Fix iOS 14 Cancellation Crash (#244)

* wip

* wip

Co-authored-by: Brandon Williams <mbw234@gmail.com>

Sources/ComposableArchitecture/Effects/Cancellation.swift

@@ -27,6 +27,30 @@ extension Effect {
   ///     canceled before starting this new one.
   /// - Returns: A new effect that is capable of being canceled by an identifier.
   public func cancellable(id: AnyHashable, cancelInFlight: Bool = false) -> Effect {
+    // NB: This check intends to work around bugs over different versions of Combine
+    #if swift(>=5.3) && !os(macOS)
+    let effect = Deferred<
+      Publishers.PrefixUntilOutput<Publishers.HandleEvents<Self>, PassthroughSubject<Void, Never>>
+    > {
+      let subject = PassthroughSubject<Void, Never>()
+      lock.sync { subjects[id, default: []].append(subject) }
+      let cleanup = {
+        lock.sync {
+          subjects[id]?.removeAll(where: { $0 === subject })
+          if subjects[id]?.isEmpty == true {
+            subjects[id] = nil
+          }
+        }
+      }
+      return self
+        .handleEvents(
+          receiveCompletion: { _ in cleanup() },
+          receiveCancel: cleanup
+        )
+        .prefix(untilOutputFrom: subject)
+    }
+    .eraseToEffect()
+    #else
     let effect = Deferred { () -> Publishers.HandleEvents<PassthroughSubject<Output, Failure>> in
       cancellablesLock.lock()
       defer { cancellablesLock.unlock() }
@@ -56,6 +80,7 @@ extension Effect {
       )
     }
     .eraseToEffect()
+    #endif
 
     return cancelInFlight ? .concatenate(.cancel(id: id), effect) : effect
   }
@@ -66,13 +91,26 @@ extension Effect {
   /// - Returns: A new effect that will cancel any currently in-flight effect with the given
   ///   identifier.
   public static func cancel(id: AnyHashable) -> Effect {
+    #if swift(>=5.3) && !os(macOS)
+    return .fireAndForget {
+      lock.sync {
+        subjects[id]?.forEach { $0.send(()) }
+      }
+    }
+    #else
     return .fireAndForget {
       cancellablesLock.sync {
         cancellationCancellables[id]?.forEach { $0.cancel() }
       }
     }
+    #endif
   }
 }
 
+#if swift(>=5.3) && !os(macOS)
+var subjects: [AnyHashable: [PassthroughSubject<Void, Never>]] = [:]
+let lock = NSRecursiveLock()
+#else
 var cancellationCancellables: [AnyHashable: Set<AnyCancellable>] = [:]
 let cancellablesLock = NSRecursiveLock()
+#endif

Tests/ComposableArchitectureTests/EffectCancellationTests.swift

@@ -116,7 +116,11 @@ final class EffectCancellationTests: XCTestCase {
       .sink(receiveValue: { _ in })
       .store(in: &self.cancellables)
 
-    XCTAssertEqual([:], cancellationCancellables)
+    #if swift(>=5.3) && !os(macOS)
+    XCTAssertTrue(subjects.isEmpty)
+    #else
+    XCTAssertTrue(cancellationCancellables.isEmpty)
+    #endif
   }
 
   func testCancellablesCleanUp_OnCancel() {
@@ -132,7 +136,11 @@ final class EffectCancellationTests: XCTestCase {
       .sink(receiveValue: { _ in })
       .store(in: &self.cancellables)
 
-    XCTAssertEqual([:], cancellationCancellables)
+    #if swift(>=5.3) && !os(macOS)
+    XCTAssertTrue(subjects.isEmpty)
+    #else
+    XCTAssertTrue(cancellationCancellables.isEmpty)
+    #endif
   }
 
   func testDoubleCancellation() {
@@ -222,7 +230,11 @@ final class EffectCancellationTests: XCTestCase {
       .store(in: &self.cancellables)
     self.wait(for: [expectation], timeout: 999)
 
+    #if swift(>=5.3) && !os(macOS)
+    XCTAssertTrue(subjects.isEmpty)
+    #else
     XCTAssertTrue(cancellationCancellables.isEmpty)
+    #endif
   }
 
   func testNestedCancels() {
@@ -240,7 +252,11 @@ final class EffectCancellationTests: XCTestCase {
 
     cancellables.removeAll()
 
-    XCTAssertEqual([:], cancellationCancellables)
+    #if swift(>=5.3) && !os(macOS)
+    XCTAssertTrue(subjects.isEmpty)
+    #else
+    XCTAssertTrue(cancellationCancellables.isEmpty)
+    #endif
   }
 
   func testSharedId() {