src/test/compile-fail/cross-fn-cache-hole.rs

   1 // Copyright 2012 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 // Check that when there are vacuous predicates in the environment
  12 // (which make a fn uncallable) we don't erroneously cache those and
  13 // then consider them satisfied elsewhere. The current technique for
  14 // doing this is just to filter "global" predicates out of the
  15 // environment, which means that we wind up with an error in the
  16 // function `vacuous`, because even though `i32: Bar<u32>` is implied
  17 // by its where clause, that where clause never holds.
  18
  19 trait Foo<X,Y>: Bar<X> {
  20 }
  21
  22 trait Bar<X> { }
  23
  24 // We don't always check where clauses for sanity, but in this case
  25 // wfcheck does report an error here:
  26 fn vacuous<A>() //~ ERROR the trait bound `i32: Bar<u32>` is not satisfied
  27     where i32: Foo<u32, A>
  28 {
  29     // ... the original intention was to check that we don't use that
  30     // vacuous where clause (which could never be satisfied) to accept
  31     // the following line and then mess up calls elsewhere.
  32     require::<i32, u32>();
  33 }
  34
  35 fn require<A,B>()
  36     where A: Bar<B>
  37 {
  38 }
  39
  40 fn main() {
  41     require::<i32, u32>();
  42 }