Add Publishers.AgainAt

[atdrendel]

• Add Publishers.AgainAt
• Add comprehensive test coverage for existing publishers

[atdrendel]

@copilot Update the README.md to ensure it is up-to-date. The next version will be v6.1.0

[Copilot]

@copilot Update the README.md to ensure it is up-to-date. The next version will be v6.1.0

Done in a74f63a. The README now lists all publishers (including AgainAt, Distinct, MulticastLatest), adds an Extensions section (Cancellable.onCancel(), Publisher.sink()), a Schedulers section (TestScheduler, UIScheduler), and updates the version reference to 6.1.0.

[Copilot]

Pull request overview

Adds a new Combine operator Publishers.AgainAt / Publisher.againAt(scheduler:options:) that pairs each emitted value with a timer object that can schedule re-publication of the latest value at a requested scheduler time. Also expands unit test coverage across many existing publishers/operators in CombineExtensions and helpers in CombineTestExtensions.

Changes:

• Introduce Publishers.AgainAt operator and extensive behavioral tests (republish scheduling, demand handling, cancellation/completion behavior).
• Add/expand test coverage for multiple existing operators (distinct, enumerate, reduceLatest, retryIf, throttleWhile, stream publishers, subscription stores, etc.).
• Minor cleanup and concurrency annotation updates (e.g., _Expectation Sendable annotation, small formatting updates).

Reviewed changes

Copilot reviewed 22 out of 22 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
Tests/CombineExtensionsTests/UISchedulerTests.swift	Adds coverage for UIScheduler.now/minimumTolerance mirroring main queue.
Tests/CombineExtensionsTests/ThrottleWhileTests.swift	Adds more edge-case tests (completion/failure while throttled, regulator timing), plus whitespace cleanup.
Tests/CombineExtensionsTests/TestSchedulerTests.swift	Adds more behavioral tests around run/advance, ordering, and interval cancellation.
Tests/CombineExtensionsTests/SingleSubscriptionStoreTests.swift	Adds tests for initializer behavior and replacement/removal semantics.
Tests/CombineExtensionsTests/RetryIfTests.swift	Adds additional tests for retry convenience and cancellation/attempt counting behavior.
Tests/CombineExtensionsTests/ReduceLatestTests.swift	Adds demand/backpressure and completion/failure/cancel tests with a manual subscriber helper.
Tests/CombineExtensionsTests/PublisherTestExtensionsTests.swift	Adds tests for various expectation helpers and updates call-site formatting.
Tests/CombineExtensionsTests/PublisherSinkTests.swift	New tests for sink overloads in CombineExtensions.
Tests/CombineExtensionsTests/OutputStreamPublisherTests.swift	Adds tests around demand forwarding, failure behavior, and append-to-URL semantics; minor formatting cleanup.
Tests/CombineExtensionsTests/OnCancelTests.swift	Adds tests to validate ordering and “only once” behavior of onCancel, plus a spy cancellable helper.
Tests/CombineExtensionsTests/MulticastLatestTests.swift	Adds tests for late subscribers, no initial emission, and completion/failure propagation; minor formatting cleanup.
Tests/CombineExtensionsTests/KeyedSubscriptionStoreTests.swift	Adds tests for initializer, replacement cancellation, and removed-subscription lifetime behavior.
Tests/CombineExtensionsTests/InputStreamPublisherTests.swift	Adds tests for empty inputs, demand-driven chunking, and empty file behavior with a manual subscriber helper.
Tests/CombineExtensionsTests/EnumeratedTests.swift	Adds tests for negative start index, per-subscriber state isolation, and failure propagation.
Tests/CombineExtensionsTests/DistinctTests.swift	Adds tests for empty/duplicate dropping and subscriber state behavior; minor loop refactor in concurrency test.
Tests/CombineExtensionsTests/BufferPassthroughSubjectTests.swift	Adds tests around buffered demand, buffered completion, post-completion behavior, and repeated completion; adds manual-demand subscriber helper.
Tests/CombineExtensionsTests/AnyConnectablePublisherTests.swift	Adds tests ensuring erased connectable publisher forwards, connects, autoconnects, and cancels properly.
Tests/CombineExtensionsTests/AgainAtTests.swift	New comprehensive test suite for againAt/Publishers.AgainAt.
Sources/CombineTestExtensions/Publisher+Test.swift	Marks internal _Expectation as @unchecked Sendable.
Sources/CombineExtensions/MulticastLatest.swift	Minor formatting change to multicast factory closure style.
Sources/CombineExtensions/AgainAt.swift	New implementation of Publishers.AgainAt and Publisher.againAt(...).

Comments suppressed due to low confidence (1)

Sources/CombineTestExtensions/Publisher+Test.swift:532

• _Expectation is now marked @unchecked Sendable, but it has mutable state (token, fulfillmentCount) that is mutated in fulfill(). If fulfill() can be invoked from multiple threads (e.g., when expectations are fulfilled from publishers emitting on different queues), this becomes a potential data race. Consider protecting the mutable state with synchronization (lock/atomic), or ensuring fulfill() and token cancellation always run on a single executor/queue before asserting Sendable conformance.

private class _Expectation: XCTestExpectation, @unchecked Sendable {
    var token: AnyCancellable?

    private var fulfillmentCount: Int = 0

    override func fulfill() {
        super.fulfill()

        fulfillmentCount += 1
        if fulfillmentCount == expectedFulfillmentCount {
            token?.cancel()
            token = nil
        }
    }

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