From 49e13c350521e3d934da3f36cd3f8c55a0314277 Mon Sep 17 00:00:00 2001
From: Jakob Blomer <jblomer@cern.ch>
Date: Fri, 31 Jul 2026 23:23:25 +0200
Subject: [PATCH] [ntuple] fix cloning RStreamerField

(cherry picked from commit 9bc2c4207dce6678aa03b58b87c11c743c8ea01a)
---
 tree/ntuple/src/RFieldMeta.cxx    | 3 ++-
 tree/ntuple/test/rfield_class.cxx | 4 ++++
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/tree/ntuple/src/RFieldMeta.cxx b/tree/ntuple/src/RFieldMeta.cxx
index 1747e6f180c17..16157f7c875a3 100644
--- a/tree/ntuple/src/RFieldMeta.cxx
+++ b/tree/ntuple/src/RFieldMeta.cxx
@@ -879,7 +879,8 @@ void ROOT::RStreamerField::BeforeConnectPageSource(ROOT::Internal::RPageSource &
 
 std::unique_ptr<ROOT::RFieldBase> ROOT::RStreamerField::CloneImpl(std::string_view newName) const
 {
-   return std::unique_ptr<RStreamerField>(new RStreamerField(newName, GetTypeName()));
+   // To get the correct TClass instance in the clone, we clone using the un-normalized type name
+   return std::unique_ptr<RStreamerField>(new RStreamerField(newName, fClass->GetName()));
 }
 
 std::size_t ROOT::RStreamerField::AppendImpl(const void *from)
diff --git a/tree/ntuple/test/rfield_class.cxx b/tree/ntuple/test/rfield_class.cxx
index 5cc9ab4a94e0a..bc2cdfb28d2bc 100644
--- a/tree/ntuple/test/rfield_class.cxx
+++ b/tree/ntuple/test/rfield_class.cxx
@@ -377,6 +377,10 @@ TEST(RNTuple, TClassMetaName)
    ROOT::RStreamerField f6("f", "EdmWrapper<long long>");
    EXPECT_STREQ("EdmWrapper<Long64_t>", f6.GetClass()->GetName());
    EXPECT_EQ("EdmWrapper<Long64_t>", f6.GetTypeAlias());
+   auto clone = f6.Clone("f");
+   auto streamerFieldPtr = static_cast<ROOT::RStreamerField *>(clone.get());
+   EXPECT_STREQ("EdmWrapper<Long64_t>", streamerFieldPtr->GetClass()->GetName());
+   EXPECT_EQ("EdmWrapper<Long64_t>", streamerFieldPtr->GetTypeAlias());
 }
 
 TEST(RNTuple, StreamerInfoRecords)