src/test/ui/nll/ty-outlives/projection-one-region-closure.rs

   1 // Copyright 2016 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 cases where we constrain `<T as Anything<'b>>::AssocType` to
  12 // outlive `'a` and there are no bounds in the trait definition of
  13 // `Anything`. This means that the constraint can only be satisfied in two
  14 // ways:
  15 //
  16 // - by ensuring that `T: 'a` and `'b: 'a`, or
  17 // - by something in the where clauses.
  18 //
  19 // As of this writing, the where clause option does not work because
  20 // of limitations in our region inferencing system (this is true both
  21 // with and without NLL). See `projection_outlives`.
  22 //
  23 // Ensuring that both `T: 'a` and `'b: 'a` holds does work (`elements_outlive`).
  24
  25 // compile-flags:-Zborrowck=mir -Zverbose
  26
  27 #![allow(warnings)]
  28 #![feature(rustc_attrs)]
  29
  30 use std::cell::Cell;
  31
  32 trait Anything<'a> {
  33     type AssocType;
  34 }
  35
  36 fn with_signature<'a, T, F>(cell: Cell<&'a ()>, t: T, op: F)
  37 where
  38     F: FnOnce(Cell<&'a ()>, T),
  39 {
  40     op(cell, t)
  41 }
  42
  43 fn require<'a, 'b, T>(_cell: Cell<&'a ()>, _t: T)
  44 where
  45     T: Anything<'b>,
  46     T::AssocType: 'a,
  47 {
  48 }
  49
  50 #[rustc_regions]
  51 fn no_relationships_late<'a, 'b, T>(cell: Cell<&'a ()>, t: T)
  52 where
  53     T: Anything<'b>,
  54 {
  55     with_signature(cell, t, |cell, t| require(cell, t));
  56     //~^ WARNING not reporting region error due to nll
  57     //~| ERROR the parameter type `T` may not live long enough
  58     //~| ERROR does not outlive free region
  59 }
  60
  61 #[rustc_regions]
  62 fn no_relationships_early<'a, 'b, T>(cell: Cell<&'a ()>, t: T)
  63 where
  64     T: Anything<'b>,
  65     'a: 'a,
  66 {
  67     with_signature(cell, t, |cell, t| require(cell, t));
  68     //~^ WARNING not reporting region error due to nll
  69     //~| ERROR the parameter type `T` may not live long enough
  70     //~| ERROR does not outlive free region
  71 }
  72
  73 #[rustc_regions]
  74 fn projection_outlives<'a, 'b, T>(cell: Cell<&'a ()>, t: T)
  75 where
  76     T: Anything<'b>,
  77     T::AssocType: 'a,
  78 {
  79     // This error is unfortunate. This code ought to type-check: we
  80     // are projecting `<T as Anything<'b>>::AssocType`, and we know
  81     // that this outlives `'a` because of the where-clause. However,
  82     // the way the region checker works, we don't register this
  83     // outlives obligation, and hence we get an error: this is because
  84     // what we see is a projection like `<T as
  85     // Anything<'?0>>::AssocType`, and we don't yet know if `?0` will
  86     // equal `'b` or not, so we ignore the where-clause. Obviously we
  87     // can do better here with a more involved verification step.
  88
  89     with_signature(cell, t, |cell, t| require(cell, t));
  90     //~^ WARNING not reporting region error due to nll
  91     //~| ERROR the parameter type `T` may not live long enough
  92     //~| ERROR free region `ReEarlyBound(1, 'b)` does not outlive free region `ReEarlyBound(0, 'a)`
  93 }
  94
  95 #[rustc_regions]
  96 fn elements_outlive<'a, 'b, T>(cell: Cell<&'a ()>, t: T)
  97 where
  98     T: Anything<'b>,
  99     T: 'a,
 100     'b: 'a,
 101 {
 102     with_signature(cell, t, |cell, t| require(cell, t));
 103 }
 104
 105 fn main() {}