implement feature gate bind_by_move_pattern_guards

implementation of issue rust-lang#15287

Author: Andreas Jonson

src/doc/unstable-book/src/SUMMARY.md

@@ -17,6 +17,7 @@
     - [associated_consts](language-features/associated-consts.md)
     - [associated_type_defaults](language-features/associated-type-defaults.md)
     - [attr_literals](language-features/attr-literals.md)
+    - [bind_by_move_pattern_guards](language-features/bind_by_move_pattern_guards.md)
     - [box_patterns](language-features/box-patterns.md)
     - [box_syntax](language-features/box-syntax.md)
     - [catch_expr](language-features/catch-expr.md)

src/doc/unstable-book/src/language-features/bind_by_move_pattern_guards.md

@@ -0,0 +1,10 @@
+# `bind_by_move_pattern_guards`
+
+The tracking issue for this feature is: [#15287]
+
+[#15287]: https://github.com/rust-lang/rust/issues/15287
+
+------------------------
+
+
+

src/librustc_const_eval/check_match.rs

@@ -486,7 +486,7 @@ fn check_legality_of_move_bindings(cx: &MatchVisitor,
                              "cannot bind by-move with sub-bindings")
                 .span_label(p.span, "binds an already bound by-move value by moving it")
                 .emit();
-        } else if has_guard {
+        } else if has_guard && !cx.tcx.sess.features.borrow().bind_by_move_pattern_guards {
             struct_span_err!(cx.tcx.sess, p.span, E0008,
                       "cannot bind by-move into a pattern guard")
                 .span_label(p.span, "moves value into pattern guard")

src/libsyntax/feature_gate.rs

@@ -355,6 +355,9 @@ declare_features! (
 
     // Allows use of the :vis macro fragment specifier
     (active, macro_vis_matcher, "1.18.0", Some(41022)),
+
+    // Allows use of pattern guards with Bind-By-Move
+    (active, bind_by_move_pattern_guards, "1.18.0", Some(15287)),
 );
 
 declare_features! (

src/test/compile-fail/bind-by-move-move-in-guard.rs

@@ -0,0 +1,24 @@
+// Copyright 2012 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.
+
+#![feature(bind_by_move_pattern_guards)]
+
+use std::sync::Arc;
+fn dispose(_x: Arc<bool>) { }
+
+pub fn main() {
+    let p = Arc::new(true);
+    let x = Some(p);
+    match x {
+        Some(z) if {dispose(z); true} => { dispose(z); },//~ ERROR use of moved value: `z`
+        _ => panic!()
+    }
+}
+

src/test/compile-fail/bind-by-move-no-guards.rs

@@ -8,6 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+// gate-test-bind_by_move_pattern_guards
 use std::sync::mpsc::channel;
 
 fn main() {

src/test/run-pass/bind-by-move-with-guard.rs

@@ -0,0 +1,23 @@
+// Copyright 2012-2014 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.
+
+#![feature(bind_by_move_pattern_guards)]
+
+use std::sync::Arc;
+fn dispose(_x: Arc<bool>) { }
+
+pub fn main() {
+    let p = Arc::new(true);
+    let x = Some(p);
+    match x {
+        Some(z) if z == true => { dispose(z); },
+        None => panic!()
+    }
+}