---

yaml
---
r: 120703
b: refs/heads/dist-snap
c: f2a1378
h: refs/heads/master
i:
  120701: 8f983b6
  120699: 6fe457d
  120695: c89e93a
  120687: daf9708
  120671: 82c80e7
  120639: 62a8f0a
  120575: 1551f2c
v: v3

Author: huonw

[refs]

@@ -6,7 +6,7 @@ refs/heads/try: 1813e5aa1a03b0596b8de7abd1af31edf5d6098f
 refs/tags/release-0.1: 1f5c5126e96c79d22cb7862f75304136e204f105
 refs/heads/ndm: f3868061cd7988080c30d6d5bf352a5a5fe2460b
 refs/heads/try2: 147ecfdd8221e4a4d4e090486829a06da1e0ca3c
-refs/heads/dist-snap: 6ddd40d4368b1dbbc6bfa18d73d47beb05a55447
+refs/heads/dist-snap: f2a137829e07505aaaa2be4ae97d6ecfb6ef6823
 refs/tags/release-0.2: c870d2dffb391e14efb05aa27898f1f6333a9596
 refs/tags/release-0.3: b5f0d0f648d9a6153664837026ba1be43d3e2503
 refs/heads/try3: 9387340aab40a73e8424c48fd42f0c521a4875c0

branches/dist-snap/src/librustc/middle/check_match.rs

@@ -864,8 +864,13 @@ fn default(cx: &MatchCheckCtxt, r: &[@Pat]) -> Option<Vec<@Pat> > {
 fn check_local(cx: &mut MatchCheckCtxt, loc: &Local) {
     visit::walk_local(cx, loc, ());
     if is_refutable(cx, loc.pat) {
+        let name = match loc.source {
+            LocalLet => "local",
+            LocalFor => "`for` loop"
+        };
+
         cx.tcx.sess.span_err(loc.pat.span,
-                             "refutable pattern in local binding");
+                             format!("refutable pattern in {} binding", name).as_slice());
     }
 
     // Check legality of move bindings.

branches/dist-snap/src/libsyntax/ext/expand.rs

@@ -147,11 +147,17 @@ pub fn expand_expr(e: @ast::Expr, fld: &mut MacroExpander) -> @ast::Expr {
             //       ['<ident>:] loop {
             //         match i.next() {
             //           None => break,
-            //           Some(<src_pat>) => <src_loop_block>
+            //           Some(mut value) => {
+            //             let <src_pat> = value;
+            //             <src_loop_block>
+            //           }
             //         }
             //       }
             //     }
             //   }
+            //
+            // (The use of the `let` is to give better error messages
+            // when the pattern is refutable.)
 
             let local_ident = token::gensym_ident("__i"); // FIXME #13573
             let next_ident = fld.cx.ident_of("next");
@@ -167,11 +173,33 @@ pub fn expand_expr(e: @ast::Expr, fld: &mut MacroExpander) -> @ast::Expr {
                 fld.cx.arm(span, vec!(none_pat), break_expr)
             };
 
-            // `Some(<src_pat>) => <src_loop_block>`
+            // let <src_pat> = value;
+            let value_ident = token::gensym_ident("__value");
+            // this is careful to use src_pat.span so that error
+            // messages point exact at that.
+            let local = @ast::Local {
+                ty: fld.cx.ty_infer(src_pat.span),
+                pat: src_pat,
+                init: Some(fld.cx.expr_ident(src_pat.span, value_ident)),
+                id: ast::DUMMY_NODE_ID,
+                span: src_pat.span,
+                source: ast::LocalFor
+            };
+            let local = codemap::respan(src_pat.span, ast::DeclLocal(local));
+            let local = @codemap::respan(span, ast::StmtDecl(@local, ast::DUMMY_NODE_ID));
+
+            // { let ...; <src_loop_block> }
+            let block = fld.cx.block(span, vec![local],
+                                     Some(fld.cx.expr_block(src_loop_block)));
+
+            // `Some(mut value) => { ... }`
+            // Note the _'s in the name will stop any unused mutability warnings.
+            let value_pat = fld.cx.pat_ident_binding_mode(span, value_ident,
+                                                          ast::BindByValue(ast::MutMutable));
             let some_arm =
                 fld.cx.arm(span,
-                           vec!(fld.cx.pat_enum(span, some_path, vec!(src_pat))),
-                           fld.cx.expr_block(src_loop_block));
+                           vec!(fld.cx.pat_enum(span, some_path, vec!(value_pat))),
+                           fld.cx.expr_block(block));
 
             // `match i.next() { ... }`
             let match_expr = {

branches/dist-snap/src/test/compile-fail/for-loop-refutable-pattern-error-message.rs

@@ -0,0 +1,16 @@
+// Copyright 2014 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() {
+    for
+        &1 //~ ERROR refutable pattern in `for` loop binding
+        in [1].iter() {}
+}