From 1b6f721648a500f59eda475564238e787a1967d8 Mon Sep 17 00:00:00 2001
From: Steve Sanderson <SteveSandersonMS@users.noreply.github.com>
Date: Wed, 3 Jul 2019 16:19:10 +0100
Subject: [PATCH] Don't try to unsubscribe from fixed cascading parameters.
 Fixes #11653

---
 .../src/Rendering/ComponentState.cs           |  6 +++-
 .../Components/test/CascadingParameterTest.cs | 32 +++++++++++++------
 2 files changed, 28 insertions(+), 10 deletions(-)

diff --git a/src/Components/Components/src/Rendering/ComponentState.cs b/src/Components/Components/src/Rendering/ComponentState.cs
index 7aace974a0..bc9b7e3277 100644
--- a/src/Components/Components/src/Rendering/ComponentState.cs
+++ b/src/Components/Components/src/Rendering/ComponentState.cs
@@ -165,7 +165,11 @@ namespace Microsoft.AspNetCore.Components.Rendering
             var numCascadingParameters = _cascadingParameters.Count;
             for (var i = 0; i < numCascadingParameters; i++)
             {
-                _cascadingParameters[i].ValueSupplier.Unsubscribe(this);
+                var supplier = _cascadingParameters[i].ValueSupplier;
+                if (!supplier.CurrentValueIsFixed)
+                {
+                    supplier.Unsubscribe(this);
+                }
             }
         }
     }
diff --git a/src/Components/Components/test/CascadingParameterTest.cs b/src/Components/Components/test/CascadingParameterTest.cs
index f898fcb8eb..5f6a01e364 100644
--- a/src/Components/Components/test/CascadingParameterTest.cs
+++ b/src/Components/Components/test/CascadingParameterTest.cs
@@ -188,16 +188,25 @@ namespace Microsoft.AspNetCore.Components.Test
             var renderer = new TestRenderer();
             var component = new TestComponent(builder =>
             {
-                builder.OpenComponent<CascadingValue<string>>(0);
-                builder.AddAttribute(1, "Value", providedValue);
-                builder.AddAttribute(2, RenderTreeBuilder.ChildContent, new RenderFragment(childBuilder =>
+                // At the outer level, have an unrelated fixed cascading value to show we can deal with combining both types
+                builder.OpenComponent<CascadingValue<int>>(0);
+                builder.AddAttribute(1, "Value", 123);
+                builder.AddAttribute(2, "IsFixed", true);
+                builder.AddAttribute(3, RenderTreeBuilder.ChildContent, new RenderFragment(builder2 =>
                 {
-                    if (displayNestedComponent)
+                    // Then also have a non-fixed cascading value so we can show that unsubscription works
+                    builder2.OpenComponent<CascadingValue<string>>(0);
+                    builder2.AddAttribute(1, "Value", providedValue);
+                    builder2.AddAttribute(2, RenderTreeBuilder.ChildContent, new RenderFragment(builder3 =>
                     {
-                        childBuilder.OpenComponent<CascadingParameterConsumerComponent<string>>(0);
-                        childBuilder.AddAttribute(1, "RegularParameter", "Goodbye");
-                        childBuilder.CloseComponent();
-                    }
+                        if (displayNestedComponent)
+                        {
+                            builder3.OpenComponent<SecondCascadingParameterConsumerComponent<string, int>>(0);
+                            builder3.AddAttribute(1, "RegularParameter", "Goodbye");
+                            builder3.CloseComponent();
+                        }
+                    }));
+                    builder2.CloseComponent();
                 }));
                 builder.CloseComponent();
             });
@@ -219,7 +228,7 @@ namespace Microsoft.AspNetCore.Components.Test
             Assert.Equal(2, renderer.Batches.Count);
             var secondBatch = renderer.Batches[1];
             Assert.Equal(1, nestedComponent.NumRenders);
-            Assert.Equal(2, secondBatch.DiffsByComponentId.Count); // Root + CascadingValue, but not nested one
+            Assert.Equal(3, secondBatch.DiffsByComponentId.Count); // Root + CascadingValue + CascadingValue, but not nested component
 
             // We *did* send updated params during the first render where it was removed,
             // because the params are sent before the disposal logic runs. We could avoid
@@ -386,5 +395,10 @@ namespace Microsoft.AspNetCore.Components.Test
                 builder.AddContent(0, $"CascadingParameter={CascadingParameter}; RegularParameter={RegularParameter}");
             }
         }
+
+        class SecondCascadingParameterConsumerComponent<T1, T2> : CascadingParameterConsumerComponent<T1>
+        {
+            [CascadingParameter] T2 SecondCascadingParameter { get; set; }
+        }
     }
 }