Fixes ReactiveValidationObject NullReferenceException and enhances performance and thread-safety of ValidationText

src/ReactiveUI.Validation.Tests/API/ApiApprovalTests.ValidationProject.net472.approved.txt

@@ -10,15 +10,35 @@ namespace ReactiveUI.Validation.Collections
 {
     public class ValidationText : System.Collections.Generic.IEnumerable<string>, System.Collections.IEnumerable
     {
+        public static readonly ReactiveUI.Validation.Collections.ValidationText Empty;
+        public static readonly ReactiveUI.Validation.Collections.ValidationText None;
+        [System.Diagnostics.CodeAnalysis.ExcludeFromCodeCoverage]
+        [System.Obsolete("Calling the constructor is deprecated, please use ValidationText.Create() overloa" +
+            "d instead.")]
         public ValidationText() { }
+        [System.Diagnostics.CodeAnalysis.ExcludeFromCodeCoverage]
+        [System.Obsolete("Calling the constructor is deprecated, please use ValidationText.Create(IEnumerab" +
+            "le<ValidationText>) overload instead.")]
         public ValidationText(System.Collections.Generic.IEnumerable<ReactiveUI.Validation.Collections.ValidationText> validationTexts) { }
+        [System.Diagnostics.CodeAnalysis.ExcludeFromCodeCoverage]
+        [System.Obsolete("Calling the constructor is deprecated, please use ValidationText.Create(string) o" +
+            "verload instead.")]
         public ValidationText(string text) { }
         public int Count { get; }
         public string this[int index] { get; }
+        [System.Diagnostics.CodeAnalysis.ExcludeFromCodeCoverage]
+        [System.Obsolete("ValidationText will be made immutable in future versions, please do not use the A" +
+            "dd(string) method.")]
         public void Add(string text) { }
+        [System.Diagnostics.CodeAnalysis.ExcludeFromCodeCoverage]
+        [System.Obsolete("ValidationText will be made immutable in future versions, please do not use the C" +
+            "lear() method.")]
         public void Clear() { }
         public System.Collections.Generic.IEnumerator<string> GetEnumerator() { }
         public string ToSingleLine(string? separator = ",") { }
+        public static ReactiveUI.Validation.Collections.ValidationText Create(System.Collections.Generic.IEnumerable<ReactiveUI.Validation.Collections.ValidationText> validationTexts) { }
+        public static ReactiveUI.Validation.Collections.ValidationText Create(System.Collections.Generic.IEnumerable<string> validationTexts) { }
+        public static ReactiveUI.Validation.Collections.ValidationText Create(params string[] validationTexts) { }
     }
 }
 namespace ReactiveUI.Validation.Comparators

src/ReactiveUI.Validation.Tests/API/ApiApprovalTests.ValidationProject.netcoreapp3.1.approved.txt

@@ -10,15 +10,35 @@ namespace ReactiveUI.Validation.Collections
 {
     public class ValidationText : System.Collections.Generic.IEnumerable<string>, System.Collections.IEnumerable
     {
+        public static readonly ReactiveUI.Validation.Collections.ValidationText Empty;
+        public static readonly ReactiveUI.Validation.Collections.ValidationText None;
+        [System.Diagnostics.CodeAnalysis.ExcludeFromCodeCoverage]
+        [System.Obsolete("Calling the constructor is deprecated, please use ValidationText.Create() overloa" +
+            "d instead.")]
         public ValidationText() { }
+        [System.Diagnostics.CodeAnalysis.ExcludeFromCodeCoverage]
+        [System.Obsolete("Calling the constructor is deprecated, please use ValidationText.Create(IEnumerab" +
+            "le<ValidationText>) overload instead.")]
         public ValidationText(System.Collections.Generic.IEnumerable<ReactiveUI.Validation.Collections.ValidationText> validationTexts) { }
+        [System.Diagnostics.CodeAnalysis.ExcludeFromCodeCoverage]
+        [System.Obsolete("Calling the constructor is deprecated, please use ValidationText.Create(string) o" +
+            "verload instead.")]
         public ValidationText(string text) { }
         public int Count { get; }
         public string this[int index] { get; }
+        [System.Diagnostics.CodeAnalysis.ExcludeFromCodeCoverage]
+        [System.Obsolete("ValidationText will be made immutable in future versions, please do not use the A" +
+            "dd(string) method.")]
         public void Add(string text) { }
+        [System.Diagnostics.CodeAnalysis.ExcludeFromCodeCoverage]
+        [System.Obsolete("ValidationText will be made immutable in future versions, please do not use the C" +
+            "lear() method.")]
         public void Clear() { }
         public System.Collections.Generic.IEnumerator<string> GetEnumerator() { }
         public string ToSingleLine(string? separator = ",") { }
+        public static ReactiveUI.Validation.Collections.ValidationText Create(System.Collections.Generic.IEnumerable<ReactiveUI.Validation.Collections.ValidationText> validationTexts) { }
+        public static ReactiveUI.Validation.Collections.ValidationText Create(System.Collections.Generic.IEnumerable<string> validationTexts) { }
+        public static ReactiveUI.Validation.Collections.ValidationText Create(params string[] validationTexts) { }
     }
 }
 namespace ReactiveUI.Validation.Comparators

src/ReactiveUI.Validation.Tests/ValidationBindingTests.cs

@@ -706,7 +706,7 @@ private class CustomValidationState : IValidationState
             public CustomValidationState(bool isValid, string message)
             {
                 IsValid = isValid;
-                Text = new ValidationText(isValid ? string.Empty : message);
+                Text = isValid ? ValidationText.Empty : ValidationText.Create(message);
             }
 
             public ValidationText Text { get; }
@@ -723,4 +723,4 @@ private class ConstFormatter : IValidationTextFormatter<string>
             public string Format(ValidationText validationText) => _text;
         }
     }
-}
+}

src/ReactiveUI.Validation.Tests/ValidationTextTests.cs

@@ -0,0 +1,231 @@
+// Copyright (c) 2020 .NET Foundation and Contributors. All rights reserved.
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for full license information.
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using ReactiveUI.Validation.Collections;
+using ReactiveUI.Validation.Contexts;
+using Xunit;
+
+namespace ReactiveUI.Validation.Tests
+{
+    /// <summary>
+    /// Tests for <see cref="ValidationContext"/>.
+    /// </summary>
+    public class ValidationTextTests
+    {
+        /// <summary>
+        /// Verifies that <see cref="ValidationText.None"/> is genuinely empty.
+        /// </summary>
+        [Fact]
+        public void NoneValidationTextIsEmpty()
+        {
+            ValidationText vt = ValidationText.None;
+
+            Assert.Equal(0, vt.Count);
+
+            // Calling Count() checks the enumeration returns no results, unlike the Count property.
+#pragma warning disable CA1829 // Use Length/Count property instead of Count() when available
+            Assert.Equal(0, vt.Count());
+#pragma warning restore CA1829 // Use Length/Count property instead of Count() when available
+            Assert.Equal(string.Empty, vt.ToSingleLine());
+        }
+
+        /// <summary>
+        /// Verifies that <see cref="ValidationText.Empty"/> has a single empty item.
+        /// </summary>
+        [Fact]
+        public void EmptyValidationTextIsSingleEmpty()
+        {
+            ValidationText vt = ValidationText.Empty;
+
+            Assert.Equal(1, vt.Count);
+
+            // Calling Count() checks the enumeration returns no results, unlike the Count property.
+#pragma warning disable CA1829 // Use Length/Count property instead of Count() when available
+            Assert.Equal(1, vt.Count());
+#pragma warning restore CA1829 // Use Length/Count property instead of Count() when available
+            Assert.Same(string.Empty, vt.Single());
+            Assert.Equal(string.Empty, vt.ToSingleLine());
+        }
+
+        /// <summary>
+        /// Verifies that calling <see cref="ValidationText.Create(string[])"/> without parameters returns <see cref="ValidationText.None"/>.
+        /// </summary>
+        [Fact]
+        public void ParameterlessCreateReturnsNone()
+        {
+            ValidationText vt = ValidationText.Create();
+
+            Assert.Same(ValidationText.None, vt);
+        }
+
+        /// <summary>
+        /// Verifies that calling <see cref="ValidationText.Create(IEnumerable{string})"/> with an empty enumerable <see cref="ValidationText.None"/>.
+        /// </summary>
+        [Fact]
+        public void CreateEmptyStringEnumerableReturnsNone()
+        {
+            ValidationText vt = ValidationText.Create((IEnumerable<string>)Array.Empty<string>());
+
+            Assert.Same(ValidationText.None, vt);
+        }
+
+        /// <summary>
+        /// Verifies that calling <see cref="ValidationText.Create(IEnumerable{ValidationText})"/> with an empty enumerable <see cref="ValidationText.None"/>.
+        /// </summary>
+        [Fact]
+        public void CreateEmptyValidationTextEnumerableReturnsNone()
+        {
+            ValidationText vt = ValidationText.Create(Array.Empty<ValidationText>());
+
+            Assert.Same(ValidationText.None, vt);
+        }
+
+        /// <summary>
+        /// Verifies that calling <see cref="ValidationText.Create(string[])"/> with <see langword="null"/> returns <see cref="ValidationText.None"/>.
+        /// </summary>
+        [Fact]
+        public void CreateNullReturnsNone()
+        {
+            ValidationText vt = ValidationText.Create((string)null);
+
+            Assert.Same(ValidationText.None, vt);
+        }
+
+        /// <summary>
+        /// Verifies that calling <see cref="ValidationText.Create(IEnumerable{string})"/> with <see langword="null"/> enumerable returns <see cref="ValidationText.None"/>.
+        /// </summary>
+        [Fact]
+        public void CreateNullStringEnumerableReturnsNone()
+        {
+            ValidationText vt = ValidationText.Create((IEnumerable<string>)null);
+
+            Assert.Same(ValidationText.None, vt);
+        }
+
+        /// <summary>
+        /// Verifies that calling <see cref="ValidationText.Create(IEnumerable{ValidationText})"/> with <see langword="null"/> returns <see cref="ValidationText.None"/>.
+        /// </summary>
+        [Fact]
+        public void CreateNullValidationTextEnumerableReturnsNone()
+        {
+            ValidationText vt = ValidationText.Create((IEnumerable<ValidationText>)null);
+
+            Assert.Same(ValidationText.None, vt);
+        }
+
+        /// <summary>
+        /// Verifies that calling <see cref="ValidationText.Create(IEnumerable{string})"/> with an enumerable containing <see langword="null"/> returns <see cref="ValidationText.None"/>.
+        /// </summary>
+        [Fact]
+        public void CreateNullItemStringEnumerableReturnsNone()
+        {
+            ValidationText vt = ValidationText.Create((IEnumerable<string>)new string[] { null });
+
+            Assert.Same(ValidationText.None, vt);
+        }
+
+        /// <summary>
+        /// Verifies that calling <see cref="ValidationText.Create(IEnumerable{ValidationText})"/>  with an enumerable containing <see cref="ValidationText.None"/> returns <see cref="ValidationText.None"/>.
+        /// </summary>
+        [Fact]
+        public void CreateNoneItemValidationTextEnumerableReturnsNone()
+        {
+            ValidationText vt = ValidationText.Create(new[] { ValidationText.None });
+
+            Assert.Same(ValidationText.None, vt);
+        }
+
+        /// <summary>
+        /// Verifies that calling <see cref="ValidationText.Create(IEnumerable{string})"/>  with an enumerable containing <see cref="ValidationText.None"/> returns <see cref="ValidationText.None"/>.
+        /// </summary>
+        [Fact]
+        public void CreateNoneItemStringEnumerableReturnsNone()
+        {
+            ValidationText vt = ValidationText.Create(ValidationText.None);
+
+            Assert.Same(ValidationText.None, vt);
+        }
+
+        /// <summary>
+        /// Verifies that calling <see cref="ValidationText.Create(string[])"/> with <see cref="string.Empty"/> returns <see cref="ValidationText.Empty"/>.
+        /// </summary>
+        [Fact]
+        public void CreateStringEmptyReturnsEmpty()
+        {
+            ValidationText vt = ValidationText.Create(string.Empty);
+
+            Assert.Same(ValidationText.Empty, vt);
+        }
+
+        /// <summary>
+        /// Verifies that calling <see cref="ValidationText.Create(IEnumerable{string})"/> with an enumerable containing <see cref="string.Empty"/> returns <see cref="ValidationText.Empty"/>.
+        /// </summary>
+        [Fact]
+        public void CreateSingleStringEmptyReturnsEmpty()
+        {
+            ValidationText vt = ValidationText.Create((IEnumerable<string>)new[] { string.Empty });
+
+            Assert.Same(ValidationText.Empty, vt);
+        }
+
+        /// <summary>
+        /// Verifies that calling <see cref="ValidationText.Create(IEnumerable{string})"/> with an enumerable containing <see cref="string.Empty"/> returns <see cref="ValidationText.Empty"/>.
+        /// </summary>
+        [Fact]
+        public void CreateValidationTextEmptyReturnsEmpty()
+        {
+            ValidationText vt = ValidationText.Create(new[] { ValidationText.Empty });
+
+            Assert.Same(ValidationText.Empty, vt);
+        }
+
+        /// <summary>
+        /// Verifies that calling <see cref="ValidationText.Create(IEnumerable{ValidationText})"/> with an enumerable containing two <see cref="ValidationText.None"/> returns <see cref="ValidationText.None"/>.
+        /// </summary>
+        [Fact]
+        public void CombineValidationTextNoneReturnsNone()
+        {
+            ValidationText vt = ValidationText.Create(new[] { ValidationText.None, ValidationText.None });
+
+            Assert.Same(ValidationText.None, vt);
+        }
+
+        /// <summary>
+        /// Verifies that calling <see cref="ValidationText.Create(IEnumerable{ValidationText})"/> with an enumerable containing <see cref="ValidationText.None"/> and <see cref="ValidationText.Empty"/> returns <see cref="ValidationText.Empty"/>.
+        /// </summary>
+        [Fact]
+        public void CombineValidationTextEmptyAndNoneReturnsEmpty()
+        {
+            ValidationText vt = ValidationText.Create(new[] { ValidationText.None, ValidationText.Empty });
+
+            Assert.Same(ValidationText.Empty, vt);
+        }
+
+        /// <summary>
+        /// Verifies that calling <see cref="ValidationText.Create(IEnumerable{ValidationText})"/> with an enumerable containing two <see cref="ValidationText.Empty"/>
+        /// returns a single <see cref="ValidationText"/> with two empty strings.
+        /// </summary>
+        [Fact]
+        public void CombineValidationTextEmptyReturnsTwoEmpty()
+        {
+            ValidationText vt = ValidationText.Create(new[] { ValidationText.Empty, ValidationText.Empty });
+
+            Assert.NotSame(ValidationText.Empty, vt);
+            Assert.Equal(2, vt.Count);
+
+            // Calling Count() checks the enumeration returns no results, unlike the Count property.
+#pragma warning disable CA1829 // Use Length/Count property instead of Count() when available
+            Assert.Equal(2, vt.Count());
+#pragma warning restore CA1829 // Use Length/Count property instead of Count() when available
+            Assert.Equal(string.Empty, vt[0]);
+            Assert.Equal(string.Empty, vt[1]);
+
+            Assert.Equal("|", vt.ToSingleLine("|"));
+        }
+    }
+}