rustc_typeck: fix binops needing more type informations to coerce.

Author: eddyb

src/librustc_typeck/check/op.rs

@@ -411,6 +411,8 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
         match method {
             Some(ok) => {
                 let method = self.register_infer_ok_obligations(ok);
+                self.select_obligations_where_possible();
+
                 let method_ty = method.ty;
 
                 // HACK(eddyb) Fully qualified path to work around a resolve bug.

src/test/run-pass/coerce-overloaded-autoderef.rs

@@ -68,4 +68,8 @@ fn use_vec_ref(v: &Vec<u8>) {
     use_slice(&&&mut &&&v);
 }
 
+fn use_op_rhs(s: &mut String) {
+    *s += {&String::from(" ")};
+}
+
 pub fn main() {}