Fix RCS1246

ChangeLog.md

@@ -11,6 +11,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - [CLI] Fix loading of `slnf` files ([PR](https://github.com/dotnet/roslynator/pull/1447))
 - [CLI] Fix `--severity-level` ([PR](https://github.com/dotnet/roslynator/pull/1449))
+- Fix analyzer [RCS1246](https://josefpihrt.github.io/docs/roslynator/analyzers/RCS1246) ([PR](https://github.com/dotnet/roslynator/pull/1451))
 
 ## [4.12.1] - 2024-04-15
 

src/Core/SymbolUtility.cs

@@ -121,6 +121,9 @@ public static bool HasAccessibleIndexer(
                 return hasIndexer.Value;
         }
 
+        if (originalDefinition.EqualsOrInheritsFrom(MetadataNames.System_Collections_Generic_List_T))
+            return true;
+
         if (originalDefinition.ImplementsAny(
             SpecialType.System_Collections_Generic_IList_T,
             SpecialType.System_Collections_Generic_IReadOnlyList_T,

src/Tests/Analyzers.Tests/RCS1246UseElementAccessTests.cs

@@ -40,6 +40,36 @@ void M()
 ", source, expected);
     }
 
+    [Fact, Trait(Traits.Analyzer, DiagnosticIdentifiers.UseElementAccess)]
+    public async Task Test_UseElementAccessInsteadOfFirst_DerivedFromList()
+    {
+        await VerifyDiagnosticAndFixAsync(@"
+using System.Linq;
+using System.Collections.Generic;
+
+class C : List<string>
+{
+    void M()
+    {
+        var list = new C();
+        var x = list.[|First()|];
+    }
+}
+", @"
+using System.Linq;
+using System.Collections.Generic;
+
+class C : List<string>
+{
+    void M()
+    {
+        var list = new C();
+        var x = list[0];
+    }
+}
+");
+    }
+
     [Theory, Trait(Traits.Analyzer, DiagnosticIdentifiers.UseElementAccess)]
     [InlineData("((List<object>)x).[|ElementAt(1)|]", "((List<object>)x)[1]")]
     [InlineData("((IList<object>)x).[|ElementAt(1)|]", "((IList<object>)x)[1]")]
@@ -68,6 +98,36 @@ void M()
 ", source, expected);
     }
 
+    [Fact, Trait(Traits.Analyzer, DiagnosticIdentifiers.UseElementAccess)]
+    public async Task Test_UseElementAccessInsteadOfElementAt_DerivedFromList()
+    {
+        await VerifyDiagnosticAndFixAsync(@"
+using System.Linq;
+using System.Collections.Generic;
+
+class C : List<string>
+{
+    void M()
+    {
+        var list = new C();
+        var x = list.[|ElementAt(1)|];
+    }
+}
+", @"
+using System.Linq;
+using System.Collections.Generic;
+
+class C : List<string>
+{
+    void M()
+    {
+        var list = new C();
+        var x = list[1];
+    }
+}
+");
+    }
+
     [Fact, Trait(Traits.Analyzer, DiagnosticIdentifiers.UseElementAccess)]
     public async Task TestNoDiagnostic_UseElementAccessInsteadOfElementAt()
     {