refactor(lib): use type macro to detect impl Trait

src/common/macros.rs

@@ -0,0 +1,21 @@
+#[macro_export]
+#[cfg(__hyper_impl_trait_available)]
+macro_rules! impl_trait {
+    (ty: $($t:tt)+) => {
+        impl $($t)+
+    };
+    (e: $e:expr) => {
+        $e
+    }
+}
+
+#[macro_export]
+#[cfg(not(__hyper_impl_trait_available))]
+macro_rules! impl_trait {
+    (ty: $($t:tt)+) => {
+        Box<$($t)+>
+    };
+    (e: $e:expr) => {
+        Box::new($e)
+    }
+}

src/common/mod.rs

@@ -2,6 +2,8 @@ mod buf;
 mod exec;
 pub(crate) mod io;
 mod lazy;
+#[macro_use]
+mod macros;
 mod never;
 
 pub(crate) use self::buf::StaticBuf;