Add more boolean simplification cases

src/Analyzers/CSharp/Analyzers/RemoveRedundantEquality/CSharpRemoveRedundantEqualityDiagnosticAnalyzer.cs

@@ -9,10 +9,7 @@
 namespace Microsoft.CodeAnalysis.CSharp.RemoveRedundantEquality;
 
 [DiagnosticAnalyzer(LanguageNames.CSharp)]
-internal sealed class CSharpRemoveRedundantEqualityDiagnosticAnalyzer
-    : AbstractRemoveRedundantEqualityDiagnosticAnalyzer
+internal sealed class CSharpRemoveRedundantEqualityDiagnosticAnalyzer()
+    : AbstractRemoveRedundantEqualityDiagnosticAnalyzer(CSharpSyntaxFacts.Instance)
 {
-    public CSharpRemoveRedundantEqualityDiagnosticAnalyzer() : base(CSharpSyntaxFacts.Instance)
-    {
-    }
 }

src/Analyzers/CSharp/Tests/RemoveRedundantEquality/RemoveRedundantEqualityTests.cs

@@ -15,7 +15,7 @@ namespace Microsoft.CodeAnalysis.Editor.CSharp.UnitTests.RemoveRedundantEquality
    CSharpRemoveRedundantEqualityDiagnosticAnalyzer,
    RemoveRedundantEqualityCodeFixProvider>;
 
-public class RemoveRedundantEqualityTests
+public sealed class RemoveRedundantEqualityTests
 {
     [Fact]
     public async Task TestSimpleCaseForEqualsTrue()
@@ -88,7 +88,7 @@ public bool M1(bool x)
     }
 
     [Fact]
-    public async Task TestSimpleCaseForNotEqualsTrue_NoDiagnostics()
+    public async Task TestSimpleCaseForNotEqualsTrue()
     {
         await VerifyCS.VerifyCodeFixAsync("""
             public class C
@@ -252,7 +252,7 @@ public bool M3(bool x)
     }
 
     [Fact, WorkItem("https://github.com/dotnet/roslyn/issues/48236")]
-    public async Task TestNullableValueTypes_DoesntCrash()
+    public async Task TestNullableValueTypes_DoesNotCrash()
     {
         var code = """
             public class C
@@ -265,4 +265,83 @@ public bool M1(int? x)
             """;
         await VerifyCS.VerifyAnalyzerAsync(code);
     }
+
+    [Fact]
+    public async Task TestSimpleCaseForIsFalse()
+    {
+        var code = """
+            public class C
+            {
+                public bool M1(bool x)
+                {
+                    return x [|is|] false;
+                }
+            }
+            """;
+        var fixedCode = """
+            public class C
+            {
+                public bool M1(bool x)
+                {
+                    return !x;
+                }
+            }
+            """;
+        await VerifyCS.VerifyCodeFixAsync(code, fixedCode);
+    }
+
+    [Fact]
+    public async Task TestSimpleCaseForIsTrue1()
+    {
+        var code = """
+            public class C
+            {
+                public bool M1(bool x)
+                {
+                    return x [|is|] true;
+                }
+            }
+            """;
+        var fixedCode = """
+            public class C
+            {
+                public bool M1(bool x)
+                {
+                    return x;
+                }
+            }
+            """;
+        await VerifyCS.VerifyCodeFixAsync(code, fixedCode);
+    }
+
+    [Fact]
+    public async Task TestSimpleCaseForIsTrue2()
+    {
+        var code = """
+            public class C
+            {
+                public const bool MyTrueConstant = true;
+                public bool M1(bool x)
+                {
+                    return x is MyTrueConstant;
+                }
+            }
+            """;
+        await VerifyCS.VerifyCodeFixAsync(code, code);
+    }
+
+    [Fact]
+    public async Task TestNotForNullableBool()
+    {
+        var code = """
+            public class C
+            {
+                public bool M1(bool? x)
+                {
+                    return x is true;
+                }
+            }
+            """;
+        await VerifyCS.VerifyCodeFixAsync(code, code);
+    }
 }

src/Analyzers/Core/Analyzers/RemoveRedundantEquality/AbstractRemoveRedundantEqualityDiagnosticAnalyzer.cs

@@ -21,13 +21,42 @@ public override DiagnosticAnalyzerCategory GetAnalyzerCategory()
         => DiagnosticAnalyzerCategory.SemanticSpanAnalysis;
 
     protected override void InitializeWorker(AnalysisContext context)
-        => context.RegisterOperationAction(AnalyzeBinaryOperator, OperationKind.BinaryOperator);
+    {
+        context.RegisterOperationAction(AnalyzeBinaryOperator, OperationKind.BinaryOperator);
+        context.RegisterOperationAction(AnalyzeIsPatternOperator, OperationKind.IsPattern);
+    }
+
+    private void AnalyzeIsPatternOperator(OperationAnalysisContext context)
+    {
+        if (ShouldSkipAnalysis(context, notification: null))
+            return;
+
+        var syntax = context.Operation.Syntax;
+        if (!syntaxFacts.IsIsPatternExpression(syntax))
+            return;
+
+        var operation = (IIsPatternOperation)context.Operation;
+        if (operation.Pattern is not IConstantPatternOperation { Value.ConstantValue.Value: true or false } constantPattern)
+            return;
+
+        syntaxFacts.GetPartsOfIsPatternExpression(syntax, out _, out var isToken, out _);
+        AnalyzeOperator(
+            context,
+            leftOperand: operation.Value,
+            rightOperand: constantPattern.Value,
+            isOperatorEquals: true,
+            isToken);
+    }
 
     private void AnalyzeBinaryOperator(OperationAnalysisContext context)
     {
         if (ShouldSkipAnalysis(context, notification: null))
             return;
 
+        var syntax = context.Operation.Syntax;
+        if (!syntaxFacts.IsBinaryExpression(syntax))
+            return;
+
         // We shouldn't report diagnostic on overloaded operator as the behavior can change.
         var operation = (IBinaryOperation)context.Operation;
         if (operation.OperatorMethod is not null)
@@ -36,26 +65,32 @@ private void AnalyzeBinaryOperator(OperationAnalysisContext context)
         if (operation.OperatorKind is not (BinaryOperatorKind.Equals or BinaryOperatorKind.NotEquals))
             return;
 
-        if (!syntaxFacts.IsBinaryExpression(operation.Syntax))
-        {
-            return;
-        }
-
-        var rightOperand = operation.RightOperand;
-        var leftOperand = operation.LeftOperand;
+        var isOperatorEquals = operation.OperatorKind == BinaryOperatorKind.Equals;
+        syntaxFacts.GetPartsOfBinaryExpression(syntax, out _, out var operatorToken, out _);
+        AnalyzeOperator(
+            context,
+            operation.LeftOperand,
+            operation.RightOperand,
+            isOperatorEquals,
+            operatorToken);
+    }
 
-        if (rightOperand.Type is null || leftOperand.Type is null)
-            return;
+    private void AnalyzeOperator(
+        OperationAnalysisContext context,
+        IOperation leftOperand,
+        IOperation rightOperand,
+        bool isOperatorEquals,
+        SyntaxToken operatorToken)
+    {
+        var leftType = leftOperand.Type;
+        var rightType = rightOperand.Type;
 
-        if (rightOperand.Type.SpecialType != SpecialType.System_Boolean ||
-            leftOperand.Type.SpecialType != SpecialType.System_Boolean)
+        if (leftType?.SpecialType != SpecialType.System_Boolean ||
+            rightType?.SpecialType != SpecialType.System_Boolean)
         {
             return;
         }
 
-        var isOperatorEquals = operation.OperatorKind == BinaryOperatorKind.Equals;
-        syntaxFacts.GetPartsOfBinaryExpression(operation.Syntax, out _, out var operatorToken, out _);
-
         var properties = ImmutableDictionary.CreateBuilder<string, string?>();
         if (TryGetLiteralValue(rightOperand) is bool rightBool)
         {
@@ -76,12 +111,12 @@ private void AnalyzeBinaryOperator(OperationAnalysisContext context)
 
         context.ReportDiagnostic(Diagnostic.Create(Descriptor,
             operatorToken.GetLocation(),
-            additionalLocations: [operation.Syntax.GetLocation()],
+            additionalLocations: [operatorToken.GetLocation()],
             properties: properties.ToImmutable()));
 
         return;
 
-        static bool? TryGetLiteralValue(IOperation operand)
+        static bool? TryGetLiteralValue(IOperation? operand)
         {
             // Make sure we only simplify literals to avoid changing
             // something like the following example:

src/Analyzers/Core/CodeFixes/RemoveRedundantEquality/RemoveRedundantEqualityCodeFixProvider.cs

@@ -49,19 +49,30 @@ protected override async Task FixAsync(
 
         SyntaxNode RewriteNode()
         {
-            // This should happen only in error cases.
-            if (!syntaxFacts.IsBinaryExpression(node))
-                return node;
+            if (syntaxFacts.IsBinaryExpression(node))
+            {
+                syntaxFacts.GetPartsOfBinaryExpression(node, out var left, out var right);
+                var rewritten =
+                    properties[RedundantEqualityConstants.RedundantSide] == RedundantEqualityConstants.Right ? left :
+                    properties[RedundantEqualityConstants.RedundantSide] == RedundantEqualityConstants.Left ? right : node;
+
+                if (properties.ContainsKey(RedundantEqualityConstants.Negate))
+                    rewritten = generator.Negate(generatorInternal, rewritten, semanticModel, cancellationToken);
 
-            syntaxFacts.GetPartsOfBinaryExpression(node, out var left, out var right);
-            var rewritten =
-                properties[RedundantEqualityConstants.RedundantSide] == RedundantEqualityConstants.Right ? left :
-                properties[RedundantEqualityConstants.RedundantSide] == RedundantEqualityConstants.Left ? right : node;
+                return rewritten;
+            }
+            else if (syntaxFacts.IsIsPatternExpression(node))
+            {
+                syntaxFacts.GetPartsOfIsPatternExpression(node, out var left, out _, out var right);
+                var rewritten = left;
+                if (properties.ContainsKey(RedundantEqualityConstants.Negate))
+                    rewritten = generator.Negate(generatorInternal, rewritten, semanticModel, cancellationToken);
 
-            if (properties.ContainsKey(RedundantEqualityConstants.Negate))
-                rewritten = generator.Negate(generatorInternal, rewritten, semanticModel, cancellationToken);
+                return rewritten;
+            }
 
-            return rewritten;
+            // This should happen only in error cases.
+            return node;
         }
 
         static SyntaxNode WithElasticTrailingTrivia(SyntaxNode node)

src/Analyzers/VisualBasic/Tests/RemoveRedundantEquality/RemoveRedundantEqualityTests.vb

@@ -28,7 +28,7 @@ End Module
         End Function
 
         <Fact>
-        Public Async Function TestSimpleCaseForEqualsFalse_NoDiagnostics() As Task
+        Public Async Function TestSimpleCaseForEqualsFalse() As Task
             Await VerifyVB.VerifyCodeFixAsync("
 Public Module Module1
     Public Function M1(x As Boolean) As Boolean