Fix --use-core for functions, since we used the aster helper.

Signed-off-by: Emilio Cobos Álvarez <ecoal95@gmail.com>

1 files changed, 2 insertions, 1 deletions

diff --git a/src/codegen/mod.rs b/src/codegen/mod.rs
index bf6af82b..7fa8b19c 100755
--- a/src/codegen/mod.rs
+++ b/src/codegen/mod.rs
@@ -1489,7 +1489,8 @@ impl ToRustTy for Type {
             }
             TypeKind::Function(ref fs) => {
                 let ty = fs.to_rust_ty(ctx, item);
-                aster::AstBuilder::new().ty().option().build(ty)
+                let prefix = ctx.trait_prefix();
+                quote_ty!(ctx.ext_cx(), ::$prefix::option::Option<$ty>)
             }
             TypeKind::Array(item, len) => {
                 let inner = item.to_rust_ty(ctx);