auto merge of #7000 : Blei/rust/fix-6155, r=catamorphism

Author: bors

src/librustc/middle/typeck/check/mod.rs

@@ -2728,8 +2728,13 @@ pub fn check_expr_with_unifier(fcx: @mut FnCtxt,
         });
         let mut bot_field = false;
         let mut err_field = false;
+
         let elt_ts = do elts.mapi |i, e| {
-            check_expr_with_opt_hint(fcx, *e, flds.map(|fs| fs[i]));
+            let opt_hint = match flds {
+                Some(ref fs) if i < fs.len() => Some(fs[i]),
+                _ => None
+            };
+            check_expr_with_opt_hint(fcx, *e, opt_hint);
             let t = fcx.expr_ty(*e);
             err_field = err_field || ty::type_is_error(t);
             bot_field = bot_field || ty::type_is_bot(t);

src/test/compile-fail/tuple-arity-mismatch.rs

@@ -0,0 +1,17 @@
+// Copyright 2013 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.
+
+// Issue #6155
+
+fn first((value, _): (int, float)) -> int { value }
+
+fn main() {
+    let y = first ((1,2,3)); //~ ERROR expected a tuple with 2 elements but found one with 3 elements
+}