src/test/run-pass/regions-relate-bound-regions-on-closures-to-inference-variables.rs

   1 // Copyright 2014 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 // Test that this fairly specialized, but also reasonable, pattern
  12 // typechecks. The pattern involves regions bound in closures that
  13 // wind up related to inference variables.
  14 //
  15 // NB. Changes to the region implementations have broken this pattern
  16 // a few times, but it happens to be used in the compiler so those
  17 // changes were caught. However, those uses in the compiler could
  18 // easily get changed or refactored away in the future.
  19
  20
  21 #![allow(unknown_features)]
  22 #![feature(box_syntax)]
  23
  24 struct Ctxt<'tcx> {
  25     x: &'tcx Vec<isize>
  26 }
  27
  28 struct Foo<'a,'tcx:'a> {
  29     cx: &'a Ctxt<'tcx>,
  30 }
  31
  32 impl<'a,'tcx> Foo<'a,'tcx> {
  33     fn bother(&mut self) -> isize {
  34         // FIXME (#22405): Replace `Box::new` with `box` here when/if possible.
  35         self.elaborate_bounds(Box::new(|this| {
  36             // (*) Here: type of `this` is `&'f0 Foo<&'f1, '_2>`,
  37             // where `'f0` and `'f1` are fresh, free regions that
  38             // result from the bound regions on the closure, and `'2`
  39             // is a region inference variable created by the call. Due
  40             // to the constraints on the type, we find that `'_2 : 'f1
  41             // + 'f2` must hold (and can be assumed by the callee).
  42             // Region inference has to do some clever stuff to avoid
  43             // inferring `'_2` to be `'static` in this case, because
  44             // it is created outside the closure but then related to
  45             // regions bound by the closure itself. See the
  46             // `region_inference.rs` file (and the `givens` field, in
  47             // particular) for more details.
  48             this.foo()
  49         }))
  50     }
  51
  52     fn foo(&mut self) -> isize {
  53         22
  54     }
  55
  56     fn elaborate_bounds(
  57         &mut self,
  58         mut mk_cand: Box<for<'b> FnMut(&mut Foo<'b, 'tcx>) -> isize>)
  59         -> isize
  60     {
  61         mk_cand(self)
  62     }
  63 }
  64
  65 fn main() {
  66     let v = vec![];
  67     let cx = Ctxt { x: &v };
  68     let mut foo = Foo { cx: &cx };
  69     assert_eq!(foo.bother(), 22); // just so the code is not dead, basically
  70 }