rustc: Allow return to return from a closure.

With the old `for` gone, this behaviour is no longer conflicting with
that use of `return` in closures, and this allows shortcircuiting in a
closure.

src/librustc/middle/check_loop.rs

@@ -47,12 +47,6 @@ impl Visitor<Context> for CheckLoopVisitor {
             }
             ast::ExprBreak(_) => self.require_loop("break", cx, e.span),
             ast::ExprAgain(_) => self.require_loop("continue", cx, e.span),
-            ast::ExprRet(oe) => {
-                if cx == Closure {
-                    self.tcx.sess.span_err(e.span, "`return` in a closure");
-                }
-                visit::walk_expr_opt(self, oe, cx);
-            }
             _ => visit::walk_expr(self, e, cx)
         }
     }

src/test/run-pass/return-from-closure.rs

@@ -0,0 +1,41 @@
+// 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.
+
+// just to make sure that `return` is only returning from the closure,
+// not the surrounding function.
+static mut calls: uint = 0;
+
+fn surrounding() {
+    let return_works = |n: int| {
+        unsafe { calls += 1 }
+
+        if n >= 0 { return; }
+        fail!()
+    };
+
+    return_works(10);
+    return_works(20);
+
+
+    let return_works_proc = proc(n: int) {
+        unsafe { calls += 1 }
+
+        if n >= 0 { return; }
+        fail!()
+    };
+
+    return_works_proc(10);
+}
+
+pub fn main() {
+    surrounding();
+
+    assert_eq!(unsafe {calls}, 3);
+}