rustc: Turn a Box ICE into an error

Closes #14092

src/librustc/middle/typeck/astconv.rs

@@ -433,9 +433,10 @@ pub fn ast_ty_to_builtin_ty<AC:AstConv,
                             }
                         }))
                     }
-                    this.tcx().sess.span_bug(path.span,
+                    this.tcx().sess.span_err(path.span,
                                              "not enough type parameters \
-                                              supplied to `Box<T>`")
+                                              supplied to `Box<T>`");
+                    Some(ty::mk_err())
                 }
                 _ => None
             }

src/test/compile-fail/issue-14092.rs

@@ -0,0 +1,14 @@
+// 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 fn1(0: Box) {} //~ ERROR: not enough type parameters supplied to `Box<T>`
+
+fn main() {}
+