Allow passing a dictionary to ValidationProblemDetails

Fixes https://github.com/aspnet/Mvc/issues/8645

src/Microsoft.AspNetCore.Mvc.Core/ValidationProblemDetails.cs

@@ -22,6 +22,10 @@ namespace Microsoft.AspNetCore.Mvc
             Title = Resources.ValidationProblemDescription_Title;
         }
 
+        /// <summary>
+        /// Initializes a new instance of <see cref="ValidationProblemDetails"/> using the specified <paramref name="modelState"/>.
+        /// </summary>
+        /// <param name="modelState"><see cref="ModelStateDictionary"/> containing the validation errors.</param>
         public ValidationProblemDetails(ModelStateDictionary modelState)
             : this()
         {
@@ -63,7 +67,22 @@ namespace Microsoft.AspNetCore.Mvc
         }
 
         /// <summary>
-        /// Gets or sets the validation errors associated with this instance of <see cref="ValidationProblemDetails"/>.
+        /// Initializes a new instance of <see cref="ValidationProblemDetails"/> using the specified <paramref name="errors"/>.
+        /// </summary>
+        /// <param name="errors">The validation errors.</param>
+        public ValidationProblemDetails(IDictionary<string, string[]> errors)
+            : this()
+        {
+            if (errors == null)
+            {
+                throw new ArgumentNullException(nameof(errors));
+            }
+
+            Errors = new Dictionary<string, string[]>(errors, StringComparer.Ordinal);
+        }
+
+        /// <summary>
+        /// Gets the validation errors associated with this instance of <see cref="ValidationProblemDetails"/>.
         /// </summary>
         [JsonProperty(PropertyName = "errors")]
         public IDictionary<string, string[]> Errors { get; } = new Dictionary<string, string[]>(StringComparer.Ordinal);

test/Microsoft.AspNetCore.Mvc.Core.Test/ValidationProblemDetailsTest.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.Collections.Generic;
 using Microsoft.AspNetCore.Mvc.ModelBinding;
 using Xunit;
 
@@ -73,5 +74,34 @@ namespace Microsoft.AspNetCore.Mvc
                     Assert.Equal(new[] { "The input was not valid." }, item.Value);
                 });
         }
+
+        [Fact]
+        public void Constructor_CopiesPassedInDictionary()
+        {
+            // Arrange
+            var errors = new Dictionary<string, string[]>
+            {
+                ["key1"] = new[] { "error1", "error2" },
+                ["key2"] = new[] { "error3", },
+            };
+
+            // Act
+            var problemDescription = new ValidationProblemDetails(errors);
+
+            // Assert
+            Assert.Equal("One or more validation errors occurred.", problemDescription.Title);
+            Assert.Collection(
+                problemDescription.Errors,
+                item =>
+                {
+                    Assert.Equal("key1", item.Key);
+                    Assert.Equal(new[] { "error1", "error2" }, item.Value);
+                },
+                item =>
+                {
+                    Assert.Equal("key2", item.Key);
+                    Assert.Equal(new[] { "error3" }, item.Value);
+                });
+        }
     }
 }