {
+    pub local: bool,
+}
+
+mod kw {
+    syn::custom_keyword!(Send);
+}
+
+impl Parse for Args {
+    fn parse(input: ParseStream) -> Result<Self> {
+        match try_parse(input) {
+            Ok(args) if input.is_empty() => Ok(args),
+            _ => Err(error()),
+        }
+    }
+}
+
+fn try_parse(input: ParseStream) -> Result<Args> {
+    if input.peek(Token![?]) {
+        input.parse::<Token![?]>()?;
+        input.parse::<kw::Send>()?;
+        Ok(Args { local: true })
+    } else {
+        Ok(Args { local: false })
+    }
+}
+
+fn error() -> Error {
+    let msg = "expected #[async_trait] or #[async_trait(?Send)]";
+    Error::new(Span::call_site(), msg)
+}