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7954: stream: impl FromStream for BTreeSet #74

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b0439d8
stream: impl FromStream for BTreeSet
figsoda Mar 6, 2026
d4bded6
Merge branch 'master' into stream-btreeset
figsoda Mar 7, 2026
090a530
Merge branch 'master' into stream-btreeset
Darksonn Mar 9, 2026
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20 changes: 20 additions & 0 deletions tokio-stream/src/stream_ext/collect.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -6,6 +6,7 @@ use core::mem;
use core::pin::Pin;
use core::task::{ready, Context, Poll};
use pin_project_lite::pin_project;
use std::collections::BTreeSet;

// Do not export this struct until `FromStream` can be unsealed.
pin_project! {
Expand Down Expand Up @@ -135,6 +136,25 @@ impl<T> sealed::FromStreamPriv<T> for Vec<T> {
}
}

impl<T: Ord> FromStream<T> for BTreeSet<T> {}

impl<T: Ord> sealed::FromStreamPriv<T> for BTreeSet<T> {
type InternalCollection = BTreeSet<T>;

fn initialize(_: sealed::Internal, _lower: usize, _upper: Option<usize>) -> BTreeSet<T> {
BTreeSet::new()
}

fn extend(_: sealed::Internal, collection: &mut BTreeSet<T>, item: T) -> bool {
collection.insert(item);
true
}

fn finalize(_: sealed::Internal, collection: &mut BTreeSet<T>) -> BTreeSet<T> {
mem::take(collection)
}
}

impl<T> FromStream<T> for Box<[T]> {}

impl<T> sealed::FromStreamPriv<T> for Box<[T]> {
Expand Down
23 changes: 23 additions & 0 deletions tokio-stream/tests/stream_collect.rs
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Original file line number Diff line number Diff line change
@@ -1,3 +1,5 @@
use std::collections::BTreeSet;

use tokio_stream::{self as stream, StreamExt};
use tokio_test::{assert_pending, assert_ready, assert_ready_err, assert_ready_ok, task};

Expand Down Expand Up @@ -61,6 +63,27 @@ async fn collect_vec_items() {
assert_eq!(vec![1, 2], coll);
}

#[tokio::test]
async fn collect_btreeset_items() {
let (tx, rx) = mpsc::unbounded_channel_stream();
let mut fut = task::spawn(rx.collect::<BTreeSet<i32>>());

assert_pending!(fut.poll());

tx.send(2).unwrap();
assert!(fut.is_woken());
assert_pending!(fut.poll());

tx.send(1).unwrap();
assert!(fut.is_woken());
assert_pending!(fut.poll());
Comment on lines +77 to +79
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@gemini-code-assist gemini-code-assist bot Mar 9, 2026

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medium

This test correctly verifies ordering. To make it more comprehensive, consider also verifying that BTreeSet's uniqueness property is handled correctly by sending a duplicate item.

Suggested change
tx.send(1).unwrap();
assert!(fut.is_woken());
assert_pending!(fut.poll());
tx.send(1).unwrap();
assert!(fut.is_woken());
assert_pending!(fut.poll());
// Send a duplicate item.
tx.send(2).unwrap();
assert!(fut.is_woken());
assert_pending!(fut.poll());

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@martin-augment martin-augment Mar 9, 2026

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value:good-to-have; category:bug; feedback: The Gemini AI reviewer is correct! Currently the test verifies that the items in the BTreeSet are ordered (2 is sent first but it is printed after 1 in the final result). It would be good to extend the test with sending a duplicate (either 1 or 2) and verifying that there is only one occurrence of it in the result.


drop(tx);
assert!(fut.is_woken());
let coll = assert_ready!(fut.poll());
assert_eq!(BTreeSet::from([1, 2]), coll);
}

#[tokio::test]
async fn collect_string_items() {
let (tx, rx) = mpsc::unbounded_channel_stream();
Expand Down