futures-core 0.3.34

# This file is automatically @generated by Cargo.
# It is not intended for manual editing.
version = 4

[[package]]
name = "futures-core"
version = "0.3.34"
source = "registry+https://github.com/rust-lang/crates.io-index"
checksum = "92d699e522242e69e3003b94ecc1f960f3a5e015aa7c5d7486e65ad01dd94f5e"

[[package]]
name = "sample-futures-core"
version = "1.0.0"
dependencies = [
 "futures-core",
]

[package]
name = "sample-futures-core"
version = "1.0.0"
edition = "2021"
publish = false

[dependencies]
futures-core = "=0.3.34"

[[bin]]
name = "contract"
path = "test/contract.rs"

Clean-room public code sample — generation instructions

Write a brand-new, minimal, self-contained code sample in this clean-room directory.
Do not copy, paraphrase, or reference any existing project source. Work only from this spec.

A csx.json manifest scaffold already exists. Do not recreate it from memory. Preserve its case.goal, packages and symbols; fill its empty case.contract with exact assertions and correct its environment, commands and verifierAdapter for the files you generate.

Goal: verify pkg:cargo/futures-core@0.3.34
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:cargo/futures-core@0.3.34

Rules:
  - One focused purpose; the smallest project that proves the goal.
  - Include a contract test (test/contract.*) that runs OFFLINE and exits 0 exactly when the goal behavior works.
  - Pin every dependency with a lockfile so resolution is reproducible.
  - No secrets, credentials, or tokens. No real URLs (only example.com or localhost). No absolute paths.
  - No personal names, emails, company names, or project identifiers of any kind.
  - No binaries and no generated output (node_modules, dist, target, venv, .git, .env).
  - Keep it under 200 files and 256KB packed.

{"case":{"caseId":"case:sha256:679b1619ea7a27408ede048053c8967a38c1c8ee4686ffde1c693e4bbbf37066","contract":["Stream trait implementation emits items and signals completion","Stream size_hint correctly calculates remaining elements","TryFuture blanket implementation enables try_poll on Result futures"],"goal":"verify pkg:cargo/futures-core@0.3.34","kind":"HOW","packages":["pkg:cargo/futures-core@0.3.34"],"schemaVersion":1},"contractCommand":["cargo","run","--offline"],"environment":{"arch":"x64","distro":"alpine","ecosystem":"cargo","libc":"musl","os":"linux","packageManager":"cargo","schemaVersion":1},"license":"MIT-0","packages":["pkg:cargo/futures-core@0.3.34"],"schemaVersion":1,"subject":"pkg:cargo/futures-core@0.3.34","verifierAdapter":"cargo@1"}

{
  "schemaVersion": 1,
  "goal": "verify pkg:cargo/futures-core@0.3.34",
  "kind": "HOW",
  "packages": [
    "pkg:cargo/futures-core@0.3.34"
  ]
}

//! Clean-room verification sample for futures-core.

pub use futures_core::*;

use core::pin::Pin;
use core::task::{Context, Poll, RawWaker, RawWakerVTable, Waker};
use futures_core::future::TryFuture;
use futures_core::stream::Stream;

fn dummy_waker() -> Waker {
    fn noop(_: *const ()) {}
    fn clone(p: *const ()) -> RawWaker {
        RawWaker::new(p, &VTABLE)
    }
    static VTABLE: RawWakerVTable = RawWakerVTable::new(clone, noop, noop, noop);
    unsafe { Waker::from_raw(RawWaker::new(core::ptr::null(), &VTABLE)) }
}

struct CounterStream {
    current: usize,
    limit: usize,
}

impl CounterStream {
    fn new(limit: usize) -> Self {
        Self { current: 0, limit }
    }
}

impl Stream for CounterStream {
    type Item = usize;

    fn poll_next(mut self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
        if self.current < self.limit {
            self.current += 1;
            Poll::Ready(Some(self.current))
        } else {
            Poll::Ready(None)
        }
    }

    fn size_hint(&self) -> (usize, Option<usize>) {
        let remaining = self.limit - self.current;
        (remaining, Some(remaining))
    }
}

struct ReadyTryFuture<T, E> {
    result: Option<Result<T, E>>,
}

impl<T: Unpin, E: Unpin> core::future::Future for ReadyTryFuture<T, E> {
    type Output = Result<T, E>;

    fn poll(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<Self::Output> {
        match self.get_mut().result.take() {
            Some(res) => Poll::Ready(res),
            None => Poll::Pending,
        }
    }
}

fn main() {
    let waker = dummy_waker();
    let mut cx = Context::from_waker(&waker);

    // 1. Stream trait implementation emits items and signals completion
    let mut stream = CounterStream::new(3);
    let mut pinned_stream = Pin::new(&mut stream);
    assert_eq!(pinned_stream.as_mut().poll_next(&mut cx), Poll::Ready(Some(1)));
    assert_eq!(pinned_stream.as_mut().poll_next(&mut cx), Poll::Ready(Some(2)));
    assert_eq!(pinned_stream.as_mut().poll_next(&mut cx), Poll::Ready(Some(3)));
    assert_eq!(pinned_stream.as_mut().poll_next(&mut cx), Poll::Ready(None));

    // 2. Stream size_hint correctly calculates remaining elements
    let mut stream2 = CounterStream::new(2);
    assert_eq!(stream2.size_hint(), (2, Some(2)));
    let mut pinned_stream2 = Pin::new(&mut stream2);
    let _ = pinned_stream2.as_mut().poll_next(&mut cx);
    assert_eq!(pinned_stream2.size_hint(), (1, Some(1)));
    let _ = pinned_stream2.as_mut().poll_next(&mut cx);
    assert_eq!(pinned_stream2.size_hint(), (0, Some(0)));

    // 3. TryFuture blanket implementation enables try_poll on Result futures
    let mut ok_fut = ReadyTryFuture { result: Some(Ok::<i32, &'static str>(42)) };
    let mut pinned_ok = Pin::new(&mut ok_fut);
    assert_eq!(pinned_ok.as_mut().try_poll(&mut cx), Poll::Ready(Ok(42)));

    let mut err_fut = ReadyTryFuture { result: Some(Err::<i32, &'static str>("failed")) };
    let mut pinned_err = Pin::new(&mut err_fut);
    assert_eq!(pinned_err.as_mut().try_poll(&mut cx), Poll::Ready(Err("failed")));

    println!("All futures-core contract assertions passed.");
}