In SSR, supply HttpContext as cascading value (#50253)

Fixes #48769

### Usage

```cs
[CascadingParameter] public HttpContext? Context { get; set; }
```

In SSR, this will receive the `HttpContext`. In other rendering modes where there is no HTTP context, no value will be supplied so the property will remain `null`.

### Alternative design considered

In #48769 I suggested using `[SupplyParameterFromHttpContext]` but that turns out not to be practical unless we either (a) make `ICascadingValueSupplier` public, or (b) add an IVT from `M.A.Components` to `.Endpoints`.

I'm not keen on doing either of the above on a whim. Plus, use of `[CascadingValue]` has advantages:

 * It's consistent with the existing pattern for authentication state (we have `[CascadingParameter] Task<AuthenticationState> AuthenticationStateTask { get; set; }`).
 * Longer term, if we add more things like this, it would be nice not to add a separate special attribute for each one when `[CascadingParameter]` is already descriptive enough. Special attributes are needed only when the type of thing being supplied might reasonably clash with something else the application is doing (for example, we do need it for form/query, as they supply arbitrary types).

## Review notes

It's best to look at the two commits in this PR completely separately:

1. The first commit fixes an API design problem I discovered while considering how to do this. I realised that when we added `CascadingParameterAttributeBase`, we made a design mistake:
   * We put the `Name` property on the abstract base class just because `CascadingParameterAttribute`, `SupplyParameterFromQuery`, and `SupplyParameterFromForm` all have a `Name`.
   * However, in all three cases there, the `Name` has completely different meanings. For `CascadingParameterAttribute`, it's the name associated with `<CascadingValue Name=...>`, whereas for form it's the `Request.Form` entry or fall back on property name, and for query it's the `Request.Query` entry or fall back on property name. In general there's no reason why a `CascadingParameterAttributeBase` subclass should have a `Name` at all (`SupplyParameterFromHttpContext` wasn't going to), and if it does have one, its semantics are specific to it. So these should not be the same properties.
   * The change we made to make `CascadingParameterAttribute.Name` virtual might even be breaking (see https://learn.microsoft.com/en-us/dotnet/core/compatibility/library-change-rules stating *DISALLOWED: Adding the virtual keyword to a member*). So it's good we can revert that here.
2. The second commit is the completely trivial implementation of supplying `HttpContext` as a cascading value, with an E2E test.

src/Components/Components/src/CascadingParameterAttribute.cs

@@ -20,5 +20,5 @@ public sealed class CascadingParameterAttribute : CascadingParameterAttributeBas
     /// <see cref="CascadingValue{T}"/>  that supplies a value with a compatible
     /// type.
     /// </summary>
-    public override string? Name { get; set; }
+    public string? Name { get; set; }
 }

src/Components/Components/src/CascadingParameterAttributeBase.cs

@@ -8,12 +8,6 @@ namespace Microsoft.AspNetCore.Components;
 /// </summary>
 public abstract class CascadingParameterAttributeBase : Attribute
 {
-    /// <summary>
-    /// Gets or sets the name for the parameter, which correlates to the name
-    /// of a cascading value.
-    /// </summary>
-    public abstract string? Name { get; set; }
-
     /// <summary>
     /// Gets a flag indicating whether the cascading parameter should
     /// be supplied only once per component.

src/Components/Components/src/CascadingValueServiceCollectionExtensions.cs

@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using Microsoft.AspNetCore.Components;
+using Microsoft.Extensions.DependencyInjection.Extensions;
 
 namespace Microsoft.Extensions.DependencyInjection;
 
@@ -50,4 +51,59 @@ public static IServiceCollection AddCascadingValue<TValue>(
     public static IServiceCollection AddCascadingValue<TValue>(
         this IServiceCollection serviceCollection, Func<IServiceProvider, CascadingValueSource<TValue>> sourceFactory)
         => serviceCollection.AddScoped<ICascadingValueSupplier>(sourceFactory);
+
+    /// <summary>
+    /// Adds a cascading value to the <paramref name="serviceCollection"/>, if none is already registered
+    /// with the value type. This is equivalent to having a fixed <see cref="CascadingValue{TValue}"/> at
+    /// the root of the component hierarchy.
+    /// </summary>
+    /// <typeparam name="TValue">The value type.</typeparam>
+    /// <param name="serviceCollection">The <see cref="IServiceCollection"/>.</param>
+    /// <param name="valueFactory">A callback that supplies a fixed value within each service provider scope.</param>
+    /// <returns>The <see cref="IServiceCollection"/>.</returns>
+    public static void TryAddCascadingValue<TValue>(
+        this IServiceCollection serviceCollection, Func<IServiceProvider, TValue> valueFactory)
+    {
+        serviceCollection.TryAddEnumerable(
+            ServiceDescriptor.Scoped<ICascadingValueSupplier, CascadingValueSource<TValue>>(
+                sp => new CascadingValueSource<TValue>(() => valueFactory(sp), isFixed: true)));
+    }
+
+    /// <summary>
+    /// Adds a cascading value to the <paramref name="serviceCollection"/>, if none is already registered
+    /// with the value type, regardless of the <paramref name="name"/>. This is equivalent to having a fixed
+    /// <see cref="CascadingValue{TValue}"/> at the root of the component hierarchy.
+    /// </summary>
+    /// <typeparam name="TValue">The value type.</typeparam>
+    /// <param name="serviceCollection">The <see cref="IServiceCollection"/>.</param>
+    /// <param name="name">A name for the cascading value. If set, <see cref="CascadingParameterAttribute"/> can be configured to match based on this name.</param>
+    /// <param name="valueFactory">A callback that supplies a fixed value within each service provider scope.</param>
+    /// <returns>The <see cref="IServiceCollection"/>.</returns>
+    public static void TryAddCascadingValue<TValue>(
+        this IServiceCollection serviceCollection, string name, Func<IServiceProvider, TValue> valueFactory)
+    {
+        serviceCollection.TryAddEnumerable(
+            ServiceDescriptor.Scoped<ICascadingValueSupplier, CascadingValueSource<TValue>>(
+                sp => new CascadingValueSource<TValue>(name, () => valueFactory(sp), isFixed: true)));
+    }
+
+    /// <summary>
+    /// Adds a cascading value to the <paramref name="serviceCollection"/>, if none is already registered
+    /// with the value type. This is equivalent to having a fixed <see cref="CascadingValue{TValue}"/> at
+    /// the root of the component hierarchy.
+    /// 
+    /// With this overload, you can supply a <see cref="CascadingValueSource{TValue}"/> which allows you
+    /// to notify about updates to the value later, causing recipients to re-render. This overload should
+    /// only be used if you plan to update the value dynamically.
+    /// </summary>
+    /// <typeparam name="TValue">The value type.</typeparam>
+    /// <param name="serviceCollection">The <see cref="IServiceCollection"/>.</param>
+    /// <param name="sourceFactory">A callback that supplies a <see cref="CascadingValueSource{TValue}"/> within each service provider scope.</param>
+    /// <returns>The <see cref="IServiceCollection"/>.</returns>
+    public static void TryAddCascadingValue<TValue>(
+        this IServiceCollection serviceCollection, Func<IServiceProvider, CascadingValueSource<TValue>> sourceFactory)
+    {
+        serviceCollection.TryAddEnumerable(
+            ServiceDescriptor.Scoped<ICascadingValueSupplier, CascadingValueSource<TValue>>(sourceFactory));
+    }
 }

src/Components/Components/src/PublicAPI.Unshipped.txt

@@ -1,6 +1,4 @@
 #nullable enable
-abstract Microsoft.AspNetCore.Components.CascadingParameterAttributeBase.Name.get -> string?
-abstract Microsoft.AspNetCore.Components.CascadingParameterAttributeBase.Name.set -> void
 abstract Microsoft.AspNetCore.Components.RenderModeAttribute.Mode.get -> Microsoft.AspNetCore.Components.IComponentRenderMode!
 Microsoft.AspNetCore.Components.CascadingParameterAttributeBase
 Microsoft.AspNetCore.Components.CascadingParameterAttributeBase.CascadingParameterAttributeBase() -> void
@@ -83,24 +81,19 @@ Microsoft.AspNetCore.Components.Rendering.RenderTreeBuilder.AddComponentParamete
 Microsoft.AspNetCore.Components.StreamRenderingAttribute
 Microsoft.AspNetCore.Components.StreamRenderingAttribute.Enabled.get -> bool
 Microsoft.AspNetCore.Components.StreamRenderingAttribute.StreamRenderingAttribute(bool enabled) -> void
-*REMOVED*Microsoft.AspNetCore.Components.CascadingParameterAttribute.Name.get -> string?
-*REMOVED*Microsoft.AspNetCore.Components.CascadingParameterAttribute.Name.set -> void
 Microsoft.AspNetCore.Components.SupplyParameterFromQueryProviderServiceCollectionExtensions
 Microsoft.Extensions.DependencyInjection.CascadingValueServiceCollectionExtensions
-override Microsoft.AspNetCore.Components.CascadingParameterAttribute.Name.get -> string?
-override Microsoft.AspNetCore.Components.CascadingParameterAttribute.Name.set -> void
 override Microsoft.AspNetCore.Components.EventCallback.GetHashCode() -> int
 override Microsoft.AspNetCore.Components.EventCallback.Equals(object? obj) -> bool
 override Microsoft.AspNetCore.Components.EventCallback<TValue>.GetHashCode() -> int
 override Microsoft.AspNetCore.Components.EventCallback<TValue>.Equals(object? obj) -> bool
-*REMOVED*Microsoft.AspNetCore.Components.SupplyParameterFromQueryAttribute.Name.get -> string?
-*REMOVED*Microsoft.AspNetCore.Components.SupplyParameterFromQueryAttribute.Name.set -> void
-override Microsoft.AspNetCore.Components.SupplyParameterFromQueryAttribute.Name.get -> string?
-override Microsoft.AspNetCore.Components.SupplyParameterFromQueryAttribute.Name.set -> void
 static Microsoft.AspNetCore.Components.SupplyParameterFromQueryProviderServiceCollectionExtensions.AddSupplyValueFromQueryProvider(this Microsoft.Extensions.DependencyInjection.IServiceCollection! services) -> Microsoft.Extensions.DependencyInjection.IServiceCollection!
 static Microsoft.Extensions.DependencyInjection.CascadingValueServiceCollectionExtensions.AddCascadingValue<TValue>(this Microsoft.Extensions.DependencyInjection.IServiceCollection! serviceCollection, string! name, System.Func<System.IServiceProvider!, TValue>! valueFactory) -> Microsoft.Extensions.DependencyInjection.IServiceCollection!
 static Microsoft.Extensions.DependencyInjection.CascadingValueServiceCollectionExtensions.AddCascadingValue<TValue>(this Microsoft.Extensions.DependencyInjection.IServiceCollection! serviceCollection, System.Func<System.IServiceProvider!, Microsoft.AspNetCore.Components.CascadingValueSource<TValue>!>! sourceFactory) -> Microsoft.Extensions.DependencyInjection.IServiceCollection!
 static Microsoft.Extensions.DependencyInjection.CascadingValueServiceCollectionExtensions.AddCascadingValue<TValue>(this Microsoft.Extensions.DependencyInjection.IServiceCollection! serviceCollection, System.Func<System.IServiceProvider!, TValue>! valueFactory) -> Microsoft.Extensions.DependencyInjection.IServiceCollection!
+static Microsoft.Extensions.DependencyInjection.CascadingValueServiceCollectionExtensions.TryAddCascadingValue<TValue>(this Microsoft.Extensions.DependencyInjection.IServiceCollection! serviceCollection, string! name, System.Func<System.IServiceProvider!, TValue>! valueFactory) -> void
+static Microsoft.Extensions.DependencyInjection.CascadingValueServiceCollectionExtensions.TryAddCascadingValue<TValue>(this Microsoft.Extensions.DependencyInjection.IServiceCollection! serviceCollection, System.Func<System.IServiceProvider!, Microsoft.AspNetCore.Components.CascadingValueSource<TValue>!>! sourceFactory) -> void
+static Microsoft.Extensions.DependencyInjection.CascadingValueServiceCollectionExtensions.TryAddCascadingValue<TValue>(this Microsoft.Extensions.DependencyInjection.IServiceCollection! serviceCollection, System.Func<System.IServiceProvider!, TValue>! valueFactory) -> void
 virtual Microsoft.AspNetCore.Components.NavigationManager.Refresh(bool forceReload = false) -> void
 virtual Microsoft.AspNetCore.Components.Rendering.ComponentState.DisposeAsync() -> System.Threading.Tasks.ValueTask
 virtual Microsoft.AspNetCore.Components.RenderTree.Renderer.AddPendingTask(Microsoft.AspNetCore.Components.Rendering.ComponentState? componentState, System.Threading.Tasks.Task! task) -> void

src/Components/Components/src/Reflection/ComponentProperties.cs

@@ -184,8 +184,7 @@ private static void ThrowForUnknownIncomingParameterName([DynamicallyAccessedMem
             {
                 throw new InvalidOperationException(
                     $"Object of type '{targetType.FullName}' has a property matching the name '{parameterName}', " +
-                    $"but it does not have [{nameof(ParameterAttribute)}], [{nameof(CascadingParameterAttribute)}] or " +
-                    $"[SupplyParameterFromFormAttribute] applied.");
+                    $"but it does not have [Parameter], [CascadingParameter], or any other parameter-supplying attribute.");
             }
             else
             {

src/Components/Components/src/SupplyParameterFromQueryAttribute.cs

@@ -14,5 +14,5 @@ public sealed class SupplyParameterFromQueryAttribute : CascadingParameterAttrib
     /// Gets or sets the name of the querystring parameter. If null, the querystring
     /// parameter is assumed to have the same name as the associated property.
     /// </summary>
-    public override string? Name { get; set; }
+    public string? Name { get; set; }
 }

src/Components/Components/src/SupplyParameterFromQueryProviderServiceCollectionExtensions.cs

@@ -50,7 +50,8 @@ public bool CanSupplyValue(in CascadingParameterInfo parameterInfo)
                 UpdateQueryParameters();
             }
 
-            var queryParameterName = parameterInfo.Attribute.Name ?? parameterInfo.PropertyName;
+            var attribute = (SupplyParameterFromQueryAttribute)parameterInfo.Attribute; // Must be a valid cast because we check in CanSupplyValue
+            var queryParameterName = attribute.Name ?? parameterInfo.PropertyName;
             return _queryParameterValueSupplier.GetQueryParameterValue(parameterInfo.PropertyType, queryParameterName);
         }
 

src/Components/Components/test/CascadingParameterStateTest.cs

@@ -476,8 +476,6 @@ class ComponentWithNamedCascadingParam : TestComponentBase
 
     class SupplyParameterWithSingleDeliveryAttribute : CascadingParameterAttributeBase
     {
-        public override string Name { get; set; }
-
         internal override bool SingleDelivery => true;
     }
 
@@ -523,19 +521,3 @@ public TestNavigationManager()
         }
     }
 }
-
-[AttributeUsage(AttributeTargets.Property, AllowMultiple = false, Inherited = true)]
-public sealed class SupplyParameterFromFormAttribute : CascadingParameterAttributeBase
-{
-    /// <summary>
-    /// Gets or sets the name for the parameter. The name is used to match
-    /// the form data and decide whether or not the value needs to be bound.
-    /// </summary>
-    public override string Name { get; set; }
-
-    /// <summary>
-    /// Gets or sets the name for the handler. The name is used to match
-    /// the form data and decide whether or not the value needs to be bound.
-    /// </summary>
-    public string Handler { get; set; }
-}

src/Components/Components/test/CascadingParameterTest.cs

@@ -727,15 +727,58 @@ public void OmitsSingleDeliveryCascadingParametersWhenUpdatingDirectParameters()
             });
     }
 
+    [Fact]
+    public void CanUseTryAddPatternForCascadingValuesInServiceCollection_ValueFactory()
+    {
+        // Arrange
+        var services = new ServiceCollection();
+
+        // Act
+        services.TryAddCascadingValue(_ => new Type1());
+        services.TryAddCascadingValue(_ => new Type1());
+        services.TryAddCascadingValue(_ => new Type2());
+
+        // Assert
+        Assert.Equal(2, services.Count());
+    }
+
+    [Fact]
+    public void CanUseTryAddPatternForCascadingValuesInServiceCollection_NamedValueFactory()
+    {
+        // Arrange
+        var services = new ServiceCollection();
+
+        // Act
+        services.TryAddCascadingValue("Name1", _ => new Type1());
+        services.TryAddCascadingValue("Name2", _ => new Type1());
+        services.TryAddCascadingValue("Name3", _ => new Type2());
+
+        // Assert
+        Assert.Equal(2, services.Count());
+    }
+
+    [Fact]
+    public void CanUseTryAddPatternForCascadingValuesInServiceCollection_CascadingValueSource()
+    {
+        // Arrange
+        var services = new ServiceCollection();
+
+        // Act
+        services.TryAddCascadingValue(_ => new CascadingValueSource<Type1>("Name1", new Type1(), false));
+        services.TryAddCascadingValue(_ => new CascadingValueSource<Type1>("Name2", new Type1(), false));
+        services.TryAddCascadingValue(_ => new CascadingValueSource<Type2>("Name3", new Type2(), false));
+
+        // Assert
+        Assert.Equal(2, services.Count());
+    }
+
     private class SingleDeliveryValue(string text)
     {
         public string Text => text;
     }
 
     private class SingleDeliveryCascadingParameterAttribute : CascadingParameterAttributeBase
     {
-        public override string Name { get; set; }
-
         internal override bool SingleDelivery => true;
     }
 
@@ -852,13 +895,11 @@ class SecondCascadingParameterConsumerComponent<T1, T2> : CascadingParameterCons
     [AttributeUsage(AttributeTargets.Property, AllowMultiple = false, Inherited = true)]
     class CustomCascadingParameter1Attribute : CascadingParameterAttributeBase
     {
-        public override string Name { get; set; }
     }
 
     [AttributeUsage(AttributeTargets.Property, AllowMultiple = false, Inherited = true)]
     class CustomCascadingParameter2Attribute : CascadingParameterAttributeBase
     {
-        public override string Name { get; set; }
     }
 
     class CustomCascadingValueProducer<TAttribute> : AutoRenderComponent, ICascadingValueSupplier
@@ -904,7 +945,7 @@ void ICascadingValueSupplier.Unsubscribe(ComponentState subscriber, in Cascading
 
     class CustomCascadingValueConsumer1 : AutoRenderComponent
     {
-        [CustomCascadingParameter1(Name = nameof(Value))]
+        [CustomCascadingParameter1]
         public object Value { get; set; }
 
         protected override void BuildRenderTree(RenderTreeBuilder builder)
@@ -915,7 +956,7 @@ protected override void BuildRenderTree(RenderTreeBuilder builder)
 
     class CustomCascadingValueConsumer2 : AutoRenderComponent
     {
-        [CustomCascadingParameter2(Name = nameof(Value))]
+        [CustomCascadingParameter2]
         public object Value { get; set; }
 
         protected override void BuildRenderTree(RenderTreeBuilder builder)
@@ -944,4 +985,7 @@ public void ChangeValue(string newValue)
             StringValue = newValue;
         }
     }
+
+    class Type1 { }
+    class Type2 { }
 }

src/Components/Components/test/ParameterViewTest.Assignment.cs

@@ -183,7 +183,7 @@ public void IncomingParameterMatchesPropertyNotDeclaredAsParameter_Throws()
         Assert.Equal(default, target.IntProp);
         Assert.Equal(
             $"Object of type '{typeof(HasPropertyWithoutParameterAttribute).FullName}' has a property matching the name '{nameof(HasPropertyWithoutParameterAttribute.IntProp)}', " +
-            $"but it does not have [{nameof(ParameterAttribute)}], [{nameof(CascadingParameterAttribute)}] or [{nameof(SupplyParameterFromFormAttribute)}] applied.",
+            "but it does not have [Parameter], [CascadingParameter], or any other parameter-supplying attribute.",
             ex.Message);
     }
 

src/Components/Endpoints/src/DependencyInjection/RazorComponentsServiceCollectionExtensions.cs

@@ -63,6 +63,7 @@ public static IRazorComponentsBuilder AddRazorComponents(this IServiceCollection
         services.TryAddScoped<EndpointRoutingStateProvider>();
         services.TryAddScoped<IRoutingStateProvider>(sp => sp.GetRequiredService<EndpointRoutingStateProvider>());
         services.AddSupplyValueFromQueryProvider();
+        services.TryAddCascadingValue(sp => sp.GetRequiredService<EndpointHtmlRenderer>().HttpContext);
 
         // Form handling
         services.AddSupplyValueFromFormProvider();

src/Components/Endpoints/src/Rendering/EndpointHtmlRenderer.cs

@@ -52,6 +52,8 @@ public EndpointHtmlRenderer(IServiceProvider serviceProvider, ILoggerFactory log
         _services = serviceProvider;
     }
 
+    internal HttpContext? HttpContext => _httpContext;
+
     private void SetHttpContext(HttpContext httpContext)
     {
         if (_httpContext is null)