generalize impl_froms to nested enums

crates/ra_hir/src/lib.rs

@@ -8,13 +8,20 @@
 //! applied. So, the relation between syntax and HIR is many-to-one.
 
 macro_rules! impl_froms {
-    ($e:ident: $($v:ident),*) => {
+    ($e:ident: $($v:ident $(($($sv:ident),*))?),*) => {
         $(
             impl From<$v> for $e {
                 fn from(it: $v) -> $e {
                     $e::$v(it)
                 }
             }
+            $($(
+                impl From<$sv> for $e {
+                    fn from(it: $sv) -> $e {
+                        $e::$v($v::$sv(it))
+                    }
+                }
+            )*)?
         )*
     }
 }