use UFCS in `#[deriving(Hash)]`

expansion now uses `::std::hash::Hash::hash(&*__self_0_0, __arg_0)` instead of
`(*__self_0_0).hash(__arg_0)`

closes #21160

1 files changed, 12 insertions, 2 deletions

diff --git a/src/libsyntax/ext/deriving/hash.rs b/src/libsyntax/ext/deriving/hash.rs
index db99c142443..98b7fae0341 100644
--- a/src/libsyntax/ext/deriving/hash.rs
+++ b/src/libsyntax/ext/deriving/hash.rs
@@ -65,9 +65,19 @@ fn hash_substructure(cx: &mut ExtCtxt, trait_span: Span, substr: &Substructure)
         [ref state_expr] => state_expr,
         _ => cx.span_bug(trait_span, "incorrect number of arguments in `deriving(Hash)`")
     };
-    let hash_ident = substr.method_ident;
+    let hash_path = {
+        let strs = vec![
+            cx.ident_of("std"),
+            cx.ident_of("hash"),
+            cx.ident_of("Hash"),
+            cx.ident_of("hash"),
+        ];
+
+        cx.expr_path(cx.path_global(trait_span, strs))
+    };
     let call_hash = |&: span, thing_expr| {
-        let expr = cx.expr_method_call(span, thing_expr, hash_ident, vec!(state_expr.clone()));
+        let ref_thing = cx.expr_addr_of(span, thing_expr);
+        let expr = cx.expr_call(span, hash_path.clone(), vec!(ref_thing, state_expr.clone()));
         cx.stmt_expr(expr)
     };
     let mut stmts = Vec::new();