Rollup merge of rust-lang#21353 - sanxiyn:upvar, r=nikomatsakis

Fix rust-lang#20558.

Author: Manishearth

src/librustc/middle/traits/select.rs

@@ -1549,6 +1549,14 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                     return Ok(ParameterBuiltin);
                 }
 
+                // Upvars are always local variables or references to
+                // local variables, and local variables cannot be
+                // unsized, so the closure struct as a whole must be
+                // Sized.
+                if bound == ty::BoundSized {
+                    return Ok(If(Vec::new()));
+                }
+
                 match self.closure_typer.closure_upvars(def_id, substs) {
                     Some(upvars) => {
                         Ok(If(upvars.iter().map(|c| c.ty).collect()))

src/test/run-pass/unboxed-closures-infer-upvar.rs

@@ -0,0 +1,22 @@
+// Copyright 2015 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.
+
+// Test that the type variable in the type(`Vec<_>`) of a closed over
+// variable does not interfere with type inference.
+
+fn f<F: FnMut()>(mut f: F) {
+    f();
+}
+
+fn main() {
+    let mut v: Vec<_> = vec![];
+    f(|| v.push(0));
+    assert_eq!(v, vec![0]);
+}