Fix switched types in type mismatch

Author: GuillaumeGomez

src/librustc_typeck/check/mod.rs

@@ -4194,7 +4194,7 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
             // type of the lvalue it is referencing, and not some
             // supertype thereof.
             let init_ty = self.check_expr_with_lvalue_pref(init, LvaluePreference::from_mutbl(m));
-            self.demand_eqtype(init.span, init_ty, local_ty);
+            self.demand_eqtype(init.span, local_ty, init_ty);
             init_ty
         } else {
             self.check_expr_coercable_to_type(init, local_ty)

src/test/ui/switched-expectations.rs

@@ -0,0 +1,14 @@
+// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+fn main() {
+    let var = 10i32;
+    let ref string: String = var; //~ ERROR mismatched types [E0308]
+}

src/test/ui/switched-expectations.stderr

@@ -0,0 +1,11 @@
+error[E0308]: mismatched types
+  --> $DIR/switched-expectations.rs:13:30
+   |
+13 |     let ref string: String = var; //~ ERROR mismatched types [E0308]
+   |                              ^^^ expected struct `std::string::String`, found i32
+   |
+   = note: expected type `std::string::String`
+              found type `i32`
+
+error: aborting due to previous error
+