From 39e4240db8cbe15c5c52ac9198d47f28574242c7 Mon Sep 17 00:00:00 2001
From: Andrea Bocci <andrea.bocci@cern.ch>
Date: Tue, 7 Nov 2023 19:08:12 +0100
Subject: [PATCH] Test a user-defined implementation of the ROOT read rules

---
 .../PortableTestObjects/src/classes.cc        | 55 +++++++++++++++++++
 .../PortableTestObjects/src/classes_def.xml   |  4 +-
 2 files changed, 57 insertions(+), 2 deletions(-)
 create mode 100644 DataFormats/PortableTestObjects/src/classes.cc

diff --git a/DataFormats/PortableTestObjects/src/classes.cc b/DataFormats/PortableTestObjects/src/classes.cc
new file mode 100644
index 0000000000000..8ea09ac6afb10
--- /dev/null
+++ b/DataFormats/PortableTestObjects/src/classes.cc
@@ -0,0 +1,55 @@
+// required by <RtypesImp.h>
+#define G__DICTIONARY
+
+#include <Rtypes.h>
+#include <RtypesImp.h>
+#include <TGenericClassInfo.h>
+#include <TVirtualObject.h>
+
+#include "classes.h"
+
+namespace ROOT {
+
+  // forward declaration
+  TGenericClassInfo *GenerateInitInstance(portabletest::TestHostCollection const *);
+
+}  // namespace ROOT
+
+// read function for portabletest::TestHostCollection
+// called for every event
+static void setROOTReadStreamerFor_portabletest_TestHostCollection(char *target, TVirtualObject *oldObj) {
+  // address in memory of the buffer containing the object being read from file
+  char *onfile_address = (char *)oldObj->GetObject();
+  // offset of the "layout_" data member
+  static ptrdiff_t onfile_offset = oldObj->GetClass()->GetDataMemberOffset("layout_");
+  // reference to the Layout object being read from file
+  portabletest::TestHostCollection::Layout &onfile(
+      *(portabletest::TestHostCollection::Layout *)(onfile_address + onfile_offset));
+  // pointer to the portabletest::TestHostCollection object being constructed in memory
+  portabletest::TestHostCollection *newObj = (portabletest::TestHostCollection *)target;
+
+  portabletest::TestHostCollection::ROOTReadStreamer(newObj, onfile);
+}
+
+// set the read function for portabletest::TestHostCollection
+// called when the dictionary is loaded
+static bool set_portabletest_TestHostCollection_ReadRules() {
+  // build the read rules
+  std::vector<::ROOT::Internal::TSchemaHelper> readrules(1);
+  ::ROOT::Internal::TSchemaHelper *rule = &readrules[0];
+  rule->fSourceClass = "portabletest::TestHostCollection";
+  rule->fSource = "portabletest::TestHostCollection::Layout layout_;";
+  rule->fFunctionPtr = (void *)TFunc2void(setROOTReadStreamerFor_portabletest_TestHostCollection);
+  rule->fTarget = "buffer_,layout_,view_";
+  rule->fCode = "";
+  rule->fVersion = "[1-]";
+  rule->fEmbed = false;
+
+  // set the read rules
+  ::ROOT::GenerateInitInstance((portabletest::TestHostCollection const *)nullptr)->SetReadRules(readrules);
+
+  return true;
+}
+
+static const bool has_the_portabletest_TestHostCollection_ReadRules_been_set =
+    set_portabletest_TestHostCollection_ReadRules();
diff --git a/DataFormats/PortableTestObjects/src/classes_def.xml b/DataFormats/PortableTestObjects/src/classes_def.xml
index 3470c65a70c23..c1c3e27e622c0 100644
--- a/DataFormats/PortableTestObjects/src/classes_def.xml
+++ b/DataFormats/PortableTestObjects/src/classes_def.xml
@@ -3,7 +3,7 @@
   <class name="portabletest::TestSoA::View"/>
 
   <class name="portabletest::TestHostCollection"/>
-  <read
+  <!--read
     sourceClass="portabletest::TestHostCollection"
     targetClass="portabletest::TestHostCollection"
     version="[1-]"
@@ -13,6 +13,6 @@
   <![CDATA[
     portabletest::TestHostCollection::ROOTReadStreamer(newObj, onfile.layout_);
   ]]>
-  </read>
+  </read-->
   <class name="edm::Wrapper<portabletest::TestHostCollection>" splitLevel="0"/>
 </lcgdict>