Fix analyzer RCS1246 (#1543)

Author: josefpihrt

ChangeLog.md

@@ -10,6 +10,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Fixed
 
 - Fix analyzer [RCS1202](https://josefpihrt.github.io/docs/roslynator/analyzers/RCS1202) ([PR](https://github.com/dotnet/roslynator/pull/1542))
+- Fix analyzer [RCS1246](https://josefpihrt.github.io/docs/roslynator/analyzers/RCS1246) ([PR](https://github.com/dotnet/roslynator/pull/1543))
 
 ## [4.12.6] - 2024-09-23
 

src/Common/CSharp/Analysis/UseElementAccessAnalysis.cs

@@ -77,7 +77,7 @@ public static bool IsFixableLast(
         if (((CSharpCompilation)semanticModel.Compilation).LanguageVersion < LanguageVersion.CSharp8)
             return false;
 
-        if (semanticModel.Compilation.GetTypeByMetadataName("System.Index") is null)
+        if (semanticModel.Compilation.GetTypeByMetadataName("System.Index")?.DeclaredAccessibility != Accessibility.Public)
             return false;
 
         IMethodSymbol methodSymbol = semanticModel.GetReducedExtensionMethodInfo(invocationInfo.InvocationExpression, cancellationToken).Symbol;

src/Tests/Analyzers.Tests/RCS1246UseElementAccessTests.cs

@@ -182,6 +182,24 @@ void M()
 ", source, expected);
     }
 
+    [Fact, Trait(Traits.Analyzer, DiagnosticIdentifiers.UseElementAccess)]
+    public async Task Test_UseElementAccessInsteadOfLast_CSharp7()
+    {
+        await VerifyNoDiagnosticAsync(@"
+using System.Linq;
+using System.Collections.Generic;
+
+class C
+{
+    void M()
+    {
+        List<string> x = null;
+        var y = x.Last();
+    }
+}
+", options: WellKnownCSharpTestOptions.Default_CSharp7);
+    }
+
     [Fact, Trait(Traits.Analyzer, DiagnosticIdentifiers.UseElementAccess)]
     public async Task TestNoDiagnostic_UseElementAccessInsteadOfLast()
     {