Error on unexpected extra tokens in attribute

macro/src/ir.rs

@@ -175,6 +175,7 @@ impl Parse for InternalAttr {
             "default" => {
                 let _: Token![=] = input.parse()?;
                 let expr = Expr::from_lit(input.parse()?)?;
+                assert_empty(input)?;
                 Ok(Self::Default(expr))
             }
 
@@ -182,3 +183,11 @@ impl Parse for InternalAttr {
         }
     }
 }
+
+fn assert_empty(input: ParseStream) -> Result<(), Error> {
+    if input.is_empty() {
+        Ok(())
+    } else {
+        Err(Error::new(input.span(), "unexpected tokens, expected no more tokens in this context"))
+    }
+}