assert-unmoved

一个类型，断言在经过固定和可变访问后，其底层类型未被移动。

这是对futures-test的AssertUnmoved的重新编写，以便在更多用例中使用。它还支持除了futures之外的其他特性和类型。

在此项目中进行的许多更改也已反映在上游：rust-lang/futures-rs#2148，rust-lang/futures-rs#2208

使用方法

将此添加到您的Cargo.toml

[dependencies]
assert-unmoved = "0.1"

示例

检测不正确的Pin::new_unchecked使用（应崩溃）的示例

use std::pin::Pin;

use assert_unmoved::AssertUnmoved;
use futures::{
    future::{self, Future},
    task::{noop_waker, Context},
};

let waker = noop_waker();
let mut cx = Context::from_waker(&waker);

// First we allocate the future on the stack and poll it.
let mut future = AssertUnmoved::new(future::pending::<()>());
let pinned_future = unsafe { Pin::new_unchecked(&mut future) };
assert!(pinned_future.poll(&mut cx).is_pending());

// Next we move it back to the heap and poll it again. This second call
// should panic (as the future is moved).
let mut boxed_future = Box::new(future);
let pinned_boxed_future = unsafe { Pin::new_unchecked(&mut *boxed_future) };
let _ = pinned_boxed_future.poll(&mut cx).is_pending();

检测不正确的StreamExt::next实现（应崩溃）的示例

use std::pin::Pin;

use assert_unmoved::AssertUnmoved;
use futures::{
    future::Future,
    stream::{self, Stream},
    task::{noop_waker, Context, Poll},
};

struct Next<'a, S: Stream>(&'a mut S);

impl<S: Stream> Future for Next<'_, S> {
    type Output = Option<S::Item>;

    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
        // This is `Pin<&mut Type>` to `Pin<Field>` projection and is unsound
        // if `S` is not `Unpin` (you can move `S` after `Next` dropped).
        //
        // The correct projection is `Pin<&mut Type>` to `Pin<&mut Field>`.
        // In `Next`, it is `Pin<&mut Next<'_, S>>` to `Pin<&mut &mut S>`,
        // and it needs to add `S: Unpin` bounds to convert `Pin<&mut &mut S>`
        // to `Pin<&mut S>`.
        let stream: Pin<&mut S> = unsafe { self.map_unchecked_mut(|f| f.0) };
        stream.poll_next(cx)
    }
}

let waker = noop_waker();
let mut cx = Context::from_waker(&waker);

let mut stream = AssertUnmoved::new(stream::pending::<()>());

{
    let next = Next(&mut stream);
    let mut pinned_next = Box::pin(next);
    assert!(pinned_next.as_mut().poll(&mut cx).is_pending());
}

// Move stream to the heap.
let mut boxed_stream = Box::pin(stream);

let next = Next(&mut boxed_stream);
let mut pinned_next = Box::pin(next);
// This should panic (as the future is moved).
let _ = pinned_next.as_mut().poll(&mut cx).is_pending();

可选特性

• futures03 — 为assert-unmoved类型实现futures v0.3特性和类型。
• tokio1 — 为assert-unmoved类型实现tokio v1特性和类型。
• tokio03 — 为assert-unmoved类型实现tokio v0.3特性和类型。
• tokio02 — 为assert-unmoved类型实现tokio v0.2特性和类型。

注意：启用这些特性时的MSRV取决于这些Crate的MSRV。

许可证

许可根据您的选择，在Apache License, Version 2.0或MIT许可证下。

除非您明确声明，否则根据Apache-2.0许可证定义，您有意提交以包含在作品中的任何贡献，将采用上述双重许可，无需任何附加条款或条件。