delegation: Support async, const, extern "ABI" and C-variadic functions

Also allow `impl Trait` in delegated functions.
The delegation item will refer to the original opaque type from the callee, fresh opaque type won't be created.

1 files changed, 27 insertions, 0 deletions

diff --git a/tests/ui/delegation/impl-trait.rs b/tests/ui/delegation/impl-trait.rs
new file mode 100644
index 00000000000..13df0155485
--- /dev/null
+++ b/tests/ui/delegation/impl-trait.rs
@@ -0,0 +1,27 @@
+//@ check-pass
+
+#![feature(fn_delegation)]
+#![allow(incomplete_features)]
+
+mod to_reuse {
+    pub fn foo() -> impl Clone { 0 }
+}
+
+reuse to_reuse::foo;
+
+trait Trait {
+    fn bar() -> impl Clone { 1 }
+}
+
+struct S;
+impl Trait for S {}
+
+impl S {
+    reuse to_reuse::foo;
+    reuse <S as Trait>::bar;
+}
+
+fn main() {
+    foo().clone();
+    <S>::bar().clone();
+}