Fix RCS1202 - check if expr flow state is not null (#1542)

ChangeLog.md

@@ -7,6 +7,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Fixed
+
+- Fix analyzer [RCS1202](https://josefpihrt.github.io/docs/roslynator/analyzers/RCS1202) ([PR](https://github.com/dotnet/roslynator/pull/1542))
+
 ## [4.12.6] - 2024-09-23
 
 ### Added

src/Analyzers/CSharp/Analysis/AvoidNullReferenceExceptionAnalyzer.cs

@@ -198,6 +198,9 @@ private static void AnalyzeAsExpression(SyntaxNodeAnalysisContext context)
  if (topExpression is null)
  return;
 
+ if (semanticModel.GetTypeInfo(expression, cancellationToken).Nullability.FlowState == NullableFlowState.NotNull)
+ return;
+
  if (semanticModel
  .GetTypeSymbol(asExpression, cancellationToken)?
  .IsReferenceType != true)

src/Tests/Analyzers.Tests/RCS1202AvoidNullReferenceExceptionTests2.cs

@@ -146,6 +146,34 @@ public void M()
  (this as I).M();
  }
 }
+");
+ }
+
+ [Fact, Trait(Traits.Analyzer, DiagnosticIdentifiers.AvoidNullReferenceException)]
+ public async Task TestNoDiagnostic_ExpressionIsDefinitelyNotNull()
+ {
+ await VerifyNoDiagnosticAsync(@"
+#nullable enable
+
+public interface I
+{
+ void M() { }
+}
+
+public class P : I;
+
+public class C
+{
+ public required P P { get; set; }
+
+ public void M()
+ {
+ if (this.P is not null)
+ {
+ (this.P as I).M();
+ }
+ }
+}
 ");
  }
 }