Disposed change token registration should not raise consumer (#79966)

Author: mapogolions

src/libraries/Microsoft.Extensions.Primitives/src/ChangeToken.cs

@@ -98,9 +98,12 @@ private void RegisterChangeTokenCallback(IChangeToken? token)
                 {
                     return;
                 }
-
                 IDisposable registraton = token.RegisterChangeCallback(s => ((ChangeTokenRegistration<TState>?)s)!.OnChangeTokenFired(), this);
-
+                if (token.HasChanged && token.ActiveChangeCallbacks)
+                {
+                    registraton?.Dispose();
+                    return;
+                }
                 SetDisposable(registraton);
             }
 

src/libraries/Microsoft.Extensions.Primitives/tests/ChangeTokenTest.cs

@@ -179,6 +179,28 @@ public void DisposingChangeTokenRegistrationDoesNotRaiseConsumerCallbackStateOve
             Assert.Equal(5, count);
         }
 
+        [Fact]
+        public void DisposingChangeTokenRegistrationDoesNotRaiseConsumerIfTokenProviderReturnsCancelledToken()
+        {
+            var provider = new ResettableChangeTokenProvider();
+            Func<Func<IChangeToken>> changeTokenProviderFactory = () =>
+            {
+                int n = 0;
+                return () =>
+                {
+                    var token = provider.GetChangeToken();
+                    if (n++ is 0) provider.Changed();
+                    return token;
+                };
+            };
+            int count = 0;
+            var reg = ChangeToken.OnChange(changeTokenProviderFactory(), () => count++);
+            reg.Dispose();
+            provider.Changed();
+
+            Assert.Equal(1, count);
+        }
+
         [Fact]
         public void DisposingChangeTokenRegistrationDuringCallbackWorks()
         {