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use std::{future::Future, pin::Pin, task};
use futures::stream;
// Combinators for futures that prevent waits, even when the underlying future
// would block.
//
// These are only useful for futures with no bound on how long they may wait,
// and this trait is only implemented on futures that are likely to have that
// characteristic. Trying to apply this to futures that already have some
// bounded wait time may make tests fail inappropriately and can hide other
// logic errors.
pub trait Expect: Sized {
// The returned future expects the underlying future to be ready immediately,
// and panics with the provided message if it is not.
//
// For stream operations, can be used to assert immediate completion.
fn expect_ready(self, message: &str) -> Ready<Self>
where
Self: Future;
// The returned future expects the underlying future _not_ to be ready, and
// panics if it is. This is usually a useful proxy for "I expect this to never
// arrive" or "to not be here yet." The future is transformed to return `()`,
// since the underlying future can never provide a value.
//
// For stream operations, can be used to assert that completion hasn't happened
// yet.
fn expect_wait(self, message: &str) -> Wait<Self>
where
Self: Future;
// The returned future expects the underlying future to resolve immediately, to
// a `Some` value. If it resolves to `None` or is not ready, it panics. The
// future is transformed to return the inner value from the `Some` case, like
// [`Option::expect`].
//
// For stream operations, can be used to assert that the stream has at least one
// message.
fn expect_some<T>(self, message: &str) -> Some<Self>
where
Self: Future<Output = Option<T>>;
// The returned future expects the underlying future to resolve immediately, to
// a `None` value. If it resolves to `Some(_)`, or is not ready, it panics. The
// future is transformed to return `()`, since the underlying future's value is
// fixed.
//
// For stream operations, can be used to assert that the stream has ended.
fn expect_none<T>(self, message: &str) -> None<Self>
where
Self: Future<Output = Option<T>>;
}
impl<St> Expect for stream::Next<'_, St> {
fn expect_ready(self, message: &str) -> Ready<Self> {
Ready {
future: self,
message,
}
}
fn expect_wait(self, message: &str) -> Wait<Self> {
Wait {
future: self,
message,
}
}
fn expect_some<T>(self, message: &str) -> Some<Self>
where
Self: Future<Output = Option<T>>,
{
Some {
future: self,
message,
}
}
fn expect_none<T>(self, message: &str) -> None<Self>
where
Self: Future<Output = Option<T>>,
{
None {
future: self,
message,
}
}
}
impl<St, C> Expect for stream::Collect<St, C> {
fn expect_ready(self, message: &str) -> Ready<Self> {
Ready {
future: self,
message,
}
}
fn expect_wait(self, message: &str) -> Wait<Self> {
Wait {
future: self,
message,
}
}
fn expect_some<T>(self, message: &str) -> Some<Self>
where
Self: Future<Output = Option<T>>,
{
Some {
future: self,
message,
}
}
fn expect_none<T>(self, message: &str) -> None<Self>
where
Self: Future<Output = Option<T>>,
{
None {
future: self,
message,
}
}
}
#[pin_project::pin_project]
pub struct Ready<'m, F> {
#[pin]
future: F,
message: &'m str,
}
impl<F> Future for Ready<'_, F>
where
F: Future + std::fmt::Debug,
{
type Output = F::Output;
fn poll(self: Pin<&mut Self>, cx: &mut task::Context<'_>) -> task::Poll<Self::Output> {
let this = self.project();
if let task::Poll::Ready(value) = this.future.poll(cx) {
task::Poll::Ready(value)
} else {
panic!("{}", this.message);
}
}
}
#[pin_project::pin_project]
pub struct Wait<'m, F> {
#[pin]
future: F,
message: &'m str,
}
impl<F> Future for Wait<'_, F>
where
F: Future + std::fmt::Debug,
{
type Output = ();
fn poll(self: Pin<&mut Self>, cx: &mut task::Context<'_>) -> task::Poll<Self::Output> {
let this = self.project();
if this.future.poll(cx).is_pending() {
task::Poll::Ready(())
} else {
panic!("{}", this.message);
}
}
}
#[pin_project::pin_project]
pub struct Some<'m, F> {
#[pin]
future: F,
message: &'m str,
}
impl<F, T> Future for Some<'_, F>
where
F: Future<Output = Option<T>> + std::fmt::Debug,
{
type Output = T;
fn poll(self: Pin<&mut Self>, cx: &mut task::Context<'_>) -> task::Poll<Self::Output> {
let this = self.project();
if let task::Poll::Ready(Option::Some(value)) = this.future.poll(cx) {
task::Poll::Ready(value)
} else {
panic!("{}", this.message)
}
}
}
#[pin_project::pin_project]
pub struct None<'m, F> {
#[pin]
future: F,
message: &'m str,
}
impl<F, T> Future for None<'_, F>
where
F: Future<Output = Option<T>> + std::fmt::Debug,
{
type Output = ();
fn poll(self: Pin<&mut Self>, cx: &mut task::Context<'_>) -> task::Poll<Self::Output> {
let this = self.project();
if let task::Poll::Ready(Option::None) = this.future.poll(cx) {
task::Poll::Ready(())
} else {
panic!("{}", this.message)
}
}
}
|
