Use T? for unconstrained nullable types (#25261)

* Use T? for unconstrained nullable types

* Apply suggestions from code review

src/Components/Components/src/BindConverter.cs

@@ -25,8 +25,8 @@ namespace Microsoft.AspNetCore.Components
         private delegate object? BindFormatter<T>(T value, CultureInfo? culture);
         private delegate object BindFormatterWithFormat<T>(T value, CultureInfo? culture, string format);
 
-        internal delegate bool BindParser<T>(object? obj, CultureInfo? culture, out T value);
-        internal delegate bool BindParserWithFormat<T>(object? obj, CultureInfo? culture, string? format, out T value);
+        internal delegate bool BindParser<T>(object? obj, CultureInfo? culture, [MaybeNullWhen(false)] out T value);
+        internal delegate bool BindParserWithFormat<T>(object? obj, CultureInfo? culture, string? format, [MaybeNullWhen(false)] out T value);
 
         /// <summary>
         /// Formats the provided <paramref name="value"/> as a <see cref="System.String"/>.
@@ -1276,7 +1276,7 @@ namespace Microsoft.AspNetCore.Components
         /// <param name="culture">The <see cref="CultureInfo"/> to use for conversion.</param>
         /// <param name="value">The converted value.</param>
         /// <returns><c>true</c> if conversion is successful, otherwise <c>false</c>.</returns>
-        public static bool TryConvertTo<T>(object? obj, CultureInfo? culture, out T value)
+        public static bool TryConvertTo<T>(object? obj, CultureInfo? culture, [MaybeNullWhen(false)] out T value)
         {
             var converter = ParserDelegateCache.Get<T>();
             return converter(obj, culture, out value);

src/Components/Components/src/EventCallbackOfT.cs

@@ -46,11 +46,11 @@ namespace Microsoft.AspNetCore.Components
         /// </summary>
         /// <param name="arg">The argument.</param>
         /// <returns>A <see cref="Task"/> which completes asynchronously once event processing has completed.</returns>
-        public Task InvokeAsync(TValue arg)
+        public Task InvokeAsync(TValue? arg)
         {
             if (Receiver == null)
             {
-                return EventCallbackWorkItem.InvokeAsync<TValue>(Delegate, arg);
+                return EventCallbackWorkItem.InvokeAsync<TValue?>(Delegate, arg);
             }
 
             return Receiver.HandleEventAsync(new EventCallbackWorkItem(Delegate), arg);

src/Components/Components/src/ParameterView.cs

@@ -88,9 +88,8 @@ namespace Microsoft.AspNetCore.Components
         /// <typeparam name="TValue">The type of the value.</typeparam>
         /// <param name="parameterName">The name of the parameter.</param>
         /// <returns>The parameter value if found; otherwise the default value for the specified type.</returns>
-        [return: MaybeNull]
-        public TValue GetValueOrDefault<TValue>(string parameterName)
-            => GetValueOrDefault<TValue>(parameterName, default!);
+        public TValue? GetValueOrDefault<TValue>(string parameterName)
+            => GetValueOrDefault<TValue?>(parameterName, default);
 
         /// <summary>
         /// Gets the value of the parameter with the specified name, or a specified default value

src/Components/Server/src/Circuits/CircuitId.cs

@@ -2,7 +2,6 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
-using System.Diagnostics.CodeAnalysis;
 using System.Runtime.InteropServices;
 using System.Security.Cryptography;
 
@@ -29,7 +28,7 @@ namespace Microsoft.AspNetCore.Components.Server.Circuits
 
         public string Secret { get; }
 
-        public bool Equals([AllowNull] CircuitId other)
+        public bool Equals(CircuitId other)
         {
             // We want to use a fixed time equality comparison for a *real* comparisons.
             // The only use case for Secret being null is with a default struct value,

src/Components/Web/src/Forms/InputBase.cs

@@ -35,10 +35,8 @@ namespace Microsoft.AspNetCore.Components.Forms
         /// <example>
         /// @bind-Value="model.PropertyName"
         /// </example>
-        [AllowNull]
-        [MaybeNull]
         [Parameter]
-        public TValue Value { get; set; } = default;
+        public TValue? Value { get; set; }
 
         /// <summary>
         /// Gets or sets a callback that updates the bound value.
@@ -69,17 +67,15 @@ namespace Microsoft.AspNetCore.Components.Forms
         /// <summary>
         /// Gets or sets the current value of the input.
         /// </summary>
-        [AllowNull]
-        protected TValue CurrentValue
+        protected TValue? CurrentValue
         {
-            [return: MaybeNull]
-            get => Value!;
+            get => Value;
             set
             {
                 var hasChanged = !EqualityComparer<TValue>.Default.Equals(value, Value);
                 if (hasChanged)
                 {
-                    Value = value!;
+                    Value = value;
                     _ = ValueChanged.InvokeAsync(Value);
                     EditContext.NotifyFieldChanged(FieldIdentifier);
                 }
@@ -148,7 +144,7 @@ namespace Microsoft.AspNetCore.Components.Forms
         /// </summary>
         /// <param name="value">The value to format.</param>
         /// <returns>A string representation of the value.</returns>
-        protected virtual string? FormatValueAsString([AllowNull] TValue value)
+        protected virtual string? FormatValueAsString(TValue? value)
             => value?.ToString();
 
         /// <summary>
@@ -159,7 +155,7 @@ namespace Microsoft.AspNetCore.Components.Forms
         /// <param name="result">An instance of <typeparamref name="TValue"/>.</param>
         /// <param name="validationErrorMessage">If the value could not be parsed, provides a validation error message.</param>
         /// <returns>True if the value could be parsed; otherwise false.</returns>
-        protected abstract bool TryParseValueFromString(string? value, [MaybeNull] out TValue result, [NotNullWhen(false)] out string? validationErrorMessage);
+        protected abstract bool TryParseValueFromString(string? value, [MaybeNullWhen(false)] out TValue result, [NotNullWhen(false)] out string? validationErrorMessage);
 
         /// <summary>
         /// Gets a string that indicates the status of the field being edited. This will include

src/Components/Web/src/Forms/InputDate.cs

@@ -2,6 +2,7 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
+using System.Diagnostics;
 using System.Diagnostics.CodeAnalysis;
 using System.Globalization;
 using Microsoft.AspNetCore.Components.Rendering;
@@ -34,7 +35,7 @@ namespace Microsoft.AspNetCore.Components.Forms
         }
 
         /// <inheritdoc />
-        protected override string FormatValueAsString([AllowNull] TValue value)
+        protected override string FormatValueAsString(TValue? value)
         {
             switch (value)
             {
@@ -48,7 +49,7 @@ namespace Microsoft.AspNetCore.Components.Forms
         }
 
         /// <inheritdoc />
-        protected override bool TryParseValueFromString(string? value, [MaybeNull] out TValue result, [NotNullWhen(false)] out string? validationErrorMessage)
+        protected override bool TryParseValueFromString(string? value, [MaybeNullWhen(false)] out TValue result, [NotNullWhen(false)] out string? validationErrorMessage)
         {
             // Unwrap nullable types. We don't have to deal with receiving empty values for nullable
             // types here, because the underlying InputBase already covers that.
@@ -70,6 +71,7 @@ namespace Microsoft.AspNetCore.Components.Forms
 
             if (success)
             {
+                Debug.Assert(result != null);
                 validationErrorMessage = null;
                 return true;
             }
@@ -80,7 +82,7 @@ namespace Microsoft.AspNetCore.Components.Forms
             }
         }
 
-        static bool TryParseDateTime(string? value, [MaybeNullWhen(false)] out TValue result)
+        private static bool TryParseDateTime(string? value, [MaybeNullWhen(false)] out TValue result)
         {
             var success = BindConverter.TryConvertToDateTime(value, CultureInfo.InvariantCulture, DateFormat, out var parsedValue);
             if (success)
@@ -95,7 +97,7 @@ namespace Microsoft.AspNetCore.Components.Forms
             }
         }
 
-        static bool TryParseDateTimeOffset(string? value, [MaybeNullWhen(false)] out TValue result)
+        private static bool TryParseDateTimeOffset(string? value, [MaybeNullWhen(false)] out TValue result)
         {
             var success = BindConverter.TryConvertToDateTimeOffset(value, CultureInfo.InvariantCulture, DateFormat, out var parsedValue);
             if (success)

src/Components/Web/src/Forms/InputExtensions.cs

@@ -9,7 +9,7 @@ namespace Microsoft.AspNetCore.Components.Forms
 {
     internal static class InputExtensions
     {
-        public static bool TryParseSelectableValueFromString<TValue>(this InputBase<TValue> input, string? value, [MaybeNull] out TValue result, [NotNullWhen(false)] out string? validationErrorMessage)
+        public static bool TryParseSelectableValueFromString<TValue>(this InputBase<TValue> input, string? value, [MaybeNullWhen(false)] out TValue result, [NotNullWhen(false)] out string? validationErrorMessage)
         {
             try
             {

src/Components/Web/src/Forms/InputFile.cs

@@ -73,6 +73,11 @@ namespace Microsoft.AspNetCore.Components.Forms
         {
             var imageFile = await JSRuntime.InvokeAsync<BrowserFile>(InputFileInterop.ToImageFile, _inputFileElement, file.Id, format, maxWidth, maxHeight);
 
+            if (imageFile is null)
+            {
+                throw new InvalidOperationException("ToImageFile returned an unexpected null result.");
+            }
+
             imageFile.Owner = this;
 
             return imageFile;

src/Components/Web/src/Forms/InputFile/RemoteBrowserFileStream.cs

@@ -4,6 +4,7 @@
 using System;
 using System.Buffers;
 using System.IO.Pipelines;
+using System.Text.Json;
 using System.Threading;
 using System.Threading.Tasks;
 using Microsoft.JSInterop;
@@ -64,10 +65,10 @@ namespace Microsoft.AspNetCore.Components.Forms
                         offset,
                         segmentSize);
 
-                    if (bytes.Length != segmentSize)
+                    if (bytes is null || bytes.Length != segmentSize)
                     {
                         throw new InvalidOperationException(
-                            $"A segment with size {bytes.Length} bytes was received, but {segmentSize} bytes were expected.");
+                            $"A segment with size {bytes?.Length ?? 0} bytes was received, but {segmentSize} bytes were expected.");
                     }
 
                     bytes.CopyTo(pipeBuffer);

src/Components/Web/src/Forms/InputNumber.cs

@@ -55,7 +55,7 @@ namespace Microsoft.AspNetCore.Components.Forms
         }
 
         /// <inheritdoc />
-        protected override bool TryParseValueFromString(string? value, [MaybeNull] out TValue result, [NotNullWhen(false)] out string? validationErrorMessage)
+        protected override bool TryParseValueFromString(string? value, [MaybeNullWhen(false)] out TValue result, [NotNullWhen(false)] out string? validationErrorMessage)
         {
             if (BindConverter.TryConvertTo<TValue>(value, CultureInfo.InvariantCulture, out result))
             {
@@ -74,7 +74,7 @@ namespace Microsoft.AspNetCore.Components.Forms
         /// </summary>
         /// <param name="value">The value to format.</param>
         /// <returns>A string representation of the value.</returns>
-        protected override string? FormatValueAsString([AllowNull] TValue value)
+        protected override string? FormatValueAsString(TValue? value)
         {
             // Avoiding a cast to IFormattable to avoid boxing.
             switch (value)

src/Components/Web/src/Forms/InputRadio.cs

@@ -27,10 +27,8 @@ namespace Microsoft.AspNetCore.Components.Forms
         /// <summary>
         /// Gets or sets the value of this input.
         /// </summary>
-        [AllowNull]
-        [MaybeNull]
         [Parameter]
-        public TValue Value { get; set; } = default;
+        public TValue? Value { get; set; }
 
         /// <summary>
         /// Gets or sets the name of the parent input radio group.

src/Components/Web/src/Forms/InputRadioGroup.cs

@@ -52,7 +52,7 @@ namespace Microsoft.AspNetCore.Components.Forms
         }
 
         /// <inheritdoc />
-        protected override bool TryParseValueFromString(string? value, [MaybeNull] out TValue result, [NotNullWhen(false)] out string? validationErrorMessage)
+        protected override bool TryParseValueFromString(string? value, [MaybeNullWhen(false)] out TValue result, [NotNullWhen(false)] out string? validationErrorMessage)
             => this.TryParseSelectableValueFromString(value, out result, out validationErrorMessage);
     }
 }

src/Components/Web/src/Forms/InputSelect.cs

@@ -29,7 +29,7 @@ namespace Microsoft.AspNetCore.Components.Forms
         }
 
         /// <inheritdoc />
-        protected override bool TryParseValueFromString(string? value, [MaybeNull] out TValue result, [NotNullWhen(false)] out string? validationErrorMessage)
+        protected override bool TryParseValueFromString(string? value, [MaybeNullWhen(false)] out TValue result, [NotNullWhen(false)] out string? validationErrorMessage)
             => this.TryParseSelectableValueFromString(value, out result, out validationErrorMessage);
     }
 }

src/JSInterop/Microsoft.JSInterop/src/IJSInProcessRuntime.cs

@@ -11,10 +11,10 @@ namespace Microsoft.JSInterop
         /// <summary>
         /// Invokes the specified JavaScript function synchronously.
         /// </summary>
-        /// <typeparam name="T">The JSON-serializable return type.</typeparam>
+        /// <typeparam name="TResult">The JSON-serializable return type.</typeparam>
         /// <param name="identifier">An identifier for the function to invoke. For example, the value <c>"someScope.someFunction"</c> will invoke the function <c>window.someScope.someFunction</c>.</param>
         /// <param name="args">JSON-serializable arguments.</param>
-        /// <returns>An instance of <typeparamref name="T"/> obtained by JSON-deserializing the return value.</returns>
-        T Invoke<T>(string identifier, params object?[]? args);
+        /// <returns>An instance of <typeparamref name="TResult"/> obtained by JSON-deserializing the return value.</returns>
+        TResult Invoke<TResult>(string identifier, params object?[]? args);
     }
 }

src/JSInterop/Microsoft.JSInterop/src/Implementation/JSInProcessObjectReference.cs

@@ -23,7 +23,6 @@ namespace Microsoft.JSInterop.Implementation
         }
 
         /// <inheritdoc />
-        [return: MaybeNull]
         public TValue Invoke<TValue>(string identifier, params object?[]? args)
         {
             ThrowIfDisposed();

src/JSInterop/Microsoft.JSInterop/src/JSInProcessRuntime.cs

@@ -23,7 +23,6 @@ namespace Microsoft.JSInterop
                     id => new JSInProcessObjectReference(this, id)));
         }
 
-        [return: MaybeNull]
         internal TValue Invoke<TValue>(string identifier, long targetInstanceId, params object?[]? args)
         {
             var resultJson = InvokeJS(
@@ -32,12 +31,15 @@ namespace Microsoft.JSInterop
                 JSCallResultTypeHelper.FromGeneric<TValue>(),
                 targetInstanceId);
 
+            // While the result of deserialization could be null, we're making a
+            // quality of life decision and letting users explicitly determine if they expect
+            // null by specifying TValue? as the expected return type.
             if (resultJson is null)
             {
-                return default;
+                return default!;
             }
 
-            return JsonSerializer.Deserialize<TValue>(resultJson, JsonSerializerOptions);
+            return JsonSerializer.Deserialize<TValue>(resultJson, JsonSerializerOptions)!;
         }
 
         /// <summary>
@@ -47,7 +49,6 @@ namespace Microsoft.JSInterop
         /// <param name="identifier">An identifier for the function to invoke. For example, the value <c>"someScope.someFunction"</c> will invoke the function <c>window.someScope.someFunction</c>.</param>
         /// <param name="args">JSON-serializable arguments.</param>
         /// <returns>An instance of <typeparamref name="TValue"/> obtained by JSON-deserializing the return value.</returns>
-        [return: MaybeNull]
         public TValue Invoke<TValue>(string identifier, params object?[]? args)
             => Invoke<TValue>(identifier, 0, args);
 

src/JSInterop/Microsoft.JSInterop/src/JSRuntime.cs

@@ -102,7 +102,7 @@ namespace Microsoft.JSInterop
         {
             var taskId = Interlocked.Increment(ref _nextPendingTaskId);
             var tcs = new TaskCompletionSource<TValue>();
-            if (cancellationToken != default)
+            if (cancellationToken.CanBeCanceled)
             {
                 _cancellationRegistrations[taskId] = cancellationToken.Register(() =>
                 {

src/JSInterop/Microsoft.JSInterop/src/JSRuntimeExtensions.cs

@@ -41,7 +41,7 @@ namespace Microsoft.JSInterop
         /// <param name="identifier">An identifier for the function to invoke. For example, the value <c>"someScope.someFunction"</c> will invoke the function <c>window.someScope.someFunction</c>.</param>
         /// <param name="args">JSON-serializable arguments.</param>
         /// <returns>An instance of <typeparamref name="TValue"/> obtained by JSON-deserializing the return value.</returns>
-        public static ValueTask<TValue> InvokeAsync<TValue>(this IJSRuntime jsRuntime, string identifier, params object[] args)
+        public static ValueTask<TValue> InvokeAsync<TValue>(this IJSRuntime jsRuntime, string identifier, params object?[]? args)
         {
             if (jsRuntime is null)
             {
@@ -63,7 +63,7 @@ namespace Microsoft.JSInterop
         /// </param>
         /// <param name="args">JSON-serializable arguments.</param>
         /// <returns>An instance of <typeparamref name="TValue"/> obtained by JSON-deserializing the return value.</returns>
-        public static ValueTask<TValue> InvokeAsync<TValue>(this IJSRuntime jsRuntime, string identifier, CancellationToken cancellationToken, params object[] args)
+        public static ValueTask<TValue> InvokeAsync<TValue>(this IJSRuntime jsRuntime, string identifier, CancellationToken cancellationToken, params object?[]? args)
         {
             if (jsRuntime is null)
             {
@@ -102,7 +102,7 @@ namespace Microsoft.JSInterop
         /// <param name="timeout">The duration after which to cancel the async operation. Overrides default timeouts (<see cref="JSRuntime.DefaultAsyncTimeout"/>).</param>
         /// <param name="args">JSON-serializable arguments.</param>
         /// <returns>A <see cref="ValueTask"/> that represents the asynchronous invocation operation.</returns>
-        public static async ValueTask<TValue> InvokeAsync<TValue>(this IJSRuntime jsRuntime, string identifier, TimeSpan timeout, params object[] args)
+        public static async ValueTask<TValue> InvokeAsync<TValue>(this IJSRuntime jsRuntime, string identifier, TimeSpan timeout, params object?[]? args)
         {
             if (jsRuntime is null)
             {

src/JSInterop/Microsoft.JSInterop/test/JSRuntimeTest.cs

@@ -3,6 +3,7 @@
 
 using System;
 using System.Collections.Generic;
+using System.Diagnostics;
 using System.Linq;
 using System.Text;
 using System.Text.Json;
@@ -145,6 +146,7 @@ namespace Microsoft.JSInterop
                 ref reader);
             Assert.True(task.IsCompleted);
             var poco = task.Result;
+            Debug.Assert(poco != null);
             Assert.Equal(10, poco.Id);
             Assert.Equal("Test", poco.Name);
         }
@@ -167,6 +169,7 @@ namespace Microsoft.JSInterop
                 ref reader);
             Assert.True(task.IsCompleted);
             var poco = task.Result;
+            Debug.Assert(poco != null);
             Assert.Equal(10, poco.Id);
             Assert.Equal("Test", poco.Name);
         }