From 0b550e75b80261aea078ddd2ca69d8c39faa6b64 Mon Sep 17 00:00:00 2001
From: Tanner Gooding <tagoo@outlook.com>
Date: Sun, 12 Jul 2026 22:35:14 -0700
Subject: [PATCH] Qualify nested type references with their containing types

A reference to a nested type (e.g. A::Inner) was reduced to just its last name
segment, so referencing it from another scope produced an unqualified name that
doesn't resolve in C#. Walk the enclosing record decls and prefix them (A.Inner),
while continuing to flatten namespaces as before.

Fixes #579

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
---
 .../PInvokeGenerator.TypeResolution.cs        | 14 +++++
 .../NestedTypeReferenceTest.cs                | 54 +++++++++++++++++++
 2 files changed, 68 insertions(+)
 create mode 100644 tests/ClangSharp.PInvokeGenerator.UnitTests/NestedTypeReferenceTest.cs

diff --git a/sources/ClangSharp.PInvokeGenerator/PInvokeGenerator.TypeResolution.cs b/sources/ClangSharp.PInvokeGenerator/PInvokeGenerator.TypeResolution.cs
index f5e4d03c..0ec17839 100644
--- a/sources/ClangSharp.PInvokeGenerator/PInvokeGenerator.TypeResolution.cs
+++ b/sources/ClangSharp.PInvokeGenerator/PInvokeGenerator.TypeResolution.cs
@@ -388,6 +388,20 @@ private string GetTypeName(Cursor? cursor, Cursor? context, Type rootType, Type
                 {
                     result.typeName = result.typeName.Split(s_doubleColonSeparator, StringSplitOptions.RemoveEmptyEntries).Last();
                     result.typeName = GetRemappedName(result.typeName, cursor, tryRemapOperatorName: false, out _, skipUsing: true);
+
+                    // A nested type needs to be qualified by its containing type(s) so it resolves
+                    // when referenced from another scope (e.g. `A::Inner` -> `A.Inner`). Namespaces
+                    // are flattened away, so only walk the enclosing record decls.
+
+                    var qualificationBuilder = new StringBuilder();
+
+                    for (var declContext = tagType.Decl.DeclContext; declContext is RecordDecl parentRecordDecl; declContext = parentRecordDecl.DeclContext)
+                    {
+                        var parentRecordDeclName = GetRemappedCursorName(parentRecordDecl, out _, skipUsing: true);
+                        _ = qualificationBuilder.Insert(0, '.').Insert(0, EscapeName(parentRecordDeclName));
+                    }
+
+                    result.typeName = qualificationBuilder.Append(result.typeName).ToString();
                 }
             }
             else if (type is TemplateSpecializationType templateSpecializationType)
diff --git a/tests/ClangSharp.PInvokeGenerator.UnitTests/NestedTypeReferenceTest.cs b/tests/ClangSharp.PInvokeGenerator.UnitTests/NestedTypeReferenceTest.cs
new file mode 100644
index 00000000..10688ab5
--- /dev/null
+++ b/tests/ClangSharp.PInvokeGenerator.UnitTests/NestedTypeReferenceTest.cs
@@ -0,0 +1,54 @@
+// Copyright (c) .NET Foundation and Contributors. All Rights Reserved. Licensed under the MIT License (MIT). See License.md in the repository root for more information.
+
+using System.Threading.Tasks;
+using NUnit.Framework;
+
+namespace ClangSharp.UnitTests;
+
+/// <summary>
+/// Regression test for https://github.com/dotnet/ClangSharp/issues/579.
+/// A nested type referenced from another scope must be qualified by its containing type(s)
+/// (e.g. <c>A::Inner</c> -&gt; <c>A.Inner</c>) so it resolves in the generated C#.
+/// </summary>
+[Platform("win")]
+public sealed class NestedTypeReferenceTest : PInvokeGeneratorTest
+{
+    [Test]
+    public Task NestedTypeIsQualified()
+    {
+        var inputContents = @"struct A
+{
+    struct Inner
+    {
+        int value;
+    };
+};
+
+struct B
+{
+    A::Inner inner;
+};
+";
+
+        var expectedOutputContents = @"namespace ClangSharp.Test
+{
+    public partial struct A
+    {
+
+        public partial struct Inner
+        {
+            public int value;
+        }
+    }
+
+    public partial struct B
+    {
+        [NativeTypeName(""A::Inner"")]
+        public A.Inner inner;
+    }
+}
+";
+
+        return ValidateGeneratedCSharpLatestWindowsBindingsAsync(inputContents, expectedOutputContents);
+    }
+}