1 files changed, 42 insertions, 1 deletions
diff --git a/macros/src/declare_interface_args.rs b/macros/src/declare_interface_args.rs
index b54f458..bd2f24e 100644
--- a/macros/src/declare_interface_args.rs
+++ b/macros/src/declare_interface_args.rs
@@ -1,10 +1,17 @@
 use syn::parse::{Parse, ParseStream, Result};
+use syn::punctuated::Punctuated;
 use syn::{Path, Token, Type};
 
+use crate::macro_flag::MacroFlag;
+use crate::util::iterator_ext::IteratorExt;
+
+pub const DECLARE_INTERFACE_FLAGS: &[&str] = &["async"];
+
 pub struct DeclareInterfaceArgs
 {
     pub implementation: Type,
     pub interface: Path,
+    pub flags: Punctuated<MacroFlag, Token![,]>,
 }
 
 impl Parse for DeclareInterfaceArgs
@@ -15,9 +22,43 @@ impl Parse for DeclareInterfaceArgs
 
         input.parse::<Token![->]>()?;
 
+        let interface: Path = input.parse()?;
+
+        let flags = if input.peek(Token![,]) {
+            input.parse::<Token![,]>()?;
+
+            let flags = Punctuated::<MacroFlag, Token![,]>::parse_terminated(input)?;
+
+            for flag in &flags {
+                let flag_str = flag.flag.to_string();
+
+                if !DECLARE_INTERFACE_FLAGS.contains(&flag_str.as_str()) {
+                    return Err(input.error(format!(
+                        "Unknown flag '{}'. Expected one of [ {} ]",
+                        flag_str,
+                        DECLARE_INTERFACE_FLAGS.join(",")
+                    )));
+                }
+            }
+
+            let flag_names = flags
+                .iter()
+                .map(|flag| flag.flag.to_string())
+                .collect::<Vec<_>>();
+
+            if let Some(dupe_flag_name) = flag_names.iter().find_duplicate() {
+                return Err(input.error(format!("Duplicate flag '{}'", dupe_flag_name)));
+            }
+
+            flags
+        } else {
+            Punctuated::new()
+        };
+
         Ok(Self {
             implementation,
-            interface: input.parse()?,
+            interface,
+            flags,
         })
     }
 }