From af0f82c7a318bf0af3378ec8d87af09770469337 Mon Sep 17 00:00:00 2001
From: Vipul Cariappa <vipulcariappa@gmail.com>
Date: Thu, 26 Jun 2025 14:09:22 +0200
Subject: [PATCH] fix: handle cases where a class is declared before defining

---
 lib/CppInterOp/CppInterOp.cpp                 |  6 ++++--
 .../CppInterOp/VariableReflectionTest.cpp     | 19 +++++++++++++++++++
 2 files changed, 23 insertions(+), 2 deletions(-)

diff --git a/lib/CppInterOp/CppInterOp.cpp b/lib/CppInterOp/CppInterOp.cpp
index b7fe67392..f0d7b2b38 100755
--- a/lib/CppInterOp/CppInterOp.cpp
+++ b/lib/CppInterOp/CppInterOp.cpp
@@ -1325,6 +1325,8 @@ void GetDatamembers(TCppScope_t scope, std::vector<TCppScope_t>& datamembers) {
 
   if (auto* CXXRD = llvm::dyn_cast_or_null<CXXRecordDecl>(D)) {
     getSema().ForceDeclarationOfImplicitMembers(CXXRD);
+    if (CXXRD->hasDefinition())
+      CXXRD = CXXRD->getDefinition();
 
     llvm::SmallVector<RecordDecl::decl_iterator, 2> stack_begin;
     llvm::SmallVector<RecordDecl::decl_iterator, 2> stack_end;
@@ -1445,7 +1447,7 @@ intptr_t GetVariableOffset(compat::Interpreter& I, Decl* D,
       }
       offset += C.toCharUnitsFromBits(C.getFieldOffset(FD)).getQuantity();
     }
-    if (BaseCXXRD && BaseCXXRD != FieldParentRecordDecl) {
+    if (BaseCXXRD && BaseCXXRD != FieldParentRecordDecl->getCanonicalDecl()) {
       // FieldDecl FD belongs to some class C, but the base class BaseCXXRD is
       // not C. That means BaseCXXRD derives from C. Offset needs to be
       // calculated for Derived class
@@ -1474,7 +1476,7 @@ intptr_t GetVariableOffset(compat::Interpreter& I, Decl* D,
       }
       if (auto* RD = llvm::dyn_cast<CXXRecordDecl>(FieldParentRecordDecl)) {
         // add in the offsets for the (multi level) base classes
-        while (BaseCXXRD != RD) {
+        while (BaseCXXRD != RD->getCanonicalDecl()) {
           CXXRecordDecl* Parent = direction.at(RD);
           offset +=
               C.getASTRecordLayout(Parent).getBaseClassOffset(RD).getQuantity();
diff --git a/unittests/CppInterOp/VariableReflectionTest.cpp b/unittests/CppInterOp/VariableReflectionTest.cpp
index b9baf6c55..f75d1839a 100644
--- a/unittests/CppInterOp/VariableReflectionTest.cpp
+++ b/unittests/CppInterOp/VariableReflectionTest.cpp
@@ -299,6 +299,25 @@ TEST(VariableReflectionTest, GetVariableOffset) {
 
   auto* VD_C_s_a = Cpp::GetNamed("s_a", Decls[4]); // C::s_a
   EXPECT_TRUE((bool) Cpp::GetVariableOffset(VD_C_s_a));
+
+  struct K {
+    int x;
+    int y;
+    int z;
+  };
+  Cpp::Declare("struct K;");
+  Cpp::TCppScope_t k = Cpp::GetNamed("K");
+  EXPECT_TRUE(k);
+
+  Cpp::Declare("struct K { int x; int y; int z; };");
+
+  datamembers.clear();
+  Cpp::GetDatamembers(k, datamembers);
+  EXPECT_EQ(datamembers.size(), 3);
+
+  EXPECT_EQ(Cpp::GetVariableOffset(datamembers[0]), offsetof(K, x));
+  EXPECT_EQ(Cpp::GetVariableOffset(datamembers[1]), offsetof(K, y));
+  EXPECT_EQ(Cpp::GetVariableOffset(datamembers[2]), offsetof(K, z));
 }
 
 #define CODE                                                                   \