From fa98aa7fa789f9315dcfa031fac132068c1c42b4 Mon Sep 17 00:00:00 2001
From: Louis Zanella <louis.zanella@gmail.com>
Date: Mon, 23 Dec 2024 11:06:50 -0500
Subject: [PATCH] Fix CA1862 false positive with same variable on both sides of
 comparison

---
 ...aseInsensitiveStringComparison.Analyzer.cs | 19 +++++++++++++++
 ...nsensitiveStringComparison.CSharp.Tests.cs | 24 +++++++++++++++++++
 2 files changed, 43 insertions(+)

diff --git a/src/NetAnalyzers/Core/Microsoft.NetCore.Analyzers/Performance/RecommendCaseInsensitiveStringComparison.Analyzer.cs b/src/NetAnalyzers/Core/Microsoft.NetCore.Analyzers/Performance/RecommendCaseInsensitiveStringComparison.Analyzer.cs
index 87cc05d5cc..1a6ecdc050 100644
--- a/src/NetAnalyzers/Core/Microsoft.NetCore.Analyzers/Performance/RecommendCaseInsensitiveStringComparison.Analyzer.cs
+++ b/src/NetAnalyzers/Core/Microsoft.NetCore.Analyzers/Performance/RecommendCaseInsensitiveStringComparison.Analyzer.cs
@@ -322,6 +322,15 @@ private static void AnalyzeBinaryOperation(OperationAnalysisContext context, IBi
                 return;
             }
 
+            // If using the same parameter on both sides of the binary operation, don't emit a diagnostic.
+            var lParam = GetParameter(binaryOperation.LeftOperand);
+            var rParam = GetParameter(binaryOperation.RightOperand);
+
+            if (lParam is not null && lParam == rParam)
+            {
+                return;
+            }
+
             ImmutableDictionary<string, string?> dict = new Dictionary<string, string?>()
                 {
                     { LeftOffendingMethodName, leftOffendingMethodName },
@@ -380,5 +389,15 @@ private static bool IsOffendingMethod(IInvocationOperation invocation, ITypeSymb
             offendingMethodName = invocation.TargetMethod.Name;
             return true;
         }
+
+        private static IParameterSymbol? GetParameter(IOperation op)
+        {
+            return op switch
+            {
+                IParameterReferenceOperation paramRefOp => paramRefOp.Parameter,
+                IInvocationOperation invocationOp => GetParameter(invocationOp.Children.FirstOrDefault()),
+                _ => null,
+            };
+        }
     }
 }
diff --git a/src/NetAnalyzers/UnitTests/Microsoft.NetCore.Analyzers/Performance/RecommendCaseInsensitiveStringComparison.CSharp.Tests.cs b/src/NetAnalyzers/UnitTests/Microsoft.NetCore.Analyzers/Performance/RecommendCaseInsensitiveStringComparison.CSharp.Tests.cs
index 6b835da3a7..9692ea30e1 100644
--- a/src/NetAnalyzers/UnitTests/Microsoft.NetCore.Analyzers/Performance/RecommendCaseInsensitiveStringComparison.CSharp.Tests.cs
+++ b/src/NetAnalyzers/UnitTests/Microsoft.NetCore.Analyzers/Performance/RecommendCaseInsensitiveStringComparison.CSharp.Tests.cs
@@ -431,6 +431,30 @@ void M(string s)
             }.RunAsync();
         }
 
+        [Theory]
+        [InlineData("s != s.ToLowerInvariant()")]
+        [InlineData("s.ToLower() == s")]
+        [InlineData("s.ToUpperInvariant() == s.ToUpper()")]
+        [InlineData("s.ToLower().ToUpper() != s")]
+        [WorkItem(7074, "https://github.com/dotnet/roslyn-analyzers/issues/7074")]
+        public async Task NoDiagnostic_SameParameterOnBothSidesOfComparison(string expression)
+        {
+            var originalCode = $$"""
+                using System;
+
+                class C
+                {
+                    void M(string s)
+                    {
+                        if ({{expression}})
+                            Console.WriteLine("string comparison was true");
+                    }
+                }
+                """;
+
+            await VerifyNoDiagnosticCSharpAsync(originalCode);
+        }
+
         private async Task VerifyNoDiagnosticCSharpAsync(string originalSource)
         {
             VerifyCS.Test test = new()