From 7c8bda2463a187c62f2a993fbb3ccf94117436d6 Mon Sep 17 00:00:00 2001
From: Jiaxu Li <138670014+Jiaxu-Li@users.noreply.github.com>
Date: Fri, 19 Dec 2025 23:31:39 +0800
Subject: [PATCH] [Observations] Prevent duplicate emissions on re-iterating
 Observations after cancellation

Fix #85683: avoid duplicated values when re-iterating `Observations` after cancelling a prior iteration.

This changes `Observations` to allocate its internal `_ManagedCriticalState<State>` per iterator (in `makeAsyncIterator()`), rather than sharing a single state across all iterations. Sharing state allowed change notifications from a cancelled iteration to interfere with subsequent iterations, resulting in duplicated emissions.
---
 .../public/Observation/Sources/Observation/Observations.swift | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/stdlib/public/Observation/Sources/Observation/Observations.swift b/stdlib/public/Observation/Sources/Observation/Observations.swift
index 3aa6d91ba56c6..ff82b96b81a8b 100644
--- a/stdlib/public/Observation/Sources/Observation/Observations.swift
+++ b/stdlib/public/Observation/Sources/Observation/Observations.swift
@@ -133,7 +133,6 @@ public struct Observations<Element: Sendable, Failure: Error>: AsyncSequence, Se
   // internal funnel method for initialziation
   internal init(emit: Emit) {
     self.emit = emit
-    self.state = _ManagedCriticalState(State())
   }
   
   /// Constructs an asynchronous sequence for a given closure by tracking changes of `@Observable` types.
@@ -167,7 +166,6 @@ public struct Observations<Element: Sendable, Failure: Error>: AsyncSequence, Se
     // the state ivar serves two purposes:
     // 1) to store a critical region of state of the mutations
     // 2) to idenitify the termination of _this_ sequence
-    var state: _ManagedCriticalState<State>?
     let emit: Emit
     var started = false
     
@@ -251,6 +249,6 @@ public struct Observations<Element: Sendable, Failure: Error>: AsyncSequence, Se
   }
   
   public func makeAsyncIterator() -> Iterator {
-    Iterator(state: state, emit: emit)
+     Iterator(state: _ManagedCriticalState(State()), emit: emit)
   }
 }