MA0182: treat is type checks as internal type usage

src/ListDotNetTypes/ListDotNetTypes.csproj

@@ -6,7 +6,7 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="NuGet.Protocol" Version="7.0.0" />
+    <PackageReference Include="NuGet.Protocol" Version="7.3.1" />
   </ItemGroup>
 
 </Project>

src/Meziantou.Analyzer/Rules/AvoidUnusedInternalTypesAnalyzer.cs

@@ -41,6 +41,7 @@ public override void Initialize(AnalysisContext context)
             ctx.RegisterOperationAction(analyzerContext.AnalyzeMemberReference, OperationKind.PropertyReference, OperationKind.FieldReference, OperationKind.MethodReference, OperationKind.EventReference);
             ctx.RegisterOperationAction(analyzerContext.AnalyzeVariableDeclarator, OperationKind.VariableDeclarator);
             ctx.RegisterOperationAction(analyzerContext.AnalyzeConversion, OperationKind.Conversion);
+            ctx.RegisterOperationAction(analyzerContext.AnalyzeIsType, OperationKind.IsType);
             ctx.RegisterOperationAction(analyzerContext.AnalyzeIsPattern, OperationKind.IsPattern);
             ctx.RegisterOperationAction(analyzerContext.AnalyzeDelegateCreation, OperationKind.DelegateCreation);
             ctx.RegisterCompilationEndAction(analyzerContext.AnalyzeCompilationEnd);
@@ -278,6 +279,15 @@ public void AnalyzeIsPattern(OperationAnalysisContext context)
             }
         }
 
+        public void AnalyzeIsType(OperationAnalysisContext context)
+        {
+            var operation = (IIsTypeOperation)context.Operation;
+            if (operation.TypeOperand is not null)
+            {
+                AddUsedType(operation, operation.TypeOperand);
+            }
+        }
+
         public void AnalyzeDelegateCreation(OperationAnalysisContext context)
         {
             var operation = (IDelegateCreationOperation)context.Operation;

tests/Meziantou.Analyzer.Test/Rules/AvoidUnusedInternalTypesAnalyzerTests.cs

@@ -1717,6 +1717,33 @@ await CreateProjectBuilder()
               .ValidateAsync();
     }
 
+    [Fact]
+    public async Task InternalInterfaceOnlyUsedInTypeCheck_NoDiagnostic()
+    {
+        const string SourceCode = """
+            public sealed class Foo
+            {
+                public static string? Run(object x)
+                {
+                    if (x is IRunnable)
+                    {
+                        return null;
+                    }
+
+                    return "X";
+                }
+            }
+
+            internal interface IRunnable
+            {
+                void Run();
+            }
+            """;
+        await CreateProjectBuilder()
+              .WithSourceCode(SourceCode)
+              .ValidateAsync();
+    }
+
     [Fact]
     public async Task InternalRecordUsedInPatternMatching_NoDiagnostic()
     {