mirror of https://github.com/rust-lang/rust
124 lines
4.0 KiB
Rust
124 lines
4.0 KiB
Rust
#![feature(dropck_eyepatch)]
|
|
|
|
// 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() {
|
|
use std::cell::Cell;
|
|
|
|
// We use separate blocks with separate variable to prevent the error
|
|
// messages from being deduplicated.
|
|
|
|
{
|
|
let c_long;
|
|
let (mut dt, mut dr): (Dt<_>, Dr<_>);
|
|
c_long = Cell::new(1);
|
|
|
|
// No error: sufficiently long-lived state can be referenced in dtors
|
|
dt = Dt("dt", &c_long);
|
|
dr = Dr("dr", &c_long);
|
|
}
|
|
|
|
{
|
|
let (c, mut dt, mut dr): (Cell<_>, Dt<_>, Dr<_>);
|
|
c = Cell::new(1);
|
|
|
|
// No Error: destructor order precisely modelled
|
|
dt = Dt("dt", &c);
|
|
dr = Dr("dr", &c);
|
|
}
|
|
|
|
{
|
|
let (mut dt, mut dr, c_shortest): (Dt<_>, Dr<_>, Cell<_>);
|
|
c_shortest = Cell::new(1);
|
|
|
|
// 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);
|
|
}
|
|
|
|
{
|
|
let c_long;
|
|
let (mut pt, mut pr, c_shortest): (Pt<_, _>, Pr<_>, Cell<_>);
|
|
c_long = Cell::new(1);
|
|
c_shortest = Cell::new(1);
|
|
|
|
// 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);
|
|
}
|
|
|
|
{
|
|
let c_long;
|
|
let (mut pt, mut pr, c_shortest): (Pt<_, _>, Pr<_>, Cell<_>);
|
|
c_long = Cell::new(1);
|
|
c_shortest = Cell::new(1);
|
|
// 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);
|
|
}
|
|
|
|
{
|
|
let (st, sr, c_shortest): (St<_>, Sr<_>, Cell<_>);
|
|
c_shortest = Cell::new(1);
|
|
// No error: St and Sr have no destructor.
|
|
st = St("st", &c_shortest);
|
|
sr = Sr("sr", &c_shortest);
|
|
}
|
|
}
|
|
fn use_imm<T>(_: &T) { }
|