Added support for GATs

.github/workflows/test.yml

@@ -28,7 +28,7 @@ jobs:
     strategy:
       matrix:
         rust:
-          - stable # It's useful to test applications of these macros to newer features so a 1.53 test doesn't work
+          - beta # It's useful to test applications of these macros to newer features so a 1.53 test doesn't work (beta to test GATs)
     steps:
       - uses: actions/checkout@v1
       - uses: actions-rs/toolchain@v1

ambassador/src/register.rs

@@ -234,10 +234,9 @@ fn build_trait_items(
         TraitItem::Type(TraitItemType {
             ident, generics, ..
         }) => {
-            let _where_clause = &generics.where_clause;
+            let where_clause = &generics.where_clause;
             let item = quote! {
-                type #ident #generics = <$ty as #trait_ident<#gen_pat>>::#ident #generics;
-                // TODO add #where_clase to appropriate place once it is decided
+                type #ident #generics = <$ty as #trait_ident<#gen_pat>>::#ident #generics #where_clause;
             };
             (
                 item.clone(),

ambassador/tests/run-pass/gat.rs

@@ -0,0 +1,32 @@
+extern crate ambassador;
+
+use ambassador::{delegatable_trait, Delegate};
+
+#[delegatable_trait]
+pub trait StreamingIterator {
+    type Output<'a>
+    where
+        Self: 'a;
+    fn next(&mut self) -> Option<Self::Output<'_>>;
+}
+
+struct RepeatMut<T>(T);
+
+impl<T> StreamingIterator for RepeatMut<T> {
+    type Output<'a> = &'a mut T where T: 'a;
+
+    fn next(&mut self) -> Option<Self::Output<'_>> {
+        Some(&mut self.0)
+    }
+}
+
+#[derive(Delegate)]
+#[delegate(StreamingIterator)]
+pub struct Wrap<X>(X);
+
+pub fn main() {
+    let mut x = Wrap(RepeatMut("forever".into()));
+    let m: &mut String = x.next().unwrap();
+    m.push('?');
+    assert_eq!(x.next().unwrap(), "forever?");
+}