Root-level cascading values + CascadingAuthenticationState at root

src/Components/Authorization/src/CascadingAuthenticationStateServiceCollectionExtensions.cs

@@ -0,0 +1,57 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using Microsoft.AspNetCore.Components;
+using Microsoft.AspNetCore.Components.Authorization;
+
+namespace Microsoft.Extensions.DependencyInjection;
+
+/// <summary>
+/// Extension methods for configuring cascading authentication state on a service collection.
+/// </summary>
+public static class CascadingAuthenticationStateServiceCollectionExtensions
+{
+    /// <summary>
+    /// Adds cascading authentication state to the <paramref name="serviceCollection"/>. This is equivalent to
+    /// having a <see cref="CascadingAuthenticationState"/> component at the root of your component hierarchy.
+    /// </summary>
+    /// <param name="serviceCollection">The <see cref="IServiceCollection"/>.</param>
+    /// <returns>The <see cref="IServiceCollection"/>.</returns>
+    public static IServiceCollection AddCascadingAuthenticationState(this IServiceCollection serviceCollection)
+    {
+        return serviceCollection.AddCascadingValue<Task<AuthenticationState>>(services =>
+        {
+            var authenticationStateProvider = services.GetRequiredService<AuthenticationStateProvider>();
+            return new AuthenticationStateCascadingValueSource(authenticationStateProvider);
+        });
+    }
+
+    private sealed class AuthenticationStateCascadingValueSource : CascadingValueSource<Task<AuthenticationState>>, IDisposable
+    {
+        // This is intended to produce identical behavior to having a <CascadingAuthenticationStateProvider>
+        // wrapped around the root component.
+
+        private readonly AuthenticationStateProvider _authenticationStateProvider;
+
+        public AuthenticationStateCascadingValueSource(AuthenticationStateProvider authenticationStateProvider)
+            : base(authenticationStateProvider.GetAuthenticationStateAsync, isFixed: false)
+        {
+            _authenticationStateProvider = authenticationStateProvider;
+            _authenticationStateProvider.AuthenticationStateChanged += HandleAuthenticationStateChanged;
+        }
+
+        private void HandleAuthenticationStateChanged(Task<AuthenticationState> newAuthStateTask)
+        {
+            // It's OK to discard the task because this only represents the duration of the dispatch to sync context.
+            // It handles any exceptions internally by dispatching them to the renderer within the context of whichever
+            // component threw when receiving the update. This is the same as how a CascadingValue doesn't get notified
+            // about exceptions that happen inside the recipients of value notifications.
+            _ = NotifyChangedAsync(newAuthStateTask);
+        }
+
+        public void Dispose()
+        {
+            _authenticationStateProvider.AuthenticationStateChanged -= HandleAuthenticationStateChanged;
+        }
+    }
+}

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

@@ -1 +1,3 @@
 #nullable enable
+Microsoft.Extensions.DependencyInjection.CascadingAuthenticationStateServiceCollectionExtensions
+static Microsoft.Extensions.DependencyInjection.CascadingAuthenticationStateServiceCollectionExtensions.AddCascadingAuthenticationState(this Microsoft.Extensions.DependencyInjection.IServiceCollection! serviceCollection) -> Microsoft.Extensions.DependencyInjection.IServiceCollection!

src/Components/Components/src/CascadingParameterState.cs

@@ -57,6 +57,7 @@ public static IReadOnlyList<CascadingParameterState> FindCascadingParameters(Com
 
     private static ICascadingValueSupplier? GetMatchingCascadingValueSupplier(in CascadingParameterInfo info, ComponentState componentState)
     {
+        // First scan up through the component hierarchy
         var candidate = componentState;
         do
         {
@@ -68,6 +69,15 @@ public static IReadOnlyList<CascadingParameterState> FindCascadingParameters(Com
             candidate = candidate.LogicalParentComponentState;
         } while (candidate != null);
 
+        // We got to the root and found no match, so now look at the providers registered in DI
+        foreach (var valueSupplier in componentState.Renderer.ServiceProviderCascadingValueSuppliers)
+        {
+            if (valueSupplier.CanSupplyValue(info))
+            {
+                return valueSupplier;
+            }
+        }
+
         // No match
         return null;
     }

src/Components/Components/src/CascadingValueServiceCollectionExtensions.cs

@@ -0,0 +1,53 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using Microsoft.AspNetCore.Components;
+
+namespace Microsoft.Extensions.DependencyInjection;
+
+/// <summary>
+/// Extension methods for configuring cascading values on an <see cref="IServiceCollection"/>.
+/// </summary>
+public static class CascadingValueServiceCollectionExtensions
+{
+    /// <summary>
+    /// Adds a cascading value to the <paramref name="serviceCollection"/>. 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 IServiceCollection AddCascadingValue<TValue>(
+        this IServiceCollection serviceCollection, Func<IServiceProvider, TValue> valueFactory)
+        => serviceCollection.AddScoped<ICascadingValueSupplier>(sp => new CascadingValueSource<TValue>(() => valueFactory(sp), isFixed: true));
+
+    /// <summary>
+    /// Adds a cascading value to the <paramref name="serviceCollection"/>. 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 IServiceCollection AddCascadingValue<TValue>(
+        this IServiceCollection serviceCollection, string name, Func<IServiceProvider, TValue> valueFactory)
+        => serviceCollection.AddScoped<ICascadingValueSupplier>(sp => new CascadingValueSource<TValue>(name, () => valueFactory(sp), isFixed: true));
+
+    /// <summary>
+    /// Adds a cascading value to the <paramref name="serviceCollection"/>. This is equivalent to having
+    /// a <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 IServiceCollection AddCascadingValue<TValue>(
+        this IServiceCollection serviceCollection, Func<IServiceProvider, CascadingValueSource<TValue>> sourceFactory)
+        => serviceCollection.AddScoped<ICascadingValueSupplier>(sourceFactory);
+}

src/Components/Components/src/CascadingValueSource.cs

@@ -0,0 +1,177 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Collections.Concurrent;
+using Microsoft.AspNetCore.Components.Rendering;
+
+namespace Microsoft.AspNetCore.Components;
+
+/// <summary>
+/// Supplies a cascading value that can be received by components using
+/// <see cref="CascadingParameterAttribute"/>.
+/// </summary>
+public class CascadingValueSource<TValue> : ICascadingValueSupplier
+{
+    // By *not* making this sealed, people who want to deal with value disposal can subclass this,
+    // add IDisposable, and then do what they want during shutdown
+
+    private readonly ConcurrentDictionary<Dispatcher, List<ComponentState>>? _subscribers;
+    private readonly bool _isFixed;
+    private readonly string? _name;
+
+    // You can either provide an initial value to the constructor, or a func to provide one lazily
+    private TValue? _currentValue;
+    private Func<TValue>? _initialValueFactory;
+
+    /// <summary>
+    /// Constructs an instance of <see cref="CascadingValueSource{TValue}"/>.
+    /// </summary>
+    /// <param name="value">The initial value.</param>
+    /// <param name="isFixed">A flag to indicate whether the value is fixed. If false, all receipients will subscribe for update notifications, which you can issue by calling <see cref="NotifyChangedAsync()"/>. These subscriptions come at a performance cost, so if the value will not change, set <paramref name="isFixed"/> to true.</param>
+    public CascadingValueSource(TValue value, bool isFixed) : this(isFixed)
+    {
+        _currentValue = value;
+    }
+
+    /// <summary>
+    /// Constructs an instance of <see cref="CascadingValueSource{TValue}"/>.
+    /// </summary>
+    /// <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="value">The initial value.</param>
+    /// <param name="isFixed">A flag to indicate whether the value is fixed. If false, all receipients will subscribe for update notifications, which you can issue by calling <see cref="NotifyChangedAsync()"/>. These subscriptions come at a performance cost, so if the value will not change, set <paramref name="isFixed"/> to true.</param>
+    public CascadingValueSource(string name, TValue value, bool isFixed) : this(value, isFixed)
+    {
+        ArgumentNullException.ThrowIfNull(name);
+        _name = name;
+    }
+
+    /// <summary>
+    /// Constructs an instance of <see cref="CascadingValueSource{TValue}"/>.
+    /// </summary>
+    /// <param name="valueFactory">A callback that produces the initial value when first required.</param>
+    /// <param name="isFixed">A flag to indicate whether the value is fixed. If false, all receipients will subscribe for update notifications, which you can issue by calling <see cref="NotifyChangedAsync()"/>. These subscriptions come at a performance cost, so if the value will not change, set <paramref name="isFixed"/> to true.</param>
+    public CascadingValueSource(Func<TValue> valueFactory, bool isFixed) : this(isFixed)
+    {
+        _initialValueFactory = valueFactory;
+    }
+
+    /// <summary>
+    /// Constructs an instance of <see cref="CascadingValueSource{TValue}"/>.
+    /// </summary>
+    /// <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 produces the initial value when first required.</param>
+    /// <param name="isFixed">A flag to indicate whether the value is fixed. If false, all receipients will subscribe for update notifications, which you can issue by calling <see cref="NotifyChangedAsync()"/>. These subscriptions come at a performance cost, so if the value will not change, set <paramref name="isFixed"/> to true.</param>
+    public CascadingValueSource(string name, Func<TValue> valueFactory, bool isFixed) : this(valueFactory, isFixed)
+    {
+        ArgumentNullException.ThrowIfNull(name);
+        _name = name;
+    }
+
+    private CascadingValueSource(bool isFixed)
+    {
+        _isFixed = isFixed;
+
+        if (!_isFixed)
+        {
+            _subscribers = new();
+        }
+    }
+
+    /// <summary>
+    /// Notifies subscribers that the value has changed (for example, if it has been mutated).
+    /// </summary>
+    /// <returns>A <see cref="Task"/> that completes when the notifications have been issued.</returns>
+    public Task NotifyChangedAsync()
+    {
+        if (_isFixed)
+        {
+            throw new InvalidOperationException($"Cannot notify about changes because the {GetType()} is configured as fixed.");
+        }
+
+        if (_subscribers?.Count > 0)
+        {
+            var tasks = new List<Task>();
+
+            foreach (var (dispatcher, subscribers) in _subscribers)
+            {
+                tasks.Add(dispatcher.InvokeAsync(() =>
+                {
+                    foreach (var subscriber in subscribers)
+                    {
+                        subscriber.NotifyCascadingValueChanged(ParameterViewLifetime.Unbound);
+                    }
+                }));
+            }
+
+            return Task.WhenAll(tasks);
+        }
+        else
+        {
+            return Task.CompletedTask;
+        }
+    }
+
+    /// <summary>
+    /// Notifies subscribers that the value has changed, supplying a new value.
+    /// </summary>
+    /// <param name="newValue"></param>
+    /// <returns>A <see cref="Task"/> that completes when the notifications have been issued.</returns>
+    public Task NotifyChangedAsync(TValue newValue)
+    {
+        _currentValue = newValue;
+        _initialValueFactory = null; // This definitely won't be used now
+
+        return NotifyChangedAsync();
+    }
+
+    bool ICascadingValueSupplier.IsFixed => _isFixed;
+
+    bool ICascadingValueSupplier.CanSupplyValue(in CascadingParameterInfo parameterInfo)
+    {
+        if (parameterInfo.Attribute is not CascadingParameterAttribute cascadingParameterAttribute || !parameterInfo.PropertyType.IsAssignableFrom(typeof(TValue)))
+        {
+            return false;
+        }
+
+        // We only consider explicitly requested names, not the property name.
+        var requestedName = cascadingParameterAttribute.Name;
+        return (requestedName == null && _name == null) // Match on type alone
+            || string.Equals(requestedName, _name, StringComparison.OrdinalIgnoreCase); // Also match on name
+    }
+
+    object? ICascadingValueSupplier.GetCurrentValue(in CascadingParameterInfo parameterInfo)
+    {
+        if (_initialValueFactory is not null)
+        {
+            _currentValue = _initialValueFactory();
+            _initialValueFactory = null;
+        }
+
+        return _currentValue;
+    }
+
+    void ICascadingValueSupplier.Subscribe(ComponentState subscriber, in CascadingParameterInfo parameterInfo)
+    {
+        Dispatcher dispatcher = subscriber.Renderer.Dispatcher;
+        dispatcher.AssertAccess();
+
+        // The .Add is threadsafe because we are in the sync context for this dispatcher
+        _subscribers?.GetOrAdd(dispatcher, _ => new()).Add(subscriber);
+    }
+
+    void ICascadingValueSupplier.Unsubscribe(ComponentState subscriber, in CascadingParameterInfo parameterInfo)
+    {
+        Dispatcher dispatcher = subscriber.Renderer.Dispatcher;
+        dispatcher.AssertAccess();
+
+        if (_subscribers?.TryGetValue(dispatcher, out var subscribersForDispatcher) == true)
+        {
+            // Threadsafe because we're in the sync context for this dispatcher
+            subscribersForDispatcher.Remove(subscriber);
+            if (subscribersForDispatcher.Count == 0)
+            {
+                _subscribers.Remove(dispatcher, out _);
+            }
+        }
+    }
+}

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

@@ -46,6 +46,13 @@ Microsoft.AspNetCore.Components.CascadingParameterInfo.Attribute.get -> Microsof
 Microsoft.AspNetCore.Components.CascadingParameterInfo.CascadingParameterInfo() -> void
 Microsoft.AspNetCore.Components.CascadingParameterInfo.PropertyName.get -> string!
 Microsoft.AspNetCore.Components.CascadingParameterInfo.PropertyType.get -> System.Type!
+Microsoft.AspNetCore.Components.CascadingValueSource<TValue>
+Microsoft.AspNetCore.Components.CascadingValueSource<TValue>.CascadingValueSource(string! name, System.Func<TValue>! valueFactory, bool isFixed) -> void
+Microsoft.AspNetCore.Components.CascadingValueSource<TValue>.CascadingValueSource(string! name, TValue value, bool isFixed) -> void
+Microsoft.AspNetCore.Components.CascadingValueSource<TValue>.CascadingValueSource(System.Func<TValue>! valueFactory, bool isFixed) -> void
+Microsoft.AspNetCore.Components.CascadingValueSource<TValue>.CascadingValueSource(TValue value, bool isFixed) -> void
+Microsoft.AspNetCore.Components.CascadingValueSource<TValue>.NotifyChangedAsync() -> System.Threading.Tasks.Task!
+Microsoft.AspNetCore.Components.CascadingValueSource<TValue>.NotifyChangedAsync(TValue newValue) -> System.Threading.Tasks.Task!
 Microsoft.AspNetCore.Components.ComponentBase.DispatchExceptionAsync(System.Exception! exception) -> System.Threading.Tasks.Task!
 Microsoft.AspNetCore.Components.IComponentRenderMode
 Microsoft.AspNetCore.Components.Infrastructure.ComponentStatePersistenceManager.PersistStateAsync(Microsoft.AspNetCore.Components.IPersistentComponentStateStore! store, Microsoft.AspNetCore.Components.Dispatcher! dispatcher) -> System.Threading.Tasks.Task!
@@ -103,6 +110,7 @@ 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.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
@@ -113,6 +121,9 @@ override Microsoft.AspNetCore.Components.EventCallback<TValue>.Equals(object? ob
 *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.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!
 virtual Microsoft.AspNetCore.Components.Binding.CascadingModelBindingProvider.Subscribe(Microsoft.AspNetCore.Components.Rendering.ComponentState! subscriber) -> void
 virtual Microsoft.AspNetCore.Components.Binding.CascadingModelBindingProvider.Unsubscribe(Microsoft.AspNetCore.Components.Rendering.ComponentState! subscriber) -> void
 virtual Microsoft.AspNetCore.Components.Rendering.ComponentState.DisposeAsync() -> System.Threading.Tasks.ValueTask