Fix ContentPathObservers.notifyPathChanged

Sources/OpenSwiftUICore/Event/Responder/LeafViewResponder.swift

@@ -32,13 +32,12 @@ struct ContentPathObservers {
     mutating func notifyPathChanged(for parent: ViewResponder, changes: ContentPathChanges, transform: (old: ViewTransform, new: ViewTransform)) {
         let oldObservers = observers
         observers = []
-        var failedObservers: [Observer] = []
         for observer in oldObservers {
             var result = true
             guard let value = observer.value else { continue }
             value.contentPathDidChange(for: parent, changes: changes, transform: transform, finished: &result)
             guard !result else { continue }
-            failedObservers.append(observer)
+            observers.append(observer)
         }
     }
 }

Tests/OpenSwiftUICoreTests/Event/ContentPathObserverTests.swift

@@ -0,0 +1,46 @@
+//
+//  ContentPathObserverTests.swift
+//  OpenSwiftUICoreTests
+
+@_spi(ForOpenSwiftUIOnly) import OpenSwiftUICore
+@testable import OpenSwiftUICore
+import Testing
+
+struct ContentPathObserverTests {
+    @Test
+    func unfinishedObserverIsRetainedUntilFinished() {
+        var observers = ContentPathObservers()
+        let observer = TestContentPathObserver()
+        // The test observer does not inspect its parent. Avoid constructing a
+        // ViewResponder, whose public initializer requires a live ViewGraph.
+        let parentObject: AnyObject = ResponderNode()
+        let parent = unsafeBitCast(parentObject, to: ViewResponder.self)
+        let transform = (old: ViewTransform(), new: ViewTransform())
+
+        observers.addObserver(observer)
+        observers.notifyPathChanged(for: parent, changes: [], transform: transform)
+        #expect(observer.callCount == 1)
+
+        observers.notifyPathChanged(for: parent, changes: [], transform: transform)
+        #expect(observer.callCount == 2)
+
+        observers.notifyPathChanged(for: parent, changes: [], transform: transform)
+        #expect(observer.callCount == 2)
+    }
+}
+
+private final class TestContentPathObserver: ContentPathObserver {
+    private(set) var callCount = 0
+
+    func respondersDidChange(for parent: ViewResponder) {}
+
+    func contentPathDidChange(
+        for parent: ViewResponder,
+        changes: ContentPathChanges,
+        transform: (old: ViewTransform, new: ViewTransform),
+        finished: inout Bool
+    ) {
+        callCount += 1
+        finished = callCount >= 2
+    }
+}