From c5e9f1d2ec635ef097c755c50dc264d3ea953c90 Mon Sep 17 00:00:00 2001
From: silverweed <giacomo.parolini@cern.ch>
Date: Mon, 15 Dec 2025 17:31:20 +0100
Subject: [PATCH] [core] Add TGenericClassInfo::AdoptMemberStreamer()

---
 core/meta/inc/TGenericClassInfo.h   |  3 +++
 core/meta/src/TGenericClassInfo.cxx | 21 ++++++++++++++++++++-
 2 files changed, 23 insertions(+), 1 deletion(-)

diff --git a/core/meta/inc/TGenericClassInfo.h b/core/meta/inc/TGenericClassInfo.h
index da75aab3dc652..bcd0fd49901eb 100644
--- a/core/meta/inc/TGenericClassInfo.h
+++ b/core/meta/inc/TGenericClassInfo.h
@@ -21,6 +21,7 @@
 #include "TSchemaHelper.h"
 #include <vector>
 #include <string>
+#include <unordered_map>
 
 // Forward declarations
 class TVirtualIsAProxy;
@@ -72,6 +73,7 @@ namespace ROOT {
       std::vector<ROOT::Internal::TSchemaHelper>  fReadRules;
       std::vector<ROOT::Internal::TSchemaHelper>  fReadRawRules;
       std::vector<ROOT::TClassAlt*>               fAlternate;
+      std::unordered_map<std::string, TMemberStreamer *> fAdoptedMemberStreamers;
 
    public:
       TGenericClassInfo(const char *fullClassname,
@@ -118,6 +120,7 @@ namespace ROOT {
       TClass                           *IsA(const void *obj);
 
       void                              AdoptAlternate(ROOT::TClassAlt *alt);
+      void                              AdoptMemberStreamer(const char *name, TMemberStreamer *strm);
       Short_t                           AdoptStreamer(TClassStreamer*);
       Short_t                           AdoptCollectionProxy(TVirtualCollectionProxy*);
       void                              AdoptCollectionProxyInfo(Detail::TCollectionProxyInfo*);
diff --git a/core/meta/src/TGenericClassInfo.cxx b/core/meta/src/TGenericClassInfo.cxx
index 41baf10255b3d..84d905c40290a 100644
--- a/core/meta/src/TGenericClassInfo.cxx
+++ b/core/meta/src/TGenericClassInfo.cxx
@@ -281,7 +281,11 @@ namespace Internal {
          fClass->SetConvStreamerFunc(fConvStreamerFunc);
          fClass->SetMerge(fMerge);
          fClass->SetResetAfterMerge(fResetAfterMerge);
-         fClass->AdoptStreamer(fStreamer); fStreamer = nullptr;
+         fClass->AdoptStreamer(fStreamer);
+         fStreamer = nullptr;
+         for (const auto &[name, strm] : fAdoptedMemberStreamers)
+            fClass->AdoptMemberStreamer(name.c_str(), strm);
+         fAdoptedMemberStreamers.clear();
          // If IsZombie is true, something went wrong and we will not be
          // able to properly copy the collection proxy
          if (!fClass->IsZombie()) {
@@ -434,6 +438,21 @@ namespace Internal {
       fAlternate.push_back(alt);
    }
 
+   void TGenericClassInfo::AdoptMemberStreamer(const char *name, TMemberStreamer *strm)
+   {
+      if (fClass) {
+         assert(fAdoptedMemberStreamers.empty());
+         fClass->AdoptMemberStreamer(name, strm);
+         return;
+      }
+
+      auto [it, inserted] = fAdoptedMemberStreamers.emplace(name, strm);
+      if (!inserted) {
+         delete it->second;
+         it->second = strm;
+      }
+   }
+
    void TGenericClassInfo::AdoptCollectionProxyInfo(TCollectionProxyInfo *info)
    {
       // Set the info for the CollectionProxy and take ownership of the object