BUGFIX IDISP005 when local function

Fix #172.

Author: JohanLarsson

IDisposableAnalyzers.Test/IDISP005ReturnTypeShouldBeIDisposableTests/Valid.cs

@@ -972,5 +972,33 @@ public static object M()
 
             RoslynAssert.Valid(Analyzer, Descriptor, DisposableCode, code);
         }
+
+        [Test]
+        public static void LocalFactory()
+        {
+            var code = @"
+namespace N
+{
+    using System;
+
+    public class C
+    {
+        public static object M()
+        {
+            using (var disposable = Create())
+            {
+            }
+
+            return null;
+            IDisposable Create()
+            {
+                return new Disposable();
+            }
+        }
+    }
+}";
+
+            RoslynAssert.Valid(Analyzer, Descriptor, DisposableCode, code);
+        }
     }
 }

IDisposableAnalyzers/Analyzers/ReturnValueAnalyzer.cs

@@ -223,10 +223,15 @@ private static bool IsIgnored(ISymbol symbol)
 
         private static ITypeSymbol? ReturnType(SyntaxNodeAnalysisContext context)
         {
-            var anonymousFunction = context.Node.FirstAncestorOrSelf<AnonymousFunctionExpressionSyntax>();
-            if (anonymousFunction != null)
+            if (context.Node.FirstAncestorOrSelf<AnonymousFunctionExpressionSyntax>() is {} lambda)
             {
-                var method = context.SemanticModel.GetSymbolSafe(anonymousFunction, context.CancellationToken) as IMethodSymbol;
+                var method = context.SemanticModel.GetSymbolSafe(lambda, context.CancellationToken) as IMethodSymbol;
+                return method?.ReturnType;
+            }
+
+            if (context.Node.TryFirstAncestor(out LocalFunctionStatementSyntax? local))
+            {
+                var method = context.SemanticModel.GetDeclaredSymbol(local, context.CancellationToken) as IMethodSymbol;
                 return method?.ReturnType;
             }