57 lines
1.9 KiB
Rust
57 lines
1.9 KiB
Rust
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// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution and at
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// http://rust-lang.org/COPYRIGHT.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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// Demonstrate the use of the unguarded escape hatch with a type param in negative position
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// to assert that destructor will not access any dead data.
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//
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// Compare with compile-fail/issue28498-reject-lifetime-param.rs
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// Demonstrate that a type param in negative position causes dropck to reject code
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// that might indirectly access previously dropped value.
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//
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// Compare with run-pass/issue28498-ugeh-with-passed-to-fn.rs
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#![feature(dropck_parametricity)]
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#[derive(Debug)]
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struct ScribbleOnDrop(String);
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impl Drop for ScribbleOnDrop {
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fn drop(&mut self) {
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self.0 = format!("DROPPED");
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}
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}
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struct Foo<T>(u32, T, Box<for <'r> fn(&'r T) -> String>);
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impl<T> Drop for Foo<T> {
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#[unsafe_destructor_blind_to_params]
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fn drop(&mut self) {
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// Use of `unsafe_destructor_blind_to_params` is sound,
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// because destructor never passes a `self.1` to the callback
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// (in `self.2`) despite having it available.
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println!("Dropping Foo({}, _)", self.0);
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}
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}
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fn callback(s: & &ScribbleOnDrop) -> String { format!("{:?}", s) }
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fn main() {
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let (last_dropped, foo0);
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let (foo1, first_dropped);
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last_dropped = ScribbleOnDrop(format!("last"));
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first_dropped = ScribbleOnDrop(format!("first"));
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foo0 = Foo(0, &last_dropped, Box::new(callback));
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foo1 = Foo(1, &first_dropped, Box::new(callback));
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println!("foo0.1: {:?} foo1.1: {:?}", foo0.1, foo1.1);
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}
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