| // Copyright 2016 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. |
| |
| #![feature(dropck_eyepatch, rustc_attrs)] |
| |
| // The point of this test is to illustrate that the `#[may_dangle]` |
| // attribute specifically allows, in the context of a type |
| // implementing `Drop`, a generic parameter to be instantiated with a |
| // lifetime that does not strictly outlive the owning type itself. |
| // |
| // Here we test that only the expected errors are issued. |
| // |
| // The illustration is made concrete by comparison with two variations |
| // on the type with `#[may_dangle]`: |
| // |
| // 1. an analogous type that does not implement `Drop` (and thus |
| // should exhibit maximal flexibility with respect to dropck), and |
| // |
| // 2. an analogous type that does not use `#[may_dangle]` (and thus |
| // should exhibit the standard limitations imposed by dropck. |
| // |
| // The types in this file follow a pattern, {D,P,S}{t,r}, where: |
| // |
| // - D means "I implement Drop" |
| // |
| // - P means "I implement Drop but guarantee my (first) parameter is |
| // pure, i.e. not accessed from the destructor"; no other parameters |
| // are pure. |
| // |
| // - S means "I do not implement Drop" |
| // |
| // - t suffix is used when the first generic is a type |
| // |
| // - r suffix is used when the first generic is a lifetime. |
| |
| use std::fmt; |
| |
| struct Dt<A: fmt::Debug>(&'static str, A); |
| struct Dr<'a, B:'a+fmt::Debug>(&'static str, &'a B); |
| struct Pt<A,B: fmt::Debug>(&'static str, A, B); |
| struct Pr<'a, 'b, B:'a+'b+fmt::Debug>(&'static str, &'a B, &'b B); |
| struct St<A: fmt::Debug>(&'static str, A); |
| struct Sr<'a, B:'a+fmt::Debug>(&'static str, &'a B); |
| |
| impl<A: fmt::Debug> Drop for Dt<A> { |
| fn drop(&mut self) { println!("drop {} {:?}", self.0, self.1); } |
| } |
| impl<'a, B: fmt::Debug> Drop for Dr<'a, B> { |
| fn drop(&mut self) { println!("drop {} {:?}", self.0, self.1); } |
| } |
| unsafe impl<#[may_dangle] A, B: fmt::Debug> Drop for Pt<A, B> { |
| // (unsafe to access self.1 due to #[may_dangle] on A) |
| fn drop(&mut self) { println!("drop {} {:?}", self.0, self.2); } |
| } |
| unsafe impl<#[may_dangle] 'a, 'b, B: fmt::Debug> Drop for Pr<'a, 'b, B> { |
| // (unsafe to access self.1 due to #[may_dangle] on 'a) |
| fn drop(&mut self) { println!("drop {} {:?}", self.0, self.2); } |
| } |
| |
| fn main() { #![rustc_error] // rust-lang/rust#49855 |
| use std::cell::Cell; |
| let c_long; |
| let (c, mut dt, mut dr, mut pt, mut pr, st, sr, c_shortest) |
| : (Cell<_>, Dt<_>, Dr<_>, Pt<_, _>, Pr<_>, St<_>, Sr<_>, Cell<_>); |
| c_long = Cell::new(1); |
| c = Cell::new(1); |
| c_shortest = Cell::new(1); |
| |
| // No error: sufficiently long-lived state can be referenced in dtors |
| dt = Dt("dt", &c_long); |
| dr = Dr("dr", &c_long); |
| |
| // Error: destructor order imprecisely modelled |
| dt = Dt("dt", &c); |
| //~^ ERROR `c` does not live long enough |
| dr = Dr("dr", &c); |
| //~^ ERROR `c` does not live long enough |
| |
| // Error: `c_shortest` dies too soon for the references in dtors to be valid. |
| dt = Dt("dt", &c_shortest); |
| //~^ ERROR `c_shortest` does not live long enough |
| dr = Dr("dr", &c_shortest); |
| //~^ ERROR `c_shortest` does not live long enough |
| |
| |
| // No error: Drop impl asserts .1 (A and &'a _) are not accessed |
| pt = Pt("pt", &c_shortest, &c_long); |
| pr = Pr("pr", &c_shortest, &c_long); |
| |
| // Error: Drop impl's assertion does not apply to `B` nor `&'b _` |
| pt = Pt("pt", &c_long, &c_shortest); |
| //~^ ERROR `c_shortest` does not live long enough |
| pr = Pr("pr", &c_long, &c_shortest); |
| //~^ ERROR `c_shortest` does not live long enough |
| |
| // No error: St and Sr have no destructor. |
| st = St("st", &c_shortest); |
| sr = Sr("sr", &c_shortest); |
| |
| println!("{:?}", (dt.0, dr.0, pt.0, pr.0, st.0, sr.0)); |
| } |