Fix analyzer RCS1172

ChangeLog.md

@@ -7,6 +7,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Fixed
+
+- Fix analyzer [RCS1172](https://josefpihrt.github.io/docs/roslynator/analyzers/RCS1172) ([PR](https://github.com/dotnet/roslynator/pull/1710))
+
 ## [4.14.1] - 2025-10-05
 
 ### Added

src/Analyzers/CSharp/Analysis/UseIsOperatorInsteadOfAsOperatorAnalyzer.cs

@@ -58,6 +58,15 @@ private static void Analyze(SyntaxNodeAnalysisContext context, SyntaxNode node)
         if (!nullCheck.Success)
             return;
 
+        if ((nullCheck.Style & NullCheckStyles.ComparisonToNull) != NullCheckStyles.None
+            && context.SemanticModel
+                .GetMethodSymbol(nullCheck.NullCheckExpression)?
+                .ContainingType?
+                .SpecialType != SpecialType.System_Object)
+        {
+            return;
+        }
+
         AsExpressionInfo asExpressionInfo = SyntaxInfo.AsExpressionInfo(nullCheck.Expression);
 
         if (!asExpressionInfo.Success)

src/Tests/Analyzers.Tests/RCS1172UseIsOperatorInsteadOfAsOperatorTests.cs

@@ -33,6 +33,28 @@ void M(object item)
         }
     }
 }
+");
+    }
+
+    [Fact, Trait(Traits.Analyzer, DiagnosticIdentifiers.UseIsOperatorInsteadOfAsOperator)]
+    public async Task TestNoDiagnostic_OverloadedEqualityOperator()
+    {
+        await VerifyNoDiagnosticAsync(@"
+internal class C
+{
+    public static implicit operator C(int i) => new C();
+    public static bool operator ==(C left, C right) => default;
+    public static bool operator !=(C left, C right) => default;
+    public override bool Equals(object obj) => default;
+    public override int GetHashCode() => default;
+
+    void M(object x)
+    {
+        if (x as C != null)
+        {
+        }
+    }
+}
 ");
     }
 }