Validation fixes for Blazor

* Ensure validation result that are not associated with a member are recorded. Fixes #10643
* Add support for showing model-specific errors to ValidationSummary
* Add support for nested validation and a more suitable CompareAttribute. Fixes #10526

eng/ProjectReferences.props

@@ -137,6 +137,7 @@
     <ProjectReferenceProvider Include="Microsoft.AspNetCore.Blazor" ProjectPath="$(RepoRoot)src\Components\Blazor\Blazor\src\Microsoft.AspNetCore.Blazor.csproj" RefProjectPath="$(RepoRoot)src\Components\Blazor\Blazor\ref\Microsoft.AspNetCore.Blazor.csproj" />
     <ProjectReferenceProvider Include="Microsoft.AspNetCore.Blazor.HttpClient" ProjectPath="$(RepoRoot)src\Components\Blazor\Http\src\Microsoft.AspNetCore.Blazor.HttpClient.csproj" RefProjectPath="$(RepoRoot)src\Components\Blazor\Http\ref\Microsoft.AspNetCore.Blazor.HttpClient.csproj" />
     <ProjectReferenceProvider Include="Microsoft.AspNetCore.Blazor.Server" ProjectPath="$(RepoRoot)src\Components\Blazor\Server\src\Microsoft.AspNetCore.Blazor.Server.csproj" RefProjectPath="$(RepoRoot)src\Components\Blazor\Server\ref\Microsoft.AspNetCore.Blazor.Server.csproj" />
+    <ProjectReferenceProvider Include="Microsoft.AspNetCore.Blazor.DataAnnotations.Validation" ProjectPath="$(RepoRoot)src\Components\Blazor\Validation\src\Microsoft.AspNetCore.Blazor.DataAnnotations.Validation.csproj" RefProjectPath="$(RepoRoot)src\Components\Blazor\Validation\ref\Microsoft.AspNetCore.Blazor.DataAnnotations.Validation.csproj" />
     <ProjectReferenceProvider Include="Microsoft.AspNetCore.Components" ProjectPath="$(RepoRoot)src\Components\Components\src\Microsoft.AspNetCore.Components.csproj" RefProjectPath="$(RepoRoot)src\Components\Components\ref\Microsoft.AspNetCore.Components.csproj" />
     <ProjectReferenceProvider Include="Microsoft.AspNetCore.Components.Forms" ProjectPath="$(RepoRoot)src\Components\Forms\src\Microsoft.AspNetCore.Components.Forms.csproj" RefProjectPath="$(RepoRoot)src\Components\Forms\ref\Microsoft.AspNetCore.Components.Forms.csproj" />
     <ProjectReferenceProvider Include="Microsoft.AspNetCore.Components.Server" ProjectPath="$(RepoRoot)src\Components\Server\src\Microsoft.AspNetCore.Components.Server.csproj" RefProjectPath="$(RepoRoot)src\Components\Server\ref\Microsoft.AspNetCore.Components.Server.csproj" />

src/Components/Blazor/Validation/src/BlazorCompareAttribute.cs

@@ -0,0 +1,33 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+namespace System.ComponentModel.DataAnnotations
+{
+    /// <summary>
+    /// A <see cref="ValidationAttribute"/> that compares two properties
+    /// </summary>
+    public sealed class BlazorCompareAttribute : CompareAttribute
+    {
+        /// <summary>
+        /// Initializes a new instance of <see cref="BlazorCompareAttribute"/>.
+        /// </summary>
+        /// <param name="otherProperty">The property to compare with the current property.</param>
+        public BlazorCompareAttribute(string otherProperty)
+            : base(otherProperty)
+        {
+        }
+
+        /// <inheritdoc />
+        protected override ValidationResult IsValid(object value, ValidationContext validationContext)
+        {
+            var validationResult = base.IsValid(value, validationContext);
+            if (validationResult == ValidationResult.Success)
+            {
+                return validationResult;
+            }
+
+            return new ValidationResult(validationResult.ErrorMessage, new[] { validationContext.MemberName });
+        }
+    }
+}
+

src/Components/Blazor/Validation/src/BlazorDataAnnotationsValidator.cs

@@ -0,0 +1,116 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System.Collections.Generic;
+using System.ComponentModel.DataAnnotations;
+using System.Linq;
+
+namespace Microsoft.AspNetCore.Components.Forms
+{
+    public class BlazorDataAnnotationsValidator : ComponentBase
+    {
+        private static readonly object ValidationContextValidatorKey = new object();
+        private ValidationMessageStore _validationMessageStore;
+
+        [CascadingParameter]
+        internal EditContext EditContext { get; set; }
+
+        protected override void OnInitialized()
+        {
+            _validationMessageStore = new ValidationMessageStore(EditContext);
+
+            // Perform object-level validation (starting from the root model) on request
+            EditContext.OnValidationRequested += (sender, eventArgs) =>
+            {
+                _validationMessageStore.Clear();
+                ValidateObject(EditContext.Model);
+                EditContext.NotifyValidationStateChanged();
+            };
+
+            // Perform per-field validation on each field edit
+            EditContext.OnFieldChanged += (sender, eventArgs) =>
+                ValidateField(EditContext, _validationMessageStore, eventArgs.FieldIdentifier);
+        }
+
+        internal void ValidateObject(object value)
+        {
+            if (value is null)
+            {
+                return;
+            }
+
+            if (value is IEnumerable<object> enumerable)
+            {
+                var index = 0;
+                foreach (var item in enumerable)
+                {
+                    ValidateObject(item);
+                    index++;
+                }
+
+                return;
+            }
+
+            var validationResults = new List<ValidationResult>();
+            ValidateObject(value, validationResults);
+
+            // Transfer results to the ValidationMessageStore
+            foreach (var validationResult in validationResults)
+            {
+                if (!validationResult.MemberNames.Any())
+                {
+                    _validationMessageStore.Add(new FieldIdentifier(value, string.Empty), validationResult.ErrorMessage);
+                    continue;
+                }
+
+                foreach (var memberName in validationResult.MemberNames)
+                {
+                    var fieldIdentifier = new FieldIdentifier(value, memberName);
+                    _validationMessageStore.Add(fieldIdentifier, validationResult.ErrorMessage);
+                }
+            }
+        }
+
+        private void ValidateObject(object value, List<ValidationResult> validationResults)
+        {
+            var validationContext = new ValidationContext(value);
+            validationContext.Items.Add(ValidationContextValidatorKey, this);
+            Validator.TryValidateObject(value, validationContext, validationResults, validateAllProperties: true);
+        }
+
+        internal static bool TryValidateRecursive(object value, ValidationContext validationContext)
+        {
+            if (validationContext.Items.TryGetValue(ValidationContextValidatorKey, out var result) && result is BlazorDataAnnotationsValidator validator)
+            {
+                validator.ValidateObject(value);
+
+                return true;
+            }
+
+            return false;
+        }
+
+        private static void ValidateField(EditContext editContext, ValidationMessageStore messages, in FieldIdentifier fieldIdentifier)
+        {
+            // DataAnnotations only validates public properties, so that's all we'll look for
+            var propertyInfo = fieldIdentifier.Model.GetType().GetProperty(fieldIdentifier.FieldName);
+            if (propertyInfo != null)
+            {
+                var propertyValue = propertyInfo.GetValue(fieldIdentifier.Model);
+                var validationContext = new ValidationContext(fieldIdentifier.Model)
+                {
+                    MemberName = propertyInfo.Name
+                };
+                var results = new List<ValidationResult>();
+
+                Validator.TryValidateProperty(propertyValue, validationContext, results);
+                messages.Clear(fieldIdentifier);
+                messages.Add(fieldIdentifier, results.Select(result => result.ErrorMessage));
+
+                // We have to notify even if there were no messages before and are still no messages now,
+                // because the "state" that changed might be the completion of some async validation task
+                editContext.NotifyValidationStateChanged();
+            }
+        }
+    }
+}

src/Components/Blazor/Validation/src/Microsoft.AspNetCore.Blazor.DataAnnotations.Validation.csproj

@@ -0,0 +1,17 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>netstandard2.0</TargetFramework>
+    <Description>Provides experimental support for validation of complex properties using DataAnnotations.</Description>
+    <IsShippingPackage>true</IsShippingPackage>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <Reference Include="Microsoft.AspNetCore.Components.Forms" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <InternalsVisibleTo Include="Microsoft.AspNetCore.Blazor.DataAnnotations.Validation.Tests" />
+  </ItemGroup>
+
+</Project>

src/Components/Blazor/Validation/src/ValidateComplexTypeAttribute.cs

@@ -0,0 +1,29 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using Microsoft.AspNetCore.Components.Forms;
+
+namespace System.ComponentModel.DataAnnotations
+{
+    /// <summary>
+    /// A <see cref="ValidationAttribute"/> that indicates that the property is a complex or collection type that further needs to be validated.
+    /// <para>
+    /// By default <see cref="Validator"/> does not recurse in to complex property types during validation. When used in conjunction with <see cref="BlazorDataAnnotationsValidator"/>,
+    /// this property allows the validation system to validate complex or collection type properties.
+    /// </para>
+    /// </summary>
+    [AttributeUsage(AttributeTargets.Property, AllowMultiple = false)]
+    public sealed class ValidateComplexTypeAttribute : ValidationAttribute
+    {
+        /// <inheritdoc />
+        protected override ValidationResult IsValid(object value, ValidationContext validationContext)
+        {
+            if (!BlazorDataAnnotationsValidator.TryValidateRecursive(value, validationContext))
+            {
+                throw new InvalidOperationException($"{nameof(ValidateComplexTypeAttribute)} can only used with {nameof(BlazorDataAnnotationsValidator)}.");
+            }
+
+            return ValidationResult.Success;
+        }
+    }
+}