[Observation] ensure event triggers on deinitialization passes as if all properties that are being observed have changed (for weak storage) (#79823)

* [Observation] ensure event triggers on deinitialziation passes as if all properties that are being observed have changed (for weak storage)

* Add missing deinitialize method for synthetically triggering willSet

* Correct the weak location for tests

* Correct the test to actually test the deinitialization willSet trigger instead of testing weak value deinitialization time

* Refine the tests for deinit triggers to more tightly trigger deinitialization and weak references

* Correct missing trailing closure on deinit replacement

* Ensure all potential ids are triggered at the deinitialization edge trigger

Author: phausler

stdlib/public/Observation/Sources/Observation/ObservationRegistrar.swift

@@ -110,9 +110,20 @@ public struct ObservationRegistrar: Sendable {
       }
     }
 
-    internal mutating func cancelAll() {
+    internal mutating func deinitialize() -> [@Sendable () -> Void] {
+      var trackers = [@Sendable () -> Void]()
+      for (keyPath, ids) in lookups {
+        for id in ids {
+          if let tracker = observations[id]?.willSetTracker {
+             trackers.append({
+               tracker(keyPath)
+             })
+          }
+        }
+      }
       observations.removeAll()
       lookups.removeAll()
+      return trackers
     }
 
     internal mutating func willSet(keyPath: AnyKeyPath) -> [@Sendable (AnyKeyPath) -> Void] {
@@ -157,8 +168,11 @@ public struct ObservationRegistrar: Sendable {
       state.withCriticalRegion { $0.cancel(id) }
     }
 
-    internal func cancelAll() {
-      state.withCriticalRegion { $0.cancelAll() }
+    internal func deinitialize() {
+      let tracking = state.withCriticalRegion { $0.deinitialize() }
+      for action in tracking {
+        action()
+      }
     }
 
     internal func willSet<Subject: Observable, Member>(
@@ -189,7 +203,7 @@ public struct ObservationRegistrar: Sendable {
     }
 
     deinit {
-      context.cancelAll()
+      context.deinitialize()
     }
   }
 

test/stdlib/Observation/Observable.swift

@@ -287,6 +287,21 @@ final class CowTest {
   var container = CowContainer()
 }
 
+@Observable
+final class DeinitTriggeredObserver {
+  var property: Int = 3
+  let deinitTrigger: () -> Void
+
+  init(_ deinitTrigger: @escaping () -> Void) {
+    self.deinitTrigger = deinitTrigger
+  }
+
+  deinit {
+    deinitTrigger()
+  }
+}
+
+
 @main
 struct Validator {
   @MainActor
@@ -511,6 +526,22 @@ struct Validator {
       expectEqual(subject.container.id, startId)
     }
 
+    suite.test("weak container observation") {
+      let changed = CapturedState(state: false)
+      let deinitialized = CapturedState(state: false)
+      var test = DeinitTriggeredObserver {
+        deinitialized.state = true
+      }
+      withObservationTracking { [weak test] in
+        _blackHole(test?.property)
+      } onChange: {
+        changed.state = true
+      }
+      test = DeinitTriggeredObserver { }
+      expectEqual(deinitialized.state, true)
+      expectEqual(changed.state, true)
+    }
+
     runAllTests()
   }
 }