1 files changed, 34 insertions, 0 deletions
diff --git a/third_party/rust/async-trait/src/parse.rs b/third_party/rust/async-trait/src/parse.rs
new file mode 100644
index 0000000000..ebd253514f
--- /dev/null
+++ b/third_party/rust/async-trait/src/parse.rs
@@ -0,0 +1,34 @@
+use proc_macro2::Span;
+use syn::parse::{Error, Parse, ParseStream, Result};
+use syn::{Attribute, ItemImpl, ItemTrait, Token};
+
+pub enum Item {
+    Trait(ItemTrait),
+    Impl(ItemImpl),
+}
+
+impl Parse for Item {
+    fn parse(input: ParseStream) -> Result<Self> {
+        let attrs = input.call(Attribute::parse_outer)?;
+        let mut lookahead = input.lookahead1();
+        if lookahead.peek(Token![unsafe]) {
+            let ahead = input.fork();
+            ahead.parse::<Token![unsafe]>()?;
+            lookahead = ahead.lookahead1();
+        }
+        if lookahead.peek(Token![pub]) || lookahead.peek(Token![trait]) {
+            let mut item: ItemTrait = input.parse()?;
+            item.attrs = attrs;
+            Ok(Item::Trait(item))
+        } else if lookahead.peek(Token![impl]) {
+            let mut item: ItemImpl = input.parse()?;
+            if item.trait_.is_none() {
+                return Err(Error::new(Span::call_site(), "expected a trait impl"));
+            }
+            item.attrs = attrs;
+            Ok(Item::Impl(item))
+        } else {
+            Err(lookahead.error())
+        }
+    }
+}