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.
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.
11 #![feature(dropck_eyepatch, rustc_attrs)]
13 // The point of this test is to illustrate that the `#[may_dangle]`
14 // attribute specifically allows, in the context of a type
15 // implementing `Drop`, a generic parameter to be instantiated with a
16 // lifetime that does not strictly outlive the owning type itself.
18 // Here we test that only the expected errors are issued.
20 // The illustration is made concrete by comparison with two variations
21 // on the type with `#[may_dangle]`:
23 // 1. an analogous type that does not implement `Drop` (and thus
24 // should exhibit maximal flexibility with respect to dropck), and
26 // 2. an analogous type that does not use `#[may_dangle]` (and thus
27 // should exhibit the standard limitations imposed by dropck.
29 // The types in this file follow a pattern, {D,P,S}{t,r}, where:
31 // - D means "I implement Drop"
33 // - P means "I implement Drop but guarantee my (first) parameter is
34 // pure, i.e. not accessed from the destructor"; no other parameters
37 // - S means "I do not implement Drop"
39 // - t suffix is used when the first generic is a type
41 // - r suffix is used when the first generic is a lifetime.
45 struct Dt<A: fmt::Debug>(&'static str, A);
46 struct Dr<'a, B:'a+fmt::Debug>(&'static str, &'a B);
47 struct Pt<A,B: fmt::Debug>(&'static str, A, B);
48 struct Pr<'a, 'b, B:'a+'b+fmt::Debug>(&'static str, &'a B, &'b B);
49 struct St<A: fmt::Debug>(&'static str, A);
50 struct Sr<'a, B:'a+fmt::Debug>(&'static str, &'a B);
52 impl<A: fmt::Debug> Drop for Dt<A> {
53 fn drop(&mut self) { println!("drop {} {:?}", self.0, self.1); }
55 impl<'a, B: fmt::Debug> Drop for Dr<'a, B> {
56 fn drop(&mut self) { println!("drop {} {:?}", self.0, self.1); }
58 unsafe impl<#[may_dangle] A, B: fmt::Debug> Drop for Pt<A, B> {
59 // (unsafe to access self.1 due to #[may_dangle] on A)
60 fn drop(&mut self) { println!("drop {} {:?}", self.0, self.2); }
62 unsafe impl<#[may_dangle] 'a, 'b, B: fmt::Debug> Drop for Pr<'a, 'b, B> {
63 // (unsafe to access self.1 due to #[may_dangle] on 'a)
64 fn drop(&mut self) { println!("drop {} {:?}", self.0, self.2); }
67 fn main() { #![rustc_error] // rust-lang/rust#49855
70 let (c, mut dt, mut dr, mut pt, mut pr, st, sr, c_shortest)
71 : (Cell<_>, Dt<_>, Dr<_>, Pt<_, _>, Pr<_>, St<_>, Sr<_>, Cell<_>);
72 c_long = Cell::new(1);
74 c_shortest = Cell::new(1);
76 // No error: sufficiently long-lived state can be referenced in dtors
77 dt = Dt("dt", &c_long);
78 dr = Dr("dr", &c_long);
80 // Error: destructor order imprecisely modelled
82 //~^ ERROR `c` does not live long enough
84 //~^ ERROR `c` does not live long enough
86 // Error: `c_shortest` dies too soon for the references in dtors to be valid.
87 dt = Dt("dt", &c_shortest);
88 //~^ ERROR `c_shortest` does not live long enough
89 dr = Dr("dr", &c_shortest);
90 //~^ ERROR `c_shortest` does not live long enough
93 // No error: Drop impl asserts .1 (A and &'a _) are not accessed
94 pt = Pt("pt", &c_shortest, &c_long);
95 pr = Pr("pr", &c_shortest, &c_long);
97 // Error: Drop impl's assertion does not apply to `B` nor `&'b _`
98 pt = Pt("pt", &c_long, &c_shortest);
99 //~^ ERROR `c_shortest` does not live long enough
100 pr = Pr("pr", &c_long, &c_shortest);
101 //~^ ERROR `c_shortest` does not live long enough
103 // No error: St and Sr have no destructor.
104 st = St("st", &c_shortest);
105 sr = Sr("sr", &c_shortest);
107 println!("{:?}", (dt.0, dr.0, pt.0, pr.0, st.0, sr.0));