[Observation] Restrict deinitialization fired events to be limited to one per registrar and send a \Self.self as the keypath to avoid property confusions

Author: phausler

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

@@ -110,20 +110,27 @@ public struct ObservationRegistrar: Sendable {
       }
     }
 
-    internal mutating func deinitialize() -> [@Sendable () -> Void] {
-      var trackers = [@Sendable () -> Void]()
+    internal mutating func deinitialize() -> (@Sendable () -> Void)? {
+      func extractSelf<T>(_ ty: T.Type) -> AnyKeyPath {
+        return \T.self
+      }
+
+      var tracker: (@Sendable () -> Void)?
       for (keyPath, ids) in lookups {
         for id in ids {
-          if let tracker = observations[id]?.willSetTracker {
-             trackers.append({
-               tracker(keyPath)
-             })
+          if let found = observations[id]?.willSetTracker {
+            // convert the keyPath into its \Self.self version 
+            let selfKp = _openExistential(type(of: keyPath).rootType, do: extractSelf)
+            found = {
+               tracker(selfKp)
+            }
+            break
           }
         }
       }
       observations.removeAll()
       lookups.removeAll()
-      return trackers
+      return tracker
     }
 
     internal mutating func willSet(keyPath: AnyKeyPath) -> [@Sendable (AnyKeyPath) -> Void] {
@@ -169,10 +176,7 @@ public struct ObservationRegistrar: Sendable {
     }
 
     internal func deinitialize() {
-      let tracking = state.withCriticalRegion { $0.deinitialize() }
-      for action in tracking {
-        action()
-      }
+      state.withCriticalRegion { $0.deinitialize() }?()
     }
 
     internal func willSet<Subject: Observable, Member>(

test/stdlib/Observation/Observable.swift

@@ -290,6 +290,7 @@ final class CowTest {
 @Observable
 final class DeinitTriggeredObserver {
   var property: Int = 3
+  var property2: Int = 4
   let deinitTrigger: () -> Void
 
   init(_ deinitTrigger: @escaping () -> Void) {
@@ -528,17 +529,18 @@ struct Validator {
 
     suite.test("weak container observation") {
       let changed = CapturedState(state: false)
-      let deinitialized = CapturedState(state: false)
+      let deinitialized = CapturedState(state: 0)
       var test = DeinitTriggeredObserver {
-        deinitialized.state = true
+        deinitialized.state += 1
       }
       withObservationTracking { [weak test] in
         _blackHole(test?.property)
+        _blackHole(test?.property2)
       } onChange: {
         changed.state = true
       }
       test = DeinitTriggeredObserver { }
-      expectEqual(deinitialized.state, true)
+      expectEqual(deinitialized.state, 1) // ensure only one invocation is done per deinitialization
       expectEqual(changed.state, true)
     }