fix: [Bug Report] The regions in the expansion block will be displaye…

src/CodeNav.OutOfProc/Languages/CSharp/Mappers/ClassMapper.cs

@@ -80,8 +80,9 @@ public static CodeClassItem MapClass(ClassDeclarationSyntax member,
             }
         }
 
-        // Add regions to class
-        codeItem.Members.AddRange(regions);
+        // Add regions to class, but skip any that are already nested inside
+        // a member that maps its own regions (e.g. a nested extension block)
+        RegionMapper.AddRegionsIfNotPresent(codeItem.Members, regions);
 
         return codeItem;
     }

src/CodeNav.OutOfProc/Languages/CSharp/Mappers/ExtensionBlockMapper.cs

@@ -43,8 +43,10 @@ public static CodeClassItem MapExtensionBlock(ExtensionBlockDeclarationSyntax me
             codeItem.Members.Add(memberItem);
         }
 
-        // Add regions to block
-        codeItem.Members.AddRange(regions);
+        // Add regions to block, but skip any that are already nested inside
+        // a member that maps its own regions
+        RegionMapper.AddRegionsIfNotPresent(codeItem.Members, regions);
+
 
         return codeItem;
     }

src/CodeNav.OutOfProc/Languages/CSharp/Mappers/InterfaceMapper.cs

@@ -174,17 +174,9 @@ private static CodeImplementedInterfaceItem MapImplementedInterface(string name,
             }
         }
 
-        // Add regions to interface if they have a region member inside them
-        if (regions.Any())
-        {
-            foreach (var region in regions)
-            {
-                if (region?.Members.Any() == true)
-                {
-                    codeItem.Members.Add(region);
-                }
-            }
-        }
+        // Add regions to interface, but skip any that are already nested inside
+        // a member that maps its own regions
+        RegionMapper.AddRegionsIfNotPresent(codeItem.Members, regions);
 
         return codeItem;
     }

src/CodeNav.OutOfProc/Languages/CSharp/Mappers/NamespaceMapper.cs

@@ -29,16 +29,7 @@ public static CodeNamespaceItem MapNamespace(BaseNamespaceDeclarationSyntax memb
         }
 
         // Add regions to namespace if they are not present in any children of the namespace
-        if (regions.Any())
-        {
-            foreach (var region in regions)
-            {
-                if (codeItem.Members.Flatten().FilterNull().Any(i => i.Id == region?.Id) == false)
-                {
-                    codeItem.Members.AddIfNotNull(region);
-                }
-            }
-        }
+        RegionMapper.AddRegionsIfNotPresent(codeItem.Members, regions);
 
         return codeItem;
     }

src/CodeNav.OutOfProc/Languages/CSharp/Mappers/RegionMapper.cs

@@ -1,4 +1,5 @@
 using CodeNav.OutOfProc.Constants;
+using CodeNav.OutOfProc.Extensions;
 using CodeNav.OutOfProc.Helpers;
 using CodeNav.OutOfProc.Interfaces;
 using CodeNav.OutOfProc.Mappers;
@@ -7,6 +8,7 @@
 using Microsoft.CodeAnalysis.CSharp;
 using Microsoft.CodeAnalysis.CSharp.Syntax;
 using Microsoft.CodeAnalysis.Text;
+using System.Drawing;
 
 namespace CodeNav.OutOfProc.Languages.CSharp.Mappers;
 
@@ -288,4 +290,37 @@ public static bool IsPartOfRegion(IEnumerable<CodeRegionItem> regions, CodeItem
 
         return null;
     }
+
+    /// <summary>
+    /// Add regions to the given list of members, but only if a region with the same
+    /// <see cref="CodeItem.Id"/> is not already present somewhere within those members.
+    /// </summary>
+    /// <remarks>
+    /// A region can be discovered more than once: a container (class, interface,
+    /// namespace, extension block) scans its entire span for regions, which also
+    /// picks up regions that live inside a nested member (e.g. a nested class or an
+    /// extension block) that maps its own regions independently. That nested member
+    /// already nests its region correctly, so the outer scan's copy is a duplicate
+    /// (and ends up empty, since none of its members could be matched to it) and
+    /// should not be added again. Regions that are genuinely empty and not nested
+    /// inside another member (e.g. an intentionally empty `#region` directly in a
+    /// class) are still added, since no item with their Id exists elsewhere.
+    /// </remarks>
+    /// <param name="members">The list of members regions should be added to</param>
+    /// <param name="regions">The regions found for this scope</param>
+    public static void AddRegionsIfNotPresent(List<CodeItem> members, List<CodeRegionItem> regions)
+    {
+        foreach (var region in regions)
+        {
+            var alreadyPresent = members
+                .Flatten()
+                .FilterNull()
+                .Any(item => item.Id == region?.Id);
+
+            if (!alreadyPresent)
+            {
+                members.AddIfNotNull(region);
+            }
+        }
+    }
 }

test/Files/ExtensionBlock/TestExtensionBlockRegion.cs

@@ -0,0 +1,14 @@
+namespace CodeNav.Test.Files.ExtensionBlock;
+
+internal static class TestExtensionBlockRegion
+{
+    extension(object obj)
+    {
+        #region Foo
+        public bool IsNull()
+        {
+            return obj is null;
+        }
+        #endregion
+    }
+}

test/MapperTests/MapperTestExtensionBlock.cs

@@ -4,7 +4,7 @@
 internal class MapperTestExtensionBlock : BaseTest
 {
     [Test]
-    public async Task TestInlineBaseClassShouldBeOk()
+    public async Task ExtensionBlockShouldBeOk()
     {
         var codeItems = await MapToCodeItems("ExtensionBlock/TestExtensionBlock.cs");
 
@@ -18,4 +18,33 @@ public async Task TestInlineBaseClassShouldBeOk()
         // Extension block item should have 2 members
         Assert.That(extensionBlockItem!.Members, Has.Count.EqualTo(2));
     }
+
+    [Test]
+    public async Task RegionInsideExtensionBlockShouldNotBeDuplicated()
+    {
+        // Regression test for https://github.com/sboulema/CodeNav/issues/180
+        var codeItems = await MapToCodeItems("ExtensionBlock/TestExtensionBlockRegion.cs");
+
+        var namespaceItem = GetNamespace(codeItems);
+        var classItem = GetFirstClass(namespaceItem);
+
+        // The class should only have the extension block as a member, the region
+        // inside the extension block should not also show up as a sibling of it
+        Assert.That(classItem.Members, Has.Count.EqualTo(1));
+
+        var extensionBlockItem = GetMemberAtIndex(classItem, 0) as CodeClassItem;
+
+        // The extension block should have a single member: the "Foo" region
+        Assert.That(extensionBlockItem!.Members, Has.Count.EqualTo(1));
+
+        var regionItem = GetFirstRegion(extensionBlockItem);
+
+        using (Assert.EnterMultipleScope())
+        {
+            Assert.That(regionItem.Name, Is.EqualTo("Foo"));
+
+            // The region should contain the IsNull method
+            GetMemberByName<CodeItem>(regionItem, "IsNull");
+        }
+    }
 }