Ensure type is copyable before emitting note suggesting adding manual deref.

Author: pnkfelix

src/librustc_typeck/check/op.rs

@@ -206,7 +206,8 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
                             lhs_ty);
 
                         if let TypeVariants::TyRef(_, ref ty_mut) = lhs_ty.sty {
-                            if self.lookup_op_method(expr, ty_mut.ty, vec![rhs_ty_var],
+                            if !self.infcx.type_moves_by_default(ty_mut.ty, lhs_expr.span) &&
+                                self.lookup_op_method(expr, ty_mut.ty, vec![rhs_ty_var],
                                     token::intern(name), trait_def_id,
                                     lhs_expr).is_ok() {
                                 err.span_note(

src/test/compile-fail/str-concat-on-double-ref.rs

@@ -13,7 +13,6 @@ fn main() {
     let b: &str = &"2";
     let c = a + b;
     //~^ ERROR binary operation `+` cannot be applied to type `&std::string::String`
-    //~| NOTE this is a reference of type that `+` can be applied to
     //~| NOTE an implementation of `std::ops::Add` might be missing for `&std::string::String`
     println!("{:?}", c);
 }