Implement 'Use proper Assert methods' analyzer

src/Analyzers/MSTest.Analyzers/AnalyzerReleases.Unshipped.md

@@ -1,3 +1,8 @@
 ; Unshipped analyzer release
 ; https://github.com/dotnet/roslyn-analyzers/blob/main/src/Microsoft.CodeAnalysis.Analyzers/ReleaseTrackingAnalyzers.Help.md
 
+### New Rules
+
+Rule ID | Category | Severity | Notes
+--------|----------|----------|-------
+MSTEST0037 | `Usage` | Disabled | UseProperAssertMethodsAnalyzer

src/Analyzers/MSTest.Analyzers/Helpers/DiagnosticIds.cs

@@ -41,4 +41,5 @@ internal static class DiagnosticIds
     public const string UseClassCleanupBehaviorEndOfClassRuleId = "MSTEST0034";
     public const string UseDeploymentItemWithTestMethodOrTestClassRuleId = "MSTEST0035";
     public const string DoNotUseShadowingRuleId = "MSTEST0036";
+    public const string UseProperAssertMethodsRuleId = "MSTEST0037";
 }

src/Analyzers/MSTest.Analyzers/Resources.resx

@@ -529,4 +529,10 @@ The type declaring these methods should also respect the following rules:
   <data name="DoNotUseShadowingTitle" xml:space="preserve">
     <value>Do not use shadowing</value>
   </data>
+  <data name="UseProperAssertMethodsTitle" xml:space="preserve">
+    <value>Use proper 'Assert' methods</value>
+  </data>
+  <data name="UseProperAssertMethodsMessageFormat" xml:space="preserve">
+    <value>Use 'Assert.{0}' instead of 'Assert.{1}'</value>
+  </data>
 </root>

src/Analyzers/MSTest.Analyzers/RoslynAnalyzerHelpers/IOperationExtensions.cs

@@ -25,4 +25,19 @@ internal static class IOperationExtensions
 
         _ => null,
     };
+
+    /// <summary>
+    /// Walks down consecutive conversion operations until an operand is reached that isn't a conversion operation.
+    /// </summary>
+    /// <param name="operation">The starting operation.</param>
+    /// <returns>The inner non conversion operation or the starting operation if it wasn't a conversion operation.</returns>
+    public static IOperation WalkDownConversion(this IOperation operation)
+    {
+        while (operation is IConversionOperation conversionOperation)
+        {
+            operation = conversionOperation.Operand;
+        }
+
+        return operation;
+    }
 }

src/Analyzers/MSTest.Analyzers/UseProperAssertMethodsAnalyzer.cs

@@ -0,0 +1,238 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+using System.Collections.Immutable;
+using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
+
+using Analyzer.Utilities.Extensions;
+
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.Diagnostics;
+using Microsoft.CodeAnalysis.Operations;
+
+using MSTest.Analyzers.Helpers;
+using MSTest.Analyzers.RoslynAnalyzerHelpers;
+
+namespace MSTest.Analyzers;
+
+/// <summary>
+/// MSTEST0037: Use proper 'Assert' methods.
+/// </summary>
+/// <remarks>
+/// The analyzer captures the following cases:
+/// <list type="bullet">
+/// <item>
+/// <code>Assert.[IsTrue|IsFalse](x [==|!=|is|is not] null)</code>
+/// </item>
+/// <item>
+/// <code>Assert.[IsTrue|IsFalse](x [==|!=] y)</code>
+/// </item>
+/// <item>
+/// <code>Assert.AreEqual([true|false], x)</code>
+/// </item>
+/// <item>
+/// <code>Assert.[AreEqual|AreNotEqual](null, x)</code>
+/// </item>
+/// </list>
+/// </remarks>
+[DiagnosticAnalyzer(LanguageNames.CSharp, LanguageNames.VisualBasic)]
+internal sealed class UseProperAssertMethodsAnalyzer : DiagnosticAnalyzer
+{
+    private enum NullCheckStatus
+    {
+        Unknown,
+        IsNull,
+        IsNotNull,
+    }
+
+    private enum EqualityCheckStatus
+    {
+        Unknown,
+        Equals,
+        NotEquals,
+    }
+
+    private static readonly LocalizableResourceString Title = new(nameof(Resources.UseProperAssertMethodsTitle), Resources.ResourceManager, typeof(Resources));
+    private static readonly LocalizableResourceString MessageFormat = new(nameof(Resources.UseProperAssertMethodsMessageFormat), Resources.ResourceManager, typeof(Resources));
+
+    internal static readonly DiagnosticDescriptor Rule = DiagnosticDescriptorHelper.Create(
+        DiagnosticIds.UseProperAssertMethodsRuleId,
+        Title,
+        MessageFormat,
+        null,
+        Category.Usage,
+        DiagnosticSeverity.Info,
+        isEnabledByDefault: false);
+
+    public override ImmutableArray<DiagnosticDescriptor> SupportedDiagnostics { get; }
+        = ImmutableArray.Create(Rule);
+
+    public override void Initialize(AnalysisContext context)
+    {
+        context.ConfigureGeneratedCodeAnalysis(GeneratedCodeAnalysisFlags.None);
+        context.EnableConcurrentExecution();
+
+        context.RegisterCompilationStartAction(context =>
+        {
+            if (!context.Compilation.TryGetOrCreateTypeByMetadataName(WellKnownTypeNames.MicrosoftVisualStudioTestToolsUnitTestingAssert, out INamedTypeSymbol? assertTypeSymbol))
+            {
+                return;
+            }
+
+            context.RegisterOperationAction(context => AnalyzeInvocationOperation(context, assertTypeSymbol), OperationKind.Invocation);
+        });
+    }
+
+    private static void AnalyzeInvocationOperation(OperationAnalysisContext context, INamedTypeSymbol assertTypeSymbol)
+    {
+        var operation = (IInvocationOperation)context.Operation;
+        IMethodSymbol targetMethod = operation.TargetMethod;
+        if (!SymbolEqualityComparer.Default.Equals(targetMethod.ContainingType, assertTypeSymbol))
+        {
+            return;
+        }
+
+        if (!TryGetFirstArgumentValue(operation, out IOperation? firstArgument))
+        {
+            return;
+        }
+
+        switch (targetMethod.Name)
+        {
+            case "IsTrue":
+                AnalyzeIsTrueOrIsFalseInvocation(context, firstArgument, isTrueInvocation: true);
+                break;
+
+            case "IsFalse":
+                AnalyzeIsTrueOrIsFalseInvocation(context, firstArgument, isTrueInvocation: false);
+                break;
+
+            case "AreEqual":
+                AnalyzeAreEqualOrAreNotEqualInvocation(context, firstArgument, isAreEqualInvocation: true);
+                break;
+
+            case "AreNotEqual":
+                AnalyzeAreEqualOrAreNotEqualInvocation(context, firstArgument, isAreEqualInvocation: false);
+                break;
+        }
+    }
+
+    private static bool IsIsNullPattern(IOperation operation)
+        => operation is IIsPatternOperation { Pattern: IConstantPatternOperation { Value: { } constantPatternValue } } &&
+            constantPatternValue.WalkDownConversion() is ILiteralOperation { ConstantValue: { HasValue: true, Value: null } };
+
+    private static bool IsIsNotNullPattern(IOperation operation)
+        => operation is IIsPatternOperation { Pattern: INegatedPatternOperation { Pattern: IConstantPatternOperation { Value: { } constantPatternValue } } } &&
+        constantPatternValue.WalkDownConversion() is ILiteralOperation { ConstantValue: { HasValue: true, Value: null } };
+
+    // TODO: Recognize 'null == something' (i.e, when null is the left operand)
+    private static bool IsEqualsNullBinaryOperator(IOperation operation)
+        => operation is IBinaryOperation { OperatorKind: BinaryOperatorKind.Equals, RightOperand: { } rightOperand } &&
+            rightOperand.WalkDownConversion() is ILiteralOperation { ConstantValue: { HasValue: true, Value: null } };
+
+    // TODO: Recognize 'null != something' (i.e, when null is the left operand)
+    private static bool IsNotEqualsNullBinaryOperator(IOperation operation)
+        => operation is IBinaryOperation { OperatorKind: BinaryOperatorKind.NotEquals, RightOperand: { } rightOperand } &&
+            rightOperand.WalkDownConversion() is ILiteralOperation { ConstantValue: { HasValue: true, Value: null } };
+
+    private static NullCheckStatus RecognizeNullCheck(IOperation operation)
+    {
+        if (IsIsNullPattern(operation) || IsEqualsNullBinaryOperator(operation))
+        {
+            return NullCheckStatus.IsNull;
+        }
+        else if (IsIsNotNullPattern(operation) || IsNotEqualsNullBinaryOperator(operation))
+        {
+            return NullCheckStatus.IsNotNull;
+        }
+
+        return NullCheckStatus.Unknown;
+    }
+
+    private static EqualityCheckStatus RecognizeEqualityCheck(IOperation operation)
+    {
+        if (operation is IIsPatternOperation { Pattern: IConstantPatternOperation } or
+            IBinaryOperation { OperatorKind: BinaryOperatorKind.Equals })
+        {
+            return EqualityCheckStatus.Equals;
+        }
+        else if (operation is IIsPatternOperation { Pattern: INegatedPatternOperation { Pattern: IConstantPatternOperation } } or
+            IBinaryOperation { OperatorKind: BinaryOperatorKind.NotEquals })
+        {
+            return EqualityCheckStatus.NotEquals;
+        }
+
+        return EqualityCheckStatus.Unknown;
+    }
+
+    private static void AnalyzeIsTrueOrIsFalseInvocation(OperationAnalysisContext context, IOperation conditionArgument, bool isTrueInvocation)
+    {
+        NullCheckStatus nullCheckStatus = RecognizeNullCheck(conditionArgument);
+        if (nullCheckStatus != NullCheckStatus.Unknown)
+        {
+            Debug.Assert(nullCheckStatus is NullCheckStatus.IsNull or NullCheckStatus.IsNotNull, "Unexpected NullCheckStatus value.");
+            bool shouldUseIsNull = isTrueInvocation
+                ? nullCheckStatus == NullCheckStatus.IsNull
+                : nullCheckStatus == NullCheckStatus.IsNotNull;
+
+            // The message is: Use 'Assert.{0}' instead of 'Assert.{1}'.
+            context.ReportDiagnostic(context.Operation.CreateDiagnostic(
+                Rule,
+                shouldUseIsNull ? "IsNull" : "IsNotNull",
+                isTrueInvocation ? "IsTrue" : "IsFalse"));
+            return;
+        }
+
+        EqualityCheckStatus equalityCheckStatus = RecognizeEqualityCheck(conditionArgument);
+        if (equalityCheckStatus != EqualityCheckStatus.Unknown)
+        {
+            Debug.Assert(equalityCheckStatus is EqualityCheckStatus.Equals or EqualityCheckStatus.NotEquals, "Unexpected EqualityCheckStatus value.");
+            bool shouldUseAreEqual = isTrueInvocation
+                ? equalityCheckStatus == EqualityCheckStatus.Equals
+                : equalityCheckStatus == EqualityCheckStatus.NotEquals;
+
+            // The message is: Use 'Assert.{0}' instead of 'Assert.{1}'.
+            context.ReportDiagnostic(context.Operation.CreateDiagnostic(
+                Rule,
+                shouldUseAreEqual ? "AreEqual" : "AreNotEqual",
+                isTrueInvocation ? "IsTrue" : "IsFalse"));
+            return;
+        }
+    }
+
+    private static void AnalyzeAreEqualOrAreNotEqualInvocation(OperationAnalysisContext context, IOperation expectedArgument, bool isAreEqualInvocation)
+    {
+        // Don't flag a warning for Assert.AreNotEqual([true|false], x).
+        // This is not the same as Assert.IsFalse(x).
+        if (isAreEqualInvocation && expectedArgument is ILiteralOperation { ConstantValue: { HasValue: true, Value: bool expectedLiteralBoolean } })
+        {
+            bool shouldUseIsTrue = expectedLiteralBoolean;
+
+            // The message is: Use 'Assert.{0}' instead of 'Assert.{1}'.
+            context.ReportDiagnostic(context.Operation.CreateDiagnostic(
+                Rule,
+                shouldUseIsTrue ? "IsTrue" : "IsFalse",
+                isAreEqualInvocation ? "AreEqual" : "AreNotEqual"));
+        }
+        else if (expectedArgument is ILiteralOperation { ConstantValue: { HasValue: true, Value: null } })
+        {
+            bool shouldUseIsNull = isAreEqualInvocation;
+
+            // The message is: Use 'Assert.{0}' instead of 'Assert.{1}'.
+            context.ReportDiagnostic(context.Operation.CreateDiagnostic(
+                Rule,
+                shouldUseIsNull ? "IsNull" : "IsNotNull",
+                isAreEqualInvocation ? "AreEqual" : "AreNotEqual"));
+        }
+    }
+
+    private static bool TryGetFirstArgumentValue(IInvocationOperation operation, [NotNullWhen(true)] out IOperation? argumentValue)
+        => TryGetArgumentValueForParameterOrdinal(operation, 0, out argumentValue);
+
+    private static bool TryGetArgumentValueForParameterOrdinal(IInvocationOperation operation, int ordinal, [NotNullWhen(true)] out IOperation? argumentValue)
+    {
+        argumentValue = operation.Arguments.FirstOrDefault(arg => arg.Parameter?.Ordinal == ordinal)?.Value?.WalkDownConversion();
+        return argumentValue is not null;
+    }
+}

src/Analyzers/MSTest.Analyzers/xlf/Resources.cs.xlf

@@ -726,6 +726,16 @@ Typ deklarující tyto metody by měl také respektovat následující pravidla:
         <target state="translated">Explicitně povolit nebo zakázat paralelizaci testů</target>
         <note />
       </trans-unit>
+      <trans-unit id="UseProperAssertMethodsMessageFormat">
+        <source>Use 'Assert.{0}' instead of 'Assert.{1}'</source>
+        <target state="new">Use 'Assert.{0}' instead of 'Assert.{1}'</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="UseProperAssertMethodsTitle">
+        <source>Use proper 'Assert' methods</source>
+        <target state="new">Use proper 'Assert' methods</target>
+        <note />
+      </trans-unit>
     </body>
   </file>
 </xliff>

src/Analyzers/MSTest.Analyzers/xlf/Resources.de.xlf

@@ -728,6 +728,16 @@ Der Typ, der diese Methoden deklariert, sollte auch die folgenden Regeln beachte
         <target state="translated">Parallelisierung von Tests explizit aktivieren oder deaktivieren</target>
         <note />
       </trans-unit>
+      <trans-unit id="UseProperAssertMethodsMessageFormat">
+        <source>Use 'Assert.{0}' instead of 'Assert.{1}'</source>
+        <target state="new">Use 'Assert.{0}' instead of 'Assert.{1}'</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="UseProperAssertMethodsTitle">
+        <source>Use proper 'Assert' methods</source>
+        <target state="new">Use proper 'Assert' methods</target>
+        <note />
+      </trans-unit>
     </body>
   </file>
 </xliff>

src/Analyzers/MSTest.Analyzers/xlf/Resources.es.xlf

@@ -726,6 +726,16 @@ El tipo que declara estos métodos también debe respetar las reglas siguientes:
         <target state="translated">Habilitar o deshabilitar explícitamente la paralelización de pruebas</target>
         <note />
       </trans-unit>
+      <trans-unit id="UseProperAssertMethodsMessageFormat">
+        <source>Use 'Assert.{0}' instead of 'Assert.{1}'</source>
+        <target state="new">Use 'Assert.{0}' instead of 'Assert.{1}'</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="UseProperAssertMethodsTitle">
+        <source>Use proper 'Assert' methods</source>
+        <target state="new">Use proper 'Assert' methods</target>
+        <note />
+      </trans-unit>
     </body>
   </file>
 </xliff>

src/Analyzers/MSTest.Analyzers/xlf/Resources.fr.xlf

@@ -726,6 +726,16 @@ Le type doit être une classe
         <target state="translated">Activer ou désactiver explicitement la parallélisation des tests</target>
         <note />
       </trans-unit>
+      <trans-unit id="UseProperAssertMethodsMessageFormat">
+        <source>Use 'Assert.{0}' instead of 'Assert.{1}'</source>
+        <target state="new">Use 'Assert.{0}' instead of 'Assert.{1}'</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="UseProperAssertMethodsTitle">
+        <source>Use proper 'Assert' methods</source>
+        <target state="new">Use proper 'Assert' methods</target>
+        <note />
+      </trans-unit>
     </body>
   </file>
 </xliff>

src/Analyzers/MSTest.Analyzers/xlf/Resources.it.xlf

@@ -726,6 +726,16 @@ Anche il tipo che dichiara questi metodi deve rispettare le regole seguenti:
         <target state="translated">Abilitare o disabilitare in modo esplicito la parallelizzazione dei test</target>
         <note />
       </trans-unit>
+      <trans-unit id="UseProperAssertMethodsMessageFormat">
+        <source>Use 'Assert.{0}' instead of 'Assert.{1}'</source>
+        <target state="new">Use 'Assert.{0}' instead of 'Assert.{1}'</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="UseProperAssertMethodsTitle">
+        <source>Use proper 'Assert' methods</source>
+        <target state="new">Use proper 'Assert' methods</target>
+        <note />
+      </trans-unit>
     </body>
   </file>
 </xliff>