Fix S3247 FP: Should not report on member access objects

analyzers/its/expected/akka.net/S3247-Akka-netstandard2.0.json

@@ -1,11 +1,5 @@
 {
   "Issues": [
-    {
-      "Id": "S3247",
-      "Message": "Replace this type-check-and-cast sequence with an \u0027as\u0027 and a null check.",
-      "Uri": "https://github.com/SonarSource/sonar-dotnet/blob/master/analyzers/its/Projects/akka.net/src/core/Akka/Actor/ActorRefProvider.cs#L516",
-      "Location": "Line 516 Position 17-54"
-    },
     {
       "Id": "S3247",
       "Message": "Replace this type-check-and-cast sequence with an \u0027as\u0027 and a null check.",

analyzers/src/SonarAnalyzer.CSharp/Rules/CastShouldNotBeDuplicated.cs

@@ -107,7 +107,8 @@ bool IsDuplicatedCastOnSameSymbol(ExpressionSyntax expression, SyntaxNode type)
             && !CSharpFacade.Instance.Syntax.IsInExpressionTree(context.SemanticModel, expression); // see https://github.com/SonarSource/sonar-dotnet/issues/8735#issuecomment-1943419398
 
         bool IsCastOnSameSymbol(ExpressionSyntax expression) =>
-            Equals(context.SemanticModel.GetSymbolInfo(expression).Symbol, typeExpressionSymbol);
+            IsEquivalentVariable(expression, typedVariable)
+            && Equals(context.SemanticModel.GetSymbolInfo(expression).Symbol, typeExpressionSymbol);
     }
 
     private static void ProcessPatternExpression(SonarSyntaxNodeReportingContext analysisContext, SyntaxNode isPattern, SyntaxNode mainVariableExpression, SyntaxNode parentStatement)
@@ -228,4 +229,24 @@ private static void ReportPatternAtCastLocation(SonarSyntaxNodeReportingContext
             context.ReportIssue(Rule, castLocation, [patternLocation.ToSecondary()], message);
         }
     }
+
+    private static bool IsEquivalentVariable(ExpressionSyntax expression, SyntaxNode typedVariable)
+    {
+        var left = RemoveThisExpression(typedVariable).WithoutTrivia();
+        var right = RemoveThisExpression(expression).WithoutTrivia();
+
+        return left.IsEquivalentTo(right)
+            || (StandaloneIdentifier(left) is { } leftIdentifier && leftIdentifier == StandaloneIdentifier(right));
+
+        static string StandaloneIdentifier(SyntaxNode node) =>
+            node switch
+            {
+                IdentifierNameSyntax name => name.Identifier.ValueText,
+                _ when node.IsKind(SyntaxKindEx.SingleVariableDesignation) => ((SingleVariableDesignationSyntaxWrapper)node).Identifier.ValueText,
+                _ => null
+            };
+
+        static SyntaxNode RemoveThisExpression(SyntaxNode node) =>
+            node is MemberAccessExpressionSyntax { Expression: ThisExpressionSyntax } memberAccess ? memberAccess.Name : node;
+    }
 }

analyzers/tests/SonarAnalyzer.Test/TestCases/CastShouldNotBeDuplicated.cs

@@ -1,13 +1,19 @@
 using System;
 using System.Collections.Generic;
 
-class Fruit { }
+class Fruit
+{
+    public object Property => null;
+}
+
 struct SomeStruct { }
 
 class Program
 {
     private object someField;
 
+    private object LocalProperty => null;
+
     public void Foo(Object x)
     {
         if (x is Fruit)  // Noncompliant
@@ -25,6 +31,32 @@ public void Foo(Object x)
         }
     }
 
+    public void IgnoreMemberAccess(Fruit arg)
+    {
+        var differentInstance = new Fruit();
+        var f = new Fruit();
+
+        if (arg.Property is Fruit)                  // Compliant, the cast is on a different instance
+        {
+            _ = (Fruit)differentInstance.Property;
+        }
+
+        if (f.Property is Fruit)                    // Compliant, the cast is on a different instance
+        {
+            _ = (Fruit)differentInstance.Property;
+        }
+
+        if (f.Property is Fruit)        // Noncompliant
+        {
+            _ = (Fruit)f.Property;      // Secondary
+        }
+
+        if (LocalProperty is Fruit)     // Noncompliant
+        {
+            _ = (Fruit)LocalProperty;   // Secondary
+        }
+    }
+
     public void Bar(object x)
     {
         if (!(x is Fruit))